Nondestructive Methods and Special Test Instrumentation Supporting NASA Composite

Overwrapped Pressure Vessel Assessments

AIAA-2007-2324

Regor Saulsberry1 and Nathanael Greene2

NASA Johnson Space Center White Sands Test Facility, Las Cruces, New Mexico, 88012

Ken Cameron3 and Eric Madaras4 NASA Langley Research Center, Hampton, Virginia 23681-2199

Lorie Grimes-Ledesma5 Jet Propulsion Laboratory, Pasadena, California, 91109

John Thesken6 Ohio Aerospace Institute-NASA Glenn Research Center, Cleveland, Ohio, 44135

Leigh Phoenix7 Cornell University, Ithaca, New York, 14853

Pappu Murthy8 and Duane Revilock9 NASA Glenn Research Center, Cleveland, Ohio, 44135

Many aging composite overwrapped pressure vessels (COPVs), being used by the National Aeronautics and Space Administration (NASA) are currently under evaluation to better quantify their reliability and clarify their likelihood of failure due to stress rupture and age-dependent issues. As a result, some test and analysis programs have been successfully accomplished and other related programs are still in progress at the NASA Johnson Space Center (JSC) White Sands Test Facility (WSTF) and other NASA centers, with assistance from the commercial sector. To support this effort, a group of Nondestructive Evaluation (NDE) experts was assembled to provide NDE competence for pretest evaluation of test articles and for application of NDE technology to real-time testing. Techniques were required to provide assurance that the test article had adequate structural integrity and manufacturing consistency to be considered acceptable for testing and these techniques were successfully applied. Destructive testing is also being accomplished to better understand the physical and chemical property changes associated with progression toward “stress rupture” (SR) failure, and it is being associated with NDE response, so it can potentially be used to help with life prediction. Destructive work also includes the evaluation of residual stresses during dissection of the overwrap, laboratory evaluation of specimens extracted from the overwrap to evaluate physical property changes, and quantitative microscopy to inform the theoretical micromechanics.

1 Project Manager, NESC Independent Technical Assessment NDE Lead, Laboratories Office, P.O. Box 20/201LD. 2 Project Manager, Laboratories Office, P.O. Box 20/201LD. 3 NESC COPV Independent Technical Assessment Leader, NASA Langley Research Center, Hampton, Virginia. 4 Ph.D., NDE Test Office, NASA Langley Research Center, Hampton, Virginia. 5 Ph.D., NESC COPV Team Leader, 4800 Oak Grove Drive. 6 Ph.D., 21000 Brookpark Road. 7 Professor, Cornell University, Ithaca, New York. 8 Deputy Structural Fellow, NESC, NASA Glenn Research Center, Cleveland, Ohio. 9 Project Manager, Structures and Acoustics Division, NASA Glenn Research Center, Cleveland, Ohio.

https://ntrs.nasa.gov/search.jsp?R=20070010588 2020-04-03T12:07:55+00:00Z

I. Introduction ASA is engaged with recertification and life extension of the many aging Kevlar®* composite overwrapped pressure vessels (COPVs). The COPVs have varying criticality, usage histories, damage and repair histories,

time at pressure, and number of pressure cycles. When NASA reviewed the COPVs, a concern was raised with respect to “stress rupture” (SR) life predictions.

Similarly, concerns arose regarding the graphite (carbon) epoxy COPVs also used in newer systems. A Nondestructive Evaluation (NDE) Super Problem Resolution Team (SPRT) was formed to provide NDE competence for the necessary technical assessment. The NDE SPRT evaluated the data available and established observations and recommendations; however, immediate application of NDE to COPVs was found limited by the “state of the art” and specific experience base. Additionally, assisted by observations of the SPRT, the NASA NDE Working Group (NNWG) recognized the need for development of NDE specifically applicable to COPVs, some of which is actively underway.

As a resolution to the life prediction issue, a COPV test project was initiated at NASA Johnson Space Center White Sands Test Facility (WSTF) to better understand where these vessels stood in their available life. Additionally, carbon COPV SR test programs have been ongoing at WSTF for several years, and recent investigations have been supported by the SPRT. Pretest NDE was needed and applied to screen the COPVs prior to testing, and NDE technology was also needed and applied during testing to gather critical test data. Since validated processes were not always available, “best practices” were applied. This effort is producing very valuable results.

II. Assessment of NDE Applicable to COPVS NDE techniques were reviewed to identify those applicable to the COPVs of concern. Traditional and mature

techniques had been used successfully to find isolated or discrete mechanical damage (e.g., impact damage) in COPVs;1 however, methods that may help characterize global degradation or damage resulting in creep and/or SR were not as well documented. An in-depth research program would be necessary to determine the COPV material properties undergoing degradation leading to SR. A technology assessment of NDE for SR degradation in COPVs was accomplished and published in November 2004 by a COPV NDE SPRT subcontractor, the Department of Defense (DOD) Nondestructive Testing Information Analysis Center (NTIAC); and it represents a good compilation of technology that is applicable and leads to further work in this area.2 The SPRT recognized that a comprehensive research and development program was needed to further identify potential NDE methods and evaluate their potential to monitor SR in COPVs.

III. Methods for Characterizing Global Damage As of this study, no NDE technique is currently known to be directly applicable to prediction of SR and other

life-dependent COPV issues. For life issues, we still need to better identify the only partially defined physical attributes or phenomena producing failure to allow appropriate NDE techniques to be down-selected from the list of potential candidate methods. These down-selected methods will then need to be further developed and applied.

Since essentially all current and future NASA spacecraft utilize COPVs subject to SR, this creates a major concern that needs to be addressed. In response to this, the NDE SPRT identified and ranked possible candidate NDE methods that may potentially be used to assess the COPV material properties that are undergoing degradation leading to SR, and information was collected to delineate future research needs. In addition, the NTIAC technology assessment of NDE for SR degradation in COPVs represents a useful compilation of current technology that may be applicable in the future, but requires further work as described in the formal report. A study is currently being undertaken by the NASA NDE Working Group (NNWG) to help understand the degradation process leading to SR, so as to target and develop NDE that may be useful in detection. It is noted that the NNWG SR NDE research effort does not have adequate funding to fully resolve this issue, and other synergistic funding and complementary efforts are being sought to fill this important need for future NASA space programs.

IV. Methods for Locating Isolated Damage Although detection of delaminations in COPVs has been successfully accomplished by various methods,

detection of small fibers that have previously broken, independently of matrix damage, is far more difficult, and success is limited. Discontinuities in the extremely small fibers (typically only a few micrometers) are very difficult

* Kevlar® is a registered trademark of E. I. Du Pont de Nemours and Co., Wilmington, DE.

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to detect with direct imaging techniques. New developments such as high resolution x-ray computed tomography (XCT) hold some promise for laboratory-level analysis. Additionally, the acoustic emissions method allows detection of the origin and monitoring of active defect growth in COPVs under load. Generally, significant acoustic emissions only occur when new peak pressures are reached, and the vessels are generally acoustically silent at pressure variations below the last peak pressure. However, even with this limitation, it is effective in identifying new impact damage or areas where fiber has been strained to the point of damage or breakage. Also as discuss later in this paper, Shearography has also been found effective in identifying delaminations, impact damage, and localized variations in stress fields in COPVs.

One if the largest issues was also noted to be the general lack of a correlation between the specific NDE response and specific loss in structural integrity of the vessel. This is another area the NNWG has started looking at. An initial project to establish a correlation between calibrated inpacts, NDE response, and specific reduction in burst strength of certain carbon bottles is in progress.

V. Brief NNWG “Stress Rupture” NDE Project Overview The NNWG Stress Rupture NDE started in late 2005 and is currently continuing. The objective of the NNWG

project is to advance the state-of-the-art by developing NDE techniques that are capable of assessing SR degradation in COPVs in either a health-monitoring mode or a traditional remove-and-inspect mode. NDE techniques resulting from this effort will be a challenge to field and it will likely take several years.

The general approach is to determine the feasibility of a selected number of candidate NDE techniques for detecting degradation leading to SR in COPVs in either a health-monitoring mode or a traditional remove-and-inspect mode. This is done by submitting specimens of various SR age to many different type of NDE and evaluating for response that can be correlated. In parallel, destructive analysis (DA) is used to better understand SR failure signatures so as to better target NDE techniques.

The study is using Kevlar as the model COPV SR system for initial study, due to the substantial knowledge base in literature and numerous test specimens. An extensive number of Kevlar test articles with varying amount of actual age and time at stress are available for NDE evaluations. Additional, accelerated aging is being accomplished and the NDE response compared to the old Kevlar specimens. After knowledge is gained from the Kevlar study, it will be applied to COPVs made from carbon new and emerging fibers.

Kevlar composite specimens were developed by overwrapping aluminum-lined cylinders and aged to simulated long term stress rupture degradation. The accelerated aging efforts were accomplished using two different approaches: 1) by elevated stress levels, and 2) separately by stepped increases in temperature ASTM D 69923 to provide sets of test specimens (cylinders and coupons made from cylinders) for evaluation by NDE and destructive analysis. These methods provide test specimens with creep degradation without the complexities that result from oxidation, moisture, and ultraviolet light. During the aging, In addition to temperature and pressure transducers, Fiber Bragg grating (FBG) strain sensors and Acoustic Emission (AE) sensors were use in an effort to correlate their respective response to the stress rupture age progression and help develop data for later health monitoring applications. The FBG were predominantly surface-bonded, although a few were embedded to compare surface strain near the liner. Due to their extensive experience with ASTM D 6992, the Texas Research Institute accomplished the aging of the specimens in consultation with researchers at Cornell University, and NASA is accomplishing most of the NDE.

Aging has gone as anticipated and interesting relationships are being observed in the data FBG, AE, and temperature data. This data will be assemble and reported following data analysis. Each of the cylinder specimen sets will now be evaluated by each NDE technique and also by destructive assay. The most likely candidates for health monitoring are thought to be acoustic emission, eddy current sensors to evaluate composite and liner thinning through changes in stand-off, Bragg gratings, and other conventional strain sensing techniques. Following this, all NDE and DA results are to be analyzed and the most promising NDE methods selected. Various fleet leader specimens (virgin, aged, and failed) will then be evaluated with down-selected NDE and DA to determine capability of NDE and DA methods on complex specimens with “real” age.

VI. NDE for WSTF Experimental Carbon Bottle Burst Testing The NDE SPRT supported the commercially available† Carbon COPV Bottle Burst Testing at WSTF in 2004

and the project provided an excellent example of successful applications of pretest NDE and optical FBGs. The objectives were to screen for detectable impact damage or manufacturing defects, assess any notable tank-to-tank

† Manufactured by Luxfer® Inc., Riverside, CA.

manufacturing variance, and assess the potential use of multiple FBG strain sensors for COPV ground test monitoring and/or flight COPV health monitoring purposes. Pretest NDE included ultrasonic testing (UT), eddy current testing (ET), flash thermography, and shearography. Following pretest NDE, 18 FBG sensors were bonded to the COPVs and monitored during the testing.

A. Pretest NDE NDE SPRT members at the Aerospace Corporation (El Segundo, California) accomplished the UT and ET. For

UT, the COPVs were filled with water and immersed. The cylindrical region of each COPV was subjected to pulse-echo testing at 25-MHz using a commercial system. Reflected radio frequency wave trains were digitized and stored for each point on a 0.05-in. axial by 2-degree circumferential grid. These data were analyzed in a number of ways to reveal potential delaminations between the overwrap layers, unbonds between the overwrap and liner, and potential wind anomalies.

For ET, a commercial 2.5-MHz anisotropic probe was held in dry contact with the cylindrical surface of the COPV. Data were accumulated on a 0.05-in. axial by 2-degree circumferential grid. Scans were then performed for two orientations of the probe: with the induced current 1) perpendicular and 2) parallel to the hoop fiber direction. The results reflected variations in the overwrap (fiber conductivity, fiber density, wind anomalies, etc.).

For example, there was one prominent indication (in bottle No. 1894) evident in both the UT and ET results. The material was at least one ply thinner on one side of the indication and at least one ply thicker on the other side; therefore, it appeared that a ply had slipped. There was nothing to indicate that a ply was twisted (no local high spot). This was not thought to have a significant effect on the burst data, and proved not to since it had the second-highest burst pressure of the lot.

Flash thermography was performed at NASA Marshall Space Flight Center (MSFC) using a thermal wave imaging data acquisition system running EchoTherm®‡ software and an Indigo Merlin§ infrared camera. The bottles were prepared for the thermographic test by painting with water-soluble flat black paint and applying temporary 0.125-in. square lead tape markers placed on 60-degree centers. The thermographic evaluation was relatively quick, taking approximately 1 h per bottle, including setup. Thermography provided a screening for handling damage (delaminations) and process variations (such as porosity or misplaced fibers/tows) that may be present in the vessels. Enhanced thermography images were made by subtracting the pre-trigger image from the images acquired after flash heating. Many small regions of porosity, voids, or low consolidation were noted. These regions show up as small white “hot” patches in the thermograms. The regions were noted to be scattered and numerous, but not thought to be significant enough to affect the structural integrity of the vessels.

Shearography was also performed at MSFC using a Laser Technology, Inc. (LTI) (Norristown, Pennsylvania) SC-5100 system (Figure 1). The bottles were prepared for testing by coating them with water-washable penetrant developer. The bottles were pressurized to less than 5 psig during the shearography test. This evaluation was nearly as quick as the thermography, with surface preparation for each vessel taking less than 0.5 h each and the actual test taking no more than 1 h for each vessel. Shearography provided a measure of the expected strain field generated during pressurization, but at a very low proof level. Variations in the strain field will show in the out-of-plane surface deformation that shearography measures. The test locates regions of the vessel that have lower stiffness properties as a result of handling damage, manufacturing/process variations, or aging. No indications were noted in raw data or wrapped or unwrapped phase maps. The NDE testing helped ensure that the data collected during burst testing were not biased by poor bottle quality.

B. Fiber Bragg Grating Strain Sensors The NDE SPRT used FBG sensors to monitor the stress strain relation in the carbon fiber/matrix during the

testing at WSTF with consultation from MSFC staff. Twelve FBG sensors were laid out and attached to the bottle surface as described below.

VII. Sensor Layout and Installation Figure 2 shows the layout orientation of the sensor strings on the bottle. Four sensor strings (three sensors in

each string, two strings to a channel) were adhered to the bottle surface with the fiber along the bottle axis, and two sensor strings were aligned with the fiber along the hoop direction.

‡ EchoTherm® is a registered trademark of Thermal Wave Imaging, Inc., Ferndale, MI. § Merlin® is a registered trademark of Indigo Systems Corporation, Santa Barbara, CA.

When looking down at the bottle from the pressure port, the origin is designated to be at the transition from curved surface to the bottle flat directly below the first digit of the serial number on the bottle pressure port (see Figure 2), the axial sensors are centered in the flat along the y direction (along the bottle axis) with 2.5 in. between sensors, and are placed every 90 degrees in the φ (hoop) direction. The hoop sensors were placed as close as possible to six of the axial sensors.

VIII. Sensor Interrogator Setup The sensor interrogation unit consisted of a tunable laser module, beam coupling optics, wavelength reference,

light detectors, and a personal computer with a high-speed data acquisition card. An optical diagram of the interrogation unit is shown in Figure 3. Light emitted from the tunable laser was split equally into four paths: three sensor channels and one reference channel. In each sensor channel the light was split equally into each of two sensor strings. The sensor reflections passed back through the 2 x 2 coupler to the detector. In the reference channel, light passed through a gas reference cell in which it was absorbed at a series of well-known wavelengths. As the laser swept through its wavelength range, the channel waveforms were collected by an external computer using a high-speed analog-to-digital (A/D) data acquisition card that monitored the voltages output by the detector amplifier modules. Each channel supported six sensor wavelengths, three each on two strings. A spare A/D channel was used to collect the pressure transducer voltage so that the FBG sensor strain values could be directly plotted with bottle pressure.

IX. Experimental Procedure and Results For each of the ten commercial Carbon bottles that were tested, the pressure was ramped up at 50 psi/s to

roughly 2000 psi, held constant for roughly 3 min, allowed to drop to 0 psi and held for another 3 min. Then the pressure was ramped at 50 psi/s to 2000 psi and held for one min, then ramped up at the same rate until the bottle burst. The baseline strain readings were taken at time = 0 s.

After the bottles were burst and removed from the test chamber, the burst locations were recorded. The burst locations for each bottle are depicted in Figure 4 and listed in Table 1. All of the burst locations were within 1 in. of the center of the bottle in the axial direction, and were well distributed in the hoop direction.

Figure 1. Shearography setup.

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Figure 2. FBG sensor layout.

Tunable Laser Sensor Strings

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Figure 3. Sensor interrogation unit.

The graphs in Figures 5 through 9 depict the data corresponding to the 50-percent pressure cycle and burst

cycle. The plots display the ramp up to 2000 psi, the 3-min hold, the ramp back down to 0 psi, and the following 3-min hold. The plots are of the sensor strains as a function of time. These plots are useful when looking for creep during the 50-percent load cycle: creep is indicated if the sensor strains do not return to their starting position. An example of this effect is depicted in Figures 5 and 6: the strain curves during the 50-percent load cycle for the hoop sensors for a previously cycled bottle, No. 2179, and a pristine bottle, No. 2139. The hoop strains all return to within 15 microstrains of their starting strain for the previously exercised bottle, but remain as much as 600 microstrains above their starting strain for the pristine bottle, indicating residual fiber stress.

For an elastic material, assuming that the bottle stress is proportional to bottle pressure, the strain-versus-pressure plots should be linear, and should not show any appreciable gap between the rising and falling pressure curves. Most of the well-conditioned bottles exhibit elastic behavior during the 50-percent pressure cycle, as shown in Figure 7. However, a similar plot for a pristine bottle exhibits a far larger degree of hysteresis (Figure 8), indicative of material stretching in the hoop direction during the load cycle. There is also a difference in onset of non-elastic behavior during the burst testing between the pristine and well-conditioned bottles. Although the burst pressures for bottle Nos. 2179 and 2139 were different by only 220 psi (4430 psi versus 4210 psi, respectively),

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Figure 4. Bottle burst location depicted on the same plot as sensor location.

Table 1. Hoop and Axial Coordinates of the Burst Locationa

Bottle Number φ

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2189 45 4.75 2052 210 4.25 2099 20 3.75 2139 10 4.00 1903 350 4.50 2175 100 4.75 2179 120 3.75 2069 40 4.00 2176 285 4.00 1894 240 4.25

a Bottle numbers are listed in the order they were burst

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Figure 5. Strain as a function of time during the 50-percent load cycle for the channel 3 sensors (all in the hoop direction) for bottle No. 2179.

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Figure 6. Strain as a function of time during the 50-percent load cycle for the channel 3 sensors (all in the hoop direction) for bottle No. 2139.

Figure 9 shows that a large increase in slope of the strain curve occurs at approximately 3700 psi for the well-conditioned bottle (left), but close to 2300 psi for the pristine bottle (right). This increase in slope is likely a first indication of fiber and liner realignment of load sharing characteristics. This occurs at different pressures depending on the previous stress state of the bottle. Figure 9 also shows the first attempt to model the bottles and compare it with the actual measurement. This was done using ANSYS®** failure analysis software, without taking plastic behavior of the aluminum liner into account; hence it did not predict the liner’s behavior at the point of rapid strain transfer to the fiber.

A second model, constructed using the GENOA Progressive Failure Analysis (PFA)†† software, applied nonlinear elastic/plastic behavior for the liner material and micromechanics modeling of the fiber/matrix composite layers based on the manufacturing wind patterns. This particular model was only performed using data for a pristine vessel. The GENOA model indicates the onset of plastic behavior and the subsequent shift of stress to the composite layers. A plot of the stress at the surface in the hoop direction near the equator of the vessel is shown in Figure 10. The lower curve represents the stress in the composite, while the upper curve is the computed stress in the fibers themselves. The plot supports the assessment of the knee occurring near the same point as measured by the Bragg sensor.

X. General FBG Experimental Conclusions Since the testing was performed on the ten articles, interesting trends and repeatable measurements were made

showing in the strain fields during initial pressurization to 2000 psi and then from ambient to burst pressurization up to burst. Clear differences were seen in the behavior of virgin versus previously pressurized vessels that could be correlated with a structural analysis of the tanks. Additionally, the FBG results were instrumental in determining the true stress ratio. This resulted in substantial upward revisions to the actual stress ratios that were present in the

** ANSYS® is a registered trademark of Swanson Analysis Systems, Inc., Houston, PA. †† GENOA-PFA is licensed by Alpha STAR Corp., Long Beach, CA.

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Figure 8. Strain as a function of pressure during the 50-percent load cycle for the channel 3 sensors (all in the hoop direction) for bottle No. 2139.

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Figure 7. Strain as a function of pressure during the 50-percent load cycle for the channel 3 sensors (all in the hoop direction) for bottle No. 2179.

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Figure 9. Strain as a function of pressure during the burst cycle for the channel 3 sensors (all in the hoop direction) with predictions made with ANSYS software.

WSTF SR testing. One of the vessels was first thought to have ruptured at a problematic 52-percent stress ratio

and the FBG system provided the data necessary to correct the stress ratio to 58 percent. Many of the FBGs also indicated valuable information on fiber load redistribution and matrix micro cracking. This, like acoustic emissions data, helps give the location of active areas of load redistribution and needs more study to better utilize the capability. The method also shows promise for longer-term monitoring of other bottles during testing at WSTF and for potential flight application.

XI. NDE Supporting Current WSTF Kevlar COPV Testing A test program is in progress at WSTF with the objective of providing data that can be used to better predict the

reliability of certain Kevlar COPVs types that have been in use for many years, and hopefully extend their useful life. Volumetric/strain testing and associated laboratory analysis are being accomplished to understand composite/liner interaction, the “through-wall” stress gradient, and evaluate other strain and volume changes as the as COPVs are pressure cycled and then finally burst. Age and environmental related material degradation are also being evaluated. Stress rupture testing may also be accomplished to evaluate the life prediction model. To effectively accomplish this testing, both pretest NDE to verify the structural integrity of the test articles and real-time NDE are being used during testing to develop critical data.

Table 2 indicates the typical NDE and test instrumentation being applied, with a brief indication of what is being measured. Pretest NDE and other NDE used to gather test data are discussed in more detail in the following sections (such as eddy current used to determine composite thickness change with pressurization).

A. Overview of COPV FBG Strain Measurement The basic FBG system and sensor interrogation unit is the same as discussed previously under NDE for the

earlier WSTF Experimental Carbon Bottle Burst Testing; however, additional strain sensors are utilized. The FBG sensor attachment area on the Kevlar COPV was cleaned and the surface conditioned. The sensor strings were routed to the dome section of the bottle, where they were taped in place and terminated to the fiber optic connector block using double-sided adhesive foam tape. The sensors were all placed on the bottom hemisphere, under the rationale that the bottle was symmetrical about the equator, the sensors would be more out of the way on the bottom side, and the fiber cables could be more easily mounted to a connector block near the bottom pressure port for patching and routing.

Most of the sensors were aligned in the direction of the tow that makes up the wrap, since this should be the direction of the critical strain that would determine when the wrap will fail; but a few sensors were also oriented perpendicular to the tow orientation. The FBG were routed to avoid the location of several acoustic emission sensors, and none of the fibers were allowed to pass over the bottle equator, since two “belly band” wire

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Table 2. Typical WSTF COPV Test NDE and Instrumentation.

Method Measurement

Visual inspection (pretest) External inspection of overwrap. Indication of gross damage

Flash thermography (pretest) Heat signature decay. Sub-surface ply delamination

Borescope inspection (pretest) Internal inspection of liner. Indication of damage or buckling

IR heat soak thermography (pretest) Heat signature decay. Sub-surface ply delamination

Shearography (pretest) Differential strain resulting from anything that would cause it (e.g., impacts, delaminations, broken fiber)

Fiduciary marking (pre/posttest) Measurement of distance between marks

Pressure, temperature (test) Time, pressure, and temperature

Cabled girth linear variable displacement transducer (LVDT) (test)

Circumferential displacement measured at 0, 45, and 80 degrees

Boss LVDT (test) Axial displacement

Conventional Strain gauge (test) Change in length. Fiber strain

Fiber Bragg grating (test) Change in length. High resolution

Acoustic emission (test) Acoustic noise. Fiber breakage or delamination

Volume displacement (load cell and supply weight)

Vessel test fluid mass. Strain and fiber creep (weighed from supply and expulsion volumes)

Full field digital image correlation Vessel strain

Eddy current probes Composite thickness change

Raman Spectroscopy – portable Residual stress and stress changes while pressurizing

displacement sensors were installed there to measure the bottle diameter as a function of pressure. After the FBG sensors were installed, foil strain gauges were installed adjacent to them to allow comparison of data. It was found that the method of attachment was much more critical for application of surface mount FBG and in general the data

as not as accurate or repeatable as the conventional strain gauges.

. Eddy Current Composite Thickness Measurement During pressurization, a thinning of the Kevlar composite of the COPVs was predicted. Eddy current techniques

rovide a means to measure this change in composite thickness, and have been implemented for the pressurization nd burst tests at WSTF. Additionally, it was determined that liner thickness variations could also be evaluated by sing both the horizontal and vertical component of the signal. NASA Langley Research Center (LaRC), in onjunction with WSTF, has instrumented a COPV eddy current composite thickness gauging measurement system. brief description of the inspection system and anticipated results are discussed in the following paragraphs.

Eddy current techniques are primarily designed to operate based upon the electromagnetic induction of current nto a conducting object due to the applied alternating magnetic field of a test coil. The induced current acts to ppose changes in the applied field, and results in a change in impedance of the test coil. Eddy current instruments re designed to measure these changes in the test coil impedance, which are then correlated with physical properties uch as the conductivity of the material under test and lift-off distance (test coil to conductor spacing). For COPV omposite thickness inspections, eddy current lift-off measurements can be performed to measure the probe-to-liner pacing. With the probe bonded to the Kevlar surface, this effectively measures the thickness of the Kevlar omposite.

Figure 11 displays the system supporting the WSTF COPV studies. A commercial Zetec MIZ-27®‡‡ SI eddy urrent instrument is used to simultaneously drive four custom-wound eddy current coils on the Kevlar COPV and

‡‡ MIZ® is a registered trademark of Zetec, Inc., Issaquah, WA.

eight on the larger gaseous helium tanks. The coils, shown in the right-hand side of Figure 11, are each enclosed in a housing 1-in. in diameter and 0.75-in. tall. Each coil has been placed on an insulating surface (Delrin®§§ sheet) over a stainless steel conductor. In this laboratory environment, the simple geometry mimics the Kevlar composite over a COPV with a metal. A laptop computer is used to acquire and archive the data in real-time during testing. In the figure, the normalized impedance of the four coils is displayed in the four dots in the center of the MIZ-27 screen. The signals have been nulled, or balanced, at the respective composite thicknesses seen by each probe and rotated such that a change in lift-off results in a vertical deflection of the eddy current signal. The probe response is digitized and stored on the laptop computer, while the vertical components of the signals are displayed in a strip chart on the computer screen. A separate analog input channel is reserved to acquire timing information from the pressurization tests.

In order to determine the voltage change caused by a given change in composite thickness, calibration of the probes and equipment is needed. This is performed using nonconductive shim material to measure the change in probe output for a known thickness change. The calibration range should encompass the range-of-thickness change anticipated during the test. In Figure 12, the computer display for the removal of a 0.001-in. plastic shim over the 0.25-in. insulator block is shown. For these tests, a 15-kHz drive signal was supplied to the test coils. A unit drop in the voltage measured when the shim was removed was clearly well above the background variation of the system. The sensitivity of the measurement is dependent upon the nominal composite thickness and is typically inversely proportional to probe-to-conductor spacing. Table 3 shows the voltage change corresponding to a 0.001-in. change in composite thickness at nominal composite thickness values of 0.25, 0.375, 0.5, and 0.75 in.

0mttn

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Figure 12. Screenshot of data in Plot 2 shows voltage change associated with change in thickness from 0.251 to 0.250 in. as a 1-mil shim is removed from probe 2 at T ~ 100. All other channels remained at nominal coating thicknesses.

Figure 11. Eddy current inspection system for COPV composite thickness measurement

Table 3. Eddy Current System Response for Various Nominal Lift-Off Values. Nominal Composite

Thickness 0.25 in. 0.375 in. 0.5 in. 0.625 in. 0.75 in.

∆V/mil 0.35 V/mil 0.18 V/mil 0.12 V/mil 0.065 V/mil .04 V/mil

The noise floor of the system has been measured at about 0.02 V, providing an absolute sensitivity of near

.5 mil for the 0.75-in. composite thickness, and greater sensitivities at smaller composite thicknesses. In reality, the easurable composite thickness change is likely to be limited by external system noise and instrumentation drift. In

he open laboratory, sensor outputs were seen to drift by approximately 0.1 V over a 1-h time period, due in part to emperature variations. An equivalent value for sensors bonded onto a COPV configured for pressurization testing is ot currently available.

After laboratory validation at the NASA-Langley Research Center, the eddy current system was shipped to STF for installation on a COPV vessel. Figure 13 shows an example COPV with the eddy current sensors

ttached. One of the sensors is clearly visible just above the equatorial belly band.

§§ Delrin® is a registered trademark of E. I. Dupont de Nemours, Wilmington, DE.

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Figure 13. Eddy current sensors installed on COPV.

ollowing laboratory calibration, COPVs were installed on at the pressurization facility. Various pressurization s were applied while the composite overwrap thickness was measured with the eddy current sensors. Figures 14 5 display resulting composite and liner thickness change in a sample final ramp to burst. A decrease in the osite and liner thickness is measured on all channels as the pressure increases. An x-ray correlation was plished on the first vessel to help validate the eddy current thickness measurements and found the eddy

nt measurements to be accurate to the resolution of the x-ray technique. Although data from up to eight eddy nt sensors per COPV was sometimes a bit time consuming to reduce and analyze, it has been instrumental and dicated how the composite and liner strain together through yield and all the way to burst.

igital Image Correlation igital image correlation (DIC) was accomplished using ARAMIS software. This technology uses the

iples of 3D image correlation photogrammetry that gives full-field displacement and strain measurements. The principles of 3D image correlation photogrammetry have been known for about 15 years.4 The particular 3D e correlation system being utilized, ARAMIS, has been commercially available for about 10 years. he system requires spraying random high-contrast dot patterns onto a sample; this pattern is then tracked in

MIS by thousands of unique correlation areas known as facets. The center of each facet is a measurement point an be thought of as a 3D extensometer. Arrays of them form in-plane strain rosettes. The facet centers are ed in each successive pair of images, with accuracy up to one-hundredth of a pixel.5

For the typical WSTF COPV installation (Figure 16)a resolution of 512 x 512 pixels, giving a recording speedspeeds were used for some tests due to the negative heatinsurface mounted instrumentation. The Phantom cameras aARAMIS software can take measurements. The volume vcamera setup consisted of 35-mm lenses with the camerasvolume of 1060 mm/875 mm/875 mm. To calibrate for thpixels, and a 1200 mm NIST-traceable calibration cross wsensor. After successful computation, the calibration devithan the 15 degrees required for a successful calibration. Ttime for synchronization, which provided accuracy withinthe vessel consisted of a white background with 0.25-in. bFigure 16. The system was particularly useful in indicatinthe COPV pressurization range as indicated in Figure 17 aalso provided excellent strain data in areas where conventto these, as indicated in Figure 18, except where cables or

*** Phantom® is a registered trademark of Vision Research

Figure 16. Digital image correlation camera view o

Figure 15. Example Liner thickness reduction with pressure.

Figure 14. Example Composite thickness reduction with pressure.

, digital high-speed Phantom®*** v7.0 cameras were used at ranging from 100 to 3000 frames per second (fps). Lower g affect that supplemental lighting had on other COPV ct as a stereo pair to create a volume of area in which the aries with the calibration method and field of view. This at a typical angle of 15.7 degrees, giving a measuring is volume, the camera resolution was set at 800 x 1200 as rotated and moved in specified locations to calibrate the

ation was below 0.04 and the angle variance was larger he cameras used inter-range instrumentation group (IRIG) 1 microsecond between images. The pattern sprayed on lack dots sprayed on the surface viewed, as noted in g overall principal strain fields that developed higher in nd indicating surface fiber failure near burst. The system ional strain gauges were not installed and correlated well other instrumentation interfered.

, Inc., Wayne, NJ.

f COPV (Black dots sprayed over area of interest).

Figure 17. Digital image correlation Full Field Principal Strain .

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

Pressure (psi)

Stra

in (m

s)

h SG-13 0°h SG-37 120°h SG-24 240°DIC ARAMIS

Figure 18. Digital image data correlation to conventional strain gauges

S

train

(ms)

D. 40-in. COPV Pretest NDE Shearography To help verify the integrity of a large 40-in. COPV prior to test, shearography was utilized as shown in

Figure 19. This testing was accomplished under the guidance of John Newman††† and with equipment supplied by NASA Kennedy Space Center. This approach, in combination with heat soak thermography, was deemed to give an excellent pretest health check of the 40-in. COPV. A general discussion of the system follows. Subsequent testing of 24 additional spherical Kevlar and spherical and cylindrical carbon COPVs was then accomplished in September 2006 and provide excellent results.

The shearography camera uses a Michelson-type interferometer with two essential modifications. First, one mirror is precisely tilted to induce an offset, or sheared image, of the test part with respect to a second image of the part. Second, the sheared amount is a vector with an angle and a displacement amount. The shear vector, among other factors, determines the sensitivity of the interferometer to surface displacement derivatives.

The two laser speckle images of the test part, offset by the shear vector, interfere at every paired point over the surface in the field of view. The single frequency laser light from the two sheared images of the part is focused onto the camera array of photosensitive pixels. Light from pairs of points in each sheared image interfere. Each video frame, comprised of the complex addition of these two sheared images, can be subtracted from a stored reference image. The absolute difference yields a fringe pattern observed on the monitor. The second mirror in the Michelson interferometer may be phase-stepped using a piezoelectric device and the images combined to create a phase map (Figure 20). Further processing using any number of unwrapping algorithms may be used to generate fringe-free images of local surface deformation derivates.

In practice, each step in creating a shearogram is performed automatically using image-processing macros constructed by combining each processing function in a sequence. Shearography system operators perform a test with a single keystroke.

††† John Newman is the president and founder of

background information on shearography. He hNDT methods since 1970. Mr. Newman foundeshearography system in the mid 1980s. Mr. Newcurrent Chairman.

LTI/NASA Kennedy Figure 19. LTI SC-5100 system bein

Pressure Supply Panel COPV Support and Rotation Bearing

Laser Technology, Inc. in Norristown, PA, and author of the as worked in the field of holography, shearography, and laser d LTI in 1977 and led the development of the first electronic man initiated the ASNT Laser Methods Committee and is the

Space Center Shearography Test Team Photo

g applied to Kevlar COPV.

COPV Pressure Gauge G1 LTI-5100 ShearographyCamera

E. Quantitative Shearography Measurements Precision calibration of the shearogram image scale (pixels/in.) and the shear vector allows further processing of

shearography data to determine defect indication dimensions, area, and the deformation of the material. The digital measurement of the deformation derivative may be integrated to show the shape of the target surface deformation as well as the magnitude of the deformation at any location, as in Figure 20. Shearography can be used to measure the deformation response of a structure to an applied load and as a means for deriving material properties.

An example of composite shearography images of a Kevlar test tank is shown in Figure 21. The pressure was cycled between 70 and 90 psi to create a delta strain for each image. The sensitivity is noted by very slight strain indicated in the overwrap pattern and from tank features such as the girth weld area. Minor delaminations are also indicated in the upper right where wrap patterns cross. However, no impact damage was noted as seen on the impact standard image shown on the lower right. Shearography of a carbon test COPV is also shown in Figure 22. In this figure, damage from calibrated impacts are clearly imaged and the sensitivity of the system is indicated by the less substantial and unexpected un-programmed damage noted on the lower left.

Figure 20. A phase map shearogram with horizontal shear vector yields a fringe pattern showing the first derivative of the out-of-plane deformation, ∂w/ ∂x. Using an unwrapping agorithm, the image at right shows the positive (white) and negative (black) slope change. The metal plate with a 4.0-inch diameter flat-bottomed hole was deformed by 7.0 µm.

Strain Concentration at the equator over liner circumferential girth weld.

Quilted deformation pattern due to tape placement and thinner composite between wraps.

Minor tape delamination Near end boss.

Impact damage on a COPV at WSTF. Damaged areas are 1.3 in. diam. compared to the 0 .25 in. visual dent on the surface.

COPV Test Standard

Figure 21. Example Shearography image of Kevlar COPV as compared to a damage standard.

F. Thermography Experimental Setup NASA LaRC developed the WSTF IR thermography system that was used for single-sided data acquisition on

the 40-in. Kevlar COPV, shown in Figure 23. The IR imager is a commercial radiometer with a cooled 256 H x 320 V-element InSb (indium - antimonide) focal plane array detector. The radiometer’s noise equivalent temperature difference (NE∆T), cited by the manufacturer, is 0.025 °C when operating the detector in the 3 to 5 µm wavelength range. The radiometer produces images at both 30 fps output (video frame rate, in an RS170 format compatible with standard video equipment) and 60 fps output in a 12-bit, RS422 digital format. External optics, consisting of a wide-angle lens using germanium optical elements, were used to increase the system field-of-view by a factor of approximately two. The expanded field-of-view of this lens is 41 degrees horizontally and 31 degrees vertically.

Heating of the inspection surface is produced by focusing two 500-W quartz lamps on the inspection area, using parabolic reflectors. The heating time for the COPV was 90 s, and temperature data were acquired during the cool-down for 10 min (a reduced frame rate of 5 fps was achieved by sub-sampling). Because of the large thermal mass of these specimens, the surface temperature rise during heating was less than 10 °C. Although the surface of the specimen was somewhat reflective, it was not necessary to apply any emissivity enhancing coating since data were only acquired during the cool-down.

XII. Experimental Results Only one minor indication, possibly a small near-surface ply disband or resin lean area, was noted real-time

during data collection (Figure 24). However, additional heat soak thermography and ultrasound were done of the area and it was deemed not to be a concern.

Un-programmed Damage Figure 22. Shearography Inspection of Impact Damaged Carbon COPV

XIII. Acoustic Emissions Overview Technical support for the AE test support was provided by the NASA Langley Research center. AE sensors

were installed typically in 5 locations on smaller COPVs and 12 positions on larger COPVs. Three were installed on the upper boss, three others on the lower boss and six were installed around the equator. Using this configuration, sensors were used to triangulate the source locations for the acoustic activity. Sample data is shown super imposed on the 2D symbolic view of a spherical COPV shown in Figure 25. Lighter indications depict activity locations on the lower side. An example of the total number of acoustic events plotted during a pressurization and hold is indicated in Figure 26. In this case it is significant to note that acoustic activity continued during the pressure hold from 1500 to 2000 seconds. At lower pressure holds, this acoustic activity did not continue. This may be indicating that damage is profligating and the overwrap may be slowly failing. As more data is added to the COPV AE database, this type of data may be very valuable for COPV in situ health monitoring. During the WSTF COPV testing, a timeline of all COPV failure events was assembled and AE data was reviewed in detail and was extremely useful for correlation to DIC and other measurement techniques to substantiate and map locations of fiber breakage and fully characterize COPV performance.

Figure 23. Heat soak thermography application to Kevlar COPV.

Indication

Reflection

Figure 24. Example Kevlar COPV heat soak thermography images.

Figure 25. Example Unfiltered AE COPV Data - All Events

Events Count vs. Time and Pressure vs. Time

0

1000

2000

3000

4000

5000

6000

7000

0 500 1000 1500 2000 2500 3000 3500 4000 4500

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XIV. Conclusions The NASA COPV assessments started by the NESC in 2004 led to the evaluation of NDE applicable to COPVs

and the follow-on work is still in progress. Reasonably mature NDE methods were identified for application to detect impact and other localized damage. However, NDE response has not been quantitatively related to a specific reduction of structural integrity. Additionally, no NDE methods were found available for evaluation of global material property changes that could be related to progression toward stress rupture or that could aid in life predictions. Therefore, detailed recommendations for a stress rupture NDE program were provided by the NESC NDE SPRT, but the new NDE will likely take years to field. The NNWG is currently proceeding with the recommendations to the extent that funding is available, but more work needs to be done in this area.

The applications of several NDE methods to pretest screening of Kevlar and other carbon COPVs undergoing testing at WSTF have demonstrated their effectiveness. Additionally, NDE techniques applied real-time during COPV testing is providing excellent test data and helping to provide critical rationale to continue flying aging vessels. Due to the magnitude of these efforts, these applications are provided as an overview only and the paper serve as a pathfinder for other who may want to collaborate on COPV NDE.

XV. References 1. Johnson, E. C. and J. P. Nokes. “NDE Techniques Assessment for Gr/EP Composite Overwrapped Pressure

Vessels.” Proceedings of the Ninth International Symposium on Nondestructive Characterization of Materials, Sydney, Australia, June 28-July 2, 1999.

2. Nondestructive Evaluation for Stress-rupture Degradation in Composite Overwrapped Pressure Vessels. Prepared by the Nondestructive Testing Information Analysis Center, a DOD Information Analysis Center. Sponsored by the Defense Technical Information Center (DTIC). Prepared for the NASA Engineering and Safety Center, Contract SPO700-97-D-4003, Delivery Order No. 0033, TAT No. NT-04-0005/0038, November 2004.

3. ASTM 6992, Standard Test Method for Accelerated Tensile Creep and Creep-Rupture Of Geosynthetic Materials Based on Time-Temperature Superposition Using the Stepped Isothermal Method, American Society for Testing of Materials, West Conshohocken, PA, 2003. Method applied by J. S. Thornton, Texas Research Institute, TRI/Austin, Inc., 9063 Bee Caves Road, Austin, Texas 78733, U.S.A.

4. Kahn-Jetter, Z. L. and T. C. Chu. “Three-dimensional Displacement Measurements Using Digital Image Correlation and Photogrammetric Analysis,” Experimental Mechanics, Vol. 30:1, pp. 10-16, March 1990.

6. Schmidt, T., J. Tyson, D. M. Revilock, Jr., and M. Melis. “Full-field dynamic deformation and strain measurements using high-speed cameras.” SPIE 26th ICHSPP, September 2004.

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raph

y, u

ltras

ound

, sh

earo

grap

hy, a

nd a

cous

tic e

mis

sion

s (c

oin

tapp

ing)

.–

Det

ectio

n of

fibe

rs th

at h

ave

prev

ious

ly b

roke

n in

depe

nden

t of m

atrix

da

mag

e is

diff

icul

t, an

d su

cces

s is

lim

ited

in th

is a

rea.

•E

xtre

mel

y sm

all f

iber

s (ty

pica

lly o

nly

a fe

w m

icro

met

ers)

are

ver

y di

fficu

lt to

eva

luat

e w

ith d

irect

imag

ing

tech

niqu

es.

•S

ome

rece

nt im

prov

emen

ts in

ND

E m

etho

ds p

erm

it en

hanc

ed

dete

ctio

n an

d ch

arac

teriz

atio

n of

del

amin

atio

n, fi

ber b

reak

age,

an

d m

atrix

cra

ckin

g no

t det

ecta

ble

in e

arlie

r CO

PV

ND

E s

urve

ys.

•H

igh-

reso

lutio

n X

-ray

Com

pute

d To

mog

raph

y (X

CT)

als

o ho

lds

som

e de

gree

of p

rom

ise

for l

abor

ator

y-le

vel a

naly

sis.

•A

cous

tic e

mis

sion

s m

etho

d al

low

s de

tect

ion

of th

e or

igin

and

m

onito

ring

of a

ctiv

e de

fect

gro

wth

in C

OP

Vs

unde

r loa

d.–

Acou

stic

em

issi

ons

of in

tere

st o

nly

occu

r whe

n ne

w p

eak

pres

sure

s ar

e re

ache

d, b

ut m

ay b

e an

indi

cato

r tha

t rup

ture

is im

min

ent.

8

Met

hods

for C

hara

cter

izin

g G

loba

l Dam

age

•N

o N

DE

tech

niqu

e is

cur

rent

ly k

now

n to

be

dire

ctly

ap

plic

able

for p

redi

ctio

n of

str

ess

rupt

ure

and

othe

r life

-de

pend

ent C

OPV

issu

es.

–Fo

r life

issu

es: w

e ne

ed to

iden

tify

yet u

ndef

ined

phy

sica

l attr

ibut

es

or p

heno

men

a pr

oduc

ing

failu

re in

ord

er to

app

ly a

ppro

pria

te N

DE

.•

For K

evla

r: th

e po

ssib

ility

of “

cree

p”an

d/or

acc

umul

ated

“mic

ro-

crac

king

”or s

low

fibe

r che

mic

al d

egra

datio

n m

ay b

e ar

eas

to

targ

et fo

r dev

elop

men

t.•

For

carb

on fi

ber:

accu

mul

ated

mic

ro d

amag

e m

ay b

e a

fact

or,

alon

g w

ith th

e po

ssib

ility

of e

xtre

mel

y sl

ow c

reep

.–

Var

iatio

ns in

fibe

r res

idua

l stre

ss o

r stre

ss c

once

ntra

tions

may

also

co

ntrib

ute

to C

OP

V fa

ilure

: If s

ome

fiber

s ex

perie

nce

high

er lo

ads

than

ot

hers

, onc

e th

e m

ore

high

ly s

tress

ed fi

bers

fail,

a c

hain

reac

tion

may

re

sult

in th

e tra

nsfe

r of e

ver-

incr

easi

ng s

tress

to th

e re

mai

ning

fibe

rs,

lead

ing

to C

OP

V fa

ilure

.•

Sev

eral

CO

PV

ND

E te

chni

ques

hav

e be

en id

entif

ied

to

pote

ntia

lly a

sses

s th

e de

grad

atio

n of

fibe

r tha

t wou

ld le

ad to

st

ress

rupt

ure,

but

thes

e te

chni

ques

hav

e ye

t to

be a

dequ

atel

y ev

alua

ted.

–S

umm

ariz

ed in

the

back

up c

harts

–N

NW

G p

roje

ct ta

rget

s ev

alua

tion

of th

ese

9

NN

WG

CO

PV S

tres

s R

uptu

re N

DE

Goa

l•

To a

dvan

ce th

e st

ate-

of-th

e-ar

t by

deve

lopi

ng N

DE

te

chni

ques

that

are

cap

able

of a

sses

sing

stre

ss-

rupt

ure

degr

adat

ion

in K

evla

r CO

PV

s in

eith

er a

he

alth

-mon

itorin

gm

ode

or a

trad

ition

al re

mov

e-an

d-in

spec

tmod

e–

ND

E te

chni

ques

from

this

effo

rt w

ill ta

ke s

ever

al y

ears

to fi

eld.

Obj

ectiv

e•

Det

erm

ine

the

feas

ibili

tyof

can

dida

te N

DE

tech

niqu

es in

det

ectio

n of

deg

rada

tion

lead

ing

to

stre

ss ru

ptur

e in

Kev

lar C

OP

Vs

•In

par

alle

l, ut

ilize

des

truct

ive

anal

ysis

to b

ette

r un

ders

tand

stre

ss-r

uptu

re fa

ilure

sig

natu

res

so a

s to

be

tter t

arge

t ND

Ete

chni

ques

10

NN

WG

Tec

hnic

al A

ppro

ach

•U

sing

Kev

lar a

s th

e in

itial

CO

PV

stre

ss-r

uptu

re

syst

em fo

r ND

E s

tudy

-Sub

stan

tial k

now

ledg

e ba

se in

lite

ratu

re-D

ocum

ente

d to

resp

ond

to a

ging

tech

niqu

es-M

any

Kev

lar t

est a

rticl

es a

nd fl

eet l

eade

rs w

ith

“rea

l”ag

e ar

e av

aila

ble

for c

ompa

rison

-A fo

unda

tion

for f

ollo

w-o

n ef

forts

for C

OP

Vs

utili

zing

ca

rbon

and

em

ergi

ng c

omm

erci

al fi

bers

(e.g

., P

BO

(Z

ylon

); M

-5; a

nd h

ybrid

izin

g fib

ers

(car

bon

and

PB

O)

•A

test

pop

ulat

ion

of 1

00 K

evla

r spe

cial

test

CO

PV

s ha

ve b

een

wra

pped

and

will

be

used

to e

xam

ine

vario

us N

DE

tech

niqu

es u

nder

acc

eler

ated

agi

ng

cond

ition

s

11

NN

WG

Tec

hnic

al A

ppro

ach

(con

t.)

•A

ccel

erat

ed a

ging

is b

eing

acc

ompl

ishe

d by

two

met

hods

w

hich

use

prim

arily

ele

vate

d st

ress

(at h

igh

ambi

ent

tem

pera

ture

) and

sep

arat

ely

elev

ated

tem

pera

ture

to

prov

ide

sets

of t

est s

peci

men

s–

An

envi

ronm

enta

l cha

mbe

r has

bee

n co

nstru

cted

whe

re p

ress

ure

and

tem

pera

ture

are

con

trolle

d in

depe

nden

tly–

Req

uire

s bu

rsts

of 8

bot

tles

at 2

0 de

g. C

and

rupt

ure

of 2

6 ea

chun

der t

he tw

o ac

cele

rate

d ag

ing

cond

ition

s•

10 s

pare

bot

tles

are

rese

rved

for r

epla

cem

ents

as

need

ed.

•Th

e ag

ing

proc

ess

mon

itore

d w

ith F

BG

stra

in g

ages

and

A

E s

enso

rs b

oth

to fa

cilit

ate

agei

ng a

nd to

obt

ain

ND

E

data

12

NN

WG

Tec

hnic

al A

ppro

ach

(con

t.)

•U

se e

ach

ND

E te

chni

que

and

dest

ruct

ive

anal

ysis

to e

valu

ate

coup

on

and

cylin

der s

peci

men

set

s an

d do

cum

ent r

esul

ts

•A

naly

ze a

ll N

DE

and

DA

resu

lts a

nd s

elec

t mos

t pro

mis

ing

ND

E

met

hods

.

•E

valu

ate

vario

us e

xist

ing

spec

imen

s (v

irgin

, age

d an

d fa

iled)

with

do

wn-

sele

cted

ND

E a

nd D

A to

det

erm

ine

capa

bilit

y of

ND

E a

nd D

A

met

hods

on

mor

e co

mpl

ex s

peci

men

s w

ith “r

eal”

age.

13

Kev

lar T

est P

roje

ct O

bjec

tives

(Pig

gyba

ck)

•P

rovi

de d

ata

that

can

be

used

to e

valu

ate

and

pote

ntia

lly

exte

nd th

e us

eful

life

of t

he fl

ight

CO

PV

s –

Vol

umet

ric/s

train

test

ing

and

asso

ciat

ed la

bora

tory

ana

lysi

s: to

unde

rsta

nd c

ompo

site

/line

r stra

in in

tera

ctio

n an

d cl

arify

the

“thro

ugh-

wal

l”st

ress

gra

dien

t (co

mpl

ete)

–S

tress

rupt

ure

test

ing:

to d

eter

min

e if

relia

bilit

y m

odel

s pa

ram

eter

s ar

e co

nser

vativ

e –

Mat

eria

l deg

rada

tion

eval

uatio

n•

Bur

st te

st re

pres

enta

tive

CO

PV

s to

det

erm

ine

if bu

rst

pres

sure

has

dec

reas

ed, a

nd a

ccom

plis

h co

upon

s/st

rand

te

stin

g th

at w

ill h

elp

with

an

unde

rsta

ndin

g of

mat

eria

l de

grad

atio

n

14

NN

WG

Pro

gres

s to

Dat

e

•In

itial

Kev

lar P

iggy

back

Cam

pain

com

plet

ed w

ith e

xten

sive

ND

E d

evel

opm

ent

and

new

insi

ghts

(esp

ecia

lly fo

r stre

ss ru

ptur

e m

onito

ring)

–La

bora

tory

cha

ract

eriz

atio

n an

d fa

ilure

pre

curs

ors

note

d•

New

Agi

ng c

ham

bers

set

up a

t TR

I (pr

imar

ily T

RI R

&D

fund

s)•

Kev

lar C

OP

V A

ging

suc

cess

fully

com

plet

ed–

Age

d C

OPV

s an

d fa

iled

resi

dual

read

y fo

r “ro

und

robi

n”N

DE

ana

lysi

s•

TIM

hel

d at

TR

I to

shar

e da

ta: T

RI,

GR

C, U

of C

, WS

TF, o

ther

s•

Sig

nific

ant i

nsig

hts

gain

ed w

ith re

al-ti

me

ND

E d

urin

g ag

ing

–AE

dat

a vs

tim

e, k

nee

in th

e cu

rve

and

grow

ing

ampl

itude

pot

entia

lly w

arns

of f

ailu

re

to c

ome

–Th

erm

al e

last

ic a

ffect

at K

evla

r stra

nd fa

ilure

–La

RC

pro

vide

d A

E, W

STF

FO

BG

sys

tem

, MS

FC te

ch s

uppo

rt an

d fu

ndin

g•

Gre

at p

rogr

ess

at b

oth

GR

C U

nive

rsity

of M

isso

uri (

at C

olum

bia)

in D

A/N

DE

–

Fibe

r lev

el fa

ilure

mod

es n

oted

and

thro

ugh

the

thic

knes

s ef

fect

s of

voi

ds e

tc.

–R

aman

spe

ctro

scop

y •

Ext

ensi

ve d

ocum

enta

tion

from

GR

C o

n R

aman

for s

tress

mea

sure

men

ts a

nd e

arly

co

rrel

atio

ns o

f sam

ples

with

stre

ss ru

ptur

e ag

e•

Pap

er g

ener

ated

on

Ram

an in

sigh

ts fr

om U

of M

•

WS

TF p

rocu

red

mic

ro-lo

ad fr

ame

and

AE

sys

tem

/FO

BG

read

y to

sta

rt S

EM

te

stin

g to

imag

e st

ress

rupt

ure

of s

trand

s an

d ob

tain

AE

sig

natu

res

15

Typi

cal C

OPV

Inst

rum

enta

tion,

ND

E, a

nd D

A

Met

hod

Mea

sure

men

t V

isua

l Ins

pect

ion

(Pre

test

)Ex

tern

al in

spec

tion

of o

ver w

rap.

Indi

catio

n of

gro

ss d

amag

e

Flas

h Th

erm

ogra

phy

(Pre

test

)H

eat S

igna

ture

Dec

ay S

ub-s

urfa

ce P

ly D

elam

inat

ion

Bor

esco

pe In

spec

tion

(Pre

test

)In

tern

al in

spec

tion

of li

ner I

ndic

atio

n of

dam

age

or b

uckl

ing

IR H

eat S

oak

Ther

mog

raph

y (P

rete

st)

Hea

t Sig

natu

re D

ecay

Sub

-sur

face

Ply

Del

amin

atio

n

Shea

rogr

aphy

(Pre

test

CO

PV o

nly)

Diff

eren

tial s

train

resu

lting

from

any

thin

g th

at w

ould

cau

se it

(e.g

., im

pact

s, de

lam

inat

ions

, bro

ken

fiber

, etc

.)

Fidu

ciar

y M

arki

ng (P

re/P

ostT

est)

Mea

sure

men

t of d

ista

nce

betw

een

mar

ks

Pres

sure

, Tem

pera

ture

(Tes

t)Ti

me,

Pre

ssur

e, a

nd T

empe

ratu

re

Cab

led

Girt

h LV

DT

(Tes

t)C

ircum

fere

ntia

l dis

plac

emen

t mea

sure

d at

0, 4

5, a

nd 8

0 de

gree

s

Bos

s LV

DT

(Tes

t)A

xial

dis

plac

emen

t

Stra

in G

auge

(Tes

t)C

hang

e in

leng

th. F

iber

stra

in

Fibe

r Bra

gg G

ratin

g (T

est)

Cha

nge

in le

ngth

. Hig

h re

solu

tion

Aco

ustic

Em

issi

on (T

est)

Aco

ustic

noi

se. F

iber

bre

akag

e or

del

amin

atio

n

Vol

ume

Dis

plac

emen

t(L

oad

Cel

l and

Sup

ply

Wei

ght)

Ves

sel t

est f

luid

mas

s. St

rain

and

fibe

r Cre

ep (w

eigh

ed fr

om su

pply

and

ex

puls

ion

volu

mes

)

Full

Fiel

d D

igita

l Im

age

Cor

rela

tion

Ves

sel s

train

Eddy

Cur

rent

Pro

bes

Com

posi

te th

ickn

ess c

hang

e

Porta

ble

Ram

an S

pect

rsco

pyR

esid

ual S

tress

/iden

tific

atio

n of

stre

ss g

radi

ents

16

Hea

t Soa

k Th

erm

ogra

phy

App

licat

ion

1

2

4

3

65

Figu

re 1

Sect

ione

d C

OPV

with

def

ects

for u

se a

s a

stan

dard

•1

–4:

del

amin

atio

ns o

f Kev

lar f

iber

s•

Def

ects

5 &

6: h

ole

drille

d in

to th

e lin

er

Hea

t soa

k/co

ol-d

own

ther

mog

raph

y

17

Pret

est H

eat S

oak

Ther

mog

raph

y

•Tw

o 50

0-W

qua

rtz la

mps

wer

e fo

cuse

d on

the

insp

ectio

n ar

ea u

sing

par

abol

ic re

flect

ors.

–H

eatin

g tim

e fo

r the

CO

PV

was

90

s, a

nd te

mpe

ratu

re d

ata

was

ac

quire

d du

ring

the

cool

-dow

n fo

r 10

min

(a re

duce

d fra

me

rate

of 5

fp

s w

as a

chie

ved

by s

ub-s

ampl

ing)

.–

Bec

ause

of t

he la

rge

ther

mal

mas

s of

thes

e sp

ecim

ens,

the

surfa

ce

tem

pera

ture

rise

dur

ing

heat

ing

was

< 1

0 ºC

.–

Alth

ough

the

surfa

ce o

f the

spe

cim

en w

as s

omew

hat r

efle

ctiv

e, it

was

not

nec

essa

ry to

app

ly a

ny e

mis

sivi

ty e

nhan

cing

coa

ting

sinc

e da

ta w

as o

nly

acqu

ired

durin

g th

e co

ol-d

own.

18

Hea

t Soa

k Th

erm

ogra

hy

of S

pher

ical

CO

PV Indi

catio

n

Ref

lect

ion

Clo

se-u

p

19

Gen

eral

The

rmog

raph

y C

oncl

usio

n

•H

eat s

oak

Ther

mog

raph

y pe

rform

ed w

ell a

s an

in

spec

tion

tool

for t

he re

lativ

ely

thic

k w

all C

OP

Vs

–A

ppro

ach

finds

def

ects

dee

per t

han

conv

entio

nal F

lash

Th

erm

ogra

phy

–C

ompl

ete

insp

ectio

ns w

ere

perfo

rmed

rapi

dly.

•Th

erm

ogra

phy

used

in c

ombi

natio

n w

ith S

hear

ogra

phy,

w

as d

eem

ed to

giv

e an

exc

elle

nt h

ealth

che

ck o

f the

C

OP

V o

f con

cern

.

20

CO

PV S

hear

ogra

phy

•S

hear

ogra

phy

was

als

o re

cent

ly u

sed

to h

elp

verif

y th

e in

tegr

ity o

f 24

CO

PV

prio

r to

test

.–

Acc

ompl

ishe

d un

der t

he g

uida

nce

of J

ohn

New

man

, pr

esid

ent/f

ound

er o

f Las

er T

echn

olog

ies,

Inc.

(LTI

)–

Use

s a

Mic

hels

on ty

pe in

terfe

rom

eter

with

two

esse

ntia

l mod

ifica

tions

•O

ne m

irror

pre

cise

ly ti

lted

to in

duce

an

offs

et

(she

ared

) im

age

of th

e te

st p

art w

ith re

spec

t to

a se

cond

imag

e of

the

part

•S

hear

ed a

mou

nt is

a v

ecto

r with

an

angl

e an

d a

disp

lace

men

t am

ount

21

Sche

mat

ic D

iagr

am o

f a M

iche

lson

Typ

e Sh

earo

grap

hy In

terf

erom

eter

22

Shea

rogr

aphy

Tes

t Set

Up

–C

OPV

Insp

ectio

n CO

PVPr

essu

reG

age

G1

LTI-5

100

Shea

rogr

aphy

Cam

era

GN

2 Fl

owC

ontr

ol P

anel

CO

PV S

uppo

rtan

d R

otat

ion

Bea

ring

LTI/N

ASA

Kenn

edy

Spac

e C

ente

r She

arog

raph

y Te

st T

eam

Pho

to

23

Shea

rogr

aphy

Tes

t Set

-Up

for C

OPV

Tes

ting

Pneu

mat

ic O

pera

tion/

Shea

rogr

aphy

Dat

a C

aptu

re

Rig

id C

OPV

Sup

port

Fr

ame

allo

ws

tank

rota

tion.

CO

PV P

ress

ure

Gag

e0-

120

psi.

150

psi.

GN

2 Su

pply

Vent

V1 V2 1.V1

ope

ned,

pre

ssur

e ra

ised

to 7

0psi

., V1

clo

sed.

2.

Shea

rogr

aphy

refe

renc

e im

age

capt

ured

@ 7

0 ps

i.3.

V1 o

pene

d, p

ress

ure

rais

ed to

90p

si.,

V1 c

lose

d.4.

Shea

rogr

aphy

Str

esse

d im

age

capt

ured

@ 9

0 ps

i.5.

Fina

l she

arog

raph

y im

age

com

pute

d.

24

Exam

ple

Shea

rogr

aphy

Imag

es

•She

arog

raph

y sh

ows

surf

ace

defo

rmat

ion

deriv

ativ

es d

ue to

pre

ssur

e ch

ange

in ta

nk.

•Whi

te a

reas

are

sur

face

s sl

opin

g to

war

ds th

e ca

mer

a, d

ark

area

sar

e sl

opin

g aw

ay fr

om th

e ca

mer

a.•D

evia

tion

from

a n

eutr

al g

ray

valu

e of

128

(8-b

it, 2

56 g

ray

leve

ls) d

eter

min

e de

form

atio

n am

plitu

de.

•Fea

ture

s yi

eldi

ng a

str

ain

resp

onse

due

to lo

w in

tern

al p

ress

ure

chan

ge: T

ape

dela

min

atio

n,

impa

ct d

amag

e, C

OPV

des

ign

stra

in c

once

ntra

tions

Min

or ta

pe d

elam

inat

ion

Nea

r end

bos

s.

Stra

in C

once

ntra

tion

at th

e eq

uato

r ove

r lin

er c

ircum

fere

ntia

l gi

rth

wel

d.

Qui

lted

defo

rmat

ion

patte

rn d

ue to

tape

pl

acem

ent a

nd th

inne

r co

mpo

site

bet

wee

n w

raps

.

Impa

ct d

amag

eon

a C

OPV

at W

STF.

Dam

aged

are

as

are

1.3

in. d

iam

.co

mpa

red

to th

e 0.

25 in

. vis

ual

dent

on

the

surf

ace.

CO

PV T

est S

tand

ard

25

Car

bon

CO

PV S

hear

ogra

phy

Insp

ectio

n-1

0 ps

id

Dam

age

unde

tect

able

vis

ually

26

Cor

rela

tion

of S

hear

ogra

phy

Res

pons

e to

Im

pact

dam

age

•P

rovi

des

exce

llent

imag

e an

d ef

fect

ive

dam

age

area

to

com

pare

with

impa

ct c

hara

cter

istic

s

27

Cor

rela

tion

of S

hear

ogra

phy

Res

pons

e to

Im

pact

dam

age

Con

’t

27 ft

-lbs

15 ft

-lbs

23 ft

-lbs

•D

etec

ts a

reas

no

t rev

eale

d by

vi

sual

insp

ectio

n•

Dam

age

area

s fo

r diff

eren

t im

pact

ene

rgie

s vi

sual

ly e

vide

nt•

Dam

age

area

in

crea

ses

with

im

pact

ene

rgy

for a

ll C

OP

Vs

Dam

age

Area

(in2 )

05

1015

20

Impact Energy (ft-lbs)

010203040506070

Sm. C

yl.

Lg. C

ylin

der

28

Com

posi

te/L

iner

Thi

ckne

ss M

easu

rem

ent

Eddy

cur

rent

sys

tem

for r

eal-t

ime

CO

PV c

ompo

site

thic

knes

sN

ASA

Lang

ley

Res

earc

h C

ente

r

29

Eddy

Cur

rent

Sys

tem

X-r

ay V

erifi

catio

n

30

Exam

ple

Ove

rwra

p Th

ickn

ess

Eval

uatio

n by

Ed

dy C

urre

nt

31

Exam

ple

Line

r Thi

ckne

ss E

valu

atio

n by

Ed

dy C

urre

nt

32

Dig

ital I

mag

e C

orre

latio

n

•D

igita

l im

age

corr

elat

ion

is a

ccom

plis

hed

usin

g A

RA

MIS

so

ftwar

e –

3D im

age

corr

elat

ion

give

s fu

ll-fie

ld d

ispl

acem

ent a

nd s

train

m

easu

rem

ents

–S

yste

m w

as d

evel

oped

by

GO

M m

bh (B

raun

schw

eig,

Ger

man

y)•

Req

uire

s sp

rayi

ng ra

ndom

hig

h-co

ntra

st d

ot p

atte

rns

onto

a

sam

ple;

this

pat

tern

is th

en tr

acke

d in

by

thou

sand

s of

uni

que

corr

elat

ion

area

s (fa

cets

)•

Mea

sure

men

t poi

nts

from

cen

ter o

f eac

h fa

cet,

whi

ch c

an b

e th

ough

t of a

s 3D

ext

enso

met

er a

rrays

, for

m in

-pla

ne s

train

ro

sette

s

33

Dig

ital I

mag

e C

orre

latio

n Se

tup

Dur

ing

Bur

st T

ests

NAS

A G

RC

DIC

Tes

t Tea

m P

hoto

N

ASA

GR

C D

IC T

est T

eam

Pho

to

Blac

k do

ts s

pray

ed o

ver a

rea

of in

tere

st

34

Dig

ital I

mag

e C

orre

latio

n Vi

deo

Gre

en to

Red

ar

ea in

dica

ting

as

ymm

etric

st

ress

fiel

d du

ring

pres

suriz

atio

n (a

rea

of

acce

lera

ted

S

tress

Rup

ture

an

d gr

eate

r fa

ilure

risk

)

35

Nor

mal

ized

Str

ain

vs. P

ress

ure,

Hoo

p W

rap

on N

ASA

CO

PV T

est

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

1000

0

1100

0

1200

0

010

0020

0030

0040

0050

0060

0070

0080

00

Pres

sure

(psi

)

Strain (ms)

h SG

-13

0°h

SG-3

7 12

0°h

SG-2

4 24

0°D

IC A

RAM

IS

Strain (ms)

Pres

sure

(psi

)

36

Gen

eral

Sch

emat

ic o

f CO

PV F

BG

St

rain

Mea

sure

men

t Sys

tem

Tu

nabl

e La

ser

Sens

or S

trin

gs

Gas

Cel

l Ref

eren

ce

37

Exam

ple

Unf

ilter

ed A

E D

ata

-All

Even

ts(E

ric M

adar

as h

as d

etai

ls)

Zero

Mer

idia

n

Are

as o

f int

eres

t

Top

Vie

w

38

Exam

ple

AE

Even

ts V

s Tim

e

Even

ts C

ount

vs.

Tim

e an

d Pr

essu

re v

s. Ti

me

500

1000

1500

2000

2500

3000

3500

4000

450

Tim

e (s

)

Yie

ldin

g

Con

tinuo

us

yiel

ding

and

pr

ogre

ss to

war

d fa

ilure

(sto

pped

pr

ior t

o fa

ilure

oc

curr

ing)

39

FBG

Dis

clos

ed L

oad

Red

istr

ibut

ion

4550

4560

4570

4580

4590

4600

4610

4620

4630

4640

4650

4660

4670

4680

4690

4700

4710

4720

010

0020

0030

0040

0050

0060

0070

0080

00

Pres

sure

(psi

g)

Tank Volume (in3)

Pres

sure

(psi

g)

Tank Volume (in3)

40

OM

S R

uptu

re D

IC V

ideo

41

AC

CEL

ERA

TED

AG

ING

OF

KEV

LAR

-EPO

XY C

OPV

s

Twin

CO

PV

Tes

t Cha

mbe

rsL

= 31

o C, 0

.80

SR

R

= 8

1oC

, 0.6

5 S

R

Tem

pera

ture

and

Str

ess

Agi

ng

Test

Cha

mbe

rs

42

EXA

MPL

E A

GIN

G A

PPR

OA

CH

ES0

12

34

0.80

0.75

0.70

0.65

0.60

STRESS RATIO

TIM

E, H

RS

(Life

time

Scal

e Pa

ram

eter

, Log

Sca

le)

330

300

3000

1010

010

00

25C

40C

60C

80C

100C

Ada

pted

from

Pho

enix

18-

Aug

-06

SR

= 0

.80,

T =

31o C

SR

= 0

.65,

T =

81o C

0.85

NA

SA

/slp

/isoc

hron

al a

ging

par

amet

ers

2.xl

s

Stre

ss A

ging

Step

ped

Ther

mal

Agi

ng

43

NN

WG

Pro

gram

to Id

entif

y N

DE

met

hods

for d

etec

ting

onse

t of

Cre

ep-R

uptu

re in

Com

posi

te S

truc

ture

s

•A

E in

dica

tions

beg

in to

acc

umul

ate

wel

l bef

ore

rupt

ure

occu

rs.

The

sync

hron

izat

ion

of th

ese

data

with

the

stra

in a

nd te

mpe

ratu

re in

dica

tions

w

ill b

e ac

com

plis

hed

in th

e ne

xt p

hase

of o

ur

proj

ect.

44

Exam

ple

AE

RES

ULT

SB

ottle

82:

AE

EVEN

TS P

RO

VID

E N

OTI

CE

OF

RU

PTU

RE

S/N

82

FAIL

UR

E.x

ls

21 D

ecem

ber 2

006

0

200

400

600

800

1000

1200

1400

1600

1800

Number of AE Events

RU

PTU

RE

TIM

E: 9

1 hr

s

AD

VA

NC

E N

OTI

CE

: 1.9

8 hr

s

45

Exam

ple

Aco

ustic

Em

issi

on D

ata

Even

ts v

s Ti

me

0

100

200

300

400

500

600

050

0010

000

1500

020

000

2500

0

Sec

onds

Acoustic Emission Events

46

Exam

ple

Aco

ustic

Em

issi

on C

umul

ativ

e Ev

ent E

nerg

ies

050

0010

000

1500

020

000

2500

030

000

3500

040

000

4500

0

1

29

57

85

113

141

169

197

225

253

281

309

337

365

393

421

449

477

505

Aco

ustic

Em

issi

on E

vent

#

Cumulative Energy(all channels)

47

NN

WG

ND

E of

Cre

ep-R

uptu

re N

DE

Prel

imin

ary

Find

ings

•A

ccel

erat

ion

fact

ors,

ATσ

, of t

he o

rder

105

are

bei

ng

achi

eved

by

incr

easi

ng s

tress

and

tem

pera

ture

ove

r av

erag

e le

vels

exp

erie

nced

in s

ervi

ce.

•A

E in

dica

tions

beg

in to

acc

umul

ate

wel

l bef

ore

rupt

ure

occu

rs.

The

sync

hron

izat

ion

of th

ese

data

with

the

stra

in

and

tem

pera

ture

indi

catio

ns w

ill b

e ac

com

plis

hed

in th

e ne

xt

phas

e of

our

pro

ject

. •

Act

ive

stra

in, t

empe

ratu

re a

nd A

E m

easu

rem

ents

app

ear t

o be

giv

ing

sign

als

of im

pend

ing

rupt

ure.

Giv

en o

ur A

T x

Aσ

prod

uct,

a ye

ar o

r mor

e of

not

ice

of im

pend

ing

rupt

ure

may

be

feas

ible

usi

ng a

ctiv

e se

nsor

s.

48

Con

clus

ions

•N

AS

A C

OP

V a

sses

smen

t sta

rted

in 2

004

led

to th

e ev

alua

tion

of

ND

E a

pplic

able

to C

OP

Vs.

–R

easo

nabl

y m

atur

e N

DE

wer

e id

entif

ied

for a

pplic

atio

n to

det

ect

impa

ct a

nd o

ther

loca

lized

dam

age.

•N

DE

resp

onse

not

effe

ctiv

ely

rela

ted

to a

spe

cific

redu

ctio

n in

st

ruct

ural

inte

grity

.–

Littl

e N

DE

was

foun

d av

aila

ble

to e

valu

ate

glob

al m

ater

ial p

rope

rty

chan

ges

poss

ibly

rela

ted

to p

rogr

essi

on to

war

d st

ress

rupt

ure

orth

at

coul

d ai

d in

life

pre

dict

ions

.•

Det

aile

d re

com

men

datio

ns fo

r a s

tress

-rup

ture

pro

gram

wer

e pr

ovid

ed

to a

dvan

ce th

e st

ate-

of-th

e-ar

t, bu

t will

take

sev

eral

yea

rs to

fiel

d.•

The

NN

WG

is c

urre

ntly

mak

ing

exce

llent

pro

gres

s in

this

are

a.

•A

pplic

atio

ns o

f sev

eral

ND

E m

etho

ds to

pre

test

scr

eeni

ng K

evla

r an

d ca

rbon

CO

PV

s, in

test

at W

STF

ove

r the

last

two

year

s, h

ave

dem

onst

rate

d th

eir e

ffect

iven

ess

–N

DE

app

lied

real

-tim

e du

ring

test

ing

is a

lso

prov

idin

g ex

celle

nt te

st

data

, hel

ping

to p

rovi

de ra

tiona

le to

con

tinue

flyi

ng s

ome

vess

els

49

Add

ition

al A

ctiv

ities

Pla

nned

•E

valu

ate

and

valid

atin

g N

DE

that

can

be

inte

grat

ed in

to

man

ufac

turin

g to

ens

ure

sign

ifica

nt fl

aws

do n

ot e

xist

and

ens

ure

man

ufac

turin

g co

nsis

tenc

y.–

Pre

vent

man

ufac

turin

g is

sues

and

ens

ure

clos

er g

roup

ing

of p

hysi

cal

prop

ertie

s.•

Dev

elop

Com

posi

te N

DE

Sta

ndar

ds a

pplic

able

to C

OP

Vs

–N

AS

A to

p le

vel s

tand

ard

and

guid

es s

ite A

STM

and

con

sens

us s

tand

ards

–A

STM

ND

E s

tand

ard

Gui

de a

nd 5

sta

ndar

ds o

f pra

ctic

e in

dev

elop

men

t•

Impl

emen

t add

ition

al re

al-ti

me

ND

E d

urin

g te

stin

g to

pro

vide

an

enha

nced

und

erst

andi

ng o

f the

CO

PV

incl

udin

g lin

er a

nd C

ompo

site

inte

ract

ion:

–Fu

rther

dev

elop

men

t of S

hear

ogra

phy

appl

icat

ion

to p

rovi

de s

ensi

tive

in-

plan

e st

rain

val

ues

–C

orre

latin

g S

hear

ogra

phy

and

Aco

ustic

Em

issi

ons

(AE

) ND

E–

Ref

inem

ent o

f AE

freq

uenc

y co

nten

t to

prov

ide

a di

ffere

ntia

tion

betw

een

fiber

vs.

mat

rix c

rack

ing

and

othe

r dam

age/

prog

ress

ion

–R

efin

emen

t of e

ddy

curr

ent t

o pr

ovid

e pr

ecis

e co

mpo

site

and

line

r th

ickn

ess

varia

tion

at th

e C

OP

V is

cyc

led

(hor

izon

tal a

nd v

ertic

al

com

pone

nt)

50

Bac

kup

Cha

rts

51

CO

PV P

oten

tial A

cous

tic N

DE

Met

hods

Met

hod

Prop

erty

Mea

sure

d Pr

iorit

y

Aco

ustic

Em

issi

on

Act

ive

dam

age

grow

th d

urin

g lo

adin

g su

ch a

s m

atrix

cra

ckin

g, d

elam

inat

ion

or fi

ber b

reak

ing

Hig

h

Con

vent

iona

l Pul

se

Ech

o U

ltras

onic

s M

acro

mod

ulus

A

ttenu

atio

n M

icro

crac

king

Hig

h

Aco

usto

-Ultr

ason

ics

Aco

ustic

Atte

nuat

ion

Hig

h

Lam

b W

aves

/Pla

te

Wav

es

Aco

ustic

Pro

perti

es/M

odul

us M

icro

crac

king

Hig

h

Lase

r Ultr

asou

nd

Mac

rom

odul

us

Atte

nuat

ion

Mic

rocr

acki

ng

Hig

h

52

CO

PV P

oten

tial E

lect

rom

agne

tic M

etho

ds

Met

hod

Prop

erty

Mea

sure

d Pr

iorit

y

Edd

y C

urre

nt

Ele

ctric

al C

ondu

ctiv

ity -

prop

ertie

s

Hig

h

Mic

row

ave

Die

lect

ric P

rope

rties

Hig

h

Ter

aher

tz

Die

lect

ric P

rope

rties

H

igh

One

Sid

ed N

MR

C

hem

ical

Bon

ding

/Pol

ymer

ic S

truct

ure

Of

Kev

lar

Hig

h

MR

I C

hem

ical

Stru

ctur

e Lo

w

53

CO

PV P

oten

tial O

ptic

al M

etho

ds

Met

hod

Prop

erty

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Che

mic

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Res

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rans

form

P

hoto

acou

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pect

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Inte

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inar

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Ligh

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med

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riorit

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54

CO

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oten

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56

CO

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tial D

estr

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naly

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Expl

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stig

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f ND

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entif

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Reg

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of I

nter

est

Pote

ntia

l Ana

lytic

al T

echn

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s

Frac

ture

Sur

face

s: m

atrix

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ckin

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lam

ent

brea

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plits

, mic

rocr

acks

in fi

lam

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•

Opt

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• S

cann

ing

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n M

icro

scop

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smis

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ray

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57

Firs

t Acc

eler

ated

Tes

t Bed

(con

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Task

8•

Dis

tribu

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ampl

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ts o

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for c

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by N

DE

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Mak

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ocum

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Task

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l effo

rt to

Tas

k 8,

dis

tribu

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ets

of fl

at s

ampl

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r cha

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de

stru

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o id

entif

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orga

niza

tions

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Mak

e D

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easu

rem

ents

and

doc

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ults

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sk 1

0•

Ana

lyze

all

resu

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DE

and

DA

mea

sure

men

ts a

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own-

sele

ct b

est N

DE

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D

A m

etho

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–R

epla

n co

ntin

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pro

ject

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need

ed.

58

CO

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