K.S. Raju Department of Aerospace Engineering · – K.S. Raju – C.K. Thorbole, H. Lankarani – GRA - J.F.Acosta, V.B. Mariyanna, A.B. Deshpande, S. Dandayudhapani • FAA Technical

The Joint Advanced Materials and Structures Center of Excellence

CCRASHWORTHINESS OF RASHWORTHINESS OF CCOMPOSITE OMPOSITE FFUSELAGE USELAGE SSTRUCTURES TRUCTURES –– MMATERIAL ATERIAL DDYNAMIC YNAMIC PPROPERTIESROPERTIES

K.S. RajuK.S. RajuDepartment of Aerospace EngineeringDepartment of Aerospace Engineering

2The Joint Advanced Materials and Structures Center of Excellence

CCRASHWORTHINESS OF RASHWORTHINESS OF CCOMPOSITE OMPOSITE FFUSELAGE USELAGE

SSTRUCTURES TRUCTURES –– MMATERIAL ATERIAL DDYNAMIC YNAMIC PPROPERTIESROPERTIES

• Motivation and Key Issues – Crashworthiness

• Maintain survivable volume• Alleviate occupant loads

– Energy Absorption• Metals – Plastic deformation• Composites – controlled failure modes

– Factors affecting energy absorption• Geometry (?)• Strain rate (?)

– Experiments – expensive & expansive– Analysis – requires data for material

properties

Hull D (1991) Comp. Sci Tech, 40.Bannerman & Kindervater (1984) in Structural Impact and CrashworthinessBolukbasi & Laananen (1995) Composites, 26.Carruthers, Kettle & Robinson (1998) Appl Mech Rev, 51.




MATERIAL PROPERTY CHARACTERIZATION AT DIFFERENT STRAIN RATES - TENSION, COMPRESSION & SHEAR - CONSTITUTIVE LAWS WITH STRAIN RATE-EFFECTS - FAILURE MODES & STRENGTHS

STRAIN & STRAIN RATE GRADIENTS - OPEN-HOLE TENSION TESTS - BENCHMARK DATA FOR ANALYTICAL MODELS & FAILURE THEORIES

ENERGY ABSORPTION MECHANISMS - constant stroke rate tests - drop tests

SCALED FUSELAGE TUBES - drop tests

FUSELAGE + ENERGY ABSORPTION DEVICES - ASSEMBLIES

Phase-I

Phase-2

- APPROACH

,FLEXURE, BEARING




–Objectives: Material property characterization at different strain rates (10-4 s-1 to 103 s-1 )/dynamic loading

• Phase-1– Development of test apparatus & fixtures for high strain rate testing

» MTS high stroke rate system » Split Hopkinson Pressure Bar (SHPB) Apparatus

– Tension, Compression & Shear– Open Hole Tension

• Phase-2» Interlaminar Shear» Pin Bearing» Flexure» Honeycomb core


FAA-Sponsored Project Information

• Principal Investigators & Researchers– K.S. Raju – C.K. Thorbole, H. Lankarani– GRA - J.F.Acosta, V.B. Mariyanna, A.B. Deshpande, S. Dandayudhapani

• FAA Technical Monitor– Alan Abramowicz

• Other FAA Personnel Involved– John Zvanya, Peter Shyprykevich, Curtis Davis

• Industry Participation– Spirit Aerosystems– Raytheon– Cessna– Sikorsky – Bell Helicopter


Material Systems

– Newport NB321/3k70P– Newport NB321/7781 Fiberglass*– Newport NCT321/G150 Unitape

– Toray T800S/3900-2B[P2352W-19] BMS8-276 Rev-H- Unitape*– Toray T700G-12K-50C/3900-2 Plain Weave Carbon Fabric*

– Fibercote E-765/PW Carbon Fabric /Epoxy– Cytec PWC T300 3KNT Plain Weave Carbon Fabric

– Plascore Nomex Honeycomb core PN2-3/16-3.0

* Investigated through NIS funding (2005-06)


Material Properties

– In-Plane Tensile Properties (Strength & Modulus)• [0°]n, [±15°]ns,[±30°]ns, [± 45°]ns

– In-Plane Compressive Properties (Strength & Modulus)• [0°]n, [±15°]ns,[±30°]ns, [± 45°]ns

– In-Plane Shear Properties (Strength & Modulus)• [0°/90 °]ns

– Open- Hole Tension


Test Apparatus

• TENSION MODE TESTING– MTS servo hydraulic testing machine

• Tension, shear and flexure tests

• COMPRESSION MODE TESTING– Split- Hopkinson Pressure Bar Apparatus (SHPB)

• Compressive strength

– MTS servo hydraulic testing machine• Honeycomb core


Test Apparatus

• MTS High Stroke Rate System (MTS-HSRS)– Stroke rate ~ 500 in/sec – +/- 7 inches stroke– Load capacity

• 5 kips @ rated speed• 9 kips maximum

– Load measurement• Piezoelectric load cell (+/-10 kips)

– Data Acquisition• National Instruments PCI 6110 DAQ• 4 Channels• 5 MHz (simultaneous sampling)• 12 bits resolution

– Test control • MTS MultipurposeTestware computer program


Test Apparatus

• SLACK INDUCER MECHANISM– allows actuator acceleration to

desired speed prior to loading the specimen

• LOW-MASS GRIPS– mechanical wedge grips – 2.4 lbs – 15 kip capacity

Davis, E.A., Trans. ASME, 60, 1938 Elam, C.F., Proc. Roy. Soc. Lond., A, 165, 1938 ManJoine, M.J., Trans. ASME, 66, 1944 A-21 Milkowitz, J., Trans.ASME, 69, 1947 A-21 Morrison, J.L., Engineer, Lond., 158, 1934


Tension Testing

• SPECIMEN GEOMETRY– 2 inch gage length– 0.5 inch width– Thickness limited by loading capacity

of the testing machine• TEST RATES

– 1x10-4 in/s ( quasi-static)– 1, 10 , 100, 250 and 500 in/s– 3 specimens each

• CONSTANT STROKE RATE TESTS– Based on actuator displacement– Strain rate varies throughout the test

• Variation of strain rate is dependent on slack inducer element (s) characteristics (stiffness and mass)

90°

0°

4.50

1.25

3.25

0.5

0 0.002 0.004 0.006 0.008 0.01 0.012Measured Strain εo (in/in)

0

0.2

0.4

0.6

0.8

1

St

rain

Rat

eM

axim

um S

train

Rat

eMaterial: NB321/3K70PNOMINAL STROKE RATE (in/s)

0.00083110100250500


Tension Testing - Results

• Newport NB321/7781 Fiberglass/epoxy

0 0.01 0.02 0.03 0.04 0.05Tensile Strain (in/in)

0

50000

100000

150000

200000

250000

Tens

ile S

tress

(psi

)

Nominal Stroke Rate 10-3 in/s10 in/s100 in/s250 in/s500 in/s

Material : Newport NB321/7781 fiberglassOrientation : [0]n

10-3 100 101 102 103

Nominal Stroke Rate (in/s)

100000

200000

9000080000

70000

60000

50000

40000

30000

Tens

ile S

treng

th (

psi)

ORIENTATION[0]n

[+15/-15]ns

[+30/-30]ns

[+45/-45]ns


• Newport Material Systems– Increase in tensile strength observed

for stroke rates up to 100 in/s, irrespective of reinforcement type

– Fiberglass ( NB321/7781) was observed to be more sensitive to strain rate, with increase in tensile strength by a factor of 3.

– At stroke rates above 100in/s, modulation of load signal occurs. Load signal must be corrected using experimentally determined transfer function (under progress)

10-3 100 101 102 103


0

200,000

400,000

600,000

Tens

ile S

treng

th (p

si)

Orientation : [0]nMaterial System

Newport UnitapeNewport FiberglassNewport PWCF

LOAD SIGNAL MODULATION



• Toray Material Systems– Increase in tensile strength

observed for stroke rates up to 100 in/s, irrespective of reinforcement type

– Tensile strengths of PWCF material observed to drop to quasi-static levels at stroke rates of 250 and 500 in/s

– At stroke rates above 100in/s, modulation of load signal occurs. Load signal must be corrected using experimentally determined transfer function (under progress)

10-3 100 101 102 103


0

200,000

400,000

600,000

800,000

1,000,000

Tens

ile S

treng

th (p

si)

Orientation : [0]n

Material SystemToray UnitapeToray PWCF

LOAD SIGNAL MODULATION



In-Plane Shear Tests

• TEST METHOD– ASTM D 7078 V-Notch Rail

Shear• TEST RATES

– 1x10-4 in/s ( quasi-static)– 1, 10 , 100, 250 and 500 in/s– 3 specimens each

56

76

38

12.7

12.7

90°

All d im ensions in m m


• SHEAR STRAIN MEASURMENT

0 0.02 0.04 0.06 0.08 0.1In-Plane Shear Strain (radians)

0

20

40

60

80

100

In-p

lane

She

ar S

tress

(Mpa

)

Nominal Stroke Rate : 2.5 ×10-5 m/s

NB321/3K70 PWCFNB321/7781 SWGF

0 0.002 0.004 0.006 0.008Actuator Displacement (m)

0

40

80

120

160

In-p

lane

She

ar S

tress

(Mpa

)

Nominal Stroke Rate : 2.5 ×10-5 m/s

NB321/3K70 PWCFNB321/7781 SWGF

STR

AIN

GA

GE

LIM

IT

ε+45

ε-45

454512 −+ += εεγ

In-Plane Shear Tests


Shear Stress-Strain Behavior

• Shape of Shear Stress-strain curves similar for stroke rates up to 10 in/s

– Stress levels increase with stroke rate• Shear stress strain behavior changes at

stroke rates of 100 in/s and beyond– Reduction in shear stiffness– Dynamic effects – NB321/7781 & NB321/PWCF material exhibit

similar behavior up to strain levels of 0.05– Beyond shear strain of 0.05, NB321/7781

observed to stiffen at 250 and 500in/s

K.S.Raju, S. Dandayudhapani and C.K. Thorbole, AIAA-2006-2258


In-Plane Shear Strength

• NEWPORT MATERIAL SYSTEMS– Fabric reinforced systems ( 3k70P and

7781)• Shear strength increases with stroke rate• Failure mode changes at higher rates

– Unitape system• Shear strength increases up to stroke rate of

100in/s, but decrease at 250 and 500 in/s• No change in failure mode

10-3 100 101 102 103

NOMINAL STROKE RATE (in/s)

0

10

20

30

40

50

IN-P

LAN

E S

HE

AR

STR

ENG

TH (p

si)

Newport material systemsNB321/3K70 PWCFNB321/7781 FIBERGLASSNCT 321/G150 UNITAPE

K.S.Raju, S. Dandayudhapani and C.K. Thorbole, AIAA-2006-2258

Quasi-static 500 in/s

(ksi

)


• TORAY MATERIAL SYSTEMS– Fabric reinforced systems ()

• Shear strength increases with stroke rate

• Failure mode changes at higher rates– Unitape system

• Shear strength increases up to stroke rate of 250 in/s, but decreases at 500 in/s

• No change in failure mode

10-3 100 101 102 103


0

20

40

60

IN-P

LAN

E S

HE

AR

STR

EN

GTH

(psi

)

Toray material systemsT800S/3900-2B UNITAPET700G-12K-50C/3900-2 PWCF

UNITAPE FABRIC

(ksi

)



• COMPARISON OF SHEAR STRENGTHS

– Fabric reinforced systems • Shear strength increases with stroke rate• Failure mode changes at higher rates

– Unitape system• Shear strength increases up to stroke rate of

250 in/s, but decreases at 500 in/s• No change in failure mode

• Corrections for modulation of load signal – Transfer function ( under progress)

10-3 100 101 102 103


0

1

2

3

4

In

-Pla

ne S

hear

Stre

ngth

Qua

si-S

tatic

In-P

lane

shea

r stre

ngth

Material systems

Newport NB321/3k70 PWCFNewport NB321/7781 fiberglassNewport NCT321/G150 UnitapeToray T800S/3900-2B UnitapeToray T700G-12K-50C/3900-2 PWCFCytec PWC T300 3KNT Fibercote E-765/PW CF



Split-Hopkinson Pressure Bar Apparatus ( SHPB)

INCIDENT BAR TRANSM ITTER BARPROJECTILE

BRIDGEAM PLIFIER

OSCILLOSCOPE

BRIDGEAM PLIFIER

SPECIM EN

STRAIN GAGE STRAIN GAGE

ε (t), ε (t), ε (t)I R T

INCIDENT W AVE (I)

REFLECTED W AVE (R)TRANSM ITTED W AVE (T)

• SPECIFICATIONS– Bar diameter : 1.00 inch– Bar Material : Vascomax 350 – Bar lengths

• Incident bar : 48”• Transmitter bar : 36”

– Barrell length : 48 inches– Projectiles : 1”, 2”, 4”, 6” & 12”

• Pneumatically driven (100 psi)• Velocities ~ 2000 in/s

– PULSE SHAPING• Copper discs

– DATA ACQUISITION• Tektronix TDS 3034 Digital Oscilloscope

– SIGNAL CONDITIONING• Ectron model 778 (3 MHz bandwidth)

P.S.Follansee, Metals Handbook, vol.8, American Society for Metals, 1985K.F. Graff, Wave Motion in Elastic Solids, Dover Pub., Inc.1991


• SPECIMEN GEOMETRY*

– Rectangular cross-section– Laminate thickness (t) ~ 0.17 to 0.25 inches– Specimen width (b) ~ 0.25 inches– Specimen height (H) ~ 0.25 inches

• SPECIMEN ALIGNMENT– Centering disc & slider ring

* E. Woldesenbet & J.R. Vinson, AIAA Journal, Vol.37, Sept. 1999.* P.S.Follansee, Metals Handbook, vol.8, American Society for Metals, 1985

b

H

t

90°

0°

Split-Hopkinson Pressure Bar Apparatus ( SHPB)


Compression Test Results

• Newport NB321/7781 fiberglass– Increasing trend observed for all

laminate types– Strength increase less pronounced

compared to tensile loading.• Maximum strength increase at strain

rate of ~800 s-1 is about 1.25 times the quasi-static value

10-3 10-2 10-1 100 103

Average Strain Rate (1/s)

20000

40000

60000

80000

100000

Com

pres

sive

stre

ngth

(psi

)

SPECIMEN TYPE[0]n

[+15/-15]ns

[+30/-30]ns

[+45/-45]ns

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

0.00 0.01 0.02 0.03 0.04 0.05 0.06Compressive Strain (in/in)

Com

pres

sive

Str

ess

(psi

)

450700820quasi-static

Strain Rate (1/s)


Compression Test Results

• Newport NB32/xxxx material systems– Unidirectional tape more rate sensitive

than fabric reinforced system– Compresive strength tends to reach a

limit as strain rate approaches 103 s-1

10-3 10-2 10-1 100 103


0

40,000

80,000

120,000

160,000

Com

pres

sive

stre

ngth

( ps

i)

Orientation : [0]nMaterial System

Newport fiberglass/epoxyNewport PWCF/epoxyNewport Unitape/epoxy

10-3 10-2 10-1 100 103


0

10,000

20,000

30,000

40,000

50,000

Com

pres

sive

stre

ngth

( ps

i)

Orientation : [+45/-45]ns

Material SystemNewport fiberglass/epoxyNewport PWCF/epoxyNewport Unitape/epoxy

• Newport NB321/xxxx material systems– Rate sensitivity of [+45/-45]ns specimens

follow similar trends for different reinforcement types

– Compressive strength exhibits an increasing trend as strain rate approaches 103 s-1


Open-Hole Tension

• Material Systems– Newport NB321/7781 fiberglass– Newport NB321/3k70 PWCF– Toray T700G-12K-50C/3900-2 PWCF

• Hole diameter : 0.25 inches ( w/d = 3)• Test speeds : quasi-static, 1 in/s and 100 in/s

• RESULTS– Open-hole tensile strength observed to increase with test speed– Newport fiberglass material exhibited highest increase in open-

hole strength– No significant change in failure modes

10-3 101 102


0

1

2

3

4

5

Nor

mal

ized

Ope

n H

ole

Tens

ile S

treng

th

Toray UnitapeNewport FiberglassNewport PWCF


Current Phase

– INTERLAMINAR SHEAR– PIN BEARING– FLEXURE

– Laminated and sandwich beams– 4-point flexure tests

– CYLINDRICAL FUSELAGE SECTIONS– Compression tests

MATERIAL PROPERTY CHARACTERIZATION AT DIFFERENT STRAIN RATES - TENSION, COMPRESSION & SHEAR - CONSTITUTIVE LAWS WITH STRAIN RATE-EFFECTS - FAILURE MODES & STRENGTHS

STRAIN & STRAIN RATE GRADIENTS - OPEN-HOLE TENSION TESTS - BENCHMARK DATA FOR ANALYTICAL MODELS & FAILURE THEORIES

ENERGY ABSORPTION MECHANISMS - constant stroke rate tests - drop tests

SCALED FUSELAGE TUBES - drop tests

FUSELAGE + ENERGY ABSORPTION DEVICES - ASSEMBLIES


Pin-Bearing Response


• Laminate type – [45/0/45/0/45]s

• Pin diameter : 0.125 inches • Test speeds : quasi-static, 1 ,10,100, and 250 in/s

• RESULTS– Sustained loading past initial failure, decreases

at higher rates of loading– Failure mode

0 2 4 6 8 10

Time

Time to Peak load

0

500

1000

1500

2000

2500

Bea

ring

Load

(lbf

)

Material : Newport fiberglassQuasi-static1 in/s10 in/s100 in/s


Pin-Bearing Response

• RESULTS– Bearing strengths based on

peak recorded load• Hole deformation not

measured– Pin bearing strength increases

with test speed

10-3 100 101 102 103


0

100,000

200,000

300,000

Bea

ring

Stre

ngth

(psi

)

Newport FiberglassNewport PWCFToray PWCF


Interlaminar Shear

• Specimen Geometry– Lap shear ~ Tensile loading


• STATUS– Testing under progress

5

0.5

R0.1250

0.6250

FLEXURE & PEEL CONSTRAINT


Flexure Tests

• LAMINATED BEAMS– Material systems

• Newport NB321/7781 fiberglass

• Newport NB321/3k70 PWCF– Layup sequence

• [0/45/45/0]

• SANDWICH BEAMS– Material systems

• Newport NB321/7781 fiberglass

• Newport NB321/3k70 PWCF– Layup sequence

• [0/45/0/45/CORE]S

• STATUS : Testing under progress

SPECIMEN

LOADING ROD / ACTUATOR

LOAD CELL

0.5

1


A Look Forward

• Benefit to Aviation– Understanding of strain-rate effects on composite material properties.

Material properties can be used in simulations involving high-strain rates– Off-axis, Open-hole, flexure and bearing data could be used as

benchmarks for material models – Data can be used in dynamic applications

• Eg. Impact analysis

• Future needs– Fracture toughness– Energy absorption devices

• Tubes• Subfloor beams

Documents

K.S. Raju Department of Aerospace Engineering · – K.S. Raju – C.K. Thorbole, H. Lankarani – GRA - J.F.Acosta, V.B. Mariyanna, A.B. Deshpande, S. Dandayudhapani • FAA Technical