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3D Printing and Structural
Analysis: Is There an Alternative
to FE Analysis for Quick Design
Info & for FEM Validation?
• FW Palmieri, Ph.D.
• 3/24/2014
Copyright © 2014 Raytheon Company. All rights reserved.
Customer Success Is Our Mission is a trademark of Raytheon Company
AIAA Orange County Chapter
11th ASAT Conference
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In spite of the advances we have made in recent
years using computer technology to improve the
accuracy of stresses predicted to occur in our
aerospace structures, and in the process improve
structural efficiency and hence reduce weight, we
have not really gained much in terms of the lead time
associated therein with completion of the analyses. In
fact, in many instances our lead time from receipt of
the design/CAD details to output of information to the
designers has actually increased along with the
associated analysis costs.
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This has been justified by the fact that we have
increased the aforementioned structural
optimization (i.e., less weight).
Yet: "... recent studies have shown that,
surprisingly enough, modern methods do not do a
better job of predicting failure of the resulting
designs, as shown by recent Air Force data." This
means that, although we may have reduced
weight, we have not improved our capability for
predicting failures.
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There exists an idea for a process improvement
that would potentially produce a shorter interval
between receipt of the design and evaluation of
its structural integrity, at least as far as strength
under static or dynamic loads or stiffness is
concerned.
What is that idea?
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This idea is to simply utilize the 3D Printing design specimen
as a basis for modern photoelastic evaluation techniques.
These specimens are currently being developed as standard
practice in many industries today, including the aerospace
industry.
The PhotoStress® sheet material is cast on a flat surface and
then applied to any flat, single or doubly contoured surface of
a test item and bonded thereupon. The test item can then be
subjected to static and even dynamic applied loads and
modern photoelasticity techniques can permit the accurate
evaluation of stress fields arising in these plastic, metallic or
composite specimens through optical interference patterns
and stroboscopic technology.
PhotoStress® is a registered trademark of Vishay Precision Group
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The following material regarding the definition of 3D
Printing, the various processes and the materials that are
involved therein have been obtained with permission from
the web site*:
http://www.additive3d.com/rp_int.htm
entitled: “A Brief Tutorial – What is Rapid Prototyping”
*Worldwide Guide to Rapid Prototyping web-site
(C) Copyright Castle Island Co., All rights reserved.
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3D Printing is now the most common name given to a host of
related technologies that are used to fabricate physical objects
directly from CAD data sources. These methods are unique in
that they add and bond materials in layers to form objects. While
3D printing has displaced rapid prototyping for top honors, that
term is still quite popular. Such systems are also known by the
names: additive manufacturing, additive fabrication, solid
freeform fabrication (SFF) and layered manufacturing and many
others. Today's additive technologies offer advantages in many
applications compared to classical subtractive fabrication
methods such as milling or turning:
• Objects can be formed with any geometric complexity or intricacy without
the need for elaborate machine setup or final assembly;
• Rapid prototyping systems reduce the construction of complex objects to a
manageable, straightforward, and relatively fast process.
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This has resulted in their wide use by engineers as
a way to reduce time to market in manufacturing, to
better understand and communicate product
designs, and to make rapid tooling to manufacture
those products. Surgeons, architects, artists and
individuals from many other disciplines also
routinely use the technology. With the advent of
low-cost and open-source systems hobbyists and
consumers are also now using additive
technologies in substantial numbers.
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Additive methods aren’t a solution to every part
fabrication problem. After all, CNC technology is economical,
widely understood and available, offers wide material selection and
excellent accuracy. However, if the requirement involves producing a part
or object of even moderately complex geometry, and doing so quickly - RP
has the advantage. It's very easy to look at extreme cases and make a
determination of which technology route to pursue, CNC or RP. For many
other less extreme cases the selection crossover line is hazy, moves all
the time, and depends on a number of variably-weighted, case-dependent
factors. While the accuracy of rapid prototyping isn't generally as good as
CNC, it's adequate today for a wide range of exacting applications.
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The materials used in rapid prototyping are
limited and dependent on the method chosen.
However, the range and properties available
are growing quickly. Numerous plastics,
ceramics, metals ranging from aluminum,
stainless steel to titanium, and wood-like paper
are available. At any rate, numerous secondary
processes are available to convert patterns
made in a rapid prototyping process to final
materials or tools.
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The names of specific processes themselves are also often used
as synonyms for the entire field. Among these are stereolithography
(SLA for stereolithography apparatus), selective laser sintering (SLS),
fused deposition modeling (FDM), laminated object manufacturing
(LOM), inkjet systems and three dimensional printing (3DP). Each of
these technologies - and many others - has its singular strengths and
weaknesses.
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What is the ‘Modern’ PhotoStress® Methodology?
I have taken the liberty of extracting some of the
information presented on Vishay Precision Group’s
web site with their approval and included it in this
presentation in the following slides*:
(see: http://www.vishaypg.com/micro-
measurements/photo-stress-plus/category/photo-
stress-analysis-system/?subCategory=main-
benefits)
* Courtesy of Micro-Measurements, Raleigh, NC, USA
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So, what I have presented in the material we have just reviewed is a combination of:
1) the creation of rapid prototyping models, 2) using modern PhotoStress®
techniques, and 3) structural tests to obtain quick turn-around information on the
structural integrity of potential designs.
Of course, one could argue that it would take time and money to design and build a
test fixture and this would offset the potential savings. So, this trade-off would have
to be evaluated for each potential use.
It would be interesting to investigate the feasibility of the application of this technique
to the evaluation of the structural capability of a typical aerospace component and
compare the results with the cost and time that would be required for the structural
analysis by our conventional finite element method (as well as, perhaps, the
accuracy of the predictions).
It could also be useful for obtaining rapid validation of our analytic models (as shown
in one of the previous slides), something that ordinarily does not happen until after
the design is finalized, hardware produced and environmental tests conducted.
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I also received the following interesting comment from
Vishay’s Product Marketing Engineer, David England:
“What you didn’t mention, and may find interesting is that at
least two rapid prototype materials (clearvue and Accura 60)
are strain sensitive and bi-refringent as produced.
Unfortunately their K value or optical sensitivity isn’t enough
to be useful in practical applications. What would be ideal
would be to print an object, spray the “far side” with an
aluminized paint and use a reflection polariscope to study
the loaded structure. This would save the user from the
craftsmanship required in coating preparation.”
In the future, this method may prove to greater simplify the
whole stress/strain visualization process.
David England
Product Marketing Engineer