3D Printing and Structural Analysis: Is There an Alternative to FE Analysis for Quick Design Info & for FEM Validation?

Orange County Chapter 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 Page 1

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. Page 2

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. Page 3

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? Page 4

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 Page 5

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. Page 6

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. Page 7

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. Page 8

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. Page 9

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. Page 10

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. Page 11

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/micromeasurements/photo-stress-plus/category/photostress-analysis-system/?subcategory=mainbenefits) * Courtesy of Micro-Measurements, Raleigh, NC, USA Page 14

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. Page 19

David England Product Marketing Engineer 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. Page 20