CompositesWorld
Issue link: https://cw.epubxp.com/i/830100
JUNE 2017 28 CompositesWorld FEATURE / PHYSICAL VS. VIRTUAL TESTING molding process, environmental conditions, etc. Why add uncertainty by modeling when you can physically test to prove and bound actual variability? Believe it or not, BBA was developed (circa. 1950s, adapted for composites by the 1980s) to reduce the cost of aircraft design substantiation. Instead of testing every part of every structure, the idea was to establish material basis values and use these to calculate preliminary design allowables. en, based on the structural analysis, critical areas were identified for physical test verifica- tion. us, by testing greater numbers of cheap, small specimens, large-scale tests were mini- mized. Technology risks were assessed early in the program and analyses — traditional closed-form (i.e., hand-calcs) and, over time, finite element and other computer methods — were used in place of tests where possible. "At all different stages and scales of development, both testing and simulation are used," says Rousseau (Fig. 2). Assaker sees some common ground here, but points out that Rousseau's conservative cost estimate for coupon testing is based on an unspoken assumption. "We agree that more of the cost is in the full-size articles testing," he says. "However, we estimate US$5.7 million for all testing to generate allowables for a completely new material [Fig. 3, above]. Only for materials that are well known," he emphasizes, "can you reduce the cost [as Rousseau asserts on p. 27] to US$500,000. Our approach [for a new material] is to reduce the US$5.72 million to US$476,500 for statistical physical testing, and do the rest via simulation." "I agree that if you have to test 31,000 — or even 10,000 — coupons, then your test program cost will be in the US$5 million range or above," Rousseau responds. But he appeals to standards and expectations set by the National Center for Advanced Mate- rials Performance (NCAMP, Wichita, KS, US), which works with the US Federal Aviation Admin. (FAA, Washington, DC, US) and industry partners to qualify material systems and CMH17-1G, the latest revision of the Composites Material Handbook. NCAMP's standard test matrix, he points out, is a much lower 1,200 coupons, "and if you add up the various recommended test matrices in CMH17-1G, the total count is roughly 5,000-7,000." At this point, Rousseau specifically compares BBA to VA, as presented by Assaker (Fig. 3). Noting the large number of different layups there, he says, "I don't agree that 48 laminates would be required to test a new material." Rousseau explains, "I use six laminates for tape and three for a fabric, plus three different thick- nesses of only one laminate for compression-after-impact (CAI) testing." Rousseau's method reduces the number of laminates to 12, and the total coupon count from 31,104 to 7,776. To Assaker's dichotomy between new vs. well-known materials, Rousseau replies, "I consider 'well-known' to be any composite with continuous fiber, in tape or a 2D weave, in a polymeric matrix." is covers the entire landscape of materials used in auto- mated tape laying (ATL), automated fiber placement (AFP), as well as out of autoclave (OOA) and autoclave-cured prepreg and dry reinforcements impregnated and molded using resin infusion processes. Not included are 3D preforms used in resin transfer molding (RTM) and parts reinforced with discontinuous fibers, such as those made with molding compounds. Assaker reiterates: "I chose 48 laminates to explore the design space for a completely new material." Rousseau and Assaker concede that apples-to-apples compari- sons here are difficult because actual cost and potential savings in a physical testing program vary depending on the part and mate- rials. Although they agree that physical testing is required, Assaker asserts that simulation can reduce the need for physical testing and that what remains can be done more strategically. "Our view is that the virtual testing would drive the statistical data pooling that ROI Quantification – $5M and 500 Days Customer Baseline Test Program Test Program Augmented with Digimat VA Simulation Number of Materials 1 Number of Materials 1 Number of Layups 48 Number of Layups 12 Number of Batches 3 Number of Batches 1 Number of Panels per Batch 2 Number of Panels per Batch 2 Number of Coupons per Panel Number of Coupons per Panel Un-Notched Tension (UNT) 3 Un-Notched Tension (UNT) 3 Un-Notched Compression (UNC) 3 Un-Notched Compression (UNC) 3 Open-Hole Tension (OHT) 3 Open-Hole Tension (OHT) 3 Open-Hole Compression (OHC) 3 Open-Hole Compression (OHC) 3 Filled-Hole Tension (FHT) 3 Filled-Hole Tension (FHT) 3 Filled-Hole Compression (FHC) 3 Filled-Hole Compression (FHC) 3 Bearing, Single-Shear Tension 3 Bearing, Single-Shear Tension 3 Bearing, Double-Shear Tension 3 Bearing, Double-Shear Tension 3 50% Bearing-Bypass, Tension 3 50% Bearing-Bypass, Tension 3 50% Bearing-Bypass, Compression 3 50% Bearing-Bypass, Compression 3 V-Notch Rail Shear 3 V-Notch Rail Shear 3 Compression After Impact (CAI) 3 Compression After Impact (CAI) 3 Other 0 Other 0 Number of Conditions 3 Number of Conditions 3 Total Coupons 31,104 Total Coupons 2,592 Full Program Cost $5,717,952 Full Program Cost $476,496 Test Program Duration 600 days Test Program Duration 50 days FIG. 3 Biggest impact with entirely new materials e-Xstream's Assaker estimates a cost of US$5.7 million for the physical testing required to generate allowables using BBA for a completely new material, but he says that figure can be reduced to less than US$500,000 through the use of virtual testing. Rousseau disagrees. Source | e-Xstream engineering