CompositesWorld
Issue link: https://cw.epubxp.com/i/830100
JUNE 2017 30 CompositesWorld FEATURE / PHYSICAL VS. VIRTUAL TESTING underlying physics and damage progression of the environmental conditioning process. Rousseau counters that there are better fits for this simulation technology than in generating allowables. "is specific type of simulation enables more modeling and less testing of structural failure events, including failure with various sorts of assumed damage or manufacturing flaws. ese are required for certification but are expensive to replicate experimentally." He notes that PDA-based simulations are also useful for modeling complex failure mode interactions at the assembly level (elements, compo- nents, full-scale test articles, etc.). "is makes more sense than trying to replace coupon-level design allowables." But can virtual testing be used to help speed up the insertion of new materials? "Abso- lutely," says Rousseau. "Once you get into non-laminated processes like 3D preforms, resin transfer molding (RTM) and injec- tion molding with discontinuous fibers, all of the methodology we use for design allowables on fiber-placed airframe parts — which are fairly flat and behave basi- cally like shells or plates — breaks down." Assaker agrees and says using VA at the more complex levels is already on e-Xstream's roadmap, "but we need to start with the coupon level because we have to show accuracy and earn industry confi- dence before testing by simulation can be accepted at these higher levels." Assaker also agrees with VA's potential role with RTM and short-fiber composites. "We don't have to be relegated to non- traditional laminates [NTL], but we handle them quite well." He notes that e-Xstream has been working with the auto industry on chopped fiber parts for 13 years, and can analyze them with as much accuracy as continuous fibers. "We simulate both the part and the process in order to address issues like fiber orientation and porosity." However, Assaker points out that for automotive, "we move to direct engi- neering of parts, which is a very different approach from the current step-by-step BBA process in aerospace. In order to make changes where BBA methodologies break down, I believe it is necessary to first show how they break down and possible solu- tions." For example, in a directly engi- neered RTM part, observed defects, such as porosity, are introduced in the simulated laminates. "We can then study the knock- down factors in resin-rich and resin-poor areas," he explains. "For short-fiber parts, we follow this same process, because you basically have a different laminate at each point in the material due to changes in fiber orientation." He acknowledges that there is no CMH-17 equivalent for testing short-fiber materials. But Assaker sees value in virtual test- ing's capability to expand the design space (e.g., by examining hybrid layups and mixtures of product forms, such as tape inner laminate with fabric outer plies). He says physical testing for this is impractical because the number of layup combina- tions grows significantly. "Virtual testing can provide high-quality information early, guiding design and physical testing Building our future...together! 815-987-6000 | www.ingersoll.com AUTOMATED FIBER PLACEMENT MACHINES LEADING THE PRODUCTIVITY CHALLENGE