CompositesWorld

SEP 2017

CompositesWorld

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SEPTEMBER 2017 8 CompositesWorld DESIGN & TESTING » Despite the many advantages that come with using composites materials in aerospace appli- cations, designing weight-bearing structures from these materials remains a significant chal- lenge. Compared to legacy metals, multi-mate- rial, multi-ply composites remain much more mathematically complex to model and design. at said, computing tools have improved dramatically over the past 10-15 years, enabling composites analysis, simulation and optimiza- tion to be carried out more quickly and accu- rately. ese more sophisticated digital tools also have enhanced the ability of engineers to design for optimum weight reduction, as well as to refine manufacturing processes on the shop floor — significantly cutting time and cost. is led directly to greater acceptance and deploy- ment of composites and enabled the production of the larger, lighter aircraft we see today. It's all about speed to certification No matter the aircraft or the materials used to make it, manufac- turers have a common goal of reducing the total project schedule, from kickoff to FAA certification. Yet, adding composites into the product development equation can introduce greater complexity because so many processes are brought together — design, analysis, testing, curing of the laminate, the robotic application of the fiber on the tool, etc. Further, each of the assembled tech- nologies needs to be in communication with the others on which they have an impact: How a laminate is designed or optimized affects every other downstream function, so passing the data more efficiently between disciplines is critical. As design iterations progress, a tight feedback loop is essential to achieve a fully opti- mized composite design. OEMs that work with composites are increasingly aware of how significantly early design decisions affect the downstream efforts of the manufacturing team to produce a final, certifiable part. e technology continues to mature, but software devel- opers and part designers are already identifying the "sweet spots" where processes can be automated and improved upon. Although composites are still in the relatively early stage of adoption in aero- space, we're at the point where we are able to take lessons learned and apply them to improve processes with measurable results. Demonstrating certifiability to the FAA Analysis traceability and visibility are highly important for certifica- tion so, on the pathway to achieving it, an OEM must prove to the Software has a critical role in certification of composite designs for aerospace US Federal Aviation Admin. (FAA) that it has done its due diligence. Every aircraft manufacturer must prove flight-worthiness of each proposed aircraft configuration, so there can be no ambiguity in the structural analysis process. It must be fully traceable and repeat- able. It's unacceptable to use a "black box" of computational tools. Strong support for an OEM's submission for certification can be provided by finite element analysis (FEA) output files of computed internal loads with, for example, NASTRAN or Abaqus — along with test data that validates methods and allowables. Software tools are now available to automate the processes that provide these, giving the design engineer the ability to trace through the analyses, visu- alize the results and understand the response of a composite struc- ture, thereby confirming that the software and material input data are producing the correct answers. Templates of a wingskin, a rib or a fuselage (Fig. 1, above) guide the user through the analysis. e software reports to the engineer all the analysis details, including input and intermediate data results, with stress methods fully documented by references to the published literature. e test/data correlation capability enables the user to store such data for later demonstration of the agreement between analytical prediction and test. Collier Research's HyperSizer software, for example, can now automate the setup of a design/feedback loop, based on the internal-load data from whatever number of FEA load cases (these can be numbered in the thousands) are needed to reach an opti- mized design — and then compute the failure margins of safety (Fig. 2, p. 10). At this point, the final deliverable from the software is FIG. 1 For a portion of an aircraft fuselage (left), HyperSizer software produces screenshots of post- buckling stability analysis of fuselage skins, stiffeners and frames. Source | Collier Research Corporation

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