FiberSIM® composites engineering software
Waltham, MA

When NASA originally considered employing composites in manned spacecraft, it had to consider concerns that composites might have an unacceptable leak rate and insufficient damage tolerance. On the other hand, composites potentially offered reduced weight and lower lifecycle costs. The NASA Engineering and Safety Center (NESC) put together a team of government and industry structures experts to gain experience in making use of new composite construction and inspection technologies specifically for manned spaceflight structures.

(Left) The CMM during the assembly splice operation at ATK in Iuka, MS prior to the installation of graphite epoxy doublers, and (Right) a simulation generated by FiberSIM showing how fibers deviate from the specified orientation as a ply of composite material is draped over a tool for making the CMM. The areas highlighted in white indicate fibers whose orientations fall within an acceptable range, while the yellow and red areas indicate where fibers mildly (yellow) or significantly (red) deviate.
The most appealing aspect of applying composites to the Composite Crew Module (CCM) primary structure was a potential 10-15 percent reduction in weight on complex shapes compared to its aluminum counterpart. One of the primary goals of the project was to determine which composite materials are best suited for future NASA spacecraft.

The team considered nearly a dozen concepts and decided to make the CCM primary structure a stiffened honeycomb sandwich of carbon fiber. It is composed of upper and lower pressure shells spliced together to help meet the accelerated schedule and keep non-recurring costs under control. Further strengthening the shell are gussets, panels, and various metallic fittings to distribute point loads. The lower shell is stiffened by the floor backbone forming a unified structure that carries pressure and inertial loads via bending.

FiberSIM software was used to calculate what shape the flat pattern of the structure needed to be, and the data was exported to manufacturing for the NC cutting machine. FiberSIM generated data to drive accurate laser projections of the flag boundary. The software also was used to produce laser projection files to help locate and trim the core (in place on the tool), and to create an inspection grid on the skins.

Testing will be performed on a static test rig that will apply force to critical parts of the CCM, simulating the stresses encountered during a mission.

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