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UBC Theses and Dissertations

Implementation and evaluation of a coupled thermal-structural analysis module for laminated composites in an open-source finite element code Beaton, Douglas Brian


The aerospace industry invests heavily in the design and manufacture of composite materials. Aircraft components are produced by placing unprocessed composite materials in an autoclave and applying heat and pressure. The desired part geometry is achieved by forming raw composite materials around a tool, typically made of aluminum or other metal. Throughout the cure cycle, temperature changes cause the part and tool to expand at different rates. This differential expansion, combined with composite material properties that evolve over time, produces residual stresses in the part and leads to geometric instabilities (warpage) upon removal from the tool. Excessive warpage can render a part unusable. Errors of this nature can be quite costly, particularly in the aerospace industry where the tools created can be very large. A strong desire exists to predict the warpage and residual stresses imposed by the curing process and incorporate these stresses in the structural design of a component. To accomplish this goal for complex geometries, special additions to the finite element method are required. Commercial finite element programs provide some flexibility for users to implement custom elements and materials. Though, this flexibility has limits: some material models, such as non-local damage models, cannot be incorporated in proprietary software. This work selects an open-source finite element program and implements the ability to model curing processes of composite materials. The thermal and structural equations are solved in a coupled manner during each time step. This contrasts previous work by the UBC Composites Group, wherein the heat equation is solved over the entire model before the structural equations are considered. Numerous verification models are run to confirm the implementation, along with several example problems. Recommendations are made for further work to improve the process modeling and facilitate a link to subsequent structural models. Ultimately, the code produced represents the first step in seamlessly modeling composite structures during manufacturing processes through to in-service conditions.

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