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UBC Theses and Dissertations

Efficient numerical techniques for predicting process-induced stresses and deformations in composite structures Arafath, Abdul Rahim Ahamed


During the last two decades of research work in numerical modelling of autoclave processing of composite structures, several models have been developed ranging from simple one-dimensional elastic to sophisticated three dimensional viscoelastic models. Some of the common problems faced by these numerical models are the non-familiarity of general users with these models, their non-versatility, their inefficiency when running large problems and the interpretation and validation of the results produced by these models. The main objective of this research work is to initiate the development of the next generation process model for autoclave processing of composite structures to address the above problems. This development is carried out by building on the already established knowledge of process modelling within the UBC Composites Group. The developed next generation process model consists of a set of numerical tools which range in complexity from a simple and robust closed-form analytical tool to a more general and adaptive shell-based finite element analysis tool that provides a modeller with a choice depending on the time and cost constraints. According to the developed closed-form solution, the axial stress variation in the thickness direction of a flat composite part varies exponentially with the through-thickness coordinate and its gradient depends on the part material and geometrical properties. It is shown that the process-induced unbalanced moment develops mainly at the initial stages of the curing process where the through-thickness stress gradient is significant. The process-induced effects in a curved part due to the thermal strain mismatch between the part and the tool in the tangential direction is similar to the process-induced effects in a flat part. Apart from the tangential thermal strain mismatch, the radial thermal strain mismatch between the part and the tool also induces stresses in a curved part. These stresses are due to the radial and tangential constraints applied by the tool on the part to conform the part to the tool shape. The unbalanced moment due to these stresses mostly develop at the cool-down portion of the cure cycle when the material is fully cured.

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