Buckling analyses of triaxial weave fabric composites under thermal and mechanical loading

Abstract

This thesis presents the formulation and numerical computation of the buckling behaviour of triaxial weave fabric (TWF) composites subjected to mechanical and thermal loads. The formulation was constructed by adopting two types of numerical method, namely the finite element method (FEM) and the meshfree (MFree) method, based on the classical plate theory. A combination of Lagrange and Hermite interpolation functions was adopted in the FEM formulation whereas the Multi-Quadrics radial basis function was employed in the MFree formulation. The formulation complexities, high time-consumption and tedious computation attributed to previous studies, which considered a variety of modelling techniques for the description of the complex tow geometry, were identified as the primary disadvantages, preventing them from widespread use. Therefore, simplification of modelling the TWF is vital for convenience and practicality. Such simplification was provided from the literature by describing the constitutive relation of the TWF using the contemporary 6 × 6 ABD matrix, adopting the homogenized and segmentation methods. The former employs the periodic boundary condition while the latter considers the volume segment of a unit cell. These material expressions were employed in both FEM and MFree methods in order to study the behaviour, especially the stability of the TWF composite when subjected to uniaxial compressive mechanical and uniform thermal loads, focusing on the cases of all edges clamped and simply supported. The source codes for the mechanical buckling and thermal buckling for both FEM and MFree were developed in this study. Authentication and verification of the source codes were done by making comparison with selected problems from the literature. As aspect ratio increases, the TWF plate was found to be less resistant towards mechanical buckling, which was in contrast to the thermal buckling behaviour. Overall, good agreement has been found in models adopting the homogenized and segmentation methods especially for the plates that were fully clamped for both thermal and mechanical bucklings using the FEM and MFree methods. The plates with fully clamped edges were identified to have higher resistance towards mechanical and thermal loads in comparison with those of simply supported edges.