Composites with bundle mesostructure: Elastic properties and Damage

Abstract: Many types of composite materials are today used in various types of load carrying structures, due to their excellent strength and stiffness to weight ratio. Simplicity, reliability and low cost of the material processing are important factors affecting the final selection.With the textile reinforced composites, the cost-efficiency is reached by using dry preforms which are impregnated by resin infusion, resin transfer molding etc.; this have made a break-through and have been widely used. Textile composites with bundle meso-structure have been studied in this thesis for elastic properties and damage investigations. The first part of this thesis deals with elastic properties modeling for Non-crimp fabric (NCF) based composites for investigating the effect of meso-structure defects on mechanical properties degradation. The objective of the work is to formulate a model for the NCF composite mesostructure in an attempt to investigate the effect of the waviness on stiffness reduction. Moreover, the stiffness calculation methods for the complex geometry are explained and justified and finally, the different geometrical parameters changes are taken into consideration and included in the calculation.The damage initiation and development is presented is the second part, where woven fabric composites designated for high temperature application were investigated under severe thermal conditions to study their thermal stability and their resistance to thermal damage. The mechanical performance of the same composites was studied. The effect of aging was also investigated. 3D models were realized with Finite elements in order to explain the edge effect on the evolution of the cracks observed during the tensile tests. In addition, the differences and similarities in cracking in different layers were analysed using probabilistic approaches (a simple one as well as Monte Carlo simulations with Hashin’s and also shear lag model) and fracture mechanics arguments.