14 - Micromechanical failure analysis of advanced composite materials

This chapter sets out to introduce the reader to the important area of micromechanical modelling for the analysis of failure in advanced composite materials. A general introduction to the micromechanical failure in composite laminates is described along with finite element modelling of unidirectional composites to model such failure. The concept of representative volume elements is introduced and statistical methods to characterise composite microstructures are described in detail. A novel approach to recreate statically equivalent microstructure geometries, termed the Nearest Neighbour Algorithm is then developed and used to create advanced 2- and 3- dimensional finite element models. The important concepts of periodicity and homogenisation are introduced, and then used to extract macroscale elastic moduli. Matrix plasticity and fibre-matrix interface failure models are then introduced and used to predict macroscale strength properties, where extensive material parameter, thermal and cyclic loading studies are carried out. Applications towards modelling macroscale materials and structures are then developed by creating macroscopic failure surfaces and extending the micromechanical models to model composite adhesive joints, where adhesive and composite failure coexist in one single microscale model. Again, extensive parameter studies are carried out. A number of experimental techniques to both calibrate and validate micromechanical models are then described, with some applications. Among the many interesting findings in the chapter, it is shown that while the micromechanical models require a solid understanding of composites, geometric topology, finite element analysis and non-linear material modelling, once they are created they can be used for extensive and cost efficient parameter studies for both composite material design and application to structural features such as bonded joints.