Micromechanical failure analysis of advanced composite materials

This chapter introduces the reader to the important area of micromechanical modelling for the analysis of failure in advanced composite materials. The chapter gives a general introduction to the micromechanical failure in composite laminates and describes finite element (FE) modelling of unidirectional composites to model such failure. We introduce the concept of representative volume elements and describe statistical methods to characterise composite microstructures in detail. A novel approach to re-create statically equivalent microstructure geometries, termed the nearest neighbour algorithm, is then developed and used to create advanced two- and three-dimensional FE 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. We then develop applications towards modelling macroscale materials and structures by creating macroscopic failure surfaces and extending the micromechanical models to model composite-adhesive joints, where adhesive and composite failure coexist in one 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. It is shown that whereas the micromechanical models require a solid understanding of composites, geometric topology, FE 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.