Effect of Indenter Size on Damage of Carbon Fibre-Reinforced Polymer Composites under Impact Loads

The applications of composite materials have been increasing significantly in recent decades. The major effect limiting the use composite materials is the lack of understanding of their response and their structural integrity under dynamic loads. Delamination under dynamic load is particularly recognised as the most critical damage process in laminated composites. The objective of this thesis is to experimentally and numerically investigate the fundamental phenomena associated with delamination. This is important develop a further knowledge of the response and damage mechanisms of composite materials under low-velocity impact and static load. Various parameters that affect the delamination of composite material have been studied in this work, including the diameter of the hemi-spherical indenter and the type of load at the same energy level. The difference between the shape and size of delamination area between different plies has been examined using x-ray commutated tomography. Cohesive elements have been used in the ABAQUS finite element modelling to determine failure criteria that correspond with the experimental work. It is found that the main delamination area occurs on the tension side of laminates subjected to bending, and that it also depends on the difference in angle between adjacent plies. The effect of the indenter radius to thickness of plate ratio on the relation between force and damage evolution have been studied numerically for different thickness of plate. This analytical study was repeated for both isotropic and anisotropic materials to show the effect of material type on the previous relation. It is found that the initiation of the delamination can be assessed from the existence of a delamination threshold load in a force-displacement curve under quasi-static load or in a displacement-time curve under dynamic load.