Delamination Initiation and Propagation in Composite Laminates

Fibre-reinforced polymer composite laminates are used extensively nowadays in various applications due to their superior mechanical properties. However, a great weakness of composite laminates is their susceptibility to out-of-plane concentrated loading (which can be broadly divided into quasi-static indentation and impact) owing to their weak interlaminar strength. Delamination is a typical damage type for composite laminates under such loading conditions. The occurrence of delamination in composite laminates could significantly degrade their load-carrying capabilities, especially the compressive performance.

Principles of strength of materials and fracture mechanics can be adopted to apply specific delamination initiation and propagation prediction methods to composite laminates. It is known that fracture mechanics methods have advantages in addressing delamination growth problems. On the other hand, it is also shown in the literature that strength of materials methods are generally best suited for quasi-static delamination growth. This implies that the growth of low-velocity impact or quasi-static indentation delaminations in composite laminates could also be predicted with an appropriate strength of materials approach. It is therefore necessary to comprehensively assess the ability of strength of material approaches to predict delamination of a composite laminate under out-of-plane concentrated loading. Since a stable stress field is the basic condition for the application of the strength of materials methods, the out-of-plane quasi-static indentation loading condition is first considered in this thesis.