Modelling delamination of composites using cohesive zone techniques

Composite materials are used in many specialised armour applications such as spall-liners and inserts in bullet proof vests. Fibre reinforced composites with a laminate lay-up (or laminates) are the most typically used composites. When laminates are subject to projectile impact, very local failure of the different laminate components is observed, such as fibre fracture, matrix failure and delamination. When failure occurs, the laminate is locally weakened.
From a practical point of view, it is desirable to be able to predict how especially delamination weakens the structure during and after the impact process.
In this research, the focus is on predicting mode I delamination and more specifically the amount and the exact location of delamination in the laminate. Predicting delamination of a laminate due to projectile impact is one of the most challenging subjects in (fracture) mechanics. This is because the behaviour of the laminate highly depends on the mixed mode behaviour under very high strain rates. In addition, it is in general difficult to obtain realistic material properties at such high strain rates.
In this research, delamination is modelled using cohesive zones between layers with a traction separation criterion. Using cohesive zone techniques, it is possible to describe mode I fracture initiation and fracture development up to failure. This technique is very general and can be used to predict delamination of other laminates with only minor adjustments.