Modelling of Composite Damage

Damage in composite laminate materials can be categorised into fibre damage, matrix damage and delamination. Most of the techniques currently available for modelling composite laminate materials and structures only compute fibre and matrix damage and not delamination. However, the presence of delaminations may severely affect the strength and stiffness of a structure. In practice, this damage may not even be visible to the naked eye. Any analysis technique that is able to predict such damage is therefore invaluable.

Damage modelling techniques have been developed using failure criteria based upon material yield/failure strengths. The solutions are produced in the time domain, using the LS-DYNA computer program and predict the damage as it evolves. The techniques have been validated for a range of impact conditions from low velocity 10ms-1 to 2000ms-1.To validate the models, a series of tests were carried out in which spherical projectiles were fired at simply supported composite sheets at a range of velocities. Validation was on the basis of the residual kinetic energy of the projectile, and the level of damage in the composite sheet.

Sections taken through the composite sheet following the simulated impact show that the composite material is deformed and fails as a result of the impact, absorbing energy and reducing the velocity of the projectile. Ply delamination occurred and contact algorithms were used to control the subsequent inter-layer behaviour.
If the velocity of the projectile is sufficiently high, the projectile will penetrate through the sheet. The simulations produced a good match with the area of delamination, the hole size, and the residual velocity of the projectile and were used to validate the modelling methods.