Defects in composite structures like impact damages have a major influence on the fatigue behaviour. These defects may occur during lifetime of composite parts and lead to delaminations between adjacent layers with different fibre orientations and to matrix cracks within these layers. We investigated the relationship between impact damage and fatigue lifetime. Specimens made of a glass fibre non-crimp fabric (NCF) were produced by vacuum assisted resin transfer moulding (VARTM). Impact damage was introduced using a drop weight with a hemispherical head and a canon. Two types of specimens were used: coupons with dimensions of 250 mm x 30 mm and a stringer-panel with the dimensions of about 1000 mm x 1000 mm. The panel was tested in a hexapod test rig applying multiaxial loads. In comparison, the obtained results from the coupon tests can be transferred to larger scale composite structures. In coupon tests, it was purposed to characterise the damage development in fatigue of fibre reinforced polymers as a function of impact damage, lifetime and stress ratio as precise as possible. Therefore, the stiffness degradation during fatigue due to matrix cracks, delaminations, fibre failure and temperature development of the specimens was plotted vs. the number of load cycles. In interrupted fatigue tests at defined numbers of load cycles the influence of defects on the matrix crack development was determined and correlated with the stiffness degradation. Furthermore, thermoelastic stress analysis was performed during the interrupted tests in order to determine the stress concentrations in the area of the impact damage. The coupons were tested under fatigue loading using a stress ratio of R=-1 (tension-compression) and R=10 (compression-compression).
