Experimental investigation of the fatigue behaviour of off-axis CFRP laminates using Non Destructive Techniques

Composite materials are in practice subjected to fatigue loading, which most of the times happens to be multiaxial. This multiaxiality can for example appear in tubular specimens under combined tension/torsion loading or in cruciform specimens tested bi-axially. Due to the anisotropy that characterizes composite materials, multiaxial internal loads also occur even under simple uniaxial external loading. Therefore, it is preferable to use external uniaxial fatigue loading of flat coupons in order to study the local multiaxial fatigue behaviour of composites. In this study, Carbon Fibre Reinforced Epoxy (CFRE) flat specimens of two different lay-ups are tested under fatigue in different stress levels and R-ratios. 30° and 75° off-axis flat specimens are tested under uniaxial fatigue and the developed internal multiaxial loads are taken into account to investigate their influence on the fatigue behaviour of the material. Two different advanced monitoring methods, namely Digital Image Correlation (DIC) and Acoustic Emission (AE) are used during testing to clarify the damage processes.