Effects of local fibre waviness on damage mechanisms and fatigue behaviour of biaxially loaded tube specimens

Damage development in and final failure process of glass fibre winding specimens during biaxial fatigue loading are investigated. The phenomena in nominally defect-free tubes and specimens exhibiting local fibre waviness in one layer are compared. A subset of wound tubes is analysed using non-destructive testing methods, i.e. air-coupled guided waves, thermography, optical fracture analysis by a high-speed camera, and discrete damage monitoring. Air-coupled guided waves are employed for detection of fibre waviness and for monitoring the failure progress initiated by this waviness. Stiffness degradation due to fatigue damage corresponds to a decline in guided wave velocity. Using infrared inspection, the fibre waviness can be detected in an early stage of fatigue life. Non-destructive evaluation reveals that initiation of final failure in the specimens is caused by local fibre waviness. Finally, the effect of local fibre waviness on the S–N curves of the specimens is illustrated.