Multiaxial fatigue behaviour of GFRP with evenly distributed or accumulated voids monitored by various NDT methodologies

The effect of evenly distributed voids (dv) and regions of large accumulated voids (lav) on damage evolution and fatigue life during biaxial cyclic loading is studied. Various non-destructive test methods (thermography, microscopy and optical fracture analysis with high-speed photography) are presented for monitoring the void formation, multiaxial fatigue damage mechanisms and final failure process in glass-fibre reinforced plastics (GFRPs) manufactured by a filament winding machine. In addition, air-coupled guided wave measurements (non-contact and single-sided configuration) are applied to a subset of composite tubes for detection of voids and for observing the development of fatigue damages initiated by voids. Thermal imaging during cyclic loading reveals large accumulated voids as well. Variations of stiffness degradation, matrix cracking and guided wave velocities caused by finely distributed or accumulated voids are shown. Finally, the detrimental effect of the two types of porosity on the durability of multiaxially loaded composites is illustrated.