Monitoring of multiaxial fatigue damage evolution in impacted composite tubes using non-destructive evaluation

Damage evolution in wound glass fibre reinforced tubes due to impact (8.4 J and 14 J) and subsequent biaxial cyclic loading is studied. Nominally defect-free and impact damaged specimens are compared to investigate the effect of the impact damage on the fatigue life of multiaxial composites. Non-destructive inspection (air-coupled guided waves, thermography, high-speed photography, and microscopy) is applied to a subset of tubes. Air-coupled guided wave scans for characterisation of the delaminations due to impact agree well with visual inspection. Decline in guided wave velocity is consistent to a decrease in stiffness caused by fatigue damage. Using thermal imaging the impact is detectable during cyclic loading. Strong anomalies of the surface temperature in the vicinity of the impact at the end of the fatigue life correspond to the initiation spot of final failure observed by high-speed imaging. The considerable effect of impact damage on the durability of the specimens is discussed.