Fatigue behaviour of a barely visible impact damaged carbon fibre reinforced epoxy laminate

Abstract

Composite materials have high in-plane mechanical properties, but are susceptible to out-of-plane impact damage. The use of non-destructive evaluation techniques, combined with mechanical testing, was investigated to characterize the progression of post-impact static and fatigue damage of composite laminates. Quasi-isotropic carbon/epoxy specimens were impacted at energy levels of 35 J and 50 J. The initial damage was characterized using ultrasonic C-scan and thermography. Residual strength testing revealed that the compressive static strength of the test specimens was reduced by over 50%. Digital image correlation was used to characterize the growth of damage and the local strain during compression-compression fatigue tests. Initially, no significant statistical trend could be measured when the fatigue data was plotted as a stress-life curve. When stress concentration factors were used to calculate and plot the local stress amplitude, a correlation with fatigue life was observed. The undamaged fatigue data was altered using damage factors which allowed for post-impact fatigue life predictions.