Experimental investigation of the microscopic damage development at mode i fatigue delamination tips in carbon/epoxy laminates

This paper investigates the damage development ahead of mode I delamination tips in carbon /epoxy laminates using scanning electron microscope (SEM). Two techniques were adopted for the investigation; the first technique consisted of the application of stepwise load increments on DCB (double cantilever beam) specimens inside the SEM, while images were recorded until delamination onset. For the second technique, the DCB specimens were fatigue tested under different combinations of monotonic and cyclic loading. After the fatigue tests, the specimens were kept open in the microscope by insertion of steel wedges allowing the inspection of the delamination tips. The investigation revealed that multiple micro-cracks are formed parallel to the delamination growth direction ahead of the tip that coalesces. Micro-cracks that were formed 2 or 3 plies away from the delamination plane were observed to cause fibre bridging