Non-destructive Detection of Drilling-induced Delamination in CFRP and its Effect on Mechanical Properties

Delamination is the most dominant damage phenomenon during drilling of thermoset carbon fibre reinforced plastics (CFRP). In this paper, novel approaches in non-destructive delamination testing of drilled CFRP are presented. Furthermore, it contributes for a better understanding on the effect of delamination on static strength. CFRP laminates based on prepreg T800S/M21 manufactured by Hexcel were drilled using step drills. In wear series the effect of tool geometry on delamination was studied. The size of delamination was measured by means of optical inspection techniques, ultrasonic testing and computed tomography. After delamination analysis, several samples with a wide range of typical delamination were tested in open hole bending experiments. The point angle of the step drill was found to affect the delamination damage on the entry and exit side of the laminate. The quantitative results of the three non-destructive methods applied were in good accordance, but some systematic deviations are still present. In the mechanical tests, a clear decrease in flexural strength was found with increasing delamination factor, but the correlation with the delamination factor Fd was quite weak.