Effects of friction and strain hardening on ELS mode II interlaminar fracture test

Accurate determination of the interlaminar mode II fracture toughness is much more difficult than that of mode I delamination, due to friction and crack closure. In this paper, A-scan is used to measure the crack growth length of end-loaded split (ELS) test through cyclic unloading and reloading. Interesting hysteresis loops are observed in the experimental load-displacement curve, which has not been fully understood by the existing literature. The frictional effect from the load fixture is analytically determined and numerically validated. It absorbs considerable energy during the creation of new crack surface, but has been overlooked. A simple method is proposed to determine the frictional coefficient and effect. To reduce the frictional effect, a new load fixture is proposed and validated by finite element analysis. The hysteresis loop is found to be caused by the friction and strain hardening during cyclic loading.