Effect of curved delamination front on mode-I fracture toughness of adhesively bonded joints

•Effect of curved crack front on mode-I fracture toughness is studied.•Influence of curved crack front is incorporated into the three common methods.•The measured crack length is modified using visual deviation λv.•The practical formulas for visual deviation of curved crack front are put forward.

The influence of curved delamination front on mode-I fracture toughness of adhesively-bonded composite joint is investigated using double cantilever beam (DCB) with an adhesive layer. The model of curved delamination front is converted to the model of straight crack front based on the principle of equivalent crack area. With visual deviation λv and non-uniformity coefficient β, the effect of curved delamination front can be incorporated into determination of fracture toughness for DCB specimens. Then, the parametric analyses concerning λv are studied with virtual crack closure technique (VCCT). Meanwhile, the practical formulas of λv are put forward.