Modified F-criterion and its influence on potential crack deflection range

With the development of interface-rich composites, crack penetration deflection at the interfaces have been the focus of considerable research studies. Because the F-criterion may imperceptibly enlarge the potential crack deflection range, a modification was made and related numerical analyses were then conducted. It was found that the modified F-criterion is as effective as the F-criterion and not affected by the fracture toughness ratio of mode II to mode I, when predicting the crack penetration direction. Furthermore, based on the modified F-criterion, the potential crack deflection range gradually shrinks, as the friction coefficient on crack surfaces and the fracture toughness ratio of mode II to mode I increase. However, as the surface pressure increases, the potential crack deflection range gradually broadens. In general, the result that is based on the modified F-criterion is no more than the one that is based on the F-criterion, when predicting the potential crack deflection range. Additionally, in accordance with the modified F-criterion, crack deflection caused by shear failure occurs only when the mode II fracture toughness is similar to the mode I fracture toughness. Otherwise, tensile failure is the exclusive reason for crack deflection. (C) 2018 Elsevier Ltd. All rights reserved.