Crack propagation in mixed-mode specimens described via multi-parameter fracture mechanics

The main objective of the paper is to employ a multi-parameter fracture mechanics concept to describe crack propagation through a specimen loaded in mixed-mode. This concept in particular was used because it has been shown that application of the generalized fracture mechanics concept can play a key role for materials with specific fracture behaviour, i.e. when fracture processes occur not only in the very vicinity of the crack tip, but also at larger distances from it. Two mixed-mode (I+II) geometries for the investigation of crack behaviour are presented here. The Williams series expansion is used for crack-tip stress field approximation. Then, considering the higher-order terms of the Williams expansion with regard to maximum tangential stress criterion can provide better estimates of the crack deflection angle. The coefficients of the Williams expansion were determined by means of the over-deterministic method for the purposes of this work. This analysis was performed for each cracked configuration, which is very time-consuming and makes the analysis very extensive. The crack propagation angle obtained by means of the generalized fracture criterion is discussed in detail. It was found that single-parameter fracture mechanics is sufficient when applied close to the crack tip and when mode I of loading prevails, while multi-parameter fracture mechanics can be recommended at larger distances from the crack tip and for configurations where mode II becomes dominant.