Two crack parameters, namely, the Crack-Tip Opening Angle (CTOA) and the Crack Volume Ratio (CVR) are examined in an effort to develop a universal and practical criterion of tearing under biaxial loading. Preference is given to the CVR used within the framework of the Unified Methodology (UM) of fracture analysis. This approach is based on the following assumption: that accumulation of structural damage in a naturally-forming neck, initiation of a short tear crack within the neck and its propagation can be modelled in terms of elastic response and fracture behaviour of long tear cracks. Our analysis and estimates support the basic postulate of the UM that the dominant mechanism of fracture is essentially the same for any combination of tensile and/or compressive loads P and Q applied, respectively, across and along the crack path.
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