A note on the coupled and dual energy release rates for VCCT

The coupled energy release rate may be used with the virtual crack closure technique (VCCT) method to determine the stress intensity factors of interface cracks. Different equations were presented over the years using this parameter. In recent papers, a new approach was presented by the authors. This approach includes two additional energy release rates, called here, the dual energy release rates. Here, the coupled and dual energy release rates are explored and well established. This leads to a new and more suitable equation for calculating the mode mixity or phase angle. In addition, a geometrical interpretation between the energy release rates for both homogeneous and interface crack problems is found. A problem of an interface crack between two linear elastic, isotropic, and homogeneous materials in an infinite body is presented. This problem emphasizes the advantage of the new equation, and the geometrical relation between the energy release rates is illustrated.