“…Extensive contributions have been made by Bowie and his colleagues [4,5,6] Work on finite-element fracture mechanics analysis at MIT has followed the path of assumed-stress hybrid elements, first proposed by Pian [8] for ordinary continuum elements. The hybrid method was subsequently extended by Tong, Pian, Luk, and Lasry [9,10,11,12] to formulation of rectangular elements which incorporate an elastic crack-tip singularity, but which also have an assumed linear or quadratic variation of displacements along the element edges and are thus compatible with ordinary elements (Figure 1).…”