The 8-node quadratic element is described by Figure 5 in both parent space with local coordinates ξ ξ and η η , and by the mapped element in physical/global space by x and y . The parent element is mapped from the local space to the physical space by the shape functions N i ( ξ ξ , η η ) and the degree of freedom coordinates ( x i , y i ) . The crack tip is located at ξ ξ = − − 1 , η η = − − 1 or x = 0 , y = 0.