An improved cohesive element for shell delamination analyses

In this paper, an improved cohesive element is proposed for accurate quantification of delamination in laminar composites. The improved cohesive element employs a mixed Gaussian and sub-domain integration scheme for cohesive stress integration. Level set description of crack front geometry is used to accurately track the evolving delamination crack front. The new element offers significant improvement in solution accuracy and numerical stability, as compared with conventional cohesive elements using either Gaussian integration or Newton-Cotes integration. The much enhanced numerical accuracy and stability permit the use of bonded structural element size as large as 1 ~ 1.5 times the cohesive zone size without significantly compromising numerical accuracy and efficiency. This greatly alleviates the strict mesh size requirement imposed by conventional cohesive elements that require the bonded structural element size be smaller than 1/3 ~ 1/5 of the cohesive zone size. Furthermore, the new element offers the benefit of easy insertion of arbitrary initial crack geometry for a structured mesh.