Mesh design in finite element analysis of post-buckled delamination in composite laminates

The role of mesh design in the post-buckling analysis of delamination in co mposite laminates is addressed in this paper. The determination of the stra in energy release rate (SERR) along the crack front is central to the analy sis. Frequently, theoretical analysis is limited to treatment of the proble m in two dimensions, since considerable complexity is encountered in extend ing the analysis to three dimensions. However, many practical problems of e mbedded delamination in composite laminates are inherently three-dimensiona l in nature. Although ill such cases, the finite element (FE) method can be employed, there are some issues that must be examined more closely to ensu re physically realistic models. One of these issues is the effect of mesh d esign on the determination of the local SERR along the delamination front. There are few studies that deal with this aspect systematically. In this pa per, the effect of mesh design in the calculation of SERR in two-dimensiona l (2D) and three-dimensional (3D) FE analyses of the post-buckling behavior of embedded delaminations is studied and some guidelines on mesh design ar e suggested. Two methods of calculation of the SERR are considered: the vir tual crack closure technique (VCCT) and crack closure technique (CCT). The 2D analyses confirm that if the near-tip mesh is symmetric and consists of square elements, then the evaluation of the SERR is not sensitive to mesh r efinement, and a reasonably coarse mesh is adequate. Despite agreement in t he global post-buckling response of the clclaminatcld part, the SERR calcul ated using different unsymmetrical near-tip meshes could be different. Ther efore, unsymmetrical near-tip meshes should be avoided, as convergence of t he SERR with mesh refinement could not be assured. While the results using VCCT and CCT for 2D analyses agree well with each other, these techniques y ield different quantitative results when applied to 3D analyses. The reason may be due to the way in which the delamination growth is modeled. The CCT allows simultaneous delamination advance over finite circumferential lengt hs, but it is very difficult to implement and the results exhibit mesh depe ndency. Qualitatively, however, the two sets of results show similar distri butions of Mode I and Mode II components of the SERR. This is fortunate, si nce the VCCT is relatively easy to implement. (C) 2000 Elsevier Science Ltd . All rights reserved.