Three Dimensional Finite Element Analysis of Multidirectional Composite DCB, SLB and ENF Specimens

Results are presented from a numerical investigation of the effect of stacking sequence on energy release rate distribution in laminated carbon fibre reinforced epoxy double cantilever beam, single leg bending and end-notched flexure test specimens. The deformation behaviour of the specimens has been computed by three-dimensional nonlinear finite element analyses using a recently developed layered 3D-shell element. The distributions of the local mixed mode energy release rates along straight and measured curved delamination fronts have been determined by the virtual crack closure method. The dependency of computed total energy release rate and the individual mode contributions on element types and local mesh sizes is discussed. It is shown that for all three specimen types the distribution depends on the ply angles at the interface of crack propagation. In addition, it also depends on the bending-twisting coupling and the longitudinal-transverse bending coupling in the individual arms of the specimens caused by different stacking sequences. Results are used to verify existing and proposed new design recommendations for all three types of specimens [1, 2, 3].