Effect of stacking sequence on energy release rate distributions in multidirectional DCB and ENF specimens

Results are presented from a theoretical investigation of the effect of stacking sequence on energy release rate distributions in laminated composite double cantilever beam and end-notched flexure test specimens. Eight different stacking sequences are investigated; four of these will result in delamination growth at a 30°/30° interface and four will result in growth at a 30°/ - 30° interface. Each set of four sequences is chosen to exhibit varying amounts of coupling between the primary bending curvature and either the transverse bending curvature or the twist curvature. For a set number of plies, sequences that minimize one type of coupling will have increased coupling of the other type. The sequences chosen for study span a range of possible choices for practical use. Three-dimensional finite element analyses are used to obtain the total energy release rate and its distribution along an initially straight delamination front for the eight sequences under DCB and ENF loadings. As expected, for the DCB loading, peak energy release rates occur near the center of the specimen's width, whereas for the ENF loading the peak occurs at one or both edges. It is shown that larger bending-twisting coupling results in larger asymmetries in the energy release rate, whereas larger longitudinal-transverse bending coupling results in larger peak values. Practical application to DCB and ENF testing is discussed.