Three-dimensional analysis of center-delaminated unidirectional and multidirectional single-leg bending specimens

Results are presented from a theoretical investigation of the effects of stacking sequence on the energy release rate in laminated composite single-leg bending test specimens. Deflections and energy release rates of unidirectional and multidirectional single-leg bending specimens are obtained by classical laminated plate theory based methods and by three-dimensional finite element analyses. It is shown that the distribution of energy release rate varies across the front of an initially straight delamination and that, regardless of stacking sequence, all three energy release rate components will occur. The percentage of the mode III energy release rate is generally small. Its relative magnitude, as well as the differences between the maximum and minimum values of all the energy release rate components, are shown to correlate with a non-dimensional ratio comprised of the flexural rigidities of the specimen. The classical plate theory based methods are shown to predict accurately both the total energy release rate and the average mode ratio, i.e. with respect to the full width of the specimen, for all stacking sequences evaluated.