Effect of Stacking Sequence on the Notched Strength of Laminated Composites

The effect of laminate stacking sequence on the notched and unnotched tensile strength of quasi-isotropic graphite/epoxy laminates is investigated. Notch geometry includes circular holes and center cracks. Experimental data are presented for two different stacking sequences of quasi-isotropic graphite/epoxy laminates. One stacking sequence produces large interlaminar tensile stresses along straight free-edges of a tensile coupon, while the second yields compression at the same free-edges. Three different notch sizes are used for the circular hole and center crack in conjunction with both stacking sequences. Each data point is represented by a minimum of 15 replicates so that statistical distributions of notched and unnotched strengths can be obtained. The experimental data indicate that unnotched tensile strength is reduced by the presence of interlaminar tensile stresses at the straight free-edge, while notched strength appears to be independent of stacking sequence for notch sizes which produce tensile failure prior to delamination at the straight free-edge.

Experimental results also are compared against theoretical notch strengths obtained from the average stress criterion and the point stress criterion, two recently developed criteria for predicting notch strength of laminated composites.