A SINGLE-LAP SHEAR SPECIMEN FOR DETERMINING THE EFFECT OF STRAIN-RATE ON THE INTERLAMINAR SHEAR-STRENGTH OF CARBON-FIBER-REINFORCED LAMINATES

A new design of single-lap shear specimen for determining the effect of loading rate on the interlaminar shear strength of laminated composites is described. Finite element analyses are used to optimize the specimen geometry and minimize the variation in the shear stress and the magnitude of the normal stress along the interlaminar failure plane. Experimental results are obtained at a quasi-static and an impact rate of loading for the interlaminar shear strength parallel to the fibres in both unidirectional carbon/epoxy and unidirectional carbon/polyetheretherketone (PEEK) laminates and at interfaces across which the fibre orientation is 0 degrees/90 degrees and +/-45 degrees. Results for carbon/epoxy laminates are compared with those from an earlier investigation using a double-lap specimen geometry and show a similar small dependence on loading rate. No significant effect of loading rate was observed for the carbon/PEEK laminates.