ESTIMATION OF THE 90-DEGREES PLY STRENGTH DISTRIBUTION AND SHEAR LAG PARAMETER FROM MULTIPLE TRANSVERSE CRACKING IN GRAPHITE EPOXY CROSS-PLY LAMINATES

A method to estimate the Weibull parameters for the strength distribution of a transverse ply and the shear lag parameter (the ratio of the shear modulus G to the thickness b of the shear transfer region) in cross-ply 0(2)/90(4)/0(2), 0(2)/90(6)/0(2) and 0(2)/90(12)/0(2) graphite-epoxy laminates from multiple transverse cracking was proposed and applied to experimental results. The estimated values of the Weibull parameters were essentially the same as those estimated by the Peters method. The value of the shear lag parameter G/b was found to be 50-100 MPa mum-1 for 02/90(4)/0(2) and 0(2)/90(6)/0(2) laminates.On the contrary, the experimental results on the multiple cracking of the 90-degrees ply in a 0(2)/90(12)/02 laminate at high applied stresses could not be described by the value of G/b = 50-100 MPa mum-1, possibly owing to the occurrence of plastic deformation and/or shear failure in the 0-degrees-90-degrees interface.