EVALUATING WEIBULL PARAMETERS FOR TRANSVERSE CRACKING IN CROSS-PLY LAMINATES

The conventional method of statistical analysis of multiple transverse cracking in cross-ply laminates is improved by correcting the strains in the cracked plies using finite element modelling. The correction t akes into account the non-uniform stress distribution associated with each crack and the stress interactions between adjacent cracks. These effects are normally ignored, although they become important as the cr ack density increases. The strain distribution in the cracked 90 degre es plies is determined first. An equivalent constant strain is calcula ted for a given crack density to give equal probability of failure to the actual variable strain distribution. This is then used to evaluate the Weibull parameters based on the true non-uniform strain distribut ion in the 90 degrees plies. The cases studied include a cross-ply [0/ 90], laminate, a hybrid GFRP/8-ply CFRP and a hybrid GFRP/16-ply CFRP. The resultant Weibull plots show much greater linear regions and the evaluated Weibull parameters are not sensitive to the segment length p rovided that it is short enough to avoid multiple cracking. The normal problem of choosing the appropriate segment length is therefore overc ome, and more reliable Weibull parameters can be obtained.