A statistical approach to the analysis of ultimate strengths of bolted joints in laminated composites

The general linear models (GLM) routine in the statistical software package SAS has been utilized to develop a statistical model for the prediction of joint failure in single-shear joints in IM7/8551 graphite/epoxy laminates on the basis of the results of an extensive bolted-joint strength resting program. Ultimate joint strength values from the experimental study were utilized as input for the development of a statistical approach which combines a set of submodels into a general joint failure Fortran routine. Ultimate joint strength in IM7/8551 graphite/epoxy laminates is statistically predicted from geometric and material input parameters. Each submodel predicts ultimate joint strength with an R(2) value of approximately 0.95. The general test parameters include angle of loading, bolt/hole diameter, edge distance, type of fastener head, laminate lay-up and coupon width. The effects of some anomalous factors on bolted joint strength were also tested and evaluated; these factors include the choice of fabric or tape lamina, use of metallic hole inserts (bushings and sleeves), nutplated fasteners, oversized holes and under-torqued joints. The approach is general and could be utilized with a laminate joint strength data base to predict joint strengths in newly developed material systems with minimal testing. (C) 1996 Published by Elsevier Science Limited