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 pa ckage SAS has been utilized to develop a statistical model for the pre diction of joint failure in single-shear joints in IM7/8551 graphite/e poxy laminates on the basis of the results of an extensive bolted-join t strength resting program. Ultimate joint strength values from the ex perimental study were utilized as input for the development of a stati stical 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 materia l input parameters. Each submodel predicts ultimate joint strength wit h an R(2) value of approximately 0.95. The general test parameters inc lude angle of loading, bolt/hole diameter, edge distance, type of fast ener head, laminate lay-up and coupon width. The effects of some anoma lous factors on bolted joint strength were also tested and evaluated; these factors include the choice of fabric or tape lamina, use of meta llic hole inserts (bushings and sleeves), nutplated fasteners, oversiz ed holes and under-torqued joints. The approach is general and could b e utilized with a laminate joint strength data base to predict joint s trengths in newly developed material systems with minimal testing. (C) 1996 Published by Elsevier Science Limited