Effects of Orthotropy and Width on the Compression Strength of Graphite-Epoxy Panels with Holes

An experimental study was conducted to evaluate the effect of laminate orthotropic properties and panel width on the compression strength of 48-ply graphite-epoxy laminates with drilled holes. The test results were evaluated on the basis of hole size and specimen width and were used to determine parameters necessary to predict trends using the point-stress failure criterion. Good agreement was obtained between experimental and predicted values of failure for panels fabricated from two quasi-isotropic laminates and one orthotropic laminate. The results indicate that panels of different widths that have large holes in relation to the failure prediction parameter should be included in any test program conducted to develop predictions. Panel failures are shown to have an upper limit given by the reduction in specimen cross-sectional area and a lower limit given by the effect of stress concentration. Limited tests of a quasi-isotropic laminate were conducted on panels with machined cracks and panels with punched holes and the results compared to those with drilled holes. The sequence of events that occurs in the vicinity of a hole during failure was identified and provides insight into the mechanisms associated with failure. a d