Published: Jan 1991
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An analytical and empirical study was conducted to investigate delamination behavior in composite structures.
The objective of the analysis was to predict the threshold stress for the initiation of delamination growth in compressively loaded composite laminates. MSC/NASTRAN geometrically nonlinear finite element analysis and a virtual crack opening technique were used to compute strain energy release rate distributions around circular delaminations. The distributions were computed for various compressive stress levels and the threshold stress for delamination growth was then determined by applying the strain energy release rates in a mixed-mode fracture criterion.
A number of static compression tests were conducted on specimens made from AS4/3501-5A graphite fabric-reinforced epoxy. The specimens contained circular delaminations of various sizes. The delaminations had been created by implanting Teflon inclusions in the prepreg layup.
Computed predictions of the delamination growth threshold stresses were significantly in error relative to the test data. The analysis did, however, concur with observed trends and provided qualitative insight into the process of quasi-static delamination growth.
composite materials, delamination, fracture, graphite-epoxy materials, mixed-mode loading, strain energy release rate
Senior research engineer, Rohr Industries, Inc., Chula Vista, CA