Application of the T*-integral and S criteria in finite element analysis of impact damage at fastener holes in graphite/epoxy laminates under compression

T. E. Tay, J. F. Williams, R. Jones

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This paper illustrates the application of two fracture criteria, Atluri's T*-integral and Sih's strain energy density factor S for estimating the residual strength of an impact damaged fastener hole in a composite laminate. Finite element analyses are performed, and the magnitude and distribution of T* and S are determined around the delamination. It is found that the profiles of these distributions are extremely complex and sensitive to the modelling of the stress fields close to the delamination. The effects of local closure, shear moduli and cracktip singularity are investigated. It is also shown that the representation of the stress singularity in the finite element model has a strong effect on the distribution of T* and S. The distribution of both T* and S is such that three local maxima occur and are situated at the same locations around the delamination. These locations approximately coincide with the points of maximum growth as revealed by ultrasonic C-scan of the damage growth of several specimens. The T*-integral is shown to be more sensitive to the values of interlaminar shear moduli than S. The results of the analyses suggest that both the T*-integral and S criteria may be successfully employed in the prediction of residual strength. However, S is better at predicting the direction of damage growth provided the stress fields near the delamination can be accurately modelled.

Original languageEnglish
Pages (from-to)233-253
Number of pages21
JournalComposite Structures
Issue number4
Publication statusPublished - 1987
Externally publishedYes

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