Delamination Growth in a Notched Graphite/Epoxy Laminate Under Compression Fatigue Loading

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Abstract
This paper is concerned with the propagation of delamination in a graphite/epoxy composite laminate with an unloaded circular hole subjected to compression fatigue loading. Experimental and theoretical aspects of the problem are investigated. In the experimental phase, coupon specimens were fatigue loaded in pure compression. The tests were performed at different constant-load amplitudes in ambient and humid environments at room temperature. To monitor delamination growth, the specimens were removed from the testing machine after certain numbers of load cycles and were nondestructively inspected using a tetrabromoethane (TBE)-enhanced X-ray technique. In this way a measure of the delamination shape and area as a function of applied load level and number of cycles was obtained. Fatigue damage in terms of modulus degradation was also monitored. In the case of specimens which suffered severe damage, the residual compression strength was measured. A three-dimensional finite-element analysis was used in conjunction with the experimental results to characterize the delamination crack growth in dry specimens. Results of this analysis enabled a power-law relationship between the strain energy release rate and the crack growth rate to be established.

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