Fatigue damage in centrally notched GR/EP laminates |
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Authors: | M -H R Jen J -M Hsu C -H Lee |
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Affiliation: | (1) Department of Mechanical Engineering, National Sun Yat-Sen University, 80424 Kaohsiung, Taiwan |
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Abstract: | The fatigue properties of graphite/epoxy (Gr/Ep) T300/5208 composite laminates of 16 plies with a central circular hole subjected
to tension-tension (T-T) constant-stress amplitudes at room temperature and low humidity have been fully investigated. Studied
are four types of notched laminates which are classified as unidirectional, off-axis, orthotropic shear and quasi-isotropic.
Some of them were precracked to initiate and guide the crack growth transversely. Our work is experimental and the analysis
is based on a semiempirical approach.
We have experimentally measured S-N curves, failure surfaces, crack lengths and their corresponding growth directions, delamination
areas and transverse delamination lengths for the above series of composites. The fatigue failure mechanism was observed and
expressed schematically. To analyze the experimental results, we have categorized the S-N curves by three common equations.
The effective transverse crack length of quasi-isotropic laminates was found to be independent of the applied stress. For
simplicity, it was modeled by a power law of applied cycles. It was also found that the delamination area could be expressed
by a power law of applied cycles. Hence, the so-called modified Paris law, i.e., the power law of cycles, proposed here has
been verified as satisfactorily acceptable. |
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