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Progressive Damage Growth of Composites Under Variable-Amplitude Fatigue Testing
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2022-04-01
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[PDF-18.54 MB]
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Alternative Title:Progressive Damage Growth of Composites under Variable-Amplitude Fatigue
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Edition:Final Report
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Abstract:Anisotropic heterogeneous characteristics and changes in failure modes over the fatigue life as well as multiple failure mechanisms that interact with each other make it challenging to predict damage growth in composite structures. Therefore, overly conservative assumptions (e.g. load and life factors based on lower-level building block testing) are made for fatigue life assessment without taking full advantage of the fatigue capabilities of composites. To design efficient composite structures, a greater understanding of the fundamentals of fatigue damage initiation and growth characteristics is needed. A significant body of work on monotonic fatigue loading has been performed, and significant milestones in predicting the damage extent of specific failure modes, such as transverse cracking in cross-ply laminates and delamination, have been reached. The interaction of matrix cracking and delamination under monotonic fatigue loading has also been addressed. First, damage accumulation based on constant-amplitude (monotonic) fatigue was studied in detail with high-fidelity inspection methods. Then, several block-spectrum configurations, sequencing various high-, medium-, and low-load blocks were investigated for determining the sequencing effects. These block spectra included cases with a constant stress ratio across the spectrum as well as cases with variable stress ratios. Several key findings concerning damage initiation progression are reported for several combinations of block spectra. For the open-hole specimen configuration, it was noted that a high load at the beginning resulted in the least damaging scenario. Supplementary studies on load-sequencing effects by altering laminate configurations, varying stress levels, and mixed stress ratio are also included.
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