Fatigue damage mechanisms in fiber reinforced composite materials including the effect of cyclic loading frequency

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Virginia Polytechnic Institute and State University

A broad-based investigation seeking to characterize fatigue damage mechanisms in fiber reinforced composite materials, accounting for the effect of cyclic loading frequency, is presented. A many faceted approach to the investigation was utilized; which included well documented strain-controlled fatigue tests, a scanning electron microscopy study, implementation of energy emission techniques (such as acoustic and thermal emissions), and the development of an energy-based failure theory.

A detailed discussion of each aspect of the investigation is presented and, in each case, pertinent conclusions are drawn.

The effect of cyclic loading frequency on fatigue damage development is documented and found to be substantial. A micro-mechanical damage model, which accounts for the effects of frequency and fiber/matrix interface strength, is developed. Using a first law analysis, a good correlation between acoustic and thermal emission with damage propagation and extent is developed. Finally, a new conceptual theory, called the Strain Energy Release-Potential Theory, is postulated. Predictions based on this theory are made and compared with experimental findings, resulting in substantial agreement.