On the role of damage energy in the fatigue degradation characterization of a composite laminate

The results of a series of experiments to characterize the damage behavior of a glass/epoxy laminate are presented in terms of hysteresis energy dissipation, damage energy variation, energy associated with thermal capacity, temperature rise, and a new method that utilizes thermodynamic entropy production. Results are presented for the observed damage stages and their durations. Different life spans for damage stages are observed based on the plots of damage energy and hysteresis energy. A theoretical model based on the energy balance and the second law of thermodynamics is presented that takes into account the role of hysteresis, damage energy and energy associated with thermal capacity as well as the thermodynamic entropy in the fatigue degradation of a composite laminate. The results of thermodynamic entropy indicate that interpretation of degradation within the laminate requires consideration of both the damage energy and hysteresis energy.