A numerical-experimental evaluation of the fatigue strain limits of CFRP subjected to dynamic compression loads

The use of composite materials in the most varied industrial sectors has increased considerably in recent years, especially those made of carbon fiber/epoxy resin. For this reason, the use of these materials need a better understanding of their mechanical behavior, especially when submitted to cyclical load requests, especially about compression, which is the object of study of this work. Residual strength degradation in CFRP is evaluated by numerical models and experimental tests relating the residual strength to the applied fatigue cycles and the maximum stress. The present work proposes to characterize the static and fatigue mechanical properties in compression of a carbon fiber/epoxy resin composite, used in the aeronautical industry, to present a mathematical model to determine the residual strength. The experimental methodology for strain limit evaluation has involved the residual strength after the fatigue test limited to 120,000 or 240,000 cycles, considering frequency of 12 Hz and stress ratio R=10 in different strain levels. This study establishes that the strain limit corresponds to deformation in which the residual strength becomes equal to the design stress (stress reduced statically to the B - basis value). Lastly, the adjusted mathematical model for determining the residual strength and the finite element simulations showed consistent results when compared with experimental tests. This study shows the relevance of the allowable levels determined from static strength to the onset of abrupt failure as a function of increasing maximum fatigue stress level that is a significant finding for the fatigue design community.