Fatigue of short fiber thermoplastic composites: A review of recent experimental results and analysis

Abstract Cyclic deformation and fatigue behavior of two short fiber thermoplastic composites (SFTCs) under a number of loading and environmental conditions are investigated. The considered environmental effects include those of low and elevated temperatures as well as moisture (or water absorption). Fatigue behavior is also explored under the action of non-zero mean stress (or R ratio) in addition to fully-reversed ( R = −1), as well as various cyclic loading frequencies. Material anisotropy and geometrical discontinuity effects (i.e. stress concentration) are other aspects considered in this study. Mechanisms of fatigue failure are also assessed under environmental effects. Based on experimental observations and analysis, a number of analytical and empirical models are developed for estimating fatigue behavior under different conditions. Empirical equations are presented to characterize self-heating under cyclic loading. Tsai-Hill criterion is applied to account for the effect of fiber orientation on fatigue life. Mean stress effect is corrected with several mean stress parameters and a shift factor of Arrhenius type is defined to characterize the effect of temperature on fatigue life. Two methodologies are presented to estimate fatigue properties based on tensile properties, in addition to approximation of strain-life curves based on load-controlled fatigue data. Estimation of notched fatigue behavior based on smooth (un-notched) fatigue behavior is also presented.