Effect of creep damage and mean stress on the fatigue life of short Fiber-Reinforced polypropylene composites

The use of short fiber-reinforced thermoplastics in mobility applications has become more prominent owing to their lightweight nature and favorable material properties. Fatigue life analysis is crucial for the safe and reliable design of short fiber-reinforced thermoplastic components. Because most load-bearing components are subjected to mean stress, an accurate evaluation of the mean stress effect is essential. In this study, fatigue life tests with various load ratios and flexural creep tests were performed on polypropylene composites with different short glass fiber compositions to characterize the viscous damage in the positive mean stress fatigue tests of short fiber-reinforced thermoplastics. The varying mean stress effect due to viscous damage was characterized by applying a creep-dependent mean stress sensitivity parameter to the parabolic σ_a-σ_m relation. The results of the proposed mean stress correction for the positive load ratio data showed a high correlation with the test results under full reversal conditions.