Time-dependent failure of off-axis loaded unidirectional glass/iPP composites

In our previous study, we demonstrated that the time-dependent failure of transversely loaded UD (unidirectional) glass/iPP is fully plasticity-controlled and proposed a lifetime prediction method based on plasticity to predict transverse failure. In the present work, extending our previous study to other off-axis angles, we aim to investigate the effect of the off-axis angle on the time-dependent failure of UD glass/iPP, and to propose a lifetime prediction method for the off-axis failure. Glass/iPP specimens with different off-axis angles are tested at various strain rates, creep, and fatigue loads to characterize the anisotropic, time-dependent mechanical response. It is demonstrated that the influences of strain rate and fiber orientation angle on tensile strength are multiplicatively separable; also referred to as factorizable, enabling one to characterize the angle dependence at a single strain rate and the strain rate dependence at a single angle. Moreover, similar to transverse loading, off-axis failure is also observed to be plasticity-controlled. Based on these observations, the lifetime prediction method for the plasticity-controlled transverse failure is extended to off-axis loading using the aforementioned factorazibility, which resulted in lifetime predictions in agreement with the experimental creep and fatigue data.