Study of cyclic behavior, displacement-controlled low-cycle fatigue lifetime and failure in open-hole polymer-matrix composite reinforced by carbon fibers under various loading rates and amplitudes

In this article, effects of the loading rate on low-cycle fatigue behaviors in carbon fiber reinforced composites have been investigated. Firstly, open-hole composite specimens were exposed to two different tensile loading rates to achieve displacements in low-cycle fatigue tests. Then, samples were subjected to cyclic loading, in three displacements and five loading frequencies. Fracture surfaces and scanning electron microscopy images were also shown. Obtained results indicated that increasing the rate enhanced the maximum stress due to the material tend to the brittle behavior. The maximum stress in different frequencies had a small enhancement; however, it enhanced at various displacements. The lifetime had a decreasing trend in a constant displacement, with increasing the frequency and increased in a constant frequency, with increasing the displacement. By analyzing the sensitivity, the change in the loading frequency (at constant displacements) and the displacement (frequencies: 1-5 Hz) were not effective on the maximum stress. However, under 10-20 Hz, it was effective on the maximum stress. The material cyclic behavior demonstrated that the maximum stress decreased during loading cycles due to the damage accumulation and the composite stiffness reduced. The failure mechanisms changed by changing the frequency and the percentage of the fiber breakage increased by increasing the loading frequency.