Fatigue Residual Strength and Fatigue Fracture Mechanism on FRP (SMC).

Abstract

Static tensile strength of fatigued material, that is, residual strength was investigated and it is tried to make relationship between tensile fracture mechanisms and fatigue mechanisms clear. It is recognized that materials clearly fatigued because of degradation of the materials'stiffness and occurrence of AE waves in fatigue process. Generally, fatigue damages lead deccrease of tensile strength on some high-polymers and metals. However the residual strength of fatigue-damaged SMC didn't degraded in spite of increasing of fatigue cycles. This is why the static tensile fracture mechnism is different from fatigue mechanism. Thereby the tensile fracture mechanism is also investigated by observation of fatigue crack and fracture surface. As a result, in fatigue process, fatigue crack progress across specimen. Simultaneously, longitudinal debonding occurred around and in chopped strands. And it is showed that residual strength depend on longitudinal damages and that the fracture toughness of fatigue-damaged SMC is larger than that of virgin one. This means that fatigue-damaged SMC needs more energy to be fractured and that the longitudinal damages prevent transverse crack from progressing in static tensile process. Therefore the residual strength didn't degrade in spite of the fatigue damage