Time Dependent Probabilistic Failure Model for the Strength of Fiber Reinforced Plastics

Abstract

The fracture strength of GRP (Glassfiber Reinforced Plastics), which depends on the applied time of stress and the stress rate, was analyzed by using a time dependent probabilistic failure model. The fracture process was assumed to be a 1-step stochastic process and the transition probability of failure to be γS^δf(t) where S and t represent stress and time, respectively and γ and δare constants. The evaluation of the damage in the case when the stress varied was done by "the reduced time method" proposed in this paper. When f(t)=t^γ and S=at (γ, a; constants), the fracture stress S_c was calculated as follows. [numerical formula] where D_c is a constant. The constant a is stress rate and so the effect of stress rate on the fracture stress could be clearly presented. Static fatigue strength was also analyzed. The analytical results showed a good agreement with experimental results For glass plates and glassfiber composites, the constants γ and δ were found to be about -0.7 and 6.26, respectively. therefore, the traditional time independent probabilistic theory overestimates the effect of strain rate on the strength of materials.