Fatigue Strength and Reliability of Fiber Reinforced Plastics Subjected to Repeated Impact Tensile Load

Abstract

The impact tensile strength and impact tensile fatigue strength of non-woven polyester cloth reinforced epoxy resin were investigated by using a repeated impact tensile loading apparatus. The allowable stress and the safety factor under repeated impact tensile loading were analysed on the probability theory of failure.
The results obtained are summarized as follows;
(1) Both the impact strength σ_f and the impact fatigue strength σ are represented by a logarithmic normal distribution and can be estimated as the probability values by the following formula.
σ_f=(A+Bεⁿ)μ_σfs_σf^u, and σN_f^m=Dμ_σs_σ^u
where ε is the strain rate, N_f is the fatigue life to failure, μ is the mean value, s is the standard deviation, u is a parameter of probability, m, n, D, A and B are the material constants, and the suffixes σ_f and σ denote the impact test and the impact fatigue one, respectively.
(2) The effect of strain-rate on the impact fatigue strength can be estimated by
σN_f^m=A+B(σ/ET)ⁿ
where E is elastic modulus of the material and T is the time during stress rising by the impact loading.
(3) It is found that the material can be used as a structural element of high reliability.