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 σf 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.
σf=(A+Bεn)μσfsσfu, and σNfm=Dμσsσu
where ε is the strain rate, Nf 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 σf 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
σNfm=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.