Strain and rupture behaviour under high-stress reversals

Abstract

A rheological approach to fatigue behaviour has been extended to the push-pull fatigue of an 11 per cent chromium steel and a nickel-chromium alloy at room temperature and the influence of the direction of first loading stroke has been examined. At the high stresses involved, strain was shown to accumulate ultimately in a tensile direction in a manner similar to elevated temperature creep and the strain-time curves were shown to have the form ∊ = Σ Cσ^βt^κ where ∊ is strain, σ is stress, t is time, β and κ are discrete exponents, and C is a material constant. The widths of the hysteresis loops (strain amplitudes) were found to be dependent upon time in a manner similar to the cumulative strains and were analysed by a similar expression. The growth of tensile strain occurred irrespective of whether tension or compression was applied first but the application of compression first caused lower values of cumulative strain and longer endurances for similar load limits.