Abstract
Under typical service conditions of creep resistant metallic materials, cyclic loading is frequently superimposed on the nominally time invariant creep loading. In the present paper, some results are presented of an investigation into the effects of low-frequency cyclic applied stress superposition in the primary creep stage on the strain and fracture behaviour of a commercial heat-resistant nickel-base 16Cr-10W-4Mo-TiAl alloy. It is shown that such a superposition affects the strain rate as well as the fracture behaviour of the alloy in a rather complicated way. Thus, (i) measurements of the strain rates immediately before and immediately after any applied stress change clearly suggest that the strain rate behaviour cannot be described by a simple constitutive equation ; (ii) the time to fracture seems to increase with the applied stress amplitude to the mean applied stress ratio, Δσ/σ, at low, but certainly decreases at high, values of this ratio and depends significantly on the period of superimposed loading, A t c , and, (iii) the strain to fracture increases with the Δσ/σ ratio approximately independently of the period Δt c .
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