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This paper describes an investigation on annealed Nickel A to explore the effects of simultaneously applied cyclic and monotonic strains. The results are presented in terms of the true stress-strain envelope of the end points of individual hysteresis loops. During mixed straining, early increased hardening, and later softening with progressive mean strain, occurs in comparison to simple tension. In the limit, the stress level required for deformation is controlled by the stress amplitude of the stabilized hysteresis loop associated with cyclic strain component, and monotonic hardening effects are absent. For tensile monotonic strains, superimposed cyclic strains lead to early necking, until, in the limit, necking occurs with zero mean strain and provides a mechanism for low-cycle fatigue crack nucleation. A failure criterion which fits the results is developed. Here ∈f/∈f0 = 1 − (Nf/Nf0)0.563 where ∈f0 is the tensile ductility, Nf0 the fatigue life for the cyclic strain component alone, ∈f and Nf the fracture strain and fatigue life, respectively, for the mixed mode of deformation.
deformation, fracturing, strains, fatigue (materials), ductility, nickel, hardening (materials), evaluation
Metallurgy and Ceramics Laboratory, Research and Development Center, General Electric Co., Schenectady, N. Y.