Change characteristics of static mechanical property parameters and dislocation structures of 45# medium carbon structural steel during fatigue failure process

A series of experiments at both macroscopic and microscopic levels were carried out to investigate the variation in static mechanical property parameters ( yield stress σ0.2, elastic modulus E, reduction of area ϕ, elongation δ, strain hardening exponent n, ultimate strength σb) of 45# medium carbon structural steel during fatigue damage process. The possible reasons for the variation of the static mechanical property parameters are qualitatively discussed through analyzing the evolution of dislocation substructures in the steel during cycling. A composite parameter of the static mechanical property called static toughness is proposed for characterizing comprehensively the variation of the static mechanical property parameters, and a quantitative relationship between the variation of static toughness and the dissipation of cyclic plastic strain energy is established.