No abstract

a b s t r a c tThe present paper evaluates the fatigue life of ductile nodular cast iron EN-GJS-400-18LT with four different microstructures. Characterisation of the graphite morphology and the matrix microstructure is performed on 50 samples for every material type. Tensile stress-strain curves, symmetrical and unsymmetrical stress-strain hysteresis loops, cyclic stress-strain curves, crack resistance curves and fatigue life curves of these four microstructures are obtained. Experimental results show that size, shape and distribution of the graphite nodules has no significant influence on cyclic hardening of the material but they play a great role in the crack initiation and propagation process. It is shown that the larger irregularly shaped nodules reduce fracture toughness and fatigue strength. Furthermore, the results demonstrated that pearlitic phase does not strongly affect fatigue life if its proportion does not exceed 10%. The monitoring of crack length during the tests is performed by an optical method developed in the present work.

In this work, the phase-field approach to fracture is extended to model fatigue failure in high- and low-cycle regime. The fracture energy degradation due to the repeated externally applied loads is introduced as a function of a local energy accumulation variable, which takes the structural loading history into account. To this end, a novel definition of the energy accumulation variable is proposed, allowing the fracture analysis at monotonic loading without the interference of the fatigue extension, thus making the framework generalised. Moreover, this definition includes the mean load influence of implicitly. The elastoplastic material model with the combined nonlinear isotropic and nonlinear kinematic hardening is introduced to account for cyclic plasticity. The ability of the proposed phenomenological approach to naturally recover main features of fatigue, including Paris law and Wöhler curve under different load ratios is presented through numerical examples and compared with experimental data from the author’s previous work. Physical interpretation of additional fatigue material parameter is explored through the parametric study.

No abstract

No abstract