On the influence of the external load cycle asymmetry coefficient on the characteristics of the loading cycle taking place at apex of crack-like cut

Аuthors

Shakirtov M. M.

Siberian State Transport University, Str. Dusi Kovalchuk, 191, Novosibirsk, 630049, Russia

e-mail: legion-mpf@yandex.ru

Abstract

The connection between the external load cycle asymmetry coefficient and the characteristics of loading cycle of the material at the apex of crack-like cut is observed.

The development of fatigue cracks is defined by loading cycle characteristics. The fatigue strength of the material depends on the external loading cycle asymmetry coefficient. Symmetrical loading cycle produces considerably lower fatigue strength than the pulsating loading cycle. Fatigue process is determined by the stress-strain state at of the tip of the cut. The material around the tip also undergoes cyclic loading. The load is transferred by the surrounding elastically working material.

The cyclic loading of a flat specimen with central crack-like cut is observed. The specimen is made of cyclically hardening material. The external load cycle asymmetry coefficients differ from 0 to 0.9. The problem is solved by finite element method in two-dimensional formulation. The specimen is in plane stress conditions. The finite element model is analytically verified. It is confirmed that the proposed model produces nonlinear static simulation with sufficient accuracy.

For cycles with different values of the asymmetry coefficients stress values at the tip of the cut have been tracked throughout loading history. It was found out that the stress state evolution process radically changes when reverse plasticity takes place at the crack-like cut tip.

It was illustrated that any asymmetry coefficient of the external load produces symmetrical loading cycle at the tip of the crack-like cut. The amplitude of this symmetrical loading cycle increases from cycle to cycle. Moreover, the closer the external load asymmetry coefficient value comes to the unity, the smaller the loading cycle amplitude rate of increase becomes.When its value is close to unity, reverse plasticity does not occur. In this case material around the tip undergoes asymmetrical loading cycle with constant amplitude.

Keywords:

crack-like cut, cyclic loading, the asymmetry coefficient, plastic zone, stress concentration

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