Micromechanism of Plastic Accumulation and Damage Initiation in Bearing Steels under Cyclic Shear Deformation: A Molecular Dynamics Study

Yachao Sun,Hongrui Cao,Xunkai Wei

doi:10.3390/machines10030199

Yachao Sun, Hongrui Cao + Show 1 more

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https://doi.org/10.3390/machines10030199

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Abstract

Fatigue failure usually occurs on the subsurface in rolling bearings due to multiaxial and non-proportional fatigue loadings between rolling elements. One of the main stress components is the alternating shear stress. This paper focuses on the micromechanism of plastic accumulation and damage initiation in bearing steels under cyclic shear deformation. The distribution of subsurface shear stress in bearings was firstly investigated by finite element simulation. An atomic model containing bcc-Fe and cementite phases was built by molecular dynamics (MD). Shear stress–strain characteristics were discussed to explore the mechanical properties of the atomic model. Ten alternating shear cycles were designed to explore the mechanism of cyclic plastic accumulation and damage initiation. Shear stress responses and evolutions of dislocaitons, defect meshes and high-strain atoms were discussed. The results show that cyclic softening occurs when the model is in the plastic stage. Severe cyclic shear deformation can accelerate plastic accumulation and result in an earlier shear slip of the cementite phase than that under monotonic shear deformation, which might be the initiation of microscopic damage in bearing steels.

Highlights

Rolling bearings with bearing steels as the main component are widely used in important equipment such as aircraft engines and high-speed trains because of the strong bearing capacity and wide range of applicable speeds and temperatures
The atomic simulations based on the two-phase model of bcc-Fe and cementite in this work characterize the micromechanism of plastic accumulation and damage initiation in bearing steels under cyclic shear deformation
The stress response of the atomic model is cyclic softening when the model is in the plastic stage, and shear deformation along x-axis is more likely to appear cyclic softening than that along the y-axis

Summary

Introduction

Rolling bearings with bearing steels as the main component are widely used in important equipment such as aircraft engines and high-speed trains because of the strong bearing capacity and wide range of applicable speeds and temperatures. Fatigue failure in bearings involves the initiation and propagation of damage originating from the contact surface or subsurface [1–3]. In stage I, microplastic strain accumulation tends to occur near the inclusions, which indicates the starting point of damage initiation [23] Such damage evolution behavior is inconducive to the fatigue life of rolling bearings. The mechanism of fatigue failure can be revealed to some extent by studying the influence of the interface between bcc-Fe and cementite on cyclic plastic accumulation in bearing steels. Machines 2022, 10, 199 ferrite–cementite interface strongly depends on the size, temperature and different loading directions of cementite, and revealed the hindrance mechanism of cementite lay3eorfo1n6 dislocation, as well as the influence of temperature and lamellar thickness on the ductility of the model. The system was cooled down to 5 K within 100 ps and further equilibrated atth5erKmfaollry 5a0t 8p00s.KTfohre1t0e0mpsp.eArfatteurrtehios,fth5eKsywstaesmcwhoasecnootloedbdeottwenr toob5seKrvweiththine100 ps interface reactiaonnds fcuaruthseerdebqyuislihberaatremd aotti5oKn froarth5e0rptsh. aTnhebteeimngpedroatmurienaotfe5dKbwyatsecmhposeernattuorbee.tter observe the interface reactions caused by shear motion rather than being dominated by tem-

Loading Conpderitaitounrse

Shear Stress Responses

Evolution of Dislocations and Defect Meshes

Evolution of High-Strain

Shear Deformation of Cementite

Conclusions