Voronoi Finite Element Model Research Articles

Risk assessment of initial crack propagation in bearing steel based on finite element analysis and machine learning

This study analyzes the initial subsurface crack propagation in bearing steel by utilizing a 3D Voronoi finite element model to simulate the bearing steel’s grain structure. Subsurface stress calculations validate the model. Stress intensity factors were computed to determine crack propagation as a function of initial crack orientation, length, and depth. A novel aspect of this study is the integration of FE analysis with an Artificial Neural Network for predictive modeling. A grid search method was employed for hyperparameter tuning, and ten-fold cross-validation was used to evaluate the ANN’s performance, ensuring robust and accurate predictions. This hybrid approach enables the prediction of SIFs based on various load and crack parameters, facilitating a rapid assessment of crack propagation risk. The results provide valuable insights into the reliability and lifespan of bearing steel, contributing significantly to the field of bearing failure analysis.

Numerical analysis of rolling contact fatigue crack initiation Considering material microstructure

The material microstructure of plays an important role in crack initiation of rolling contact fatigue. To address crack initiation of tapered roller bearings, the inhomogeneous characteristic of material is considered. The random distribution of material grains is simulated with Voronoi graph, and a Voronoi finite element model of rolling contact fatigue is given. Numerical analysis of damage-life constitutive relation is carried out with finite element analysis. The effect of material microstructure inhomogeneity on initiation life of fatigue crack is studied. Researches show that the smaller the grain size, the more difficult the fatigue crack appearing. The larger the difference of elasticity modulus between non-metallic inclusions and matrix material, the greater the impact on fatigue life of crack initiation. The angular and sharp non-metallic inclusions reduce fatigue life more than rounded shape inclusions. Initiation life of fatigue crack has a minimum value on a critical depth of nonmetallic inclusion. The longer distance between two laterally arranged inclusions, the greater it affect the initiation life of fatigue crack. The effect of distance between two vertically arranged inclusions on fatigue crack initiate depends on the depth of inclusions.

Fatigue crack nucleation and propagation at clustered metallic carbides in M50 bearing steel

Abstract This paper focuses on the crack nucleation and crack propagation induced by a cluster of carbides. The morphology of the carbides is extracted from scanning electron microscope images of M50 bearing steel. Subsequently, a continuum damage accumulation model is incorporated into the Voronoi finite element model to investigate the damage evolution in the material. It can be observed that nearly all the micro-cracks nucleate on the boundary of the carbide and propagate through the bearing material matrix around those carbides until they become large enough to coalesce to failure. With the increasing of friction coefficient, cracks gradually grow to the contact surface. The result also shows that the carbides deeper than a certain depth are not harmful to the material.

Effects of non-metallic inclusions on the crack propagation in bearing steel

The crack propagation in bearing steel with a non-metallic inclusion is analyzed by Voronoi finite element method. The load applied on the Voronoi finite element model is obtained by combination of quasi-dynamic method and Hertzian contact theory. Von Mises stress distribution in the micro-domain is calculated to determine the crack initiation. The result shows that the non-metallic inclusion acts as stress raiser and the maximum von Mises stress appears near the inclusion. Thus, we can conclude that the crack is initiated near the inclusion. Stress intensity factors (SIFs) were calculated to study the crack propagation as a function of inclusion elastic modulus, size, and depth. The crack is more likely to grow when the inclusion is soft, small and shallow.

Effects of surface roughness on micro deep drawing of circular cups with consideration of size effects

Surface roughness, compared with tiny sizes of micro products, can be relatively large and has significant influences on micro forming processes and products’ quality. In this study, a voronoi finite element model that considers size effects of material was developed. Next the surface roughness information was assigned to this voronoi model through different elemental thickness distributions. Furthermore, springback simulation was conducted for the micro deep drawn circular cups. Simulation results demonstrate that the surface roughness with consideration of size effects has significant influences on the overall springback, the drawability represented by the minimum thickness and products’ quality regarding thickness evenness and shape accuracy. This study also shows that the results from the new models are close to the experimental results concerning the diameter of cup mouth and the maximum drawing force. The developed model for the micro deep drawing is accurate and beneficial for the development of micro deep drawing process.

Microstructural Alterations in Bearing Steels under Rolling Contact Fatigue: Part 2—Diffusion-Based Modeling Approach

The microstructure of rolling element bearings can experience significant transformation when subjected to repetitive contact cycling. In Part 1 of this article, a detailed overview of the known microstructure alteration phenomena was presented and the different mechanisms for describing them proposed by various investigators were critically reviewed. It is agreed generally that the primary path of these structural changes is the decay of martensite due to carbon diffusion, leading to the formation of ferrite and lenticular carbides. Furthermore, these altered regions in the material microstructure can be stress concentration regions leading to crack initiation and propagation. In this article, a J2-based elastic–plastic Voronoi finite element model (previously developed by the authors) is coupled with a carbon diffusion–based model. Using Fick's law for stress-assisted diffusion, the dispersion of carbon in the bearing microstructure is evaluated. A backward Euler finite difference scheme is employed to solve the partial differential equations. The model can accurately predict the onset of martensitic decay and formation of the white etching bands along with their distinctive orientation. A comparison of the numerical results shows good corroboration with experimental observations.

Effects of surface defects on rolling contact fatigue of heavily loaded lubricated contacts

Surface-initiated fatigue caused by surface defects is one of the most dominant failure modes for bearing contacts. In this study, a damage mechanics-based Voronoi finite-element model (VFEM) is developed and used to investigate the effects of surface defects (such as dents and fretting wear) in elastohydrodynamic lubricated line contacts. A line contact elastohydrodynamic lubricated model is used to calculate the pressure distributions acting over the surface defects, which are then employed by Voronoi finite-element model to determine subsurface stresses. Continuum damage mechanics-based approach is used to incorporate cyclic damage accumulation and progressive degradation of material properties with rolling contact cycling. The model also takes into account the effects of residual stresses generated during the debris denting process. Using this methodology, the model is used to simulate microcrack initiation, coalescence, and propagation stages, finally a fatigue spall. The locations and patterns of dent-initiated spalls are found to be consistent with experimental observations. The fatigue model is used to study the effects of the topology of the material microstructure, dent sharpness, and material properties on rolling contact fatigue (RCF) life and Weibull slopes.

A new finite element fatigue modeling approach for life scatter in tensile steel specimens

This paper presents the results of a finite element model developed to investigate the effects of material microstructure topology on fatigue damage evolution in dog-bone tensile specimens. The Voronoi finite element model (VFEM) developed was used to study fatigue damage evolution in AISI 4142 steel under various loading conditions. An environmental scanning electron microscope (ESEM) coupled with an Instron fatigue testing machine was used to determine the strain and fatigue life of the dog-bone 4142 steel specimens at different mean stress levels. The damage variable was obtained using the method of variation of elasticity modulus. The experimental damage versus cycle curve was then used to determine the material properties (i.e. resistance stress σ R and exponent m) needed for the VFEM fatigue damage model. The VFEM model was used to corroborate the analytical and experimental fatigue results. A comparison of the results obtained from the VFEM model and ESEM indicate that they are in good agreement.

A Numerical Fatigue Damage Model for Life Scatter of MEMS Devices

This paper presents a fatigue damage model to estimate fatigue lives of microelectromechanical systems (MEMS) devices and account for the effects of topological randomness of material microstructure. For this purpose, the damage mechanics modeling approach is incorporated into a new Voronoi finite-element model (VFEM). The VFEM developed for this investigation is able to consider both intergranular crack initiation (debonding) and propagation stages. The model relates the fatigue life to a damage parameter " <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> " which is a measure of the gradual material degradation under cyclic loading. The fatigue damage model is then used to investigate the effects of microstructure randomness on the fatigue of MEMS. In this paper, three different types of randomness are considered: (1) randomness in the microstructure due to random shapes and sizes of the material grains; (2) the randomness in the material properties considering a normally (Gaussian) distributed elastic modulus; and (3) the randomness in the material properties considering a normally distributed resistance stress, which is the experimentally determined material property controlling the ability of a material to resist the damage accumulation. Thirty-one numerical models of MEMS specimens are considered under cyclic axial and bending loading conditions. It is observed that the stress-life results obtained are in good agreement with the experimental study. The effects of material inhomogeneity and internal voids are numerically investigated.