An experimentally validated numerical model of indentation and abrasion by debris particles in machine-element contacts considering micro-hardness effects

Abstract

Indentation and abrasion of machine-element contacts by solid contamination particles is a major problem in many industries and manufacturing processes involving the automotive, aerospace, medical and electronics industries among others. Published theoretical studies on indentation and soft abrasion of surfaces by ductile debris particles other than those of the author are based on several major simplifications concerning material properties, hardness, plasticity modelling, interfacial friction, kinematic conditions, etc. None of the studies published in the literature to date (2011) have those simplifications concurrently relaxed.In view of the shortcomings of existing numerical models on debris particle indentation and abrasion, and given the importance of dent geometry and size on fatigue life of machine elements, a greatly improved numerical model has been developed based on the previous studies of the author. The new model deals with elastoplastic indentation and abrasion of rolling-sliding, dry and lubricated contacts by spherical particles of any hardness, from very soft (e.g. 40 HV) to very hard (e.g. over 1000 HV), including harder than the contact counterfaces. The model incorporates strain-hardening and strain-gradient or indentation-size micro-hardness effects with an expanding-cavity plasticity model, a localised treatment of friction, generalised boundary and kinematic conditions involving localised stick and slip of the particle, linear and nonlinear work-hardening models of the particle, a basic approach on pile-up/sink-in plasticity effects and several other improvements. The model has passed extensive validation tests and found to give realistic predictions that are quantitatively quite close to the experimental results published by independent researchers in the literature concerning dent dimensions and slope. Moreover, it has verified and explained theoretically for the first time the formation of dimples inside and outside dents experimentally observed in rolling and rolling-sliding contacts. This article presents the mathematics of the model, the validation procedure with several real cases from the experimental literature, and a parametric study to show the model's predictions on precise dent geometry in several realistic cases.

Strain-rate effects on the plastic indentation and abrasion of elastohydrodynamic contacts by debris particles

“…Both the isothermal model 70 and, especially, the thermal model 71 have shown very good agreement with experimental data published by independent researchers, 66,77,78 as thoroughly documented in references. 70,71 The two models have also verified for the first time dimples inside and outside dents observed experimentally by Ville and Nelias.…”

“…91 The results of the study in terms of dent and abrasive mark precise geometry are compared with those of Nikas 70,71 and the experimental results of Dwyer-Joyce 66,77 and Ville and Nelias 78 on copper and high-carbon steel particles through the same rigorous validation programme compiled in the previous studies of the author. 70,71 Further, excellent agreement is found in the comparison of theoretical and experimental results. Following this, a parametric study is presented about the influence of strain rate on dent geometry under a variety of conditions.…”

“…Its presence is owed to the progression of plastic strain from the area of highest stress and radially outwards. 70,71 Strain-hardening, strain gradient and Quasi-static strain rate (s À1 ) 1 0 À4 10 À4 10 À4 J-C parameters for the contact solids:…”

“…In fact, the incorporation of strain-rate effects further improved the agreement between theoretical and experimental results previously established with simpler versions of the model. 70,71 Strain rate was also shown to Figure 5. Strain-rate effects on indentation data for a 30 mm copper particle (input data in Table 1).…”

Particle extrusion in elastohydrodynamic line contacts: Dynamic forces and energy consumption

“…51 Given the complexity of the contact mechanics to analyse the passage of even a single particle through a contact, it comes as no surprise that numerical models are rare and variable in their features and limitations. According to the author's own research, [51][52][53][54][55][56][57][58][59][60][61][62][63] the model of the passage of a single particle through a concentrated contact with clearance smaller than the particle's minimum dimension includes the following elements: (a) particle entrainment via the lubricating medium prior to reaching the contact; 53 (b) particle entrapment based on force-equilibrium criteria once the particle is pinched; [57][58][59] (c) stress, strain and damage analysis during particle compression, including thermoelastic effects, [54][55][56] elastoplastic effects, 60 thermoelastoplastic effects 51 or thermoviscoplastic effects, 61 depending on the operating conditions, as well as geometrical effects in case of surface pile-up around dents 63 and tribochemical effects in cases of high frictional heating. 62 With a numerical model as the one just described, calculating contact forces on a squashing particle is part of the stress analysis.…”