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.

A numerical model was developed to study the sealing performance of rectangular elastomeric seals for reciprocating piston rods used in linear hydraulic actuators. The model takes into account a large number of parameters and has been applied in the study of seals for aircraft actuation assemblies in a broad range of temperatures (−55°C to +135°C) and sealed pressures (1–50 MPa or more). The model is used to calculate the contact pressures and film thickness maps as well as the leakage rates and friction for the dynamic or static contact between a seal and a reciprocating piston rod, aiming at the minimization of both the leakage and the wear of the seals.

A model presented earlier by the author (Nikas et al., 1998, 1999) for the study of the possible risks associated with the entrapment of debris particles in lubricated contacts has been refined to account for additional influential factors that could affect the results obtained from the initial model. The new results showed that soft contaminants could indeed be very destructive and damage a concentrated sliding contact mainly due to the thermal stresses developed from the frictional heating of the contact during the plastic compression and shearing of a particle. This model yielded flash temperatures of the order of 100°C and up to 2000°C (or more, until local yield occurs). It also showed that it is often the thermal stresses which cause the problems, rather than the mechanical stresses from particles’ deformation.

For a very long time, debris particles have been blamed to causing serious problems in machine-element contacts such as those of bearings and gears. This involves a huge number of mechanisms and machines worldwide. The financial cost associated with machinery failure under such circumstances is enormous. Past research has identified the main mechanisms governing damage from debris particles. A few theoretical models have been built on the experience accumulated on damage mechanics. The capabilities of said models vary a lot. The model originally developed by this author in the 1990s was recently expanded. The previous version of the model, which was published in this journal in May 2012, offered a number of innovative features to calculate spherical-particle indentation and soft abrasion in lubricated rolling-sliding contacts. It was experimentally validated following a rigorous programme. However, it neglected frictional heating from particle extrusion. This study significantly expands the previous model of the author by integrating thermal effects. It includes flash temperature calculations with moving sources of heat, dynamic heat partition, three-dimensional conduction and convection, and thermally anisotropic surfaces with temperature-dependent thermal and mechanical properties, all integrated in the elastoplastic model of indentation and abrasion. These are in addition to model features such as nonlinear strain hardening, strain-gradient plasticity, particle work hardening, generalised local kinematics, pile-up/sink-in plasticity effects and many more. The same rigorous experimental verification programme as in the previous model of the author is used here, too. It is shown that in some cases, the theoretical results on dent geometry are even closer to the experimental ones than with the isothermal model of the author. Furthermore, the thermal analysis reveals that extreme frictional heating can take place, often leading to melting wear in a fraction of a millisecond. The formation of dimples inside and outside main dents, which have been shown experimentally and verified theoretically by this author’s previous model, is revisited in light of frictional heating. A parametric study shows the effects of particle size and hardness, kinetic friction coefficients, and strain hardening on dent geometry and flash temperatures, including effects on particle and surface melting. Finally, the reality of flash temperatures is explored.

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