In the early development of tapered roller bearings, the rollers and raceways were typically designed with straight profiles under the assumption that the load would be uniformly distributed along the roller generatrix. However, both theoretical analyses and experimental investigations of line-contact mechanics have demonstrated the presence of significant stress concentrations near the roller ends. This phenomenon, commonly referred to as the edge effect, arises from the interaction between the roller’s straight end profile and the raceway surface. The presence of these edge-induced stress concentrations markedly reduces bearing fatigue life and is a primary cause of premature fatigue failure. The main objective of this paper is to evaluate the impact of the roller profile in a tapered roller bearing subjected to axial and radial loads and intense working conditions. The load distribution and contact deformation of tapered roller bearings for three roller profile geometries (straight, circular crowning, and logarithmic crowning) are investigated using Palmgren’s analytical formulation and a numerical approach based on the influence-coefficient method. The result shows high peaks on pressure distributions at the ends of tapered roller for the straight profile, with a negative impact in the bearing fatigue life.

The paper presents semi-analytical methods (SAMs) for determination of pressures distributions on the flank surfaces of spur and helical gears with both pinion and gear shafts deformed. In case of spur gear pair, a nonstandard gear pair was chosen. It is well known that the curvature of the tooth profile decreases when a negative correction of the gears is made, this thing leading to higher contact pressures and a decrease of durability. The SAMs starts from Hartnett's approach based on Boussinesq equation from half-space theory of linear elasticity, which means implicitly an infinite width of gear's flank. To simulate the more realistic quarter-space conditions, a correction based on virtual mirror pressures is introduced in the computational algorithm. For spur gears, the elements of the matrix of separations are obtained using analytical equations derived from involute properties while a methodology dedicated to helical gears was developed. The pressures distributions obtained with worked up SAMs have been validated by comparisons with results obtained by neutral research by using FEM or a dedicated SAM. The present paper took into consideration both deflections of pinion and gear's shaft, so that a more realistic pressures distribution is obtained. The contact surfaces are considered smooth surfaces and the contact between mating surfaces is considered as dry contact.

The data that support the findings of this study are available from the corresponding author upon reasonable request.

The paper presents semi-analytical methods based on novel and original algorithms for the determination of contact pressures distributions for helical gears meshing teeth taking into account real gearing situations – shaft misalignment, montage errors and teeth profiles modifications. The semi-analytical methods start from Hartnett approach based on Boussinesq equation from half-space theory of linear elasticity. In case of tooth contact analysis, semi-analytical methods are more suitable than FEA due to the lower time to obtain the outputs. In addition, ideal cases of coincident edges were considered in order to emphasize the higher amplitude of stress-raisers when coincident edges cases are nonexistent.

Acne diagnosis, severity assessment and treatment follow-up rely primarily on clinical examination. In vivo reflectance confocal microscopy (RCM) provides non-invasively, real-time images of skin lesions with a level of detail close to histopathology. This systematic literature review aims to provide an overview of RCM utility in acne and a summary of specific features with clinical application that may increase objectivity in evaluating this condition. We used the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for reporting our results. We systematically searched three databases: PubMed, Clarivate and Google Scholar (January 2022). All included studies used RCM to investigate acne in human patients and reported the investigated skin area and type (acne lesions or clinically uninvolved skin), the substance used in the case of treatment. Our search identified 2184 records in the three databases investigated. After duplicate removal, 1608 records were screened, 35 were selected for full-text assessment, and 14 were included in this review. We used the QUADAS-2 tool to evaluate the risk of bias and applicability concerns. RCM was selected as the index test and clinical examination as the reference standard. The total number of patients from all studies was 291, with 216 acne patients and 60 healthy participants aged between 13 and 45 years. The 14 considered studies analysed 456 follicles from healthy participants, 1445 follicles from uninvolved skin in acne patients and 1472 acne lesions. Consistent RCM findings concerning follicles of acne patients reported across studies were increased follicular infundibulum size, thick, bright border, intrafollicular content and inflammation. Our analysis indicates that RCM is a promising tool for acne evaluation. Nevertheless, standardization, a unified terminology, consistent research methods and unitary reporting of RCM findings are necessary. PROSPERO registration number CRD42021266547.

SC, MD and SRG report no conflicts of interest. CMS declares the following, not related to the work: royalties from Springer Nature, consulting fees from Vichy International and support for attending meetings from Leo Pharma.

Microtopography of the working surfaces subjected on rolling contact can be realized by various manufacturing technologies (lapping, polishing, turning, grinding, etc.). The aim of this work is to point out the impact of the initial surface asperities on running-in phenomenon, geometry of active surface and rolling contacts durability. At first, the article exhibit the experimental tests carried out by using the two discs AMSLER machine with proper samples for pure rolling motion. The microtopography of the working surfaces have been measured before and after tests. Secondly, a numerical study is presented for the samples used on the two discs AMSLER machine, where the measured topography data and loading conditions are used as input data in the analysis model. The last part of the article exhibit a numerical investigation for the rolling bearing CARB C2318 where the modified rating life have been computed with methodology given by ISO 16281.

The standards for gears design use the maximum value of the normal stress sigma(zz), depicted sigma(H), as critical stress for RCF of gears. This value sigma(H) can't sustain evidences regarding the stress risers influences. The paper uses the von Mises stress sigma(vM) as critical stress responsible for the initiation of RCF. For concentrated contacts analyses the drawback of FEM is the very long computing time and therefore the author used a semi-analytical method (SAM) based on the numerical formulation for the involved equations of linear half-space theory. The finite width of gears' teeth imposes quarter-space limitations and consequently the virtual pressures and correction coefficient were considered in the iterative process for pressures distribution. The pressure distribution was further used to evaluate the stress tensor components and 3D distributions of von Mises stresses. Examples are presented for spur gears with different values for end chamfers.

The active surfaces topography of bodies in rolling contact can be obtained by different manufacturing technology. The scope of this paper is to evidence the influence of the initial surface roughness on running-in process, working surface geometry and durability of rolling contacts. The paper presents a numerical study applied on a toroidal roller bearing where the modified rating lives have been evaluated with the methodologies mentioned by ISO 16281.

The paper presents tooth contact analysis (TCA) of modified gears using semi-analytical methods (SAMs). The semi-analytical methods use Love’s analytical formulation for Boussinesq equation of linear half-space theory and Hartnett approach for numerical formulation. The linear contact between two teeth has a finite length and during meshing process the edge effect appears, with a harmful influence on the gear reliability. To eliminate this, some tooth profile modifications are needed. To turn a line contact into a point contact, the crowned lead profile surface is considered. The ways used to obtain the matrices of separation are discussed for both spur and helical cylindrical gears. The large pressures’ systems of equations were solved using the method of conjugate gradients and fast Fourier transform. For validation, in cases of hertzian geometries the SAM results have been compared with results obtained analytically, while for non-hertzian geometries, the SAM results have been compared with FEM results as presented in the specific literature. The developed SAM proved to be an accurate, robust and very fast tool for TCA of spur and helical cylindrical gear.

The topography of the active surfaces in rolling contact depends on the surface roughness obtained by different manufacturing process technology (turning, grinding, polishing, lapping, etc.). The aim of this paper work is to evidence the influence of the surface roughness on surface geometry of rolling contacts. The experimental tests were carried out on the AMSLER machine and an experimental setup for pure rolling motion. The surfaces of the rolling samples were analyzed with SEM (scanning electron microscopy) and EDS (energy dispersive X-ray spectroscopy) techniques for structural and chemical analysis and measured with the Taylor Hobson profilometer before and after the experimental tests for surface topography.

The standard methodology to verify gears' strength to rolling contact fatigue (RCF) is to compare the value for maximum Hertz pressure with a permissible value. However some experimental evidences can not be explained by this approach. Therefore the TCA was focused on both the surface distribution of contact pressures and depth distribution of von Mises stresses. Semi-analytic methods SAM and its variant for linear contacts with finite length SAM-C have been involved to obtain the pressures distribution, contact area and stresses state inside the stressed volume. For theoretical case of coincident line contact there are no edge effect but any modification of the relative position changes it to a non-coincident contact type where the end effects manifest. The spur gears with pinion teeth having a longitudinal crowned profile have indicated a good capacity to avoid the end edge effect when the operating conditions included a misalignment. For operating conditions without misalignment, the lead modification by end relief causes a quasi-Henzian pressures distribution; however, the existence even of a small misalignment changes it to a skewed distribution. The semi-analytical procedure appears as an accurate and very fast tool to establish the suitable values for parameters that define the flank modification of gears.

The rail and wheel surfaces with numerically generated roughness have been incorporated into a computerized analysis model for concentrated contacts. In normal running operations the contacting surfaces undergo very complex loading regimes characterized by: the lack of lubrication, existence of normal, tangential and traction loads with the presence of different degrees of slippage. An inevitable wear evolves that determines time dependencies for profiles of active surfaces The role played by the running in process as well as the main roughness parameters on the pressures distribution, contact area and depth distribution of von Mises equivalent stress, have been pointed out. Important criteria as the traffic safety and maintenance costs require optimized profiles. To fulfill this requirement the knowledge of wear evolution becomes a priority and consequently the contact areas and pressures distributions corresponing to different stages of wear is one of the primary needs. The profiles measurements of new and worn wheels revield the modification in pressures distribuion, contact areas and vonMises stresses caused by time evolutuon of wear.

The meshing process of two gears is altered by elastic deformations of the machine parts involved in the power transmission chain The edge effect appears and some additional manufacturing procedures are necessary to be done. The paper presents a computerized program used to establish the suitable value for the profile correction according to the particular running parameters as torques and misalignments. Semi-analytical methods were used to obtain the elastic state, developed during the meshing process, around the concentrated contact of pinion and gear. For spur gears the separation is possible to be obtained analytically, while for helical gears a numerical algorithm has been developed to obtain the matrix of separations. The two approaches were validated and some numerical results regarding the 2D and 3D pressures distributions as well as the contact areas, are presented. For operating condition without misalignment, the lead modification by end relief could led to a very favourable, quasi-Hertzian, pressures distribution. The presence even of a quite small value of misalignment changes the quasi-Hertzian distribution to a skewed one with detrimental effect on gear's life.

The involute gears are sensitive to the misalignment of their axes which determines transmission errors and perturbations of pressures distributions along the tooth flank. The concentrated contacts in gears are no longer as Hertz type. A semi-analytical method was developed to find the contact area, pressures distribution and depth stresses state. The matrix of initial separations is found analytically for standard and non-standard spur gears. The presence of misalignment as well as the flank crowning and flank end relief are included in the numerical analysis process.

The misalignment between gears axes or direction deviations of teeth leads accentuate the edge effect, Modified spur gears which localize the initial bearing contact by proper modifications of the lead profile are used to avoid the development of the edge effect. A semi-analytical method was involved to find the contact area, pressures distribution and depth stresses states for the standard gears and gears with modified lead profile. The lead modifications concerned the crowning of the flank surface and the end relieving of the tooth flanks, both being applied to the pinion teeth only.

The cross-section of roller profile controls the pressure distribution in the contact area and radically affects the roller bearings basic dynamic load rating and rating lives. Today the most used roller profiles are the logarithmic profile and cylindrical-crowned (ZB) profile. The logarithmic profile has a continuous evolution with no discontinuities till the intersection with the end fillet while ZB profile has two more discontinuities at the intersections points between the crowning circle and straight line generatrix. Using a semi-analytical method, a numerical study has been carried out to find the optimum ZB profile for rollers incorporated in cylindrical rollers bearings. The basic reference rating life (L-10_r) has been used as optimization criterion.

An initial loading of cylindrical roller bearings in the elastic-plastic domain was performed to induce elastic shakedown phenomena able to change the basic profiles of both, rollers and raceways, which endorses a different value for the basic reference rating life. Fatigue life tests carried out on four lots of NJ206 cylindrical roller bearings revealed much higher values of L-10 and L-m criteria for the bearings lots which experienced a suitable initial loading operation in the elastic-plastic domain. The reference rating lives, evaluated by using the lamina technique, confirmed the superiority of bearings lots which undergone an appropriate primary loading in the elastic-plastic domain.

Heavy loads, transient overloads or high misalignments applied to cylindrical roller bearings create uneven pressures distributions with overloading of the yield limit, plastic deformations and shakedown phenomena, able to change the basic rolling contact geometry. To consider these phenomena an elastic-plastic contact model is developed. The model is based on the incremental theory of plasticity comprising the von Mises yield criterion and Prandtl-Reuss equations. Considering isotropic and nonlinear kinematic hardening laws the model accounts for the cyclic hardening phenomena. As result of the elastic-shakedown a new contact geometry is established in less than two hundred of loading cycles. Further, the basic reference rating lives are evaluated using the methodology presented in ISO-16281:2008. The favourable effect of the contact geometry changes due to local plastic deformations is finally revealed.