Contact Pressure Research Articles

An analytical approach to incomplete spherical conformal contact: application on self-lubricating spherical plain bearings

Purpose Contact pressure is a critical factor that significantly influences the wear of self-lubricating spherical plain bearings. The purpose of this paper is to address the issue of conformal contact in spherical plain bearings with a self-lubricating fabric liner, and then a universal theoretical analytical model for conformal contact between frictionless spheres is proposed. Design/methodology/approach This study establishes an analytical model to calculate the conformal contact in spherical plain bearings and verifies the new model by finite element analysis. Findings The new model proposed in this paper overcomes the limitations of elastic half-space and small-deformation assumptions. After conducting accuracy validation, it was observed that the computational error of the new model has significantly decreased in comparison to the Johnson model. For a conformal contact with a clearance of 0, the error is nearly 0. Practical implications The analytical model can calculate the contact pressure distribution of self-lubricating spherical plain bearings bonded with a self-lubricating layer and can be extended to the conformal contact problem of spherical contact surfaces in biomechanics and other fields. Originality/value The model presented here overcomes the limitations of the elastic half-space and small deformation assumptions. It accurately calculates the contact pressure distribution of self-lubricating spherical bearings. Moreover, the complex nonlinear relationship between variables such as normal force, clearance, maximum contact pressure and contact radius was investigated using this model. The model can also be extended and applied to the conformal contact problem of spherical contact surfaces in various fields, including biomechanics. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2024-0296/

Frictional Abrasion of Rubber: Transition from Sliding to Rolling

ABSTRACT To develop applicable friction and wear models on tire scale, reliable test data are required. Consequently, friction tests on block level are requested because the distribution of contact pressure as well as slip velocity is nearly homogeneous at the contact surface of the sliding rubber block. However, wear mechanism and energy intensity levels of sliding rubber blocks and rolling rubber wheels or tires differ significantly. Consequently, linking both sliding and rolling frictional abrasion is required; thus, a wear model for rubber material is introduced to consider both deformation slip and sliding. The model input for sliding friction and resulting wear rate is derived from linear friction test experiments using sliding rubber blocks at different loading. A unique and sophisticated re-mesh algorithm ensures proper mesh modification due to abrasion of the structure. A wear energy evolution approach is developed to consider low abrasion with small sliding distances to predict wear at rolling rubber wheels. The simulation framework of abrasion modeling is successfully validated using laboratory abrasion tests.

Study on influence of friction conditions on the friction and wear performance of high-speed rail brake materials under high humidity environment

Purpose Using the multifunctional friction and wear testing machine independently developed by the research group, the friction and wear tests of different friction conditions (contact pressure and sliding speed) are conducted on the brake materials of high-speed trains with the ambient humidity of 95% and the initial temperature of the disk of 200°C. Design/methodology/approach Friction and wear. Findings The test results show that changing the friction conditions has a significant effect on the braking performance of high-speed trains. Originality/value YES. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2024-0171/

Quantitative Comparison of Age-Related Development of Oral Functions During Growing Age.

This cross-sectional study aimed to investigate the age-related development of five major oral functions-tongue pressure, lip pressure, masticatory efficiency, bite force, and occlusal contact area-in subjects aged 5-20 years. Ninety-two subjects were divided into four age groups: 5-8, 9-12, 13-16, and 17-20 years. Oral functions were evaluated using standardized methods, including Chew Check Gum for assessing masticatory efficiency, Dental Prescale II for measuring occlusal force and contact area, JMS tongue pressure measuring device for evaluating tongue pressure, and Ripple-Kun for measuring lip pressure. Occlusal contact area, maximum bite force, tongue pressure, and masticatory efficiency gradually increased with age, whereas lip pressure remained stable. The occlusal contact area temporarily decreased between 5 and 12 years of age, likely due to the replacement of erupting lateral teeth. Some differences were observed between males and females; however, overall trends in oral function parameters were similar. Spearman's rank correlation analyses revealed significant positive correlations between age and occlusal contact area, bite force, tongue pressure, and masticatory efficiency. Oral function parameters exhibited different age-related development patterns. Occlusal contact area, maximum bite force, tongue pressure, and masticatory efficiency gradually increased with age. Interestingly, the occlusal contact area tended to reduce temporarily between 5 and 12 years of age due to the replacement of erupting lateral teeth. Conversely, lip pressure was almost stable during this period. Our findings provide valuable insights into the developmental patterns of oral functions during the growing years.

On a contact problem for a homogeneous plane with a finite crack under friction

An exact solution to the contact problem of indentation of an absolutely rigid punch with a straight base, taking into account friction, into one of the edges of a finite crack located in a homogeneous elastic plane was derived. It is assumed that shear contact stresses are directly proportional to normal contact pressure. In this case, it is assumed that the friction coefficient is directly proportional to the coordinates of the contacting points of the contacting surfaces. The governing system of equations for the problem was derived in the form of the heterogeneous Riemann problem for two functions with variable coefficients and its closed solution is constructed in quadratures. Simple formulas for contact stresses and the normal dislocation component of displacements of crack edge points were obtained. The patterns of changes in contact stresses and crack opening depending on the maximum value of the friction coefficient have been studied.

Leakage Control Mechanisms and Strategies for Hydraulically Driven Controllable Rod Seals

Abstract The primary function of rod seals in hydraulic systems is to prevent the leakage of the hydraulic medium, which would otherwise result in environmental pollution and the loss of energy. However, the leakage control performance of conventional rod seals is limited by the level of product design. As a result, the performance of these seals will gradually degrade during the service process. Furthermore, it is not possible to adaptively adjust the performance of these seals in response to changes in operating conditions. Hydraulically controllable rod seals (HCRS) can be driven hydraulically to adjust the internal stress distribution of the seal to regulate the sealing performance. This may be an effective solution, although the leakage control mechanism and strategy remain unclear. This paper employs a thermoelastohydrodynamic mixed lubrication model to comparatively analyze the behaviors and performances of the HCRS with or without a cavity structure. The leakage control mechanism of the HCRS is revealed, namely that it is achieved by increasing the interface contact pressure and reducing the fluid film thickness through external pressurization. Furthermore, the functional relationship between the sealing performance and the regulating variables under different operating conditions is obtained through multivariate regression analysis, thereby forming the quantitative leakage control strategy of the HCRS.

A Novel Cooling System for High-Speed Axial-Flux Machines Using Soft Magnetic Composites

Demand is high for small, lightweight, and power-dense machines. However, as power increases and size decreases, rejecting losses becomes more difficult. Many novel cooling systems have been developed, which have allowed machines to be made smaller while increasing power. This paper proposes a cooling system making use of soft magnetic composite (SMC) cores to improve cooling specifically in a high-speed axial-flux machine via the use of an integrated cooling channel in the SMC core. A series of experiments on a prototype machine are performed and the experimental data are used to determine a set of parameters for the FEA thermal model. Using the thermal FEA model, a comparison is completed with a traditional closed cooling system using laminated steels and an attached cooling plate.The SMC machine is then simulated at speeds up to 160 krpm and currents up to 8 A. To achieve the same coil temperature between the two designs, the laminated steel model required 4 MPa contact pressure at 10 krpm and 5 MPa contact pressure at 20 krpm. At the same time, the novel design removed approximately 20% more heat per shear air gap surface area and approximately 15% more heat per total machine surface area than the version with the attached cooling plate. Extending the operating range of the model to 160 krpm demonstrated that the maximum temperature rise remained below 180 °C.

Research on prediction of surrounding rock deformation and optimization of construction parameters of high ground stress tunnel based on WOA-LSTM

To accurately understand the deformation behavior of surrounding rock in the jiugongshan No.2 high ground stress tunnel and optimize construction parameters for improved efficiency, on-site monitoring was used to gather data on rock deformation and initial support contact pressure. A WOA-LSTM regression prediction model was proposed, and excavation advance depth was optimized using numerical simulation. The WOA-LSTM regression prediction model demonstrated high accuracy in tunnel deformation monitoring. The absolute errors between predicted and actual values of tunnel settlement and convergence at various measurement points average 2.53− 04 mm and 1.96− 04 mm, with relative errors averaging 2.15% and 2.34%. These results meet the requirements for guiding construction. Additionally, based on the results of numerical simulation calculations, when the step length is 12 m during the construction of high-stress tunnels using the benching method, excavation advances of 2 m and 3 m result in settlement and convergence increases of 35.1% and 63.4%, and 25.5% and 55.2%, respectively, compared to an excavation advance of 1 m. However, no sudden jumps in these values were observed, indicating that with a 3 m excavation advance, the integrity of the surrounding rock remains in good condition, effectively guiding safe and rapid construction methods.

THE COMPUTER MODELING STUDY OF INTERACTIONS BETWEEN CONTACT SURFACES OF METAL OR POLIMERIC SCREWS AND CORTICAL BONE TISSUE

The continuous growth of fracture rates and surgeries with the use of screws requires modern approaches to improve treatment results. The interaction between a screw and bone tissue is one of the critical factors that affects the stability of a fracture and remains not thoroughly researched until now. The computer modeling method allows for studying precisely the strains and deformities in the contact areas of metal screws, polymeric screws, and cortical bone.Material and methods. The computer modeling was performed in Autodesk Fusion 360 for biomechanical interactions of 3.5 mm AO screws made of stainless steel and polyamide-12 (P-12) with monocortical diaphyseal part of long tubular bone. The static stress study was performed for different loads applied in the pull-out direction with the bonded contact used between the screw and the bone. The displacement and strains were revealed in different parts of the screw thread and surrounding bone tissue for the force applied along the screw axis in the range from 100 N to 1000 N.Results. The increase of the force resulted in stress and strains in the screw and surrounding bone tissue, and the maximum force values can lead to unstable fixation. It was determined that polymeric P-12 screws in all study cases were affecting the bone with less contact pressure than metal screws. In the superficial bone areas this difference was more significant – 24.8 %, and in the deep bone areas it was 8.9 %. The areas of von Mises stress in both superficial and deep parts of polymeric screws were in the range from 1.414 MPa to 20.74 MPa which was lower than that of metal screws (3.484 MPa to 56.24 MPa).Conclusions. Polymeric P-12 screws will fix bone fractures better under low intensive but long-lasting loads, as their destructive effect on bone tissue around screws will be less than of metal ones. On the other hand, metal screws will have the advantage to resist the short lasting but intensive “peak” loads. The less stress areas in the polymeric screw can somehow compensate the lower mechanical strength parameters of P-12 material.Perspective of further research. The obtained results can be taken into account during orthopedics surgeries when screws are used for fixation, as well as for further biomechanical studies.

Strength gradient in impact-induced metallic bonding

Solid-state bonding can form when metallic microparticles impact metallic substrates at supersonic velocities. While the conditions necessary for impact-induced metallic bonding are relatively well understood, the properties emerging at the bonded interfaces remain elusive. Here, we use in situ microparticle impact experiments followed by site-specific micromechanical measurements to study the interfacial strength across bonded interfaces. We reveal a gradient of bond strength starting with a weak bonding near the impact center, followed by a rapid twofold rise to a peak strength significantly higher than the yield strength of the bulk material, and eventually, a plateau covering a large portion of the interface towards the periphery. We show that the form of the native oxide at the bonded interface—whether layers, particles, or debris—dictates the level of bond strength. We formulate a predictive framework for impact-induced bond strength based on the evolution of the contact pressure and surface exposure.

Optimal Sliding Speed and Contact Pressure Design of On-Load Tap Changer Based on Multivariate Nonlinear Regression

During the voltage regulation of on-load tap changers (OLTCs), the movement of the contacts can easily cause arcing, which may lead to erosion or malfunction. To reduce the energy and probability of arcing, we focus on designing an optimal range for the sliding speed and contact pressure of the contacts to minimize arc energy. Initially, our research introduces a novel OLTC arc testing platform to simulate the motion of static and dynamic contacts, exploring the relationship between different sliding speeds, contact pressures, and factors like arc voltage waveform, arcing rate, arc resistance, and arc energy. Subsequently, by employing multiple nonlinear regression methods, we establish functional relationships between sliding speed and arc energy, as well as contact pressure and arc energy, evaluating the fit using correlation coefficients. Finally, through analyzing their nonlinear behaviors, we determine the ideal sliding speed and contact pressure. The results indicate that when the OLTC contacts slide at an optimal speed between 89 and 103 mm/s and optimal contact pressure between 1.5 and 1.7 N, the arc energy can be minimized, thereby enhancing the performance and lifespan of the on-load tap changer. This study offers feasible insights for the design and operation of OLTCs, aiding in the improvement of power system regulation.

A Different Perspective on the Solid Lubrication Performance of Black Phosphorous: Friend or Foe?

Black phosphorous (BP), a promising 2D material with exceptional electronic and optical properties, has shown remarkable potential in tribology as an additive in liquid lubrication and a composite in solid lubrication. However, its potential as the standalone solid lubricant is still at its early stage. This study evaluates BP's solid lubrication performance as deposited coating (by drop casting) on a variety of metallic substrates (polished AISI 52 100 steel, aluminum, copper, and iron) under different contact pressures using a ball‐on‐disc linear‐reciprocating test machine in dry conditions. The results demonstrate that BP does not systematically reduce friction and wear. Depending on the contact pressure and the characteristic of the substrate material (particularly surface roughness), its friction and wear behavior vary a great deal. The best results observed are a 33% reduction in friction with increased surface roughness on iron and a 23% reduction in wear on aluminum. While no general trend is observed for contact pressure effects, increased substrate roughness proves beneficial, enhancing lubricant retention and exploiting BP's low interlayer shear mechanism. Therefore, this study demonstrates that while promising, BP's solid lubrication performance is not exceptional. It also highlights the importance of optimizing test conditions and materials for enhanced lubrication.

Circular Spline Tooth Longitudinal Modification Design and Contact Analysis for Harmonic Drives with Short Flexspline

Harmonic drives (HDs) with short flexspline (FS) always suffer from small meshing areas and severe stress concentration caused by large cone angles when a short FS is assembled and loaded. To address this issue, a tooth longitudinal modification method for the circular spline (CS) with a double circular arc common-tangent tooth profile (DCTP) is proposed. Using neutral layer and envelope conjugation theories, a mathematical model of the conventional straight CS tooth was developed. A shaping cutter for this tooth profile was then designed through coordinate transformation and meshing principles. The proposed longitudinal modification for the CS was achieved by adjusting the cutter’s trajectory. A precise finite element model of the HD was developed, revealing that tooth longitudinal modification can reduce the maximum contact pressure by 69.6% and significantly increase the contact area for HDs with short FS. This work provides valuable technical references for improving the contact state of HDs with short FS.

Optimizing Railway Tribology: A Systematic Review and Predictive Modeling of Twin-Disc Testing Parameters

Twin-disc testing is crucial for understanding wheel–rail interactions in railway systems, but the vast array of testing parameters and conditions makes data interpretation challenging. This review presents a comprehensive analysis of the twin-disc literature experimental data, focusing on how various parameters influence friction and wear characteristics under stationary contaminant conditions. We systematically collected and analyzed data from numerous studies, considering factors such as contact pressure, speed, material hardness, sliding speeds, adhesion, and a range of contaminants. This research showed inconsistent data reporting across different studies and statistical analyses revealed significant correlations between testing parameters and wear rates. For sand-contaminated tests, a correlation between particle size and flow rate was also highlighted. Based on these findings, we developed a simple predictive model for forecasting wear rates under varying conditions. This model achieved an adjusted R2 of 0.650, demonstrating its potential for optimizing railway component design and maintenance strategies. Our study provides a valuable resource for researchers and practitioners in railway engineering, offering insights into the complex tribological interactions in wheel–rail systems and a tool for predicting wear behavior.

Modelling and theoretical research on transient lubrication and wear coupling behavior of main bearing during start-up of low-speed diesel engine

This study endeavors to establish a transient mixed lubrication model for time-varying wear of main bearings under dynamic loading conditions during the startup process. This model accounts for variations in oil film thickness attributable to deformation, wear profiles, and journal misalignment throughout the operational cycle. The evolution of main bearing lubrication characteristics during the startup process was analyzed, as well as the evolution of wear profiles and their effects on lubricating properties under different numbers of startups. The results indicate that as the number of startup cycles increases, the wear rate gradually levels off. With increasing startup times, there is a decrease in contact pressure and a slight reduction in oil film pressure, resulting in enhanced lubricating performance. Furthermore, the influence of startup duration on wear is significantly greater than that of radial clearance.

Multi‐Scenario Applications of Multi‐Dimensional Yarn‐Based Wearable Integrated Sensors

Abstract1D yarn sensors, crucial for smart textiles, face challenges in achieving diverse functionalities, multiple applications, and durability in harsh environments. Herein, a simple strategy is proposed to prepare reduced graphene oxide‐polyimide yarns (rGO‐PYs), constructing functional and multi‐dimensional sensors for multi‐scenario applications. rGO‐PYs can detect multiple mechanical stimuli, and exhibit a broad bending and pressure response range (0°–180° and 0.12–62.39 KPa), quick response and recovery time (both <100 ms), and excellent cyclic stability. It features real‐time monitoring of human activities, such as joint movements, speech, writing, respiratory, pulse, and heart rate. rGO‐PYs exhibit a remarkable resilience to harsh environments, whether in liquid nitrogen (−196 °C), high temperature (300 °C), acid, or base. Crucially, expanded into an integrated 2D fabric, rGO‐PYs maintain their exceptional multi‐dimensional sensing. The point contact pressure sensor (PCPS) and pressure sensing array showed remarkable sensing performance in identifying pressure and its distribution. This work establishes a comprehensive system from preparation to application, encompassing 1D yarns large‐scale fabrication, functional sensing validation, integration into multi‐dimensional sensors, and diverse cross‐scenario applications. The innovative system would transform traditional yarns into intelligent fabrics, further advancing functional yarns into multi‐dimensional sensors (1D to 2D and 3D), enabling their diverse multi‐scenario applications.

Enhancing pressure ulcer prevention through optimized design of a multi-cellular foam mattress

Sustained mechanical loading on skeletal muscle tissue can lead to degeneration and cell damage over time, resulting in the development of pressure ulcers, particularly in hospital mattresses or for wheelchair-bound users. The primary risk factors for this damage are tissue ischemia caused by pressure in the contact area and tissue compressive strain. In this study, a multi-cell, multi-material foam mattress for the upper comfort layer was developed, with the aim of simultaneously minimizing soft tissue compressive strain and maximum surface pressure on the human buttocks zone. The levels of these factors were estimated using the finite element method (FEM). A multi-objective optimization (MOO) approach was employed, coupling the non-dominated sorting genetic algorithm (NSGA-II) with FEM. This algorithm helped determine the required compressive strength and the optimal cell configurations to achieve the desired outcomes. The majority of the optimal solutions exhibited contact pressures (Cpresss) below the recommended threshold to avoid local tissue ischemia. The optimized cellular material configurations resulted in soft tissue compressive strain of 12% and Cpress of 3.4 kPa, indicating longer safety times for supine support on the foam mattress without the need for repositioning. The optimization process utilized 5 softer foam materials out of the 9 firmness levels tested to achieve these results. The proposed multi-cell, multi-material foam mattress model shows promise for the prevention of pressure sores, as suggested by the optimization findings.

Lateral Meniscus Allograft Transplant With Capsulodesis and an Osteochondral Allograft to the Lateral Femoral Condyle

Background: Anterior cruciate ligament (ACL) injuries frequently present with lateral meniscal injuries, and when irreparable, this may lead to meniscectomy, increasing the risk for osteoarthritis. Lateral meniscal allograft transplant (LMAT) can restore knee function and proper contact pressures. When combined with osteochondral allograft (OCA) for chondral defects, results are highly positive. Indications: LMAT is indicated in relatively young patients (<50 years of age) with a symptomatic, meniscus-deficient knee that has failed conservative treatment. The knee must be stable, without articular cartilage damage that cannot be repaired, and patients should be able to adhere to postoperative rehabilitation and future care. Indications for OCA include young, active patients with posttraumatic osteochondral defects, osteonecrosis, osteochondritis dissecans, large focal defects, previous cartilage repair failure, or patellofemoral joint cartilage lesions. Technique Description: After a diagnostic arthroscopy is performed and concomitant injuries are ruled out, the lateral meniscal tissue is debrided to a 1- to 2-mm rim for the recipient site preparation. Tibial sockets for root fixation are created using tibial guides and passing sutures are placed. A capsulodesis is performed to reduce meniscal extrusion by securing the lateral capsule through a transtibial tunnel to the anteromedial tibial cortex with high-strength sutures. A meniscal allograft, prepared with bone plugs, is introduced through an enlarged anterolateral portal. After it is accurately positioned, it is stabilized using Fast-Fix Flex devices and circumferential sutures. The bone plug sutures are then fixed through the tibial tunnels to the anteromedial tibial cortex with a button. The large cartilage defect is addressed with an OCA transplant, involving defect measurement, careful reaming, and press-fit insertion of a donor plug, ensuring congruent articulation. Results: Patients can expect improved clinical outcomes and high patient satisfaction with LMAT and concomitant OCA. The use of bone plugs minimizes soft tissue dissection while achieving solid osseous fixation. Discussion/Conclusions: LMAT with OCA leads to restored contact pressures to near-physiological levels, a high patient satisfaction of over 85%, and mean allograft survival of 16 years. Patient Consent Disclosure Statement: The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.

ANALYSIS OF REINFORCED BOLTED JOINTS IN HIGH-CAPACITY SILOS

ABSTRACT: This paper presents an analysis of the mechanical performance of bolted joints used in silos for storing bulk materials. In particular, we investigated the effectiveness of three types of bolted joints: one without reinforcement, one with angular reinforcement, and one with squared reinforcement. Our analysis involved the use of the finite element analysis sub-modeling technique, which allowed us to construct a large finite element model with shell elements and a sub-model with solid elements. By analyzing the stress state of each joint, we were able to determine the contact state and contact pressure of the bolted joint. Our findings showed that bolted joints reinforced with triangular and square plates were effective in maintaining contact pressure, even under high-pressure conditions. This study provides valuable insights into the design of bolted joints used in silos, which can help ensure their reliable and safe operation. Keywords: bolted joints, high-capacity silo, FEA sub-modeling.

Simulation of thermal-mechanical coupling in Al alloy/steel inertia friction welding

Inertia friction welding (IFW) is a complicated thermal-mechanical coupling process. In-depth understanding of the thermal-mechanical process can improve the joint quality. In this study, a three-dimensional (3D) thermal-mechanical coupling model was successfully established to simulate the evolution of temperature, energy density, stress, strain, and flow behavior of the IFW process between 2219-O Al alloy and 304 stainless steel. The developed model was validated by comparing it with the measured temperature and deformation. Results show a transforming distribution of interface temperature from a M-shape to a squished V-shape during the IFW process. The characterization is attributed to the transformation of the accumulated friction energy density at the interface from a M-shape to an approximate V-shape due to the combined effect of varying sliding velocity and contact pressure. The Mises stress at the region near the interface is high and low at the steel and Al alloy sides, respectively. A significant portion of the kinetic energy stored in the flywheel is dissipated in the form of plastic deformation energy and cannot be neglected. The tracer particles show that most Al alloy at the initial interface is extruded to form flash, while a small amount of Al alloy is sticky and remains at the interface center. Increasing friction pressure and initial rotation speed result in higher interface temperature, axial shortening distance, and proportion of plastic work in total energy input.