Surface Contact Pressure Research Articles

Friction Coefficient of Slip Critical Bolted Joints with Inorganic Zinc-Rich Paint Focusing on Contact Surface Pressure

Friction Coefficient of Slip Critical Bolted Joints with Inorganic Zinc-Rich Paint Focusing on Contact Surface Pressure

Smart Cushions with Machine Learning-Enhanced Force Sensors for Pressure Injury Risk Assessment.

Prolonged sitting can easily result in pressure injury (PI) for certain people who have had strokes or spinal cord injuries. There are not many methods available for tracking contact surface pressure and shear force to evaluate the PI risk. Here, we propose a smart cushion that uses two-dimensional force sensors (2D-FSs) to measure the pressure and shear force in the buttocks. A machine learning algorithm is then used to compute the shear stresses in the gluteal muscles, which helps to determine the PI risk. The 2D-FS consists of a ferroelectret coaxial sensor (FCS) unit placed atop a ferroelectret film sensor (FFS) unit, allowing it to detect both vertical and horizontal forces simultaneously. To characterize and calibrate, two experimental approaches are applied: one involves simultaneously applying two perpendicular forces, and one involves applying a single force. To separate the two forces, the 2D-FS is decoupled using a deep neural network technique. Multiple FCSs are embedded to form a smart cushion, and a genetic algorithm-optimized backpropagation neural network is proposed and trained to predict the shear strain in the buttocks to prevent PI. By tracking the danger of PI, the smart cushion based on 2D-FSs may be further connected with home-based intelligent care platforms to increase patient equality for spinal cord injury patients and lower the expense of nursing or rehabilitation care.

Effect of corrosion on fretting wear morphology and mechanical behaviors of wires

Corrosion and fretting wear inevitably occur in wires, which are important parts of cables. To study the wear morphology and surface mechanical behavior of wires for different fretting and corrosion times, a numerical model of fretting wear of wire with different corrosion conditions is established using MATLAB and ABAQUS software’s. Firstly, according to the surface roughness of wires under different corrosion times, the node coordinates in the numerical model are modified to simulate different rough surfaces. Secondly, the wear characteristics of wires under different fretting cycles are obtained by using a cycle jump concept and an ABAQUS user subroutine. Finally, the numerical model is validated using experimental data. The results show that when the corrosion time is 0 h, the wear area has a regular oval shape. The wear volumes of wires with corrosion times of 120 h and 480 h are the largest and the smallest, respectively. As wear volume increases, both residual surface contact pressure and stress decrease. When the corrosion time is 0 h and 120 h, the residual surface contact pressure is maximum and minimum, respectively.

Friction-reduction effect of the hierarchical surface microstructure of carrion beetle by controlling the real contact area.

The discovery and elucidation of the surface microstructure functions of living organisms are crucial to resolving issues, such as friction. We newly discovered that Necrophila japonica, a type of carrion beetle that lives on the ground surface, exhibited a hierarchical surface microstructure comprising a submicron-sized wrinkle structure on top of a micron-sized microstructure. The surface microstructure of this beetle improved wettability but did not exhibit superhydrophobicity, a well-known function of hierarchical structures, so it was expected to have a different function. By combining the insights in the field of structural mechanics that avoidance of stress concentration by the structural geometry affects deformation with the basic principles of friction, the frictional properties and mechanisms of the hierarchical surface microstructure of carrion beetle were investigated. The measurements of frictional force indicated that the mimicked structure exerted lower frictional forces than flat and single-layer microstructure surfaces. Analysis of finite element method simulations showed that even though the mimicked structure was prone to pressure concentration due to small contact points, the surface contact pressure was reduced more than that of the single-layer structure by hierarchical load dispersion like that of metamaterials. As a result, the suppression of the increase in the real contact area due to deformation suppression contributed to effective friction-reduction. The effective friction-reduction by the hierarchical structure provides not only new insight into the surface microstructure function of various organisms, but also new design for the lubricant-free friction reduction that has been the focus of attention in carbon neutrality and other fields.

Corrosion and wear interplay: Tribo-electrochemical evaluation of NiTiNOL60 alloy in sulfuric acid

The combined corrosion and wear behaviour of NiTiNOL60 alloy is important in various engineering applications. While previous studies have explored its performance in artificial seawater environments, limited information exists regarding its tribocorrosion characteristics in acidic conditions. This paper investigates the synergistic interaction between sliding wear and electrochemical processes for NiTiNOL60 alloy in a sulfuric acid environment, employing experimental procedures compliant with ASTM standards. Microscopic analysis confirms the alloy's Ni-rich composition, featuring a dense network of B2 NiTi + Ni4Ti3 cubic and rhombohedral crystal matrix structures. Our research and results reveal that material degradation during tribocorrosion arises from the combined effects of sliding wear and electrochemical reactions. Consequently, multiple wear mechanisms influenced by tribochemical wear are observed, with delamination and micro-cracks being notably prominent under higher applied loads due to surface tensile stress and contact pressure, leading to crack propagation perpendicular to the sliding direction. These findings have practical implications for optimising the performance and durability of NiTiNOL60 alloy in acidic environments, offering valuable insights for load-bearing engineering applications.

Effect of roughness, contact pressure and lubrication on the onset of galling of the 6082 aluminium alloy in cold forming, a numerical approach

The effect of surface roughness, contact pressure and lubrication on the onset of galling of aluminum 6082-T6 is studied with a pin-on-plate tribometer. The design of experiments involves pins with mean arithmetic roughness Ra equaled to 0.2, 0.35 and 0.6 μm, normal loads ranging from 5 to 600 N, and 4 different lubrications: without lubricant, with MoS2 dry lubricant, with pure mineral oil and with a highly chlorinated paraffin oil. Tests are performed at room temperature and are repeated three times. Experimental results show the great sensitivity of the onset of galling to the roughness and the beneficial effect of dry and liquid lubricants. The occurrence of galling is study by optical micrographs, by the analyses of the coefficient of friction, and by the use of finite element simulations. It comes that the variation of the coefficient of friction is not self-sufficient to detect the onset of galling. The finite element computations involves Wilson’s lubrication model and Xue’s damage model. Galling is assumed when finite elements near the contact area reach the critical damage Dc. This numerical approach leads to a good prediction of the onset of galling for the tests performed under constant normal load. For tests performed with increasing normal loads and various lubricants, the numerical prediction overestimate the sliding length before galling occurs.

Tool Surface Degradation and Adhesion in Aluminium Forging

Tool surface deterioration is a crucial effect limiting the efficiency of forging processes. Prior work on wear is limited to steel forging while investigations on tribology in aluminium forging are limited to an abstract or simplified level. The presented work aims at contributing to filling this gap with a holistic analytic approach including ball-on-disc (BoD) tests, ring compression (RC) tests and serial forging (SF) tests close to industrial applications in order to gain insights on effects and influences of surface deterioration and evaluate the suitability of different tool coatings. The results show that the primary influence on surface adhesion in aluminium forging is the superposition of surface enlargement and contact pressure of the material flow. Duplex-treated tools with the combination of a nitriding in the first step and an additional coating with chromium nitride (CrN) afterwards show a significant reduction of aluminium adhesion in ring compression and serial forging tests, representing a promising approach to tool life enhancement in forging applications.

Comparison of medial tibiofemoral joint mechanics between all-suture anchors and transtibial pullout technique for posterior medial meniscal root tears

BackgroundThe posterior medial meniscal root tear (PMMRT) seriously impacts the tibiofemoral joint biomechanics. Two available techniques for PMMRT repair include the transtibial pullout (TPO) repair and all-suture anchor (ASA) repair techniques. These techniques have not been compared biomechanically.MethodsA total of 20 fresh porcine cadaveric knee specimens were used. All 20 knees were randomly and evenly distributed into four groups (five specimens per group): (1) intact posterior meniscal root, (2) PMMRT, (3) TPO repair technique for PMMRT, and (4) ASA repair technique for PMMRT. The tibiofemoral contact mechanics were investigated using a pressure sensor. All knee specimens were tested by being loaded with 600 N axial compressive force at three different flexion angles (0°, 45°, and 90°). The contact surface area, contact pressure, peak pressure, and time-zero displacement were recorded.ResultsThe PMMRT caused a significant decrease in contact surface area, an increase in contact pressure, and peak pressure from the reference values observed in the intact meniscus group (P = 0.05, 0.016, and 0.008, respectively). After fixation, no significant difference was observed between the ASA and intact group. Meanwhile, significant differences were found between the TPO and intact group in terms of contact surface area, contact pressure, and peak pressure. In the comparison between the two techniques, the ASA group demonstrated higher contact surface area than the TPO group at the average knee flexion angle (p = 0.05).ConclusionFor most testing conditions, the ASA technique demonstrated superior biomechanical property in terms of contact surface area compared with the TPO technique under compressive loading conditions. The ASA technique could also restore the tibiofemoral contact mechanics to be comparable with those of the native intact knee. Meanwhile, a significant difference in tibiofemoral mechanics, compared with the intact knee, could be observed in the TPO technique.

Numerical Analysis of Fretting Wear Characteristics of Aluminum Cable Steel Reinforced Strands

In view of the concealment of the wind vibration of transmission lines and the technical problems that can easily lead to accidents caused by the wear of wires and fittings, overhead power lines are taken as a research object, and the contact and fretting wear characteristics of the transmission lines are studied. The important parameters such as stress during frictional contact, wear morphology and contact surface pressure during frictional wear are analyzed and appropriate conclusions are drawn from them. Taking the LGJ 150/8 transmission line as an example, through the theoretical analysis and calculation of the steel core-aluminum strand model, and according to the parameters of the power grid program, the contact mechanics model of the overhead line under the wind vibration is created using the three-dimensional modeling software. The change in the contact stress between the steel strand and the conductor layer, the change in the micro-displacement and the relationship between stress and vibration frequency are examined. The fretting properties of adjacent conductor contact points are calculated and analyzed, providing a mechanical basis for analyzing the mechanism of wear of overhead lines.

The Role of the Lateral Collateral Ligament-Capsule Complex (LCL-cc) of the Elbow Under Gravity Varus.

The lateral collateral ligament complex along with the capsule is likely to be at risk during arthroscopic ECRB release in lateral epicondylitis. We hypothesized that disruption of the lateral collateral ligament-capsule complex (LCL-cc) increases the mean contact pressure on the coronoid under the gravity varus. Eight cadaveric elbows were tested under the gravity varus and weighted varus stress tests (2Nm), using a custom-made machine designed to simulate muscle loads while allowing passive flexion of the elbow. Mean articular surface contact pressure data were collected and processed using intra-articular thin film sensors and software. Sequential testing was performed from Stage 0 to Stage 3 (Stage 0: Intact; Stage 1: release of anterior 1/3 LCL-cc; Stage 2; release of anterior 2/3 LCL-cc; and Stage 3; release of entire LCL-cc) on each specimen. The mean contact pressure of the coronoid and mean M/L ratio (ratio of contact pressure on medial coronoid to that on the lateral coronoid) were used for the comparison between stages with the intact elbow. The overall mean contact pressure significantly increased in Stage 2 (P =.0006 in gravity varus, P =.0002 in weighted varus) and Stage 3 (P <.0001 in gravity varus, P <.0001 in weighted varus) compared to that in Stage 0. In contrast, release of the anterior 1/3 of LCL-cc (Stage 1) did not significantly increase the mean contact pressure on the coronoid in any degree of flexion under gravity varus (P =.06) or weighted varus loading (P =.6). The M/L ratio difference between Stage 0 and Stage 1 was 1.1 ± 1.1 under gravity varus (P =.8) and 2.1 ± 0.9 under weighted varus. (P =.2) The overall M/L ratio in Stage 2 and Stage 3 were significantly higher compared to that seen in Stage 0 under gravity varus (P =.04 in Stage 2, P =.02 in Stage 3) or weighted varus (P =.006 in Stage 2, P <.0001 in Stage 3). Loss of the anterior 2/3 or more of the LCL-cc significantly increases the overall mean contact pressure of coronoid, especially in the medial coronoid under both gravity varus and weighted varus. The LCL-cc also plays a role in the distribution of coronoid contact pressure against gravity varus loads.

Estimation of the Friction Behaviour of Rubber on Wet Rough Road, and Its Application to Tyre Wet Skid Resistance, Using Numerical Simulation

Tyre wet skid resistance greatly affects vehicle safety, and it is dependent on the frictional behaviour at the tyre–road interface; however, the currently available numerical models, using the finite element method, either neglect the road roughness or obtain the rightness using expensive computed tomography scans, rendering them inefficient and complex. This study aims to present an estimation method of rubber slides on a rough road, to study tyre wet skid resistance. A three-dimensional rough road model was established, using the harmonic superposition method; the sealing effect of the water film on a wet road was modelled in terms of the pseudo-hydrodynamic bearing effect; the contact pressure, hysteresis friction, and water film hydrodynamic lift force were calculated. Subsequently, a friction model was established that accounted for the road surface morphology, tyre properties, sliding speed, and contact pressure. The accuracy of the friction model was experimentally validated, using the published experimental results. The friction model was then adopted, to conduct a study of the wet skid resistance of a 205/55R16 tyre with two different tread patterns. The simulation results were consistent with the experimental results of braking distance on a wet road. Finally, the effects of road roughness, tread rubber, load, and inflation pressure on wet skid resistance were carried out and analysed. The works in this paper have important significance and practical value for the development of high-performance tyres.

Study on the Performance of Liquid-Solid Contact Resistance Based on Magnetohydrodynamic Micro-Angular Vibration Sensor

In this paper, the influence of the contact resistance between the conductive fluid and the metal electrode on the output characteristics of the magnetic fluid micro-angular vibration sensor (MHD sensor) is theoretically analyzed. The contact resistance models based on the solid-solid electric contact theory are established based on the resistivity, temperature, pressure and angular vibration of the materials between the conductive fluid and the metal electrode. The contact resistance was tested by setting up an experimental platform and making conductive fluid rings with electrode materials of Ag, Cu and Ti. The results show that the static contact resistance between the conductive fluid and the metal electrode is positively correlated with the material resistivity and temperature, and negatively correlated with the surface roughness and contact pressure of the metal electrode. The dynamic contact resistance fluctuation is proportional to the amplitude of the input voltage of the angle shaker and inversely proportional to the square of the input frequency. At the same time, reducing contact resistance can improve the MHD sensor's performance.

Noninvasive Technique to Monitor the Pressure under a Cast: A Mobile Application-Friendly Bluetooth Pressure Sensor.

The purpose of this study was to design a sensor that could monitor the skin-cast contact surface pressure (SCCSP) of a limb under a cast and inform the user via a mobile application when the pressure increases. In this experimental study, an infant sphygmomanometer cuff was initially placed on the forearm of 10 volunteers. A pressure sensor with a Bluetooth chip was then placed on the volar aspect of the forearm. Short arm plaster was applied with synthetic cast material. The SCCSP under the plaster was measured by the sensor and the measured values were transmitted to a mobile application via a Bluetooth chip. The mobile application processed the data from the chip and converted it to mmHg. Intracompartmental pressure (ICP) values were categorized as 0, 10, 20, 30, 40, 50, 60, and 75 mmHg. The highest SCCSP was 75 mmHg CP, while the lowest was 0 mmHg CP. The correlation coefficient of the mean pressure values was 0.993 (p ≤ 0.001) (SD 0.002, range 0.989-0.997), and there was a significant relationship between ICP and SCCSP values (p ≤ 0.05). We can monitor SCCSP, detect limb swelling, and notify the user via a mobile application by using Bluetooth pressure sensors.

Structural mechanics analysis of bolt joint of rigid flexible coupling manipulator

As the key connecting part of the rigid flexible coupling manipulator, the structural dynamic characteristics of the bolted joint are analyzed by using the joint simulation technology of pro/e and ANSYS. Based on the spring equivalent principle, the finite element equivalent model of bolt joint is established, the relationship equation between contact surface pressure and bolt preload is derived, and its stress state is analyzed; Based on the micro convex deformation model and Hertz contact theory, the tangential stiffness equation and normal stiffness equation of the bolted joint are derived respectively. The three-dimensional model of the bolted joint is established by using pro/e and imported into ANSYS for joint simulation. The simulation experiments reveal the influence of bolt joint vibration characteristics under different conditions from the aspects of bolt diameter, pre tightening force, bolt group number and bolt distribution. The conclusions have important engineering value for the structural optimization of rigid flexible coupling manipulator.

Carbon brush wear calculation in marine environment based on temperature field analysis

In the marine environment, the working environment of the doubly fed wind generator carbon brush and slip-ring system is complicated, salt spray deposits and seawater erosion affect the temperature field and contact surface friction factor leading to carbon brush wear increase and shortened replacement cycle. The three-dimensional temperature field simulation model of the carbon brush and slip-ring system is established. The main factors affecting the carbon brush and slip-ring system temperature field are sliding velocity, load current, ambient temperature, contact surface condition and contact pressure applied to the brush. Wear capacity of carbon brushes is affected by contact surface temperature. An experimental platform combined with the salt spray test machine was built to carry out the contact current, contact pressure, salt spray concentration and experimental temperature experiment. The improved Coulomb-viscous friction force model was used for the wear prediction model. The sliding velocity, contact pressure, contact current, experimental temperature and salt spray concentration were introduced into the model. The experimental verification has shown that the prediction model can effectively predict the carbon brush wearing capacity under different conditions. This model can be applied to formulating the carbon brush wear amount and replacement cycle in the marine environment reducing operation and maintenance costs.

Failure Mechanism Analysis and Optimization Analysis of Tunnel Joint Waterstop Considering Bonding and Extrusion

In waterproofing mountain tunnels, the tunnel joint is the weak link. To explore the waterproof failure mechanism of the tunnel joint waterstop belt and to propose an optimization method for the waterstop belt, this paper combines tests and numerical simulations, summarizes the waterproofing mechanism of the waterstop belt, establishes a finite element model of the waterstop belt considering bonding and extrusion, and studies the waterproofing ability and mechanical properties of the waterstop. The main conclusions are as follows: (1) The waterproofing capacity of the water stop belt depends on its surface contact pressure and bonding force. (2) Waterstop deformation will partially destroy the bonding between the waterstop and concrete, reducing the reliability of the waterproofing mechanism. (3) When the deformation of the waterstop belt reaches a certain degree, its stress value is too large to meet the requirements of its service life. (4) The design can be optimized from two aspects: the bond between the waterstop and concrete, and the size of the waterstop.

Macroscopical contact pressure and microscopic leakage performance analysis of rubber seal considering thermal oxygen aging effect

Leakage performance of rubber seal is a key factor of spacecraft system, which is required long life. But the degradation law of the rubber seal performance in long service period is limited to qualitative analysis for its macro contact performance, and the quantitative research of rubber seal leakage performance is rarely involved considering thermal oxygen aging effect. Therefore, the thermal oxygen aging mathematical model is firstly established to predict the life of rubber material by aging tests. Secondly, the finite element model (FEM) of rubber seal performance analysis considering thermal oxygen aging effect is built to obtain the degradation law of its macroscopic contact performance with the increase of service time. Thirdly, the micro-leakage model of rubber seal considering thermal oxygen aging effect is established based on the material surface microstructure, contact pressure, and contact width, and the leakage rate of rubber seal is calculated by the model. Finally, the micro-leakage model of rubber seal is modified based on the experimental results, so the calculation accuracy of leakage rate is improved.

Research on Safety Early Warning Standard of Large-Scale Underground Utility Tunnel in Ground Fissure Active Period

Safety control of large-scale underground utility tunnels is vital for engineering management units. The establishment of early warning indicator systems and standards is critical for safety control. However, there is limited related research for engineering construction, operation, and maintenance management. Numerical analysis results of the mechanical response of the underground utility tunnel of the Xi’an Xingfu LinDai project (the largest underground urban complex in Asia) at different intersection angles and ground fissure displacements were obtained. The vertical surface settlement, structural stress, fissure displacement, and contact pressure are proposed as early warning indicators of the structure of the underground utility tunnel during the active period of a ground fissure. The safety control values and early warning standards are given based on the analysis of the results. The safety warning indicator system and standards proposed in this article are concise, practical, and easy to implement. The data sample required by this warning indicator system is small and can be obtained using conventional monitoring sensors, which can be referenced for similar projects.

A new method of micro-slip contact normal pressure modeling and its application in the dynamic analysis of the dovetail–tenon–mortise jointed blades

In this paper, a contact slip mechanics model based on pressure distribution is developed, it is formed from multiple contact pairs and can define the contact behavior between contact interfaces. First, we establish the jointed structure's finite element model to calculate the contact interface's nodal pressure. Following this calculation, applying the cubic spline interpolation to the nodal pressure data, we obtain the contact surface pressure. Then using the theory of load equivalence, the contact surface pressure is converted into an equivalent load. The equivalent load is used as the normal pressure of the contact pairs place on the contact surface nodes. Subsequently, to verify the developed modeling approach, we establish a simplified blade model with the tenon–mortise structure for trial calculation. Finally, the nonlinear frictional force is linearized to solve the nonlinear differential equation by the incremental harmonic balance method (IHBM). The results show that the tenon–mortise contact surface exhibits micro-slip characteristics, which means that the pressure distribution characteristics of the contact surface are retained. The contact slip mechanics model developed in this paper is general which can be applied in modeling the contact surfaces of other joints.

Effects of Contact Surface Pressure and Surface Roughness on Friction Properties of Various LB Films with the Same Tip Group

Effects of Contact Surface Pressure and Surface Roughness on Friction Properties of Various LB Films with the Same Tip Group