Changes In Contact Force Research Articles

Research on Spatial Developable Mechanism Considering Revolute Clearance Joints with Irregular Rough Surfaces

Due to assembling, manufacturing errors, and wear, irregular rough surfaces inevitably exist in joints, which will increase the contact stiffness nonlinearity at the joint of the spatial developable mechanism, and the traditional contact force model is difficult to accurately predict the contact force change of irregular rough surface clearance. Aiming at the difficulty of accurately predicting the dynamic behavior of the spatial developable mechanism caused by rough joint clearance, an improved clearance contact force modeling method based on an uncoordinated contact model is proposed in this paper. The influence of rough peak distribution on the contact area is analyzed. The stiffness of the traditional Hertz model is modified based on the probability distribution density function of the rough peak, and an improved contact force model based on dynamic contact stiffness is established. Based on the Lagrange multiplier method, the dynamics model of spatial developable mechanism is constructed. Based on the model, the dynamic analysis of the spatial expansion mechanism is carried out, and the influence of the roughness of the contact surface and the size of the clearance on the dynamic characteristics of the system are explored; as well, the influence of different clearance parameters on the dynamic characteristics of the development mechanism is revealed. Through the analysis, this paper provides a theoretical basis for predicting the effect of a spatial revolute clearance joint on the dynamic characteristics of the mechanism and lays a good foundation for the manufacture and application of the mechanism.

Inductive Paper-Based Flexible Contact Force Sensor Utilizing Natural Micro-Nanostructures of Paper: Simplicity, Economy, and Eco-Friendliness.

Inductive contact force sensors, known for their high precision and anti-interference capabilities, hold significant potential applications in fields such as wearable and medical monitoring devices. Most of the current research on inductive contact force sensors employed novel nanomaterials as sensitive elements to enhance their sensitivity and other performance characteristics. However, sensors developed through such methods typically involve complex preparation processes, high costs, and difficulty in biodegradation, which limit their further development. This article introduces a new flexible inductive contact force sensor using paper as a sensitive element. Paper inherently possesses micro- and nanostructures on its surface and interior, enabling it to sensitively convert changes in contact force into changes in displacement, making it suitable for use as the sensor's sensitive element. Additionally, the advantages of paper also include its great flexibility, low cost, wide availability, and biodegradability. Performance testing on this flexible sensor showed good repeatability, hysteresis, sensitivity, and consistency. When used in experiments for monitoring human motion and respiration, this sensor also exhibited great detection performance. The proposed inductive paper-based flexible contact force sensor, with its simple structure, easy manufacturing process, cost-effectiveness, eco-friendliness, and good sensing performance, provides new insights into research for contact force sensors.

Effect of fatigue on knee biomechanics during the sidestep cutting manoeuvre: A modelling approach

ABSTRACT Loading both lateral and medial compartments is crucial to understanding the effect of muscle fatigue during sidestep cutting. The present study investigated the changes in tibiofemoral contact forces in the medial and lateral compartments and the muscle force contributions during the sidestep-cutting manoeuvre after a handball-specific fatigue protocol. Twenty female handball athletes performed three trials of the sidestep-cutting manoeuvre before (baseline) and after the fatigue protocol. Motion capture and ground reaction forces were measured, and the data were processed in OpenSim. The variables were compared using statistical parametric mapping (SPM), with a significance level of p < 0.05. The results showed a decreased knee flexion angle during fatigue in the early stance phase. In addition, the post-fatigue analysis demonstrated significantly reduced forces in vasti muscles. Similarly, during fatigue, the SPM analysis showed decreased tibiofemoral contact forces in the vertical and anterior directions. Vertical force applied to both medial and lateral condyles demonstrated a significant reduction after the fatigue protocol. These results indicated that forces applied to the tibiofemoral joint were reduced following the fatigue protocol compared to the baseline values. However, no consistent evidence exists that fatigue increases the risk of knee injuries.

Analysis of electrical contact characteristics of strap contacts used in high voltage bushings under eccentric conditions

AbstractThe contact finger electrical connection structure is a crucial component of high voltage bushings, and its safety and reliability directly impact the operational stability of the bushing. To investigate electrical contact performance of the contact finger under eccentric conditions, a three‐dimensional electrical, thermal, and force multi‐physics coupling calculation model was established. Additionally, a test platform was constructed to measure electrical contact characteristics of the contact finger. The contact characteristics of the contact finger when the male head was axially deflected and radially offset compared to the female head were obtained. The research findings indicate when the male head deflects axially, the contact force changes of the contact finger blades on both sides are opposite. Moreover, as the axial deflection angle of the male head increases, the resistance of the electrical connection structure shows a rising‐slow decreasing‐fluctuating trend. The resistance is highest at 3°, with a resistance increase rate of 7.35%. Furthermore, the resistance of the electrical connection structure varies with the radial offset of the male head, following a power function. Contact failure occurs when the radial offset is 1.31 mm, and the resistance increase rate reaches 24.9% at a radial offset of 1.58 mm.

Analysis of Contact Force and Shape Change on Grasping a Square Object Using an Actual Fin Ray Soft Gripper.

The Fin Ray-type soft gripper (FRSG) is a typical soft gripper structure and applies the deformation characteristics of the Fin Ray structure. This structure functions to stabilize the grasping of an object by passive deformation due to external forces. To analyze the performance of detailed force without compromising the actual FRSG characteristics, it is effective to incorporate multiple force sensors into the grasping object without installing them inside the Fin Ray structure. Since the grasping characteristics of the FRSG are greatly affected by the arrangement of the crossbeams, it is also important to understand the correspondence between the forces and the geometry. In addition, the grasping characteristics of an angular object have not been verified in actual equipment. Therefore, in this study, a contact force measurement device with 16 force sensors built into the grasping object and a structural deformation measurement device using camera images were used to analyze the correspondence between force and structural deformation on an actual FRSG. In the experiment, we analyzed the influence of the crossbeam arrangement on the grasping force and the grasping conditions of the square (0°) and rectangular (45°) shapes, and state that an ideal grasp in a square-shaped (45°) grasp is possible if each crossbeam in the FRSG is arranged at a different angle.

Dynamics modelling and vibration characteristics of urban rail vehicle axle-box bearings with the cage crack

The cage crack changes the structural stiffness on different components, and therefore affects its relative contact forces. Furthermore, the crack may cause the fault characteristics on the urban rail vehicle axle-box bearing. Despite all this, there is still a lack of discussion and summary on the dynamics modelling and vibration characteristics analysis of axle-box bearings with the cage crack. For filling this gap, two cage crack models are proposed, which are respectively constructed when the crack generates in the cage bridge or arm. Then, these models are coupled to the axle-box bearing model in a vehicle-track coupling model. Thereinto, the friction force and the motion of rollers are considered, and the cage is decentralized into several segments for facilitating the study of the force between adjacent cage segments. At last, the dynamic characteristics of axle-box bearings with the cage crack are investigated, and the changes in contact forces due to the cage crack are also analyzed. This study can provide valuable information for axle-box bearing condition tracking and monitoring.

Influence of impact medium particle size on mechanical deposition layer formation process based on discrete element method

Based on the discrete element method, this study has simulated the movement of materials in the plated barrel using EDEM software to investigate the effect of the impact medium with different particle sizes on the mechanical deposition plating. The simulation analyzed the interaction between five impact mediums with different particle sizes (2, 3, 4, 5, and 6 mm) and the base body while determining the particle size ratio of the impact medium. The rationality of the particle size ratio was verified by the simulation analysis of the interreaction of two groups of mixed particle size impact medium and the base body. The samples of mechanically deposited zinc coating were prepared. The average thickness, relative density, and average deviation of the coating were measured. The results show that When the particle size is 2 and 3 mm, the effective collision frequency of the materials is higher. When it is 3, 4, and 5 mm, the kinetic energy of collision between materials fluctuates evenly. When it is 4 and 5 mm, the collision contact force of the materials changes regularly. Consequently, the obtained particle size ratio (second group) is 2 mm 23%; 3 mm 23%; 4 mm 23%; 5 mm 27%; and 6 mm 4%. Compared with mixed impact media with 20% of each of the five particle sizes (first group), in the second group of assorted particle size simulation test, the collision frequency between materials is high. The contact force changes more regularly between materials. The average thickness, relative density, and average deviation of the mechanically deposited galvanized layer are consistent with the simulation results of the two groups of mixed particle sizes. The average thickness and relative density of the galvanized layer in the second group are higher, the average deviation is smaller, and the compactness and uniformity are the best.

Flexural strains in a toughened glass panel generated by impact of an ice sphere

An analytical model for predicting flexural strains on a toughened glass panel generated by the impact of ice is presented in this paper. The time-history of the generated surface tensile strains can be used to predict the fracture probability of glass in a projected hailstorm scenario. As demonstrated in this article, the strain intensity is insensitive to changes in the panel size, positions of impact, and boundary conditions. The development of flexural strain at the point of contact is controlled purely by the initial generation of waves. This wave-controlled phenomenon can be explained by the early occurrence of the maximum flexural strain at the point of impact in advance of the arrival of reflected waves from the plate boundary. Thus, only the size of the ice sphere, impact velocity, temperature, and panel thickness are relevant to the prediction. The model for predicting flexural strain utilises considerably less computation time than numerical models. The derivation of expressions for predicting maximum strains involved investigations into the change in contact force and radius of the contact area with time. Integrating these relationships gave predictions of the maximum curvature and surface strains on the glass panel. The model has been validated by comparison of the simulated and measured quantities.

The Effects of 5 km Interval Running on the Anterior Cruciate Ligament Strain and Biomechanical Characteristic of the Knee Joint: Simulation and Principal Component Analysis

Interval running methodologies simulate competition and training conditions, with the aim of enhancing an athletes’ ability to cope with constant deceleration, acceleration, and sudden changes in direction, as associated athletic and performance challenges. Fifteen male athletes were recruited in this study, in which the anterior cruciate ligament was modeled as a nonlinear elastic passive soft tissue in OpenSim 4.2. Participants completed 5 km interval running training on a treadmill. Before and after the interval running, kinematics, kinetics, and electromyography activity of the lower leg during the cutting maneuvers were collected simultaneously. After running training, the anterior cruciate ligament strain demonstrated a decreasing trend when performing unexpected cutting maneuvers. Principal component analysis showed significant differences in knee moments during abduction-adduction; knee angles in flexion-extension, external-internal rotation, and abduction-adduction, as well as knee contact forces in the sagittal and coronal planes. The findings of the study highlight that athletes generate greater adduction moment at the onset of the cut, followed by greater abduction moment towards the end of the cut, which may have a substantial impact on the anterior cruciate ligament loading. Furthermore, athletes need to be mindful of changes in coronal plane contact forces.

Characterization of Microscopic Damage Evolution of Functional Groove in Cageless Bearings

Bearings with partial function grooves as cageless bearings related to magnetic floating bearing protection have characteristics, such as fast offsetting of the impact force caused by rotor fall, and they gradually become important parts of ultra clean and cryogenic transportation systems. However, the functional failure mechanism of the bearing, which is caused by functional groove wear, is not clear. Therefore, this paper establishes a force–motion intrinsic model of particles inside the functional groove, which is based on the discrete element method, which it itself combined with the functional groove damage evolution trend analysis. Then, a hyper-quadratic surface model of inter-particle contact is established to simulate the time-varying friction coefficient of the functional groove by combining particles of different sizes to form particle clusters. Additionally, as the boundary condition, EDEM is used to solve the contact motion state of rolling element rolling through the functional groove for one week to obtain the overlap between particles and contact force change law. The results show that the wide side of the functional groove wears more seriously than the narrow side, and the rolling element leaves the functional groove with more impact than when it enters the functional groove, and the functional groove wears more seriously. In this paper, through the study of local functional groove wear of cageless ball bearing, we propose to characterize the damage extension of functional groove by using the number of particle fracture and motion trend in discrete element method, and this study provides theoretical guidance for the design of cageless bearings.

Can static optimization detect changes in peak medial knee contact forces induced by gait modifications?

Medial knee contact force (MCF) is related to the pathomechanics of medial knee osteoarthritis. However, MCF cannot be directly measured in the native knee, making it difficult for therapeutic gait modifications to target this metric. Static optimization, a musculoskeletal simulation technique, can estimate MCF, but there has been little work validating its ability to detect changes in MCF induced by gait modifications. In this study, we quantified the error in MCF estimates from static optimization compared to measurements from instrumented knee replacements during normal walking and seven different gait modifications. We then identified minimum magnitudes of simulated MCF changes for which static optimization correctly identified the direction of change (i.e., whether MCF increased or decreased) at least 70% of the time. A full-body musculoskeletal model with a multi-compartment knee and static optimization was used to estimate MCF. Simulations were evaluated using experimental data from three subjects with instrumented knee replacements who walked with various gait modifications for a total of 115 steps. Static optimization underpredicted the first peak (mean absolute error = 0.16 bodyweights) and overpredicted the second peak (mean absolute error = 0.31 bodyweights) of MCF. Average root mean square error in MCF over stance phase was 0.32 bodyweights. Static optimization detected the direction of change with at least 70% accuracy for early-stance reductions, late-stance reductions, and early-stance increases in peak MCF of at least 0.10 bodyweights. These results suggest that a static optimization approach accurately detects the direction of change in early-stance medial knee loading, potentially making it a valuable tool for evaluating the biomechanical efficacy of gait modifications for knee osteoarthritis.

Impact of Radiocapitellar Interposition Arthroplasty on Ulnohumeral Joint Biomechanics.

Radial head excision has been shown to increase contact pressures within the ulnohumeral joint. Radiocapitellar interposition arthroplasty with the use of a soft tissue graft is an alternative for the treatment of isolated radiocapitellar arthritis or with failure of radial head replacement. We investigated contact pressures and contact area within the ulnohumeral joint after radial head excision (RHE) compared to radiocapitellar interposition arthroplasty with dermal autograft (RCIA). Six fresh-frozen cadaver elbows were tested on a custom dynamic elbow frame. A pressure sensor was inserted into the intact elbow joint, and mean contact pressure, peak contact pressure, contact area, and force within the ulnohumeral joint were recorded at 0°, 30°, 60°, 90°, and 120° of flexion as a valgus load was applied to the elbow. The radial head was then excised and specimens were retested. Finally, a dermal graft matched to the size of the resected radial head was inserted in the radiocapitellar space and the specimens were tested a third time. At 90° of flexion, contact pressure within the ulnohumeral joint was significantly lower with RCIA compared with RHE (110.8 kPa vs. 216.8 kPa.; P = 0.013). Mean peak contact pressure was also significantly lower with RCIA compared with RHE at 90° (279.4 vs. 626.7 kPa; P =0.025). No statistically significant differences were seen in mean contact area or force between the three testing conditions at any flexion position. RCIA with a dermal graft reduced contact pressures within the ulnohumeral joint compared to radial head excision at 90° of flexion without a significant change in contact area or contact force.

Numerical Investigation of Aggregate Segregation of Superpave Gyratory Compaction and Its Influence on Mechanical Properties of Asphalt Mixtures

In the laboratory, there are significant differences in mechanical properties of asphalt mixtures with the same size gradation and asphalt binder, which is not conducive to evaluating and designing the pavement structure accurately. Meanwhile, the influence of aggregate segregation in height on the mechanical properties of asphalt mixtures is unclear. This study developed a new method to generate a three-dimensional (3D) model of the real composition and aggregate shape to characterize the aggregate segregation during Superpave gyratory compaction (SGC). The graphic segregation index (GPSI) is employed to assess the mixing degree of coarse aggregate and asphalt mortar within spatially variable specimens [i.e., Superpave-13, stone mastic asphalt (SMA-13), and open-graded asphalt friction course (OGFC-13) mixtures]. The results reveal that asphalt mixtures with different aggregate gradations have different compaction characteristics. For example, the increase of fine aggregates may reduce the strain energy and the average contact force during compaction. The compaction curves of the three gradation types were very different, which is attributed to different packing states and gyratory numbers. Aggregate segregation has a significant effect on micromechanical behavior. Specifically, the contact number and the proportion of strong contact force change considerably with height. In terms of segregation degree, the GPSI of OGFC-13 specimens was the highest, and the volume change of its fine particles created a leakage zone after the compaction. Additionally, this segregation had an increasing tendency with gyration numbers, and it was influenced by gradation types. Furthermore, the uniaxial compressive strength and cohesion of the Superpave-13 specimen decreased, whereas the friction angle increased with the increase of GPSI.

Mechanical Properties of In Situ Loess under Different Combined Water State Macroscopic and Mesoscopic Studies

To study the mechanisms of strong and weak combined water on the mechanical properties of in situ loess deformation and strength, triaxial compression tests with different combined water contents were carried out to in situ loess in a region of Shaanxi Province, China. The influence on the mechanical properties and structural variation of in situ loess was discussed from the perspective of combined water. The endogenous factors of deformation and strength properties of in situ loess in triaxial tests were investigated from a fine-scale perspective by combining numerical simulations of discrete elements. The results show that the failure specimen under the condition of strong combined water has an obvious shear band and shows brittle failure. The failure mode of soil samples under weak combined water is characterized by no obvious cracks and bulging, which is plastic failure. The water content at the boundary of strong and weak combined water is the boundary to distinguish weak and strong strain hardening. With the increase of combined water, the ultimate strength, the structural strength, and structural parameters decrease, and the initial structural parameters decrease nonlinearly, resulting in the decrease of soil structure and deformation resistance. Weak combined water is the main factor affecting soil structure. The particle flow numerical simulation explains the whole process of triaxial test of in situ loess from macro to meso and explains from the meso perspective that the structural strength change of intact loess under different combined water contents is mainly caused by the change of contact force and pore between particles.

Effect of Ambient Temperature on Current Collection Quality in Pantograph–Catenary Interaction

This paper investigates the effect of the ambient temperature change on the dynamic interaction between pantograph and catenary (PAC). Thermal expansion/contraction of the components of the overhead contact system (OCS) is considered. Simulation results show that the thermal stress has a much greater influence on the longitudinal positioning of the contact wire than on the horizontal and vertical positioning. When ambient temperature reduces to [Formula: see text] from design temperature of [Formula: see text]C, the maximum longitudinal displacement of the positioner can reach as high as 301 mm, while the maximum horizontal and vertical displacement of the positioner is within 4[Formula: see text]mm. The change of ambient temperature results in the uneven tension distribution of the contact wire, especially near the central anchor. With the increase in temperature, the tension of contact wire decreases; vice versa, with the decrease in temperature, the tension of contact wire increases. For nine-span OCS, the tension change caused by ambient temperature change shall not exceed 2%. The variation of ambient temperature also leads to the deterioration of current collection quality. It is shown that a decreasing ambient temperature results in more significant changes in contact force, close to 5%. An increasing ambient temperature environment leads to a higher uplift of pantograph, close to 30%.

The analysis of frictional rolling contact behavior and key affecting factors on uneven wear in a switch panel

To analyze the wheel-rail frictional rolling contact solutions and uneven wear in a switch panel, the wheel-rail frictional rolling contact model based on explicit integral algorithm considering coupling effect of structural vibration and contact mechanics, arbitrary contact geometry and nonlinear material is established. Then the wheel-rail explicit dynamics theory, unrepeatable saturated design, wear prediction method and data statistical processing methods are integrated as a method to figure out the key affecting factors, recognizing the influence of key factors on wheel-rail contact behavior and uneven wear in switch panel, including the contact force, the instantaneous and drastic changes of size, stress and microslip in contact patch and the distribution and magnitude of wear. The results of numerical simulations can provide guidance for investigation of contact mechanism and understanding of rail maintenance in switch panel.

Study of shear induced stress redistribution in gap-graded soils by discrete element method

Combined effects of shear stress ratio, density, and fines content on stress redistribution during shearing and their implications for internal instability were investigated in this study using the discrete element method. The widely used stress reduction factor was modified in this study by introducing the Voronoi cell to account for the volume change during shearing. The response of stress in finer fraction and its relative contribution to the overall stress of the specimen as evaluated by the established stress reduction factor showed inconsistent trends. The relationship between the mean stress in finer fraction and the shear stress ratio of the entire specimen was found to be dependent on FC and density during pre-peak stress condition. At post-peak, the relationship was only governed by the soil load-bearing skeleton. The stress redistribution of dense transitional soils exhibited the most pronounced changes. The mean stress in finer fraction reached the peak and steady values quicker than the shear stress ratio. This could be attributed to the decrease in critical hydraulic gradient under a high shear stress ratio, as evidenced from previous experimental works. These nonsynchronous performances could be explained by the shift of contact force and volume change.

Failure Mode Analysis of Bridge Pier Due to Eccentric Impact Based on Separation of Pier and Beam

By considering the near-field vertical seismic spectrum and calculating the change in vertical contact force between the main beam and the pier, the possible vertical separation contact condition of a bridge is deduced. By calculating the extreme value of the pier–beam vertical contact force and the longitudinal deformation of the pier under the structural separation, the influence of the separation on the failure of the pier is determined. Separation increases the risk of pier failure under compression, bending, and shear, and different separation times lead to different longitudinal responses from the pier, and the first failure mode is different. Therefore, it is of great significance to reasonably design bridges near faults.

A Stability and Safety Control Method in Robot-Assisted Decompressive Laminectomy Considering Respiration and Deformation of Spine

Robot-assisted decompressive laminectomy is a new strategy in clinical applications. However, a stable contact force between the bone-cutting device and lamina is needed to keep it working correctly, which may be affected by respiration and deformation. The surgeon can adapt to this dynamic process quickly, but the robot could cause a considerable force that may damage the patient. This paper proposes a compensation control method based on a respiration-spine model to first improve the stability of the contact force. The model is established based on human morphology and ventilator parameters for anaesthetised patients. The control method is a combination of a surgery sleeve and active fuzzy control to improve the robustness of the robot. The control of the sleeve is related to the thickness of the bone layer, which can be calculated from the image. Furthermore, the lower boundary of the lamina in the CT image is extracted as a safety constraint that can protect the spinal nerves. Finally, an experiment is conducted to verify the safety constraint and compare the changes in contact force with or without the control method. The statistical experiment shows that the control error is 2.47 N without the force control method, while the force control error is 0.223 N when the target control force is 2 N. The robot will hover on the surface of the spine after completing the laminectomy of the planned area. These results show that the robot can be controlled safely and stably. Note to Practitioners—The purpose of this paper is to propose a stable and safe control method for lamina grinding robots under the influence of breathing and deformation factors. Most previous research only considered one of the two factors, and both factors are considered in this paper. Unlike the surgeon, who has the ability to adapt to physiological movements, the robot may cause a considerable force to be exerted on the device, which may damage the patient. Therefore, a controller based on human experience is longitudinally designed, and position constraints are added in three directions. This application can improve the stability and safety of robot-assisted surgery, which may be suitable for remote surgery and can help rural areas solve the problem of a lack of medical resources. Spinal model bone experiments have been completed and will be tested on animals in the future.

Effect of Alteration in Hip Joint Alignment following Total Hip Arthroplasty on Hip Joint Contact Force during Gait

Purpose Investigation of the relationship between changes in hip-joint center and hip loading pre- and post- total hip arthroplasty (THA) is important in evaluating the effect of surgery on motor function. However, few longitudinal studies comparing pre- and post-THA have been reported. The purpose of this study was to determine the effect of changes in hip-joint center pre- and post-THA on the magnitude and direction of hip-joint contact force during the gait cycle, using a patient-specific musculoskeletal model. Methods The simulation program AnyBody was used to create musculoskeletal models incorporating patient specific hip-joint shape and hip-joint center position for 17 patients. The relationship between the displacement distance of the hip-joint center and the amount of change in hip-joint contact force was examined by correlation analysis. Results A decrease in the medial force (p ≤ 0.049) and an increase in the anterior force (p ≤ 0.001) acting on the hip joint were observed during gait post-THA compared to pre-THA. Mediolateral displacement of the hip-joint center post-THA compared to pre-THA was significantly positively correlated with the difference in anterior hip-joint contact force, and negatively to hip-joint medial contact force. Conclusions Longitudinal observations revealed the effects of change in hip-joint center position induced by THA on the hip-joint contact force during gait. Therefore, the change of hip-joint center position during THA can be an important factor for estimating the improvement of motor function following THA.