Contact Force Research Articles

Effect of tibiofemoral alignment on simulated knee contact forces during gait in mechanically and kinematically aligned total knee arthroplasty patients

AbstractThe goal of the study was to apply a musculoskeletal knee model that considers individual tibiofemoral alignment (TFA) and to investigate its effect on knee contact force (KCF) during gait in mechanically (MA) and kinematically aligned (KA) total knee arthroplasty (TKA) patients. Total, medial, and lateral KCF was estimated from pre- and postoperative gait data of TKA patients (MA: n = 26, KA: n = 22). Preoperative KCF was compared between the generic and the adapted model using t-tests and statistical parametric mapping (SPM). The TFA-adapted model was then used to analyze pre- to postoperative differences in MA and KA patients. The factor of TFA increased estimates of KCF during the stance phase and led to higher peak contact forces (3–5%, p < 0.05). SPM analyses of pre- to postoperative KCF revealed no significant differences across the gait cycle, however, postoperative peak KCF was significantly increased in both groups (10–18%, p < 0.05). No group differences were observed when comparing KCF between MA and KA patients. Integrating TFA into the model led to higher estimations of KCF. Applying the adapted model, pre- to postoperative differences in KCF were the same for both TKA groups suggesting that both alignment techniques had comparable effects on knee loading post-TKA.

A general continuous contact force model for contact collisions of soft and hard materials

A general continuous contact force model for contact collisions of soft and hard materials

High-precision Roundness Measuring System for Tungsten Ball Tips with the Diameter of Less than 100 µm

Abstract Tungsten balls with a diameter of less 100 μm can function as probe tips for micro-coordinate measuring machines (CMMs) to measure ultraprecise workpieces with complex features. A high-precision measuring system was developed to evaluate the roundness of self-made tungsten ball tips. The system based on two-point method was composed of two oppositely placed interferometers and a turntable. The turntable rotated the tested ball, and the interferometers measured the variation in radius. A new model based on minimum zone method was proposed to evaluate roundness. The fabrication principle of tungsten balls was introduced and the analysis was conducted on the maximum permissible contact force and bending stress of tungsten ball tips. The elastic mechanism was designed based on the analysis. A ruby sphere with a sphericity of 130 nm was measured to verify the system's effectiveness. Repeated experiments were performed for two tungsten ball tips. Results show the roundness error of tungsten ball-A is between 550.9 and 586.2 nm with a standard deviation of 11.0 nm while tungsten ball-B’s roundness error is between 898.5 and 959.9 nm with a standard deviation of 21.7 nm. The uncertainty is calculated as 144.6 nm. The developed system can stably measure the roundness of tungsten ball tips.

An FBG-based method for load measurement of a cylindrical rolling element bearing

Abstract Contact forces between raceways and rolling elements of a bearing stand as crucial operational aspects defining the bearing’s performance. While monitoring bearing load through load cells or strain gauges on the shaft or housing is feasible, it may not precisely reflect the distributed load transmitted by the rollers directly to the raceways. This paper introduces a method to calculate these contact forces, relying on a linear assumption correlating the loads to the measured strains on the outer race of a bearing. In our research, we conducted both static and dynamic tests on cylindrical roller bearings through simulations and experiments. We designed an experimental test rig to conduct both static and dynamic experiments and utilized FBG optical fiber sensors for contact force measurement in bearings due to their multiple advantages, including high sensitivity, resistance to corrosion and magnetic interference, and ease of installation on the bearing outer race due to their shape and size. Our findings indicate a consistent linear relationship between contact forces and strains measured on the bearing’s outer race. Furthermore, we calculated the linear coefficient K values from three test groups: static tests under simulation study, static tests under experimental study, and dynamic tests under experimental study. The K values obtained from static tests (simulation and experimental studies) and dynamic tests (experimental study) align consistently. Following this, we calculated contact forces in both static and dynamic experiments by multiplying the measured strains with K. Our calculations resulted in an error percentage of less than 2% for static tests and below 5% for dynamic tests, highlighting the accuracy of our approach in determining these contact forces.

Compaction behavior of coarse-grained soil under various vibration frequencies: a DEM study

PurposeThis paper investigates the vibration compaction mechanism and evaluates the impact of vibration frequencies on the stability of coarse-grained soil, aiming to optimize the subgrade filling process.Design/methodology/approachThis study examines the vibratory compaction behavior of coarse-grained soils through indoor vibration tests and discrete element simulations. Focusing on angular gravel (breccias) of varying sizes, the simulations were calibrated using parameters such as Young’s modulus, restitution and friction coefficients. The analysis highlights how particle shape influences compaction, revealing mesoscopic mechanisms that drive macroscopic compaction outcomes.FindingsThis study investigates the influence of vibration frequency on the compaction behavior of coarse-grained soils using discrete element simulation. By analyzing particle contact and motion, the mesoscopic mechanisms driving compaction are explored. The study establishes a positive linear correlation between contact force anisotropy (Cv) and deformation, demonstrating that higher anisotropy leads to greater structural disruption. Additionally, the increase in sliding contact percentage (SCP) at higher frequencies indicates instability in the skeletal structure, driven by uneven contact force distribution. These findings reveal how frequency-induced stress concentration affects the stability and deformation of the soil skeleton.Originality/valueThis research explores the effect of various vibration frequencies on the compaction behavior of coarse-grained soils, examining microscopic interactions to reveal their impact on soil stability and deformation.

Application of Artificial Intelligence Technology for Prompt Diagnosis of Cast Iron Mechanical Properties

Kinetic indentation is widely used to measure physical and mechanical properties of materials as one of the most universal methods for non-destructive testing. This paper uses the latest advances in artificial intelligence and capabilities of the Python programming language libraries allowing to carry out accurate measurements of cast iron hardness based on the data of the material’s micro-impact loading diagram. It has been shown that use of machine learning allows eliminating gross errors and reducing the error of indirect hardness evaluation in several times – down to 10 units according to Brinell HB. It has also been established that formation of additional features for training models (based on traditionally used characteristics: penetration depths, indenter movement speed and contact forces at certain points in time) has a positive effect on the accuracy of measurements, but amount of measurements should also be optimized. Feasibility of effective use of machine learning to evaluate hardness has been demonstrated by comparing of calculated hardness values with data obtained with standard testing methods. Advantage of the developed testing method is the fact that the developed algorithms can be used for prompt diagnostics of cast iron hardness using existing equipment. It is appropriate to extend the proposed approach for determination of other mechanical properties of cast iron: yield strength, strain hardening index, creep, relaxation, determined by indentation methods.

Significance of the local largest bipolar voltage for the optimized ablation strategy using very high-power short duration mode.

Very high-power short-duration (vHPSD) ablation creates shallower lesions, potentially reducing efficacy. This study aims to identify factors leading to insufficient lesions during pulmonary vein antral isolation (PVAI) with vHPSD-ablation and to develop an optimized PVAI strategy using this technology. PVAI was performed on 41 atrial fibrillation patients using vHPSD-ablation (90 W/4 s). Lesion parameters were recorded and analyzed to identify predictors of insufficient lesions. An optimized PVAI strategy, based on these predictors, was tested in subsequent 42 patients. In total, 3099 RF-applications, including 103(3.3%) insufficient lesions, were analyzed. First-pass PVAI was achieved in 19/40(47.5%) right PVs and 24/41(58.5%) left PVs. Multivariate analysis identified significant predictors of insufficient lesions: local largest bipolar voltage (Bi-V), average contact force, baseline impedance, impedance drop, temperature rise, inter-lesion distance (ILD), and anatomical location (carina or not). An ILD:4-6 mm increased the risk of insufficient lesions 2.2-fold, and lesions at the carina increased it 3.6-fold for both ILD < 4 mm and ILD:4-6 mm. Local largest Bi-V was the strongest predictor for insufficient lesions. The optimized PVAI approach, utilizing vHPSD-ablation with an ILD < 4 mm in non-carinal areas with Bi-V < 4 mV, and high-power ablation-index guided ablation (HPAI, 50 W, ablation-index:450-550) in remaining areas, achieved first-pass PVAI in 92.7% of right PVs and 88.1% of left PVs, using vHPSD-ablation in approximately 65% of total RF-applications. The optimized PVAI achieved significantly higher first-pass PVI rate (p < .0001) with shorter ablation time (p = .04). Appropriate use of vHPSD and HPAI, based on local largest Bi-V and anatomical information, may achieve high first-pass PVAI rates in shorter ablation time with minimal energy delivery.

The Asymmetries in Straight Jumps on the Trampoline Under Different Sensory Conditions

The trampoline is a popular piece of sports equipment both for recreational use and for Olympic trampolining as a competitive sport. Maintaining body position during jumps is influenced by sensory inputs (visual, auditory, and somatosensory) and symmetrical muscle activity that help athletes to perform consecutive jumps as vertically as possible. To evaluate the effects of these inputs, 15 male and 15 female students (with an average age of 24.4 years, height of 174.3 cm, and average weight of 69.7 kg) performed 10 consecutive straight jumps under four sensory conditions: (1) looking at the edge of the trampoline, (2) without sight, (3) without hearing, and (4) without hearing or sight. Using insoles with integrated pressure sensors (Pedar®, novel GmbH, Munich, Germany), the contact forces on the trampoline during the jump were measured separately for the left and right feet. The results showed that the lack of visual input significantly shortened flight times and increased the asymmetry of ground reaction forces between the left and right legs. For example, in the second series without vision, the average normalized force difference between the legs increased by 0.33 G compared to the control condition. An ANOVA revealed significant differences in the ground reaction forces between sensory conditions, with vision playing a key role in maintaining body control. These results provide practical insights for coaches looking to improve jumping performance and address asymmetries during training by focusing on sensory feedback strategies.

Design and analysis of a multi-motion self-balancing lower limb exoskeleton based on flat terrain

In this study, a multi-motion self-balancing lower limb exoskeleton is designed to provide crutches-free rehabilitation training for quadriplegic patients on flat terrain without hand support. First, based on the biomechanical characteristics of the human body and the bionic mechanism configuration of the human lower limb, an exoskeleton with a full-drive series-parallel hybrid structure was established. Secondly, the D-H method, geometric method and Newton iteration method were used to establish the forward and reverse kinematic solutions of the exoskeleton. In addition, the static self-balancing principle was used to complete the planning of the multi-motion self-balancing trajectory. Finally, in order to verify the effectiveness of the proposed method, some numerical simulations were performed in this paper. The theoretical trajectories of the waist, ankle joint and foot center were compared with the simulated trajectories. The research results show that the forward and reverse kinematics model of the exoskeleton is feasible. Under the condition of contact force parameters, the exoskeleton has the ability of multi-motion self-balancing walking on flat terrain.

Analysis and Calculation of Cross-contact Force between Strands of Multi-layer Conductor

Abstract As a key component of the transmission line, the inter-layer cross-contact force of the internal strand is an important factor affecting the mechanical properties of the conductor. In this paper, the cross-contact characteristics between the strands of multi-layer conductors are analyzed. According to the relationship between the contact force and the contact distance between the strands, the finite element simulation of different material strands of different conductors at different cross angles is carried out. Through the analysis, it can be seen that the cross angle between the strands and the material of the strands have a significant impact on the contact force. Then, based on the existing Hertz contact theory model, the relationship between the contact force and the contact distance between the strands is modified, and the contact force and contact distance models suitable for different cross angles of the conductor strands are obtained, that is, the modified Hertz contact model. According to the simulation results, combined with the modified Hertz contact model, the contact force coefficient between the strands is fitted, and the calculation formula of contact force and contact displacement is proposed. The formula can be applied to the calculation of contact force at any intersection angle between strands. The calculation formula provides theoretical support for the accurate structural calculation of the conductor, which is helpful to the analysis and calculation of the contact friction between the strands.

Structural Optimization Analysis of Combined Sealing Ring

Abstract In this paper, the effect of the contact forces of the combined sealing ring by the pre-compressibility of the O-ring seal and the working pressure is studied. The influence of the structural parameters (width, thickness and chamfer) of the friction ring on the contact forces of the combined sealing ring is analyzed. The results show that, in the combined seal, it is not that the higher the pre-compressibility, the higher the sealing efficiency. Under certain working conditions, the chamfer of the friction ring increases, the contact forces of the friction ring decreases; the thickness of the friction ring increases, the contact forces of the friction ring is almost unchanged; The contact force increases with the increase of the width of the friction ring. Under the condition of a given medium pressure of 25 MPa and a compressibility of 22.5%, the optimal values of friction rings L, R, and H and three contact forces and contact forces F under the corresponding conditions are calculated by the optimization algorithm.

Multi-body dynamic assessment of vessel-floater accessibility for floating wind

Abstract The floating wind industry faces several challenges in the road map to full maturity of commercial-scale floating projects. Accessing the floating offshore wind turbines poses larger risks due to the added degrees of freedom of the platform, with respect to bottom-fixed technology. When a vessel approaches, the platform’s motion leads to the introduction of multi-body dynamic effects. This work deals with the modeling of the vessel-platform dynamics for the VolturnUS-S 15MW platform and IEA15MW Reference Wind Turbine and a generic Crew Transfer Vessel (CTV) by means of performing a fully coupled assessment. The hydrodynamic properties are computed by solving the multi-body radiation-difraction problem. The inertial and hydrodynamic properties are included in an OrcaFlex model to perform a time-domain analysis under several sea states. A P-controller represents the helmsman pushing the vessel against the access point. The contact forces are modeled using a linear fender system to represent slip-and-stick events during the CTV’s push-on maneuver. The resulting relative motions are analyzed, and industry-typical limits are considered to quantify accessibility levels. The results show that peak wave period and wave heading play a major role in the accessibility scores.

Relationship Between Stride Mechanics and Shoulder Distraction Force in Collegiate Softball Pitchers

Background: Softball pitchers experience high shoulder distraction forces, and increased stride lengths are associated with upper extremity pain. Therefore, it is important to consider the influence of stride mechanics on shoulder distraction force in softball pitchers. Purpose: To determine the relationship between stride mechanics and shoulder distraction force in collegiate softball pitchers. Study Design: Descriptive laboratory study. Methods: A total of 63 collegiate softball pitchers (age, 20.1 ± 1.3 years; height, 173.3 ± 7.4 cm; weight, 79.7 ± 11.7 kg) were included in this study. Each pitcher threw 3 maximum-effort fastballs for a strike, and kinematic data were collected using an electromagnetic tracking system with a sampling frequency of 100 Hz. A forward regression analysis was used to determine the relationship between stride parameters at foot contact (stride length, stride-foot progression angle, and stride-foot position) and shoulder distraction force. Results: Regression analysis revealed a significant and positive relationship between stride length and shoulder distraction force ( R2 = 0.11; F(1, 61) = 7.338; P = .009), where stride length accounted for 11% of the variation in shoulder distraction force. Specifically, shoulder distraction force increased by 0.94 N/kg for every 10% increase in stride length normalized as a percentage of body height. Conclusion: A positive relationship was found between stride length and peak shoulder distraction force during the acceleration phase of the softball pitch. Alternatively, no relationship was found between the other stride parameters (stride position and stride-foot progression angle) and shoulder distraction force. Clinical Relevance: Coaches should be aware of the potential negative implications of increasing stride length during softball pitching. Although prior research has shown that greater stride length may positively affect performance, this may also increase stress at the shoulder.

Multi-layered morphing soft structure with high-performance embedded electrothermal artificial muscles along with touch and temperature sensors

Abstract In this paper, we present a novel multilayered morphing structure, having similar topology resembling the structures found in nature to grasp delicate objects effectively as well as sense contact force and temperature. The structure consists of two actuation layers, two U-shaped cooling channel layers, piezoelectric based touch sensors and temperature sensors. Employing shape memory alloy (SMA) spring actuators for bending and twisted and coiled polymer fishing line with nichrome (TCPFL NMC) artificial muscles for antagonistic return, the soft silicone-based composite skin exhibits unique capabilities of large bidirectional movement, avoid rigid passive springs for return motion, soft grasping, safe interaction with humans, and ease fabrication. The SMA (0.38 mm wire diameter) serves as relatively fast actuating muscle and the TCPFL NMC (0.8 mm fiber diameter) as a slow actuating (considering mainly heating cycle), which was programmed/designed to mimic the fast and slow twitching muscles found in nature. Bending and return operations of skin samples of length 100 mm and thickness of 9 mm, with three different widths 20 mm, 25 mm, 30 mm, were experimentally studied. The 25 mm wide multilayered soft skin demonstrated cyclic actuation with a maximum bending angle of ∼70°, which was attributed due to the active cooling. The fluidic channels for active cooling were fabricated using 3D printed PVA tubes, casting within the silicone in a mold and subsequently dissolving in a circulating water. The study also included the integration and voltage response of mini-piezodisk sensor PIC255 having a diameter of 2 mm and thickness of 0.15 mm, which was embedded at different depths within the silicone (on the surface, 1 mm depth and 2 mm depth). The multilayered soft skin was also able to detect the temperature of the object during grasping, suggesting its potential application as a soft gripper in robotic systems.

Nonlinear vibration characteristics and damage detection method of blade with breathing fatigue crack

In aero-engine, blades operate under harsh conditions for extended periods, which makes them highly susceptible to fatigue cracks. The localized and nonlinear structural changes caused by blade crack lead to complex vibration characteristics that are not well understood, posing challenges to the identification of these cracks. This paper proposes an approach for identifying breathing fatigue crack in compressor blade, leveraging the nonlinear features induced by the cracks. Crucial sensitive characteristics are extracted and a crack indicator for accurate crack detection is defined. Initially addressing the typical morphology of fatigue breathing cracks, a dynamic model of blade with cracks is developed to analyze their impact on the natural frequencies. Nonlinear contact forces are introduced to characterize the "breathing" effect of the fatigue crack, allowing for the determination of the harmonic distribution patterns in the blade's vibration response under various excitation conditions. A finite element model is then established considering the crack morphology, by adopting the contact element. Based on that, the nonlinear response characteristics associated with the blade's primary, sub-harmonic, and super-harmonic resonances are explored. A crack-sensitive parameter is defined and extracted from the nonlinear responses, under different crack propagation stages. At last, effectiveness and reliability of the defined parameter for identifying cracks is validated through a vibration fatigue test.

Optimization Acceleration and Contact Force of Space Slider-Crank Mechanism with Spherical Clearance Joints

Optimization Acceleration and Contact Force of Space Slider-Crank Mechanism with Spherical Clearance Joints

Fabrication of Cu-Doped Diamond-like Carbon Film for Improving Sealing Performance of Hydraulic Cylinder of Shearers

During shearer operation, the piston rod is susceptible to wear from the invasion of pollutants, thus ruining the sealing ring in the hydraulic cylinder. This work attempts to conduct a systematic investigation of Cu-doped diamond-like carbon (Cu-DLC) film to improve the seal performance. The failure process of the cylinder was analyzed, and relevant parameters were determined. Several Cu-DLC films were deposited on the substrate of the piston rod in a multi-ion beam-assisted system, and their structures and combined tribological performances were investigated. The hardness of the film ranges from 27.6 GPa to 14.8 GPa, and the internal stress ranges from 3500 MPa to 1750 MPa. The steady-state frictional coefficient of the film ranges from 0.04 to 0.15; the wear rate decreases first and then increases, and it reaches its lowest (5.0 × 10−9 mm3/N·m) at 9.2 at.% content. a:C-Cu9.2% film presents optimal combined tribological performances in this experiment. The modification mechanism of Cu-DLC film for the seal performance may come from the synergistic effects of (i) the contact force and friction-heat-induced film graphitization, (ii) Cu doping improves the toughness of the film and acts as a solid lubricant, and (iii) the transfer layer plays a role in self-lubrication.

Effect of substrate stiffness on interfacial Schallamach wave of flexible film/substrate bilayer structure: Cohesive contact insight

As the critical feature of the stick-slip for soft materials, the interfacial Schallamach waves of flexible composite structures are essential for smart tactile sensors to realize sliding perception. Herein, the Schallamach waves of polydimethylsiloxane film/substrate bilayer structures with three substrate stiffnesses regulated by porosities are investigated by setting up in-situ sliding tests and establishing finite element models with mixed-mode cohesive contact. Inhomogeneity in microcontact stiffness disrupts the continuity and synchronization of the Schallamach waves, resulting in non-periodic fluctuations in the contact force. The buckling phenomenon of the film structure marks the transition from stick to slip. This buckling induces a shift at the crack front from normal compressive stress to tensile stress, leading to mixed-mode damage.

A comparative study of the effect of facet tropism on the index-level kinematics and biomechanics after artificial cervical disc replacement (ACDR) with Prestige LP, Prodisc-C vivo, and Mobi-C: a finite element study

IntroductionArtificial cervical disc replacement (ACDR) is a widely accepted surgical procedure in the treatment of cervical radiculopathy and myelopathy. However, some research suggests that ACDR may redistribute more load onto the facet joints, potentially leading to postoperative axial pain in certain patients. Earlier studies have indicated that facet tropism is prevalent in the lower cervical spine and can significantly increase facet joint pressure. The present study aims to investigate the changes in the biomechanical environment of the cervical spine after ACDR using different prosthese when facet tropism is present.MethodsA C2-C7 cervical spine finite element model was created. Symmetrical, moderate asymmetrical (7 degrees tropism), and severe asymmetrical (14 degrees tropism) models were created at the C5/C6 level by adjusting the left-side facet. C5/C6 ACDR with Prestige LP, Prodisc-C vivo, and Mobi-C were simulated in all models. A 75 N follower load and 1 N⋅m moment was applied to initiate flexion, extension, lateral bending, and axial rotation, and the range of motions (ROMs), facet contact forces(FCFs), and facet capsule stress were recorded.ResultsIn the presence of facet tropism, all ACDR models exhibited significantly higher FCFs and facet capsule stress compared to the intact model. In the asymmetric model, FCFs on the right side were significantly increased in neutral position, extension, left bending and right rotation, and on both sides in right bending and left rotation compared to the symmetric model. All ACDR model in the presence of facet tropism, exhibited significantly higher facet capsule stresses at all positions compared to the symmetric model. The stress distribution on the facet surface and the capsule ligament in the asymmetrical models was different from that in the symmetrical model.ConclusionsThe existence of facet tropism could considerably increase FCFs and facet capsule stress after ACDR with Prestige-LP, Prodisc-C Vivo, and Mobi-C. None of the three different designs of implants were able to effectively protect the facet joints in the presence of facet tropism. Research into designing new implants may be needed to improve this situation. Clinical trials are needed to validate the impact of facet tropism.

Microscopic simulation on triaxial compression creep of rockfill based on subcritical crack propagation theory

Over time, natural cracks within particles propagate under tensile stress, leading to the delayed breakage of these particles, which significantly contributes to the time-dependent deformation of rockfill materials. In this study, a delayed strength model for spherical particles with virtual cracks is proposed using subcritical crack propagation theory and validated through indoor single-particle creep tests. Based on the model, particles are represented as ideal spheres in the context of triaxial compression creep simulations for rockfill, with special attention to particle size effects, discreteness, and temporal factors. The combined influence of long-term strength and maximum contact force is crucial in determining the delayed particle breakage. Comparative analysis with indoor triaxial creep tests demonstrates that the Discrete Element Method (DEM) simulations accurately model the creep deformation phenomena related to delayed particle breakage in rockfill. Furthermore, statistical analysis indicates that a minor fraction of delayed particle breakage has a negligible impact on the temporal distribution of the Normalized Maximum Contact Force (NMCF).