Increase In Contact Force Research Articles

Influence of femoral anteversion angle and neck-shaft angle on muscle forces and joint loading during walking.

Femoral deformities, e.g. increased or decreased femoral anteversion (AVA) and neck-shaft angle (NSA), can lead to pathological gait patterns, altered joint loads, and degenerative joint diseases. The mechanism how femoral geometry influences muscle forces and joint load during walking is still not fully understood. The objective of our study was to investigate the influence of femoral AVA and NSA on muscle forces and joint loads during walking. We conducted a comprehensive musculoskeletal modelling study based on three-dimensional motion capture data of a healthy person with a typical gait pattern. We created 25 musculoskeletal models with a variety of NSA (93°-153°) and AVA (-12°-48°). For each model we calculated moment arms, muscle forces, muscle moments, co-contraction indices and joint loads using OpenSim. Multiple regression analyses were used to predict muscle activations, muscle moments, co-contraction indices, and joint contact forces based on the femoral geometry. We found a significant increase in co-contraction of hip and knee joint spanning muscles in models with increasing AVA and NSA, which led to a substantial increase in hip and knee joint contact forces. Decreased AVA and NSA had a minor impact on muscle and joint contact forces. Large AVA lead to increases in both knee and hip contact forces. Large NSA (153°) combined with large AVA (48°) led to increases in hip joint contact forces by five times body weight. Low NSA (108° and 93°) combined with large AVA (48°) led to two-fold increases in the second peak of the knee contact forces. Increased joint contact forces in models with increased AVA and NSA were linked to changes in hip muscle moment arms and compensatory increases in hip and knee muscle forces. Knowing the influence of femoral geometry on muscle forces and joint loads can help clinicians to improve treatment strategies in patients with femoral deformities.

Acoustic attenuation coefficient measurement in extreme environments: Experimental characterization of uncertainty in multiple-reflection method

Measuring acoustic properties in extreme environments, involving hazardous chemical samples or temperature above 50ºC or below 0ºC, is challenging yet crucial for understanding waveform interactions with materials, with applications in fields like non-destructive testing (NDT) and medical applications. Multiple-reflection methods (MRM), using a buffer-rod between transducer and sample, offer a solution. Yet, the impact of variables like contact force, buffer-rod size, and surface roughness on the accuracy and precision of MRM measurements remains unvalidated. To address this, we introduce a system and experiments to quantify the accuracy of measurements of acoustic attenuation coefficient. Results demonstrate the substantial impact of contact force on system accuracy and precision, reflected by a decrease in the measured attenuation coefficient at 0.5 MHz from 3.8 to 1.5dB/cm with increasing contact force. Effects of buffer-rod width were less pronounced and supported the theory that a cylindrical buffer-rod with twice the radius of the transducer is sufficient. Interestingly, surface roughness, despite being over 150 times smaller than the wavelength of the acoustic signal, influences measurement accuracy. This study illuminates the crucial role of system factors on measurement accuracy and uncertainty, which will aid optimization of measurements for diverse practical applications.

Biomechanical Evaluation of 4th Generation Minimally Invasive Distal First Metatarsal Osteotomy-Akin Osteotomy Technique on First Ray Articular Contact Properties

Category: Bunion; Basic Sciences/Biologics Introduction/Purpose: Hallux valgus is a common deformity encountered, but remains a complex clinical entity. Fourth generation minimally invasive (MIS) techniques consisting of a percutaneous distal metatarsal transverse osteotomy combined with an Akin osteotomy have been utilized to address mild to severe hallux valgus deformities. Benefits of a MIS approach include improved cosmesis, faster recovery, lower opiate requirement, immediate weightbearing, and favorable outcomes relative to a traditional, open procedure. An understudied area with respect to hallux valgus correction is the effect that osteotomies can have on the articular contact properties of the first ray following correction. Methods: Sixteen paired cadaveric specimens were dissected to include the first ray and tested in a customized apparatus. Specimens were randomized to receive a distal transverse osteotomy translated either 50% or 100% of the width of the first metatarsal shaft. The osteotomy was performed with either a 00or 200 distal angulation of the burr relative to the shaft in the axial plane. Specimens were tested in the intact state and following the distal first metatarsal osteotomy for peak pressure, contact area, contact force and center of pressure at the first metarsophalangeal joint (MTP) and first tarsometatarsal joint (TMT). An Akin osteotomy was then performed on each specimen and peak pressure, contact area, contact force and center of pressure were recalculated. Results: There was a notable decrease in peak pressure, contact area, and contact force across the TMT joint with greater shifts of the capital fragment. However, at 100% translation of the capital fragment, distal angulation of the osteotomy by 200 appears to improve loading across the TMT joint. Addition of the Akin osteotomy at 100% translation also aids in increasing the contact force across the TMT joint. The MTP joint is less sensitive to changes in shifts and angulation of the capital fragment. The Akin osteotomy also leads to increased contact force across the MTP joint when the capital fragment is translated 100%. Conclusion: While the clinical significance is unknown, larger shifts of the capital fragment lead to greater load alterations at the level of the TMT joint than the MTP joint. Distal angulation of the capital fragment and the addition of an Akin osteotomy can aid in reducing the size of those changes. The Akin can lead to increased contact forces at the MTP joint with 100% translation of the capital fragment.

Four-Leg Sustained Dynamic Compression Staple and Screw Generates Superior Lapidus Construct as Compared to Plate and Screw: A Biomechanical Study

Category: Ankle; Basic Sciences/Biologics Introduction/Purpose: Lapidus procedures are frequently used to treat moderate to severe hallux valgus in the setting of first tarsometatarsal instability or arthritis. The push for early weightbearing can lead to nonunion rates reaching 12%. A growing number of surgeons are utilizing orthopedic staples manufactured from NiTiNOL in foot and ankle arthrodesis procedures. These staples are inserted in an “open expanded” state which enables application of sustained dynamic compression (SDC) between bony segments, which can persist even when challenged with joint settling / bony resorption. The biomechanical performance of these devices has not been quantified in the setting of Lapidus procedures. This study determined the optimum SDC staple construct during Lapidus procedures, and to compare their performance to traditional plate and screw construct in an established model. Methods: Lapidus procedures were performed on synthetic bone replicates (Sawbones) using three SDC staple constructs and one static device construct: (1) dorsal four-leg inline SDC staple, (2) dorsal four-leg inline SDC staple with medial two-leg SDC staple (3) dorsal four-leg inline SDC staple with plantar medial-distal to lateral-proximal cannulated screw and (4) dorsomedial plate and distal dorsal to proximal plantar cannulated screw (FigA). Samples underwent four-point bending with calibrated servo- hydraulic machine (MTS). Max load and construct stiffness was calculated. Interfragmentary contact force, area, and pressure was measured with pressure sensor (Tekscan) and joint plantar gap measurements were completed with 3D motion capture system (Motion Analysis). Testing consisted of stepwise loading to 1, 2, and 3mm of crosshead displacement. For brevity, only data from 3mm displacement test are included herein. Data were analyzed with one-way ANOVA with Dunnett’s post hoc test (N=5/group). Results: The four-leg inline staple + two-leg staple and the four-leg inline staple + screw groups exhibited a 2.5x (p=0.03) and 7.5x (p <.001) increase in joint contact force as compared to the plate + screw group, respectively (FigB). The four-leg inline staple + two-leg staple and the four-leg inline staple + screw groups demonstrated a 3.5x (p=0.002) and 6.6x (p <.001) increase in joint contact area as compared to the plate + screw group, respectively (FigC). The four-leg inline staple + screw group exhibited a 65.1% reduction in plantar gap as compared to the plate + screw group (p=.039, FigD). Conclusion: The four-leg inline staple + screw group exhibited the optimal Lapidus construct biomechanical properties (greatest joint contact force, greatest joint contact area, and least plantar gap). The biomechanical testing performed herein was undertaken to simulate loading akin to early post-operative weight bearing. These data highlight the ability of the four-leg SDC NiTiNOL staple in combination with a static screw to provide meaningfully increased joint compression, uniformity of joint compression, and decreased construct motion as compared to the standard plate + screw construct that is frequently used clinically.

Effects of Crosswind on Pantograph–Catenary Wear Using Nonlinear Multibody System Dynamic Algorithms

In this study, a multibody system (MBS) computational framework is developed to determine the exact location of the contact point and wear prediction resulting from the pantograph–catenary interaction. The railroad vehicle models in the MBS computational framework comprise rigid-body railroad vehicles, rigid-body pantograph systems, and flexible catenary systems. To avoid incremental rotation, the nonlinear finite element absolute nodal coordinate formulation is used to model a flexible catenary system in the MBS computational framework. To avoid co-simulation processes, the rigid-body railroad vehicle and the pantograph and flexible catenary systems were integrated into the MBS algorithms. The pantograph–catenary interaction is modeled using an elastic contact formulation developed to include the effect of pantograph–catenary separation and sliding contact. The proposed MBS approach evaluates the location of the contact point, contact force, and normal wear rate (NWR) from the mechanical and electrical contributions. This investigation considers the vibration caused by a crosswind scenario and determines the numerical result in the case of a steady crosswind scenario. The steady crosswind scenario contains the advantage of pantograph–catenary aerodynamic design, and the vibration of the catenary system remains significant after the excitation of a steady crosswind. In the case of a steady crosswind, the higher value of the steady crosswind effect significantly increases the mean contact force and the NWR from the mechanical contribution. After crosswind load disturbances, the mean contact force decreases, but the standard deviation of the contact force increases. Therefore, the NWR from the electrical contribution increases significantly. However, the total NWR increases with the crosswind velocity.

Effect of particle surface roughness on the flowability and spreadability of Haynes 230 powder during laser powder bed fusion process

The flowability and spreadability of powders are the important factors for additive manufacturing as these two factors directly impact the powder bed packing density, which further affect the quality and mechanical properties of the built components. The flowability and spreadability of powders are dramatically influenced by particle surface roughness as well as the surface energy. The present research attempt to demonstrate the effect of the particle surface roughness on the flowability and spreadability of Haynes 230 powder. The virgin atomized Haynes 230 powder and the atomized powder after ball milling treatment were employed in the present research. The results show that after ball milling, the surface roughness root mean square (rms) of the initial powder increased from 14.87 nm to 42.54 nm and the surface energy of powder increased from 41.19 mJ/m2 to 77.21 mJ/m2, the rest angle of powder increased 30% and the static cohesion index increased from 0.63 to 2.00. According to the calculated Bog coefficient of the two powders (from 2.85 to 15.56), the increase of particle surface roughness leading to the increase of contact force and non-contact force among particles, which were caused by the increased cohesion, leading to the decrease of powder flowability and spreadability as well as the powder bed packing density.

Microscopic mechanical properties and fabric anisotropic evolution law of open graded gravel permeable base under dynamic loading

Under traffic dynamic load, the microscopic mechanical properties and the fabric anisotropic evolution of open graded gravel permeable base directly determine the ability of open graded gravel permeable base to resist external loads and maintain stability in service. Firstly, this article constructed a discrete element numerical model for open graded gravel permeable base, and verified the accuracy of the model through experiments. Then, the effects of gradation, nominal maximum particle size, friction coefficient between aggregate particles, and effective elastic modulus of aggregate on the microscopic mechanical properties, migration behavior, and the fabric anisotropic evolution of open graded gravel aggregate particles were studied in sequence. The research results indicate that the proposed image moving target tracking algorithm based on the three branches twin network can achieve precise tracking and measurement of particle microscopic migration behavior. The method proposed in this study for constructing a three-dimensional surface model of gravel particles based on the principle of multi view averaging and the scale invariant feature transformation algorithm can achieve rapid numerical reconstruction of the three-dimensional morphology of gravel particles at a low cost. The internal aggregate particles of intermediate grade gravel are more likely to form a stable network force chain topology structure that can effectively resist external loads. As the maximum nominal particle size increases, the topological structure of the contact force of gravel particles becomes sparse, and the proportion of strong contact force increases. Increasing the friction coefficient of the contact interface between aggregate particles can to some extent hinder the migration behavior of aggregate particles inside the graded gravel. As the effective elastic modulus of the aggregate increases, the internal network strong contact force chain topology of open graded gravel gradually forms. Under external loads, the migration speed and displacement of the aggregate particles inside open graded gravel decrease, and the degree of internal normal contact force and branch vector anisotropy also decrease.

Proximal fibular osteotomy as a treatment for degenerative meniscal extrusion

Meniscal extrusion treatment is a key focus area for research and clinical study of degenerative knee pathology. The contact forces between the meniscus and the bones cause external displacements of the meniscus that are resisted by the circumferential fibres. The main risk factors for the excessive deformation of the meniscus are meniscal root tears, disruption of the circumferential fibres, knee malalignment and high body mass index. Prior research has shown meniscal extrusion to be a crucial determinant of successful procedures in knee osteoarthritis treatment. The characteristics of medial knee osteoarthritis are an increase in varus malalignment and the load transferred through the medial compartment. This is associated with greatest reduction of the joint space width over the medial meniscus body and an increase in contact forces acting on the meniscus, which results in increased extrusion of the medial meniscal body. Relocating the meniscus in its anatomic position restores the correct distribution of contact force across the knee joint, and prevents destruction of the cartilage. Thus, clinical and biomechanical research focus on improving surgical techniques that allow for diminished meniscal extrusion. Proximal fibula osteotomy is a relatively new technique which involves the removal of a 10 mm piece of fibula, 4–10 cm from the fibular head. This technique has been shown to reduce the knee-lever arm, load transferred through the medial compartment and increase the medial joint space width. We hypothesise that proximal fibular osteotomy could be an effective, simple, and minimally invasive treatment for degenerative meniscal extrusion.

Biomechanical Evaluation of Fourth Generation Minimally Invasive Distal First Metatarsal Osteotomy-Akin Osteotomy Technique on First Ray Articular Contact Properties.

Hallux valgus is a common deformity encountered but remains a complex clinical entity. Fourth-generation minimally invasive surgery (MIS) techniques consisting of a percutaneous distal metatarsal transverse osteotomy combined with an Akin osteotomy have been used to address mild to severe hallux valgus deformities. The benefits of an MIS approach include improved cosmesis, faster recovery, lower opiate requirement, immediate weightbearing, and favorable outcomes relative to a traditional, open procedure. An understudied area with respect to hallux valgus correction is the effect that osteotomies can have on the articular contact properties of the first ray following correction. Sixteen paired cadaveric specimens were dissected to include the first ray and tested in a customized apparatus. Specimens were randomized to receive a distal transverse osteotomy translated either 50% or 100% of the width of the first metatarsal shaft. The osteotomy was performed with either a 0° or 20° distal angulation of the burr relative to the shaft in the axial plane. Specimens were tested in the intact state and following the distal first metatarsal osteotomy for peak pressure, contact area, contact force and center of pressure at the first metatarsophalangeal (MTP) and first tarsometatarsal (TMT) joints. An Akin osteotomy was then performed on each specimen, and peak pressure, contact area, contact force, and center of pressure were recalculated. There was a notable decrease in peak pressure, contact area, and contact force across the TMT joint with greater shifts of the capital fragment. However, at 100% translation of the capital fragment, distal angulation of the osteotomy by 20° appears to improve loading across the TMT joint. Addition of the Akin osteotomy at 100% translation also aids in increasing the contact force across the TMT joint. The MTP joint is less sensitive to changes in shifts and angulation of the capital fragment. The Akin osteotomy also leads to increased contact force across the MTP joint when the capital fragment is translated 100%. While the clinical significance is unknown, larger shifts of the capital fragment lead to greater load alterations at the level of the TMT joint than the MTP joint. Distal angulation of the capital fragment and the addition of an Akin osteotomy can aid in reducing the size of those changes. The Akin can lead to increased contact forces at the MTP joint with 100% translation of the capital fragment. Not applicable, Biomechanical study.

Increase in lateral contact force in the tibiotalar joint during walking in flatfoot patients with reduced stiffness of the spring ligament

Foot deformities in patients with flexible flatfeet, such as the flattened medial arch and hindfoot valgus, affect the force distribution around the tibiotalar joint during walking and increase the risk of secondary injuries. In this study, we developed a multi-segment foot model that could calculate the dynamics around the tibiotalar joint and investigated the difference in the kinetics between normal feet and feet with flatfoot. Ten participants with normal feet and ten with flexible flatfoot were enrolled in the study. The body kinematics, ground reaction force, and foot pressure of the participants were recorded during walking. A five-segment foot model was developed to calculate contact forces in the tibiotalar joint. A flatfoot model was developed by modifying the stiffness of the spring ligaments of a normal foot model. Ground reaction force was applied to the plantar surface of the foot models. The foot models were attached to a full-body musculoskeletal model to conduct inverse dynamic simulations of walking. Participants with flatfoot had significantly greater lateral contact force (1.19 BW vs. 0.80 BW) and more posteriorly located center of pressure (33.7 % vs. 46.6 %) in the tibiotalar joint than those with normal feet (p < 0.05). The average and peak posterior tibialis muscle forces were significantly larger in participants with flatfoot than in those with normal feet (3.06 BW vs. 2.22 BW; 4.52 BW vs. 3.33 BW). The altered mechanics may influence the risk of arthritis.

Are aligners capable of inducing palatal bodily translation or palatal root torque of upper central incisors? A biomechanical in vitro study

ObjectivesPrevious studies have shown that aligners have limited ability to control root movements. The purpose of this study was to investigate which modification geometry and foil thickness are optimal for generating the force-moment (F/M) systems required for palatal root torque of maxillary central incisors.Materials and methodsTooth 11 was separated from a maxillary acrylic model and connected to a movement unit via a 3D F/M sensor. Different modification geometries (crescent, capsular, double-spherical) with different depths were digitally implemented in the labio-cervical region of tooth 11 to induce an increased contact force. We evaluated the F/M systems exerted by aligners with thicknesses of 0.4–1.0 mm. F/M measurements were taken with tooth 11 in the neutral position and during palatal displacement of tooth 11 (simulating its initial clinical movement).ResultsThe mechanical requirements of palatal root torque are a palatally directed force (− Fy) and a palatal root torquing moment (− Mx). These requirements were reliably achieved with modification depths > 0.5 mm. The modification depth and foil thickness had a significant influence on − Fy magnitudes (linear mixed-effect models, p < 0.01). With the 0.75-mm aligners combined with 1.5-mm deep modifications, the palatal root torque range (palTR) started after an initial palatal crown displacement of 0.09, 0.12, and 0.12 mm for the capsular, crescent, and double-spherical modification geometries, respectively.ConclusionsA relatively early start of the palatal torque range (after a 0.1-mm palatal crown displacement) and appropriate − Fy magnitudes were achieved with 0.75-mm-thick aligners containing 1.5-mm deep capsular or crescent pressure regions. Subsequent clinical trials are required to confirm the clinical effects of these modifications.Clinical relevanceIn vitro testing indicated that modified aligners are capable of generating the F/M components required for palatal root torque of upper central incisors.

Quadriceps Muscle and Medial Retinaculum Combinate Effects on Patellar Instability during Knee Flexion

Background: Patellar instability can cause pain and disability. A finite element model of a healthy human knee was performed to analyze the role of quadriceps and medial retinaculum imbalance in patellar instability. Methods: The model was created by matching magnetic resonance and computed tomography images of a normal adult patient’s knee. Muscle force intensities were calculated by static optimization, considering the lower limb muscles, knee movement and the ground reaction during walking. Patellar instability was experimentally generated by progressively uncoupling muscular forces, (90 N versus 110 N), while at the same time, the load derived from the quadriceps was gradually reduced by 20%. Results: This loss in force symmetry of 10 N on the retinaculum may produce a displacement of approximately 7 mm, with an increase in patellar contact forces of approximately 44%. When the quadriceps force is reduced by 10% and the unbalanced medial retinaculum acts together, the displacements are in the order of 14 mm, and the patellar contact forces increase by 84%. Conclusion: A reduced quadriceps force alone is not able to cause significant patellar instability, while an imbalance of forces at the level of the retinaculum could lead to patellar instability, especially when the two effects are combined. A better understanding of joint relationships and muscle synergies can help to improve clinical approaches to patella instability

Reflective Optical Tactile Sensor Based on Fiber Specklegram Analysis With the Capability of Contact Position Identification

A reflective tactile sensing scheme based on fiber specklegram analysis is proposed in this study. The specially designed sensor probe with a reflector inside was 3D printed from elastic material. A section of single mode fiber (SMF) and a section of multimode fiber (MMF) were embedded under the reflector. The light emitted from the SMF is reflected by the reflector and the reflected light illuminates the MMF. At the output facet of the MMF, specklegram is detected by a camera. The reflector consists of two soft mirrors that are perpendicular to each other originally. The contact force on the sensor probe causes the variation of the angle between the two mirrors. The transmission path of the light from SMF to MMF changes accordingly, which results in a changed specklegram. In this way, the zero-mean normalized cross-correlation coefficients of the fiber specklegrams decrease linearly with the increase of contact force. The sensitivity and measurement range of contact force are examined with MMFs of different diameters under two operating wavelengths. The negligible effect of fiber bending on the force sensing was also experimentally confirmed. In addition, the convolutional neural network is used to classify the specklegrams of three contact forces applied at nine positions of the sensor probe, and the average accuracy of classification is 100%, which shows its capability to identify the contact position on the probe. On the whole, the proposed tactile sensor is confirmed with a high sensitivity of force sensing in a proper measurement range and a capability to localize the contact position. The reflective structure also facilitates the integration with robot arm and other intelligent structures.

Effect of contact force on pulsed field ablation lesions in porcine cardiac tissue.

Contact force has been used to titrate lesion formation for radiofrequency ablation. Pulsed field ablation (PFA) is a field-based ablation technology for which limited evidence on the impact of contact force on lesion size is available. Porcine hearts (n = 6) were perfused using a modified Langendorff set-up. A prototype focal PFA catheter attached to a force gauge was held perpendicular to the epicardium and lowered until contact was made. Contact force was recorded during each PFA delivery. Matured lesions were cross-sectioned, stained, and the lesion dimensions measured. A total of 82 lesions were evaluated with contact forces between 1.3and 48.6 g. Mean lesion depth was 4.8 ± 0.9 mm (standard deviation), mean lesion width was 9.1 ± 1.3 mm, and mean lesion volume was 217.0 ± 96.6 mm3 . Linear regression curves showed an increase of only 0.01 mm in depth (depth = 0.01 × contact force + 4.41, R2 = 0.05), 0.03 mm in width (width = 0.03 × contact force + 8.26, R2 = 0.13) for each additional gramof contact force, and 2.20 mm3 in volume (volume = 2.20 × contact force + 162, R2 = 0.10). Increasing contact force using a bipolar, biphasic focal PFA system has minimal effects on acute lesion dimensions in an isolated porcine heart model and achieving tissue contact is more important than the force with which that contact is made.

Calibration and Validation of Flow Parameters of Irregular Gravel Particles Based on the Multi-Response Concept

The discrete element method (DEM) often uses the angle of repose to study the microscopic parameters of particles. This paper proposes a multi-objective optimization method combining realistic modeling of particles and image analysis to calibrate gravel parameters, after obtaining the actual static angle of repose (αAoR_S) and dynamic angle of repose (βAoR_D) of the particles by physical tests. The design variables were obtained by Latin hypercube sampling (LHS), and the radial basis function (RBF) surrogate model was used to establish the relationship between the objective function and the design variables. The optimized design of the non-dominated sorting genetic algorithm II (NSGA-II) with the actual angle of repose measurements was used to optimize the design to obtain the best combination of parameters. Finally, the parameter set was validated by a hollow cylinder test, and the relative error between the validation test and the optimized simulation results was only 3.26%. The validation result indicates that the method can be reliably applied to the calibration process of the flow parameters of irregular gravel particles. The development of solid–liquid two-phase flow and the wear behavior of centrifugal pumps were investigated using the parameter set. The results show that the increase in cumulative tangential contact forces inside the volute of centrifugal pumps makes it the component most likely to develop wear behavior. The results also illustrate the significant meaning of the accurate application of the discrete element method for improving the efficient production of industrial scenarios.

Tribodynamic Modelling of High-Speed Rolling Element Bearings in Flexible Multi-Body Environments

This study presents a new flexible dynamic model for drive systems comprising lubricated bearings operating under conditions representative of electrified vehicle powertrains. The multi-physics approach importantly accounts for the tribological phenomena at the roller–race conjunction and models their effect on shaft-bearing system dynamics. This is achieved by embedding a non-linear lubricated bearing model within a flexible system level model; this is something which has not, to the authors’ knowledge, been reported on hitherto. The elastohydrodynamic (EHL) film is shown to increase contact deflection, leading to increased contact forces and total bearing stiffness as rotational speeds increase. Results show that for a 68 Nm hub motor operating up to 21,000 rpm, the input bearing EHL film reaches a thickness of 4.15 μm. The lubricant entrainment increases the roller–race contact deflection, causing the contact stiffness to increase non-linearly with speed. The contribution of the lubricant film leads to a 16.6% greater bearing stiffness at 21,000 rpm when compared to conventional dry-bearing modelling methods used in current multi-body dynamic software. This new methodology leads to more accurate dynamic response of high-speed systems necessary for the next generation of electrified vehicles.

Analyzing the influence of lifter design and ball mill speed on grinding performance, particle behavior and contact forces

Ball mills are the foremost equipment used for grinding in the mineral processing sector. Lifters are placed on the internal walls of the mill and are designed to lift the grinding media (balls) to a higher position. In the calculation of energy consumption in ball mills, classical theories mainly consider factors like the charge fill level, lifter dimensions, the number of lifters, and the rotational speed of the mill. This research recognizes the significance of lifter geometry and proposes a new lifter design aimed at optimizing the energy consumption and efficiency of ball mills. Simulation results by discrete elements obtained in this study were validated using experimental results. By conducting this comparative analysis, the aims of the study was to examine the impact of the new lifter's geometry and rotational speed of the mill on torque, power draw, particles behavior, and contact forces. The findings indicate that when the pitch of the lifters is increased, there is a reduction of 3.30% in torque and power consumption. Additionally, this change leads to an increase in the number of cataracting particles and a 6 to 7% increase in contact forces compared to lifters with a straight shape.

Simulation study on the influence of wheel irregularity on the vertical dynamics of wheel–rail interaction for high-speed railway track using bond graph

Dynamic interaction between train wheel and high-speed slab is an important issue when evaluating the contact force at the wheel–rail interface under the influence of an irregularity either on the train wheel or on the rail. In this paper, an influence of amplitude of irregularity along with the vehicle speed on the dynamics of wheel–rail interaction for high-speed railway tracks is being analyzed. For this purpose, single-wheel high-speed railway (HSR) track interaction models are developed using the bond graph modeling technique. The HSR track model consists of two layers of beam, i.e., rail and concrete slab. Both the rail and slab track is modeled using the Euler–Bernoulli beam theory. The Hertzian contact theory at the wheel–rail interface has been considered for this analysis. The vertical dynamic interaction between a train wheel and a high-speed slab track is compiled in the time domain using a bond graph approach coupled with a technique known as modal superposition. Irregularity present on the wheel is characterized as smooth, moderate, and severe depending upon the variation of irregularity amplitude. An expeditious increase of maximum contact force has been observed between the speed range of 200 and 250 km/h. Beyond the speed of 250 km/h, there is a gradual increment of contact force up to its peak value. When the train speed is beyond 288 km/h, there is a gradual decrease in maximum contact force. This kind of several other useful dynamic responses in terms of wheel acceleration and wheel–rail overlap are also evaluated.

Sliding electrical contact properties of highly oriented copper fiber brush

Metal fiber brush is a new electrical brush that has a promising application in high current density and non-lubricating conditions owing to its unique structure. The copper fiber brush comprised of highly oriented and uniformly distributed fibers was prepared by the knitting method with a packing fraction of 20%. The influence of current on the sliding electrical contact properties of the copper fiber brush as sliding against the steel disc was investigated. The worn surfaces of the copper fiber brushes and the steel discs were characterized to reveal the involved wear mechanisms. The results show that the static contact resistance decreases significantly from 55 to 18 mΩ with the gradual increase of contact force from 1 to 8 N, which is attributed to the elastic contact of multiple fibers and good compressive performance. The sliding contact resistance and electrical noise decrease with the increase of current, which is attributed to the micro-welding of contact spots induced by an electric arc. The wear rate of copper fiber brush increases significantly from 1.2 × 10−5 to 5.7 × 10−5 mm3/N·m with the increase of current from 0 to 8 A. The electrical wear caused by arc erosion becomes the dominant wear mechanism, which is more profound than mechanical wear under high currents.

The effect of surgical change to hip geometry on hip biomechanics after primary total hip arthroplasty.

The aim of this study was to determine the effect of surgical change to the acetabular offset and femoral offset on the abductor muscle and hip contact forces after primary total hip arthroplasty (THA) using computational methods. Thirty-five patients undergoing primary THA were recruited. Patients underwent a computed tomography scan of their pelvis and hip, and underwent gait analysis pre- and 6-months postoperatively. Surgically induced changes in acetabular and femoral offset were used to inform a musculoskeletal model to estimated abductor muscle and hip joint contact forces. Two experiments were performed: (1) influence of changes in hip geometry on hip biomechanics with preoperative kinematics; and (2) influence of changes in hip geometry on hip biomechanics with postoperative kinematics. Superior and medial placement of the hip centre of rotation during THA was most influential in reducing hip contact forces, predicting 63% of the variance (p < 0.001). When comparing the preoperative geometry and kinematics model, with postoperative geometry and kinematics, hip contact forces increased after surgery (0.68 BW, p = 0.001). Increasing the abductor lever arm reduced abductor muscle force by 28% (p < 0.001) and resultant hip contact force by 17% (0.6 BW, p = 0.003), with both preoperative and postoperative kinematics. Failure to increase abductor lever arm increased resultant hip contact force 11% (0.33 BW, p < 0.001). In conclusion, increasing the abductor lever arm provides a substantial biomechanical benefit to reduce hip abductor and resultant hip joint contact forces. The magnitude of this effect is equivalent to the average increase in hip contact force seen with improved gait from pre-to post-surgery.