Lateral Contact Research Articles

The influence of AAR coupler features on estimation of in-train forces

Inadequate management of large in-train forces transferred through coupler systems of a railway train leads to running and structural failures of vehicles. Understanding these phenomena and their mitigation requires accurate estimation of relative motions and in-train forces between vehicle bodies. Previous numerical studies have ignored inertia of coupling elements and the impacts between couplers. Thus, existing models underestimate the additional dynamic variations in in-train forces. Detailed multi-body dynamic models of two AAR (Association of American Railroads) coupler systems used in passenger and freight trains are developed, incorporating coupler inertia and various slacks. Due to the modeling and simulation complexities involved in a full train model, with such details of coupler system, actual longitudinal train dynamics is not studied. A system comprising only two coupling units, inter-connecting two consecutive vehicles, is modeled. Considered system has been fixed at one end and an excitation force is applied at the other end, to mimic a relative force transmission through combined coupler system. Simulation results obtained from this representative system show that, noticeable influence in in-train forces are expected due to the combined effect of inertia of couplers and intermittent impacts between couplers in the slack regime. Maximum amplitude of longitudinal reaction force, transferred from draft gear housing to vehicle body, is expected to be significantly higher than that predicted using existing models of coupler system. It is also observed that the couplers and knuckles are subjected to significant longitudinal and lateral contact forces, due to the intermittent impacts between couplers. Thus, accurate estimation of draft gear reaction force and impact forces between couplers are essential to design vehicle and coupler components, respectively.

Altered In Vivo Knee Kinematics and Lateral Compartment Contact Position During the Single-Leg Lunge After Medial Unicompartmental Knee Arthroplasty.

Osteoarthritis (OA) progression in the lateral compartment is the most common reason for revision after medial unicompartmental knee arthroplasty (UKA). Altered contact kinematics in the lateral compartment may be related to the pathogenesis of OA. To quantify the in vivo 6 degrees of freedom (6-DOF) knee kinematics and contact points in the lateral compartment during a single-leg lunge in knees after medial UKA and compare them with the contralateral native knee. Descriptive laboratory study. Included were 13 patients (3 male, 10 female; mean age, 64.7 ± 6.2 years) who had undergone unilateral medial UKA. All patients underwent computed tomography preoperatively and 6 months postoperatively, and bilateral knee posture was tracked using dual fluoroscopic imaging system during a single-leg deep lunge to evaluate the in vivo 6-DOF kinematics. The closest points between the surface models of the femoral condyle and the tibial plateau were determined to locate the lateral compartment contact positions. The Wilcoxon signed-rank test was used to compare knee kinematics and lateral contact position between the UKA and native knees. Spearman correlation was used to test the associations of bilateral 6-DOF range difference and lateral compartment contact excursion difference with bilateral limb alignment difference and functional scores. Compared with native knees, UKA knees had an increased anterior femoral translation of 2.0 ± 0.3 mm during the entire lunge (P < .05). The lateral contact position in UKA knees was located 2.0 ± 0.9 mm posteriorly and with 3.3 ± 4.0 mm less range of contact excursion than native knees (P < .05). Decreased range of lateral compartment contact excursion in the anterior-posterior direction was significantly associated with increased hip-knee-ankle angle in the UKA side (P < .05). The current study revealed altered knee 6-DOF kinematics and the reduced contact excursion range during single-leg lunge after unilateral medial UKA. The altered contact kinematics and reduced range of contact excursion in UKA knees could lead to excessive cumulative articular surface contact stress, which is implicated in the pathogenesis of OA.

Improved estimation of rail–wheel contact forces from instrumented wheel-set data through higher harmonic cancellation and a back-propagation neural network scheme

Instrumented wheelsets, equipped with numbers of strain gauges, are widely used to estimate the rail–wheel contact parameters. The accuracy in estimation of rail–wheel contact parameters from the measured strain signals depends on the layout of the strain gauges and correlation techniques adopted for processing measured signals. Harmonic components estimation is the most widely used conventional correlation technique. However, its accuracy in estimation of rail–wheel contact parameters is limited to the order of 80%–90%. This study proposes a signal modification algorithm, initially utilizing cancellation of next significant higher harmonics than those considered in the existing algorithms and then further, a novel Artificial Neural Network architecture for the same purpose.The signal modification approach is based on the realization that the seventh harmonic has significant contribution on the strain signals. The proposed algorithm is aimed at estimating and cancelling the effects of the seventh harmonic in strain signals. The accuracy thus improves to 91% in vertical contact force estimates, while the accuracy in estimation of lateral contact force and lateral contact position are improved to 97% and 95%, respectively. Due to the highly non-linear nature of the rail–wheel contact parameters, an optimized nonlinear mapping is required for further improvement in the accuracy.The viability of using artificial neural networks in estimation of rail–wheel contact parameters have been explored earlier. The proposed architectures are complicated and require extensive manual optimization of tuning parameters. A simple back-propagation artificial neural network architecture, using Bayesian regularization training function with Levenberg–Marquardt optimization technique is proposed in this study. The proposed neural network consists of 18 measured strain signals as input, three hidden layers with 20, 6 and 3 neurons, respectively, and vertical force, lateral force and lateral contact position as three outputs. Accuracies of the order of 99%, 99% and 96% are achieved in the estimation of vertical contact force, lateral contact force and lateral contact position respectively. The input and training data is generated from the multi-body dynamics and finite element simulations.

Femoral-tibial contact stresses on fixed rotational femur models.

This study aims to quantitatively evaluate the femoral-tibial contact pressure on the knee under certain malrotaional degrees. Femoral-tibial contact pressure was carried out on 14 fixed rotational knee models under 200/400/600 N vertical load using ultra-low-pressure sensitive film technology, rotation angles including neutral position (0°, anatomically reduced), 5°, 10°, and 15° internally and externally. Data were collected and analyzed with SPSS software. There are significant statistical differences between the medial contact pressure among rotational deformities (including neutral position) (P < 0.01), the increase in the degree of fixed internal malrotation of the femur resulted in a linear increase in the medial femoral-tibial contact pressures (P < 0.05) under 200/400/600 N vertical load, while increase in the degree of fixed external malrotation resulted in a linear decrease (P < 0.05). Except the 200 N compression, we can't find significant differences in lateral contact pressures (P > 0.05). In the comparison of medial to lateral contact pressures, no statistically significant differences were found in neutral and 5° internal rotation under 200/400 N, neutral, 5° internal rotation, and 15° external rotation under 600 N. In contrast, medial contact pressures were higher than lateral at other angles (P < 0.05). Obvious contact pressure changes were observed in rotatory femur. Doctors should detect rotational deformity as much as possible during operation and perform anatomical reduction. For patients with residual rotational deformities, indication of osteotomy should not be too broad.

A study on the correlation between patellofemoral joint morphology and early patella malacia in young adults: quantitative analysis based on magnetic resonance.

The aim of this study was to quantitatively measure the morphology of the patellofemoral joint by magnetic resonance imaging (MRI) in young adults, to investigate the relationship between the morphology of the patellofemoral joint and chondromalacia patellae (CP), and to provide an imaging reference for early clinical diagnosis of CP. A total of 57 cases of CP and 138 cases of normal knees were retrospectively collected and assigned to the CP group and control group, respectively. The morphological parameters of the patellofemoral joint were measured systematically. The statistical software SPSS 22.0 was used in correlation analysis. Logistic regression was used for univariate analysis. A P value <0.05 was defined as statistically significant. Wiberg index, patellar depth, and the lateral angle of the patella in the CP group were significantly lower than those in the control group (P=0.043, 0.001, 0.040, respectively). The width of the medial side of the trochlea, the ratio of the internal and external articular surfaces of the trochlea, the depth of the trochlea, and the inclination angle of the lateral trochlea in the CP group were significantly lower than those in the control group (P=0.003, 0.020, 0.000, 0.040, respectively), whereas the angle of the trochlea in the CP group was significantly higher than that in the control group (P=0.010). The lateral patellofemoral angle (LPA) and lateral patellofemoral contact width in the CP group were significantly lower than those in the control group (P=0.010, 0.010, respectively). In the CP group, with gender as a covariate, there were significant statistical differences between male and female in patellar depth, lateral patellar inclination angle, lateral trochlear inclination (LTI) angle, and lateral patellar contact surface width (P<0.05), whereas in the control group, there were significant differences in Wiberg index, patellar depth, medial trochlear width, and lateral patellofemoral contact surface width between male and female gender (P<0.05). The prevalence of CP in women was significantly higher than that in men and the reduction of trochlea width and the patella depth is an important factor for the incidence of female CP. Morphological characteristics of the patellofemoral joint are significantly correlated with the occurrence of CP in young adults.

The role of the lateral part of the distal triceps and the anconeus in varus stability of the elbow: A biomechanical study: The role of the lateral triceps tendon and anconeus under gravity varus.

The role of the lateral part of the distal triceps as a stabilizer in the lateral collateral ligament (LCL) deficient elbow and whether its effect in improving the stability is independent of that of the anconeus is unclear. Seven cadaveric elbows were tested under gravity varus stress using a custom-made machine designed to simulate muscle loads while allowing passive flexion of the elbow. An injury model was created by sectioning the LCL and sparing the common extensor origin. The lateral part of the distal triceps tendon was loaded sequentially with 0 N, 10 N, 25 N and 40 N. Each stage of the lateral part of the distal triceps loading was tested with the anconeus unloaded (inactive) or with a 25 N load applied (active). Articular contact pressure on the coronoid, the medial facet, and the lateral facet were collected and processed using TekScan sensors and software. A significant decrease in the mean coronoid contact pressure was seen with sequential loading of the lateral part of the distal triceps (p < 0.001). The ratio of medial to lateral facet contact pressures (M/L ratio) significantly decreased with sequential loading of the lateral part of the distal triceps (p < 0.001), indicating a better distribution of the contact pressure between the medial and lateral facets as the lateral part of the distal triceps was loaded. These effects were statistically significant, both with and without anconeus loading. There was no significant modification of the effect of the lateral part of the distal triceps loading on the contact pressure by the anconeus loading (p = 0.47). However, with active anconeus loading, the contact pressure and the M/L ratio were significantly lower for any stage of lateral triceps loading (p < 0.001), indicating a synergistic effect of the anconeus. In an LCL-deficient elbow, the lateral part of the distal triceps loading prevents the increased contact pressure on the coronoid under varus stress and improves the distribution of contact pressures on the coronoid. Anconeus loading further decreases and improves the distribution of the contact pressures; however, its effect is independent of that of the lateral part of the distal triceps. These results substantiate a role of the lateral part of the distal triceps as a dynamic constraint against elbow varus and have clinical implications for prevention and rehabilitation of elbow instability.

Tibiofemoral Load Magnitude and Distribution During Load Carriage.

Chronic exposure to high tibiofemoral joint (TFJ) contact forces can be detrimental to knee joint health. Load carriage increases TFJ contact forces, but it is unclear whether medial and lateral tibiofemoral compartments respond similarly to incremental load carriage. The purpose of our study was to compare TFJ contact forces when walking with 15% and 30% added body weight. Young healthy adults (n = 24) walked for 5minutes with no load, 15% load, and 30% load on an instrumented treadmill. Total, medial, and lateral TFJ contact peak forces and impulses were calculated via an inverse dynamics informed musculoskeletal model. Results of 1-way repeated measures analyses of variance (α = .05) demonstrated total, medial, and lateral TFJ first peak contact forces and impulses increased significantly with increasing load. Orthogonal polynomial trends demonstrated that the 30% loading condition led to a curvilinear increase in total and lateral TFJ impulses, whereas medial first peak TFJ contact forces and impulses responded linearly to increasing load. The total and lateral compartment impulse increased disproportionally with load carriage, while the medial did not. The medial and lateral compartments responded differently to increasing load during walking, warranting further investigation because it may relate to risk of osteoarthritis.

Self-assembly of cyclic peptide monolayers by hydrophobic supramolecular hinges

A novel supramolecular tryptophan hinge motif enables the self-assembly of nanotube monolayers by hierarchical non-covalent polymerisation of cyclic peptides in lateral contact.

MoTe2-Based Schottky Barrier Photodiode Enabled by Contact Engineering

Two-dimensional (2D) atomic crystalline materials have attracted the scientific community owing to their remarkable electrical and optical applications, such as solar cells, light-emitting diodes, and photodiodes. This study demonstrates a Schottky barrier photodiode (SPD) using different metal architectures in lateral and vertical contacts on n-type 2H phase semiconducting molybdenum ditelluride (MoTe2) synthesized by the self-flux crystal growth method. High-work-function palladium and low-work-function indium metals have been deposited on MoTe2 to fabricate a field-effect transistor confirming diode characteristics. The device shows an ideality factor of 1.09 and a rectification ratio of 102, indicating ideal diode characteristics based on a single MoTe2 channel. In addition, we measured the device in the dark and used the green laser to analyze the photodiode behavior of SPD in a wide range of light intensity. A single channel using contact architecture-based study is helpful to apply in other 2D materials to achieve the simplest fundamental diodes for future nanoelectrical and optoelectronic devices.

Failure resistance research of the dual-stage hybrid bit

Vibration failure is mainly the abnormal fracture failure of cutters, including brittle fracture, impact spalling, impact fatigue fracture, and cutter loss. The weak core area of the existing drill bit is prone to develop into core failure. Vibration failure and core failure will seriously affect drilling performance of the drill bit. To limit vibration and improve stability, we proposed a dual-stage hybrid bit with a polycrystalline diamond compact bit as the primary cutting unit and a tri-cone bit as the secondary cutting unit. Polycrystalline diamond compact bit only breaks the outer rock to form a central rock pillar, while the tri-cone bit breaks the central rock pillar. The existence of the central rock pillar enables the hybrid bit to have a larger lateral contact area with the bottom hole, which can reduce lateral force and limit lateral vibration. The tri-cone bit strengthens the impact and wear resistance of the core area, which can effectively prevent core failure. The experimental results showed that the working parameters of the dual-stage hybrid bit fluctuated less, its drilling stability was better. The experiment verified that the lateral force of the dual-stage hybrid bit was smaller. The vibration test results showed that, with small weight-on-bit, the vibration accelerations of the two drill bits were relatively close. With higher weight-on-bit, the accelerations in all directions of the dual-stage hybrid bit were smaller than those of the polycrystalline diamond compact bit. Specifically, the lateral acceleration differed by more than 40%, which proved the lateral vibration resistance of the dual-stage hybrid bit. The axial and tangential accelerations were reduced accordingly. In the validation experiments, the lateral force of the dual-stage hybrid bit decreased by 11.7%, 21.3% and 26.7%, its vibration acceleration reduced by 12.2%, 26.4% and 14.9%. Therefore, the dual-stage hybrid bit could reduce vibration and enhance stability.

DYNAMIC FINITE ELEMENT SIMULATION OF WHEEL–RAIL CONTACT RESPONSE FOR THE CURVED TRACK CASE

The wheel–rail interaction will be intensified on account of the complexity of the wheel–rail contact geometry on a curved track. It also may become more complicated and/or have significant difference as the train speed increases, since the dynamic effects cannot be ignored then. In this study, based on explicit Finite Element (FE) software LS-DYNA 971, a Three-Dimensional (3D) elastic-plastic FE model was built to simulate the dynamic wheel–rail contact behaviour of curve negotiating, where the superelevation and roll angle as well as the strain rate effect were considered. The evolution of contact patch and pressure, wheel–rail contact force, the stress/strain state and the acceleration of the axle were employed to examine the wheel–rail transient dynamic response. Furthermore, the influences of axle load, curve radius and strain rate effect were also discussed. It is found that the maximum vertical contact force, contact pressure, stress and strain on the curved track increase with the decreasing curve radius, and they increase with the increasing axle load except for lateral contact force. The wheel–rail dynamic responses on the curved track are significantly enhanced compared to the straight track. Moreover, the strain rate effect can enhance von-Mises stress and contact pressure, suppress the plastic deformation of the rail and wheel, but it has little effect on the vertical and lateral contact forces and stable acceleration of axle. The Rate-Sensitive Factors (RSF) of the wheel and rail on the curved track are weaker than those on the straight track. These findings will be very helpful to study the competitive relationship between the rolling contact fatigue and wear, as well as the crack initiation and propagation problem.

Constraining hydrocarbon migration and accumulation by two-dimensional numerical simulation: Ordovician carbonate reservoirs of the Daniudi Area, Ordos Basin

The various types of reservoir space in carbonate reservoirs make the process of hydrocarbon migration and accumulation very complex. How to quantitatively characterize the characteristics of hydrocarbon migration and accumulation in carbonate reservoirs is one of the key problems for carbonate hydrocarbons exploration and exploitation. Taking the Ordovician in the Daniudi area of Ordos Basin as an example, three types of source rock-reservoir-cap assemblages, namely upper-generation assemblage, lateral variable assemblage, and self-generation-reservoir-cap assemblage, were determined by characterizing the forming elements of carbonate reservoirs. Petromod software is used to build a two-dimensional profile model, and vitrinite reflectance of source rock and porosity of the reservoir were used as correction parameters, and the hydrocarbon migration and accumulation process was simulated by the invasion percolation algorithm. It is confirmed that the Ordovician Majiagou formation in the study area has three periods of hydrocarbon charging and three periods of hydrocarbon adjustment. The hydrocarbon migration pathways in carbonate rocks include lateral contact in the pinch-out area, source rock-reservoir contact in the trough area, fault-connected, and source rock-reservoir superposition. The source rock-reservoir-cap assemblages of upper-generation assemblage and lateral variable assemblage correspond to the lateral contact in the pinch-out area, source rock-reservoir contact in the trough area, fault-connected, while self-generation-reservoir-cap assemblage corresponds to the fault-connected, and source rock-reservoir superposition. The high part of the structure and fault zone are the strongest structural deformation parts, whose fractures are relatively developed, controlling the location of hydrocarbon accumulation, meanwhile, the reservoir quality directly controls the degree of hydrocarbons saturation. The research results are beneficial to establish a more accurate quantitative evaluation method of hydrocarbon migration and accumulation in carbonate rocks and to understanding the controlling factors of hydrocarbon migration and accumulation in carbonate rocks.

Ambient noise tomography of Gran Canaria island (Canary Islands) for geothermal exploration

Ambient noise tomography (ANT) has proved to be efficient in resolving crustal structures for different purposes. Despite the numerous studies carried out in Gran Canaria in the past for purposes of geothermal exploration, ANT had never been used before on this island. We applied this technique to understand Gran Canaria island’s shallow structure, determining the 3-D S-wave velocity model of the island and focusing on its implications for geothermal exploration. We used data from 30 seismic stations installed between October 2019 and February 2020. Our findings revealed five relevant velocity anomalies helpful in understanding the island’s geology and its geothermal potential. In particular, we identified two high-velocity anomalies in the central part of the island aligned with the primary northwest–southeast structural trends of Gran Canaria. We interpret them as evidence of intrusive volcanic bodies emplaced during the early stages of the island’s geological history. We also identified three low-velocity zones located in different parts of the island. We maintain that these anomalies could be associated with porous and highly fractured materials produced during the more recent volcanic episodes. In addition, we observed a spatial correlation of anomalies in the electric conductivity identified in previous studies and strong lateral gradients in our S-wave velocity model. We interpret them as evidence of hydrothermal circulation and thermal anomalies in correspondence of lateral contacts between different geological units and/or faults.

TMIC-26. USING INTEGRATED MULTIDIMENSIONAL MASS CYTOMETRY AND MULTIPLEX IMMUNOHISTOCHEMISTRY TO INFER SPATIAL RELATIONSHIPS BETWEEN PHENOTYPICALLY DISTINCT GLIOBLASTOMA INFILTRATING IMMUNE CELLS

Abstract Glioblastomas (GBM) account for ~60% of adult primary brain tumors. With few advances in therapeutics, median overall survival remains 15-months post-diagnosis. Immunotherapies may provide therapeutic benefit; however, no predictive immune features have informed therapeutic stratification. Radiographic tumor contact with the lateral ventricle (C-GBM) correlates with 7-months worse prognosis compared to patients with ventricle non-contacting GBM (NC-GBM), yet the influence of ventricle contact on anti-tumor immunity is unknown. This study characterized the GBM immune microenvironment and identified targetable mechanisms of immunosuppression correlating with worse outcomes in C-GBM patients.Primary glioblastoma tissue was provided with written informed consent in accordance with the Declaration of Helsinki and with approval of the Vanderbilt Institutional Review Board (IRB #131870). Seventeen patients presented with primary, IDH-wildtype C-GBM and 15 with NC-GBM. Machine learning integrated mass cytometry and matched multiplex immunohistochemistry on FFPE embedded tissue to identify phenotypic, functional, and spatial biomarkers correlating with patient outcome. C-GBM tumors were enriched in STAT3-driven CD32+CD44+HLA-DR+ monocyte-derived macrophages (MDM) compared to NC-GBM (19 ± 8% vs. 6 ± 2%; p&amp;lt; 0.001) and depleted in lymphocytes (2.9 ± 1% vs. 7.6 ± 2%; p&amp;lt; 0.001) and tissue-resident microglia (1.8 ± 0.3% vs. 7 ± 3%; p&amp;lt; 0.001). Exhausted T cells in C-GBM co-expressed checkpoint receptors PD-1 and TIGIT. K-means clustering identified 10 immunological niches in GBM. Macrophage-tumor niches were most common in C-GBM (17.93% of niches), followed by T cell-microglia-tumor niches (17.72%). Within NC-GBM niches, T cell-T cell interactions were more prevalent (log odds ratio = 0.90) and correlated with improved outcome.These findings suggest that factors within the periventricular space negatively influence the immune microenvironment within GBM tumors. Clinically targetable immune biomarkers were identified in C-GBM. Notably, radiologic assessment of lateral ventricle contact may guide clinical trial design for immunotherapies in neuro-oncology based on tumor proximity to the ventricle wall.

Biomechanical Comparison of 3 Medial Patellofemoral Complex Reconstruction Techniques Shows Medial Overconstraint but No Significant Difference in Patella Lateralization and Contact Pressure

The purpose of this study was to investigate biomechanical differences of medial patellofemoral ligament (MPFL) reconstruction, medial quadriceps tendon femoral ligament (MQTFL) reconstruction, and a combination of these techniques to restore lateral patellar constraint and contact pressures. Eight fresh frozen cadaver knees were mounted to a custom jig with physiological quadriceps tendon loading. Flexion angles and contact pressure (CP) were dynamically measured using Tekscan® pressure sensors and Polhemus® Liberty 6 degree of freedom (6DOF) positioning sensors in the following conditions: 1) intact 2) MPFL and MQTFL deficient, 3) MPFL reconstructed, 4) Combined MPFL+ MQTFL reconstructed, and 5) MQTFL reconstructed. Lateral patellar translation was tested using horizontally directed 30 N force applied at 30° of knee flexion. The knees were flexed in dynamic fashion, and CP values were recorded for 10°, 20°, 30°, 50°, 70°, and 90° degrees of flexion. Group differences were assessed with ANOVA's followed by pairwise comparisons with Bonferroni correction. MPFL (P= .002) and combined MPFL/MQTFL (P= .034) reconstruction significantly reduced patellar lateralization from+19.28% (9.78%, 28.78%) in the deficient condition to-17.57% (-27.84%,-7.29%) and-15.56% (-33.61%, 2.30%), respectively. MPFL reconstruction was most restrictive and MQTFL reconstruction the least-7.29% (-22.01%, 7.45%). No significant differences were found between the three reconstruction techniques. Differences in CP between the three reconstruction techniques were not significant (<.02 MPa) at all flexion angles. The present study found no significant difference for patellar lateralization and patellofemoral CP between MPFL, combined MPFL/MQTFL, and MQTFL reconstruction. All 3 techniques resulted in stronger lateral patellar constraint compared to the native state, while the MQTFL reconstruction emulated the intact state the closest. Various surgical techniques for medial patellofemoral complex reconstruction can restore patellar stability with similar patellofemoral articular pressures.

Chipping of ceramic‐based dental materials by micrometric particles

AbstractChipping caused by micrometric particles poses a threat to the structural integrity of modern dental prosthetic materials. It can degrade their fracture strength and cause wear of both artificial crowns and antagonist teeth. Here, surface chipping of the main types of commercial ceramic‐based dental materials at the microcontact/particle level is investigated by means of indentation tests. Conical tips of different sizes (radii 20 and 200 μm) under axial and sliding loading are employed to simulate individual microcontacts. Both decreasing particle size and adding a lateral contact force decrease the chipping load below typical bite forces. Specific damage mechanisms are identified as predominantly brittle fracture in ceramics with small, equiaxed crystals, with significant quasi‐plastic damage in ceramics containing large, elongated crystals and composites. Critical loads for the occurrence of chipping are quantified (lowest values in equiaxed glass–ceramics; greatest in zirconia) and analyzed within the framework of fracture mechanics. The brittleness index (BI) is proposed as a simple indicator of the resistance to chipping of dental materials—the lower the BI, the greater the resistance. Special attention is paid to the effect of the materials’ microstructure, which can result in transformation toughening (as in zirconia) or quasi‐plastic behavior (as in lithium disilicate), both highly beneficial to increasing the chipping resistance. Finally, practical implications for the selection of current dental materials as well as for the development of novel materials with improved durability are discussed.

ACL transection results in a posterior shift and increased velocity of contact on the medial tibial plateau

Our objective was to quantify the effect of ACL transection on dynamic knee joint contact force distributions during simulated gait. Given the prevalence of medial compartment osteoarthritis in un-reconstructed ACL ruptured knees, we hypothesized that changes in contact mechanics after ACL transection would be most prevalent in the medial compartment. Twelve human cadaveric knees were tested using a dynamic knee gait simulator which was programmed to mimic a clinical Lachman exam and gait. An electronic pressure sensor was placed on the medial and lateral tibial plateaus under the menisci to quantify dynamic contact forces before and after ACL transection. Tibial translations and rotations, medial and lateral plateau peak contact stress, and position and velocity of the Weighted Center of Contact (WCoC) were computed. After ACL transection, the tibia translated more anteriorly in the Lachman examination and at heel strike during gait. Changes in contact mechanics across the medial tibial plateau during simulated gait were: an increase in the velocity of WCoC and a posterior shift in the WCoC, both of which occurred at heel strike; increased peak contact forces in the posterior-peripheral quadrant of the tibial plateau at 45% of the gait cycle; and an additional posterior shift in WCoC from 25 to 55% of the gait cycle. The only change in contact mechanics in the lateral plateau was a decrease in WCoC velocity in late stance. This data is suggested to further the study of biomechanical pathways (biomechanical biomarkers) in the relationship between altered knee contact mechanics and chondrocyte metabolic responses after ACL transection.

Influence of lower-limb muscle inactivation on medial and lateral knee contact forces during walking.

The main objective of this study was to determine which muscle force reduction, among the vastus muscles (VAS), rectus femoris (RF), gluteus medius (Gmed), and gluteus maximus (Gmax) most significantly influenced the knee contact force. Ten young adults walked at a comfortable speed. The medial and lateral knee contact forces (KCF_med and KCF_lat) were computed by a musculoskeletal model with full-force-generating capacity and four muscle inactivation models that separately constrained the forces of Gmed, Gmax, VAS, and RF. Additionally, we evaluated compensatory alterations in muscle forces caused by the reduction of each muscle activity. Reduction in Gmed force induced an increase in KCF_med and a decrease in KCF_lat through the stance phase, along with compensatory increase in VAS and Gmax forces in the early stance phase and RF and Gmax forces in the late stance phase. Conversely, when the RF force was constrained, decreases in KCF_med and KCF_lat and compensatory increases in VAS and Gmed were observed in the late stance phase. Our results indicated that Gmed and RF most significantly influence the knee contact force during walking.

Biomechanical Analysis on Skilled Badminton Players during Take-Off Phase in Forehand Overhead Strokes: A Pilot Study.

Simple SummaryDifferent movement speeds can contribute to different joint loading in sports. Joint contact force is the actual force acting on the articular surface, which could predict performance and injury, but is rarely reported for badminton overhead strokes. From the perspective of sports biomechanics, this paper analyzes the characteristics of kinematics and mechanics at each stage of the fast and moderately paced movements and studies the changes in the force of the lower extremity joints caused by the characteristics of the movements at different speeds so that athletes and enthusiasts can clarify the essentials of the movements and prevent sports injuries.Different movement speeds can contribute to different joint loading in sports. Joint contact force is the actual force acting on the articular surface, which could predict performance and injury, but is rarely reported for badminton overhead strokes. Through an approach using musculoskeletal modelling, six male elite badminton players performed forehand overhead strokes at different movement speeds (fast (100%) vs. moderate (90%)). The synchronized kinematics and ground reaction force (GRF) data were measured using a motion capturing system and a force platform. All kinematics and GRF information were input into the AnyBody musculoskeletal modelling to determine the three-dimensional hip, knee and ankle contact forces. Paired t-tests were performed to assess the significant differences among the GRF, joint kinematics and contact force variables between the movement speed conditions. The results showed that when compared with the moderate movement condition, participants performing faster stroke movements induced larger first and second vertical peaks and larger first horizontal peak but lower second horizontal peak, and it also led to higher peak ankle lateral and distal contact forces, knee lateral and distal contact forces, and hip distal contact forces. Additionally, fast movements corresponded with distinct joint angles and velocities at the instant of initial contact, peak and take-off among the hip, knee and ankle joints compared with moderate movement speeds. The current results suggest that changes in joint kinematics and loading could contribute to changes in movement speeds. However, the relationship between lower limb joint kinematics and contact forces during overhead stroke is unclear and requires further investigation.

An isogeometric finite element formulation for frictionless contact of Cosserat rods with unconstrained directors

This paper presents an isogeometric finite element formulation for nonlinear beams with impenetrability constraints, based on the kinematics of Cosserat rods with unconstrained directors. The beam cross-sectional deformation is represented by director vectors of an arbitrary order. For the frictionless lateral beam-to-beam contact, a surface-to-surface contact algorithm combined with an active set strategy and a penalty method is employed. The lateral boundary surface of the beam is parameterized by its axis and cross-sectional boundary curves with NURBS basis functions having at least C^2-continuity, which yields a continuous surface metric and curvature for the closest point projection. Three-dimensional constitutive laws of hyperelastic materials are considered. Several numerical examples verify the accuracy and efficiency of the proposed beam contact formulation in comparison to brick element solutions. The lateral contact pressure distribution of the beam formulation is in excellent agreement with the contact pressure of the brick element formulation while requiring much less degrees-of-freedom.