Increase In Contact Pressure Research Articles

Biomechanical Changes in the Ankle Joint after Syndesmosis and Deltoid Injury and Subsequent Repair in a Cadaveric Model

Category: Ankle; Trauma Introduction/Purpose: Recent studies have stressed the important role of the deltoid ligament in maintaining global ankle stability. However, controversy remains around whether deltoid ligament repair is necessary in addition to syndesmotic repair when addressing injuries to both. The purpose of this study was to measure differences in tibiotalar joint contact pressures and tibiotalar contact area in the presence of deltoid ligament injury, syndesmotic injury, and after their respective repairs using a cadaveric model. Our hypotheses were 1) injury to the syndesmosis and deltoid would increase contact pressures and decrease contact area, 2) repaired injuries would restore biomechanics to near native state, and 3) that there would be similar tibiotalar contact pressures and contact area with syndesmosis repair alone compared to syndesmosis and deltoid ligament repair. Methods: Twelve human cadaveric lower extremities were randomized and tested under a series of conditions: 1) native, 2) sectioning of syndesmosis or deltoid, 3) sectioning of both the syndesmosis and deltoid, 4) repair of syndesmosis or deltoid, 5) repair of both. In one group, the syndesmosis was sectioned and repaired first and in the other the deltoid was sectioned and repaired first. The syndesmosis was repaired with a single high-tensile strength suture mechanism and deltoid ligament repairs were performed with a single suture anchor. Specimens were tested under each condition with an axial compressive and torsional load. Contact pressures and area within the ankle were measured with a digitized pressure sensor (Tekscan, Boston MA). Changes in contact pressure and area were compared with two-way repeated measure analysis of variance and significant findings were tested with post-hoc pairwise comparisons of estimated marginal means with Bonferroni-adjusted p-values for multiple comparisons (α = 0.05). Results: The highest mean contact pressure was seen when the deltoid was injured, but the syndesmosis was still intact (4.43 +/- 1.328 mPa) compared to mean contact pressure of 3.142 +/-0.511 mPa in the native condition. The lowest mean contact pressure was seen when the deltoid was repaired, but the syndesmosis was still disrupted (3.068 +/- 0.477). However, these differences in mean contact pressures did not differ significantly with pairwise comparison. Total contact area was significantly less following syndesmosis repair in isolation when compared to the native condition (609.55+-312.37mm2 vs 903.854mm2 p=0.0183). When the syndesmosis was repaired, irrespective of the state of the deltoid, the distribution of contact pressures shifted from the medial half of the joint to the lateral half of the joint in all but one specimen. Conversely, after deltoid ligament repair the distribution of pressure remain concentrated in the medial half of the joint, like the native state. Conclusion: We did not find a significant difference in overall mean ankle contact pressures between the various tested conditions. However, there can be a significant decrease in the joint contact area and a shift in the distribution of contact pressures within the joint after syndesmosis repair that was not seen after deltoid repair. In fact, with a deltoid repair alone, the distribution of contact pressures and the joint contact area did not differ significantly from the native state. These changes in contact area and distribution of pressures may affect long-term clinical and radiographic outcomes.

Analytical Model of the Frictional Heating in a Railway Brake Disc at Single Braking with Experimental Verification.

A one-dimensional thermal problem of friction was formulated, taking into account the contact pressure increase at the beginning of the process. The obtained solution to this problem allows for the quick calculation of the transient temperature distribution in a railway brake disc during single braking application. In order to validate the developed model, the experimental tests were performed for two friction pairs consisting of the cast iron brake disc and pads comprising two composite materials. Theoretical results were compared with the data measured by thermocouples embedded in the brake disc during the full-size dynamometer tests. The maximum temperature values found based on the analytical solution are convergent with the corresponding empirical data. The consistency of the results obtained for two friction couples demonstrates the usefulness of the proposed computational model.

Correlation between frictional heat and triboelectric charge: In operando temperature measurement during metal-polymer physical contact

In operando techniques have emerged to elucidate the fundamental mechanism of triboelectrification via relevant physical quantity measurement during the physical contact of two materials. Here, a correlation between frictional heat and triboelectric charge is reported in a metal-polymer triboelectric nanogenerator through the in operando temperature measurement. Fluorine-doped tin oxide (FTO) metal is slid back-and-forth under different contact pressures across polydimethylsiloxane (PDMS) polymers having different degrees of crosslinking, i.e., mixing ratio. Both the triboelectric charge and temperature variation increase and become saturated with different time-constants. Notably, the saturated triboelectric charge increases, while the saturated temperature decreases, with increasing mixing ratio. In contrast, both saturated triboelectric charge and temperature increase with increasing contact pressure. X-ray photoemission spectroscopy reveals that chemical bonds are modified inhomogeneously at the surface, and that charged materials are transferred from PDMS to FTO in accordance with the mixing ratio- and sliding time-dependent triboelectric charges. Frictional heat plays a distributive role in bond rupture and temperature variation, depending on the activation energy and frictional coefficient of PDMS. In operando temperature variation measurement provides important information on the specific bonds for triboelectrification and detailed charge-transfer process during physical contact.

РАСЧЕТ КОЭФФИЦИЕНТА СОПРОТИВЛЕНИЯ СВОБОДНОМУ КАЧЕНИЮ КОЛЕСА С ДЕФОРМИРУЕМЫМ ОБОДОМ

A new method for calculating rolling resistance is developed. This method includes a simplified structural model of a wheel in the form of a rigid cylinder with a thin viscoelastic rim. The wheel loading mode is considered in the absence of shearing (horizontal) force. In the entire contact area, it is assumed that the wheel is gripped with a non-deformable support surface. Deformation of the viscoelastic layer is analyzed on the basis of the Winkle model. In contrast to the previously known ones, the proposed method implies a description of the symmetry breaking in the distribution of contact pressure when a small torque is applied to the wheel, not exceeding the rolling resistance at rest. Contact pressure diagrams are obtained at different values of the torque applied to the wheel. It is shown that as the torque increases, the maximum value of the contact pressure increases, and the position of this maximum shifts in the direction of possible rolling. From the condition of violating the contact area dimensions at the beginning of rolling, an analytical expression is derived for the moment of rolling resistance at rest. The calculated dependence of this moment on the wheel draft is compared with known experimental data. When describing stationary free rolling, the asymmetry of the contact pressure corresponding to the beginning of rolling and the loss of energy during deformation of the viscoelastic material of the wheel rim are taken into account. The dependences of the coefficient of rolling resistance and wheel draft on the speed of the wheel center of mass at a fixed value of the vertical load are obtained. It is shown that taking into account the initial asymmetry of the contact pressure leads to a more intensive increase in the calculated estimates of the resistance coefficient and a less marked decrease in the wheel draft with an increase in rolling speed.

Effect of Anterior Horn Tears of the Lateral Meniscus on Knee Stability.

Background:Investigations on the biomechanical characteristics of the anterior horn of the lateral meniscus (AHLM) related to anterior cruciate ligament (ACL) tibial tunnel reaming have revealed increased contact pressure between the femur and tibia, decreased attachment area, and decreased ultimate failure strength.Purpose/Hypothesis:The purpose of this study was to investigate the influence of a complete radial tear of the AHLM on force distribution in response to applied anterior and posterior drawer forces and internal and external rotation torques. We hypothesized that the AHLM plays an important role in knee stability, primarily at lower knee flexion angles.Study Design:Controlled laboratory study.Methods:A total of 9 fresh-frozen cadaveric knee specimens and a robotic testing system were used. Anterior and posterior drawer forces up to 89 N and internal and external rotation torques up to 4 N·m were applied at 0°, 30°, 60°, and 90° of knee flexion. A complete AHLM tear was then made 10 mm from the lateral border of the tibial attachment of the ACL, and the same tests performed in the intact state were repeated. Next, the recorded intact knee motion was reproduced in the AHLM-torn knee, and the change in the resultant force after an AHLM tear was determined by calculating the difference between the 2 states.Results:In the torn AHLM, the reduction in the resultant force at 0° for external rotation torque (34.8 N) was larger than that at 60° (5.2 N; P < .01) and 90° (6.7 N; P < .01).Conclusion:The AHLM played a role in facilitating knee stability against an applied posterior drawer force of 89 N and external rotation torque of 4 N·m, especially at lower knee flexion angles.Clinical Relevance:This study provides information about the effects of AHLM injuries that may occur during single-bundle ACL reconstruction using a round tunnel.

Investigation of interfacial heat transfer characterization for TC4 alloy in triple-layer sheet hot stamping process

During the hot stamping process, heat exchange always occurs between the hot sheet and cold tools. The interfacial heat transfer in the whole-forming process will not only affects the forming quality of the parts but also partially determines their post-form mechanical properties and microstructure distribution. As an essential parameter, the interface heat transfer coefficient (IHTC) is of great significance for the prediction of temperature fields in the finite element simulations, especially for the novel-forming process named triple-layer sheet hot stamping. In this study, the triple-layer sheet heat exchange experiment is carried out to investigate the interfacial heat transfer behavior of the titanium alloy sheet in the triple-layer sheet hot stamping process. The effects of contact pressure, cladding steel sheet thickness, and contact gap on the interfacial heat transfer behavior and post-form mechanical properties of titanium alloy sheet are analyzed, and the interface heat transfer coefficient between the titanium alloy and high-strength steel sheets is calculated. The finite element model of triple-layer sheet heat transfer is established to verify the accuracy of the calculated interfacial heat transfer coefficient. The results show that the upper and lower steel sheets maintain the temperature of the titanium alloy sheets at a higher level in the triple-layer sheet hot stamping compared with the single-layer one. The temperature of the titanium alloy sheet under the single-layer hot stamping decreases from 900 to 781.6 °C after transferring, a decrease of 118.4 °C. The temperature of the titanium alloy sheet only declines by 57.5 °C during this period in the triple-layer sheet hot stamping process. In addition, the titanium alloy parts obtained by the triple-layer sheet hot stamping process have better mechanical properties. The IHTC increases with the increase of contact pressure and decreases with the increase of steel sheet thickness and contact gap. The accuracy of the calculated IHTC between the titanium alloy and cladding steel sheets is validated by comparing the results of the experiment and simulation. The maximum error between the simulation results and the experimental measurements is 5.5%.

Biomechanics evaluation of sacroiliac joint pain after lumbosacral fusion: A finite element analysis.

The sacroiliac joint (SIJ) constitutes the predominant pain source following lumbar or lumbosacral fusion. Although studies have investigated the biomechanical patterns of SIJ behaviors after lumbosacral fusion, the relationship between ligament strain and SIJ pain following lumbosacral fusion remains unclear. The present study developed a three-dimensional finite element model including L4, L5, sacrum, ilium, SIJ, and seven mainly ligaments. After successful validation, the model was used to investigate the biomechanics of SIJ and ligaments in simulating lumbosacral fusion process. Our results showed that small motion in a stable SIJ may significantly increases the contact pressure and stress of the SIJ, which increase the maximum contact pressure by 171%, 676%, 199%, and 203% and stress by 130%, 424%, 168%, and 241% for flexion, extension, bending, and axial rotation, respectively. An increase in contact pressure and stress in SIJ possibly causes pain at the SIJ, especially in extension and axial rotation. A comparison between the lumbosacral and intact models exhibited the maximum strain increase in the iliosacral ligament (ISL)and the ileal ligament (IL)under all loading conditions. The present study suggests that after lumbosacral fusion process, the ligament sudden increase or decrease is likely to lead sprain or strain ligament, especially ISL and IL thereby causing SIJ pain. This study may contribute to understand the relationship between SIJ ligaments and SIJ pain.

Proximal Row Carpectomy Does Not Alter Contact Pressures of the Lunate Fossa: A Cadaveric Study.

Previous studies have suggested that proximal row carpectomy (PRC) results in increased contact pressures and decreased contact areas in the radiocarpal joint. Such experiments, however, used older technologies that may be associated with considerable measurement errors. The purpose of this study was to determine whether there was a significant difference in contact pressure and contact area before and after PRC using Tekscan, a newer pressure sensing technology. Ten nonpaired cadaveric specimens were dissected proximal to the carpal row and potted. An ultra-thin Tekscan sensor was secured in the lunate fossa of the radius. The wrists were loaded with 200 N of force for 60 seconds to simulate clenched-fist grip; contact pressure and area was assessed before and after PRC. Performing a PRC did not significantly increase mean contact pressure at the lunate fossa compared to the native state (mean increase of 17.4 ± 43.2 N/cm2, P = .184). Similarly, the PRC did not significantly alter peak contact pressures at the lunate fossa (intact: 617.2 ± 233.46 N/cm2, median = 637.5 N/cm2; PRC: 707.8 ± 156.6 N/cm2, median = 728.5 N/cm2; P = .169). In addition, the PRC (0.46 ± 0.15 cm2, median = 0.48 cm2) and intact states (0.49 ± 0.25 cm2, median = 0.44 cm2) demonstrated similar contact areas (P = .681). In contrast to prior studies that demonstrated significant increases in contact pressure and decreases in contact area after PRC, our findings propose that performing a PRC does not significantly alter the contact pressures or area of the lunate fossa of the radiocarpal joint.

Paper 93: Biomechanical Comparison of Tibiotalar Contact Pressures After Syndesmosis Injury With or Without Deltoid Ligament Repair

Objectives:Recent studies have stressed the important role of the deltoid ligament in maintaining global ankle stability. However, controversy remains around whether deltoid ligament repair is necessary in addition to syndesmotic repair when addressing injuries that disrupt both the syndesmosis and deltoid ligament. The purpose of this study was to measure differences in tibiotalar joint contact pressures and tibio-talar torsional stability in the presence of deltoid ligament injury, syndesmotic injury, and after their respective repairs using a cadaveric model. Our hypotheseis were 1) injury to the syndesmoosis and deltoid would increase contact pressures and decrease torsional stability, 2) repaired injuries would restore biomechanics to near native state, and 3)that there would be similar tibiotalar contact pressures and torsional stability with syndesmosis repair alone compared to syndesmosis and deltoid ligament repair.Methods:Twelve fresh-frozen human cadaveric lower extremity specimens with intact ankle joints were randomized and tested under a series of conditions: 1) intact syndesmosis and deltoid, 2) sectioning of syndesmosis or deltoid, 3) sectioning of both the syndesmosis and deltoid, 4) repair of syndesmosis or deltoid, 5) repair of both the syndesmosis and deltoid. In one group, the syndesmosis was sectioned and repaired first and in the other the deltoid was sectioned and repaired first. The syndesmosis was repaired with a single high-tensile strength suture mechanism (TightRope, Arthrex), and deltoid ligament repairs were performed with a single suture anchor (FiberTak, Arthrex). Specimens were tested under each condition with 800 N axial compression load, followed by cyclic torsional preconditioning of 5 Nm internal tibial torque (i.e., external foot rotation) at a rate of 2.5 Nm/s, and then a single rotation test of 7.5 Nm internal tibial torque at 1 Nm/s under 800 N axial compression load on a servohydraulic mechanical testing system. Contact pressures within the tibiotalar joint were measured with a digitized pressure sensor film (Tekscan, Boston MA), and coronal plane motion about the tibia was measured in angular displacement.Results:There was no significant difference in peak contact pressures between conditions except when the comparing an isolated deltoid ligament injury to a combined deltoid and syndesmosis injury (4.43±1.33MPa vs 2.67±0.45MPa, p=0.038). Total contact area was less following syndesmosis repair in isolation (609.55±312.37mm2) and combined syndesmosis and deltoid repair (598.28±181.47mm2) compared to all other conditions (p<0.001). There was also a decrease in total contact area compared to native state when the deltoid was repaired in isolation (951.51±72.79mm2 vs 888.72±105.74mm2, p=0.027). The mean external rotation angle was greater when the syndesmosis (15.67±5.39°), deltoid (13.21±3.28°), and both injuries combined (16.59±4.01°) compared to native state (8.55±2.02°), however these values did not achieve statistical significance. Additionally, There was no statistically significant difference in external rotation angle between isolated syndesmosis, isolated deltoid, or combined repairs.Conclusions:These findings demonstrate that ankle contact pressures and torsional stability do not differ significantly when a deltoid ligament repair is performed in conjunction with a syndesmosis repair for a purely ligamentous injury. However, the change in contact area following syndesmosis repair may play a role in the development of post-traumatic arthritis. This finding reinforces the importance of striving for an anatomic syndesmotic reduction, and care should be taken not to over-reduce the syndesmosis during repair.

Poster 216: The Effects of Lateral Opening Wedge Distal Femoral Osteotomy on Meniscus Allograft Transplantation: A Biomechanical Evaluation

Objectives:Lateral meniscus deficiency with valgus malalignment increases the risk and rate of lateral compartment osteoarthritis. Lateral meniscus allograft transplantation (LMAT) with concomitant varus-producing lateral opening wedge distal femoral osteotomy (LOWDFO) is an available option to treat this pathology. No biomechanical data currently exists evaluating the effect on joint forces with these combined procedures. The purpose of this study is to evaluate the effects of LMAT with concomitant varus-producing LOWDFO on lateral and medial compartment biomechanics. We hypothesize that LMAT restores lateral compartment biomechanics back to native intact forces, varus-producing LOWDFO improves lateral compartment forces following LMAT, and medial compartment forces change to a lesser degree in response to mechanical varus.Methods:Ten human cadaveric knees underwent varus-producing LOWDFO and were placed in an external fixator. Anatomic alignment was standardized for each knee and utilized as a proxy for mechanical alignment. Thin film Tekscan pressure sensors were placed sub-meniscal and specimens were loaded on a biaxial dynamic testing machine to 800N within a custom designed apparatus, with loading angles between 9° valgus and 6° varus of mechanical alignment. Testing conditions included the intact meniscus, lateral meniscus deficiency, and LMAT. Statistical analysis was performed by creating two-factor random-intercepts linear mixed-effects models to compare peak pressure and contact area among the three experimental meniscus conditions.Results:Isolated varus-producing LOWDFO to 6° varus in the setting of meniscus deficiency was unable to restore joint forces to the level of the intact meniscus in neutral alignment (Mean Contact Pressure: 175%, Peak Pressure 135%, Contact Area -41%, P>0.05). LMAT restored mean contact and peak pressures, with no significant differences compared to the intact meniscus (P<0.05). LMAT resulted in significantly lower contact areas from 9° valgus to 0° (P>0.05), but this was restored to intact state at 3° and 6° varus (P<0.05). Within the lateral compartment following LMAT, every additional 1° of DFO correction contributes to a decreased in mean contact pressure of 5.6% (-0.0479 N/mm2)(Figure 1), a decrease in peak pressure of 5.9% (-0.154 N/mm2)(Figure 2), and a decrease in contact area of 1.4% (6.99 mm2)(Figure 3), as compared to forces in neutral alignment. Within the medial compartment following LMAT, every additional 1° of DFO correction contributes to an increase in mean contact pressure of 7.3% (+0.034 N/mm2), an increase in peak pressure of 12.6% (+0.160 N/mm2), and an increase in contact area of 4.3% (20.53 mm2), as compared to forces in neutral alignment. However, baseline forces in the medial compartment are significantly lower at baseline compared to lateral compartment forces (P>0.05).Conclusions:This is the first biomechanical study evaluating the effects of concomitant LMAT and varus-producing LOWDFO. Isolated varus-producing LOWDFO is inadequate to restore forces in the meniscus deficient knee. LMAT restores near normal forces, and concomitant LOWDFO improves the lateral compartment biomechanical profile. Although to a smaller magnitude, force changes in the medial compartment are significant with varus-producing LOWDFO. Unloading to 0° following LMAT may be ideal. Overall, this study provides tools to for the surgeon to individualize alignment correction for each patient to optimize outcomes.Figure 1.Mean Contact PressureFigure 2.Peak Contact PressureFigure 3.Contact Area

Paper 72: How Much Glenoid Bone Loss Needs to be Restored with a Latarjet?

Objectives:Significant anterior glenoid bone loss in the setting of recurrent instability may warrant a coracoid transfer (Latarjet). However, the amount of glenoid width that must be restored with a Latarjet in order to reestablish glenohumeral stability has not been studied.We hypothesize that restoration of greater than 90% of glenoid width with a Latarjet will be necessary to restore glenohumeral stability. We also hypothesize that there will be significant increases in anterior humeral head translation when 90% or less of the native glenoid width is restored and that contact pressures on the coracoid graft will increase.Methods:Seven cadaveric specimens were prepared and mounted on an established shoulder simulator, which loads shoulder tendons through a system of pulleys and weights. A motion tracking system to record glenohumeral translations was placed on the scapula and humerus and registered based on a computed tomography (CT) scan. Contact pressures were mapped and recorded using a TekScan secured to the glenoid face and coracoid graft transfer (Figure 1). The humerus was placed in 90 degrees of humerothoracic abduction.Coracoid osteotomy was performed, and the coracoid graft was sized to a depth of 10mm. A lesser tuberosity osteotomy (LTO) was performed to allow accurate removal of glenoid bone. The amount of bone loss needed to re-establish 110%, 100%, 90% and 80% of native glenoid width after Latarjet was calculated by directly measuring the widest point of the glenoid and confirming accuracy based on the CT scan. Glenoid bone loss was established using a burr and the coracoid graft transfer was secured to the anteroinferior glenoid with two screws. The conjoined tendon was passed through a subscapularis split and the LTO was repaired with multiple Kirshner wires prior to each testing condition (Figure 2). Additionally, the rotator interval was closed and the capsule was repaired prior to each testing condition.The supraspinatus, subscapularis, infraspinatus and conjoined tendons were each loaded with 22N. Testing conditions included native glenohumeral joint, LTO, Bankart tear, and then 110%, 100%, 90% and 80% of glenoid width restoration with Latarjet. Glenohumeral translations and contact pressures were recorded with an anteroinferior load of 0 or 44N at 0 degrees of glenohumeral external rotation.Results:Progressive increases in anterior humeral head translation occurred with an anteroinferior load as the amount of glenoid width restored decreased (Figure 3). An anteroinferior load created an average of 5.5mm, 9.6mm, 3.3mm, 3.6mm, 9.2mm and 10.2mm of anterior translation in the LTO, Bankart, 110%, 100%, 90% and 80% of glenoid restoration cohorts, respectively. Greater glenoid bone loss also led to more contact pressure on the coracoid graft after Latarjet (Figure 4). An anteroinferior load produced 26.4%, 46.9%, 86.2% and 94.4% of the contact pressures on the coracoid graft relative to the native glenoid with glenoid width restored to 110%, 100%, 90% and 80%, respectively.Conclusions:There is an increase in anterior humeral head translation and contact pressure on the coracoid graft when 90% or less of the native glenoid width is restored with Latarjet. By determining the goals for glenoid width restoration after Latarjet, the findings of this study may provide guidance for patient-specific size requirements for the coracoid based on preoperative imaging. When greater than 90% of glenoid width cannot be restored with a Latarjet, surgeons may consider alternative graft sources.

Toward Controllable Wet Etching of Monocrystalline Silicon: Roles of Mechanically Driven Defects.

Wet chemical etching is essential not only for processing silicon (Si) wafers but also for forming diverse structures, significantly promoting the development of the semiconductor industry. However, tight control of etched topography at the nanoscale and even atom-scale in a controllable and reproducible fashion can be hardly achieved in either laboratory research or industrial production, seriously hindering further enhancement of high-performance Si-based electronic devices. Herein, the roles of mechanically driven defects in wet etching were systematically investigated toward promoting controllable wet etching of monocrystalline Si. The role of antietching of mechanically driven amorphous Si (a-Si) and the role of promoting etching of distorted Si (including dislocations and stacking faults) were revealed in anisotropic or isotropic etchants. It was also found that the nucleation of nanocrystals in the a-Si area with increasing contact pressure can lead to deactivation of the antietching mask, and the required contact pressure for deactivation in KOH and tetramethyl ammonium hydroxide solutions was much higher than that in HF/HNO3 mixtures. The selective etching mechanisms for every defect including a-Si, distorted Si, and nanocrystals were further addressed down to the atom-scale based on the proposed dissolution model. This study provides insights into deeply understanding the role of defects in wet etching and pushes forward the idea of controllable wet chemical etching in the Si-based semiconductor industry.

ZDDP Tribofilm Formation from a Formulated Oil on Textured Cylinder Liners

Surface texturing can improve lubrication and entrap wear debris but increases the effective roughness of the surfaces, which can induce higher contact pressures. On the one hand, this can be detrimental, but on the other hand, the increase in contact pressure could be used to activate the formation of a ZDDP tribofilm from fully-formulated lubricants. This work investigates the synergistic effect between surface texturing via Maskless Electrochemical Texturing (MECT) and ZDDP additive. The surface texture consisted of an array of annular pockets manufactured on a gray cast iron cylinder liner. These textured surfaces were evaluated by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX). The results indicated that surface texturing via MECT changes the chemical composition of the surfaces, by inducing a preferential dissolution of the metal matrix. Consequently, it exposed the carbon present in the material. The tribological performance was evaluated by a ring-on-cylinder-liner tribometer in reciprocating sliding under boundary lubrication conditions using both a base oil and a commercial formulated oil containing ZDDP additive. For comparison, a commercially honed liner was also tested. After the tribological tests, the surfaces were evaluated by white light interferometry and SEM/EDX. Although the textured surfaces showed higher friction, they induced more ZDDP-tribofilm formation than conventional cylinder liner finish.

Influence of Contact Pressure on the Specific Electrical Contact Resistance of Copper

The specific electrical contact resistance (SECR) [<inline-formula> <tex-math notation="LaTeX">$\Omega \text{m}^{2}$ </tex-math></inline-formula>] of Cu-ETP (CW004A) contacts is characterized in dependence of contact pressure up to high pressures close to the tensile strength of the base material. Two different material states are considered, R200 (soft) and R300. Static four-wire measurements are carried out on a special experimental setup, which favors homogeneous contact states during mechanical loading. A finite-element simulation is utilized for interpretation and evaluation of the measurements, including the deformation of the samples during the test. The results show that the SECR of the harder material state R300 is higher than that of the softer material R200. The developed data show a decrease of SECR with increasing contact pressure. For contact pressures up to 0.5 of the tensile strength <inline-formula> <tex-math notation="LaTeX">$\sigma _{t}$ </tex-math></inline-formula> of the base material, the SECR decreases according to a power law. For contact pressures above <inline-formula> <tex-math notation="LaTeX">$0.6~\sigma _{t}$ </tex-math></inline-formula>, the decrease shifts toward a linear behavior. In addition, the measurements show that the SECR vanishes at contact pressures in region of the tensile strength of the base material.

Experimental determination of the contact pressures produced by a nasal continuous positive airway pressure mask: A case study

BackgroundA continuous positive airway pressure (CPAP) mask is a respiratory ventilation method used for treating breathing disorders including respiratory failure and obstructive sleep apnoea (OSA). The forces applied by a CPAP mask may affect facial development and lead to pressure ulcers. In an experimental setting, the magnitude and the distribution of the contact pressures developed by a CPAP mask on the face were investigated for providing information aiming at optimizing the design of the device. Materials and methodsA nasal CPAP mask with forehead support was placed via its headgear straps on a rigid phantom head and then a controlled load was incrementally applied via a mechanical testing system (5848 Micro Tester, Instron), up to 4 maximum levels of exerted force, namely 5 N, 10 N, 15 N, and 20 N. Real-time pressure mapping was realized by means of sensor matrixes (I-Scan System, Tekscan) applied on the facial surface in four regions (forehead, nasal bridge, zygoma, and maxilla). The data were then transferred on a virtual model created by 3D scans of both the CPAP mask and the phantom head used in the experiments. ResultsAt increasing applied force, increases in average contact pressure were present at the zygomatic region (1–8 kPa), nasal bridge (12–14 kPa), and forehead (13–29 kPa), while the maxillary region showed relatively stable values (9 kPa). Despite the overall increase in average contact pressure with increasing applied force, no direct proportionality was present. Contact areas did not show clear increments, despite force may redistribute on a larger area, as sensors did not cover the entire mask perimeter. Peak contact pressure values were somehow affected by pressure concentrations that led to saturation in some areas of the sensors (up to 2% of the sensels). ConclusionsThe CPAP mask exerts pressures that may be not uniformly distributed on the face of a subject. This information underlines the clinical importance of assessing both the pressure exerted and the areas that are interested by the mask contact, so as to optimise the CPAP masks design for obtaining a good compromise between ventilation performance and reduction of possible side effects on living tissues.

Preventive measures of fretting wear in railway axle bearings: Combined effect of grooving and amorphous carbon coating towards their backing rings

Fretting wear is surface damage caused by repeated slight relative slips between two contact surfaces. In railway applications, the fretting wear may occur between the inner ring and the backing ring of an axle journal tapered roller bearing. The authors found that a nonuniform pressure distribution between the inner ring and the backing ring deteriorates the fretting wear; a backing ring grooved on its oil seal sliding surface has been proposed to attain a uniform distribution in the radial direction. In this paper, to further reduce the fretting wear, we have conducted a rotation test on a full-scale railway axle bearing with the backing ring both coated its contact surface to the inner ring with diamond-like carbon (DLC) film and grooved its outer surface, and investigated the combined effect of these two approaches on the fretting wear prevention. We have found that the wear prevention effect is superior to the backing ring with only DLC film, but partial decohesion of the DLC film occurs. It is conceivable that the DLC film delaminated from the contact surface of the backing ring due to the locally increased contact pressure between them, even though the grooved backing ring relaxed the contact pressure. We, therefore, conclude that the combined effect of the above approaches is not very apparent. To improve the combined effect of “the grooving” and “the conventional continuous DLC coating,” preventing the decohesion of the DLC film is a challenge. Additionally, we recommend that a continuous structured film be selected as hard film coating the grooved backing ring, which has higher bonding strength than DLC film and a lower friction coefficient.

Arthroscopic Repair of Posterior Root Tears of the Lateral Meniscus with All-Suture Anchor

Meniscus root tears are increasingly being recognized and treated because of improved awareness and diagnostics. These injuries commonly occur in combination with knee ligament injuries. Untreated posterior meniscus root teats have been demonstrated to increase contact pressure and decrease contact area, ultimately leading to unfavorable joint loading and development of early osteoarthritis. Posterior lateral meniscus root tears (PLMRTs) also have been reported to increase anterior tibial translation and pivot shift in anterior cruciate ligament–deficient knees. Therefore, it is crucial to repair meniscal root tears when possible to restore knee joint loading and kinematics. Several techniques for repair of the PLMRT have been described. In this Technical Note, we describe our preferred technique for repair of PLMRT using an all-suture anchor. This technique is reproducible, does not need a tunnel, mitigates bungee effect of transtibial technique, and the anchor can easily be inserted on the footprint without a need for a guide.

High Wear Resistance of Ultralow-Wear Polyethylene with Different Molecular Weights Under Different Contact Pressure

Ultralow-wear polyethylene (ULWPE), a type of polyethylene homocomposite with excellent wear resistance, has recently been reported; however, its underlying wear mechanism has yet to be clarified. In the current study, three different molecular weights of ULWPE from 205 to 748 kg/mol were experimentally evaluated on a multidirectional motion pin-on-disk wear tester under a contact pressure from 2 to 4 MPa, compared with conventional UHMWPE. The high wear resistance mechanism of ULWPE was investigated with respect to mechanical, microstructural, and surface properties. Compared with UHMWPE, ULWPE had excellent wear resistance. Structure and mechanical characterization showed that the crystallinity and lamellar thickness of ULWPE were significantly higher than those of UHMWPE, which endowed ULWPE with high hardness and strength. Despite its considerably smaller molecular weight than that of UHMWPE, ULWPE still had high interphase content, leading to its superior toughness. The crystallinity, lamellar thickness, Young’s modulus, yield stress, and elongation at break of ULWPE exhibited a downward trend with the increase of molecular weight. Conversely, the interphase content of ULWPE increased with the molecular weight increase. Among all the ULWPE samples, ULWPE with a molecular weight 748 kg/mol had the least wear, as a result of combined both excellent strength and adequate toughness. With an increase in contact pressure, the wear losses of different polymers tended to increase. The wear losses of the least wear ULWPE were 4.71 ± 0.04 mm3/Million Cycles (Mc), 5.11 ± 0.37 mm3/Mc, and 5.77 ± 0.62 mm3/Mc under 2, 3, and 4 MPa. Comprehensive strength and toughness reduced abrasive wear and adhesion wear, endowing ULWPE with excellent wear resistance.

Interfacial heat transfer coefficients in cold forging of stainless steel

In numerical simulations of cold forging processes, the heat transfer coefficient has a significant influence on the resulting temperature fields. However, the values determined so far for steel materials are not in the load range of cold forging processes. In this paper, a test stand for the determination of the interfacial heat transfer coefficient under typical loads of metal forming processes is presented. The results are discussed at an example of a cold extrusion forming process. It can be shown that the value increases significantly with increasing contact pressures and are higher compared to values known from literature. The investigations also disclose the influences of lubricants and the mechanical surface treatment on the heat transfer coefficient.

Исследование механизмов трения и оценка трибологических характеристик твердосмазочных покрытий, нанесенных разными методами

The article analyzes the wear dynamics of solid lubricant coatings (SLC) of suspension, magnetron-high-frequency and diffusion methods of application. Calculated dependences are presented to assess the tribotechnical characteristics of the SLC. It was found that the service life of SLC based on MoS2 HF application in the considered ranges of surface temperature variations differs slightly from the that of SLC suspension application VNII NP 212. The wear of diffusion SLC M804 (Dimolit-4) in the steady-state friction mode is 34 µm. The wear rate of diffusion SLC М804 under vacuum conditions at a sliding speed of V = 0.2 m/s with the increase in contact pressure from 1 to 8 MPa increases by a factor of 2 and is on average 4.5 times higher than that of friction pairs with SLC VNII NP 212. Anti-friction characteristics of diffusion SLC in steady state friction modes at temperatures up to 600 °C were slightly higher than the similar characteristics for SLC with a binder. With an increase in heating temperatures to the limiting value of 800 °C, the friction coefficient of the diffusion SLC M801 and M810 (based on NbS2) decreases to the values of ffr = 0.03–0.04.