Measurement Of Contact Area Research Articles

Baseline rolling resistance for tires’ on-road fuel efficiency using finite element modeling

Calculation of truck tires rolling resistance, using the finite element method and considering variables such as incompressible visco-hyperelastic rubber materials, accurate tire geometry and steady temperature distribution, is presented. The model was validated using experimentally measured contact area and contact stresses. Rolling resistance was calculated for three values of axle load, tire inflation pressure, temperature and speed. In addition, regression analysis was used to propose a mathematical expression for predicting rolling resistance as a function of the considered variables. Finally, the contribution of tire’s rubber components to the internal energy was quantified, and it was found that sidewall and subtread were the most relevant. The results of this study will help differentiate the contribution of pavement parameters, such as mean profile depth and international roughness index, to fuel efficiency.

Effect of Chemically Adsorbed Molecules on the Viscous Friction of Nanometer-Thick Liquid Lubricant Films Coated on a Diamond-Like Carbon Surface

Nanometer-thick liquid lubricant films are used for lubrication of miniaturized mechanical systems such as hard disk drives and microelectromechanical systems. In particular at the head–disk interface of hard disk drives, the lubricant thin film is coated on a diamond-like carbon surface, and the films are usually composed of both chemically and physically adsorbed lubricant molecules. The combination of these two types of molecules leads to high lubrication performance. However, the detailed mechanism is not fully understood. The aim of this study was to clarify the effect of chemically adsorbed lubricant molecules on the viscous friction of lubricant films. Two different samples were tested: One was the lubricant film composed of both chemically and physically adsorbed molecules, and the other was the lubricant film with only physically adsorbed molecules. We used a fiber wobbling method (FWM), which we developed in our previous study, to measure the viscous friction. The FWM uses a spherical-ended glass fiber as a shearing probe and enables friction forces in the order of 0.1 nN to be measured at precisely controlled nanometer-scale gap widths. For the fair comparison of friction forces between the samples with different compositions, the contact area between the probe tip and the lubricant film must be the same. To determine the contact area in the friction measurement, we improved the FWM system to enable simultaneous measurement of friction force and contact area. Experimental results showed the 1-nm-thick layer of chemically adsorbed molecules in the lubricant film effectively reduced the viscous friction.

Transition from stick to slip in Hertzian contact with “Griffith” friction: The Cattaneo–Mindlin problem revisited

Classically, the transition from stick to slip is modelled with Amonton–Coulomb law, leading to the Cattaneo–Mindlin problem, which is amenable to quite general solutions using the idea of superposing normal contact pressure distributions – in particular superposing the full sliding component of shear with a corrective distribution in the stick region. However, faults model in geophysics and recent high-speed measurements of the real contact area and the strain fields in dry (nominally flat) rough interfaces at macroscopic but laboratory scale, all suggest that the transition from ‘static’ to ‘dynamic’ friction can be described, rather than by Coulomb law, by classical fracture mechanics singular solutions of shear cracks. Here, we introduce an ‘adhesive’ model for friction in a Hertzian spherical contact, maintaining the Hertzian solution for the normal pressures, but where the inception of slip is given by a Griffith condition. In the slip region, the standard Coulomb law continues to hold. This leads to a very simple solution for the Cattaneo–Mindlin problem, in which the “corrective” solution in the stick area is in fact similar to the mode II equivalent of a JKR singular solution for adhesive contact. The model departs from the standard Cattaneo–Mindlin solution, showing an increased size of the stick zone relative to the contact area, and a sudden transition to slip when the stick region reaches a critical size (the equivalent of the pull-off contact size of the JKR solution). The apparent static friction coefficient before sliding can be much higher than the sliding friction coefficient and, for a given friction fracture “energy”, the process results in size and normal load dependence of the apparent static friction coefficient. Some qualitative agreement with Fineberg's group experiments for friction exists, namely the stick–slip boundary quasi-static prediction may correspond to the arrest of their slip “precursors”, and the rapid collapse to global sliding when the precursors arrest front has reached about half the interface may correspond to the reach of the “critical” size for the stick zone.

Biomechanical Consequences of Lateral Meniscal Posterior Root Avulsions

Objectives:Lateral meniscal posterior root avulsions are commonly found with anterior cruciate ligament (ACL) tears. The purpose of this study was to investigate the biomechanical effects of lateral meniscal posterior root avulsions with and without intact meniscofemoral ligaments (MFLs), and with concurrent ACL tears, on lateral compartment contact mechanics.Methods:A controlled laboratory study was performed using ten nonpaired fresh-frozen cadaveric knees. Tekscan sensors were used to simultaneously measure contact area and pressure (Figure) in the lateral and medial compartments. Specimens were tested with 6 conditions (1: Intact; 2: Lateral meniscal posterior root avulsion; 3: Root avulsion and torn MFL; 4: Condition 3 with ACL tear; 5: Condition 4 with ACL reconstruction; 6: ACL reconstruction with root repair) at 5 flexion angles (0, 30, 45, 60, and 90 degrees), under a 1000 N axial load.Results:Compared to the intact state, condition 2 did not significantly alter lateral compartment contact area or pressure (p < 0.05). A significant decrease in contact area and increase in mean contact pressure occurred in condition 3. Conditions 4 and 5 (ACL tear and reconstruction of the ACL, respectively, both with deficient MFLs and lateral meniscal posterior root avulsion) also produced significantly lower contact areas than the intact condition (p < 0.05), and were not substantially different than Condition 3 (Figure). Changes in contact mechanics tended to be greater at increased flexion angles; for condition 3 at 0 and 90 degrees, contact area decreased 37% and 52% (95% CI [21,53] and [39,66], respectively) and mean contact pressure increased 55% and 87% (95% CI [33,76] and [59,114], respectively). Condition 6 (root repair with ACL reconstruction) was not significantly different from the intact state (p < 0.05).Conclusion:The meniscofemoral ligaments protect the lateral compartment from changes in contact mechanics in the setting of a lateral meniscal posterior root avulsion, whereas combined lateral meniscal root avulsion and deficient meniscofemoral ligaments leads to substantial changes. Concurrent ACL reconstruction and root repair restores contact area and mean contact pressure to the intact state.

Labral Reconstruction with Iliotibial Band Autograft and Semitendinosus Allograft Improves Hip Joint Contact Area and Contact Pressure: An In-Vitro Analysis

Objectives:Labral reconstruction using iliotibial band (ITB) autograft and semitendinosus (Semi-T) allograft have recently been described in cases of labral deficiency. The current study seeks to understand the biomechanical effects of an intact labrum, segmental labral resection, and labral reconstruction on joint contact area, contact pressure, and peak force.Methods:Ten fresh-frozen human cadaver hips were analyzed utilizing thin-film piezoresistive load sensors to measure contact area, contact pressure, and peak force 1) with the native intact labrum, 2) after segmental labral resection and 3) after graft labral reconstruction with either ITB autograft or Semi-T allograft. Each specimen was examined at 20° extension and 60° flexion. Statistical analysis was conducted through one-way ANOVA with post-hoc Games-Howell tests.Results:For the ITB group, labral resection significantly decreased contact area (20°: 73.2%±5.38, P=0.0010; 60°: 78.5%±6.93, P=0.0063) and increased contact pressures (20°: 106.7%±4.15, P=0.0387; 60°: 103.9%±1.15, P=0.0428). ITB reconstruction improved contact area (20°: 87.2%±12.3, P=0.0130; 60°: 90.5%±8.81, P=0.0079) and contact pressures (20°: 98.5%±5.71, P=0.0476; 60°: 96.6%±1.13, P=0.0056) from the resected state. Contact pressure at 60° flexion was significantly lower compared to the native labrum (P = 0.0420). For the Semi-T group, labral resection significantly decreased contact area (20°: 68.1±12.57, P=0.0002; 60°: 67.5%±6.70, P=0.0002) and increased contact pressures (20°: 105.3%±3.73, P=0.0304; 60°: 106.8%±4.04, P=0.0231). Semi-T reconstruction improved contact area (20°: 87.9%±7.95, P=0.0087; 60°: 92.9%±13.2, P=0.0014) and contact pressures (20°: 97.1%±3.18, P=0.0017; 60°: 97.4%±4.39, P=0.0027) from the resected state. Comparative analysis demonstrated no statistically significant differences between either graft reconstruction in relation to contact area, contact pressure, or peak forces. (Figure 1).Conclusion:Segmental anterosuperior labral resection results in significantly decreased contact area and increased contact pressures, while labral reconstruction partially restores time-zero acetabular contact areas and pressures as compared to the resected state. Although labral reconstruction improved the measured biomechanical properties as compared to the resected state, some of these properties remained significantly different compared to the native intact labrum.

Basic study on grip generation mechanism based on quantitative contact area measurement

An outer sole of shoe is mainly designed to control grip. Grip condition is generally figured out with horizontal ground reaction force (GRF) component and traction coefficient, which is the ratio ...

Labral Reconstruction with Iliotibial Band Autograft and Semitendinosus Allograft Improves Hip Joint Contact Area and Contact Pressure: An In-Vitro Analysis

Labral reconstruction using iliotibial band (ITB) autograft and semitendinosus (Semi-T) allograft have been described in cases of labral deficiency. This study explores the biomechanical effects of the intact labrum, segmental labral resection, and labral reconstruction on joint contact area, contact pressure, and peak force. Ten fresh-frozen human cadaver hips were analyzed utilizing thin-film piezoresistive load sensors to measure contact area, contact pressure, and peak force 1) with the native intact labrum, 2) after segmental labral resection and 3) after graft labral reconstruction with either ITB autograft or Semi-T allograft. Each specimen was examined at 20° extension and 60° flexion. Statistical analysis was conducted through one-way ANOVA with post-hoc Games-Howell tests. For the ITB group, labral resection decreased contact area (20°: 73.2%±5.38, P=0.0010; 60°: 78.5%±6.93, P=0.0063) and increased contact pressures (20°: 106.7%±4.15, P=0.0387; 60°: 103.9%±1.15, P=0.0428). ITB reconstruction improved contact area (20°: 87.2%±12.3, P=0.0130; 60°: 90.5%±8.81, P=0.0079) and contact pressures (20°: 98.5%±5.71, P=0.0476; 60°: 96.6%±1.13, P=0.0056) from the resected state. Contact pressure at 60° flexion was lower compared to the native labrum (P = 0.0420). For the Semi-T group, labral resection decreased contact area (20°: 68.1±12.57, P=0.0002; 60°: 67.5%±6.70, P=0.0002) and increased contact pressures (20°: 105.3%±3.73, P=0.0304; 60°: 106.8%±4.04, P=0.0231). Semi-T reconstruction improved contact area (20°: 87.9%±7.95, P=0.0087; 60°: 92.9%±13.2, P=0.0014) and contact pressures (20°: 97.1%±3.18, P=0.0017; 60°: 97.4%±4.39, P=0.0027) from the resected state. Comparative analysis demonstrated no statistically significant differences between either graft reconstruction in relation to contact area, contact pressure, or peak forces Segmental labral resection results in significantly decreased contact area and increased contact pressures, while labral reconstruction partially restores time-zero acetabular contact areas and pressures as compared to the resected state. Although labral reconstruction improved the measured biomechanical properties, some properties remained significantly different compared to the native intact labrum.

Analysis of main parameters affecting substrate/mortar contact area through tridimensional laser scanner

This study assesses the influence of the granulometric composition of sand, application energy and the superficial tension of substrates on the contact area of rendering mortars. Three substrates with distinct wetting behaviors were selected and mortars were prepared with different sand compositions. Characterization tests were performed on fresh and hardened mortars, as well as the rheological characterization. Mortars were applied to substrates with two different energies. The interfacial area was then digitized with 3D scanner. Results show that variables are all of influence on the interfacial contact in the development area. Furthermore, 3D laser scanning proved to be a good method to contact area measurement.

Stress distribution and contact area measurements of a gecko toe using a high-resolution tactile sensor

The adhesive systems of geckos have been widely studied and have been a great source of bioinspiration. Load-sharing (i.e. preventing stress concentrations through equal distribution of loads) is necessary to maximize the performance of an adhesive system, but it is not known to what extent load-sharing occurs in gecko toes. In this paper, we present in vivo measurements of the stress distribution and contact area on the toes of a tokay gecko (Gekko gecko) using a custom tactile sensor with 100 μm spatial resolution. We found that the stress distributions were nonuniform, with large variations in stress between and within lamellae, suggesting that load-sharing in the tokay gecko is uneven. These results may be relevant to the understanding of gecko morphology and the design of improved synthetic adhesive systems.

Measurement of Real Contact Area Using Light Interferometry and Its Application

Measurement of Real Contact Area Using Light Interferometry and Its Application

Optical measurements of real contact area and tangential contact stiffness in rough contact interface between an adhesive soft elastomer and a glass plate

Optical measurements of real contact area and tangential contact stiffness in rough contact interface between an adhesive soft elastomer and a glass plate

1P1-W08 弾性波を用いた人体間皮膚接触量計測

In this paper, we propose a method of human-to-human skin contact area measurement. Human-to-human skin contact is a primitive communication way to express intimacy, encouragement, etc. Additionally, skin contact is used for therapy of autism, mood disorder, etc. Its quantitative measurement and visualization would contribute for related researches in scientific, medical and physiological fields. Our proposed system utilizes bio-acoustic signals which propagate through bodies. When one wears a vibration device and another wears a vibration sensor device, the sensor captures bio-acoustic waves whose magnitude depends on how large area they touch. We describe design and fabrication of the devices. Then we report about our fundamental experiment and its positive results.

The Effect of Prosthetic Radial Head Geometry on the Distribution and Magnitude of Radiocapitellar Joint Contact Pressures

To determine if radiocapitellar contact pressures would be elevated with nonanatomical (circular) prostheses over those mimicking native anatomy and if such pressures would be related to the depth and contour of the articular dish and to the pattern of prosthetic articulation against the lateral trochlear ridge. Three commercially available circular radial head designs were compared with an anatomical radial head and 2 modified anatomical prototype radial head designs in 10 cadaveric specimens. Each prosthesis and specimen combination was loaded in neutral rotation and maximal extension with a custom testing apparatus while measuring contact areas and pressures using thin-film pressure sensors. Anatomical radial head prototype 2 had similar radiocapitellar contact areas and mean pressures as the native radial head; all other designs showed significant decreases in contact area and increased mean pressures. Peak contact pressures were also measured and were significantly elevated with all prostheses tested. Anatomical designs are statistically more likely to mimic normal contact with the lateral trochlear ridge and its adjacent sulcus than circular prostheses. They are also significantly less likely to have contact pressures above the 5 MPa threshold that is thought to be harmful to cartilage. The depth of the articular dish had a significant effect on contact area and pressure. Commercially available radial head prostheses demonstrated reduced radiocapitellar contact areas and elevated contact pressures during compressive loading. These were significantly greater with symmetrical circular prostheses than with asymmetrical elliptical designs. The prosthesis that best mimicked native contact behavior was the anatomical radial head prototype 2 owing to its design for articulating with the capitellum, the lateral trochlear ridge, and the sulcus between. Because radial head prostheses have the potential to cause capitellar erosion or arthritic change, those with lower contact pressures may lead to fewer such complications.

Effect of Distal Ulnar Collateral Ligament Tear Pattern on Contact Forces and Valgus Stability in the Posteromedial Compartment of the Elbow

Background: It is not known whether the pattern of ulnar collateral ligament (UCL) tear affects elbow biomechanics. Hypothesis: There will be a significant change in elbow biomechanics with 50% proximal but not 50% distal simulated rupture of the UCL. Study Design: Controlled laboratory study. Methods: Pressure sensors in the posteromedial elbow joint of 25 male cadaveric elbows (average age, 54.9 years; range, 26-66 years) were used to measure contact area, pressure, and valgus torque at 90° and 30° of elbow flexion. Thirteen specimens were tested with the UCL intact, then with proximal-to-distal detachment of 50%, and then with proximal-to-distal detachment of 100% of the anterior band of the UCL from the ulnar attachment. This method was repeated in the remaining 12 specimens in a distal-to-proximal direction. Results: With 50% proximal-to-distal detachment, contact area decreased significantly versus intact at 90° (91.3 ± 23.6 vs 112.2 ± 26.0 mm2; P < .001) and 30° (69.3 ± 14.8 vs 83.1 ± 21.6 mm2; P < .001) of elbow flexion; the center of pressure (COP) moved significantly proximally versus intact at 90° (3.8 ± 2.5 vs 5.4 ± 2.3 mm; P < .001) and 30° (5.9 ± 2.8 vs 7.4±1.9 mm; P < .001). With 50% distal-to-proximal UCL detachment versus intact, no significant change was observed in contact area, movement of the COP, or valgus laxity at either flexion position. With 100% proximal-to-distal and distal-to-proximal detachment, significant change in contact area, movement of the COP, and valgus laxity versus intact was found at 90° and 30° of elbow flexion (P < .05). No significant difference in contact pressure was observed in any test conditions. Conclusion: Significant change in contact area and proximal movement of the COP with 50% proximal UCL detachment and the lack of significant change with 50% distal UCL detachment suggest that the proximal half of the UCL ulnar footprint has a primary role in maintaining posteromedial elbow biomechanics. Clinical Relevance: The findings suggest that surgical reconstruction should aim to reestablish at least the proximal 50% of the UCL ulnar footprint.

Labral Reconstruction With Iliotibial Band Autografts and Semitendinosus Allografts Improves Hip Joint Contact Area and Contact Pressure

Background: Labral reconstruction using iliotibial band (ITB) autografts and semitendinosus (Semi-T) allografts has recently been described in cases of labral deficiency. Purpose/Hypothesis: To characterize the joint biomechanics with a labrum-intact, labrum-deficient, and labrum-reconstructed acetabulum in a hip cadaveric model. The hypothesis was that labral resection would decrease contact area, increase contact pressure, and increase peak force, while subsequent labral reconstruction with ITB autografts or Semi-T allografts would restore these values toward the native intact labral state. Study Design: Controlled laboratory study. Methods: Ten fresh-frozen human cadaveric hips were analyzed utilizing thin-film piezoresistive load sensors to measure contact area, contact pressure, and peak force (1) with the native intact labrum, (2) after segmental labral resection, and (3) after graft labral reconstruction with either ITB autografts or Semi-T allografts. Each specimen was examined at 20° of extension and 60° of flexion. Statistical analysis was conducted through 1-way analysis of variance with post hoc Games-Howell tests. Results: For the ITB group, labral resection significantly decreased contact area (at 20°: 73.2% ± 5.38%, P = .0010; at 60°: 78.5% ± 6.93%, P = .0063) and increased contact pressure (at 20°: 106.7% ± 4.15%, P = .0387; at 60°: 103.9% ± 1.15%, P = .0428). In addition, ITB reconstruction improved contact area (at 20°: 87.2% ± 12.3%, P = .0130; at 60°: 90.5% ± 8.81%, P = .0079) and contact pressure (at 20°: 98.5% ± 5.71%, P = .0476; at 60°: 96.6% ± 1.13%, P = .0056) from the resected state. Contact pressure at 60° of flexion was significantly lower compared with the native labrum (P = .0420). For the Semi-T group, labral resection significantly decreased contact area (at 20°: 68.1% ± 12.57%, P = .0002; at 60°: 67.5% ± 6.70%, P = .0002) and increased contact pressure (at 20°: 105.3% ± 3.73%, P = .0304; at 60°: 106.8% ± 4.04%, P = .0231). Semi-T reconstruction improved contact area (at 20°: 87.9% ± 7.95%, P = .0087; at 60°: 92.9% ± 13.2%, P = .0014) and contact pressure (at 20°: 97.1% ± 3.18%, P = .0017; at 60°: 97.4% ± 4.39%, P = .0027) from the resected state. Comparative analysis demonstrated no statistically significant differences between either graft reconstruction in relation to contact area, contact pressure, or peak force. Conclusion: Segmental anterosuperior labral resection results in significantly decreased contact areas and increased contact pressures, while labral reconstruction partially restores time-zero acetabular contact areas and pressures as compared with the resected state. Although labral reconstruction improved the measured biomechanical properties as compared with the resected state, some of these properties remained significantly different compared with the native intact labrum. Clinical Relevance: Labral reconstruction appears to improve femoroacetabular joint biomechanics as compared with the labrum-resected state; these improved biomechanics may translate into increased joint function clinically.

Comparison of Compression Screw and Perpendicular Clamp in Ulnar Shortening Osteotomy

To biomechanically quantify 2 techniques, compression screw and perpendicular clamp, for generating compression during ulnar shortening osteotomy (USO) in order to promote reliable primary bone healing. Fourteen fresh-frozen cadaveric human forearms were randomly assigned to 1 of 2 groups. Group I (n= 7) underwent USO according to the traditional AO plate fixation technique using a screw placed eccentrically in an oblong hole to generate compression at the osteotomy site. Group II (n= 7) underwent USO with a commercially available USO plating system using a clamp placed perpendicular to the osteotomy site to generate compression. Both techniques involved a 2-mm resection osteotomy performed with cutting jigs to minimize variability and an interfragmentary lag screw to augment compression. A digital pressure sensor measured contact area at the osteotomy site and average pressure in the observed contact area; these values were used to calculate force across the osteotomy site. Measurements were obtained after the following steps: reduction of osteotomy, compression screw placement (group 1 only), lag screw placement, and final construct with all clamps removed. Group II demonstrated significantly greater force than group I, and lag screw placement resulted in significantly increased force independent of fixation technique. The effect of the lag screw on force was maintained after clamp removal. Although technique of fixation did not significantly influence contact area, lag screw placement significantly increased contact area independent of fixation method. However, this effect was not maintained after clamp removal. Average pressure in the observed contact area was not significantly influenced by fixation technique or stage of fixation. Perpendicular clamp compression significantly increased force as compared with traditional compression screw technique, and lag screw placement significantly increased force in both constructs. Larger compressive forces across the osteotomy may promote primary bone union and decrease the rates of delayed union or nonunion.

Measurement of real contact area on thermal print head using a laser microscope with a wide field of view

In a dye-sublimation printer, a thermal print head presses and heats a dye-based ribbon to diffuse ink dyes to the desired positions into the receiving layer of paper. The print quality will deteriorate if the contact condition between the thermal print head and the paper is insufficient. Thus, it is necessary to analyze the contact condition for finer printing. Direct observation of the contact area with an optical microscope is effective to clarify the contact conditions of the thermal print head. However, conventional optical microscopes take too much time to observe the whole apparent contact area, because their fields of view are not sufficiently wide. Previously, we developed a laser microscope with a wide field of view and applied this laser microscope to observe the whole apparent contact area of rubber elements. In this study, we examined the contact conditions between the thermal print head and the paper. In general, when we observe the contact area of two solid surfaces, one is restricted to a transparent material such as a glass plate. Instead of the thermal print head, a glass head of the same shape as an existing thermal print head was pressed on the paper and observed through the glass head. This allowed us to clearly determine the contact situations of the interface and measure the contact widths and distributions of real contact area. In this method, it was confirmed that the contact width and the real contact area changed in accordance with the type of paper used, steps of the printing process, and density of color printing.

The Biomechanical Effect of Loading Speed on Metal-on-UHMWPE Contact Mechanics.

Ultra high molecular weight polyethylene (UHMWPE) is a material commonly used in total hip and knee joint replacements. Numerous studies have assessed the effect of its viscoelastic properties on phenomena such as creep, stress relaxation, and tensile stress. However, these investigations either use the complex 3D geometries of total hip and knee replacements or UHMWPE test objects on their own. No studies have directly measured the effect of vertical load application speed on the contact mechanics of a metal sphere indenting UHMWPE. To this end, a metal ball was used to apply vertical force to a series of UHMWPE flat plate specimens over a wide range of loading speeds, namely, 1, 20, 40, 60, 80, 100, and 120 mm/min. Pressure sensitive Fujifilm was placed at the interface to measure contact area. Experimental results showed that maximum contact force ranged from 3596 to 4520 N and was logarithmically related (R2=0.96) to loading speed. Average contact area ranged from 76.5 to 79.9 mm2 and was linearly related (R2=0.56) to loading speed. Average contact stress ranged from 45.1 to 58.2 MPa and was logarithmically related (R2=0.95) to loading speed. All UHMWPE specimens displayed a circular area of permanent surface damage, which did not disappear with time. This study has practical implications for understanding the contact mechanics of hip and knee replacements for a variety of activities of daily living.

Classical shear cracks drive the onset of dry frictional motion.

Frictional processes entail the rupture of the ensemble of discrete contacts defining a frictional interface. There are a variety of views on how best to describe the onset of dry frictional motion. These range from modelling friction with a single degree of freedom, a 'friction coefficient', to theoretical treatments using dynamic fracture to account for spatial and temporal dynamics along the interface. We investigated the onset of dry frictional motion by performing simultaneous high-speed measurements of the real contact area and the strain fields in the region surrounding propagating rupture tips within the dry (nominally flat) rough interfaces formed by brittle polymer blocks. Here we show that the transition from 'static' to 'dynamic' friction is quantitatively described by classical singular solutions for the motion of a rapid shear crack. We find that these singular solutions, originally derived to describe brittle fracture, are in excellent agreement with the experiments for slow propagation, whereas some significant discrepancies arise as the rupture velocity approaches the Rayleigh wave speed. In addition, the energy dissipated in the fracture of the contacts remains nearly constant throughout the entire range in which the rupture velocity is less than the Rayleigh wave speed, whereas the size of the dissipative zone undergoes a Lorentz-like contraction as the rupture velocity approaches the Rayleigh wave speed. This coupling between friction and fracture is critical to our fundamental understanding of frictional motion and related processes, such as earthquake dynamics.

Biomechanical Consequences of a Complete Radial Tear Adjacent to the Medial Meniscus Posterior Root Attachment Site

Objectives:Complete radial tears near the medial meniscus posterior root attachment site disrupt the circumferential integrity of the meniscus (similar to a posterior root avulsion). These tears can compromise the circumferential integrity and have been reported in biomechanical studies to simulate the meniscectomized state. The purpose of the study was to quantify the tibiofemoral contact load and contact area changes that occur in cadaveric knees from complete posterior horn radial tears and subsequent repairs of the medial meniscus adjacent to the posterior root attachment site.Methods:Six non-paired fresh-frozen human cadaveric knees each underwent 45 different testing conditions: 9 medial meniscus conditions (intact, root avulsion, root repair, serial radial tear and in-situ repair at 3, 6, and 9 mm from the root attachment site) at 5 flexion angles (0°, 30°, 45°, 60° and 90°); under a 1000-N axial load. Tekscan sensors were used to measure contact area and pressure in the medial and lateral compartments.Results:The medial meniscus root avulsion and all radial tear conditions resulted in significantly decreased contact area and increased mean contact pressure compared with the intact state for knee flexion angles beyond 0° (P < .05). Medial Compartment Contact Area Individual comparisons of meniscus conditions for results at 30°, 45°, 60° and 90° of flexion demonstrated the following. At each angle, the root avulsion and 3, 6 and 9 mm radial tears resulted in a significant reduction (range 33%-45% decrease) in medial compartment contact area. Medial Compartment Contact PressureIndividual comparisons of meniscus conditions were performed at 30°, 45°, 60° and 90° of flexion. At each angle, the root avulsion and all radial tears resulted in a significant increase in average contact pressure (range 46%-110%) when compared to the intact meniscus. Root Repair and In-situ Repairs The root repair and in-situ repairs restored contact area and pressure to levels statistically indistinguishable from the intact meniscus, and increased contact area and decreased contact pressure when compared to the corresponding tear conditions (Figure).Conclusion:Posterior horn radial tears adjacent to the medial meniscus root that extend to the meniscocapsular junction can lead to derangement of the loading profiles of the medial compartment that are similar to a root avulsion. Repair of these radial tears with an in-situ pullout technique restored joint mechanics to the intact state. Clinical Relevance Complete radial tears of the posterior horn of the medial meniscus, are biomechanically equivalent to root avulsions and could potentially lead to medial compartment arthrosis. An in-situ repair offers an alternative treatment to meniscectomy and can reestablish the posterior anchor point, thus improving load distribution in the medial compartment.