Estimation Of Contact Area Research Articles

Magnetic resonance imaging of in vivo patellofemoral kinematics after total knee arthroplasty

Simulated partial weight bearing during magnetic resonance imaging of the knee was used to measure patellar tilt, medial–lateral patellar shift, and patellofemoral contact area in three groups of subjects; patients with posterior cruciate retaining (PCR) TKA, patients with bicruciate substituting (BCS) TKA, and healthy controls. Contact stress was also calculated based on the contact area and body weight-based estimates of contact force. Contact stress was significantly (p<0.05) higher in PCR knees (2.5±3.0 MPa) than in BCS knees (0.2±0.1 MPa) when knees were fully extended, but this difference was not significant (3.7±3.5 MPa for PCR knees vs. 1.4±1.9 MPa for BCS knees; p>0.05) in early flexion. The results also indicate that patellar tilt (normal=2.4°±4.8°, BCS=5.5°±5.5°, PCR=−3.0°±6.9° change in lateral tilt when moving from full extension to early flexion) and contact area (full extension: normal=267±111 mm2, BCS=344±201 mm2, PCR=83±80 mm2; early flexion: normal=723±306 mm2, BCS=417±290 mm2, PCR=246±108 mm2) in BCS TKA mimic those in the normal knees more closely than PCR knees do. These results suggest that the patellar component in BCS TKA may be expected to experience less wear than the patellar component in PCR TKA over time.

Atomic force microscopy investigations on nanoindentation impressions of some metals: effect of piling-up on hardness measurements

In the indentation test, the hardness and the elastic modulus depend strongly on the estimate of the indenter-material contact area at peak load. However, many elastic–plastic behaviours such as elastic recoveries during unloading and piling-up or sinking-in of surface profiles during indentation affect the determination of the hardness and the elastic modulus. So, atomic force microscopy is a method of utmost importance to provide an accurate knowledge of the indentation impression especially when plastic deformations occur, that leads to errors in the determination of the contact area. Atomic force measurements of vanadium, tungsten, molybdenum and tantalum pure metals as well as stainless steels, often used as substrates for thin films depositions, highlight the difficulties to estimate the contact area. The variation of hardness values determined by atomic force microscopy measurements and nanoindentation test is correlated to the formation of folds of 150 and 100 nm high, around the residual impression of vanadium and tungsten indented at 0.1 N, respectively. Some folds which increase with increasing loads are detected on the residual impressions of both 35CD4 and 30NCD16 stainless steels indented under loads of 0.01 N, only. Such structures are related to piling-up of surface profiles that could lead to an underestimate of the contact area in the indentation test. So, the hardness value of tungsten could be closer to 6 than to 7 GPa whereas the effect of piling-up on the estimation of contact area of vanadium could be lower. Almost no deformation is seen on tantalum and molybdenum. So, the hardness values determined by the various methods are consistent. These results show that atomic force microscopy measurements are quite complementary of the nanoindentation test.

Impact of non-elliptic contact modelling in wheel wear simulation

Advances in simulation of railway wheel wear in the sense of material removal have drawn the attention to the importance of wheel–rail contact modelling. As a further step of enhancing the used simulation procedure in direction of increased generality and reduced need for application-dependent calibration, the focus of this investigation is the influence of non-elliptic contact models on the wheel wear rate and profile shape. To facilitate evaluation the semi-Hertzian contact procedure Stripes, developed by INRETS in France, has been implemented. To investigate the capabilities of Stripes to assess the contact area and pressure, shape comparisons have been made with other numerical methods for a set of wheel–rail contact situations. The referenced results are based on the linear elastic half-space assumption, elastic finite element analysis, and elastic–plastic finite element analysis. For reference also the elliptic contact area according to Hertz is shown as given by the contact data table of the multi-body simulation code. After exploring the properties of the Stripes procedure with respect to contact area estimation and pressure distribution, the focus is moved to the influence on wear rate, being the principal objective of this investigation. First the wear distribution over the contact patch is studied and compared to results using the elliptic model from the MBS code Gensys and the non-elliptic approach with Kalker's code Contact. Finally the evolution of the wheel profile is simulated for a few typical cases. This investigation of wear distributions over non-elliptic patches under different operating conditions indicates significant differences compared to both Contact and the applied Hertzian approach. The expansion from single contact occasions to complete simulations indicates comparable material removal rates but relocation towards the flange side. This tendency is apparent in all of the cases shown, however limited to initial wear in tangent run or reasonably mild curve negotiation.

B106 膝蓋大腿関節の生体内接触面積の評価(B1-2 関節2)

B106 膝蓋大腿関節の生体内接触面積の評価(B1-2 関節2)

Sliding friction of polyethylene on snow and ice: Contact area and modeling

A numerical model for sliding on ice including dry friction and generation of and lubrication by water films is described. The model is verified by comparison with experimentally determined friction coefficients and slider temperatures. Real contact area estimates based on actual topography can explain the experimentally observed temperature dependence, while squeeze out of water at the junctions can explain the observed load dependence of friction.

Three-dimensional dynamic hip contact area and pressure distribution during activities of daily living

Estimation of the hip joint contact area and pressure distribution during activities of daily living is important in predicting joint degeneration mechanism, prosthetic implant wear, providing biomechanical rationales for preoperative planning and postoperative rehabilitation. These biomechanical data were estimated utilizing a generic hip model, the Discrete Element Analysis technique, and the in vivo hip joint contact force data. The three-dimensional joint potential contact area was obtained from the anteroposterior radiograph of a subject and the actual joint contact area and pressure distribution in eight activities of daily living were calculated. During fast, normal, and slow walking, the peak pressure of moderate magnitude was located at the lateral roof of the acetabulum during mid-stance. In standing up and sitting down, and during knee bending, the peak pressures were located at the edge of the posterior horn and the magnitude of the peak pressure during sitting down was 2.8 times that of normal walking. The peak pressure was found at the lateral roof in climbing up stairs which was higher than that in going down stairs. These results can be used to rationalize rehabilitation protocols, functional restrictions after complex acetabular reconstructions, and prosthetic component wear and fatigue test set up. The same model and analysis can provide further insight to soft tissue loading and pathology such as labral injury. When the pressure distribution on the acetabulum is inverted onto the femoral head, prediction of subchondral bone collapse associated with avascular necrosis can be achieved with improved accuracy.

3D Measurement of Electrode Contact Area in Resistance Spot Welding of Coated Steel

The document discusses the possibility of contact area estimation during resistance spot welding employing post-weld 3D measurement of electrode indentation. Experimental welding of a common type of mild zinc-coated steel was conducted using two different electrode tip types varying welding time, RMS current and number of successive welds. The other parameters (clamping force, voltage, pre- and post-weld time, weld-piece thickness) were constant. The results show that this approach gives valuable information on the conditions under which the weld-spot was formed.

Quantitative impedance measurement using atomic force microscopy

Obtaining quantitative electrical information with scanning probe microscopy techniques poses a significant challenge since the nature of the probe/sample contact is frequently unkown. For example, obtaining quantitative kinetic data from the recently developed atomic force microscopy (AFM) impedance technique requires normalization by the probe/sample contact area. In this paper, a methodology is proposed that enables the extraction of quantitative information from the AFM impedance technique. This methodology applies results from nanoindentation experiments and contact mechanics theory to characterize AFM probe contacts. Using these results, probe/sample contact forces (which can be accurately measured in the AFM) may be converted into probe/sample contact area estimates. These contact area estimates, when included in model of the probe/sample contact, enable the extraction of quantitative data. This methodology is applied to the recently developed AFM impedance measurement technique, enabling a quantitative study of the oxygen reduction reaction (ORR) at nanometer length scales. Using the AFM impedance system, kinetic data for the (ORR) at nanoscale Platinum/Nafion contacts is extracted. The kinetic data obtained from the AFM impedance technique match previous bulk measurements—affirming the technique’s quantitative potential.

Estimation of real contact area in a wheel-rail system by means of ultrasonic waves

The application of an ultrasonic technique to estimate the Real Contact Area (RCA) in a wheel-rail system is proposed. The method is based on the analysis of the reflection of ultrasonic waves which are sent over the contact region and reflected by it according to the state of contact. The interaction of the experimental data with a theoretical model formulated in the early 1990s by Krolikowski allows us to calculate the RCA for the area illuminated by the ultrasonic beam. By varying the external load and the surface conditions of the contacting elements, it is possible to obtain the trend of the RCA with increasing load (for a certain roughness) as well to explore changes in RCA for different roughness while the load is kept fixed. Results showed that RCA grows almost linearly with the applied load and that an increase of one order of magnitude in combined roughness of the wheel-rail system leads to a roughly sevenfold reduction in RCA under a given load.

Investigation of Wear of Microelectromechanical Contacts

AbstractA test system has been assembled to examine factors controlling the reliability of microdevice switching. The system consists of a spherically tipped sputter-coated post driven by a piezoresistive actuator into a sputter-coated micromechanical membrane. Contact forces are calculated based upon the measured deflection of the micromechanical membrane, which is induced by post actuation. Membrane deflection is measured using white light interferometry. The known geometry of the membrane and probe tip permits the estimation of contact area and, hence, contact pressure. Preliminary testing of sputtered gold contacts resulted in localized melting, material transport to the membrane and failure of contact surfaces at relatively low contact pressures and current densities. Further testing will examine the factors governing the reliability of microdevice contacts, such as material properties, contact pressure and current density.

Mechanics of Contacts at Less than 100Å Scale: Indentation and AFM

ABSTRACTUnderstanding of both low load Nanoindentation and Atomic Force Microscopy relies on a knowledge of the mechanical response of contacts at the few nanometre scale. To investigate this area we have developed a new type of AFM/Indenter which applies forces (&lt;1nN up to 1mN) to a tip mounted on a cantilever. The displacement of the cantilever is detected using laser heterodyne interferometry. The combination gives a direct measurement of contact compliance at very low loads. Contacts of diameter below 100Å can be repeatably made.We show that a water film is generally present in the contact during operation in air, and show how its size can be estimated from our data. One implication is that ambient operation of AFM in both repulsive and attractive modes may necessitate the presence of a liquid lubricating film, explaining the relative lack of damage in many AFM measurements. The estimation of contact area from stiffness is complicated by this layer. We show that the contact stresses are likely to be very high.