Surface Contact Pressure Research Articles

Three-Dimensional Dry/Wet Contact Analysis of Multilayered Elastic/Plastic Solids With Rough Surfaces

Friction/stiction and wear are among the main issues in microelectromechanical systems (MEMS/NEMS) devices having contact interfaces. Relevant parameters, i.e., layers thickness, need to be optimized. The contact analyses of multilayered structure under both dry and wet conditions are necessary to optimize these parameters. This study presents a first attempt to perform three-dimensional contact analysis of multilayered solids with rough surfaces in both dry and wet conditions. The surface displacements and contact pressure distributions are obtained based on variational principle with fast Fourier transform scheme. The effective hardness is modeled and plays a role when the local displacement meets the maximum displacement criterion. Simulations are performed to obtain the contact pressures, fractional total contact area, fractional plastic contact area, surface/subsurface stresses. Relative meniscus forces are obtained with the presence of an ultrathin liquid film for different loads and layers properties. These contact statistics and meniscus forces are analyzed to study the effects of layer-to-substrate ratios of stiffness and hardness, and the layers thickness of rough, two-layered elastic/plastic solids. The methods to decrease friction/stiction and wear are investigated, and the optimum layer parameters are identified.

Modeling Thermal Contact Resistance: A Scale Analysis Approach

A compact analytical model is developed for predicting thermal contact resistance (TCR) of nonconforming rough contacts of bare solids in a vacuum. Instead of using probability relationships to model the size and number of microcontacts of Gaussian surfaces, a novel approach is taken by employing the “scale analysis method.” It is demonstrated that the geometry of heat sources on a half-space for microcontacts is justifiable for an applicable range of contact pressure. It is shown that the surface curvature and contact pressure distribution have no effect on the effective microthermal resistance. The present model allows TCR to be predicted over the entire range of nonconforming rough contacts from conforming rough to smooth Hertzian contacts. A new nondimensional parameter, i.e., ratio of the macro- over microthermal resistances, is introduced as a criterion to identify three regions of TCR. The present model is compared to collected TCR data for SS304 and showed excellent agreement. Additionally, more than 880 experimental data points, collected by many researchers, are summarized and compared to the present model, and relatively good agreement is observed. The data cover a wide range of materials, mechanical and thermophysical properties, micro- and macrocontact geometries, and similar and dissimilar metal contacts.

Laser beam surface hardening of CVD TiN-coated steels

Properties of hard coatings deposited by chemical vapor deposition (CVD) processes are usually excellent. However, high deposition temperatures may influence the properties of steel substrates negatively. Therefore, a subsequent heat treatment is necessary to restore the properties of steel substrates that are ready for operation (e.g., sheet-forming tools in the automotive industry). By duplex treatment of CVD coating with laser beam hardening, a composite material with flat strength and hardness gradients from the interface to the core, together with a high surface hardness, can be implemented. The supporting effect of the laser beam-hardened substrate leads to an increase of the wear resistance under high surface contact pressures and, at the same time, to an increased material resistance against high mechanical load. Laser beam hardening is applied on CVD TiN-coated AISI 4140 (EN 42CrMo4), AISI A2 (EN X100CrMoV5-1), and AISI D2 (EN X153CrMoV12) substrates. For characterization of composite materials, the chemical composition of the coating and the substrate are analyzed by glow discharge optical spectroscopy (GDOS). Additionally, the microstructure and the substrate hardness are examined. To show the characteristic improvements in comparison with individual processes, scratch tests are executed. The results show great advantages of laser beam surface hardening because only low distortion occurs and the properties of the steel substrates are improved without losing good coating properties.

Surface Shape and Contact Pressure Evolution in Two Component Surfaces: Application to Copper Chemical Mechanical Polishing

Two defects that arise from the polishing process in integrated circuits technology are erosion and dishing. In this manuscript a generic numerical model that is capable of describing these defects from a mechanics perspective is presented. This numerical model formulates evolution of surface shape for an initially flat sample made up of two distinct materials with different wear rates under constant average polishing pressure. A two parameter elastic foundation model is used for contact pressure calculations. Qualitatively, the results compare favorably to published experimental data collected for copper chemical mechanical polishing. Although entirely mechanical, such modeling may perhaps provide insight into the mechanics of the surface defects and errors encountered during polishing.

Thermal contact conductance of pressed contacts at low temperatures

The influence of variations of interface temperature in the range 50–300 K on the thermal contact conductance between aluminium and stainless steel joints was determined. Predictions were done by modeling the deformation at the interface for different values of surface finish and contact pressure over the range of interface temperatures. Both elastic and plastic deformation was considered. Experiments were carried out in a closed loop cryostat and the results were shown to compare well with the predictions. A reduction of the interface temperature resulted in a smaller value of thermal contact conductance. Interfacial pressure variation had much lower influence at the smaller value of temperatures. The role of surface roughness at the contact was also seen to be less significant at lower interface temperatures and the zone of hysteresis was smaller. A correlation was developed for estimating thermal contact conductance at joints over this temperature range. An explicit dependence of contact conductance on temperature was not seen to be necessary as long as the changes in the hardness and thermal conductivity of the material with temperature are incorporated in the correlation.

Thermal Contact Resistance of Nonconforming Rough Surfaces, Part 2: Thermal Model

A new analytical model is developed for thermal contact resistance (TCR) of nonconforming rough surfaces. TCR is considered as the superposition of macro- and microthermal resistances. The effects of roughness, load, and radius of curvature on TCR are investigated. It is shown that there is a value of surface roughness that minimizes the TCR for a fixed load and geometry. Simple correlations for determining TCR, using relationships introduced in Part 1 of this study, are derived that cover the entire range of TCR from conforming rough to smooth spherical contacts. With introduction of an approximate model, it is shown that the effective microthermal resistance is not a function of surface curvature and contact pressure profile. The comparison of the present model with 600 experimental data points shows good agreement in the entire range of TCR. A criterion for conforming contacts is proposed that gives a range for the ratio of out-of-flatness to surface roughness.

The Effect of Graft Height Mismatch on Contact Pressure following Osteochondral Grafting

Hypothesis Incongruity of the articular cartilage following osteochondral transplantation affects surface contact pressure. Study Design An 80 N load was applied for 120 seconds to the femoral condyles of 10 swine knees. Contact pressures were measured using Fuji prescale film. Seven conditions were tested: (1) intact articular surface; (2) 4.5-mm diameter defect; (3) grafted with 4.5-mm diameter plug elevated 1 mm above adjacent cartilage; (4) plug elevated 0.5 mm; (5) plug flush; (6) plug sunk 0.5 mm below surface; and (7) sunk 1.0 mm. Conclusions Peak contact pressures were significantly (P< .001) elevated by ~20% after defect creation and were reduced to normal when plugs were flush. There were large and significant (P< .001) increases in pressure with plugs elevated 1 and 0.5 mm. Contact pressures with plugs sunk 0.5 and 1 mm were significantly (P< .01) higher than intact cartilage but were significantly (P < .01) lower than an empty defect. Clinical Relevance Normal contact pressures and patterns can be duplicated with flush articular surface grafts. However, small incongruities, particularly when the plug is elevated, can lead to significantly increased pressure. This reinforces the importance of articular surface congruity in the initial biomechanical state following osteochondral implantation.

The effect of slip regime on fretting wear-induced stress evolution

A numerical approach to simulate fretting wear, based on a modified version of the Archard equation, is applied to a cylinder-on-flat fretting configuration for gross sliding and partial slip conditions. The evolution of contact geometry, surface contact variables, including, contact pressure and relative slip, and sub-surface stresses are predicted. Surface wear damage is predicted to have a significant effect on the near-surface tangential and shear stress distributions for both slip regimes, with significant differences between the partial slip and gross slip cases. The implications of these effects are discussed with respect to fatigue prediction, leading to new insight into experimentally observed effects of slip regime on crack initiation. The more detrimental effects of partial slip conditions, with respect to cracking risk, are demonstrated quantitatively. In addition, the results suggest an explanation for the observed variations in location of crack initiation within the slip zone under partial slip conditions. The work establishes a basis for direct incorporation of the effect of slip amplitude on fretting fatigue life prediction.

107 工作機械の熱変形低減に関する研究 : 接触面の熱遮断効果に及ぼす断熱材の影響(OS3 最新工作機械)

Recent machine tools have been required both high-efficient and high-precision machining. The increase of a calorific amount due to the speed-ups of the rotational speed and the feed rate becomes one of the major cause of the machine tools' thermal deformation. The authors have proposed an efficient reduction method for the machine tools' thermal deformation. This method is aimed to collect and remove the heat, which have generated inside the machine tools, before it is spread over the adjacent components. For the basis of establishing the method to.reduce the thermal deformation, this report indicates the experimental results of the insulation effects of an insulator being sandwiched between the contact surfaces and clarifies the effects of both material and thickness of the insulator and the contact surface pressure on the thermal contact resistance. The experimental results show that the thermal contact resistance of CFRP with 1mm in the thickness was about 10 times as much as the resistance of the direct contact.

Measurement of Trocar Insertion Force Using a Piezoelectric Transducer

We attempted to establish a model to measure the force required for trocar insertion at laparoscopy. A 3-cm, circular transducer was constructed from piezoresistive material that changes its impedance as force is exerted on its surface. The transducer is connected by an interface box to a personal computer to record surface contact pressure digitally (pressure = force/area) profile continuously during trocar insertion. Each subject had three trocars inserted: a 10-mm trocar at the umbilicus after creation of pneumoperitoneum, and 5-mm trocars at corresponding sites on the left and right sides of the lower abdomen. All insertions were performed by the same operator using reusable trocar with a conical tip. Each subject acted as her own control. Recordings were successfully obtained from eight women. There was no instance of transducer failure. The mean (SE) peak contact surface pressure for the 10-mm and 5-mm left and right trocars were 5.3 (0.32), 6.4 (0.51), and 6.81 (0.27) pounds/square inch, respectively. Placement of the 10-mm trocar required less insertion force than placement of the 5-mm trocars. There was a strong negative correlation (r = −0.97, p <0.001) between body weight and peak insertion force for the 10-mm trocar.

Quantification of contact surface pressure exerted during external cephalic version.

The amount of force exerted on the uterus and fetus during external cephalic version (ECV) may be associated with fetal effects or complications. We have designed an instrument to quantify the contact pressure exerted during the performance of ECV, as an indirect measurement of the applied force. We have designed a pair of custom-made gloves. Each glove contains 16 piezo-resistive sensors positioned on the palmer surface of the fingers, thenar and hypothenar areas. Pressure readings were recorded simultaneously from all sensors every 0.22 s during each version procedure. Each recording was analyzed with a computer program written according to specified algorithms to ascertain the number of attempts in a version operation, and the duration and pressure changes of each attempt during the operation. Ten subjects having a singleton breech presentation at term underwent an operation of ECV. The number of attempts of version in each operation ranged from one to four. The median pressure-time integral and the duration of an attempt were 19,227 mmHg s (range 5089-42,597 mmHg s) and 42.5 s (range 11.9-80.3 s), respectively. The median pressure-time integral of a whole version operation was 38,110 mmHg s (range 5089-107,511 mmHg s). Subjects with a failed version operation received a higher pressure-time integral (p < 0.05). The number of attempts of each operation was accurately identified by the program. Measurement of force applied during ECV can be quantified indirectly in terms of contact surface pressure. The indirect measurement of the applied force may further improve the safety of this procedure by preventing excessive use of force by the operator.

Transition from static to kinetic friction of unlubricated or oil lubricated steel/steel, steel/ceramic and ceramic/ceramic pairs

Tribological tests were conducted on different pairs of the bearing steel 100Cr6 and a commercial alumina under unlubricated and oil lubricated conditions where the transition behaviour from static to kinetic friction as a function of surface finish and contact pressure was of particular interest. Static and kinetic friction were measured using a laboratory tribometer with ball-on-plate geometry at an extremely low tangential speed of 8.3 μm/s applied to the plate specimen. Results showed a significant effect of surface finish on both the static and kinetic coefficients of friction as well as on the transition behaviour. Transition behaviour was strongly dependent on the materials mated. The self-mated steel pairs showed greater values of kinetic than static coefficient of friction while no significant difference of both friction values was measured on self-mated alumina pairs with ground plate specimens. Influence of oil lubrication on static friction was small compared with that on kinetic friction where the last one was substantially reduced by oil lubrication with 100Cr6/100Cr6 and 100Cr6/Al 2O 3 pairs, particularly. Stick-slip effects occurred with both unlubricated and lubricated pairs under high normal loads and depending on surface finish.

Quantification of contact surface pressure exerted during external cephalic version

Quantification of contact surface pressure exerted during external cephalic version

Constriction resistance at high signal frequencies

Constriction resistance arises in practical electrical interfaces because contact is made at discrete spots as defined by the surface roughness and contact pressure. This paper describes the dependence of constriction resistance on signal frequency. This dependence was calculated for circular constrictions ranging in diameter from 10 to 100 /spl mu/m, and for frequencies ranging from DC to 1 GHz. The results indicate that the magnitude of constriction resistance does not deviate appreciably from values predicted by Helm's classical analytical expression, as long as the skin depth is large compared with the constriction radius. For skin depths that are much smaller than the constriction radius, constriction resistance decreases with increasing frequency to an apparent limiting value independent of the constriction radius. At high frequencies, constriction resistance constitutes only one of two components of the total connection resistance measured in practice. The second component of connection resistance is determined by details of the geometry and dimensions of the contact interface, and increases with signal frequency.

Effects of clothing pressure caused by different types of brassieres on autonomic nervous system activity evaluated by heart rate variability power spectral analysis.

The present study was designed to investigate the effects of clothing skin pressures exerted by two different types of brassieres (a conventional higher skin-pressured brassiere and a newly devised low skin-pressured brassiere) on the autonomic nervous system (ANS) activity. Six healthy young women (22.8 +/- 1.4 yrs.) with regular menstrual cycles participated in this study. The ANS activities were assessed by means of heart rate variability power spectral analysis. The skin pressures exerted by the brassieres were measured with an air-pack type contact surface pressure sensor at five different points. The total amount of clothing pressure, and the pressures at the center and the side regions of the brassieres were significantly greater in the high than in the low skin-pressured brassiere (Total 9816.1 +/- 269.0 vs. 6436.8 +/- 252.4 Pa, P < 0.01; Center 2212.1 +/- 336.3 vs. 353.8 +/- 85.8 Pa, P < 0.01; Side 2556.8 +/- 316.1 vs. 1747.2 +/- 199.2 Pa, P < 0.05). Concerning the ANS activity, the Total power, and the very low frequency (VLF) and the high frequency (HF) components were significantly decreased in the high skin-pressured brassiere than those in the low skin-pressured brassiere (Total 531.6 +/- 57.3 vs. 770.5 +/- 54.2 ms2, P < 0.01; VLF 60.7 +/- 14.6 vs. 179.2 +/- 38.1 ms2, P < 0.05; HF 209.5 +/- 33.2 vs. 283.2 +/- 61.5 ms2, P < 0.01). Our data indicate that the higher clothing pressures exerted by a conventional brassiere have a significant negative impact on the ANS activity, which is predominantly attributable to the significant decrease in the parasympathetic as well as the thermoregulatory sympathetic nerve activities. Since the ANS activity plays an important role in modulating the internal environment in the human body, excess clothing pressures caused by constricting types of foundation garments on the body would consequently undermine women's health.

Estimation of rubber sliding friction from asperity interaction modeling

Interaction between a soft rubber asperity and its hard counterpart is traced with the help of a finite element computation. The analysis is aimed to estimate the influence of adhesion between rubber and rigid surfaces and the energy losses arising from the deformation of rubber bulk to the sliding resistance. At the contact zone, interfacial bonds are formed due to adhesion and their resistance to sliding is represented by the shear strength of the contact interface. In the rubber bulk, the hysteresis loss is calculated using an appropriate model of the viscoelastic mechanical behavior of rubber for large strains. Dependence of friction on sliding speeds and temperature is hence detected. Influence of surface roughness and contact pressure on friction is also examined.

On the Sliding Friction Characteristics of Unidirectional Continuous FRP Composites

By applying a closed-form analytical solution Hwu and Fan (1998) for an anisotropic half-plane, the contact characteristics of unidirectional continuous fiber-reinforced plastic (FRP) composites are investigated. The particular condition of a rigid parabolic cylinder in normal sliding contact with the composite is evaluated. The influence of FRP composite matrix material, friction coefficient, fiber material, fiber orientation, and fiber volume fraction on the surface contact pressure are determined and evaluated by comparison to published experimental data and results from the finite element method. From the analytical results, several important trends for the contact characteristics of fiber-reinforced plastics are ascertained and discussed with respect to the wear and design-ability of FRP materials.

Biomechanical and topographic considerations for autologous osteochondral grafting in the knee.

This study characterizes the donor and recipient sites involved in osteochondral autograft surgery of the knee with respect to articular cartilage contact pressure, articular surface curvature, and cartilage thickness. Five cadaveric knees were tested in an open chain activity simulation and kinematic data were obtained at incremental knee flexion angles from 0 degrees to 110 degrees. Surface curvature, cartilage thickness, and contact pressure were determined using a stereophotogrammetry method. In all knees, the medial trochlea, intercondylar notch, and lateral trochlea demonstrated nonloadbearing regions. Donor sites from the distal-medial trochlea were totally nonloadbeadng. For the intercondylar notch, lateral trochlea, and proximal-medial trochlea, however, the nonloadbearing areas were small, and typical donor sites in these areas partially encroached into adjacent loadbearing areas. The lateral trochlea (77.1 m(-1)) was more highly curved than the typical recipient sites of the central trochlea (23.3 m(-1)), medial femoral condyle (46.8 m(-1)), and lateral femoral condyles (42.9 m(-1)) (P < 0.05). Overall, the donor sites had similar cartilage thickness (average, 2.1 mm) when compared with the typical recipient sites (average, 2.5 mm). The lateral trochlea and medial trochlea curvatures were found to better match the recipient sites on the femoral condyles, while the intercondylar notch better matched the recipient sites of the central trochlea. The distal-medial trochlea was found to have the advantage of being nonloadbearing. Preoperative planning using the data presented will assist in more conforming, congruent grafts, thereby maximizing biomechanical function.

Experimental Measurement of the Interface Heat Conductance Between Nonconforming Beryllium and Type 316 Stainless Steel Surfaces Subjected to Nonuniform Thermal Deformations

In fusion blanket designs that employ beryllium as a neutron multiplier, the interface conductance h plays a key role in evaluating the blanket’s thermal profile. Therefore, an extensive experimental program was conducted to measure the magnitude of h between nonconforming beryllium and Type 316 stainless steel surfaces subjected to nonuniform thermal deformations. The magnitude of h was measured as a function of relevant environmental, surface, and geometric parameters, including surface roughness, contact pressure, gas pressure, gas type, and magnitude and direction of heat flow. The results indicate the following: (a) Decreasing the interfacial surface roughness from 6.28 to 0.28 μm, in 760 Torr of helium, increased the magnitude of h by up to 100%; however, increasing the surface roughness reduced the dependence of h on the magnitude of the contact pressure. (b) The interface conductance was significantly higher for measurements made in helium gas as opposed to air. Additionally, the sensitivity of h to the gas pressure was significantly greater for runs conducted in helium and/or with smoother surfaces. This sensitivity was reduced in air and/or with roughened surfaces, and it was essentially nonexistent for the 6.25-μm specimen for air pressures exceeding 76 Torr. (c) For runs conducted in vacuum, the interface conductance was more sensitive to heat flux than when runs were conducted in 760 Torr of helium. (d) The interface conductance was found to be dependent on the direction of heat flux. When the specimens were arranged so that heat flowed from the steel to the beryllium disk, the magnitude of h was generally greater than in the opposite direction.

Medium Term Results of a Mobile Bearing Total Knee Replacement

Mobile bearing total knee arthroplasty kinematically allows the advantages of large and congruent surface contact and low contact pressures, while preserving flexion, extension, and rotation in knee motion. In allowing for these degrees of freedom, the interface between bone and component also is protected from high stress. The Self Aligning I total knee arthroplasty initially was implanted in patients after its development at the authors' institution in 1990. Between 1990 and 1994, 141 patients with osteoarthritis of the knee underwent 172 total knee replacements using this system. At average followup of 5.6 years (range, 5-8 years), clinical results using this system showed a 94% satisfaction rate (good or very good). Two revision surgeries have been performed for polyethylene wear, with none of the remaining knees showing evidence of discernible wear. Complications included four cases of deep infection, four cases where a press fit femoral component failed (nonporous coated) and the patients required revision surgery, four traumatic fractures (three patellar and one supracondylar), one popliteal artery occlusion, and one revision for stiffness. Three patients required manipulation under anesthesia for arthrofibrosis. Kaplan-Meier survival curves show the probability of survival to be 91.7%, with revision surgery for any reason as an end point, and 98.8% for revision surgery because of polyethylene wear as an end point. Following the initial learning curve with this prosthesis, the medium term results using this system show maintenance of clinical success. No progressive evidence of polyethylene wear with time has been found, supporting the concept of mobile bearing arthroplasty in extending the service life of total knee arthroplasty.