Total Contact Area Research Articles

Anatomic Double-Bundle Anterior Cruciate Ligament Reconstruction Restores Patellofemoral Contact Areas and Pressures More Closely Than Nonanatomic Single-Bundle Reconstruction

To investigate the effects of anterior cruciate ligament (ACL) deficiency and nonanatomic single-bundle (SB) and anatomic double-bundle (DB) ACL reconstruction on the contact characteristics of the patellofemoral (PF) joint. By use of a materials testing system, 7 fresh-frozen human cadaveric knees were tested. The following states were tested: ACL-intact knee, nonanatomic SB ACL reconstruction, anatomic DB ACL reconstruction, and ACL-deficient knee. Hamstring autografts were used. PF contact pressures and areas were measured with pressure-sensitive film at 30°, 60°, and 90° of knee flexion with a constant 100-N load on the quadriceps tendon. The total contact area of ACL-deficient and nonanatomic SB ACL-reconstructed knees (123.8 ± 63.9 and 149.6 ± 79.3 mm(2), respectively) significantly decreased when compared with those of the intact knee (206.1 ± 83.6 mm(2)) at 30° of knee flexion. The lateral-facet peak pressure of ACL-deficient and nonanatomic SB ACL-reconstructed knees (1.12 ± 0.52 and 1.22 ± 0.54 MPa, respectively) significantly decreased when compared with those of the intact knee (0.68 ± 0.38 MPa) at 90° of knee flexion. Anatomic DB ACL reconstruction restored the contact pressures and areas to values similar to those of the intact knee (no significant difference). ACL deficiency resulted in a significant decrease in the total and medial PF contact areas and in an increase in the lateral PF contact pressure. Anatomic DB ACL reconstruction more closely restored normal PF contact area and pressure than did nonanatomic SB ACL reconstruction. Our findings suggest that the changes in the PF contact area and pressures in ACL deficiency and after nonanatomic SB ACL reconstruction may be one of the causes of PF osteoarthritis or other related PF problems found at long-term follow-up. Anatomic DB ACL reconstruction may reduce the incidence of PF problems by closely restoring the contact area and pressure.

Development of a reconstructive posterior acetabular defect model in dogs and related biomechanical research

Objective To construct a model of posterior acetabular defect and evaluate the effect of the reconstructive posterior wall on the contact of the acetabulum and femoral head.Methods The entire pelvis and articulated femur were obtained from six fresh adult canine cadavers.Animal models of posterior acetabular defects were developed by removing the 60° arc fragment.Different measures were used to reconstruct the defect areas with iliac crest autograft.The pressure-sensitive films were used to calculate the contact area,the mean pressure and the distribution of the pressure between the acetabulum and femoral head.Results The contact area was smaller after reconstruction of posterior wall compared with that of intact posterior wall.The contact areas were not significantly different between the common reconstruction group and the anatomic reconstruction group under a load of 250 N(P0.05).The mean contact stress of the anatomic reconstruction group was significantly less than that of the common reconstruction group(P0.05),indicating the collection of pressure was less than that of the common reconstruction group.Conclusion Animal models of posterior acetabular defects induced by posterior wall osteotomy can effectively mimic the clinical condition;the anatomic reconstruction of the posterior wall can restore the total contact area and the distribution of the pressure within the acetabulum similar to the normal condition.

Experimental investigation of the effect of free openings of current collectors on a direct methanol fuel cell

A current collector is one of the key components of a direct methanol fuel cell (DMFC). For a planar-type DMFC, the current collector is usually fabricated from a thin metal that has open holes. The geometry of the current collector may have a significant effect on DMFC performance. Therefore, the design of the current collector is important for DMFC design. The objective of this study is to make a systematic experimental investigation of DMFC performance in the presence of current collectors with different free open ratios and total perimeter lengths of the free openings. Current collectors with 5 × 5, 7 × 7, and 10 × 10 hole arrangements under different total free open ratios of 30%, 40%, 50%, and 60% are investigated. The results show that the total free open ratio can significantly affect cell performance; they also show that decreasing the total free open ratio decreases cell performance, and increasing the total free open ratio increases cell performance. A high total free open ratio affects the total contact area between the membrane electrolyte assembly (MEA) and current collectors. Proper consideration of both the total free open ratio and the total contact area between the MEA and current collectors is necessary for the design of DMFC current collectors. In addition, a longer total perimeter of the free openings yields higher cell performance with the same free open ratio of the current collectors.

Contact Stress at the Anterior Aspect of the Tibial Post in Posterior-Stabilized Total Knee Replacement

Retrieval studies have demonstrated polyethylene wear and deformation of the anterior aspect of the tibial post of posterior-stabilized total knee replacements. We are not aware of any study that has analyzed the effects of the design of the femoral notch and the anterior aspect of the tibial post of posterior-stabilized total knee replacements on contact area, stress, and location. The purpose of the present study was to determine the levels of contact stress generated in three posterior-stabilized total knee replacement designs when the femoral intercondylar notch impinges on the anterior aspect of the tibial post. The contact area, mean and peak contact stresses, and contact location at the anterior aspect of the tibial post were determined when a posterior force of 100 N was applied to a NexGen LPS Flex, Genesis II, and Scorpio NRG total knee replacement. Measurements were performed at -15 degrees, -10 degrees, -5 degrees, 0 degrees, and 5 degrees of flexion of the femoral component both in neutral and with 5 degrees of rotation of the tibial component. Each measurement was sequentially performed five times, and the data were compared within and between the designs with use of analysis of variance and a post-hoc Scheffé F test. The NexGen LPS Flex exhibited two contact areas on the medial and lateral corners of the anterior aspect of the post, whereas both the Genesis II and Scorpio NRG exhibited a single horizontal band. The NexGen LPS Flex showed the largest total contact area of the three designs at -15 degrees, -10 degrees, and 5 degrees of flexion. The NexGen LPS showed the lowest mean contact stress at -15 degrees and 5 degrees but showed the highest peak contact stress at -5 degrees and 0 degrees. The Scorpio NRG showed the highest mean contact stress under all conditions and showed the highest peak contact stress at -15 degrees, -10 degrees, and 5 degrees. With 5 degrees of rotation of the tibial component, peak contact stress increased, relative to neutral, 1.2 to twofold (depending on the flexion angle) in the Genesis II design. The mean and peak contact stresses were variable for all three designs and the test conditions, approaching and in some cases exceeding the compressive yield stress for polyethylene. The geometry of the metal femoral notch and polyethylene tibial post in the axial and sagittal planes significantly affected contact area, mean and peak stresses, and contact location at the anterior aspect of the tibial post.

Understanding the HIV-1 protease nelfinavir resistance mutation D30N in subtypes B and C through molecular dynamics simulations

A major concern in the antiretroviral (ARV) treatment of HIV infections with protease inhibitors (PI) is the emergence of resistance, which results from the selection of distinct mutations within the viral protease (PR) gene. Among patients who do not respond to treatment with the PI nelfinavir (NFV), the D30N mutation is often observed. However, several reports have shown that D30N emerges with different frequencies in distinct HIV-1 genetic forms or subtypes. In the present work, we analyzed the binding of NFV and the Gag substrate CA/p2 to PR from HIV-1 subtypes B and C through molecular dynamics (MD) simulations. The wild-type and drug-resistant D30N mutants were investigated in both subtypes. The compensatory mutations N83T and N88D, observed in vitro and in vivo when subtype C acquires D30N, were also studied. D30N appears to facilitate conformational changes in subtype B PR, but not in that from subtype C, and this could be associated with disestablishment of an α-helical region of the PR. Furthermore, the total contact areas of NFV or the CA/p2 substrate with the mutant PR correlated with changes in the resistance patterns and replicative capacity. Finally, we observed in our MD simulations that mutant PR proteins show different patterns for hydrophobic/van der Waals contact. These findings suggest that different molecular mechanisms contribute to resistance, and we propose that a single mutation has distinct impacts on different HIV-1 subtypes.

Constructal dendritic configuration for the radiation heating of a solid stream

Here we show that the configuration of a slender enclosure can be optimized such that the radiation heating of a stream of solid is performed with minimal fuel consumption at the global level. The solid moves longitudinally at constant rate through the enclosure. The enclosure is heated by gas burners distributed arbitrarily, in a manner that is to be determined. The total contact area for heat transfer between the hot enclosure and the cold solid is fixed. We find that minimal global fuel consumption is achieved when the longitudinal distribution of heaters is nonuniform, with more heaters near the exit than the entrance. The reduction in fuel consumption relative to when the heaters are distributed uniformly is of order 10%. Tapering the plan view (the floor) of the heating area yields an additional reduction in overall fuel consumption. The best shape is when the floor area is a slender triangle on which the cold solid enters by crossing the base. These architectural features recommend the proposal to organize the flow of the solid as a dendritic design, which enters as several branches, and exits as a single hot stream of prescribed temperature. The thermodynamics of heating is presented in modern terms in the Sec. VII (exergy destruction, entropy generation). The contribution is that to optimize “thermodynamically” is the same as reducing the consumption of fuel.

Contact Area and Pressure Changes in the Medial Compartment of the Knee in Horizontal Cleavage Tears of the Medial Meniscus (SS-36)

Contact Area and Pressure Changes in the Medial Compartment of the Knee in Horizontal Cleavage Tears of the Medial Meniscus (SS-36)

A comparative stereological study of the term placenta in the donkey, pony and Thoroughbred

The aim of the study was to compare horse and donkey placentae using stereological techniques. Term placentae were collected at spontaneous foaling from seven Thoroughbred mares, seven pony mares, and six jenny donkeys. Maternal and foal weights were recorded and the mass, volume, and gross area of each allantochorion was also recorded. Ten random biopsies were recovered and processed for light microscopy from which the surface density of the microcotyledons (S v) and the total microscopic area of fetomaternal contact were calculated stereologically. Gestation length was longer in the donkeys than the other two groups (median values: 371 vs. 327 and 341 days, P < 0.05). There were significant correlations between foal birthweight and gross area (rho = 0.89; n = 20; P < 0.05), mass (rho = 0.84; n = 20; P < 0.05) and volume (rho = 0.89; n = 20; P < 0.05) of the allantochorion. S v was higher in the donkey placenta than the other groups (median values: 0.05 vs. 0.03 and 0.04 μm −1, P < 0.05) although placental efficiency was lower in the donkeys (median values: 0.87 vs. 1.33 and 1.32 kg/m 2, P < 0.01). The results of the study confirmed that, although strong morphological similarities exist between the allantochorion of the horse and donkey, that of the donkey develops more complex microcotyledons, as judged stereologically, and exhibits a lower placental efficiency. These differences may be related to maternal genotype and/or the longer gestation length shown by the donkey compared to the horse, but a negative correlation (rho = −0.92, P < 0.01) was also found between age and placental efficiency in donkeys.

Enhancement of light output power of GaN-based light-emitting diodes using a SiO2 nano-scale structure on a p-GaN surface

GaN (gallium nitride)-based light-emitting diodes (LEDs) with a nano-scale SiO2 structure between a transparent indium-tin oxide (ITO) layer and p-GaN were fabricated. The forward voltage at 20 mA for a GaN-based LED with a SiO2 nano-scale structure was slightly higher than that of a conventional GaN-based LED because the total area of the p-type metal contact between the transparent ITO layer and p-GaN was smaller. However, the light output power for the GaN-based LED with a nano-scale structured SiO2 at 20 mA was 24% higher than that for a conventional GaN-based LED structure. This increase in the light output power is mostly attributed to the scattering of light from the SiO2 photonic quasi-crystal (PQC) layer.

Effect of Carbon Graphite Foot Plate on Loading During Jumping and Landing

Fifth metatarsal stress fractures have a high incidence of non-union, delayed union, and re-fracture independent of post-injury treatment. After screw fixation for the treatment of 5th metatarsal stress fractures, many patients are being treated with a rigid carbon graphite foot plate (CFP) to decrease plantar loading. PURPOSE: To determine if total foot, lateral midfoot (LMF) and lateral forefoot (LFF) loading (peak pressure, contact area, and force-time integral) were decreased with the use of the CFP. METHODS: Plantar loading in 13 healthy male, collegiate, recreational athletes was evaluated using the Pedar-X in-shoe system collecting at 100Hz (Novel, St. Paul, MN, USA). Exclusion criteria were any history of lower extremity injuries in the past six months, foot or ankle surgery within the past 3 years, and previous metatarsal stress fractures. Prior to data collection all subjects signed informed consent. Subjects completed 7 simulated lay-ups in a standard running shoe with and without a CFP. In order to complete the task properly, subjects needed to jump and land on the same foot, which was the foot used for analysis. A 2×2 repeated measures ANOVA was used to compare the take-off (TO) and landing (LD) both with and without the CFP (a=0.05). RESULTS: The subjects had an average height of 1.76 ± 0.08 m, mass of 73.38 ± 9.87 kg, and age of 21.6 ± 2.75 years. The total foot maximum force was significantly greater during landing when compared with the take-off (p=0.012). No other significant differences existed between these two tasks. Independent of the task, the total foot contact area was significantly decreased in the CFP condition (p<0.001), while the total foot peak pressure was increased with the CFP (p<0.001). LMF Contact area was decreased (p=0.016) when wearing the CFP. No differences in the force-time integral were found in the LMF or LFF. Peak pressure was increased in the LMF (p<0.001), and LFF (p=0.002) when wearing the CFP. CONCLUSIONS: In this initial study, the results indicate that the CFP is ineffective at reducing plantar loading beneath the 5th metatarsal during jumping and landing in uninjured controls. However, CFP needs to be examined to determine its role in other sporting maneuvers and footwear in patients with a 5th metatarsal fracture history.

A Novel Quantitative Approach for Evaluating Contact Mechanics of Meniscal Replacements

One of the functions of the meniscus is to distribute contact forces over the articular surfaces by increasing the joint contact areas. It is widely accepted that total/partial loss of the meniscus increases the risk of joint degeneration. A short-term method for evaluating whether degenerative arthritis can be prevented or not would be to determine if the peak pressure and contact area coverage of the tibial plateau (TP) in the knee are restored at the time of implantation. Although several published studies already utilized TP contact pressure measurements as an indicator for biomechanical performance of allograft menisci, there is a paucity of a quantitative method for evaluation of these parameters in situ with a single effective parameter. In the present study, we developed such a method and used it to assess the load distribution ability of various meniscal implant configurations in human cadaveric knees (n=3). Contact pressures under the intact meniscus were measured under compression (1200 N, 0 deg flexion). Next, total meniscectomy was performed and the protocol was repeated with meniscal implants. Resultant pressure maps were evaluated for the peak pressure value, total contact area, and its distribution pattern, all with respect to the natural meniscus output. Two other measures--implant-dislocation and implant-impingement on the ligaments--were also considered. If any of these occurred, the score was zeroed. The total implant score was based on an adjusted calculation of the aforementioned measures, where the natural meniscus score was always 100. Laboratory experiments demonstrated a good correlation between qualitative and quantitative evaluations of the same pressure map outputs, especially in cases where there were contradicting indications between different parameters. Overall, the proposed approach provides a novel, validated method for quantitative assessment of the biomechanical performance of meniscal implants, which can be used in various applications ranging from bench testing of design (geometry and material of an implant) to correct implant sizing.

Numerical investigations of the effect of oblique impact on particle deformation in cold spraying by the SPH method

In this study, a systematic examination of the oblique impacting of copper particles in cold spraying was conducted by using the smoothed particle hydrodynamics (SPH) method compared to the Lagrangian method. 3D models were employed owing to the asymmetric characteristic of the oblique impacting. It is found that in the oblique impact, the additional tangential component of particle velocity along the substrate surface could create a tensile force and decrease the total contact area and bonding strength between the particle and the substrate. The simulation results compare fairly well to the experiment results. Meanwhile, the asymmetric deformation can result in the focus of the shear friction on a small contact zone at one side, which may rise the interfacial temperature and thus facilitate the occurrence of the possible shear instability. Therefore, there probably exists an angle range, where the deposition efficiency may be promoted rather than the normal angle. Moreover, the particle deformation behavior simulated by the SPH method is well comparable to that simulated by the Lagrangian method and the experimental results, which indicates the applicability of the SPH method for simulating the impact process in cold spraying besides the previously used Arbitrary Lagrangian Eulerian (ALE) method.

Numerical Analyses for Contact Resistance due to Constriction Effect of Current Flowing through Multi-Spot Construction

Constriction resistance is calculated by numerical analysis using Laplace's equations for electric potential of steady state in many cases of contact spot dispersion-status. The results show that contact resistance does not increase beyond 1.5 times even if the total real contact area is about 15% of the apparent contact area. When real contact area is at least about 60% of the apparent contact area, the contact resistance is approximately the same as the constriction resistance acquired from the apparent contact area. When the real contact area is about 50% of the apparent contact area, the contact resistance is approximately constant without regard to the contact shape and contact-point dispersion layout. Therefore, it is proved that contact resistance can be practically calculated using apparent contact area instead of real contact area when there are many contact points caused by metal to metal contact.

The resolution dependence of measured fractal characteristics for a real un-dismantled electrical contact interface

An electrical contact interface is visualized by rendering “contact maps” from X-ray Computer Tomography (CT) images without the need for dismantling the specimens. The contact maps consist of approximately 1500 pixels × 1500 pixels with each pixel relating to an 8.0 μm × 8.0 μm × 8.0 μm volume at the interface. The specimens consist of bolting a cable lug to a printed circuit board. The resolution dependence of measured fractal characteristics is studied for a contact interface with a normal force of 1.6 kN. The total mechanical area of contact, A m, is found to be invariant with resolution whereas the largest contact spot size, A L, is found to decrease with higher resolution. The number of spots on the apparent area of contact is found to increase with resolution but a spot increasingly has areas of non-contact within itself at higher resolution. The fractal dimension, D, of the spot area is found to converge to 1 at lower resolution consistent with self-affinity behaviour. At higher resolution D converges to a value <2.

Differences in patellofemoral contact mechanics associated with patellofemoral pain syndrome

Patellofemoral pain syndrome (PFPS) is a disorder of the patellofemoral (PF) joint in which abnormal tracking is often cited as a factor in pain development. PF tracking is partially dependent on passive stabilizers (ex: PF geometry). Relations amongst PFPS, PF tracking, and contact mechanics are poorly understood. In-vivo investigation of passive PF joint stabilizers including PF tracking, contact mechanics, cartilage thickness, and patellar shape will allow structural characterization of the PF joint and may highlight differences associated with PFPS. This study examined the role that passive stabilizers play in PFPS ( n=10) versus healthy subjects ( n=10). PF tracking (contact area centroid migration), cartilage thickness, shape, congruence, and contact patterns were quantified using magnetic resonance imaging during isometric loading at 15°, 30°, and 45° of knee flexion. Distinct relationships were identified between patellar shape and tracking and contact, particularly at low flexion (15–30°). Healthy subjects exhibited distinct PF tracking and contact patterns related to Type I patella shape (80%) with increasing total contact area ( p<0.001) and proximal centroid migration (15–30° p=0.012; 30–45° p<0.001) for increasing knee angles. PFPS subjects deviated from these patterns at low flexion, demonstrating higher total contact area than healthy subjects ( p=0.046 at 15°), lack of proximal centroid migration (15–30°), and more Type II (30%) and III (20%) patella shapes. This study highlights a new finding that patellar shape combined with low degrees of flexion (15–30°) may be important to consider, as this is where PFPS tracking and contact patterns deviate from healthy.

Cusp-catastrophe interpretation of the stick-slip behaviour of rough surfaces

The stick-slip instability is a typical manifestation of the nonlinearity of the frictional response of rough surfaces. As recently demonstrated by several researchers, the problem of contact loss is also inherently connected to the stick-slip instability and it has been detected both in elastically soft materials, such as rubber or gelatine, and in elastic stiff materials, such as for earthquake faults. Treating the problem of tangential contact in the framework of micromechanical contact models, the effect of the phenomenon of contact loss on the micro-slip behavior of rough surfaces is herein investigated. To this aim, the stick and slip components of the total applied tangential force and of the total real contact area are properly determined as functions of the total applied tangential force. A comparison with the behavior of smooth surfaces, such as spheres, cylinders and flat surfaces, is presented. Then, simulating the problem of tangential loading followed by a reduction of the applied normal force, it will be shown that the phenomenon of contact loss gives rise to energy release due to snap-back instability in the diagram relating the tangential force to the sliding displacement. This result provides for the very first time an explanation to the phenomenon of stick-slip according to the Catastrophe Theory, in close analogy with the cusp-catastrophe instability of Mode I crack propagation in cohesive solids.

Analysis of inhomogeneous Ge/SiC heterojunction diodes

In this article Schottky barrier diodes comprising of a n-n germanium-silicon carbide (Ge–SiC) heterojunction are electrically characterized. Circular transmission line measurements prove that the nickel front and back contacts are Ohmic, isolating the Ge/SiC heterojunction as the only contributor to the Schottky behavior. Current-voltage plots taken at varying temperature (IVT) reveal that the ideality factor (n) and Schottky barrier height (SBH) (Φ) are temperature dependent and that incorrect values of the Richardson constant (A∗∗) are being produced, suggesting an inhomogeneous barrier. Techniques originally designed for metal-semiconductor SBH extraction are applied to the heterojunction results to extract values of Φ and A∗∗ that are independent of temperature. The experimental IVT data are replicated using the Tung model. It is proposed that small areas, or patches, making up only 3% of the total contact area will dominate the I-V results due to their low SBH of 1.033 eV. The experimental IVT data are also analyzed statistically using the extracted values of Φ to build up a Gaussian distribution of barrier heights, including the standard deviation and a mean SBH of 1.126 eV, which should be analogous to the SBH extracted from capacitance-voltage (C-V) measurements. Both techniques yield accurate values of A∗∗ for SiC. However, the C-V analysis did not correlate with the mean SBH as expected.

A Review of Implantation and Early Placentation in the Mare

Constant, self induced mobility throughout the uterine lumen between days 6 and 17 after ovulation, complete envelopment by a self-secreted glycoprotein capsule between days 7 and 30 and ‘injection’ of specialised, gonadotrophin-secreting trophoblast cells into the maternal endometrium at days 35–37 are three unusual aspects of equine embryogenesis. The outer trophoblast layer of the allantochorion finally establishes a stable, microvillous contact with the lumenal epithelium of the endometrium around days 40–42 and placentation commences thereafter. The allantochorion elongates steadily until it occupies the whole of the interior of the uterus by day 85. It develops branched, sub-branched and highly convoluted microcotyledons over its entire surface and these interdigitate closely with accommodating endometrial upgrowths (sulci) to provide a total microscopic area of fetomaternal contact for haemotrophic exchange which exceeds 50 m 2 at term. Endometrial gland exocrine secretions, imbibed by elongated trophoblast cells that form areolae above the mouths of the endometrial glands, contribute histotrophic nutrients to the fetus throughout gestation. These dual forms of haemotrophic and histotrophic nutrition achieve a high degree of precocity in the foal at birth. This paper describes the gross and microscopic changes at the fetomaternal interface between days 20 and 80 of gestation in the pregnant mare which establishes the extensive, diffuse, non-invasive microcotyledonary placenta that supports fetal growth and development thereafter.

Fabrication of Metal Matrix Composites Based on Stainless Steel Having Low Electrical Contact Resistance by Powder Metallurgy

Metal matrix composite materials having low electrical contact resistance based on 316L stainless steel (STS) matrix alloy with ZrB2 or TiB2 particles were fabricated for PEMFC separator by powder metallurgy (PM). The addition of the boride particles remarkably enhanced electrical conductivity on the surface compared to commercial STS alloys. SEM observation on the surface of the samples revealed that the boride particles were protruded out of the matrix surface and the particle density existing on the surface increased with increasing the boride content, causing increase of the total contact area between the conductive particles and gas diffusion layer. The ICR of the samples also decreased with increasing the boride content resulted from the increased contact area. The enhanced electrical property is possibly attributed to the conductive particles protruded out of the matrix surface acting as electrically conductive channels through the passive film formed on the stainless steel matrix.

Statistical Models of Rough Surfaces for Finite Element 3D-Contact Analysis

The present study is divided in two parts. In the first one the complete elasto-plastic microcontact model of anisotropic rough surfaces is given. Rough surfaces are modelled as a random process in which the height of the surface is considered to be a two-dimensional random variable. It is assumed that the surface is statistically homogeneous. The description of anisotropic random surfaces is concentrated on strongly rough surfaces; for such surfaces the summits are represented by highly eccentric elliptic paraboloids. The model is based on the volume conservation of asperities with the plasticity index modified to suit more general geometric contact shapes during plastic deformation process. This model is utilized to determine the total contact area, contact load and contact stiffness which are a combination of the elastic, elasto-plastic and plastic components. The elastic and elasto-plastic stiffness coefficients decrease with increasing variance of the surface height about the mean plane. The standard deviation of slopes and standard deviation of curvatures have no observable effects on the normal contact stiffness. The part two deals with the solution of the fully three-dimensional contact/friction problem taking into account contact stiffnesses in the normal and tangential directions. An incremental non-associated hardening friction law model analogous to the classical theory of plasticity is used. Two numerical examples are selected to show applicability of the method proposed.