Explore the vast range of titles available.

Purpose Arthroscopic partial meniscectomy of medial meniscus tears and varus alignment are considered independent risk factors for increased medial compartment load, thus contributing to the development of medial osteoarthritis. The purpose of this biomechanical study was to investigate the effect of lower limb alignment on contact pressure and contact area in the knee joint following sequential medial meniscus resection. It was hypothesized that a meniscal resection of 50% would lead to a significant overload of the medial compartment in varus alignment. Methods Eight fresh-frozen human cadaveric knees were axially loaded with a 750 N compressive force in full extension with the mechanical axis rotated to intersect the tibia plateau at 30%, 40%, 50%, 60% and 70% of its width. Tibiofemoral mean contact pressure (MCP), peak contact pressure (PCP), and contact area (CA) of the medial and lateral compartment were measured separately using pressure-sensitive films (K-Scan 4000, Tekscan) in four different meniscal conditions, respectively, intact, 50% resection, 75% resection, and total meniscectomy. Results Medial MCP was significantly increased when comparing the intact meniscus to each meniscal resection in all tested alignments ( p  < 0.05). Following meniscal resection of 50%, MCP was significantly higher with greater varus alignment compared to valgus alignment ( p  < 0.05). Similarly, medial PCP was higher at varus alignment compared to valgus alignment ( p  < 0.05). Further resection to 75% and 100% of the meniscus resulted in a significantly higher medial PCP at 30% of tibia plateau width compared to all other alignments ( p  < 0.05). Medial CA of the intact meniscus decreased significantly after 50%, 75% and 100% meniscal resection in all alignments ( p  < 0.05). Lateral joint pressure was not significantly increased by greater valgus alignment. Conclusion Lower limb alignment and the extent of medial meniscal resection significantly affect tibiofemoral contact pressure. Combined varus alignment and medial meniscal resection increased MCP and PCP within the medial compartment, whereas valgus alignment prevented medial overload. As a clinical consequence, lower limb alignment should be considered in the treatment of patients undergoing arthroscopic partial meniscectomy with concomitant varus alignment. In patients presenting with ongoing medial joint tenderness and effusion, realignment osteotomy can be a surgical technique to unload the medial compartment.

In finite element (FE) models knee ligaments can represented either by a group of one-dimensional springs, or by three-dimensional continuum elements based on segmentations. Continuum models closer approximate the anatomy, and facilitate ligament wrapping, while spring models are computationally less expensive. The mechanical properties of ligaments can be based on literature, or adjusted specifically for the subject. In the current study we investigated the effect of ligament modelling strategy on the predictive capability of FE models of the human knee joint. The effect of literature-based versus specimen-specific optimized material parameters was evaluated. Experiments were performed on three human cadaver knees, which were modelled in FE models with ligaments represented either using springs, or using continuum representations. In spring representation collateral ligaments were each modelled with three and cruciate ligaments with two single-element bundles. Stiffness parameters and pre-strains were optimized based on laxity tests for both approaches. Validation experiments were conducted to evaluate the outcomes of the FE models. Models (both spring and continuum) with subject-specific properties improved the predicted kinematics and contact outcome parameters. Models incorporating literature-based parameters, and particularly the spring models (with the representations implemented in this study), led to relatively high errors in kinematics and contact pressures. Using a continuum modelling approach resulted in more accurate contact outcome variables than the spring representation with two (cruciate ligaments) and three (collateral ligaments) single-element-bundle representations. However, when the prediction of joint kinematics is of main interest, spring ligament models provide a faster option with acceptable outcome.

Constant contact pressure (CCP) nanoindentation method is an emerging approach to studying the creep properties of materials at the micrometer scale. However, in the literature, the possible loss of contact when applying the CCP method may not accommodate low contact pressures when testing materials at high homologous temperatures. Here, we improve the previous CCP method by changing its control strategy and achieve a steady-state CCP nanoindentation creep on an example material, β-Sn, without the loss of contact. Our results show the measured power law stress exponent on the < 001 >-oriented grain is 7.1–8.5. Nevertheless, our CCP method still suffers from the inevitable scattering of measured contact pressures and strain rates. In this study, we also find that the stress relaxation during 5-s unloading induces significant plastic strain, which affects materials’ creep thereafter. Graphical abstract

The tribological mechanisms under severe plastic deformation processes are still not fully understood. For that purpose, an extreme pressure tribo-device (EPTD) is designed using line-contact mechanism to better understand the contact under different sliding speeds and normal forces. The aim of this research is to simulate the contact conditions found on the tool-chip interface in metal cutting, with a focus on the friction behavior under different speeds and normal forces. The results reveal that the friction coefficient decreases with an increase of sliding speed and normal force for C45 steel. Wear analysis results reveal that wear resistance increases as sliding speed decreases. Finite Element Method (FEM) models have been developed to identify and validate the parameters around the contact zone. The FEM results reveal the presence of a sticking and a sliding region similar to that of real cutting conditions. The results enable a better understanding of the tribological behavior in severe plastic deformation applications by providing accurate tribological data. The results can also serve to assess new tool coatings and lubricants used under high-pressure contact.

Aircraft shelter is a structure or a reinforced hanger that has many uses in military aspects. It is used to protect military aircraft from different dangers such as enemy chemical attacks. Also, it provides housing, permitting aircraft maintenance and it can be storage for different weapons. therefore, optimum design of aircraft shelter is of a great importance. It may take several shapes to be suitable for its usage. It can be made from concrete, steel or composite materials. The foundations of an airplane shelter must be designed as best as possible. Design objectives are greatly impacted by the contact pressure between the earth and the foundation surface. Classical method in design assumes maximum uniform linear distribution of pressure under contact surface of footing. So, considering real contact pressure has a great interest for many authors. In this article, a new analytical method is proposed to study the effect of moments and load inclination on the design of rectangular isolated footing. The model proposed takes into consideration the real soil pressure. A parametric study was conducted and data obtained from classical model were larger than those from proposed model. Seven Rectangular isolated footings were designed using traditional method and proposed method. The proposed method is more economic since it provides less concrete dimensions. Results obtained from the new model were compared with FEM and achieved reasonable agreement.

The contact states including stick, slip, and separation can occur at the bolted joint interface of bolted flange joint structures, which significantly affects and complicates the vibration characteristics of connected structures. However, the mechanism of the influence of these three contact states on structural vibration is still not well understood. This paper establishes a universal theoretical model of bolted flange joint plate systems considering the stick, slip, and separation states simultaneously, which can be extended to a structure with an arbitrary number of bolts and plates. The bi-linear hysteretic model is adopted to model the three contact states. The contact pressure between the bolts and flanges is considered as two-dimensional distribution form, which is closer to real contact situation. Based on the Kirchhoff plate theory, the energy functions of plate and flange are obtained. Further, the nonlinear dynamic equation is derived using Lagrange equations, and solved by the Newmark-beta method. The experimental studies are performed on a plate system connected with bolted flange joint to illustrate the effectiveness of the theoretical model. The results highlight the influence of separation state and friction coefficient on the vibration response. It is found that as the tightening torque decreases, the resonance amplitude increases due to the occurrence of interface separation. The slip state can cause the nonlinear softening property, but this property will weaken when the separation occurs at bolted joint interfaces.

Cartilage contact pressures are major factors in osteoarthritis etiology and are commonly estimated using finite element analysis (FEA). FEA models often include subject-specific joint geometry, but lack subject-specific joint kinematics and muscle forces. Musculoskeletal models use subject-specific kinematics and muscle forces but often lack methods for estimating cartilage contact pressures. Our objective was to adapt an elastic foundation (EF) contact model within OpenSim software to predict hip cartilage contact pressures and compare results to validated FEA models. EF and FEA models were built for five subjects. In the EF models, kinematics and muscle forces were applied and pressure was calculated as a function of cartilage overlap depth. Cartilage material properties were perturbed to find the best match to pressures from FEA. EF models with elastic modulus = 15 MPa and Poisson’s ratio = 0.475 yielded results most comparable to FEA, with peak pressure differences of 4.34 ± 1.98 MPa (% difference = 39.96 ± 24.64) and contact area differences of 3.73 ± 2.92% (% difference = 13.4 ± 11.3). Peak pressure location matched between FEA and EF for 3 of 5 subjects, thus we do not recommend this model if the location of peak contact pressure is critically important to the research question. Contact area magnitudes and patterns matched reasonably between FEA and EF, suggesting that this model may be useful for questions related to those variables, especially if researchers desire inclusion of subject-specific geometry, kinematics, muscle forces, and dynamic motion in a computationally efficient framework.

Bolted joints play an important role in aerospace, machinery manufacturing, weapons and other fields, and the contact pressure distribution at the connection interface seriously affects the service performance of the bolts. Contact pressure analysis is an essential basis and reference for structural design, calibration, inspection, and safety monitoring of bolted connection structures. Considering the preload force and frictional contact between the joint components, a block mapping hexahedron mesh generation and finite element modeling method for bolted connections is presented, and the finite element models of single and double bolted structures are constructed. Then, an experimental test platform for measuring contact pressure distribution is constructed. Comparison of finite element analysis results with experimental results for the contact pressure distribution in the single and double-bolted joints; the root mean squared error of contact pressure distribution is less than 5%, which verifies the effectiveness of the finite element models. After that, the models are used to study the contact pressure distribution in single-bolted joints and contact pressure coupling effect of double-bolted joints, and the normal stress distribution features within members and contact pressure distribution contour are revealed for single and double-bolted joint. Finally, the finite element models are adopted to investigate the effects of the clamping length, preload, material properties, hole clearance, and bolt size on contact pressure distribution in single-bolted joints. The coupling effect of contact pressure distribution in double-bolted joints under different preloads and geometric parameters are also examined.

Purpose The purpose of this study was to quantify the effect of clinically relevant open-wedge high tibial osteotomies on medial collateral ligament (MCL) strain and the resultant tibiofemoral contact mechanics during knee extension and 30° knee flexion. Methods Six human cadaveric knee joints were axially loaded (1 kN) in knee extension and 30° knee flexion. Strains at the anterior and posterior regions of the MCL were determined using strain gauges. Tibiofemoral contact mechanics (contact area, mean and maximum contact pressure) were investigated using pressure-sensitive sensors. Open-wedge osteotomy was performed using biplanar cuts and osteotomy angles of 5° and 10° were maintained using an external fixator. Tests were performed first with intact and then with dissected MCL. Results Nonparametric statistical analyses indicated a significant strain increase ( p  < 0.01) in the anterior and posterior fibres of the MCL with increasing osteotomy angle of up to 8.3% and 6.0%, respectively. Only after releasing the MCL the desired lateralisation of the mechanical axis was achieved, indicating a significant decrease in the maximum contact pressure in knee extension of − 25% ( p  = 0.028) and 30° knee flexion of − 21% ( p  = 0.027). Conclusions The results of the present biomechanical study suggest, that an open-wedge high tibial osteotomy is most effective in reducing the medial contact pressure when spreading the osteotomy to 10° and concomitantly releasing the MCL. To transfer the results of this biomechanical study to the clinical day-to-day practice, it is necessary to factor in the individual ligamentous laxity of each patient into the treatment options e.g. particularly for patients with distinct knee ligament laxity or medial ligamentary instability, the release of the MCL should be performed with care. Level of evidence Controlled laboratory study.

As various errors result from manufacture and assembly processes or wear effect, clearance joint widely exists in mechanical system as a base component. The coupling analysis of tribology and dynamics of clearance joint is important to the reliability of mechanical system. A nonlinear contact pressure distribution mode (NLCP) is proposed to combine dynamics analysis with wear calculation together in this paper. The discrete thought of Winkler model is adopted to deal with contact problem with a high conformal rate. The contact relationship in a local microcontact area can be regarded as the contact between cylinder and plane. And the local contact pressure is acquired based on Hertz contact theory. The NLCP model has not only described the nonlinear relationship between contact pressure and penetration depth, but also avoided the complexity in contact pressure computation. The performance of NLCP model is demonstrated in comparison with asymmetric Winkler model, revealing that NLCP model has enhanced the calculation accuracy with a good efficiency. A comprehensive experimental study on the wear calculation of a slider–crank mechanism with clearance joint is presented and discussed to provide an experimental verification for NLCP model. The paper’s work has solved the contact problem with a high conformal rate and has described the nonlinear relationship between contact pressure and penetration depth. It has great value to the wear analysis of clearance joint.