Maximum Contact Stress Research Articles

Topology optimization of 3D-printed structurally porous cage for acetabular reinforcement in total hip arthroplasty

Aseptic loosening and mechanical failure of acetabular reinforcement components are among the main causes of their reduced service life. Current acetabular implants typically feature a structural solid layer that provides load bearing capacity, coated with a foam of uniform porosity to reduce stress shielding and implant loosening. This paper presents an alternative concept for a 3D printed cage that consists of a multifunctional fully porous layer with graded attributes that integrate both structural function and bone in-growth properties. The design comprises a hemispherical cup affixed to a superior flange with architecture featuring an optimally graded porosity. The methodology here presented combines an upscaling mechanics scheme of lattice materials with density-based topology optimization, and includes additive manufacturing constraints and bone ingrowth requirements in the problem formulation. The numerical results indicate a 21.4% reduction in the maximum contact stress on the bone surface, and a 26% decrease in the bone-implant interface peak micromotion, values that are indicative of enhanced bone ingrowth and implant long-term stability.

Design of a helical gear set with adequate linear tip-relief leading to improved static and dynamic characteristics

This study aims to improve the static and dynamic characteristics of a helical gear pair by optimizing the parameters of linear tip-relief. The static analysis intends to reduce the maximum contact stress to extend the service life of the gear pair, while the dynamic analysis attempts to reduce the dynamic transmission error (DTE).First, mathematical models of a helical gear pair generated by rack-cutters with linear tip-relief were developed based on the theory of gearing. Tooth contact analysis enabled us to estimate static transmission error and contact pattern of the gear pair under various assembly errors. Additionally, the contact stress contour and mesh stiffness were calculated through loaded tooth contact analysis by using finite element analysis. A dynamic model of the helical gear pair was also developed to simulate the dynamic characteristics under various rotational speeds, including DTE and vibration energy. Finally, the simulation results revealed that the high contact stress, DTE, and vibration energy of the original helical gear set were successfully reduced by the improved linear tip-relief parameters.

Tooth surface modification method of face-milling spiral bevel gears with high contact ratio based on cutter blade profile correction

To avoid tooth edge contact of high contact ratio spiral bevel gear under misalignment or heavy load, a tooth surface modification method based on cutter blade profile correction is proposed. Generally, an arc blade is used to substitute the straight blade of cutter-head to get the ideal tooth surface. Firstly of all, the mathematical model of the cutter blade profile is established. Secondly, the computational method of the unknown parameters used to determine the cutter blade profile is presented in details. Thirdly, the modified tooth surfaces of pinion and gear are deduced based on the principle of gear mesh and the theory of differential geometry. Finally, a numerical example is carried out to verify the effectiveness of the tooth surface modification method with the method of finite element analysis (FEA) and tooth contact analysis (TCA). The TCA result shows that the tooth surface modification method can effectively reduce tooth edge contact without affecting the location of contact path. It can also ensure the symmetry of geometric transmission error curve. The results of the FEA show that the tooth surface modification method can not only effectively avoid tooth edge contact but can also reduce the maximum contact stress on the tooth surface. It can also reduce the adverse effects of misalignment.

Maximum residual contact stress in spinning process of SS304/20 bimetallic pipe

During forming process of the bimetallic pipe, the residual contact stress between the pipes is one of the most important technical issues. In recent study, the bimetallic pipe was manufactured by internal spinning forming technology and analyzed via different theories of elasto-plastic mechanics. It was assumed that the maximum contact stresses generated between the pipes when the inside surface of the outer pipe expanded to the elasto-plastic interface position. In addition, the maximum value of the residual contact stress occurred when the spinning pressure unloaded. The theoretical model of the elasto-plastic zone and the elasto-plastic boundary position of the outer pipe during the spinning process was proposed. The validity of the proposed model was verified by finite element simulation and experimentation, and the experimental results are in good agreement with those obtained from simulation. The obtained test results exhibit that the new technology is feasible and can be provided a theoretical reference for industrial applications.

Исследование изменения максимальных контактных напряжений в зацеплении циклоидального редуктора привода поворота руки робота

Исследование изменения максимальных контактных напряжений в зацеплении циклоидального редуктора привода поворота руки робота

A finite element analysis-based study on the dynamic wheel–rail contact behaviour caused by wheel polygonization

In this study, an explicit finite element analysis method was adopted to investigate the wheel–rail impact response generated by wheel polygonization, using a three-dimensional wheel–rail rolling contact finite element model. In this model, the infrastructure below the rails and the stiffness and damping of the sleeper supports were considered. Then, the characteristics of the wheel–rail contact zone, the stress/strain state and the wheel–rail impact force of the polygonal wheel–rail system were presented and discussed and were compared with those of the ideally perfect wheel–rail system. A parametrical study was then carried out to examine the influences of train speed and the polygonal order of the wheel on the wheel–rail impact response. The finite element analysis results revealed that the vertical wheel–rail impact force induced by wheel polygonization is related to the wheel radial deviation; the maximum contact force, stress and strain are all elevated with the increase of the order of the polygonal wheel, which suggested that the wheel should be repaired when it is in the initial lower order polygonal state. These findings can provide some theoretical and technical support for the optimal design of the wheel–rail system and the safe operation of high-speed trains.

Effect of misalignment on tooth stress under varying frictional and loading conditions of polymer helical gear

The positive characteristics of polymer gears in comparison with metal gears include light weight, quiet operation, non-rusting, self-lubrication and cheaper mass production. Besides this they have drawbacks like lower load carrying capacity, tendency to hold heat, large dimensional change, and unsteady lifetime. In this study polymer gear meshed with steel gear has been analyzed considering with and without misalignment under varying loading and frictional conditions. The tooth stress of a perfectly aligned and axially misaligned helical gear pair has been studied by employing finite element method (FEM). The results show that the maximum contact stresses under varied frictional conditions increase while axial misalignments are present.

OPTIMIZATION OF PARAMETERS OF CAM MECHANISMS

The problem of task setting for cam mechanisms parameters optimization is discussed in the light of a system approach. The modern state of cam gear optimization synthesis is analyzed. Various criteria such as cam profile wear, maximum pressure angle, mechanism dimensions, etc. are set as objective functions at gear parameters optimization. Constraints can be imposed on the maximum value of pressure angle, the minimum value of curvature radii of cam profile convex and concave sections, the maximum value of contact stresses etc. The presence of a large number of criteria makes it difficult to solve the problem within the framework of a system approach to design. It is proved that minimization of the objective function (the maximum contact stresses in the highest pair), which characterizes the cam profile wear, leads to a criterion decrease, which characterizes the maximum normal wear. It is also proved that with first or second mentioned criteria, it is not necessary to impose constraints on the values of the maximum pressure angle and the minimum curvature radius of the cam profile convex portion.

Design method of LM thin flange wheel profile based on NURBS

The maintenance strategies of the worn wheels have an important impact on maintenance cost of railway. LM worn wheels of heavy haul wagons are often re-profiled to their original standard form, and this excessive removal of material could reduce the wheel service life. A new LM wheel profile reconstruction method was established by taking into account the geometrical characteristics of the LM wheel profile and applying the Non-Uniform Rational B-Spline theory. The design of LM thin flange re-profiling wheel can be accomplished by using Particle Swarm Optimization method which handles multiple objectives including train operation safety concerns, and minimizing material removal. A new wheel profile with a flange thickness of 32 mm can be designed by the integration of vehicle-track coupling dynamics model, and the results showed that the mean wear work is reduced by 55.97% compared with the original standard profile. Under the optimized wheel profile, the root mean square value of the lateral force and the maximum contact stress is reduced, and the amount of material removed is decreased. The design method can provide support for the LM wheel re-profiling maintenance, by designing the thin flange profiles of a flange thickness of 28∼33 mm.

Biomechanical influence of lateral meniscal allograft transplantation on knee joint mechanics during the gait cycle

BackgroundThis study evaluated the influence of meniscal allograft transplantation (MAT) on knee joint mechanics during normal walking using finite element (FE) analysis and biomechanical data.MethodsThe study included 20 patients in a transpatellar group and 25 patients in a parapatellar group. Patients underwent magnetic resonance imaging (MRI) evaluation after lateral MAT as a baseline input for three-dimensional (3D) and FE analyses. Three different models were compared for lateral MAT: intact, transpatellar approach, and parapatellar approach. Analysis was performed using high kinematic displacement and rotation inputs based on the kinematics of natural knees. ISO standards were used for axial load and flexion. Maximum contact stress on the grafted menisci and maximum shear stress on the articular surface of the knee joint were evaluated with FE analysis.ResultsRelatively high maximum contact stresses and maximum shear stresses were predicted in the medial meniscus and cartilage of the knee joint during the loading response for all three knee joint models. Maximum contact stress and maximum shear stress in the meniscus and cartilage increased on the lateral side after lateral MAT, especially during the first 20% of the stance phase of the gait cycle. The transpatellar approach was most similar to the intact knee model in terms of contact stresses of the lateral grafted and medial meniscus, as well as maximum shear stresses during the gait cycle. In addition, the transpatellar model had lower maximum contact stress on the menisci than did the parapatellar model, and it also had lower maximum shear stress on the tibial cartilage.ConclusionsTherefore, the transpatellar approach may reduce the overall risk of degenerative osteoarthritis (OA) after lateral MAT.

Load characteristic analysis and fatigue reliability prediction of wind turbine gear transmission system

Wind energy is the inexhaustible renewable energy source, and the number of wind power utilization in many countries is also growing rapidly. Wind turbine works in harsh natural environment, and long-term random wind load will cause tremendous damage on the internal gear transmission system. In order to accurately predict the fatigue reliability for a 5 MW large-scale wind power gear transmission system in service, a detailed system simulation model is established, and the accurate stress calculation is carried out for the contact fatigue failure mode on tooth surface. In this paper, the linear relationship between the input torque of gear system and the maximum contact stress of each gear is established, and the load history conversion between the input torque and the contact stress can be realized. Then the Miner cumulative damage theory is used to transform the complex random stress history into equivalent constant amplitude cyclic stress, which is load input variable for the reliability prediction model. At the same time, a contact fatigue test for tooth surface is carried out, and P-S-N curves of the gear samples with specific parameters are obtained, which is the strength input variable for the reliability prediction model. In order to reflect the uncertainty effect of service load on the reliability of gear transmission system, the randomness of load history is expressed complementarily at macro level and micro level, respectively. The traditional stress and strength interference theory is extended, and the reliability model of series system considering the statistical dependence among part failures is established. Finally, the advantage of the proposed model is demonstrated by comparing the prediction result of the new model with that of the traditional model.

Finite element analysis of the effect of sagittal angle on ankle joint stability in posterior malleolus fracture: A cohort study.

Aim of this study was to establish three-dimensional finite element model of the posterolateral-oblique type of posterior malleolus fracture with different sagittal angle and to explore the effect of sagittal angle on ankle joint stability. CT data of ankle were collected from a normal male volunteer.Established finite element model of the normal ankle and verified its reliability. Five posterior malleolus fracture models with different sagittal angles were established. Finite element analysis(FEA)was carried out to simulate the conditions of vertical loading in neutral position with a total weight of 600 N.Recorded the data and did statistical analyses. (1) The contact area was 483.55 mm2 and the maximum contact stress was 3.793MPa in the model of the normal ankle joint. (2) There was a positive correlation between the sagittal angle(SA)and the contact area(CA)(r=0.925,P<0.05). Regression equation was CA=316.755+1.749* SA. The correlation between the sagittal angle and the maximum contact stress(MCS)was negative (r=-0.988,P<0.01). Regression equation was MCS=5.214-0.018*SA. There was a negative correlation between the sagittal angle of fracture and relative displacement(RD)(r=-0.950,P<0.05). Regression equation was RD=1.388-0.009*SA. The greater the sagittal angle of fracture was, The more stable the ankle joint was. The sagittal angle of fracture could be used as a relative index to reflect ankle stability for posterior malleolus fracture.

The effect of stem fit on the radiocapitellar contact mechanics of a metallic axisymmetric radial head hemiarthroplasty: is loose fit better than rigidly fixed?

Radial head hemiarthroplasty is commonly used to manage comminuted displaced fractures. Regarding implant fixation, current designs vary, with some prostheses aiming to achieve a tight "fixed" fitand others using a smooth stem with an over-reamed "loose" fit. The purpose of this study was to evaluate the effect of radial head hemiarthroplasty stem fit on radiocapitellar contact using a finite element model that simulated both fixed (size-for-size) and loose (1-, 2-, and 3-mm over-reamed) stem fits. It was hypothesized that a loose stem fit would improve radiocapitellar contact mechanics, with an increased contact area and decreased contact stress, by allowing the implant to find its "optimal" position with respect to the capitellum. Finite element models of the elbow were produced to compare the effects of stem fit on radiocapitellar contact of a metallic axisymmetric radial head implant. Radiocapitellar contact mechanics (contact area and maximum contact stress) were computed for 0°, 45°, 90°, and 135° of elbow flexion with the forearm in neutral rotation, pronation, and supination. The data suggestthat the loose smooth stem radial head implant may be functioning like a bipolar implant in optimizing radiocapitellar contact. Over-reaming of 3 mm produced a larger amount of stress concentrationon the capitellum, suggesting there may be a limit to how loose a smooth stem implant should be implanted. The loose1 to 2 mm over-reamed stem provided optimal contact mechanics of the metallic axisymmetric radial head implant compared with the fixedstem.

Parameter optimization of sealing performance for packer rubber

Purpose The purpose of this paper is based on the response surface method, the authors determined the conditions for achieving the optimum rubber-sealing performance by using the maximum contact stress as the response value. Design/methodology/approach A two-dimensional model of a compression packer rubber was established by finite-element analysis software. Under the single axial load of 53.85 MPa, the four single factors of the end-face inclination angle, subthickness, height of rubber and friction coefficient of the rubber were analyzed. Findings Results show that the optimum sealing performance of the rubber tube is achieved when the end-face angle is equal to 45º and the thickness of the rubber tube is 9 mm. The response surface designed by Box–Behnken shows that the sealing performance of the rubber tube is the optimum when the end-face inclination angle is 48.1818°, the subthickness is 9 mm, the height of rubber is 90 mm and the friction coefficient is 0.1. Verification test results show that the model is reliable and effective. Originality/value Packer operations are performed downhole, and research on real experiments is limited. In this work, the feasibility of such experiments is determined by comparing finite-element modeling with actual experiments, and the results have guiding significance for actual downhole operations.

Sealing performance and fatigue life of the fracturing packer rubber of various materials

The finite element model of four packer rubber materials was established by using ABAQUS and FE-SAFE software. The initial sealing load (the load is the pressure) was 11.85 MPa, and the working load was 58.15 MPa. The sealing evaluation coefficient, maximum contact stress, and fatigue life value of four material packer rubbers were considered when considering temperature changes and fatigue unit nodes. The results show that when the working load and the structural parameters of the rubber are the same, the sealing evaluation coefficient of the four material rubber increases with the increase of temperature. When the working temperature reaches 125 ℃, the value of the rubber seal evaluation coefficient of the HNBR material is the largest, and the value of the rubber seal evaluation coefficient of the EPDM material is the smallest. Similarly, the maximum contact stress of the four material rubbers increases with increasing temperature. When the temperature reaches 125 ℃, the maximum contact stress of the HNBR material is the largest, and the maximum contact stress of the EPDM material is the smallest. The rubber of the four materials increase the fatigue life value with the increase in the temperature within the operating temperature range studied. When the temperature is lower than 120 ℃, the fatigue life value of the HNBR material rubber is the largest. When the temperature is higher than 120 ℃, the fatigue life value of the CR material rubber is the largest. Regardless of the temperature change, the fatigue life value of the EPDM is the smallest. By comparing the results of field experiments with the results of finite element models, the two are found to have good consistency, which verifies the validity and feasibility of the model. The research results have important guiding significance for the fatigue life prediction of various material packer rubbers under different temperatures.

Tire-Pavement System Modelling and Triaxial Contact Stress Analysis

In the pavement design, the tire load is usually assumed to be a circular or rectangular evenly distributed load, which is actually not like this. In order to provide data reference for the development of tire-pavement contact stress intelligent test instrument, it is necessary to model the tire-pavement system, and construct tire-pavement 3D finite element model using large finite element software. Firstly, establish three-dimensional model of tire and road surface, and impose certain loads and constraints. Secondly, the triaxial contact stress of the tire-pavement under static conditions is analyzed. Then the triaxial stress under traction conditions is analyzed, and the triaxial stress under different conditions of use of the tire is compared and analyzed. The results show that as the load of the tire gradually increases, the maximum vertical contact stress and the maximum longitudinal stress gradually decrease, but the maximum lateral pressure gradually increases. When the inflation pressure of the tire is gradually increased, the contact stresses in the three directions are correspondingly increased. However, the maximum vertical contact stress and maximum longitudinal stress increase more obviously than the maximum transverse contact stress. In addition, the transverse contact stress could be ignored under traction conditions.

Local contact characteristics of threaded surfaces in a planetary roller screw mechanism

This study investigates the local contact characteristics of the threaded surface meshing of a planetary roller screw mechanism (PRSM). First, according to the threaded surface structure and threaded surface meshing characteristics, expressions for the principal curvature and principal direction of the contact ellipse at a contact point are derived based on the differential geometry theory. Next, based on a force analysis and threaded surface equations, an analytical model is established to calculate the dimensions and principal vector direction of contact ellipses on threaded surfaces. The elastic deformation and maximum contact stress are determined using Hertz elastic contact theory. Then, finite element (FE) numerical models for a single pair of threads at the screw–roller interface and the roller–nut interface are developed to calculate the contact area and maximum contact stress. The results are compared with those of the analytical model to demonstrate the validity of the analytical model. Finally, based on the analytical model proposed in this article, the local contact characteristics of threaded surfaces with various thread pitches, flank angles, and profile radii of roller threads are analyzed in detail.

Contact and tribological properties of self-lubricating ellipsoidal plain bearings

Abstract A new type bearing named self-lubricating ellipsoidal plain bearing was proposed and successfully prepared by cold extrusion forming technology. Through finite element method and experiment, the dynamic distributions of the contact stress, wear depth and the worn morphology of the fabric liner were investigated. Results show that the contact and wear performances can be improved by reasonable design of bearing flatness. When the radial load is 1000 N, the contact stress distribution of the bearing with flatness of 0.005 is the most uniform. Compared with traditional spherical plain bearings, the maximum contact stress is decreased from 32.407 MPa to 26.880 MPa, and the maximum wear depth is decreased from 0.0754 mm to 0.0688 mm after 25000 swings.

Numerical and experimental study on the friction of O ring for hydraulic seals

ABSTRACT O-ring is one of the most widely used sealing components in hydraulic seals to prevent oil leakage. In triaxial test equipment, however, due to the existence of O-ring between the transmission rod and the sealing components, the accuracy of the measurement can be affected because the seal friction is also recorded by the external force sensor. In order to study the influencing degree of the seal friction, a friction model is established with ϕ30 rod diameter. The axial friction, maximum friction stress and maximum contact stress of the O-ring are analysed using finite element method as the confining pressure varying from 50 to 300 kPa. Then the friction is measured experimentally. A good agreement has been obtained through the comparison between the numerical and experimental results, which indicates that the numerical simulation can be fully applied in a medium/huge triaxial apparatus with higher confining pressure. In the end, a transmission rod with ϕ120 diameter is further investigated. The discrepancy is observed as the movement direction of transmission rod reverses. This study provides a theoretical basis for the estimation of the friction error, which would be beneficial for engineers to improve the measuring accuracy.

Kinematic Alignment in Cruciate Retaining Implants Improves the Biomechanical Function in Total Knee Arthroplasty during Gait and Deep Knee Bend.

Kinematic alignment (KA), which co-aligns the rotational axes of the components with three kinematic axes of the knee by aligning the components to the prearthritic joint lines, has been a recently introduced surgical technique. However, whether KA and cruciate retaining (CR) implants provide better biomechanical function during activities than mechanical alignment (MA) in posterior stabilized (PS) implants is unclear. We evaluated the biomechanical functions during the stance phase gait and deep knee bend, with a computer simulation and measured forces in the medial and lateral collateral ligaments and medial and lateral contact stresses in the polyethylene insert and patellar button. The forces on the medial collateral ligament in KA were lower than those in MA in both CR and PS TKA in the stance phase gait and deep knee bend conditions, whereas those on the lateral collateral ligament did not show any difference between the two surgical alignment techniques in the stance phase gait condition. The maximum contact stresses on the medial PE inserts in KA were lower than those in MA in both CR and PS TKA in the stance phase gait and deep knee bend conditions. However, the maximum contact stresses on the lateral PE inserts and the patellar button did not differ between MA and KA. The biomechanical function was superior in KA TKA than in MA TKA, and KA was more effective in CR TKA. This comparison could be used as a reference by surgeons to reduce the failure rates by using KA TKA instead of MA TKA.