Variation Of Contact Stress Research Articles

On the contact of an absolutely rigid stamp with a half-plane taking into account static friction

Abstract The plane deformable state of an elastic half-plane into which an absolutely rigid stamp is pressed with friction is considered. It is assumed that the tangential stresses acting in the contact zone are related to normal pressure by the law of dry friction, the coefficient of which is a linear function of the coordinate of the contacting points of the contacting bodies. A determining singular integral equation for the stated problem is obtained, the solution of which is constructed in closed form. Numerical analysis is conducted, and regularities in the variation of contact stresses are determined depending on the ratios of horizontal and normal loads applied to the stamp.

Analysis of Dynamic Wear Characteristics of Joint Contact Friction Pair of Excavators Working Device

The working device of an excavator in construction machinery is prone to damage and wear under ordinary working conditions. Based on a model of an excavator under typical working conditions, the dynamic load-bearing situation of the three main joint friction subsets of the working device is simulated by using the virtual prototype technology; the location of the functional device with high stress is identified based on finite element analysis, and the correctness of the simulation results is verified by designing strain gauges. Based on this, the dynamic contact stress variation law of the contact surface of the end-face friction subsets was explored, and the end-face wear depth was calculated by combining Archard wear theory and finite element wear simulation technology; the specimens were worn on the end-face wear tester, and the surface wear was observed under the scanning electron microscope to summarize the wear mechanism and analyze the element content changes of the worn surface. The results show that the three main joints of the working device produce large dynamic fluctuations and are prone to wear, and the destructive degree is more prominent; the wear process is accompanied by higher temperatures, fatigue wear, and abrasive wear on the wear surface, and the wear depth value of the right end face is significantly larger than that of the left end face. This method has a significant reference value for reliability analysis and optimization improvement when using construction machinery’s main joint friction pairs.

Study on Non-linear Contact Stress and Prognosis Analysis of Lug Joints With Misfits

Components of aircraft and other large scale structures are generally made in parts in order to facilitate easy manufacturing, assembly and dis-assembly. Lug joints with fasteners are preferred in several aerospace applications where their purpose is to connect primary load carrying members. Study on structural integrity of these types of joints becomes mandatory from the safety point of view. This requires in-depth understanding of science and technology of Structural Health Monitoring (SHM) at these joints. Analysis presented here deals with the critical locations of interference and clearance fit lug joints which continuously operate under fatigue loading. Both interference and clearance fits exhibit non-linear contact-stress variation above certain load level and this effect needs to be addressed for both fatigue and monotonic loading. The maximum Pull or Push loads causes high stress concentrations at critical locations along the pin-hole interface. With continuous usage of the component, crack like damages initiate at these locations and they grow till failure of the component. The non-linear prognosis analysis is carried out to generate the data required for SHM at any stage which can be used to estimate remaining life of the component.

Design and parametric study of flexible ball bearings: A finite element approach

Performance evaluation of flexible ball bearings throughout design is typically performed experimentally, which may be time and cost-intensive. This paper presents a finite element procedure for determining optimal design parameters of flexible ball bearings using flexibility and contact stress analysis. This methodology is validated by comparing numerical and theoretical results for the variation of contact stress with ball diameter. Results reveal that design parameters such as inner/outer race thickness and ball bearing diameter are highly dependent on loading and stresses. The proposed novel methodology can provide detailed insights regarding design parameters influencing flexible bearing performance, thereby improving design and analysis.

Fuzzy modelling of surface scratching in contact sliding

This paper presents a fuzzy modelling technique for the prediction of surface scratching problems encountered in sheet metal forming processes involving contact sliding. To generalize the contact conditions with die-sheet interactions in such processes, ball-on-disk sliding investigations, including modelling and experiment, were carried out with various ball diameters to mimic the die-contact radii effect and a range of contact loads to simulate the effect of contact stress variation experienced in forming processes. Because die-contact radius, surface roughness and contact stress changes cannot be exactly defined in a practical production process, in the modelling of the ball-on-disk configuration, ball diameter, normal load, surface roughness, sliding cycles and extent of scratching depth in a metal sheet surface were treated as fuzzy variables for the prediction. Based on the comparison between predictions with the relevant experimental measurements, it can be seen that the fuzzy modelling technique developed in this paper can predict very well the surface scratching.

Tribo-behaviour of APS and HVOF sprayed WC–Cr3C2–Ni coatings for gears

ABSTRACT The tungsten-carbide coatings could be employed to minimise failures of gears due to excessive wear in hostile operating atmospheres. In this work, WC-Cr3C2-Ni powder was deposited on the SS 316L substrate using APS and HVOF processes. The deposited coatings were characterised and investigated for the effects of dissimilar counter bodies. The unidirectional sliding experiments were conducted on the ball-on-disc tribometer (ASTM G99-95a). The variable contact pressure was applied to simulate the tangible effect of contact stress variation during the dry sliding in the gears. The wear mechanisms depicted that the wear is in the mild regime and better durability of both coatings. The results of tribo-testing and analysis of results by ANOVA confirmed that contact pressure and hardness of counter body are significant factors influencing friction and wear. Furthermore, the relation between contact surface temperature and adhesion of debris to the surface has been studied.

Spatiotemporal variations of contact stress between liquid-crystal films and fibroblasts Guide cell fate and skin regeneration

The inductions of both the mechanical microenvironment on cell behaviour and the polymeric scaffold on tissue regeneration have been well-proved. This study is aimed to investigate the possibility of guiding cell fate and tissue regeneration by the spatiotemporal controlling of contact stress between matrix materials and cells and to elucidate the mechanisms underlying. A series liquid crystal polymers of cholesteryl-oligo(lactic acid) (CLA) and an amorphous polymer of poly(lactic acid) were used as the growth substrates for fibroblast and skin tissue regeneration. The cellular and animal experiments show that, in the initial stage of wound healing, the liquid crystal texture of CLA films can provide an induced stress for the formation of focal adhesions and the activation of integrin β1/AKT signal pathway, resulting in advanced phenotypic transformation of fibroblasts to myofibroblasts, promoted collagen secretion and fast wound filling. But the gradually weakening cellular contact stress, induced by the decreasing of liquid crystal domains of matrix polymer during degradation, triggers the apoptosis of fibroblasts and myofibroblasts, resulting in non-excessive collagen accumulation. Finally, the CLA groups exhibit no obvious scar formation, more regular cell arrangement and significantly lower type I collagen proportion in regenerated tissue than other groups. This study may inspire a new, effective and safe strategy for tissue regeneration.

An investigation of contact interactions in powder compaction process through variable friction models

In this study, multiparticle finite element (MPFE) approach was used to analyze contact interactions of spherical copper particles in powder compaction process. To this goal, 74 spherical copper particles of 200μm in diameter were modeled as individual elastic–plastic bodies, and randomly filled into a die cavity. Interparticle and die-wall-particle contact interactions were investigated, and coefficients of friction were obtained using variable friction models; Wanheim–Bay׳s general friction model and Levanov׳s friction model. Variable friction models were incorporated into FE analyses through user-subroutines. It was found that the variation of contact stresses inside the die leads to different contact conditions at different zones. The range of coefficient of friction encountered in the analysis was found to be slightly higher in Levanov׳s friction model than that for Wanheim–Bay׳s general friction model. On the other hand, Levanov׳s model was found to be more appropriate for elevated temperature analyses.

Contact Stress Analysis in Wheel–Rail by Hertzian Method and Finite Element Method

Safety and economy of railway traffic is enormously influenced by the contact stress variation caused by wheel rail contact profile changes. A change in designed surface topology may result from wear that brings in a wide change in contact geometry and stresses. To study the influence of interacting wheel and rail profile topology of standard rail UIC60, the standard wheel profile as per Indian Railway standards are considered in this paper. Rail profile radii, wheel profile radii and wheel profile taper are chosen for six different values. The analytical formulation is based on Timoshenko’s approach and Finite Element Method (FEM) based simulation of the problems is undertaken. With these tools, distribution of contact zones, contact stress and contact pressure for different configuration of the wheel and rail profiles are obtained. The mesh density in contact region is found to have a direct influence on the accuracy of the solution [1]. To standardize the analysis of the contact region, mesh with an element size of 1 mm for all the configurations are chosen. Using stress response obtained through FEM analysis and multiaxial fatigue crack initiation model, the effects of vertical loading on fatigue crack initiation life are investigated. This may allow a direct design application for railways in particular.

Contact stress analysis of helical gear pairs, including frictional coefficients

Abstract In this paper an attempt has been made to study the contact stresses among the helical gear pairs, under static conditions, by using a 3D finite element method. The helical gear pairs on which the analysis was carried out were 0°, 5°, 15°, 25° helical gear sets. The Lagrange multiplier algorithm has been used between the contacting pairs to determine the stresses. The effect of friction was varied at the point of contact which made the problem nonlinear and complicated. To simplify the problem, a range of average static coefficients of friction, from 0 to 0.3, has been considered as the scope of study. The variation of contact stresses with helix angle and also with friction coefficients has been discussed. The commercial finite element software used was ANSYS and the results were compared with analytical calculations.

Comparative Study of Flange-to-Seal Contact Couplings With Bolt Relaxation Under Creep Condition

Future coal-fired steam turbines promise increased efficiency and low emissions. However, this comes at the expense of increased thermal load from higher inlet steam temperatures and pressures leading to severe creep that significantly influences the sealing behavior and high temperature strength of bolted flange-seal couplings. Flanges with different thicknesses were employed for a comparative study. The important stress/creep values in the flanges and U-type seals had been obtained for variations in flange thickness and bolt relaxation while maintaining other leading parameters constant. The variation of contact stresses due to creep deformation plays an important role in achieving a leak proof sealing. In this paper, a two-dimensional finite element analysis of bolted flange-seal couplings has been carried out by taking the relaxation of bolt stress under full-loading turbine service. The creep strength of flanges and U-type seals are investigated by Cocks–Ashby (C–A) equivalent strain method. The multiaxial state of stresses is considered in this method by using C–A multiaxial coefficient. According to ASME allowable creep limit, the C–A equivalent strains of three flange-seal couplings are evaluated and compared. Furthermore, based on the results of contact stresses, the creep behavior of U-type seals is analyzed varying flange thickness. Finally, analysis shows that the thinner flange-seal coupling has larger long-term contact stress, while the U-type seal with the thicker flange has the least creep strength.

Contact Stress Analysis for Gears of Different Helix Angle Using Finite Element Method

The gear contact stress problem has been a great point of interest for many years, but still an extensive research is required to understand the various parameters affecting this stress. Among such parameters, helix angle is one which has played a crucial role in variation of contact stress. Numerous studies have been carried out on spur gear for contact stress variation. Hence, the present work is an attempt to study the contact stresses among the helical gear pairs, under static conditions, by using a 3D finite element method. The helical gear pairs on which the analysis is carried are 0, 5, 15, 25 degree helical gear sets. The Lagrange multiplier algorithm has been used between the contacting pairs to determine the stresses. The helical gear contact stress is evaluated using FE model and results have also been found at different coefficient of friction, varying from 0.0 to 0.3. The FE results have been further compared with the analytical calculations. The analytical calculations are based upon Hertz and AGMA equations, which are modified to include helix angle. The commercial finite element software was used in the study and it was shown that this approach can be applied to gear design efficiently. The contact stress results have shown a decreasing trend, with increase in helix angle.

The effect of bolt tightening methods and sequence on the performance of gasketed bolted flange joint assembly

This paper presents results of the effect of different bolt tightening sequences and methods on the performance of gasketed bolted flange joint using nonlinear finite element analysis. Bolt preload scatter due to elastic interactions, flange stress variation and bolt bending due to flange rotation and gasket contact stress variation is difficult to eliminate in torque control method i.e. tightening one bolt at a time. Although stretch control method (tightening more than one bolt at time) eradicates the bolt preload scatter, flange stress variation is relatively high. Flange joint\'s performance is compared to establish relative merits and demerits of both the methods and different bolt tightening sequences.

Predicting the wear of hard-on-hard hip joint prostheses

The wear of the bearing surfaces of hip joint prostheses is a key problem causing their primary failure. This paper introduces a wear prediction model with the aid of the finite element analysis. To mimic walking, the most common activity of a human body, a three-dimensional physiological loading gait cycle was considered. The wear at the bearing surface in gait cycles was calculated based on the contact stress variation from the finite element analysis and the sliding distance obtained from three-dimensional hip gait motions. The geometry of the worn surface was updated considering the average routine activities of a patient. The model was applied to three hard-on-hard prostheses, i.e., PCD (polycrystalline diamond)-on-PCD, ceramic-on-ceramic and metal-on-metal couples. It was found that due to the gait motion, the intensity and location of the maximum contact stress in the bearing components change with the gait instances. With a given geometry and gait loading, the linear and volumetric wear on the cup surface increases with the number of gait cycles. With increasing the gait cycles, the surface wear can bring about scattered contact pressure distribution. Compared to the ceramic-on-ceramic and metal-on-metal couples, the PCD-on-PCD bearing has the lowest wear progression. It was also concluded that the computational wear model presented in this paper can reasonably predict the wear evolution in hard-on-hard hip implants.

A study on the sealing performance of bolted flange joints with gaskets using finite element analysis

Gaskets play an important role in the sealing performance of bolted flange joints, and their behaviour is complex due to nonlinear material properties combined with permanent deformation. The variation of contact stresses due to the rotation of the flange and the material properties of the gasket play important roles in achieving a leak proof joint. In this paper, a three-dimensional finite element analysis (FEA) of bolted flange joints has been carried out by taking experimentally obtained loading and unloading characteristics of the gaskets. Analysis shows that the distribution of contact stress has a more dominant effect on sealing performance than the limit on flange rotation specified by ASME.

Contact stress variations near the insulated rail joints

The effect of an insulated rail joint (IRJ) on the contact stress variation near wheel-rail contact zones was simulated by employing three-dimensional finite element models. Three linear elastic IRJ materials, i.e. epoxy-fibreglass, polytetrafluoroethylene (PTFE) and Nylon-66, were investigated. Contact elements were used to simulate the interaction between the wheel and rail contact points. Numerical results showed that the presence of IRJ might significantly affect the wheel-rail contact stress distributions. Results also indicated that the traditional Hertzian contact theory is no longer available to predict the contact stress distribution around the rail joints.

Numerical analysis of asymmetric rolling accounting for differences in friction

Asymmetric rolling is relevant to a number of situations of practical interest. Here, asymmetric plate rolling due to different interface friction conditions at the two rolls is analysed numerically. The variation of the normal and frictional contact stresses at the interface between the plate and the upper and lower roll is presented. The differences in contact stress variation result in curling of the plate, here illustrated by a curled plate mesh.

Static contact stress analysis of a spur gear tooth using the finite element method, including frictional effects

The literature available on gear tooth contact stress problems is not very extensive and that available does not explain the method by which analysis was carried out. In this paper an attempt has been made to study the contact stresses of a pair of mating gear teeth, under static conditions, by using a two-dimensional finite element method and the Lagrangian multiplier technique. The contact condition at the neighbouring node pair, namely, the contact existing over a number of node pairs in the contact zone, has been considered. To study the effect of friction between the mating gear teeth a range of average static friction coefficients, from 0.0 to 0.3, has been considered. The actual length of contact against the calculated length of contact is discussed. The variation of contact stress along the contact surface in a direction normal to the mating surfaces, which will give an idea about the depth of hardening required, is also presented.

Effects of osteochondral defect size on cartilage contact stress

Contact stress distributions were studied in vitro for 13 dog knees, with full-thickness osteochondral defects drilled in the weight-bearing area of both femoral condyles. Diameters of the circular defects were concentrically enlarged from 1 to 7 mm. Digitally-imaged Fuji film was used to record cartilage contact stress distribution on femoral condyles for each increment of defect diameter. All specimens showed at least some tendency for contact stress concentration at the rim of the defects. However, detailed distributions had large interspecimen variability and, within a given specimen, contact stress distributions became progressively more nonuniform around the defect rim as the diameter was enlarged. Averaged over the full series of 26 condyles, circumferential mean cartilage contact stress around the defect rim was only moderately higher (by 10-30%) than intact surface's peak local contact stress [series average = 6.2 mega pascals (MPa)]. Maximal rim stress concentration occurred for 2 mm defects, there being a consistent trend toward mild rim stress decrease with further defect enlargement. Such modest contact stress elevations, per se, are probably insufficient to inhibit defect repair or to cause degeneration of surrounding cartilage. However, near the defect rim (for all diameters), the radial component of the gradient of contact stress (i.e., radial-direction variation of contact stress) was consistently elevated by an order of magnitude above that for intact, condyle articular cartilage.

Laboratory Investigation of Wheel Rail Contact Stresses for U.S. Freight Cars

Importance of the wheel rail contact stresses in track degradation and safety of trains is discussed. Theroetical elastic contact stresses based on Hertz theory for various U.S. railroad cars are presented. These contact stresses were produced for simulation of different cars on the IIT-GM-EMD wheel rail simulation facility which is briefly discussed. Experimental measurements of contact areas at the facility for 55, 70, 95 and 125 ton cars, including changes due to the plasticity and wear effects are given. Based on these, the average contact stress variation with time is shown. It is observed that the contact stresses for cars stabilize at a nearly constant value within a range of 88–103 ksi. Due to increased plasticity effects under cyclic loading the stabilized contact stress levels for heavier cars are found to be at lower stress levels as compared to lighter cars. Stabilized contact stresses are compared with theroetical values predicted by Melan and Johnson under simplified load and material behavior conditions. Experimental values are somewhat higher as expected. Laboratory data on contact stresses is compared with contact stresses measured at the Facility for Accelerated Service Testing for 100 ton cars. Good corroboration with laboratory data was observed. A summary comparison of current industry design contact stresses with laboratory and field measurements shows that the contact stresses are too high and not stable for U.S. freight cars using the current AAR standard wheel rail designs. A concept of profile stability is proposed for future profile designs which are much needed for the heavy tonnage cars.