Magnitude Of Contact Stress Research Articles

Prediction of the driving force for a cup pig based on the distribution of contact stress

To Predict the driving force of a cup pig has significant meaning in ensuring the success of its pigging operation. The pigging process of the cup pig with a specific structure under different conditions (with different friction coefficients and interferences) was simulated based on the 3D finite element method (FEM), and the equations of contact stress on cups were studied with the method of nonlinear regression. Additionally, a prediction model of the driving force for cup pig was first established based on the integral form of the contact stress equations. The results indicate that the contact stress equations present two different forms before and after a critical interference which is proved to be related to the cup lip percentage. Besides, the friction coefficient has almost no effect on the distribution of the contact stress while it affects the magnitude of it significantly. The quantitative effect of friction coefficient on the magnitude of contact stress was described by the correction equation which perfects the prediction model, and the extent of the effect is related to the interference. According to the modeling approach introduced in this paper, the driving force of the cup pigs with arbitrary structure forms can also be predicted.

Contact stresses in point frogs

The methodology for calculating the contact stress state for various contact types of frogs and wheel is presented. The magnitudes of contact stresses in the frogs can be calculated according to the Hertz-Belyaev method, taking into account certain evaluating factors.

Tribological and dynamical analysis of a brake pad with multiple blocks for a high-speed train

In this research, the tribological and dynamical characteristics of a brake pad with multiple blocks are investigated using experimental and numerical methods. A dynamometer with a multiblock brake pad configuration on a brake disc is developed and a series of drag-type tests are conducted to study the brake squeal and wear behavior of a high-speed train brake system. Finite element analysis is performed to derive physical explanations for the observed experimental phenomena. The experimental and numerical results show that the rotational speed and braking force have important influences on the brake squeal; the trends of the multiblock and single-block systems are different. In the multiblock brake pad, the different blocks exhibit significantly different magnitudes of contact stresses and vibration accelerations. The blocks located in the inner and outer rings have higher vibration acceleration amplitudes and stronger vibration energies than the blocks located in the middle ring.

Finite element modelling and experimental validation of bolt loosening due to thread wear under transverse cyclic loading

A finite element model, considered for the wear profile evolution of a threaded surface, is proposed to simulate the self-loosening of bolted joints under transverse loading. The method for wear profile simulation is based on an energy-based approach. To verify this finite element model, interrupted bolt loosening tests were carried out. The finite element model successfully simulated the phenomenon in which fretting wear causes a gradual reduction in clamping force by changing the distribution and magnitude of contact stress between the threads. The predicted results agreed with the experimental results with respect to the evolutionary trend of the wear profile and clamping force. It can be seen from the finite element analysis that the fretting wear causes a change in the distribution and magnitude of contact stress, and an increment in the sliding distance along the radial direction on the thread surface, which can further change the distribution of the wear depth. Because the accumulation of wear debris is not considered in the finite element model, the predicted wear depth and reduction of clamping force is larger than that obtained from the experimental results.

Risk assessment of soil compaction in Europe – Rubber tracks or wheels on machinery

Subsoil compaction is persistent and affects the wide diversity of ecological services provided by agricultural soils. Efficient risk assessment tools are required to identify sustainable agricultural practices. Vehicles should not transmit stresses that exceed soil strength. Wheel load is the primary source of high stress in the subsoil. However, very low contact stress without reduction of wheel load would also help reduce stress in the subsoil. The aims of our study were to: (i) test experimentally the use of tracks instead of tires as a technical solution to increase contact area and reduce the magnitude of contact stresses, (ii) compare effects of traffic on soil physical properties using tires or tracks, and (iii) evaluate a state-of-the-art method for risk assessment of soil compaction beneath tracks or tires at the European level. We measured contact stress below a fully-loaded sugar beet harvester equipped with either a large tire or with a rubber track in a realistic harvest situation. Seventeen stress transducers were installed across the driving direction at 0.1 m depth and covered with loose soil. Dry bulk density and air permeability were measured at 0.35 m depth after traffic. The contact area was larger and the maximum and vertical stress smaller beneath the rubber track than beneath the tire. Nevertheless, stress distribution beneath the rubber track was far from uniform, presenting high peak stresses beneath the wheels and rollers. Dry bulk density was similar after traffic for the two undercarriage systems, but air permeability was lower after traffic using the rubber track. Measured stress distributions beneath the tire and the track were used as input to calculate the soil profile vertical stress for comparison with soil strength at 0.35 m depth. Wheel load carrying capacity was calculated for European soils for assessment of subsoil compaction risk when using the tire, the rubber track, and the rubber track assuming an even stress distribution. As expected from the contact area and stress measurements, the rubber track could carry higher loads than the tire. However, the air permeability results are interpreted as soil distortion due to high shear forces under the rubber track. This calls for a further development of the risk assessment method.

DETERMINATION OF CONTACT STRESSES AND GAPS IN CHAIN TRANSMISSION HINGES

The article considers the questions of determination of contact stresses in the chain transmission hinges that need to be known for assessing their wear resistance, because the wear and tear of hinges is the most common type of damage to the chain gears. In this context the main attention was paid to determining the required clearance between the bushing and the pin of roller chain drives. This gap largely determines the character of the distribution and magnitude of contact stresses in the hinge, and, consequently, the durability of chain drives. A method of calculation of the maximum contact stresses in the chain transmission hinges is developed. It is shown that decreasing clearance in the hinges increases the contact angle between the pin and the bushing and reduces the maximum contact pressure. However, for the actual angles of contact the contact stress greatly exceeds the allowable average unit pressure, causing increased wear of the hinges. One of the possible solutions to this problem is the use of transition fits in hinges, in which the gaps and interferences are relatively small. When pressing the pins into in the bushings, due to cutting microasperities from the contact surfaces, the interference in the connection virtually disappears. Examples of determining gaps and contact stresses in the chain transmission hinges are provided.

Modeling viscous dissipation during vocal fold contact: the influence of tissue viscosity and thickness with implications for hydration.

The mechanics of vocal fold contact during phonation is known to play a crucial role in both normal and pathological speech production, though the underlying physics is not well understood. Herein, a viscoelastic model of the stresses during vocal fold contact is developed. This model assumes the cover to be a poroelastic structure wherein interstitial fluid translocates in response to mechanical squeezing. The maximum interstitial fluid pressure is found to generally increase with decreasing viscous dissipation and/or decreasing tissue elasticity. A global minimum in the total contact stress, comprising interstitial fluid pressure and elastic stress in the tissue, is observed over the studied dimensionless parameter range. Interestingly, physiologically reasonable estimates for the governing parameters fall within this global minimum region. The model is validated against prior experimental and computational work, wherein the predicted contact stress magnitude and impact duration agree well with published results. Lastly, observations of the potential relationship between vocal fold hydration and increased risk of tissue damage are discussed based upon model predictions of stress as functions of cover layer thickness and viscosity.

The comparative study of W/Cr addition in Fe-base by laser surface alloying on fatigue wear resistance of GCI

Abstract Laser surface alloying technology was used to improve the fatigue wear resistance of gray cast iron. Comparative studies among the specimens with Cr or WC addition, with the Cr + WC addition and without addition were experimentally investigated. The strengthening mechanism of unit with Cr or WC addition was revealed by means of EDS. After fatigue wear tests, the improved level of fatigue wear resistance was assessed in light of the average mass loss of each group and the defects on various regions were significantly investigated and compared. A finite element method was carried out under laboratory conditions to illuminate the stress distribution on specimens' surfaces and the magnitude of contact stress along contact line. The results of fatigue wear test and finite element calculation were used to account for the fatigue wear resistance mechanisms.

Use of weight functions and photoelastic experimental hybrid method to study the contact problem

The contact problem involving flat punches has been the subject of many investigations mainly due to the crucial role it plays in many engineering applications. The contact problem has however, been widely approached from a theoretical point of view and there is a lack of experimental verifications due to the limited number of laboratory techniques capable of supplying detailed information about contact parameters. In order to gain an understanding of such problems, this study uses an experimental approach to investigate the stresses arising from photoelastic models when compressed against each other using Riemann-Hilbert's weight functions and photoelastic experimental hybrid method. The study shows that this approach is effective in determining the magnitudes of contact stresses as well as interior stresses which up to date have been scarcely investigated. It is further shown that high stresses exist when a photoelastic model with a sharp corner is pressed against straight surface of the bottom half space and by introducing fillet radii at the sharp corners, significant stress reductions of up to 62.66% is observed.

Wear Behavior of Austenitic NiTi Shape Memory Alloy

This study aims to understand the wear behavior of austenitic NiTi SMA with the hope to provide a guideline for its better use for wear-resist purposes. Ball-on-disk sliding wear tests with alumina counter ball were conducted at different temperatures and under different loads. Based on the coefficients of friction, the surface wear features, temperature-dependent stress–strain curves and the estimated contact stresses, the deformation mechanisms involved in the wear process were examined. Two wear modes were identified. Mode I is temperature-sensitive and occurred when A f < T < M d. In this mode, wear process was dominated by the interplay among contact stress, temperature and shape recovery property. Results show that, when the contact stress causes either elastic deformation of austenite or stress-induced martensitic transformation, the wear resistance was improved with increasing temperature. This was originated from increased critical stress for stress-induced martensite which retards plastic deformation. However, when contact stress is higher than yield stress of stress-induced martensite, wear resistance is deteriorated. Mode II occurs when T > M d and it is less temperature-sensitive within the testing range. In this mode, the austenitic NiTi loses its superelasticity and obeys a conventional deformation sequence, and the key factor dominating the wear process is the magnitude of contact stress.

Strain-rate effects on the plastic indentation and abrasion of elastohydrodynamic contacts by debris particles

A numerical model of plastic indentation and abrasion of elastohydrodynamic contacts by debris particles previously developed by the author is extended to include the dependence of material flow stress on strain rate. Using the Johnson–Cook viscoplasticity model, the flow stress of all materials involved in the indentation process is expressed as a function of plastic strain, strain rate and temperature. This complements other elements of the model, including strain-gradient plasticity, work-hardening, frictional heating from particle extrusion, thermal softening, melting and material loss due to adhesion. Following a laborious programme of experimental validation and numerical comparisons, the predictions of the model are shown to be in excellent agreement with the experimental results on soft and hard particles in rolling and rolling–sliding elastohydrodynamic contacts. The incorporation of strain-rate effects further improved the agreement between theoretical and experimental results previously established with simpler versions of the model that ignored the strain-rate factor. Strain rate is also shown to affect several parameters in the process of surface damage, including the magnitude of contact stresses and flash temperatures, as well as the behaviour of a particle in a concentrated contact. It is also shown that for an optimum contact velocity linked to strain-rate effects and fluid film thickness in lubricated contacts, surface damage is minimised, particularly for large and hard particles.

Fracture simulation for zirconia toughened alumina microstructure

Purpose – The purpose of this paper is to describe finite element modelling for fracture and fatigue behaviour of zirconia toughened alumina microstructures.

In situ measurements of local temperature and contact stress magnitude during wear of ceramic-on-ceramic hip joints

Fluorescence microprobe spectroscopy was applied to in situ assessments of contact stress and local temperature at the contact point of dry-sliding couples during wear tests of two commercially available ceramic-on-ceramic femoral heads. The investigated ceramic hip implants consisted of either monolithic Al2O3 or Al2O3/ZrO2 composite. A specially designed pin-on-ball tribometer was employed, which enabled directly testing the femoral head components as received from the maker without further manipulation. The strong fluorescence emission from Cr3+ impurities contained in Al2O3 served as a responsive sensor for both temperature and stress. Analytical corrections for the averaging effects arising from the finite size of the laser probe were made according to a probe response formalism in which geometrical conditions of the sliding couple were incorporated as boundary conditions. The sample-probe interaction at the contact point was then experimentally calibrated by obtaining probe response functions for the two materials investigated. Based on such theoretical and experimental procedures, deconvolutive computational routines could be set up and the true variations of local temperature and stress at the contact point of the bearing surfaces retrieved from the observed time-dependent broadening and shift of a selected spectral band, respectively. The main result of the in situ investigation was that the monolithic sliding couple showed both significantly lower temperature and lower magnitude of compressive stress at the contact point as compared to the composite one, although the composite couple wore at a significantly lower specific wear rate than the monolithic one.

Analysis of the contact stresses in curvic couplings of gas turbine in a blade-off event

The contact pressure distribution of the curvic couplings in a heavy duty gas turbine under a blade-off load condition is investigated in a three-dimensional finite element model. Several blade-off positions on each stage disk may develop the different characters on the contact pressure distributions of the curvic couplings during the application of a blade-off load. Both the position and magnitude of the applied blade-off load and the distribution of the spindle bolts have an effect on the contact pressure distribution of the curvic couplings. Further the contact stress on the left and right sides of the teeth develops different characters during the application of torque load following not only a normal centrifugal load but also a blade-off load which produces a unbalanced equivalent bending force. Furthermore the stiffness of the connection body part of the rotor between the compressor end and the turbine end associated with its section thickness is crucial in deciding the contact stress distribution on the curvic couplings. This analysis shows a change in the magnitude of contact stress of each set of the curvic couplings.

Stress-dependent fatigue mechanisms of CrC-NiCr coatings in rolling contact

The rolling contact fatigue (RCF) behaviour of the plasma-sprayed CrC-NiCr cermet coatings under different tribological conditions of contact stress was investigated. Four sets of fatigue life data of coatings were characterized by Weibull distributions. The failure modes of the coatings were classified on the basis of worn surface observations of the failed coatings. Results showed that the failure mode of the coating was related to the magnitude of contact stress. The RCF life data of the coatings tested at high contact stresses exhibited high scattering, because the bimodal distribution of the fatigue life data was seen in the Weibull plot. Generally, when the contact stress was relatively low, the coatings were prone to fail in spalling and cohesive delamination. However, at high contact stress, the coatings often failed due to interfacial delamination. At different contact stress levels, the maximum shear stress amplitude was the main reason for the generation of spall and delamination.

A Pre-Clinical Test Platform for the Functional Evaluation of Scaffolds for Musculoskeletal Defects: The Meniscus

In an attempt to delay the progression of osteoarthritis from an index injury, early intervention via repair of injured musculoskeletal soft tissue has been advocated. Despite the development of a number of scaffolds intended to treat soft tissue defects, information about their functional performance is lacking. The goal of this study was to consolidate a suite of in vitro and in vivo models into a pre-clinical test platform to assess the functional performance of meniscal repair scaffolds. Our objective was to assess the ability of a scaffold (Actifit™; Orteq, UK) to carry load without detrimentally abrading against articular cartilage. Three test modules were used to assess the functional performance of meniscal repair scaffolds. The first module tested the ability of the scaffold to carry load in an in vitro model designed to measure the change in normal contact stress magnitude on the tibial plateau of cadaveric knees after scaffold implantation. The second module assessed the in vitro frictional coefficient of the scaffold against cartilage to assess the likelihood that the scaffold would destructively abrade against articular cartilage in vivo. The third module consisted of an assessment of functional performance in vivo by measuring the structure and composition of articular cartilage across the tibial plateau 12months after scaffold implantation in an ovine model. In vitro, the scaffold improved contact mechanics relative to a partly meniscectomized knee suggesting that, in vivo, less damage would be seen in the scaffold implanted knees vs. partly meniscectomized knees. However, there was no significant difference in the condition of articular cartilage between the two groups. Moreover, in spite of the high coefficient of friction between the scaffold and articular cartilage, there was no significant damage in the articular cartilage underneath the scaffold. The discrepancy between the in vitro and in vivo models was likely influenced by the abundant tissue generated within the scaffold and the unexpected tissue that regenerated within the site of the partial meniscectomy. We are currently augmenting our suite of tests so that we can pre-clinically evaluate the functional performance at time zero and as a function of time after implantation.

On the Horizon From the ORS

On the Horizon From the ORS

On wheel–rail contact problem with material properties varying with depth

AbstractNumerous laboratory experiments indicate that the use of a layer or a coating material attached to the conventional steel body reduce the magnitude of contact stress. Therefore in this paper we solve numerically the wheel–rail contact problem with friction and wear assuming the existence of a small elastic layer on the rail surface. Material properties of this layer are changing with its depth. The friction between the bodies is governed by Coulomb law. In contact zone Archard's law of wear is assumed. We take special features of this rolling contact problem and use so‐called quasistatic approach to solve this contact problem. Finite element method is used as a discretization method. The numerical results including the distribution of normal stress along the contact boundary are provided and discussed. (© 2009 Wiley‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Study of Three-Dimensional Stress Distribution and Damage Characterization of Bolt Composite Joint

A 3D finite element model of bolt composite joint has been established to determine the stress distribution on the contact surface. The effects of clamping torque and friction on the contact stress and interlaminar normal stress are considered. From the analysis results, contact stress is bared mainly by the 0° layer. The distribution and magnitude of contact stress are conducted by friction. The effect of clamping torque on interlaminar normal stress is very strong. A 3D damage user subroutine is added to the FEM to simulate the damage of joint. By the means of damage simulation, the initiation and progression direction of three types damage are predicted. Matrix cracking and fiber-matrix shear occur at first, and fiber buckling is founded subsequently. The matrix cracking and fiber-matrix debonding initiate at circumferential angle 45°and 135°, and fiber buckling initiate at the 0° layer on the bearing plane. The friction and bolt clamping torque can restrain damage initiation and development.

Hertzian contact response of single-layer, functionally graded and sandwich coatings

The distributions of surface and subsurface stresses within single-layer, functionally graded and sandwich coatings on monolithic substrates under Hertz contact conditions (i.e., cylinder on flat contact geometry) have been analyzed by finite element method. The effect of the ratio of coating thickness to contact radius ( t/ a) on the distributions and magnitudes of contact stresses within coating and at coating/substrate interface was obtained by single-layer coating systems. With increasing the coating thickness, the depth of maximum shear stress was moved away from the substrate/coating interface. Compared to the single-layer coating, the maximum shear stress and Von Mises stress within the functionally graded coating or sandwich coating are relatively low. The studies in this paper can provide some insights regarding the design of the hard coatings in most tribological applications.