Contact Stress State Research Articles

Finite element investigations for chip scraping during orthogonal cutting process with micro-textured tools

Compared with the conventional tool (CT), the micro-textured tool (MTT) has the advantages of reducing cutting forces, lowering cutting temperatures and inhibiting tool wear. However, the chip scraping phenomenon generated in the cutting process has negative effects and degrades cutting performance when using the MTT with grooves perpendicular to the cutting edge. Due to the difficulty in observing and characterizing chip scraping in situ by experiments, its mechanism and influence on specific cutting forces and tool wear are not fully understood. To this end, finite element (FE) method is employed for simulating the cutting process with MTT. The simulation model is validated by comparing the predicted and measured specific cutting forces. The average prediction error of specific cutting and feed forces is 12.4 % and 18.8 %, respectively. The simulation results indicate that chip scraping mainly results from the discontinuity, non-uniformity and high contact stress state of the tool-chip interface. The minimum specific cutting force is achieved when the advantages of micro-texture and the chip scraping effects are balanced. The MTT rake face wear is subdivided into a severe and a sliding wear zone. This partition characteristic is closely associated with normal contact stress and temperature distributions. The work in this paper contributes to improving the understanding of chip scraping, optimizing micro-texture and cutting parameters, and promoting MTT applications in the manufacturing industry.

Effect of wear-resistant coatings based on niobium nitride on thermal and stress states of cutting tool

The results of studies of the effect of coatings based on niobium nitride on the contact characteristics, thermal and stress states of the cutting wedge of a carbide tool are presented. It is shown that the use of these coatings redistributes heat flows in the cutting zone, contact temperatures and specific loads acting on the front surface of the cutting tool, which leads to an improvement in the thermal and stress state. The greatest effect is achieved when using multilayer coatings.

Evaluating Visual Photoplethysmography Method.

Regular monitoring of common physiological signs, including heart rate, blood pressure, and oxygen saturation, can be an effective way to either prevent or detect many kinds of chronic conditions. In particular, cardiovascular diseases (CVDs) are a worldwide concern. According to the World Health Organization, 32% of all deaths worldwide are from CVDs. In addition, stress-related illnesses cost $190 billion in healthcare costs per year. Currently, contact devices are required to extract most of an individual’s physiological information, which can be uncomfortable for users and can cause discomfort. However, in recent years, remote photoplethysmography (rPPG) technology is gaining interest, which enables contactless monitoring of the blood volume pulse signal using a regular camera, and ultimately can provide the same physiological information as a contact device. In this paper, we propose a benchmark comparison using a new multimodal database consisting of 56 subjects where each subject was submitted to three different tasks. Each subject wore a wearable device capable of extracting photoplethysmography signals and was filmed to allow simultaneous rPPG signal extraction. Several experiments were conducted, including a comparison between information from contact and remote signals and stress state recognition. Results have shown that in this dataset, rPPG signals were capable of dealing with motion artifacts better than contact PPG sensors and overall had better quality if compared to the signals from the contact sensor. Moreover, the statistical analysis of the variance method had shown that at least two heart-rate variability (HRV) features, NNi 20 and SAMPEN, were capable of differentiating between stress and non-stress states. In addition, three features, inter-beat interval (IBI), NNi 20, and SAMPEN, were capable of differentiating between tasks relating to different levels of difficulty. Furthermore, using machine learning to classify a "stressed" or "unstressed" state, the models were able to achieve an accuracy score of 83.11%.

Prediction of Work Hardening in Bearing Steels Undergoing Rolling Contact Loading with a Dislocation-Based Model

The work hardening behaviour of GCr15 bearing steel during rolling contact fatigue (RCF) is investigated. Ball-on-rod RCF tests and micro-indentation tests are performed to obtain various subsurface hardness profiles in rod specimens. It is found that orthogonal shear stress is responsible for work hardening under Hertzian contact and that the extent of hardness increase is positively associated with the stress level and number of cycles. A dislocation-based work hardening model is established by combining the Kocks–Mecking theory, the bearing steel plasticity equation and the Taylor relation. The proposed model is capable of predicting hardness changes with any given rolling contact stress state and number of cycles. The modelling results are compared against the experimental results, with good agreement obtained. This research also provides a methodology for studying the work hardening of different types of bearing steels undergoing RCF, from experiment to modelling.

Numerical investigation on wheel-rail impact contact solutions excited by rail spalling failure

Rail spalling is a typical form of wheel-rail rolling contact fatigue (RCF), and is a difficult problem that has always existed in railways. Once the wheel rolls across the spalling failure area, there will be a violent dynamic wheel-rail interaction. This paper presents an explicit high-speed 3D wheel-rail rolling contact transient explicit finite element model that considers local rail spalling failure. The dynamic wheel-rail interaction under the condition of differentspalling lengths and contact stress states, as well as plastic strain of the rail when the wheel rolls across the rail spalling, are calculated using the theory of transient wheel-rail dynamics. In addition, the time–frequency analysis is carried out to obtain the distribution characteristics of dynamic response signals such as axle box acceleration, rail vibration acceleration and dynamic vertical wheel-rail force in time domain and frequency domain.Furthermore, when the vehicle travels at a high speed, the speed and radius of the wheelhave little influence on the dynamic vertical wheel-rail force, or on the wavelet energy peak and frequency. The effect of the mutual dynamic correlation is small. But the dynamic vertical wheel-rail force, along with wavelet energy peak and frequency, increase in an approximately linear fashion with the impact acceleration of wheelset and the length of spalling failure. These results can be used to guide the dynamic detection of local defects on rails.

Analysis of Rail Corrugation Characteristics on High-Speed Rail Based on Transient Finite Element Method

By using the transient finite element method, a three-dimensional wheelset-track coupled rolling contact model for high-speed rail is established, and the rationality and effectiveness of the model are verified by field measurements. Next, the wheel-rail contact stress states and relative slip characteristics are calculated and analyzed to reveal the cause of inner rail corrugation. Then, the vertical vibration acceleration of the rail/wheel is taken as the output variable to study the dynamic responses of the wheelset-track system. Finally, the parameter sensitivity analysis is carried out. The results show that the maximum normal/tangential contact stress between the inner wheel and inner rail is greater than that between outer wheel and outer rail due to the unbalanced load of inner rail caused by the excess superelevation of track structure, which indicates that the unbalanced load of the inner rail may aggravate the development of rail wear, and the rationality of the model established in this paper is verified. The wheel-rail relative slip region on the inner rail side appears periodically, and the distance between the two adjacent slip regions is close to the characteristic wavelength of the measured inner rail corrugation, which illustrates that the periodic variation of slip regions on the inner rail surface plays an important role in the formation of rail corrugation, and the validity of the model is verified. The periodic distribution of wheel-rail relative slip regions on the outer rail surface is not obvious, demonstrating that the outer rail tends to form uniform wear, which is consistent with the fact that the outer rail corrugation is slight in the measured section. The wheelset-track system has been in the process of unstable continuous oscillation in the analysis interval, combined with the analysis results of the wheel-rail relative slip characteristics, it can be concluded that the unstable self-excited vibration of wheelset-track system under the condition of tangential contact force reaching saturation is the main cause of rail corrugation. The dominant characteristic frequencies of vertical vibration accelerations of rail and wheel are all 561 Hz, the corresponding characteristic wavelength (148 mm) is close to the distance (150 mm) between the calculated adjacent slip regions, and is also close to the characteristic wavelengths (125 mm and 160 mm) of inner rail corrugation, which shows that the resonance phenomenon occurs in the wheelset-track system at the above frequency, thus leading to the increase of dynamic responses of wheelset-track system. The fastener vertical stiffness and wheel-rail coefficient of friction have significant effect on the development of rail corrugation, and the running speed determines the occurrence probability of inner/outer rail corrugation by affecting the track superelevation state.

An Optimized Design Research Based on Variable-lead Spiral Pair of Contact Stress and Elasto-hydrodynamic Lubrication State

Abstract: Variable-lead spiral pair mainly includes spiral wire and spiral roller. Design of variable-lead helix firstly conforms to the motion characteristics of variable-lead screw drive and nut-connected mechanism, then comes to lead function of the variable lead helix. At the same time, according to the range of screw lead angle and pressure angle, the angular velocity of spiral wire rod and the radius of spiral wire are concluded. Finally come to the parameter equation of helix. Then, the contact analysis and lubrication characteristics of the variable-lead helical pair are analyzed to design the helical roller with the minimum contact stress and the condition of the elasto-hydrodynamic lubrication. The radius of the variable-lead helical roller and the selectable range of the bus length are obtained. Finally, an example is given to illustrate the application of the variable-lead spiral pair in the subway door system, and the optimization design of the variable-lead spiral pair is realized.

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.

Feature extraction method of abrasive belt wear state for rail grinding

Abrasive belt has the advantages of high removal efficiency and high waste collection; furthermore, it does not easily damage the rail when applied in rail grinding. However, the poor wear consistency and short service life restrict its development in this field. It is important to explore the theory and technology of monitoring the abrasive belt wear condition to evaluate the means of improving the grinding performance of the belt. This article discusses the contact stress state between the belt and the rail surface. In addition, the study establishes the belt rail grinding force model during operation using the abrasive grain distribution function. The analysis of the force model proposes that the belt abrasion condition be monitored by using the force ratio parameter of the abrasive belt in the grinding process. The extraction method of the force ratio information is proposed in accordance with the grinding environment. The results of experiments successfully verified the validity of the method.

The stress intensity factor calculation for combined sliding wear and fatigue of GH4169 superalloy based on three-dimensional simulation

In this paper, a sliding fatigue-wear methodology based on conventional rotating bending fatigue testing device is proposed. The crack propagation characteristics of GH4169 superalloy under plain fatigue and sliding fatigue-wear conditions are investigated by fatigue tests and SEM. In addition, the crack propagation and wear analysis are carried out with the finite element program ABAQUS and the three-dimensional fracture analysis software FRANC3D. The influence factors of crack growth rate including bending stress, contact stress and wear depth are investigated based on the stress intensity factor calculation and experimental measurements. The results show that the fatigue strength is severely decreased from 780 MPa to 200 MPa due to wear, although both contact stress state and material removal mechanism have positive effects on restraining the crack propagation acceleration. This competition between fatigue and wear is discussed and it is concluded that the fatigue defeats the resisting effect of wear and occupies the dominate position after the nominal crack length reaches a critical value. However, the wear volume and depth would increase the fatigue stress and accelerate crack propagation. Therefore, the positive and negative influence of wear on material fatigue lives also have a competitive mechanism and a correction model is carried out based on the classic Paris law.

The frictional contact of coated bodies. Part I – The sliding contact

Hard coatings provide low friction, high wear resistance and corrosion protection that improve the tribological performances of the machine elements undergoing contact load. In lack of analytical solutions, a numerical study is performed in this paper for a better understanding of the engineering applications of hard coatings with consideration of friction. A previous study on the frictionless contact of bi-layered materials is extended by considering the effect of friction on the contact stress state. The assumption of a sliding contact in which the shear tractions do not affect the pressure distribution is adopted. This simplification, often present in the literature, decouples the contact problems in the normal and in the tangential direction and allows for a pressure distribution solution that is independent of the frictional regime. The shear tractions are subsequently obtained from a kinetic Coulomb-type friction law, under the assumption that the normal load is kept constant. The stress state in the coated system results by superposition of stresses due to the normal and the shear tractions. The frequency response functions needed for the calculation of the six stress tensor components induced by the shear tractions are presented for clarity and completeness. The convolution between these functions and the contact stresses is performed in the frequency domain for improved algorithmic efficiency. The performed contact analysis proves the ability of the numerical method to provide insight on the critical contact condition for plasticity failure, and to assist the optimal design of hard coatings.

Analytical model for tube hydro-forging: Prediction of die closing force, wall thickness and contact stress

The new forming technology – tube hydro-forging (THFG) was completely different from traditional tube hydroforming, the die closing force instead of internal pressure is the deformation force to compress the cross-section and increase the thickness, also result in a special contact stress state. In this paper, a mathematical model is developed to determine the strain and stress along the tube wall, also predict the die closing force, thickness distribution and contact stress; furthermore, the effects of various factors on the die closing force, thickness distribution and contact stress were discussed. At last, finite element analyses and experiments of THFG are conducted. The experimental and simulation results of die closing force, thickness distribution and contact stress are compared with the theoretical results to verify the correctness of this mathematical model. This model can provide a guideline for determining the technique parameters and designing rational die, also helps in understanding the mechanism of THFG.

Pitch bearing/raceway fretting: Influence of contact angle

In this paper, a three-dimensional numerical simulation (using ABAQUS) of the radial and tangential wear between a ball bearing and a raceway is presented. The aim was to study the influence of the contact angle between ball and raceway on the fretting. A range of contact angles was studied with critical parameters such as contact stress, relative slip, plastic deformation, and contact state. The model was validated against experimental data. The results show that with an increase in the contact angle, the area of maximum stress increases, the bearing capacity of the raceway decreases, and the maximum radial stress moves from the sub-surface to the raceway surface. The raceway surface is shown to be prone to peeling and wear, which reduces the service life of the raceway.

A novel hybrid strip finishing process to improve mechanical properties and reduce energy consumption

The growing demand for new steel grades, such as high formability steels and high or ultra-high strength steels for structural and safety-related automotive components, make manufacturing steel sheets an increasingly complex task. A novel hybrid process (HyP), that combines the skin-pass and tension levelling processes into one production step is proposed to improve the steel strip manufacturing chain. The HyP applies asymmetrical rolling (H-ASR) by using different roll diameters and by bending the strip before it enters the roll gap. The potential advantages of H-ASR, such as the introduction of through-thickness higher plastic deformation and the use of reduced roll force and power, were investigated by means of elastic-plastic finite element models and experimental data. The numerical models were validated by experiments at a HyP pilot facility and by industrial trials. Analytical estimation of the appropriate bending limits was included. The contact condition, material deformation and stress state during rolling were analysed and compared with the results of a conventional skin-pass process. It was verified that the proposed H-ASR introduced higher shear deformation throughout the strip thickness than a traditional skin-pass process. The positive influence of this fact was verified by tensile and formability tests on material processed by the HyP pilot facility. The results indicate that the HyP produces sheets with better drawability, satisfactory strength, and formability qualities comparable to those of the conventional finishing processes. What’s more, the HyP boasts all these advantages while using a space-saving layout and reducing energy consumption as compared to traditional finishing processes.

Optimization of Contact Edge Profile for Minimizing Contact Pressure in a Press-fitted Shaft

In the shrink or press-fitted shafts such as railway axles, the rotor of a steam turbine or coupling, a high-stress concentration takes place in the close of contact edge due to relative slip between shaft and boss in a press-fitted shaft and this is a major cause of fatigue failure of the shaft. The object of this paper is to build a finite element analysis model for analysing press-fitted and bending load condition in a pressfitted assembly and is to propose a hub shape optimization method to minimize a contact pressure in the close of shaft contact edge. Numerical asymmetric-axisymmetric finite element model was developed to predict the contact stress state of the press-fitted shaft. Global optimization method, genetic algorithm, and local optimization method, sequential quadratic programming, was applied to the press-fitted assembly to optimize the hub contact edge geometry. The results showed that the maximum contact pressure with optimized hub shape decreased more than 60% compared to conventional hub shape, the maximum contact stress affecting fatigue life reduced about 47%. In addition, hub shape optimization design could be a useful tool, able to increase the load capabilities of press fits concerning wear and fatigue behaviour.

The Simulation of Point Contact Stress State for APS Coatings

Surface engineering has been conquered in recent decades by the versatility of the layers produced by thermal spraying, both in terms of spraying methods, of the materials types and their applications. In some cases, the coatings can be subjected during operation to rolling contact fatigue, with the main wear factors: thermal spray coatings structure and state of stress and strain in the contact area. In this paper was studied how three types of coatings deposited by APS (Atmospheric Plasma Spray) behaved at the contact fatigue tests. Subsequently they were carried out simulation of pressures and von Mises stresses distribution. It has been observed that the presence of asperities on the surface causes the development of local micro-contacts and therefore high values of pressure and local stresses in the vicinity of the surface.

A Study of the Tribological Behavior of TiAl-10 wt.%Ag Composite Based on the Contact Stress Evolution

The contact stresses of materials in moving mechanical assemblies are rather important for minimizing friction and decreasing machinery energy dissipation. In this study, the effect of contact stresses on the friction and wear behaviors of TiAl-10 wt.%Ag was studied at 0-240 min using the united methods of experiment research, numerical simulation and theoretical analysis. The results showed that the high contact stresses led to the plastic deformation of TiAl-10 wt.%Ag at 0-50 min. The friction coefficients and wear rates decreased rapidly with the lowering of contact stresses from 1034.28 to 710.52 MPa. At elastic deformation stage (50-240 min), the forming of lubricating film was beneficial to the decrease in friction coefficients and wear rates at 50-150 min, whereas the lower contact stresses caused the increasing of friction coefficients and wear rates. The competition between film lubrication and contact stresses caused the lowering of friction coefficients and wear rates at 50-150 min. At 150-240 min, the lubricating film maintained the equivalent lubricating behaviors, whereas the lowering of contact stresses led to the slight improving of friction coefficients and wear rates. This study was meaningful for optimizing applied loads to realize the excellent contact stress state and tribological behavior of mechanical parts.

Cyclic deformation and fatigue behavior of carburized automotive gear steel and predictions including multiaxial stress states

The fatigue behavior of carburized components such as automotive transmission gears is very complex due to hardness and microstructure difference, residual stresses and multi-axial stress states developed between the case and the core and/or at stress concentrations. In addition, automotive gears in service, commonly used in helical type, are actually subjected to complex stress conditions such as bending, torsion, and contact stress states. This study presents experimental and analytical results on deformation behavior of carburized steels, widely used in automotive gears, under cyclic stress conditions including axial, torsional and combined axial-torsion loadings. Axial fatigue and rotating bending fatigue, as well as torsional fatigue and in-phase axial-torsional fatigue tests are also included. Predictions of cyclic deformation and fatigue behaviors of the carburized steel with two-layer model are compared with experimental results. Predicted results with simple two-layer model for the cyclic deformation and fatigue behaviors were comparatively similar to the experimental data.

Multi-Condition Contact Stress Analysis of High Speed Train Helical Gear

Taking traction helical gear of CRH380A high speed train for example, not only analyzing the meshing process characters of the high speed train helical gear and the tractive performance curve, but also using Pro/E to complete a three-dimensional model, combining with ANSYS workbench, helical gear contact finite element model is built in start-up, continuous and high speed conditions. A meshing period equivalent stress and contact pressure distributions of gear tooth surface are obtained by solving the model. And so are the changing regularity of gear contact state and stress on the meshing process. The result shows that based on ANSYS workbench, dynamic contact stress analysis about traction helical gear of high speed train can reflect the realistic contact stress state among the meshing process. It provides some certain references and foundations to calculate the gear’s strength analysis and modification design.

Deformation and fatigue behaviors of carburized automotive gear steel and predictions

The fatigue behavior of carburized components such as automotive transmission gears is very complex due to hardness and microstructure difference, residual stresses and multi-axial stress states developed between the case and the core. In addition, automotive gears in service, commonly used in helical type, are actually subjected to complex stress conditions such as bending, torsion, and contact stress states. This study presents experimental and analytical results on deformation behavior of carburized steels, widely used in automotive gears, under cyclic stress conditions including axial and torsion loadings. Axial fatigue tests and rotating bending fatigue tests are also included. Predictions of cyclic deformation and fatigue behaviors of the carburized steel with two-layer model are compared with experimental results. The carburized steel investigated in this study exhibited cyclic softening under both axial loading and torsional loading. Predicted results with simple two-layer model for the cyclic deformation and fatigue behaviors were comparatively similar to the experimental data.