Contact Stress Values Research Articles

Contact and Inter-laminate Stresses Minimization in Laminated Leaf Springs

A study, on the contact stresses and inter-laminate stress distributions in laminated leaf springs, is presented in this research. Several configurations and models of leaf springs are analyzed by finite element method. The aim is to find a configuration, which provides minimum values of contact stresses and inter-laminate stresses, for the same spring constant and load- deflection response. Results of the analyses show that making certain types of cuts in leaf springs could provide better designs than original unmodified springs, and leads to reduction in contact and inter-laminate stresses. This reduction in stresses is expected to increase the service life of leaf springs.

Investigation of Elastomer Seal Energization: Implications for Conventional and Expandable Hanger Assembly

Elastomer seals are extensively used in various wellhead and casing/liner hanger equipment as barriers for isolating fluids. Seal assemblies have been identified as one of the major cause of well control incidents. Majority of hangers utilize conventional weight- or mechanical-set slip-and-seal assembly. The objective of this paper is to conduct a detailed investigation of seal energization in conventional and relatively newer expandable type hanger seal assembly. To achieve the objective, the finite element modeling approach was employed. Three dimensional computer models consisting of concentric casings and annular elastomer seal element were constructed. Seal energization process was modelled by manipulating boundary conditions. Conventional seal energization was mimicked by applying rigid support at the bottom of elastomer element and compressing it from the top. Expandable hanger type seal energization was modelled by radially displacing the inner pipe to compress annular seal element. Seal quality was evaluated in terms of contact stress values and profile along the seal-pipe interface. Different amounts of seal energization were simulated. Both types of seal energization processes yielded different contact stress profiles. For the same amount of seal volumetric compression, contact stress profiles were compared. In case of conventional seal energization, contact stress profile decreases from the compression side towards support side. The seal in expandable hanger generates contact stress profile that peaks at the center of contact interface and reduces towards the ends. Convectional seal assembly has more moving parts, making it more prone to failure or under-energization. Finite Element Models were validated using analytical equations, and a good match was obtained. The majority of research related to elastomer seal is focused on material properties evaluation. Limited information is available in public domain on functional design and assessment of seal assembly. This paper adds novel information by providing detailed assessment of advantages and limitations of two different seal energization process. This opens doors for further research in functional failure modes in seal assembly.

Modeling of Stress-Strain State in Connection Resource Defines of Volumetric Hydraulic Drive

Introduction. The article explores the stress-strain state of a distribution pair of aggregates of a volumetric hydraulic drive and the search for ways to increase its durability. Materials and Methods. In the process of studying, the generally accepted principles of the theories of friction, reliability, elasticity, mechanisms and machines, and mathematical modeling were used. To simulate the stress-strain state, an engineering analysis system ANSYS was used. Distribution pairs of hydraulic pumps 313.3.112, GST-112 and Sauer Danfoss 90R075 were chosen as objects of study. Results. As a result of the study there were obtained values of the real contact stresses and long-term current stress on the distribution of pairs of units of volumetric hydraulic drive: the 313.3.112 hydraulic pump is 26,93 MPa; for GTS-112 water pump is of 22.21 MPa for the Sauer Danfoss 90R075 hydraulic pump is 27,12 MPa. It is revealed that the area located on the discharge side is a subject to the greatest loads. This is the cause of one-sided wear of spherical surfaces, which is quite common in units decommissioned. The values of contact stresses in the joints hardened by the method of electric spark machining are on average 1.4 and 9.4 % lower than in not unhardened. In the process of electric spark machining there is a redistribution of stresses on the surface that leads to a decrease of the operating load in the connections. Conclusions. The study allowed modelling the stress-strain state in new and hardened distribution pairs of volumetric hydraulic drive units under operating conditions and suggesting ways to increase its durability. It was established that to increase the wear resistance of a resolving compound and the durability of the volumetric hydraulic drive aggregates, it is necessary to ensure that in distribution pairs the maximum bearing capacity is greater than the maximum long-term operating load in these connections. To solve this problem, it is proposed to create coatings with high tribotechnical properties by the method of electricspark machining. Keywords: resource-limiting compound, volumetric hydraulic drive, modeling, finite element method, bearing capacity, operating load, wear resistance, electrospark machining For citation: Ionov P. A., Senin P. V., Stolyarov A. V. Modeling of Stress-Strain State in Connection Resource Defines of Volumetric Hydraulic Drive. Vestnik Mordovskogo universiteta = Mordovia University Bulletin. 2018; 28(4):537–551. DOI: https://doi.org/10.15507/0236-2910.028.201804.537-551 Acknowledgements: The study was conducted with the financial support of the Ministry of Education and Science of the Russian Federation (state task, direction: development of competencies) project № 11.3416.2017/4.6 “Development of technologies and tools to improve the durability of parts, assemblies, machines and equipment by creating nanostructured coatings sources of concentrated energy”.

Simulation and analysis of contact state between cycloid gear and pin wheels in RV reducer

By using the finite element method, the contact state between cycloid gear and pin wheels of RV reducer is simulated and analyzed. The comparative analysis about the number of contact teeth pairs between cycloid gear and pin wheels, and the maximum values of contact stress under different working loads (output torques) is completed. The results show that the dowel pin hole on cycloid gear has a certain extent influence on the contact state between cycloid gear and pin wheels. With the increase of working load of RV reducer, the deformation quantity of dowel pin hole on cycloid gear also increasing, it makes the number of the contact teeth pairs between cycloid gear and the pin wheels increasing at the same time. Therefore, the deformation of dowel pin hole is beneficial to improve the contact state between cycloid gear and pin wheels.

ANALYSIS INTO THE INFLUENCE OF SELECTED TOOTHED GEAR PARAMETERS ON THE VALUE OF SLIPPAGE AND CONTACT STRESSES IN A CYLINDRICAL GEARBOX

The paper presents issues concerning the geometrical and durability calculations of power shift gearboxes with multi-criterion optimization, using proprietary computer software. Among many parameters influencing the value of slippage and contact stresses, the flank ratio at P-0 correction and P correction, the value of the flank angle, and the module value were analysed. The slippage was analysed at Point B1, which belongs to the beginning of the single tooth engagement area, as well as in Point B2, where the single tooth engagement area ends. Contact stresses were calculated at Point C, which is the pitch point. Their values were referenced to experimentally determined fatigue contact durability σHlim.

CONTACT RESISTANCE MODELING

Purpose. To determine the contribution of the real contact spots distribution in the total conductivity of the conductors contact. Methodology. The electrical contact resistance research was carried out on models. The experimental part of this work was done on paper with a graphite layer with membranes (the first type) and conductive liquids with discrete partitions (the second type). Findings. It is shown that the contact electrical resistance is mainly determined by the real area of metal contact. The experimental dependence of the electrical resistance of the second type model on the distance between the electrodes and the potential distribution along the sample surface for the first type model were obtained. The theoretical model based on the principle of electric field superposition was considered. The dependences obtained experimentally and calculated by using the theoretical model are in good agreement. Originality. The regularity of the electrical contact resistance formation on a large number of membranes was researched for the first time. A new model of discrete electrical contact based on the liquid as the conducting environment with nuclear membrane partitions was developed. The conclusions of the additivity of contact and bulk electrical resistance were done. Practical value. Based on these researches, a new experimental method of kinetic macroidentation that as a parameter of the metal surface layer deformation uses the real contact area was developed. This method allows to determine the value of average contact stresses, yield point, change of the stress on the depth of deformation depending on the surface treatment.

Mechanical Material Tests by the Nanoindentation Method at Various Indenter and Specimen Temperatures

Theoretical and experimental studies have been made of the nonisothermal contact interaction of an unsharpened conical indenter and an elastic material with an inhomogeneous surface layer. A relevant contact problem of thermoelasticity with arbitrarily changed thermomechanical characteristics in the depth of the surface layer has been formulated. To solve the boundary-value problem, the apparatus of integral Hankel transforms is used. With the use of the asymptotic method, a numerical-analytical approximated solution of the problem has been constructed, the values of the corresponding heat flux and of the half-space surface displacement have been determined, and the values of contact stresses beneath the die have been found. The developed model is used to estimate the value of indenter displacement caused by the thermoelastic deformation of the specimen. The results of the experiment on nonisothermal indentation of the prepared specimen of steel 40Kh on a Nanotest 600 facility are presented. The application of nanoindentation for investigations of mechanical properties of materials at high temperatures is discussed.

Concave modifications of tooth surfaces of beveloid gears with crossed axes

The mathematical models of the beveloid gear surfaces with different scenarios of combinations of profile concave modification and lead crowning are derived. Four schemes of modifications were proposed for beveloid gears with crossed axes. Tooth contact analysis is developed to study the influences of different schemes of concave modifications on the mesh behaviors including film thickness, transmission errors, contact ratio, root stresses, and contact patterns. Comparison of the contact characteristics of a beveloid gear drive with and without concave modifications is conducted. The results show that all the concave modification schemes can increase the area of contact patterns and decrease the maximum value of contact stresses, while the minimum film thickness can be increased. For the scheme i.e. the pinion with profile crowning modification and gear with profile concave modification, the contact ratio increases firstly then decreases to a relative lower value. Also, the root stresses are increased obviously. For the scheme for pinion without modification and gear with lead concave modification and the scheme for both pinion and gear with lead concave modification, the transmission errors are decreased slightly. The scheme for the pinion with combined crowning modification and gear with combined concave modification shows the largest improvement for the mesh behaviors in terms of the transmission errors and contact patterns where an almost contact condition can be found for the crossed beveloid gear pair.

Dimensional Optimization of Helical Gear Pair Through Finite Element Analysis Using Subproblem Approximation Method

Traditional helical gear stress analysis techniques such as AGMA and ISO standards provides very often over-dimensioned gear pairs with bulky design. Therefore, it is required to optimize the gear pair design using latest techniques like finite element analysis. Stress analysis technique chosen to investigate the feasibility of dimensional optimization of a gear was Finite Element Analysis platform ANSYS 12.1. ISO 6336 standards and Hertz contact theory neglect friction between contact teeth. This work reflects coefficient of friction between contact teeth using FEA predicts more accurate results for contact stress. In this work, case hardened steel helical gear is optimised for optimum tooth root stress level subsequently to reduce the face width of gears with other geometrical parameters unaffected. Efforts has been carried out to verify contact stress value using Lagrange multiplier algorithm of optimised helical gear pair. Subproblem approximation method was implemented for searching of optimal solution of design variable. Optimized gear pair was manufactured and experimentally investigated for actual stresses and strains, as per loading condition mention in the rules of TED. Percentage saving in the material for optimised gear pair also been included in this work.

Finite Element Analysis on the Crack Growth and Stress Intensity Factor for the Contact Fatigue

In order to simulate contact fatigue crack propagation, the ANSYS APDL and Franc3D were used. The rolling contact model was established by the ANSYS APDL, then the distribution of the contact stress field under various loads was analyzed. The contact stress value demonstrated an error within ± 6%, compared to the obtained results from the Hertz theory. The contact stress field was imported into the Franc3D with a preset radical crack, the crack tip stress intensity factor distribution was calculated and the growth path of the three-dimensional contact fatigue cracks was analyzed. The comparisons with the experimental results demonstrated that the fatigue crack profile path from the peeling position of the subcutaneous layer was consistent with the simulated path, which was in a circular arc form. The main reason for this result was the fatigue crack change from the opening type I to the sliding type II. The a-N curves of the crack growth life under various load conditions were predicted based on the Franc3D, whereas the results displayed that the crack growth life decreased as the compressive stress increased.

ANALYSIS OF CONTACT AND BENDING STRESSES IN GEARBOX SWITCHING UNDER LOAD

The work analyses contact stresses that occur within the active surface of toothed gears as well as bending stresses that take place at the tooth root. Contact stresses have been designated at the beginning of the singletooth engagement area within the pitch point and in the end of single-tooth engagement area. Designation of bending stresses at the tooth root has been made by applying the interteeth force to the external point of single-tooth engagement. The calculated numerical values of contact and bending stresses were compared to fatigue contact durability σH lim and fatigue bending strength σF lim that were obtained experimentally. Calculations of contact stresses and bending stresses were done with multi-criterion optimisation, which makes it possible to select such geometrical parameters of toothed gears that allow utilizing fatigue durability σH lim and σF lim in reference to a given material and technology of manufacturing toothed gears.

Influence of Cutting Tool Wear on Contact Stresses and Temperature Distribution in Titanium Alloy Machining

This paper analyses the results of experimental research of contact stresses distribution over an artificial flank wear-land and temperature distribution in a cutting wedge in a free orthogonal turning of the disk made from titanium alloy (Ti-6Al-2Mo-2Cr) by a cutter with a sharp-cornered edge and with a rounded cutting edge. The investigation was carried out by the method of “split cutter” (sectional tool) and method of variable length of an artificial flank wear land. Experiments with variable feed rate and cutting speed show that in titanium alloy machining with a sharp-cornered cutting edge, the highest normal contact stress over the flank land (σh max = 3400…2200 MPa) is observed immediately at the cutting edge, and the curve has a horizontal region with a length of 0.2…0.6 mm. At larger distance from the cutting edge, the value of normal contact stress is dramatically reduced to 1100…500 MPa. The character of normal contact stresses for a rounded cutting edge is different: it is uniform and its value is approximately 2 times smaller as compared to machining with sharp-cornered cutting edge. In author’s opinion it is connected with generation of a seizure zone in chip formation region and explains working capacity of very worn-out cutting tools in machining titanium alloys. The results of experimental research of temperature distribution in the cutting tool wedge show that temperature reaches 1000 °С at essential wear over the flank surface. Such high value of temperature on the contact surface causes softening of work material, and explains the small value of tangential contact stresses (τh = 800…200 MPa) and reduction of normal contact stresses σh far from the cutting edge for a sharp-cornered cutting edge.

Applicability of PEEK and its composites in total ankle replacement devices and wear rate predictions

PEEK and carbon fiber reinforced PEEK (CFR-PEEK) materials have emerged as leading high-performance materials for replacing metal components in orthopedic devices. In this study these materials were critically evaluated as main load bearing components in total ankle replacement (TAR) devices. Wear characterization was determined by conducting finite element analysis on second generation Wright State University (WSU) TAR devices. Maximum von Mises stress value of 25.06 MPa was obtained for the optimized model with CFR-PEEK/UHMWPE as tibial/talar and bearing components, which is comparable with stress value of 26.85 MPa obtained for Ti-6Al-4V/UHMWPE material model. A similar trend was observed for contact stress values as well, where an average contact stress value of 6.61 MPa was obtained for CFR-PEEK/UHMWPE model which corresponds to a wear rate of 0.03 (mm3 yr−1). Based on the obtained stress and wear results, and in the absence of PEEK debris causing osteolysis data, CFR-PEEK was recommended as a potential alternative to Titanium alloy in TAR devices. Further wear simulator testing is necessary to accurately determine the wear behavior of TAR models.

THE ANALYSIS OF THE SLIPPAGE AND CONTACT STRESS IN THE MESHING OF THE POWER-SHIFT TYPE GEAR

This work is an analysis of gear slippage and contact stresses in toothed gears of a six-shaft power shift gearing. Gear meshing contains 5 characteristic contact points located within the active surface of a tooth. The contact points are as follows: A – beginning of a tooth involute profile located within double-tooth engagement area; B – the end-point of double-tooth engagement constituting the beginning of single-tooth engagement area; C – pitch point, referred to also as the central contact point; D – the last point of the single-tooth engagement being at the same time the starting point of the double-tooth engagement area, which is a part of the tooth tip; and, E – point at the tooth tip that closes the double-tooth engagement area. The location of individual contact points and the resulting slippage and contact stress values depend on the geometrical parameters of cooperating gear wheels. The inter-relationship suggests that, in power shift gearings, the contact points have as many positions within the active surface as there are cooperating gear wheels.

Microstructuring the surface of silicon carbide ceramic by laser action for reducing friction losses in rolling bearings

A possibility of microstructuring the surface of silicon carbide ceramic by pulse-periodic laser treatment was determined for reducing the coefficient of friction under actual contact stress conditions that occur in elements of the rolling bearing in operation. Temperature rate conditions for the laser treatment with pulse duration in the millisecond range were found, which lead to a change in the surface microrelief of silicon carbide ceramic obtained by diamond grinding after hot isostatic pressing. The determination of the coefficient of sliding friction was conducted with using the ball-on-disk tribometer at normal loads, which corresponds to the values of contact stresses of (0.5–1)×109Pa. When the load was increased to the upper limit of measuring range, the friction coefficient decrease after laser treatment was more than 30% compared to the initial structure. Significant reduction of friction in rolling bearings up to this level provides an opportunity to improve efficiency of various machines.

Comparative study of stress analysis of gears with different helix angle using the ISO 6336 standard and tooth contact analysis methods

With increasing demand for high speed and high power density gear applications, the need to optimise gears for minimum stress, noise and vibration becomes increasingly important. ISO 6336 contact and bending stress analysis are used to determine the surface load capacity and tooth bending strength but dates back to 1956 and although it is constantly being updated, a review of its performance is sensible. Methods to optimise gear performance include the selection of helix angle and tooth depth to optimise overlap ratio and transverse contact ratio and thus the performance of ISO 6336 and tooth contact analysis methods requires confirmation. This paper reviews the contact and bending stress predicted with four involute gear geometries and proposes recommendations for stress calculations, including a modification to contact ratio factor Zɛ which is used to predict contact stress and revisions to form factor YF and helix angle factor Yβ which are cited to evaluate bending stress. The results suggest that there are some significant deviations in predicted bending and contact stress values between proposal methods and original ISO standard. However, before the ISO standard is changed, the paper recommends that allowable stress numbers published in ISO 6336-5 are reviewed because the mechanisms that initiate bending and contact fatigue have also changed and these require updating.

Analytical and Numerical Tooth Contact Analysis (TCA) of Standard and Modified Involute Profile Spur Gear

Among all the common mechanical transmission elements, gears still playing the most dominant role especially in the heavy duty works offering extraordinary performance under extreme conditions and that the cause behind the extensive researches concentrating on the enhancement of its durability to do its job as well as possible. Contact stress distribution within the teeth domain is considered as one of the most effective parameters characterizing gear life, performance, efficiency, and application so that it has been well sought for formal gear profiles and paid a lot of attention for moderate tooth shapes. The aim of this work is to investigate the effect of pressure angle, speed ratio, and correction factor on the maximum contact and bending stress value and principal stresses distribution for symmetric and asymmetric spur gear. The analytical investigation adopted Hertz equations to find the contact stress value, distribution, and the contact zone width while the numerical part depends on Ansys software version 15, as a FE solver with Lagrange and penalty contact algorithm. The most fruitful points to be noticed are that the increasing of pressure angle and speed ratio trends to minimize all the induced stresses for the classical gears and the altered teeth shape with larger loaded side pressure angle than the unloaded side one behave better than the symmetric teeth concerning the stress reduction.
 

Accurate evaluation of the configurational forces in single-crystalline NiMnGa alloys under mechanical loading conditions

To properly predict the mechanical response of a single-crystalline NiMnGa sample, the configurational forces on the twin interfaces in the sample have to be calculated accurately. However, the conventional displacement-based finite element (DB-FE) method usually yields large numerical errors in calculating the contact stress values on the twin interfaces, which will further influence the evaluations of the configurational forces. In this paper, an interface element (IE) method is incorporated into the conventional FE framework. Through this FE-IE method, the contact stress is treated as one of the primary unknowns on the twin interfaces. By solving the governing system of the model numerically, the contact stresses on the twin interfaces can be directly obtained, based on which the configurational forces can be calculated. The obtained results are further used to predict the global mechanical response of the NiMnGa sample. For a simple example, the theoretical values of the resultant contact forces and the configurational forces on the twin interfaces can be determined. By comparing the numerical results obtained from the DB-FE method and the FE-IE method with the theoretical values, it is found that the FE-IE method can generate more accurate numerical solutions. Furthermore, the influence of the cross-sectional shapes of NiMnGa samples on their mechanical response is investigated.

Expedited patient-specific assessment of contact stress exposure in the ankle joint following definitive articular fracture reduction

Acute injury severity, altered joint kinematics, and joint incongruity are three important mechanical factors linked to post-traumatic osteoarthritis (PTOA). Finite element analysis (FEA) was previously used to assess the influence of increased contact stress due to joint incongruity on PTOA development. While promising agreement with PTOA development was seen, the inherent complexities of contact FEA limited the numbers of subjects that could be analyzed. Discrete element analysis (DEA) is a simplified methodology for contact stress computation, which idealizes contact surfaces as a bed of independent linear springs. In this study, DEA was explored as an expedited alternative to FEA contact stress exposure computation. DEA was compared to FEA using results from a previously completed validation study of two cadaveric human ankles, as well as a previous study of post-operative contact stress exposure in 11 patients with tibial plafond fracture. DEA-computed maximum contact stresses were within 19% of those experimentally measured, with 90% of the contact area having computed contact stress values within 1MPa of those measured. In the 11 fractured ankles, maximum contact stress and contact area differences between DEA and FEA were 0.85±0.64MPa and 22.5±11.5mm2. As a predictive measure for PTOA development, both DEA and FEA had 100% concordance with presence of OA (KL grade≥2) and >95% concordance with KL grade at 2 years. These results support DEA as a reasonable alternative to FEA for computing contact stress exposures following surgical reduction of a tibial plafond fracture.

Contact Stress Analysis of a Helical Gear

The main factors that cause the failure of gears are the bending stress and contact stress of the gear tooth. Out of these, failure of gears due to contact stress is high compared to bending stress. Stress analysis has been a key area of research to minimize failure and optimize design. This paper gives a finite element model for introspection of the stresses in the tooth during the meshing of gears. Specifically, helix angle is important for helical gears. Using modeling software, 3-D models for different helix angles in helical gears were generated, and the simulation was performed using ANSYS 12.0 to estimate the contact stress. The Hertz equation and AGMA standard was used to calculate the contact stress. The results of the theoretical contact stress values, using Hertz and AGMA are compared with the stress values from the FEA for different helix angles and the results are tabulated and discussed.