Thermomechanical Wear Research Articles

Thermal Simulation of Ventilated Brake Disc Based on Complex Multifield Coupled Method

In this article, considering the coupled interaction of heat, stress, material wear, and wheel–rail force transmission in the disc-braking process, a complex multifield coupled method was proposed to study thermal mechanical properties and contact state of brake discs. First, a coupled dynamic model of train, track, and brake gear was established to analyze the force transmission between brake friction pairs and wheel–rail system. Based on the coupled dynamics simulation results, a thermomechanical wear coupled model of the friction pair was established. It is found that the track irregularity results in vertical relative displacements with a range of (–2.6 mm, 2.8 mm) and makes the maximum brake force increase to 24.1 kN. As a comparison, brake bench tests without wheel–rail interaction were carried out. This showed that there was no vertical relative displacement between the friction pair, and the braking force had a stable value of 22.5 kN. The simulation results of the brake disc temperature distribution, and the friction pair contact state are consistent with the bench test results. In addition, different thermal simulation methods of the brake disc were used to verify the validity of the complex multifield coupled simulation results.

Effect of ZrB2 additions on the thermal stability of polycrystalline diamond

This study investigates the effect of ZrB2 additions on the microstructure, thermal stability, and thermo-mechanical wear resistance of polycrystalline diamond. Following high-pressure high-temperature (HPHT) sintering, the ZrB2-PCD material binder phase consisted of cobalt-boride (Co2B and B6Co23) phases. In-situ PXRD and TEM vacuum annealing experiments observed that the onset of bulk graphitisation occurred above 1000 °C for the ZrB2-PCD material, compared to 850 °C for the STD-PCD material. The ZrB2-PCD tools showed excellent thermo-mechanical wear resistance, exhibiting increased durability and a steady wear scar progression during high-temperature dry-VTL testing. However, lowered abrasion wear resistance was observed for the ZrB2-PCD tools during low-temperature wet-VTL testing, probably due the reduced diamond contiguity in the ZrB2 additive sample. Further optimisation of the ZrB2 additive phase content, mixing methodology, or sintering conditions could be explored to improve the abrasive wear resistance of this novel PCD material.

Sensitivity analysis of the artificial neural networks in a system for durability prediction of forging tools to forgings made of C45 steel

The article presents the results of a sensitivity analysis of artificial neural networks developed for a system which predicts the durability of forging tools used in the selected hot die forging process. The developed system makes it possible to calculate the geometric loss of the examined tool for the given values of its operating parameters (number of forgings, tool temperature at selected points, type of the applied protective layer, pressure and path of friction) and estimates the intensity of the occurrence of typical mechanisms of tool destruction, i.e. thermo-mechanical fatigue, mechanical wear, abrasive wear and plastic deformation. Nine neural networks operate in the developed system. Five of them determine the geometric loss of the material used for tools operating with protective layers, including a nitrided layer, a pad welded layer and three hybrid layers, i.e. AlCrTiSiN, Cr/CrN and Cr/AlCrTiN. Four networks make calculations determining the intensity of the occurrence of typical destructive mechanisms. The developed sensitivity analysis allows for each neural network to show which input parameters are most important and have the greatest impact on the explained variables. This is determined based on the network error analysis in the case of elimination of individual variables from the input data. The greater the network error calculated after rejecting an input variable relative to the error obtained for the network with all the input variables, the more sensitive the network to the lack of this variable. The best compliance was obtained for the first developed set of networks regarding the geometric loss of material, while the lowest compliance was obtained for the second developed set of networks regarding the applied protective layers, and in particular for plastic deformation and mechanical fatigue, probably due to the smallest size of these sets in the knowledge base. The obtained results of this analysis are important for the system operation, i.e. supporting the technologist’s decision in the selection of such process parameter values that will increase the die’s lifetime.

Thermomechanical Wear Testing of Metal Matrix Composite Cladding for Potential Application in Hot Rolling Mills

Laser metal deposition (LMD) is utilized to clad the surface of a miniaturized test roll (Ø 40 mm) of tool steel. The cladding consists of two layers: a nickel alloy as intermediate layer deposited onto the surface of the steel substrate, and a metal matrix composite (MMC) as top layer consisting of spherical tungsten carbide particles embedded into the nickel alloy matrix. The thermomechanical wear behavior of the cladding is investigated on a test rig, where the test roll is pressed against an inductively heated load roll. Multiple test runs up to several hours simulating industrial loading conditions are performed. The presented testing procedure enables predicting the time‐dependent abrasive wear behavior of the cladding, in particular for hot rolling mill applications. After testing for 8 h at temperature of 650 °C and at contact pressure of approximately 1 GPa, the maximum depth of the wear mark is about 0.12 mm. Partial cracking, debonding and dissolution of the tungsten carbide particles, as well as formation of iron and chromium oxides at the surface of the wear marks occur. However, as low abrasive wear is observed, the investigated MMC may potentially be applicable for cladding rolls in steel hot rolling mills.

Finite element solution of the three-dimensional system of equations of heat dynamics of friction and wear during single braking

A three-dimensional numerical model of a disk brake to study temperature on a discrete contact of rough surfaces has been developed. It includes the system of equations formulated based on thermotribological postulates of heat dynamics of friction and wear with mutual influence of contact pressure, velocity, properties of materials, and temperature. Two approaches of calculation of the flash temperature and its influence on the maximum temperature during a single braking application were studied. Changes in the contact temperature, sliding velocity, and the thermomechanical wear during braking were shown and discussed. It was found that two of the examined variants of calculation of the flash temperature agree well for the three considered materials of the brake pads combined with the cast iron disk, at each initial sliding velocity in the range from 5 to 20 m s−1.

A comparative study for the leverage of micro and nano SiC fillers on thermo-mechanical and erosion wear peculiarity of woven glass fibre-based vinyl ester composites

The impact of micro and nano silicon carbide (SiC) filler addition on thermo-mechanical behaviour and erosion wear is investigated. Woven glass-vinyl ester composites are developed, filled with 5 wt% and 10 wt% of micro and nano SiC fillers, respectively. Filler less composites are also prepared for comparative study. Thermo-mechanical characterisation of composites is done as per ASTM standards. Erosion wear test is performed on composites for various angles of impact (30°, 45°, 60°, 75° and 90°) and impact velocities (30, 55 and 80 m/s). Silica sand as an erodent particle with size of 300, 450 and 600 μm is used for the experimental work. Taguchi statistical method is used for design of experiments to optimise the process parameters. Results reflect that nanocomposites filled with 10 wt% of nano SiC filler performed best amongst the whole lot. VIKOR method is also implemented for fabricated composites to optimise their performance.

Effect of sol-gel coating on friction and thermomechanical wear

The optimization of the hot forging process strategy is essentially based on the determination of the tribological properties, which is a key point in most shaping process. In this study, the experimental process dedicated to the friction and wear of the deformed metal at high temperature. Forging test can be realized in accordance with many and different thermomechanical properties. Following this optimization policy, a numerical model was developed to simulate the process of hot forging and calibrate the experimental device before the starting test. All experimental investigations have simulated actual contact conditions encountered in industrial sites of the hot forming, particularly the different stresses at the tool/workpiece interface is discussed. Moreover, to fight against the various thermomechanical stresses, an alumina coating is developed by the sol-gel process and then was applied to the forging tool. It was concluded that the coating improves tribological and mechanical properties of AISI 304 stainless steel, compared to other antagonists used for forging. Indeed, the ability of the sol-gel coating to prevent wear and metal transfer from samples on the forging tool.

Study on the deterioration origin of thermomechanical contact fatigue

Thermomechanical wear is a complex phenomenon present in a number of industrial domains, such as rolling bearings, gears, friction wheels, rolling mill rollers. In this type of surface tribological deterioration, both fundamental and some peculiar wears are combined (abrasive, adhesive, corrosive wear and contact fatigue), with mechanical ant thermal causes. The present paper takes into account the contact fatigue type of deterioration, with both causes in mechanical variable load and the thermal tide action on the contact surface. There are some theories synthetically presented regarding the location of critical stresses in rolling contact fatigue. The Jacq thermal effect is briefly presented with some considerations concerning the temperature gradient in the metallic wall. The connection between the Jacq thermal anomaly and the thermomechanical contact fatigue is considered to be a new approach. Also, the same location for both mechanical and thermal critical stresses gives a strong support for the thermomechanical contact fatigue primary deterioration, according to the results obtained during the author's PhD research.

CVD and diamond tips: can then influence the bond strength of a total-etch adhesive to dentin?

Data (MPa) were analyzed by two-way ANOVA (Surface treatment X Etching time) and Tukey's test (5%). Results and conclusions: Surface treatment with CVD tips (27.70 ± 4.04a) produced significantly higher bond strength values compared to diamond tips (23.96 ± 5.83b), and 5 second etching time on dentin produced similar bond strength values when compared to 10 and 15 second etching times. Objectives: Evaluate the microtensile bond strength of a total-etch adhesive to dentin, using a CVD tip and a diamond tip to use in dentin preparation and varying the etching time. Material and method: The dentin from the buccal face of sixty bovine teeth was exposed and prepared using two different methods (n=30): Group 1 (DT) – a diamond tip on a high-speed handpiece; and Group 2 (CVD) – a CVD tip on an ultrasonic handpiece. Each group used 37% phosphoric acid and was divided into three subgroups, according to the etching time (n=10): Subgroup 5 - 5 seconds; Subgroup 10 - 10 seconds; and Subgroup 15 - 15 seconds. The teeth were restored with Single Bond adhesive and the composite resin Herculite Classic. The specimens were subjected to thermomechanical wear (mechanical cycling/100.000 cycles, thermal cycling/1.000 cycles). Stick-like specimens were obtained and submitted to a microtensile test in a universal testing machine.

Contact modeling in boundary element analysis including the simulation of thermomechanical wear

Computational mechanics codes include contact or over-closure models to account for contact stiffness, which can be related to surface roughness and nominal pressure from Greenwood and Williamson. We present results of wear simulation studies with adjustable contact parameters for a ring-on-ring sliding configuration. A boundary element code is used to solve the non-linear contact problem with an axisymmetric thermoelastic representation of the rings, along with a localized Archard wear model. Parametric studies indicate the extent to which the wear tracks can be affected by the roughness and wear history. The effects range from minor to moderately significant, with areas of maximum wear shifting radially. Contact parameters influence pressure, temperature and wear distributions, with stiffer contacts resulting in greater localization.

3D FE model of frictional heating and wear with a mutual influence of the sliding velocity and temperature in a disc brake

Numerical simulation of frictional heating in a disc brake of a typical passenger vehicle based on the equation of motion and the boundary-value problem of heat conduction was carried out. An influence of temperature-dependent coefficient of friction on the sliding velocity, braking time, braking distance and the thermomechanical wear was studied. Two materials of the pad combined with the cast-iron brake disc were examined. The dependencies of the coefficient of friction and wear rate on the temperature and contact pressure were derived from experimental measurements and implemented to the computational model of the brake. Comparisons of temperature for validation purposes calculated using the contact model developed in this study were made with the model introducing an approach based on the heat partition adopted from other studies.

Analysis of thermo-mechanical wear problems for reciprocal punch sliding

The relative sliding motion of two elastic bodies in contact induces wear process and contact shape evolution. In the case of a punch sliding on a substrate the transient process tends to a steady state for which the fixed contact stress and strain distribution develops in the contact zone. This state usually corresponds to a minimum of the wear dissipation power. The optimality conditions of the wear dissipation functional provide the contact stress distribution and the wear rate compatible with the rigid body punch motion. The present paper is aimed to extend the previous analyses [1–5] of steady state conditions to cases of periodic sliding of punch, assuming cyclic steady state conditions for both mechanical and thermal fields.

Analog Studies of Thermomechanical Fatigue and Abrasive Wear of Cast and Forged Steels for “Autoforge” Dies

Processes of thermomechanical fatigue and abrasive wear of suspension-cast precipitation-hardening ferrite-carbide steel 30T6NTiC-1.5 and standard steel 4Kh5MFS are studied. The dominant kinds of fracture typical for dies for semisolid stamping are determined. The factors and parameters of cyclic temperature and force loading are shown to produce a selective action on the competing kinds of damage of the die steels. A comparative analysis of the properties of the steels is performed. Steel 30T6NTiC-1.5 is shown to have substantial advantages over steel 4Kh5FMS traditionally used for making “Autoforge” dies.

Study on the Wear Behavior of Ultrafine Grained 304L Stainless Steel

An ultrafine grained 304L stainless steel with average grain size of 650±100 nm was produced by a combination of cold rolling and annealing. Wear behavior of the steel was examined by dry sliding wear tests under different loads. Different microstructural characterizations were conducted on the ultrafine grained structure after thermomechanical processing and wear tests. The results demonstrated that the steel had yield strength of 720 MPa and total elongation of 47%, which is almost twice higher than typical coarse grained strength. Also, wear tests results showed a good linear relation between the cumulative wear loss and distance in each normal load. Wear rate was about 0.024, 0.043 and 0.093 mg/m for normal loads of 10, 20 and 30N, respectively. Wear mechanism was also recognized as delamination (in the early stage) and mixture of delamination and abrasion in higher distances.

Thermomechanical wear during quasistationary heat generation by friction

The known criterial relationships of thermomechanical wear are adapted to the case of spatial quasistationary temperature and stress-strain state of the triboelement. The original data used are the distribution of temperature and stresses in the semispace exposed to the heat flux and normal pressure in the region moving over the surface with constant velocity. The dimensionless parameters Pe, Gth and p0/σf0 are used to plot the maps of thermomechanical wear which take into account the tribosurface plastic fracture (steel; ShKh15) or brittle and plastic fracture (aluminum oxide Al2O3) in response to the temperature.

Real-Time Compact Thermal Models for Health Management of Power Electronics

Implementation of real-time health assessment and thermal management of power electronic devices require real-time electrothermal models that can be used to predict the temperatures of device junctions, interfaces, etc., which cannot ordinarily be measured during service. This paper presents a real-time reduced-order compact thermal model, which is incorporated in a pulsewidth modulation and current controlled full bridge. An accurate representation of the dynamic thermal behavior was obtained experimentally and converted into a simplified multiexponential form then combined with lookup tables that provide estimates of the device losses based on measured values of the phase current. For interfaces away from the surface, such as solder layers, a validated Flotherm model is used to predict the temperatures of the hidden layers. Comparison of the real-time temperature estimates with IR measured values obtained from a high-speed IR camera showed that the reduced-order model was capable in estimating the module's temperatures over a range of modulation conditions. This real-time model is well-suited to the continuous monitoring of the internal behavior of the electrothermal effects within power electronic modules and can thus be used as part of a prognostic tool to provide knowledge through thermal cycling by combining with thermomechanical wear out models for health management of power electronics.

Some Studies on Scuffing Performance of Surface Treated AISI 4340 Steels

Scuffing or scoring is an important form of damage leading to component replacements in lubricated mechanical systems such as power drives, gears, bearings, cams and followers, piston rings etc. Since scuffing necessarily involves localized welding of asperities, suitable surface modifications or coating can impart a good resistance to scuffing. A new class of low temperature salt bath nitriding process provides good resistance to scuffing. The current work is on evaluation of the scuffing resistance of AISI 4340 steels imparted with two such treatments. Experimental investigations were conducted on Sursulf and Arcor treated AISI 4340 steel specimen using a pin on ring test system under boundary lubrication condition. Continuous monitoring of friction records and (near surface) bulk temperature were done under step loading. Limiting loads and load velocity relations were evaluated and using the data generated and a thermo-mechanical wear model, performance is indexed. Off line studies on surface finish, hardness variations and surface transformations were also accomplished. Some salient aspects of the investigation and data generated are presented here. Onset of scuffing was observed to be far delayed with pin specimen imparted with these treatments compared to hardening.

Abrasive-waterjet testing of thermo-mechanical wear of ceramics

The wear behaviour of liquid phase sintered silicon carbide and conventional single phase silicon carbide ceramics has been studied by a low impingement angle abrasive-waterjet (AWJ). Three issues were focused upon: (i) the material removal mechanisms, (ii) the stability of the wear process, and (iii) a novel technique for transmission electron microscopy (TEM) analysis of structural changes in the wear zone of the ceramic material. Thermally and deformation related wear mechanisms could be identified by TEM, viz. cracked grains and volumes, plastic deformation, formation of grain boundary cavities, surface oxidation and grain boundary oxidation and melting. The AWJ test showed good stability in performance, and the test has a potential as a ranking method of materials for tribological applications involving sliding leading to high flash temperatures. The AWJ test also enables identification of material removal mechanisms in AWJ machining.

Thermomechanical criterion of frictional wear in the process of quasistationary heat generation

We propose a thermomechanical criterion of the onset of plastic wear of materials and show how to construct the wear chart for a given friction pair (by using ShKh15 steel as an example). It is established that thermomechanical wear can be prevented by the optimization of service conditions and proper selection of materials.

Mechanical properties and recrystallization of alumina ceramics reinforced by silicon carbide whisker

The mechanical properties and recrystallization of a material consisting of Al2O3 and SiC whisker are considered for different hot pressing regimes. The best properties are obtained at an SiC whisker content of 20% in hot pressing in an argon medium at 1600°C (the ultimate bending strength is 600 MPa, the critical coefficient of stress intensityKIc=5.5 MPa · m1/2). The bending strength measured at 1000°C is at least 400 MPa for the material pressed at 1700°C in air. It is established that the presence of SiC whisker on grain boundaries of Al2O3 noticeably impedes the growth of alumina grains in recrystallization for all chosen regimes of hot pressing (1650 – 1900°C, 15 – 45 min). The dominant grain size is 1 –5 µm. A mathematical model is suggested for evaluating the maximum grain size in uniform grain growth, which isD*=0.571 [1++(1+16.151/f)1/2]d, whered, f are the diameter and the volume fraction of SiC whisker. The material can be recommended for use under conditions of thermomechanical stress and abrasive wear.