Ductile iron can acquire enhanced thermal and mechanical properties from austempering heat treatment. The present study aims to identify the function of different cutting parameters affecting machinability and to quantify its effects.... more
Ductile iron can acquire enhanced thermal and mechanical properties from austempering heat treatment. The present study aims to identify the function of different cutting parameters affecting machinability and to quantify its effects. Turning was performed to test machinability according to the ISO3685-1993 (E) standard. After austenitizing at 900 °C for 90 min, austempered ductile iron (ADI) specimens were quenched in a salt bath at 380 °C for 90 min. The cutting force signals along three directions were measured in real time, whereas flank wear and surface roughness were measured offline. For the cutting parameters, the cutting speed and depth of cut were varied, but the feed rate was kept constant. In the flank wear tests, machining length was corresponded to tool life. In addition, in order to find out the effect of cutting parameters on surface roughness (Ra), tangential force (Ft), and flank wear (VB) during turning, response surface methodology (RSM) was utilized by using exp...
On-line tool wear monitoring in metal-cutting operations is essential for an on-line process optimization. In this paper, tool flank wear is estimated on-line by utilizing a nonlinear observer with the feedback of cutting force... more
On-line tool wear monitoring in metal-cutting operations is essential for an on-line process optimization. In this paper, tool flank wear is estimated on-line by utilizing a nonlinear observer with the feedback of cutting force measurements. Based on a previously developed cutting process model for turning, a nonlinear observer is designed such that the estimated flank wear converges to the actual flank wear development in the presence of poor initial estimates. The stability analysis for the resulting observer error dynamic system is carried out using a physical limitation of the actual flank wear development and the Total Stability Theorem. The experimental results show that the proposed nonlinear observer estimates the flank wear quite well not only in the presence of poor initial estimates but also in the presence of unexpected fluctuations in the cutting force measurements. However, the method has drawbacks resulting from difficulties in obtaining accurate model parameters. An adaptive version of the presented nonlinear observer, periodically calibrated by off-line direct tool wear measurements using computer vision, is considered to be a promising strategy for industrial implementation.
The present study concerns laser surface alloying with silicon of mild steel substrate using a high-power continuous wave CO2 laser with an objective to improve wear resistance. The effect of surface remelting using nitrogen as shrouding... more
The present study concerns laser surface alloying with silicon of mild steel substrate using a high-power continuous wave CO2 laser with an objective to improve wear resistance. The effect of surface remelting using nitrogen as shrouding environment (with and without graphite coating) on microhardness and wear resistance has also been evaluated. Laser surface alloying leads to formation of a defect free microstructure consisting of iron silicides in laser surface alloyed mild steel with silicon and a combination of silicides and nitrides when remelted in nitrogen. Carbon deposition prior to remelting leads to presence of a few martensite in the microstructure. A significant improvement in microhardness is achieved by laser surface alloying and remelting to a maximum of 800 VHN when silicon alloyed surface is melted using nitrogen shroud with carbon coating. A detailed wear study (against diamond) showed that a significant improvement in wear resistance is obtained with a maximum improvement when remelted in nitrogen atmosphere followed by carbon coating.
Adaptive thin-film nanocomposite coatings comprised of crystalline ductile phases of gold and molybdenum disulfide, and brittle phases of diamond like carbon (DLC) and ytrria stabilized zirconia (YSZ) have been investigated by specialized... more
Adaptive thin-film nanocomposite coatings comprised of crystalline ductile phases of gold and molybdenum disulfide, and brittle phases of diamond like carbon (DLC) and ytrria stabilized zirconia (YSZ) have been investigated by specialized microstructurally based finite-element techniques. One of the major objectives is to determine optimal crystalline and amorphous compositions and behavior related to wear and durability over a wide range of thermo-mechanical conditions. The interrelated effects of microstructural characteristics such as grain shapes and sizes, local material behavior due to interfacial stresses and strains, varying amorphous and crystalline compositions, and transfer film adhesion on coating behavior have been studied. The computational predictions, consistent with experimental observations, indicate specific interfacial regions between DLC and ductile metal inclusions are critical regions of stress and strain accumulation that can be precursors to material failure and wear. It is shown by varying the composition, resulting in tradeoffs between lubrication, toughness, and strength, the effects of these critical stresses and strains can be controlled for desired behavior. A mechanistic model to account for experimentally observed transfer film adhesion modes was also developed, and based on these results, it was shown that transfer film bonding has a significant impact on stress and wear behavior.
The state of strain varies in a polymer material during sliding against steel. The reasons for this are, among other things, imperfections of shape of the surface of the contacting steel element and the oscillatory character of the... more
The state of strain varies in a polymer material during sliding against steel. The reasons for this are, among other things, imperfections of shape of the surface of the contacting steel element and the oscillatory character of the friction force. The viscoelastic nature of polymer materials (considerable internal friction) means that under such conditions a certain amount of friction energy is dissipated in the form of heat inside these materials, contributing to their heating up. For this reason the internal friction for selected PTFE composites has been investigated, as well as the temperature distribution on the surface of PTFE samples sliding against steel under dry friction conditions. It was observed (using a thermovision system) that the highest temperature occurred inside the polymer material, at some distance from the friction surface. That testifies to the generation of heat during friction, not only on the contact surface of the sliding materials but also inside the polymer material. Both thermovision investigations and computations demonstrated the essential role that internal friction plays in polymer materials during their sliding against metals.
The current study investigates the characteristics of particles generated from the wear of braking materials, and provides an applicable index for measuring and comparing wear particle emissions. A pin-on-disc tribometer equipped with... more
The current study investigates the characteristics of particles generated from the wear of braking materials, and provides an applicable index for measuring and comparing wear particle emissions. A pin-on-disc tribometer equipped with particle measurement instruments was used. The number concentration, size, morphology, and mass concentration of generated particles were investigated and reported for particles 10 nm-32 m in diameter. The particles were also collected on filters and investigated using EDS and SEM. The effects of wear mechanisms on particle morphology and changes in particle concentration are discussed. A new index, the airborne wear particle emission rate (AWPER), is suggested that could be used in legislation to control non-exhaust emissions from transport modes, particularly rail transport.
The increasing demands from environmental legislations are changing the conditions that the valve system is exposed to in heavy duty engines. Increased pressures, higher temperatures and lower amounts of soot which can build up a... more
The increasing demands from environmental legislations are changing the conditions that the valve system is exposed to in heavy duty engines. Increased pressures, higher temperatures and lower amounts of soot which can build up a protective film are some of the increasing challenges which the system has to endure. Three pairs of valves and valve seat inserts with the same material and design properties but with different service condition have been analyzed with a variety of analytical instruments to gain information of how the wear occurs. The wear mechanisms found were a combination of oxidation, where many different oxides were found, adhesive wear, which was seen both in form of material transfer and flow lines. On top of Sample Mild and Hard there were tribo films of thickness varying from 1 to 5 m consisting of Ca, O, P, S and Zn. The film has in all cases protected the underlying surface from wear but in some cases seems to have a corrosive impact instead.
The frictional response of a multi-component phenolic-based friction material is highly complex under a set of variable loads and speeds. The present paper discusses the sensitivity of friction coefficient () of friction composites... more
The frictional response of a multi-component phenolic-based friction material is highly complex under a set of variable loads and speeds. The present paper discusses the sensitivity of friction coefficient () of friction composites containing synthetic graphite with different particle sizes (with similar crystallinity range) to braking pressure and sliding speed. The friction studies were carried out on a sub scale brake-testrig, following 4 loads × 3 speeds experimental design. The best combination of performance properties was observed for the composite containing synthetic graphite with an average particle size of 410 m. Other particle sizes which resulted in good performance were 38 and 169 m. Very fine particle sizes were not beneficial for desired combination of performance properties. Regression analysis of following an orthogonal L 9 (3 × 3) experimental design method revealed that the first order influences of sliding speed and braking pressure were significant. When all the combinatorial influences of braking pressure and sliding speed are taken into account together their simultaneous effects would be most effective in the range of graphite particle size ∼80-250 m.
The aim of this work is to investigate the effectiveness of combining both vibration analysis and wear debris analysis in an integrated machine condition monitoring maintenance program. To this end, a series of studies was conducted on a... more
The aim of this work is to investigate the effectiveness of combining both vibration analysis and wear debris analysis in an integrated machine condition monitoring maintenance program. To this end, a series of studies was conducted on a spur gearbox test rig. After a test under normal condition was conducted to obtain the baseline information of the test rig, a number of different machine defect conditions were introduced under controlled operating conditions, corresponding to (i) constant overload conditions and (ii) cyclic load conditions. The data provided by wear debris analysis was compared with vibration analysis spectra in order to quantify the effectiveness of both vibration analysis and wear debris analysis in predicting and diagnosing machine failures.
The visual aspect of rough surfaces such as steel surfaces becomes of great importance for the quality of the final product they are dedicated to. In a previous work, we have solved the theoretically complex problem of automatically... more
The visual aspect of rough surfaces such as steel surfaces becomes of great importance for the quality of the final product they are dedicated to. In a previous work, we have solved the theoretically complex problem of automatically classifying surfaces according to the quality of their aspect. In this case, the measurements were based on topographical maps obtained through interferometric microscopy. The resulting data were analyzed by an algorithm based on morphological and statistical features extraction from surface topography, factorial analysis, bootstrap over-sampling and Bayesian classification. It was then important to apply this methodology as efficiently as possible to perform an automatic, on-line and continuous inspection of the product. In this paper, we focus on all steps leading to such an on-line application, among which choosing an optical sensor and the corresponding optical configuration adapted to an industrial environment and overcoming all difficulties to go from first laboratory tests to on-line measurements on fast moving product are particularly determining. Finally, results of on-line acquisitions are displayed, that are in good agreement with expected aspect characterization.
The impact of thermal barrier coatings by hard projectiles at high temperature has been analyzed. Three different domains have been explored: each differentiated by particle size, velocity, temperature and TBC composition. Domain I... more
The impact of thermal barrier coatings by hard projectiles at high temperature has been analyzed. Three different domains have been explored: each differentiated by particle size, velocity, temperature and TBC composition. Domain I applies when the projectile creates deeply penetrating plastic/densification zones. In this case, short time elastic effects are relatively unimportant. The response is dominated by stresses that arise
In this project, the alternating torsion fatigue test was carried out to investigate the effect of the nitrided case produced by gas and plasma nitriding processes on the fatigue endurance of the JIS SACM 645 steel. The surface layers of... more
In this project, the alternating torsion fatigue test was carried out to investigate the effect of the nitrided case produced by gas and plasma nitriding processes on the fatigue endurance of the JIS SACM 645 steel. The surface layers of the nitrided specimens exhibited hardness profiles in the range between 1000–1100HV0.1, and the white layer of the nitrided specimen was consisted of Fe3N and Fe4N. Wear test result indicated that the mass loss of JIS SACM 645 steel was greatly improved by nitriding processes. From the mass loss data, the wear resistance of the steel was significantly influenced by nitriding time. The fatigue strength of the 35C-GN48 nitrided specimen rose 51.9% to 632 MPa, which was the maximum fatigue strength in this study.
The research presented in this paper is focused on the effect of silicon carbide (SiC) on friction-wear properties of semi-metallic friction composites (FC). Semi-metallic FC with increasing content of silicon carbide (SiC: 0, 3.4, 5.6, 9... more
The research presented in this paper is focused on the effect of silicon carbide (SiC) on friction-wear properties of semi-metallic friction composites (FC). Semi-metallic FC with increasing content of silicon carbide (SiC: 0, 3.4, 5.6, 9 and 14.6 vol.%) were prepared and slid against cast iron disc and their friction-wear properties were evaluated. The friction coefficient ( ) was observed to increase with SiC content, nonetheless the highest content (14.6 vol.% of SiC) did not significantly increase its value. The volume wear rate (V) of tested friction composites slightly increases with SiC content and temperature. The character of friction layer was analyzed using scanning electron microscopy (SEM) with energy dispersive X-ray microanalysis (EDX) and the topography of friction surface was studied using atomic force microscopy (AFM). Two types of films assigned as film I and film II appearing on the friction surfaces of samples after friction test were observed. Film I originate on the friction surface of sample without SiC and is composed of debris of iron, iron oxide, stibnite and carbon. Film II is formed on the friction surface of composites containing SiC and in contrast to film I contain additional debris of SiC.
A conventional scanning reference electrode technique (SRET) has been modified to provide a novel method for characterising the real-time localised tribocorrosion behaviour of uncoated and physical vapour deposition (PVD) coated samples.... more
A conventional scanning reference electrode technique (SRET) has been modified to provide a novel method for characterising the real-time localised tribocorrosion behaviour of uncoated and physical vapour deposition (PVD) coated samples. The modification was carried out based upon the principle of a ball-on-cylinder contact. Here a sliding probe, in this case a changeable alumina ball, is positioned diametrically opposite a pseudo (Pt) reference electrode probe which is positioned 100 m away from the surface of a cylindrical specimen which rotates at a set speed. The contact probe, specimen and reference probe are immersed within a chosen electrolyte, which for this study, is aqueous 0.01% NaCl. The dynamic corrosion activity is monitored via the Pt probe by recording variations in ionic flux emanating at the surface of the corroding sample. The SRET can operate in two modes, namely line scan, in which corrosion activity along the circumference of the specimen is measured, or map scan in which a 2D corrosion activity area map of the surface of the specimen is obtained. This paper presents the design, calibration procedures, and real-time tribocorrosion behaviour of uncoated and PVD (C/Cr) coated 316 stainless steel as a function of the contact load, and test conditions. Evidence of the effects of wear damage due to contact by the alumina ball was obtained by monitoring the SRET activity during loading (contact) and unloading conditions. The real-time local tribocorrosion activity can be detected immediately a load was applied. Such activity was found to stop, due to surface repassivation, upon removal of the load (alumina ball). The results show that the applied loads affect the free corrosion potential, local current density, active anodic areas and the sample recovery time of the tested samples. The wear tracks were investigated using optical and scanning electron microscopy and laser profilometer. Correlation of tribocorrosion damage and contact load has been investigated.
Total disc replacement emerged as an alternative to fusion for the treatment of degenerative disc disease. Optimization of the bearing surfaces is critical to mitigate wear-related biological reaction. The purpose of this study was to... more
Total disc replacement emerged as an alternative to fusion for the treatment of degenerative disc disease. Optimization of the bearing surfaces is critical to mitigate wear-related biological reaction. The purpose of this study was to characterize the wear of the A-MAV TM metal-on-metal total disc replacement using a spine wear simulator, per the ASTM F2423-05 standard guide. Six specimens were tested under flexion-extension (FE) conditions for ten million cycles (MC), followed by lateral bending (LB) combined with axial rotation (AR) for an additional ten MC. A run-in wear period was observed during the first 0.5 MC for both testing conditions, followed by a steady-state wear rate of 0.33 ± 0.12 mm 3 /MC in FE and 0.43 ± 0.06 mm 3 /MC in combined motion. Phasing between LB and AR led to a crossing-path motion as observed on explanted devices. This study suggests that clinically-realistic surface morphology may be achieved by carefully selecting the wear test parameters specified in the ASTM standard guide. Furthermore, the use of metal-on-metal bearings in spinal arthroplasty may be viable in view of the low wear exhibited by this material combination.
Raman spectroscopy of solid lubricant coatings during high temperature (300-700 • C) wear testing was employed for real-time correlation of sliding contact surface chemistry to the measured friction coefficient. Two coatings were... more
Raman spectroscopy of solid lubricant coatings during high temperature (300-700 • C) wear testing was employed for real-time correlation of sliding contact surface chemistry to the measured friction coefficient. Two coatings were investigated in this work -MoS 2 and VN-Ag. Immediately prior to failure of the MoS 2 coating at 350 • C, molybdenum trioxide was detected in the wear track, and an increase in friction coefficient and ultimate failure of the coating was associated with buildup of the abrasive oxide compound. For the VN-Ag nanocomposite coating, in situ Raman analysis of the contact surface during heating revealed the appearance of silver vanadate compounds at a temperature of 375 • C. At higher temperatures, competitive evolution of different silver vanadate phases (i.e., Ag 3 VO 4 , AgVO 3 ) was observed. For the conditions examined in this work, the wear process at 700 • C inhibited formation of AgVO 3 in the sliding contact, as determined by comparison of the composition of the wear track to that of the adjacent, unworn coating surface. Additionally, the composition of the wear track was significantly different after the sample had cooled sufficiently to allow handling for post-test surface characterization with conventional Raman, XRD, and SEM techniques, further illustrating the utility of in situ diagnostics for identification of active lubricant phases during wear tests. This ability to characterize surfaces during wear tests at elevated temperatures fills an important gap left by current in situ tribology techniques that are currently used to provide insight on mechanisms governing the performance of solid lubricant film materials.
Simulation of wear evolution during abrasive processes is a very difficult task compared to that of machining processes because of the degree of randomness of geometry and disposition of cutting teeth. Superfinishing is a specific case of... more
Simulation of wear evolution during abrasive processes is a very difficult task compared to that of machining processes because of the degree of randomness of geometry and disposition of cutting teeth. Superfinishing is a specific case of abrasive process, where the temperature is not consistently involved. A wear model and a numerical method of simulating the process, involving data collected in a testing experiment that resulted in determining an abrasive function, are presented for the specific case of the superfinishing the ball track of an inner bearing ring. Four types of stones were tested while abrading a cylindrical sample of M50 steel, using a high fluidity oil as a lubricant. The abrasive function characteristic to the materials involved in the process was determined. The wear volume of stone, that resulted in simulation and superfinishing experiments, is compared for three of the stones, and a good agreement between them was obtained, endorsing the viability of the simulation. The stability of the results with mesh refinement was analyzed. Three other output parameters of the simulated process and their dependency on the stone type were discussed.
The development of railway wheel steel grades has gone towards higher strength to enhance rolling contact fatigue resistance and ability to withstand thermally induced damage throughout the service lifetime. In this study a recently... more
The development of railway wheel steel grades has gone towards higher strength to enhance rolling contact fatigue resistance and ability to withstand thermally induced damage throughout the service lifetime. In this study a recently developed wheel steel material for passenger trains containing high levels of manganese and silicon, approximately 1 wt% of each, was tested in low cycle fatigue at different total strain amplitudes. In addition, monotonic tensile and Charpy V-notch impact testings in the temperature range −60 • C to 180 • C were performed. The results were compared to another steel grade commonly used in Europe for railway wheels. The low cycle fatigue results show similar cyclic lifetime N f , and fatigue stress amplitude development for both materials, but the highly alloyed steel exhibits reduced cyclic softening and hardening during the fatigue life and is in this respect more stable in its behaviour. As is typical for pearlitic-ferritic steels both materials show a pronounced monotonic strain hardening. It was concluded that the increased levels of manganese and silicon have minor effects on monotonic behaviour but substantial influence on cyclic behaviour at ambient temperatures. At increased temperatures, though, there are indications of additional effects on monotonic behaviour. However, the high temperature properties have to be investigated further to gain full understanding of mechanisms and effects.
The main cause of damage to oil and gas equipment is wear. This paper proves that the principal wear mechanism is abrasive and shock-abrasive wear; and analyzes materials test methods and techniques for wear rate identification. The... more
The main cause of damage to oil and gas equipment is wear. This paper proves that the principal wear mechanism is abrasive and shock-abrasive wear; and analyzes materials test methods and techniques for wear rate identification. The author considers standardized and non-standardized methods and establishes that despite a large number of materials test methods, we don’t have a unique one for adequate assessment of wear resistance in metals. It is concluded that selection of test methods depends on working conditions of the equipment and use of different types of wear to assess resistance of metals.
In this paper, results from erosion-corrosion tests performed under liquid-solid erosion conditions in 3.5% NaCl liquid medium are reported. The focus of the paper is to compare the behaviour of Cast and Hot Isostatically Pressed (HIPed)... more
In this paper, results from erosion-corrosion tests performed under liquid-solid erosion conditions in 3.5% NaCl liquid medium are reported. The focus of the paper is to compare the behaviour of Cast and Hot Isostatically Pressed (HIPed) Stellite 6 alloy in terms of their electrochemical corrosion characteristics, their resistance to mechanical degradation and relationship between microstructure and degradation mechanisms. It has been shown that HIPed Stellite 6 possesses better erosion and erosion corrosion resistance than that of Cast Stellite 6 and two stainless steels (UNS S32760 and UNS S31603) under the same solid loading (200 and 500 mg/l), and same temperature (20 and 50 • C). The material removal mechanisms have been identified by using atomic force microscopy (AFM) and shown preferential removal of the Co-rich matrix to be less extensive on the HIPed material.
We describe several examples where we use cross-correlation functions to quantify the similarity of 2D surface profiles or of 3D areal surface topography images. The applications have included (1) the manufacture of standard reference... more
We describe several examples where we use cross-correlation functions to quantify the similarity of 2D surface profiles or of 3D areal surface topography images. The applications have included (1) the manufacture of standard reference material (SRM) bullets and casings, (2) methods to assess whether bullets or casings have been fired by the same firearm, and (3) research to quantify similarities or differences between profiles of the same surface measured by different techniques or between a master surface and its replicas. The cross-correlation maximum is the functional parameter used to quantify similarity. A second parameter, called the relative profile (2D) difference or relative areal topography (3D) difference, may also be used to quantify differences and to recognize the ambiguous condition when two results have different vertical (z-) scales but identical shapes. Most of these examples have been applied in support of ballistics inspection methods in crime labs, but the methods are generally useful for estimating the accuracy of surface replication techniques or the ability of different surface topography instruments to measure the same surface and provide the same result. The instruments used in these studies were a stylus instrument and a Nipkow-disk type confocal microscope. Cross-correlation functions may also be used to assess differences resulting from the use of different filters to modify the same surface profile or topography image.
This work presents the development of a method which analyzes metallic wear debris and contaminants found to be present in fuels used by Diesel engines. The particles have been isolated by following two complementary methods; firstly, a... more
This work presents the development of a method which analyzes metallic wear debris and contaminants found to be present in fuels used by Diesel engines. The particles have been isolated by following two complementary methods; firstly, a magnetic separation method and then a filtering method using membranes. Particles are subsequently characterized by means of optical and electron microscopy, where it is possible to establish the type and severity of the wear, as well as establishing how the mechanism parts are actually affected by wear. This technique allows a predictive maintenance of the fuel injection systems to be carried out, as it allows for possible breakdowns to be detected prior to a serious failure being produced.
In this paper the friction and sliding wear of WC–Co cemented carbides are studied. Friction and wear tests were carried out using six different WC–Co alloys (Co ranging from 6 to 20wt.%) under unlubricated conditions against steel... more
In this paper the friction and sliding wear of WC–Co cemented carbides are studied. Friction and wear tests were carried out using six different WC–Co alloys (Co ranging from 6 to 20wt.%) under unlubricated conditions against steel (0.45wt.% C) disk. Tests were performed at sliding velocity of 2.2ms−1 and normal load of 40 and 180N. Sliding wear tests were carried
This paper discusses the role of fillers such as solid lubricants, pure metals and inorganic compounds in modifying the tribological behavior of polymers. It examines critically the mechanisms and hypotheses proposed by a number of... more
This paper discusses the role of fillers such as solid lubricants, pure metals and inorganic compounds in modifying the tribological behavior of polymers. It examines critically the mechanisms and hypotheses proposed by a number of workers for wear reduction. This is done from the overall perspective of the data published in the literature as well as the recent work done by the authors on the subject. Some of the hypotheses have been negated while some are supported with discretion. The critical filler volume model is discussed and the filler volume for minimum wear is shown to agree with that calculated by the model. Some guidelines for the selection of fillers and their proportion for minimum wear rate are provided and the areas of research needing further attention are indicated.
Among the light metals, Mg and its alloys occupy a prominent position due to its low density, excellent machinability, and high specific strength. However, a relatively poor resistance to corrosion and wear are serious impediments against... more
Among the light metals, Mg and its alloys occupy a prominent position due to its low density, excellent machinability, and high specific strength. However, a relatively poor resistance to corrosion and wear are serious impediments against wider application of Mg alloys. In the present study, an attempt was made to enhance pitting corrosion resistance and microhardness of a commercial Mg alloy, MEZ (Zn 0.5%, Mn 0.1%, Zr 0.1%, rare earth elements 2%, Mg remaining percentage) by laser surface melting. The study included a detailed characterization of laser surface melted zone in terms of microstructure, phase analysis and its correlation with process parameters to optimize the laser processing routine. Mechanical properties like microhardness, wear, and electrochemical properties like pitting corrosion resistance of the surface melted layer were studied in detail. Microhardness of the laser surface melted layer was improved to 85–100 VHN as compared to 35 VHN of the as-received MEZ. Pitting corrosion resistance of the laser surface melted MEZ, significantly improved in a 3.56 wt.% NaCl solution because of grain refinement and redistribution of the intermetallic phases following rapid quenching associated with the process. The wear resistance of laser surface melted layer was also improved as compared to as-received MEZ.
Transportation authorities have to support high costs for track maintenance due to the wear of the rails and to crack generation at some particular points along the line. To set up the planning of the maintenance and inspection... more
Transportation authorities have to support high costs for track maintenance due to the wear of the rails and to crack generation at some particular points along the line. To set up the planning of the maintenance and inspection operations, a predictive approach could be very useful. Moreover, such an approach could help tramcar designers to design tramcars less aggressive towards the line. This paper deals with a numerical approach for the prediction of damage phenomena on tramline rails. In order to be able to foresee maintenance and inspection intervals, both wear and ratchetting analyses are carried out on the basis of load spectra that were determined with a validated multi-body tramcar model. Although the damage analysis is focused on a specific case (one single curve with a radius of 50 m), the approach is very general thus allowing to be used for assessing tramcar design.
This paper presents an experimental study of the friction noise, between two rough and dry flat surfaces. The domain of interest is the dry contact under light pressure where the roughness is the dominant cause of noise. The results show... more
This paper presents an experimental study of the friction noise, between two rough and dry flat surfaces. The domain of interest is the dry contact under light pressure where the roughness is the dominant cause of noise. The results show that, for sliding rough surfaces under light load, the fundamental mechanism of radiated noise is the presence of shocks occurring between antagonist asperities of sliding surfaces. The radiated roughness noise is controlled simultaneously by the detailed topography of the surfaces in contact, the sliding speed and the dynamics of the surfaces. In terms of topography and sliding speed, it was shown that the roughness noise is simultaneously an increasing linear function of the logarithm of the surface roughness and the sliding speed. In terms of dynamics, the roughness noise is generated for light dynamical coupling. Hence, the natural modes of samples are stiffer than the contact and therefore the resulting vibrations are not affected by the additional rigidity. The deformation of surfaces during contact is very light and its magnitude is negligible compared to the surface roughness.
The Al x CoCrCuFeNi alloys with different aluminum contents prepared by arc melting were investigated on their adhesive wear behaviors. With increasing aluminum content, both the volume fraction of BCC phase and the hardness value... more
The Al x CoCrCuFeNi alloys with different aluminum contents prepared by arc melting were investigated on their adhesive wear behaviors. With increasing aluminum content, both the volume fraction of BCC phase and the hardness value increase, and thus the wear coefficient decreases. Moreover, the wear mechanism changes from delamination wear to oxidative wear. For low aluminum content, x = 0.5, the microstructure is of simple ductile FCC phase and the worn surface is deeply grooved and undergoes a periodic delamination which produces big debris. For medium aluminum content, x = 1.0, the microstructure is a mixture of FCC and BCC phases, and the worn surface is deeply grooved in FCC region but smooth in BCC region. Delamination wear is still dominant although oxidative wear occurs in the smooth region. For high aluminum content, x = 2.0, the microstructure is of BCC phase and the worn surface is smooth and yields fine debris with high oxygen content. The high aluminum content gives a large improvement in wear resistance. This improvement is attributed to its high hardness, which not only resists plastic deformation and delamination, but also brings about the oxidative wear in which oxide film could assist the wear resistance.
Industries and researchers are trying to reduce the use of coolant lubricant fluids in metal cutting to obtain safety, environmental and economical benefits. The aim of this research is to determine if the minimal quantity lubrication... more
Industries and researchers are trying to reduce the use of coolant lubricant fluids in metal cutting to obtain safety, environmental and economical benefits. The aim of this research is to determine if the minimal quantity lubrication (MQL) technique in turning gives some advantages in terms of tool wear reduction. This paper reports the results obtained from turning tests and SEM analysis of tools, at two feed rates and two cutting lengths, using MQL on the rake and flank of the tool. The results obtained show that when MQL is applied to the tool rake, tool life is generally no different from dry conditions, but MQL applied to the tool flank can increase tool life.
Wear of ceramics under dry sliding conditions is, besides mechanical overload, often governed by frictional heating. On the basis of this study a new thermal severity parameter is introduced and applied to an existing wear map as a... more
Wear of ceramics under dry sliding conditions is, besides mechanical overload, often governed by frictional heating. On the basis of this study a new thermal severity parameter is introduced and applied to an existing wear map as a function of mechanical and thermal loading introduced by Adachi et al. [Wear 203/204 (1997) 291]. The new map is valid for a wide range of material properties and operating conditions. In this paper, a method is presented to predict the boundary between the mild wear regime and the severe wear regime due to frictional heating. To obtain this, the work of Bos [Frictional heating of tribological contacts, Ph.D. Thesis, University of Twente, Enschede, The Netherlands, 1995] was used to calculate contact temperatures. This model is essentially a fit on numerical calculations, making it possible to include heat partitioning between dissimilar materials while retaining closed form expressions. The stress resulting from the contact temperature can be compared with material properties to obtain the thermal severity of a contact. A new dimensionless thermal severity number, TS, is introduced to determine the thermal severity of a contact. The model has been experimentally justified using measurements of pins of different materials sliding against two types of tetragonal zirconia polycrystal discs. In these experiments it was observed that if the specific wear rate exceeds the value of 3 × 10 −6 mm 3 /N m, the sliding surfaces were rough and the wear was regarded as severe. This criterion is closely related to the criterion based on the ratio of process surface roughness over mean grain size Adachi et al. [Wear 203/204 (1997) 291].
Using a transparent tool entrapment, compression and eventual escape of liquid lubricant in surface pockets is observed in plane strip drawing. The two mechanisms of lubricant escape, Micro Plasto HydroDynamic and Hydrostatic Lubrication... more
Using a transparent tool entrapment, compression and eventual escape of liquid lubricant in surface pockets is observed in plane strip drawing. The two mechanisms of lubricant escape, Micro Plasto HydroDynamic and Hydrostatic Lubrication (MPHDL and MPHSL), are observed and quantified experimentally with varying viscosity, speed, reduction, workpiece material, back tension and friction. The mechanisms are influenced by all these parameters in an explicable way. Theoretical models of the escape mechanisms are established combining continuum mechanic analyses of the die pressure distribution with a fluid mechanic analysis of the lubricant escape. Oscillations in the drawing force are caused by the local escape of lubricant.
In sheet metal stamping, it is known that wear is unevenly distributed over the die radius and that multiple wear mechanisms may occur simultaneously. However, there has been little or no work that details the types of wear mechanisms,... more
In sheet metal stamping, it is known that wear is unevenly distributed over the die radius and that multiple wear mechanisms may occur simultaneously. However, there has been little or no work that details the types of wear mechanisms, and quantifies the locations at which they occur. Furthermore, the link between recently identified time-dependent contact conditions and the wear response is currently unknown. An experimental study is presented in this paper to examine the location, type and severity of wear that occurs over the die radius during a typical sheet metal stamping process. It is found that the wear over the die radius consists of a combination of ploughing and galling mechanisms. The relative severity of the ploughing mechanism is divided into two distinct zones on the die radius, which correlate well with the contact pressure and sliding distance behavior predicted in our recently published numerical study. The galling mechanism results in failure of the stamping process and is, therefore, critical to the overall tool wear response. Our analysis indicates that the severe contact pressure/small sliding distance conditions, which occur during the initial stage of the process, cause the galling behavior observed over the radius. Therefore, it is concluded that the overall tool wear response and tool life is primarily dependent on the initial transient stage of the stamping process.
This paper proposes a new strategy for surface roughness analysis and characterisation based on the wavelet transform. After a short review of wavelet-based methods used in the field of surface roughness analysis, results obtained using a... more
This paper proposes a new strategy for surface roughness analysis and characterisation based on the wavelet transform. After a short review of wavelet-based methods used in the field of surface roughness analysis, results obtained using a new tool of analysis called the frequency normalised wavelet transform (FNWT) are presented.
When a steel ball undergoes dry sliding against a boron carbide-coated steel coupon, both the steel ball and the boron carbide are polished, even though the boron carbide is several times harder than the steel. We have measured the... more
When a steel ball undergoes dry sliding against a boron carbide-coated steel coupon, both the steel ball and the boron carbide are polished, even though the boron carbide is several times harder than the steel. We have measured the abrasion rate of the steel under loads ranging from 5 to 1100 g. The average abrasion rate at and above 100 g of load shows a simple power law dependence on the number of cycles, but a deviation from this simple dependence is observed at lower loads. The loss of abrasiveness of the boron carbide correlates with a reduction of the RMS angle on the boron carbide surface, which eventually becomes nearly atomically smooth over regions as large as 1 m × 1 m. Our results suggest that under the right conditions, a boron carbide coating could be designed to polish a counterpart gear or bearing surface with little risk that the counterpart would be substantially worn and with little concern for how the load varied during a break-in period. We suggest that polishing of the boron carbide surface by steel is a chemical process, while the abrasion of the steel by boron carbide is a mechanical process.
This paper deals with understanding the evolution of tool wear of multilayer coated inserts using Confocal Laser Scanning Microscopy (CLSM). Steady-state turning experiments were carried out on 1045 steel bars with commercially available... more
This paper deals with understanding the evolution of tool wear of multilayer coated inserts using Confocal Laser Scanning Microscopy (CLSM). Steady-state turning experiments were carried out on 1045 steel bars with commercially available multi-layer coated inserts consisting of TiN /Al 2 O 3 /TiCN deposited on a C6 carbide substrate provided by Kennametal, Inc.. Topographical images of the crater wear as well as orthogonal sections of the flank and crater wears as functions of machining time are obtained. A humped island of TiN coating material next to a growing crater of Al 2 O 3 and steel traces were found. The maximum crater depth value and location respect to the edges of the insert are gathered for all machining times. The maximum crater depth location was observed to move across the rake face as machining time increased. These unexpected features of crater wear are suspected to have their origin in the competition of the abrasive and dissolution mechanisms, and the difference in wear-resistant properties between the TiN and Al 2 O 3 coatings. Validations of the confocal results are also performed using the Scanning Electron Microscope (SEM) and the Atomic force microscope (AFM).
TBM excavation has become increasingly common, despite the fact that precise evaluation of certain risks has not kept pace with the use of these machines. One of the risks easily overlooked by Engineer and Contractor alike are the effects... more
TBM excavation has become increasingly common, despite the fact that precise evaluation of certain risks has not kept pace with the use of these machines. One of the risks easily overlooked by Engineer and Contractor alike are the effects of abrasive ground on the costs and schedule of a given project. The impacts of worn and damaged TBM cutterheads have been observed on hundreds of tunnel projects around the world. It would appear that a reliable prognosis of the abrasiveness of ground on a project would be of great importance for designers, clients and contractors alike. Several well acknowledged test and prognosis methods already exist for rock; however, there is only very limited knowledge available to describe the abrasiveness of soil and its impact on wear on soft ground TBMs. This three-part article examines existing approaches to the problem and suggests a new approach based on a current project undergoing design. Defining wear For the purposes of the following discussion it...
The minimum requirements to verify tooth wear results are a three quadrant spherical surface of a molar tooth to be common area, and the fit of the common area needs to be less than 10 μm, to achieve the sensitivity of wear measurement up... more
The minimum requirements to verify tooth wear results are a three quadrant spherical surface of a molar tooth to be common area, and the fit of the common area needs to be less than 10 μm, to achieve the sensitivity of wear measurement up to the 100 μm level on the occlusal ...
The influence of the alkyl chain length and of the anion on the lubricating ability has been studied for the room-temperature ionic liquids (IL) 1-n-alkyl-3-methylimidazolium X − [X = PF 6 ; n = 6 (L-P106). X = BF 4 ; n = 2 (L102), 6... more
The influence of the alkyl chain length and of the anion on the lubricating ability has been studied for the room-temperature ionic liquids (IL) 1-n-alkyl-3-methylimidazolium X − [X = PF 6 ; n = 6 (L-P106). X = BF 4 ; n = 2 (L102), 6 (L106), 8 (L108). X = CF 3 SO 3 ; n = 2 (L-T102). X = (4-CH3C6H4SO3); n = 2 (L-To102)]. Neat IL have been used for AISI 52100 steel-ASTM 2011 aluminium contacts in pin-on-disk tests under variable sliding speed. While all IL give initial friction values lower than 0.15, real-time sharp friction increments related to tribochemical processes have been observed for L102 and L-P106, at room-temperature and at 100 • C. Electronic microscopy (SEM), energy dispersive (EDS) and X-ray photoelectron (XPS) spectroscopies show that wear scar surfaces are oxidized to Al 2 O 3 and wear debris contain aluminium and iron (for L102) fluorides. For L-P106, the steel surface is covered with a P-containing tribolayer. A change of anion (L-T102; L-To102) reduces friction and wear, but the lowest values are obtained by increasing the alkyl chain length (L106; L108). When the more reactive L102 and L-P106 are used as 1 wt.% base oil additives at 25 • C, tribocorrosion processes are not observed and a friction reduction (69-75% for 1 wt.% L102) and a change from severe (10 −3 mm 3 m −1 ) to mild wear (10 −4 to 10 −6 mm 3 m −1 ) is obtained with respect to the neat IL. 1 wt.% IL additives also show good lubricating performance at 100 • C.
According to most studies dealing with wear, abrasion can be considered on one hand as micro-cutting, leading to material removal (grinding), and on the other hand as micro-ploughing, leading to plastic deformation and lower material... more
According to most studies dealing with wear, abrasion can be considered on one hand as micro-cutting, leading to material removal (grinding), and on the other hand as micro-ploughing, leading to plastic deformation and lower material removal (abrasive wear). Understanding various flowing transitions around an abrasive particle, under well-established conditions, makes it possible to better control these processes. The aim of the present study is to understand plastic deformation and failure local phenomena induced by an abrasive process. Experimental studies have been carried out on an abrasive process which consists in scratching a soft flat surface (AISI4140 steel) by mean of a turning tool fixed on the periphery of a disc. Regulating angular and feed speeds, successive scratches are expected to study phenomena generated by a single pass of the cutting tool. Scratch topography and forces are measured in order to highlight the influence of the depth of cut and the cutting speed on these parameters and on specific energy.
In this paper, some of the complexities in developing predictive models for polymer composite materials are discussed with particular reference to models based on surface deformation energy. Although there are models available for... more
In this paper, some of the complexities in developing predictive models for polymer composite materials are discussed with particular reference to models based on surface deformation energy. Although there are models available for abrasive wear of metals, polymers and composite materials, models are suitable for a particular wear situation. Most of the cases, the wear models are based on traditional test methods, such as two-body abrasive wear test or tests in a controlled environment. Moreover models for polymer composite materials are very limited. This is due to the fact that the vast range of polymers and polymer composite materials present different wear behaviour in similar wear situations. This makes the modelling wear of polymer composite materials complicated.
The abrasive wear rates of materials may be very simply related to their mechanical properties, provided wear takes place under very simple conditions. However, wear rates in many practical situations can be controlled by effects which... more
The abrasive wear rates of materials may be very simply related to their mechanical properties, provided wear takes place under very simple conditions. However, wear rates in many practical situations can be controlled by effects which either relate to mechanical properties in more subtle ways, or which are controlled by quite different parameters. Mechanics models of the abrasive process provide a means of linking these different effects together to understand better the effects, which may determine wear under particular conditions. They can also help to design tests to measure the properties of a material under conditions similar to those pertaining in abrasion. Some progress has been made in producing integrated models of real abrasive processes, but much more could be done to improve existing models and develop new ones.
The objective of this experimental study was to determine the wear resistance of moldboard plowshares produced from 30MnB5 steel that were treated with different martempering conditions. The microstructures, the hardness distribution, and... more
The objective of this experimental study was to determine the wear resistance of moldboard plowshares produced from 30MnB5 steel that were treated with different martempering conditions. The microstructures, the hardness distribution, and the wear behavior of the martempered 30MnB5 steel were determined and compared with conventionally heat-treated samples in laboratory conditions. The wear losses of all martempered samples were less than that of the conventionally heat-treated samples in laboratory conditions, especially at the end of a longer-term wear experiment. The martempering process in which the steel was austenized at 960°C for 35 min, held at 350°C for 10 s in a salt bath, and then cooled in air produced the best results for decreasing wear loss in laboratory conditions. The martempering treatment that resulted in the lowest wear weight loss in pin-on-disc tests was selected for further testing in field conditions. The field used for the experiment was flat and free of crop residue with a uniformly dispersed soil type (sandy and sandy loam). A reversible plow was used to measure the wear. The abrasive wear losses were determined by measuring the plowshare's weight and dimensions before and after tillage. By achieving a more uniform hardness distribution, the lath-type martensitic and bainitic microstructure of the martempered plowshares significantly increased their wear resistance. The martempering process decreased the wear weight loss by 40.8% and the wear dimension loss by 38.5% compared to conventionally heat-treated plowshares in field conditions.
Silicon carbide sustains chemical and mechanical deterioration during tribological exposure under water lubrication. In particular, tribochemical wear leads to the formation of a thin (tens to hundreds of nanometre) layer composed of... more
Silicon carbide sustains chemical and mechanical deterioration during tribological exposure under water lubrication. In particular, tribochemical wear leads to the formation of a thin (tens to hundreds of nanometre) layer composed of nanoscale SiC wear debris embedded in a silica-like matrix (SiO x H y ) with possibly some minor oxycarbidic content. The SiC wear particles are plastically deformed and rounded as a result of mechanical tribolapping. Below that layer, subsurface damage builds up in the form of dislocations, ruptures and shear cracks. As a result of plastic deformation (similar to indentation plasticity) SiC single crystals within that transition zone are transformed into mosaic crystals with smaller domains due to slip plane gliding. Comparing results for static hydrothermal conditions (using a hydrothermal diamond anvil cell) and tribotest for the mild and severe wear regime (i.e., with and without external cooling) we derived a qualitative wear-model of wet silicon carbide tribo-corrosion. While mechanical contact yields pathways for water inflow and generally disrupts the structural integrity of SiC grains, hydrothermal reactions of trapped water and subsequent pressure relief leads to a mechanism of dissolution and reprecipitation. The latter produces the observed amount of SiO x H y which acts as an adhesive for the SiC wear debris.
The loss in braking effectiveness at elevated temperatures and the revival of the same at lower temperatures is referred to as fade and recovery, respectively. These characteristics are of decisive importance in the performance evaluation... more
The loss in braking effectiveness at elevated temperatures and the revival of the same at lower temperatures is referred to as fade and recovery, respectively. These characteristics are of decisive importance in the performance evaluation of friction materials. The present paper deals with the influence of four selected organic fibres, viz. Aramid (AF), PAN (poly-acrylo-nitrile), carbon (CF) and cellulose (SF), on the-fade and-recovery of friction composites. It was observed that the type of fibre significantly influenced the-fade and-recovery behaviour. It was observed that the carbon fibre based composite showed the highest resistance to-fade whereas the composite based on cellulose fibre showed the least resistance. The recovery behaviour of all the composites was more than 100% and the extent depended on the type of fibre inclusion. The composites containing AF and SF showed the highest and the lowest wear resistances, respectively, while the highest and the lowest were recorded for SF based and CF based composites, respectively. SEM analyses of the worn surfaces proved to be useful in correlating wear of the composites to the topographical changes on the surfaces.
