Showing papers by "Satish V. Kailas published in 2006"

Effect of Roughness Parameter and Grinding Angle on Coefficient of Friction When Sliding of Al–Mg Alloy Over EN8 Steel

Abstract: Surface topography of harder mating surface plays an important role in metal forming operations as it predominantly controls the frictional behavior at the interface In the present investigation, an inclined scratch tester was used to understand the effect of direction of surface grinding marks on interface friction and transfer layer formation EN8 steel flats were ground to attain different surface roughnesses with unidirectional grinding marks Al–Mg alloy pins were then scratched against the prepared EN8 steel flats The grinding angle (angle between direction of scratch and grinding marks) was varied between 0 deg and 90 deg during the scratch tests Scanning electron micrography of the contact surfaces revealed the transfer layer morphology The coefficient of friction and transfer layer formation were observed to depend primarily on the direction of grinding marks of the harder mating surface, and independent of the surface roughness of harder mating surface The grinding angle effect was attributed to the variation of plowing component of friction with grinding angle

Studies on friction and transfer layer: role of surface texture

Abstract: Friction influences the nature of transfer layer formed at the interface between tool and metal during sliding. In the present investigation, experiments were conducted using “Inclined Scratch Tester” to understand the effect of surface texture of hard surfaces on coefficient of friction and transfer layer formation. EN8 steel flats were ground to attain surfaces of different textures with different roughness. Then super purity aluminium pins were scratched against the prepared steel flats. Scanning electron micrographs of the contact surfaces of pins and flats were used to reveal the morphology of transfer layer. It was observed that the coefficient of friction and the formation of transfer layer depend primarily on the texture of hard surfaces, but independent of surface roughness of hard surfaces. It was observed that on surfaces that promote plane strain conditions near the surface, the transfer of material takes place due to the plowing action of the asperities. But, on a surface that promotes plane stress conditions the transfer layer was more due to the adhesion component of friction. It was observed that the adhesion component increases for surfaces that have random texture but was constant for the other surfaces

Effect of directionality of unidirectional grinding marks on friction and transfer layer formation of Mg on steel using inclined scratch test

Abstract: Surface topography has been known to play an important role in the friction and transfer layer formation during sliding. In the present investigation, EN8 steel flats were ground to attain different surface roughness with unidirectional grinding marks. Pure Mg pins were scratched on these surfaces using an Inclined Scratch Tester to study the influence of directionality of surface grinding marks on coefficient of friction and transfer layer formation. Grinding angle (i.e., the angle between direction of scratch and grinding marks) was varied between 0 degrees and 90 degrees during the tests. Experiments were conducted under both dry and lubricated conditions. Scanning electron micrographs of the contact surfaces of pins and flats were used to reveal the surface features that included the morphology of the transfer layer. It was observed that the average coefficient of friction and transfer layer formation depend primarily on the directionality of the grinding marks but were independent of surface roughness on the harder mating surface. In addition, a stick-slip phenomenon was observed, the amplitude of which depended both on the directionality of grinding marks and the surface roughness of the harder mating surface. The grinding angle effect on the coefficient of friction, which consists of adhesion and plowing components, was attributed to the variation of plowing component of friction. (c) 2006 Elsevier B.V. All rights reserved.

Numerical analysis of friction stir welding process

Abstract: Friction stir welding (FSW), which has several advantages over the conventional welding processes, is a solid-state welding process where no gross melting of the material being welded takes place. Despite significant advances over the last decade, the fundamental knowledge of thermomechanical processes during FSW is still not completely understood. To gain physical insight into the FSW process and the evaluation of the critical parameters, the development of models and simulation techniques is a necessity. In this article, the available literature on modeling of FSW has been reviewed followed by details of an attempt to understand the interaction between process parameters from a simulation study, performed using commercially available nonlinear finite element (FE) code DEFORM. The distributions of temperature, residual stress, strain, and strain rates were analyzed across various regions of the weld apart from material flow as a means of evaluating process efficiency and the quality of the weld. The distribution of process parameters is of importance in the prediction of the occurrence of welding defects, and to locate areas of concern for the metallurgist. The suitability of this modeling tool to simulate the FSW process has been discussed. The lack of the detailed material constitutive information and other thermal and physical properties at conditions such as very high strain rates and elevated temperatures seems to be the limiting factor while modeling the FSW process.

Properties of squeeze cast Mg-6Zn-3Cu alloy and its saffil alumina short fibre reinforced composites

Abstract: In the present work, Mg-Zn-Cu alloy (ZC63) and its saffil alumina short fibre reinforced composites produced using the squeeze casting technique were evaluated for their properties. The unreinforced base alloys and their composites were characterized for their microstructure, hardness, yield strength, impact strength, wear resistance and corrosion resistance. The dependence of the properties of composites was studied as a function of fibre volume fraction. Results showed that the composites exhibited improved hardness, yield strength at elevated temperature and wear resistance in comparison to the monolithic alloy. However, ductility, impact strength and corrosion resistance of the composites were inferior to that of the base alloy. The nature of the base alloy matrix in determining the properties of the composites was discussed based on fractographic analysis.

Role of Surface texture on Friction and Transfer Layer Formation when Mg-8Al Alloy Slid Against Steel Counterface

Abstract: Surface texture influences friction and transfer layer formation during sliding. In the present investigation, various kinds of surface texture with varying roughness were produced on steel plates. Pins made of Mg-8Al alloy were then slid against the prepared steel plates using inclined pin-on-plate sliding tester to understand the role of surface texture of the harder surface and load on coefficient of friction and transfer layer formation under both dry and lubricated conditions. Normal loads were varied from 1 to 120 N during the tests. Tests were conducted at a sliding velocity of 2 mm/s in ambient conditions. Scanning electron micrographs of the surfaces in contact for both the pins and plates were obtained to understand the morphology of the transfer layer. Surface roughness parameters of the steel plate were measured in the direction of the sliding on the bare surface away from the wear tracks using an optical profilometer. It was observed that the coefficient of friction and transfer layer formation are strongly dependent on surface texture and independent of surface roughness (Ra) of steel plate. Among the surface roughness parameters, the mean slope of the profile was found to explain the variations best. The plowing component of friction was highest for the surface that promotes plain strain conditions while it was lowest for the surface that promotes plane stress conditions near the surface.

A parameter to characterize the plowing nature of surfaces which are close to gaussian

Abstract: A hybrid, non-dimensional parameter descriptive of the plowing nature of surfaces is proposed for the case of sliding between a soft and a relatively hard metallic pair which are nominally flat, typically as one encounters in the case of hot forming. From a set of potential parameters which can be descriptive of the phenomenon, dimensionless groups are formulated and the influence of each one of them analyzed. Inter- dependence between certain groups are established which lead to retention of those which are independent. A non-dimensional parameter involving the root-mean square deviation (Rq) and the centroidal frequency (Fmean) deducted from the power-spectrum is found to have a high degree of correlation (as high as 0.93) with the coefficient of friction obtained in sliding experiments under lubricated condition. Variation of the coefficient of friction in dry condition (which brings in the effect of adhesion, in addition to plowing) as a function of the proposed parameter is also presented.

The Role of Surface Texture on Friction and Transfer Layer Formation - A Study of Aluminium and Steel Pair using Pin-on-Plate Sliding Tester

Abstract: Surface texture of a tool plays an important role as it primarily controls the frictional behavior at the tribo interface. In the present investigation, pin-on-plate sliding tester was used to identify the effect of directionality of surface grinding marks on coefficient of friction and transfer layer formation. 080 M40 steel plates were ground to achieve different surface roughness with unidirectional grinding marks. Super purity aluminium pins were slid at a sliding velocity of 2 mm/s against the prepared steel plates. Grinding angle (i.e., the angle between direction of sliding and grinding marks) was varied between 0 o and 90 o in the tests. Normal load was varied from 0 to 120 N during the tests. Experiments were conducted under both dry and lubricated conditions in ambient environment. Scanning electron micrographs of the contact surfaces of pins and plates were used to study the surface features that included the morphology of the transfer layer. Surface roughness parameters of the steel plates were measured in the direction of the sliding using an optical profilometer. It was observed that the coefficient of friction and transfer layer formation depends primarily on the directionality of the grinding marks of the harder mating surface. Under lubricated conditions, stick-slip phenomena was observed, the amplitude of which depends on the plowing component of friction. The presence of stick-slip motion under lubricated conditions could be attributed to the molecular deformation of the lubricant component confined between asperities. The grinding angle effect on coefficient of friction was attributed to the variation in plowing component of friction, which in turn depends on the mean slope of the profile of the harder mating surface.

Role of surface texture on friction and wear under boundary lubricated conditions

Abstract: Ensuring effective lubrication between sliding surfaces is one of the challenges in the field of tribology. In addition to the conventional parameters like speed, load, contact geometry and material parameters, the surface texture also influences the coefficient of friction. In the present investigation, the effect of surface texture on coefficient of friction under boundary lubricated condition was studied by sliding Al-4Mg alloy pins against EN8 steel discs of various surface textures using pin-on-disc machine. Both isotropic and directional textures were generated on the surfaces of the discs. Scanning Electron Microscopy and optical profilometer studies were carried out on the contact surfaces of both the pins and discs before and after the experiments. The result showed that the coefficient of friction varied considerably with surface textures. In addition, maximum value coefficient of friction was observed when pins slid perpendicular to the uni-directional texture and minimum when pins slid on random texture. Backscattered scanning electron micrographs revealed the transfer of iron from the disc to the pins and it was highest when pins slid perpendicular to the uni-directional texture and least for the random texture. However, no transfer layer of Al-Mg alloy was observed on the steel disc.

Influence of Roughness Parameters on Friction and Transfer Layer Formation

Abstract: Surface texture of the harder mating surfaces is one of the key factors that control the coefficient of friction during sliding. In the present investigation, various kinds of surface textures were produced on the 080 M40 steel plates. For a given kind of surface texture, roughness was varied using various grits of emery papers or polishing powders. The surface textures were characterized in terms of roughness parameters using an optical profilometer. Sliding experiments were conducted to study the effect of surface texture on coefficient of friction using inclined pin-on-plate sliding tester at a sliding velocity of 2mm/s against the prepared hard plate using a soft AlMg alloy pin under both dry and lubricated conditions in ambient environment. Normal loads were varied from 0 to 120 N during the tests. Using scanning electron microscope (SEM) the surfaces of both the plate and pin materials were examined specifically to study the transfer layer formation in the former and damage in the latter. It was observed that the coefficient of friction and transfer layer formation are controlled by the surface texture of the harder mating surfaces under both dry and lubricated conditions. In addition, it was observed that among the surface roughness parameters, the average or the mean slope of the profile was found to explain the variations best. It was concluded that the coefficient of friction and transfer layer formation are strongly dependent on the mean slope of the profile regardless of surface textures under both dry and lubricated conditions. INTRODUCTION Friction is the resistance to motion during sliding that is experienced when one solid body moves tangentially over another with which it is in contact. The resistive tangential force, which acts in a direction directly opposite to the direction of motion, is called the friction force. Friction is commonly represented by the coefficient of friction, defined as the ratio of tangential force to the normal force. It is influenced by various factors such as surface texture, sliding speed, normal load, temperature, lubricants, and material properties. Considerable work has been done by many researchers to study the influence of these parameters on coefficient of friction [1-9]. It was reported earlier that surface texture indeed has an important role on coefficient of friction values during sliding [10-17]. Menezes et al. [10-12] studied the effect of surface texture on coefficient of friction and transfer layer formation under both dry and lubricated conditions for Al-Mg alloy [10], pure copper [11] and super purity aluminium [12] using inclined scratch test. Various kinds of surface textures – namely, unidirectional grinding marks, 8-ground, and random were prepared using simple metallographic techniques. Roughness, represented by Ra, of surfaces was varied over a range as they were prepared using different grit emery papers and abrasive powders. It was found that surface texture that promotes plane strain conditions near the interface causes higher plowing component and thus the higher coefficient of friction. On the other hand, surface texture that promotes plane stress conditions at the interface results in lower value for plowing component of friction. It was found that sliding perpendicular to the unidirectional grinding marks gives maximum friction force contributed by higher plowing component, and at the other extreme random texture results in lower friction values. It was observed that the roughness as given by Ra within the test range does not significantly affect the friction values. Further, surface textures were characterized in terms of roughness parameters and in the literature many roughness parameters [18] are available. The surface roughness parameter like Ra is used in general, to describe a surface. However, such a single roughness parameter, which is the universally recognized and most used parameter of surface roughness, is not sufficient to describe a functional characteristic like friction [19] and it is possible that two surface textures can have the same Ra, but their frictional characteristics could be different [8-12]. Considerable amount of work has also been done to study the effect of various roughness parameters on friction [19-22]. Lundberg [19] studied the influence of surface roughness parameters on normal sliding lubrication and reported that the Rmax and Rt to be the most significant parameters. Myers [20] conducted experiments using an inclined plane sliding tester to study the coefficient of friction between a test slider and sample disks. Twelve samples surfaces were fabricated from cold-rolled steel disks. Five of these had lapped finishes while the others had ground finishes. The author [20] studied the correlation coefficient between coefficient of friction with the three r.m.s. values corresponding to (i) surface profiles, (ii) first derivative of surface profiles and (iii) second derivative of surface profiles and concluded that the second one, namely, the r.m.s. of first derivative was most useful in predicting friction. Koura [21] studied the effect of surface texture on friction mechanism using universal testing machine. Steel specimens were prepared to various degrees of roughness by grinding, lapping and polishing. The results showed that the behavior of surfaces and thus friction during sliding depends on the degree of roughness. In the literature many individual or hybrid surface roughness parameters are in vogue. These include amplitude, spatial and hybrid parameters. However, it was noticed that like friction, the correlation coefficient between coefficient of friction and roughness parameters, was system dependent. A systematic study on the classification of surface textures was done recently by Stout and Blunt [23]. The authors [23] introduced the concept of engineered and non engineered surfaces and have sub-divided these into random, systematic, unstructured and structured derivatives. Most of the surface textures generated in the present study belong to one of these categories and defined in the experimental section. The aim of the present study is to characterize the surface textures in terms of roughness parameters using optical profilometer and to come out with a single roughness parameter which correlates with coefficient of friction regardless of surface textures. Experiments were done on hard counter surfaces by sliding soft pins using inclined pin-on-plate sliding tester. Scanning Electron Microscope (SEM) was used to reveal the morphology of the transfer layer formed on the plate surface as well as the damage on the pin surface. EXPERIMENTAL DETAILS Four types of surface textures were produced on 080 M40 steel plates. Type I, namely, structured directional surfaces, were produced on the steel plates with varying roughness by dry grinding the steel plates against dry emery papers of 220, 400, 600, 800 or 1000 grit size. For the directional surface texture, care was taken so that the grinding marks were unidirectional in nature. Type II, namely, structured non-directional surface texture, was generated on steel plates with varying roughness by moving the steel plate on dry emery papers of 220, 400, 600, 800 or 1000 grit size along a path with the shape of an “8” for about 500 times. Type III, namely, structured directional surface textures, similar to Type I was produced. Here the grinding marks direction was perpendicular to that of Type I. Type IV, namely, random texture, with varying roughness was generated under wet grinding conditions using a polishing wheel with any one of the three abrasive media such as SiC powder (600 and 1000 grit), Al2O3 powder (0.017 μm), and diamond paste (1-3 μm). Figures 1 (a), (b), (c) and (d) show the profiles of steel plate surfaces along with its 3D roughness parameter, Ra, generated by Types I, II, III, and IV respectively. In figure 1, the surface textures, namely, Type I, II and III were generated using 1000 grit emery papers while the Type IV was produced using 1000 grit SiC powder. Figure 1: Profiles of Types (a) I, (b) II, (c) III, and (d) IV surface textures. Experiments were conducted using an inclined pin-on-plate sliding tester, details of which were explained in earlier paper [24]. In the present study, soft material made of an Al-4Mg alloy was used as pins and hard material made of 080 M40 steel plates were used as counter part. The pins were 10 mm long, 3 mm in diameter with a tip radius of 1.5 mm. The dimensions of the 080 M40 steel plates were 28 mm x 20 mm x 10 mm (thickness). The pins were first machined, and then electro-polished to remove any work-hardened layer that might have formed during the machining. Hardness measurements of pin and plate were made at room temperature using a Vickers micro hardness tester with 100 gm load and 10-second dwell time. Average hardness numbers, obtained from 5 indentations, was found to be 105 and 208 for the pin and plate respectively. Before each experiment, the pins and steel plates were thoroughly cleaned first in an aqueous soap solution and then with acetone in an ultrasonic cleaner. The steel plate was fixed horizontally in the vice of the pin-on-plate sliding tester and then the vice-setup was tilted so that surface of the plate makes an angle of 1 o ± 0.05 o with respect to horizontal base. Then pins were slid at a sliding speed of 2 mm/s against the prepared steel plates starting from lower end to the higher end of the inclined surface for a track length of 10 mm. Normal load was varied from 0 to 100 N during the test. The advantage of 1 o inclination of the steel plate was that from a single experiment, the effect of normal load (up to the test limit of 100 N) on the coefficient of friction could be studied [24]. Dry tests were performed first to obtain five parallel wear tracks on the same steel plate. Each wear track was produced by a single sliding event. It was observed that the initial sphere-on-