86 THE INTERNATIONAL JOURNAL OF ENGINEERING AND INFORMATION TECHNOLOGY (IJEIT), VOL. 2, NO. 2, JUNE 2016 www.ijeit.misuratau.edu.ly ISSN 2410-4256 Paper ID: EN020 Evaluation of Residual Stresses in Grinding by Magnetic Barkhausen Noise Mohamed M. Sawalem Department of Mechanical Engineering, Faculty of Engineering, University of Misurata, Libya m.sawalem@eng.misuratau.edu.ly Mohamed M. Blaow Department of Materials Science and Engineering/ Faculty of Engineering, University of Misurata, Libya mblaow@yahoo.co.uk Abstract— The effect of residual stresses and the lubricant type in grinding on the characteristics of magnetic Barkhausen noise (MBN) profiles were examined in low alloy steel of the type used for wear-resistant engineering components. A shotpeened and ground in different conditions specimens were tested. MBN measurements showed that the intensity of the signal increases with abusive grinding due to residual tensile stresses and decreases with shot peening due to residual compressive stresses. An increase was seen in wet grinding specimens as compared with the heat-treated specimen. The increase in MBN after grinding was due to local heating with transition from the initial stage of strong martensitic structure, with residual stress of compression, to the following stage of lower hardening with tendency to residual stress of tensile character. In addition, Barkhausen signals from surfaces ground under controlled conditions were found to be dependent on the lubricant type. The decrease in MBN after shotpeening was due to the accumulation of residual compressive stresses introduced to the martensitic structure. The observations are discussed in the light of established models of Barkhausen noise. Index Terms: Grinding, Shotpeening, Residual stresses, Lubrication, Hysteresis, Barkhausen noise. INTRODUCTION echniques based on the phenomenon of Barkhausen noise are potentially useful for non-destructive evaluation of ferromagnetic materials. For instance, residual tensile stress and over-tempering can be detected in ground-finished surfaces using measurements of magnetic Barkhausen noise. Because of the large number of influential variables, the technique produces only relative comparisons between different material states. For a given alloy, measurements have to be calibrated against a standard microstructural state for that particular alloy [1]. Barkhausen noise is produced by the irreversible movement of domain walls in a magnetisation cycle. Domain walls are pinned temporarily by microstructural inhomogeneities and then released in the increasing magnetic field [2, 3]. The discrete changes in local magnetisation can be detected as voltage pulses in a search coil or magnetic read head. Precipitates, grain boundaries and dislocations act as effective barriers to domain wall motion. Therefore MBN is sensitive to microstructure and plastic deformation in the material. The influence of magnetostriction on magnetisation also makes emission sensitive to applied or residual stress [4]. The manufacturing processes for gear components include numerous heat treatment operations which are carried out to ensure the proper surface characteristics for components to deal with wear and fatigue. These heat treatments include austenitizing and quenching in air followed by grinding. Grinding is most commonly used as a finishing process to provide good surface, dimensional and geometrical quality. Thermal shock during grinding gives rise to localized surface residual tensile stresses which result in reduced wear resistance and fatigue life during service. As thermal damage is one of the main limitations of grinding process, cooling plays a crucial role in grinding to avoid thermal damage to the workpiece surface. Cooling and lubrication are especially important to ensure workpiece quality in grinding, because of high friction and intense heat generation involved in the process [4]. The MBN technique offers certain advantages such as the greater depth of penetration, faster measurement, portability of equipment, and capability to measure components having complex geometries like gears [5]. Microhardness profile is an important surface integrity characteristic as it may alter the surface properties. Grinding, is a typically, last tooling operation, which defines the surface integrity of a ground component; however, grinding causes variation in microhardness along the depth of the ground sample. Assessment of microhardness profile of ground samples using conventional technique is destructive quite often time consuming. Literature survey indicates that the MBN technique has been successfully attempted for surface hardness assessment of optimized analysis parameters [6, 7]. In grinding, cooling and lubrication fluid type and its application to the work area are crucial factors in determining the quality of the grinding operation. Although some grinding operations are performed dry, most of the high efficiency operations utilize some of grinding fluid delivery. Fluids lubricate the grind zone, T Received 15 February 2015; revised 16 February 2016; accepted 13 March 2016. Available online 14 March 2016.