Satish V. Kailas

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

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.

Influence of Tool Geometry in Friction Stir Welding

In this article we highlight the results of a recent study undertaken to understand the influence of tool geometry on friction stir welding (FSW) of an aluminum alloy with specific reference to microstructural development, defect formation, and mechanical response. The welding trials were made on 4.4 mm thick sheets using tools made of die steel and having different diameters of the shoulder and the pin, and the profile of the pin. Throughout the welding operation, the rotational speed, traverse speed, and tool axial tilt were held constant at 1400 rpm, 80 mm/minute, and 0 degrees, respectively. For a shoulder diameter of 20 mm and a pin diameter of 6 mm, the severity of defects in the weld was found to be the least and the resultant tensile strength of the weld was high. For the welds that were made using a tool having a shoulder diameter of 10 mm and a pin diameter of 3 mm the tensile strength of the weld was the least since the degree of defects observed were higher.

An Investigation of Friction During Friction Stir Welding of Metallic Materials

The technique of friction stir welding (FSW) puts effective use frictional heat for the purpose of joining metallic materials. In this research article, we present and discuss an experimental method to determine the coefficient of friction during FSW. The experiments were conducted to study the interaction between the FSW tool (a die steel) and the base metal (a high strength aluminum alloy) at various contact pressures (13 MPa, 26 MPa, and 39 MPa) and rotation speeds (200 rpm, 600 rpm, 1000 rpm, and 1400 rpm). The experimental results, the microstructure, and the process temperature reveal the experimental setup to be capable of simulating the conditions during FSW. The coefficient of friction was found to vary from 0.15 to 1.4, and the temperature increased to as high as 450°C. The coefficient of friction was found to increase with temperature. There exists a critical temperature at which point a steep increase in the coefficient of friction was observed. The critical temperature decreases from 250°C at a contact pressure of 26 MPa to 200°C at contact pressure of 34 MPa. Below the critical temperature at a specific contact pressure the maximum coefficient of friction is 0.6, and above the critical temperature it reaches a value as high as 1.4. The steep increase in the coefficient of friction is found to be due to the seizure phenomenon and the contact condition during FSW between the tool and the workpiece (base metal) is found to be sticking.

The tensile behavior of two magnesium alloys reinforced with silicon carbide particulates

In this paper is reported the results of a study aimed at establishing an understanding the role of particulate reinforcement on tensile deformation and fracture behavior of magnesium alloys discontinuously-reinforced with silicon carbide (SiC) particulates. An increase in particulate reinforcement content was observed to decrease ultimate tensile strength and ductility of the composite when compared to the unreinforced counterpart. Cracking of the individual and clusters of reinforcing particulates present in the microstructure dominated tensile fracture of the composite, on a microscopic scale. Final fracture occurred as a result of crack propagation through the matrix between particulate clusters. The fracture behavior of the composite is discussed in light of the concurrent and mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the metal matrix and the particulate reinforcement, nature of loading and local stress state.

Tensile behaviour of squeeze cast AM100 magnesium alloy and its Al2O3 fibre reinforced composites

Magnesium alloys are increasingly used in automotive and aerospace applications mainly due to their light weight combined with reasonably high tensile properties. In addition to providing a large reduction in weight, magnesium alloys exhibit excellent machinability and good damping capacity. However, their low mechanical properties when exposed to elevated temperatures limit their usage. Making composites out of these magnesium alloys by reinforcing them with ceramic particles or fibres appears to be a viable alternative for improving their thermal stability. The work reported here involved experimental studies on the tensile behaviour of AM100 magnesium alloy and its composites at different temperatures. Fractographic studies justify the effect of temperature on the tensile behaviour.

Tribology for Scientists and Engineers

Fundamentals of Engineering Surfaces.- Friction and Wear.- Contact Mechanics.- Experimental Methods in Tribology.- Interface Temperature of Sliding Surfaces.- Tribology of Metals and Alloys.- Tribology of Ceramics and Ceramic Matrix Composites.- Tribology of Metal Matrix Composites.- Coatings Tribology.- Fundamentals of Lubrication.- Self-Lubricating Behaviour of Graphite Reinforced Composites.- Particle Tribology.- Tribology of Solid Lubricants.- Tribology of Green Lubricants.- Nano Tribology.- Surface Probe Techniques.- Biotribology and Human Tribology.- Green and Biomimetic Tribology.- Fundamentals of Linking Tribology and Corrosion for Medical Applications.- Wear of Biomedical Implants.- Tribology in Metal Cutting.- Tribo-chemistry and Tribo-corrosion.- Tribology in Chemical-Mechanical Planarization.- Tribology in Metal Forming.- Tribology in Machine Components.- Macroscale Applications in Tribology.- Microscale Applications in Tribology.

Flow Instabilities and fracture in Ti-6Al-4V deformed in compression at 298 K to 673 K

Uniaxial compression tests were conducted on Ti-6Al-4V specimens in the strain-rate range of 0.001 to 1 s−1 and temperature range of 298 to 673 K. The stress-strain curves exhibited a peak flow stress followed by flow softening. Up to 523 K, the specimens cracked catastrophically after the flow softening started. Adiabatic shear banding was observed in this regime. The fracture surface exhibited both mode I and II fracture features. The state of stress existing in a compression test specimen when bulging occurs is responsible for this fracture. The instabilities observed in the present tests are classified as “geometric” in nature and are state-of-stress dependant, unlike the “intrinsic” instabilities, which are dependant on the dynamic constitutive behavior of the material.

Study of Friction and Transfer Layer Formation in Copper-Steel Tribo-System: Role of Surface Texture and Roughness Parameters

In the present investigation, experiments were conducted on a tribological couple—copper pin against steel plate—using an inclined pin-on-plate sliding tester to understand the role of surface texture and roughness parameters of the plate on the coefficient friction and transfer layer formation. Two surface characteristics of the steel plates—roughness and texture–were varied in the tests. It was observed that the transfer layer formation and the coefficient of friction along with its two components, namely, the adhesion and plowing, are controlled by the surface texture of the plate. The plowing component of friction was highest for the surface texture that promotes plane strain conditions while it was lowest for the texture that favors plane stress conditions at the interface. Dimensionless quantifiable roughness parameters were formulated to describe the degree of plowing and hence the plane strain/stress type deformations taking place at the asperity level.

Numerical analysis of friction stir welding process

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.

Influence of initial texture on the microstructural instabilities during compression of commercial α-Titanium at 25 °C to 400 °C

Cylindrical specimens of textured commercial pure α-titanium plate, cut with the cylinder axis along the rolling direction for one set of experiments and in the long transverse direction for the other set, were compressed at strain rates in the range of 0.001 to 100 s~’ and temperatures in the range of 25 °C to 400 °C. At strain rates ≥ 1 s−1 ’, both sets of specimens exhibited adiabatic shear bands, but the intensity of shear bands was found to be higher in the rolling direction specimens than in the long transverse direction specimens. At strain rates ⪯0.1s−1 the material deformed in a microstructurally inhomogeneous fashion. For the rolling direction specimens, cracking was observed at 100 °C and at strain rates ⪯0.1 s−1. This is attributed to dynamic strain aging. Such cracking was not observed in the long transverse specimens. The differences in the intensity of adiabatic shear bands and that of dynamic strain aging between the two sets of test specimens are attributed to the strong crystallographic texture present in these plates.