S. Sankaran

Bio: S. Sankaran is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Microalloyed steel & Microstructure. The author has an hindex of 19, co-authored 69 publications receiving 898 citations. Previous affiliations of S. Sankaran include University of Münster & University of Louisiana at Lafayette.

Subsurface Pore-Induced Quilting During Machining of Metal Foams

Abstract: Metal foams made by the melt route naturally have an interface region between the porous and nonporous structures. We investigate here the possible use of monolithic foam structures with such interfaces wherein the porous structure provides needed light-weighting while the nonporous region provides a functional surface such as the one needed for optics. Face turning is carried out in the nonporous region very near the interface to the porous areas. Using micro-computed tomography scans, pore positions are determined and the proximal effect of pores on the machined surface quilting effects are studied. Studies show that pore as near as 400 μm to the machined surface can cause significant quilting. Progress in developing finite element models to enable such predictions is also shown. This study could pave the way for the use of such structures for telescopic mirrors.

Optimization of cutting parameters on turning multiphase medium carbon Microalloyed steel

Abstract: This paper discusses the optimization of process parameters such as speed, feed and depth of cut while machining multiphase ferrite-bainite-martensite (F-B-M) Vanadium-microalloyed steel using Taguchi orthogonal array. The effect of process parameters on cutting force and surface roughness were studied and the analysis of variance (ANOVA) was also employed to identify the most significant parameter that influence cutting conditions. A regression model was also developed for prediction of cutting force and surface roughness. Confirmation tests were also conducted to validate the model.

Effect of microstructure on the surface finish during machining of V-microalloyed steel: Comparison between ferrite–bainite–martensite and ferrite–pearlite microstructures

Abstract: Multiphase ferrite–bainite–martensite microalloyed steel produced through a two-step cooling followed by annealing route and a ferrite–pearlite steel obtained through air-cooling after forging were subjected to turning operation. The influence of process parameters such as cutting speed, feed and depth of cut on surface roughness on both materials was compared. The results show that the multiphase microalloyed steel exhibited high surface finish than air-cooled steel. The analysis of variance shows that the contribution of cutting speed and depth of cut on surface roughness are insignificant for both ferrite–bainite–martensite and ferrite–pearlite microstructures.

Study of Texture in Ultra Fine Grained Dual Phase Steel Sheets

Abstract: Severe cold rolling and short intercritcal annealing is often used to produce ultra-fine grained ferrite and martensite dual phase steels. In this paper, microstructure and texture of Nb-microalloyed steel following cold rolling and short intercritical annealing is investigated. The results show that cold rolling and annealing resulted in ultra-fine grained dual phase steel consisted of polygonal ferrite in the range of ~1-2 μm in size. In cold rolled material, the texture components are γ fiber (//normal direction) and α fiber (//rolling direction). Partial recrystallization texture was observed following intercritical annealing.

Investigations on Pb-Free 6000 Series Aluminum Alloy for Machining Applications

Abstract: Pb-based alloys such as AA6262, AA2011 and more recently AA6026 are used as free-machining aluminum alloys for automotive and electronic applications However, in order to comply with Automotive End of Life Vehicles (ELV) and Restriction of Hazardous Substances (RoHS) directives, Pb-based alloys slowly need to be phased out A Pb-free machining grade 6xxx aluminum alloy based on Sn was developed and its machinability evaluated Microstructure analysis of the Al–Mg–Si–Sn–Cu alloy revealed the presence of (98 wt%) Sn–Mg2Sn eutectic phases, which have a low melting point of ~203 °C, and are responsible for providing good machinability Homogenized billets of the alloy were extruded and heat treated to T6 temper Yield strength and ultimate tensile strength of the Pb-free alloy were comparable to those of the conventionally used Pb-based AA6262-T6 alloy Machinability studies of the alloy were conducted by evaluating the effect of cutting speed, feed rate and depth of cut on surface roughness, chip size and form of chip produced during the turning operation The machinability of the Sn containing alloy was found to be superior to that of non-machining grade 6xxx alloys AA6061-T6 and AA6082-T6 and comparable to that of Pb-based free-machining alloy AA6262-T6

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

An Overview of Dual-Phase Steels: Advances in Microstructure-Oriented Processing and Micromechanically Guided Design

Abstract: Dual-phase (DP) steel is the flagship of advanced high-strength steels, which were the first among various candidate alloy systems to find application in weight-reduced automotive components. On the one hand, this is a metallurgical success story: Lean alloying and simple thermomechanical treatment enable use of less material to accomplish more performance while complying with demanding environmental and economic constraints. On the other hand, the enormous literature on DP steels demonstrates the immense complexity of microstructure physics in multiphase alloys: Roughly 50 years after the first reports on ferrite-martensite steels, there are still various open scientific questions. Fortunately, the last decades witnessed enormous advances in the development of enabling experimental and simulation techniques, significantly improving the understanding of DP steels. This review provides a detailed account of these improvements, focusing specifically on (a) microstructure evolution during processing, (b) exp...