S. Sankaran

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

Low cycle fatigue behavior of a multiphase microalloyed medium carbon steel: comparison between ferrite–pearlite and quenched and tempered microstructures

Abstract: In an attempt to improve fatigue and fracture resistance, a multiphase (ferrite–bainite–martensite) microstructure was developed in a V-bearing medium carbon microalloyed steel using a two-step cooling and annealing (TSCA) treatment following finish forging. The monotonic, cyclic stress–strain and low cycle fatigue behavior of this steel are reported. These results are compared with those of ferrite–pearlite and tempered martensite microstructures obtained by air cooling (AC) and quenching and tempering (Q&T), respectively. The tensile properties of the multiphase microstructure are superior to those of the ferrite–pearlite and the Q&T microstructures. Under cyclic loading, the ferrite–pearlite microstructure showed hardening at higher total strain amplitudes (≥0.7%) and softening at lower total strain amplitudes (<0.7%). The quenched and tempered and the ferrite–bainite–martensite (TSCA) microstructures displayed cyclic softening at all total strain amplitudes employed. Despite the cyclic softening, the ferrite–bainite–martensite structure was cyclically stronger than the ferrite–pearlite and the Q&T microstructures. Bilinearity in the Coffin–Manson plots was observed in Q&T and the multiphase TSCA conditions. An analysis of fracture surface provided evidence for predominantly ductile crack growth (microvoid coalescence and growth) in the ferrite–pearlite microstructure and mixed mode (ductile and brittle) crack growth in Q&T and the multiphase TSCA microstructures.

Electroless nickel plating of arc discharge synthesized carbon nanotubes for metal matrix composites

Abstract: Electroless nickel (EN) plating was performed on arc discharge synthesized multiwalled carbon nanotubes for various deposition times. X-ray diffraction (XRD), Transmission electron microscopy (TEM), and Raman spectroscopy characterization techniques are used to identify the presence of nickel deposition on the carbon nanotubes (CNTs) and the degree of graphitization. The results indicate that impurities are less in the purified CNTs as compared to raw carbon soot. Increasing deposition time up to 60 min increases uniform deposition of nickel throughout the length of the CNTs. However, for deposition time longer than 60 min, nickel particles are seen separated from the surface of the CNTs. Uniformly coated nickel CNTs throughout their length are potential candidates for reinforcements in composite materials. Magnetic properties of the nickel coated CNTs, with deposition time of 30 and 60 min were also evaluated. The magnetic saturation of nickel coated CNTs with deposition time of 30 min is less compared to nickel coated CNTs with deposition time of 60 min.

High cycle fatigue behaviour of a multiphase microalloyed medium carbon steel: a comparison between ferrite–pearlite and tempered martensite microstructures

Abstract: To improve toughness and fatigue strength, a mutiphase (ferrite (F)–bainite (B)–martensite (M)) microstructure was developed in a V-bearing medium carbon microalloyed (MA) steel through a two-step cooling process that was followed by an annealing (two-step cooling and annealing (TSCA)) treatment In the present paper, the high cycle fatigue (HCF) response determined in terms of the endurance limit, long crack fatigue threshold (ΔKth), crack closure and fatigue crack growth rate (FCGR) in a material that has a multiphase microstructure is presented and compared with those of the same material with a ferrite–pearlite (F–P) and a tempered martensite (T–M) microstructure obtained by air-cooling (AC) and quenching and tempering (Q&T), respectively Long crack fatigue threshold (ΔKth) and crack closure were evaluated using a dynamic compliance (DYNACOMP) measurement technique The fatigue limit of the F–B–M and the T–M microstructures (∼400 MPa) was greater than that of the F–P microstructure (∼340 MPa) At load ratios less than 05, the threshold for long crack growth was lower for the F–B–M microstructure compared with that of the F–P microstructure This is attributed to the reduced roughness-induced crack closure (RICC) contribution to the threshold in the former multiphase microstructure A quantitative analysis of the near-threshold fracture surfaces validated the above conclusion Fatigue crack growth rate in the Paris regime was found to be independent of the microstructure but dependent on the load ratio

Microstructure and mechanical behavior of copper coated multiwall carbon nanotubes reinforced aluminum composites

Abstract: Electroless copper coatings were performed on purified carbon nanotubes (CNT), with varying deposition time and the optimum deposition time in terms of uniform deposition was determined to be 45 min. Different amounts of optimized Cu coated CNT (CNT (Cu)) and Al powders were ball milled. CNT (Cu) reinforced Al (Al-CNT (Cu)) composites were prepared by spark plasma sintering (SPS). Pure CNT reinforced Al (Al-CNT) composites were also prepared by SPS. The ball milled powders and composites were characterized using X-Ray diffraction, scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy (TEM). Microhardness and compression properties of the composites were measured. TEM images of ball milled powders and composites revealed uniform distribution of CNT in matrix. Mechanical properties of Al-CNT (Cu) composites are superior to Al-CNT composites. The maximum enhancement in compressive strength of Al-CNT (Cu) composites is 154% for 2 wt% reinforcement; this enhancement is attributed to the copper coating on CNT surface.

Development of high strength and ductile ultra fine grained dual phase steel with nano sized carbide precipitates in a V–Nb microalloyed steel

Abstract: Ultrafine grained dual phase steel with yield strength of 865 MPa and tensile strength of 1640 MPa with a high work hardening rate and uniform elongation of 7% was produced by cold rolling and intercritical annealing. The fine scale Nb-V based carbides contributed to improving the strength and work hardening.

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...

Simultaneous capture removal of phosphate, ammonium and organic substances by MgO impregnated biochar and its potential use in swine wastewater treatment

Abstract: Metal oxide-biochar composites have been used for removing pollutants from aqueous systems. In this work, optimized MgO-impregnated porous biochar was prepared using an integrated adsorption-pyrolysis method for absorption of phosphate, ammonium and organic matter (humate). Results revealed that the MgO-biochar was comprised of nano-sized MgO flakes and nanotube-like porous carbon. Mg content had significant effects on the development of the nanotube-like porous carbon structure in MgO impregnated biochar and its adsorption capacity for phosphate, ammonium and humate. The adsorption isotherms fitted by Langmuir model illustrated that the optimized adsorbent, 20% Mg-biochar, exhibited maximum adsorption capabilities of more than 398 mg/g for phosphate, 22 mg/g for ammonium, and 247 mg/g for humate, respectively. The phosphate adsorption fitted the pseudo-second-order kinetic model, while ammonium and humate adsorption were best described by the intra-particle diffusion model. The existence of Cl−, NO3−, SO42−, K+, Na+ and Ca2+ ions had no significant impacts on humate adsorption, but the presence of SO42− and Ca2+ affected the phosphate adsorption, and the presence of K+, Na+ and Ca2+ ions inhibited ammonium adsorption. Characterization of adsorbents by X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) before and after treating swine wastewater revealed that struvite crystallization, electrostatic attraction, and π–π interactions contributed to the adsorption of phosphate, ammonium and humate. The results demonstrated that the optimized MgO-biochar could be employed as an effective adsorbent for the simultaneous removal and recovery of phosphate, ammonium and organic substances from nutrient-rich livestock wastewaters.

Thermomechanical processing of advanced high strength steels

Abstract: Advanced high strength steels (AHSSs) are regarded as the most promising materials for vehicles in the 21st century. AHSSs are complex and sophisticated materials, with microstructures being controlled by precise thermomechanical processing (TMP) technologies. TMP is an established and strategic method for improving the mechanical properties of AHSSs through control of microstructures and is among the most important industrial technologies for producing high quality AHSSs with the necessary mechanical properties. This article aims to provide a comprehensive review of recent progress in TMP of AHSSs, with focus on the processing-microstructure-property relationships of the processed AHSSs. We first present an introduction to the background of the TMP of AHSSs. Then, the recent progress and the latest achievements in TMP of the first, second and third generations of AHSSs and Nano Hiten steels are reviewed in detail, and the mechanisms of the TMP-induced microstructural evolution and mechanical properties variation are addressed and discussed. The present review concludes with a summary on the TMP of AHSSs currently under development, and also offers an outlook of the future opportunities which will inspire more in-depth research and eventually advance practical applications of this innovative field.