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V. Sampath

Other affiliations: Ruhr University Bochum
Bio: V. Sampath is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Shape-memory alloy & Microstructure. The author has an hindex of 13, co-authored 45 publications receiving 705 citations. Previous affiliations of V. Sampath include Ruhr University Bochum.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the authors studied the effect of alloy composition and processing on actuator stability during thermomechanical cycling and found that functional fatigue of binary NiTi and ternary NiTiCu (with 5, 75, and 10 at pct Cu) shape memory actuators results in an accumulation of irreversible deformation in martensite and austenite.
Abstract: The present work addresses functional fatigue of binary NiTi and ternary NiTiCu (with 5, 75, and 10 at pct Cu) shape memory (SM) spring actuators We study how the alloy composition and processing affect the actuator stability during thermomechanical cycling Spring lengths and temperatures were monitored and it was found that functional fatigue results in an accumulation of irreversible strain (in austenite and martensite) and in increasing martensite start temperatures We present phenomenological equations that quantify both phenomena We show that cyclic actuator stability can be improved by using precycling, subjecting the material to cold work, and adding copper Adding copper is more attractive than cold work, because it improves cyclic stability without sacrificing the exploitable actuator stroke Copper reduces the width of the thermal hysteresis and improves geometrical and thermal actuator stability, because it results in a better crystallographic compatibility between the parent and the product phase There is a good correlation between the width of the thermal hysteresis and the intensity of irrecoverable deformation associated with thermomechanical cycling We interpret this finding on the basis of a scenario in which dislocations are created during the phase transformations that remain in the microstructure during subsequent cycling These dislocations facilitate the formation of martensite (increasing martensite start (M S ) temperatures) and account for the accumulation of irreversible strain in martensite and austenite

100 citations

Journal ArticleDOI
TL;DR: In this paper, a linear regression analysis was performed on four sets of Cu-Al-Mn shape memory alloys, in the range of 10-15% of aluminum and 0-10% of manganese, by ingot metallurgy.

84 citations

Journal ArticleDOI
TL;DR: In this paper, the damping behavior of the alloys was studied using a dynamic mechanical analyzer and it was shown that damping capacity increases with an increase in the aluminum content when the Cu/Mn ratio or amount of manganese is maintained constant.
Abstract: Cu–Al–Mn shape memory alloys in the range of 10–15 wt.% of aluminum and 0–10 wt.% of manganese, exhibiting β-phase at high temperatures and manifesting shape memory effect upon quenching to lower temperatures, were prepared through ingot metallurgy. The damping behavior of the alloys was studied using a dynamic mechanical analyzer. The damping capacity of the alloys increases with an increase in the aluminum content when the Cu/Mn ratio or amount of manganese is maintained constant. The damping capacity of the alloys decreases with an increase in the manganese content when the Cu/Al ratio or the amount of aluminum is maintained constant. The alloys exhibit an internal friction peak in the transition zone and that all of them exhibit higher damping capacity in the martensitic condition compared with that in the austenitic condition. While ageing of the alloys at 300 °C increases the transformation temperatures of the alloys, there is a reduction in the damping capacity of the alloys due to the formation of precipitates. The alloys aged at 500 °C do not exhibit the austenite to martensite transformation due to the formation of precipitates rich in aluminum and therefore exhibit very poor damping capacity.

84 citations

Journal ArticleDOI
TL;DR: In this article, a ternary shape memory alloy with different amounts of quaternary elements Zn, Si, Fe, Pb, Ni, Mg, Cr and Ti were added to the base alloy.

82 citations

Journal ArticleDOI
TL;DR: In this paper, the mechanical and functional properties of the wires are investigated in the stress-strain-temperature space, and functional fatigue testing of actuator springs is briefly described and preliminary results for NiTi and NiTiCu actuator spring are reported.
Abstract: Among the multifarious engineering applications of NiTi shape memory alloys (SMAs), their use in actuator applications stands out. In actuator applications, where the one-way effect (1WE) of NiTi SMAs is exploited, SM components are often applied as helical coil springs. Ingots are generally used as starting materials for the production of springs. But before SM actuator springs can be manufactured, the processing of appropriate wires from NiTi ingots poses a challenge because cold and hot working of NiTi SMAs strongly affect microstructure, and it is well known that the functional properties of NiTi SMAs are strongly dependent on their microstructure. The objective of the present paper is therefore to produce binary Ni50Ti50 and ternary Ni40Ti50Cu10 SMA actuator springs, starting from ingots produced by vacuum induction melting. From these ingots springs are produced using swaging, rolling, wire drawing and a shape-constraining procedure in combination with appropriate heat treatments. The evolution of microstructure during processing is characterized and the mechanical properties of the wires prior to spring-making are documented. The mechanical and functional characteristics of the wires are investigated in the stress-strain-temperature space. Finally, functional fatigue testing of actuator springs is briefly described and preliminary results for NiTi and NiTiCu actuator springs are reported. Untersuchungen zur Herstellung und zu den Eigenschaften von NiTi- und NiTiCu-Aktorfedern NiTi-Formgedachtnislegierungen (FGL) zeichnen sich durch eine hohe Attraktivitat fur verschiedene Aktorik-Anwendungen aus. Dabei werden FGL haufig in Form von zylindrischen Federn verwendet, wobei der Einwegeffekt genutzt wird. Die Herstellung von solchen Aktor-Federn ist jedoch keinesfalls trivial. Sowohl die Herstellung von geeignetem Drahtmaterial als auch die Formgebungsbehandlung stellen in gewisser Weise eine Herausforderung dar. Die funktionellen Eigenschaften von NiTi-FGL hangen sehr stark von mikrostrukturellen Randbedingungen ab, und erforderliche thermomechanische Behandlungen sind mit weit reichenden mikrostrukturellen Veranderungen verbunden. Das Ziel dieser Arbeit war, eine Prozesskette zur Herstellung von Ni50Ti50 und Ni40Ti50Cu10-Aktorfedern ausgehend vom Gussmaterial zu erarbeiten und metallkundlich zu charakterisieren. Aus den Gussblocken wurden durch Rundkneten, Walzen, Drahtziehen und speziellen Formgebungsbehandlungen Aktorfedern hergestellt. Dabei wurden die mikrostrukturellen und funktionellen Anderungen der beiden FGL charakterisiert. Zum Schluss wurden die mechanischen und funktionellen Eigenschaften der verschiedenen Draht-Materialien und der fertigen Federn untersucht. Dabei wurde ein besonderes Augenmerk auf die funktionelle Ermudung der Aktorfedern gelegt.

64 citations


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BookDOI
26 Sep 2018

415 citations

Journal ArticleDOI
TL;DR: In this article, the lattice parameters of quaternary shape memory alloys and the thermal hysteresis were tailored by using a thin-film composition-spread technique and high-throughput characterization methods.
Abstract: Improving the functional stability of shape memory alloys (SMAs), which undergo a reversible martensitic transformation, is critical for their applications and remains a central research theme driving advances in shape memory technology. By using a thin-film composition-spread technique and high-throughput characterization methods, the lattice parameters of quaternary Ti-Ni-Cu-Pd SMAs and the thermal hysteresis are tailored. Novel alloys with near-zero thermal hysteresis, as predicted by the geometric nonlinear theory of martensite, are identified. The thin-film results are successfully transferred to bulk materials and near-zero thermal hysteresis is observed for the phase transformation in bulk alloys using the temperature-dependent alternating current potential drop method. A universal behavior of hysteresis versus the middle eigenvalue of the transformation stretch matrix is observed for different alloy systems. Furthermore, significantly improved functional stability, investigated by thermal cycling using differential scanning calorimetry, is found for the quaternary bulk alloy Ti 50.2 Ni 34.4 Cu 12.3 Pd 3.1 .

303 citations

Journal ArticleDOI
TL;DR: In this paper, the concentration dependence of the martensite start temperature (M S ) in Ni-Ti-based shape memory alloys (SMAs) was investigated and it was shown that the strong dependence of M S on alloy composition in binary, ternary and quaternary SMAs is due to a stabilization of the B2 phase by structural relaxations around Ni antisite atoms.

294 citations

Journal ArticleDOI
TL;DR: In this article, a wide variety of ageing procedures have been developed to tailor the evolved microstructures so as to yield a good combination of mechanical capacity and corrosion resistance of 7xxx series Al alloys.

258 citations

Journal ArticleDOI
TL;DR: In this article, different oxygen (O) and carbon (C) levels affect fatigue lives of pseudoelastic NiTi shape memory alloys, and the results presented in the present work contribute to a better understanding of structural fatigue of NiTi shapes.

147 citations