Faculty Publications
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Publications by NITK Faculty
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Item Deep cryogenic treatment of plain-carbon and low-alloy steels(ASTM International service@astm.org, 2020) Sondar, P.R.; Hegde, S.R.To improve the mechanical properties of steels, cryogenic treatment is often carried out as an intermediate step between quenching and tempering. The transformation of retained austenite into martensite is the main objective and principle behind the cryogenic treatment. Generally, high-alloy and high-carbon steels are subjected to cryogenic treatment, as they produce a high fraction of retained austenite during quenching as compared with low- and medium-alloy steels. This work analyses the effect of cryogenic treatment on EN8, a plain-carbon steel, and EN47, a low-alloy steel, through microstructural characterization, hardness measurements, and tensile tests. The work shows that influence of cryogenic treatment carried out after tempering is only marginal, whereas cryogenic treatment carried out before tempering yields much better mechanical properties. Experimental results obtained in this work confirm that EN47 responds slightly better than EN8 suggesting that low-alloying additions influence the cryogenic treatment of steels. This work established that by properly applying cryogenic treatment, the strength and hardness of both EN8 and EN47 steels can be increased by about 50 MPa and 3 HRC, respectively, as compared with conventional hardening and tempering treatment. © 2021 ASTM International. All rights reserved.Item Failure of a Cooling Water Pump Shaft(Springer, 2021) Sondar, P.R.; Kumar, J.K.R.; Chawla, S.; Dsilva, P.C.; Hegde, S.R.This study investigates the failure of an industrial cooling water pump which experienced a drive shaft failure. As per the fail-safe design, during adverse loading of the shaft, key should fail by shear. The key, if fails, can be easily replaced to resume the operation of the pump. However, this investigation reveals that both the key and the shaft failed due to materials processing issues. A detailed failure analysis was carried out including design calculations, visual inspection, dye penetrant inspection, magnetic particle inspection, hardness test, microstructural analysis, and fractography. The study found that the hardness of the shaft varied radially from the core to the surface. The subsurface of the shaft near the keyway, happened to be significantly softer than the key. During operation, the keyway widened by plastic deformation and caused rattling of the key. Due to rattling and vibration, the key developed numerous fatigue cracks and eventually failed by crack linkages. The shaft eventually failed by torsional shear near the midpoint of the keyway. The analysis adjudged hardness variation in the shaft due to materials processing issues as the root cause of the failure. © ASM International 2020.Item Physico-mechanical behavior of carbon black-infused polymer composite(Springer, 2022) Hiremath, H.; Rajole, S.; Sondar, P.R.; Mathias, K.A.; Kulkarni, S.M.This article deals with the development of polymer composites by incorporating carbon blacks (CBs) into polydimethylsiloxane (PDMS) matrix material for improving the mechanical and physical properties of the polymer composites. CBs of nano-size were used as filler material in varying volume percentages (5–25%), and the polymer composite was processed by solution casting method. Density, elastic modulus and hardness were measured in order to study the effect of the CB-reinforced PDMS matrix. Experimentally obtained mechanical properties were then compared with the standard empirical model. Density of the polymer composite was increased by five times as compared to the pure polymer material. With the increase in volume percentage of CB, both hardness and elastic modulus of the polymer composites were enhanced. Scanning electron microscope images of the composite material showed uniform distribution of CBs, implying strong binding with the matrix material, which attributed to improved mechanical properties. © 2021, Indian Academy of Sciences.