Faculty Publications

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Publications by NITK Faculty

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Subject: search.filters.subject.Central composite design

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    Turn-assisted deep cold rolling: An innovative manufacturing method for the improvement of fatigue life
    (Research India Publications subscription@ripublication.com, 2015) Prabhu, P.R.; Sharma, S.S.; Kulkarni, S.M.; Gowrishankar, M.C.
    It is well recognized that mechanical surface enhancement methods, such as shot peening, laser shock peening, roller burnishing and deep cold rolling can significantly improve the fatigue performance of highly-stressed metallic components. Deep cold rolling is particularly attractive since it is possible to generate, near the surface, deep compressive residual stresses and work hardened layers while retaining a relatively smooth surface finish. In this paper, the effect of turn-assisted deep cold rolling on the fatigue behavior of AISI 4140 steel is examined. In the present study, the parameters which have significant effect on turn-assisted deep cold rolling process are identified. Fatigue experiments are performed using rotating beam fatigue testing machine. The data is plotted as cyclic stress versus number of cycles to failure. It is found that ball diameter and rolling force has significant influence on fatigue performance of 4140 steel and it exhibits well-defined fatigue limit below which continued loading does not lead to failure. It is further established that the higher the cyclic stress the shorter the life. A second order regression model is developed to predict the fatigue life using response surface methodology and central composite design. Based on cyclic deformation and stress/life (S/N) fatigue behavior, it is found that turn-assisted deep cold rolling can be quite effective in retarding the initiation and initial propagation of fatigue cracks in AISI 4140 steel. © Research India Publications.
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    An Efficient Approach to Optimize Wear Behavior of Cryogenic Milling Process of SS316 Using Regression Analysis and Particle Swarm Techniques
    (Springer, 2019) Karthik, M.C.; Malghan, R.L.; Shettigar, S.; Rao, S.S.; Herbert, M.A.
    The present work is an endeavor to carry out a machining using LN2 in face milling operations and to produce the milling samples with excellent wear resistance property. The output response (wear rate) depends on appropriate choice of speed, feed, and depth of cut. The experimental data are conducted (collected) for SS316 as per central composite design. The present work exemplifies an employment of conventional and nonconventional strategies for optimizing the milling factors of cryogenically treated samples in face milling to achieve the desired wear (response). The results of nonlinear regression (desirability strategy) and nonconventional [particle swarm optimization, (PSO)] optimization techniques are compared, and PSO is found to outperform the desirability function approach. The present work even highlights the effect and results of LN2 on wear in contrast to wet condition. © 2018, The Indian Institute of Metals - IIM.
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    Exploring welding parameter effects on friction stir weld joints in aluminum 8006 alloy using response surface methodology
    (MIM RESEARCH GROUP, 2025) Chandrakumar, C.; Sogalad, I.; Shettigar, A.K.; Korgal, A.; Nagaral, M.
    This study aims to develop mathematical models that can predict the characteristics related to mechanics, such as microhardness and impact resistance, of Aluminum that has been friction stir-welded 8006 alloy joints with 95% confidence. The four process parameters tool tilt angle, welding speed, tool pin shape, and rotating speed were systematically varied across three levels. Following a response surface and central composite design approach that is face-centered, the influence of different factors on the mechanical properties of aluminum 8006 alloy joints was assessed. The highest impact toughness of 58 joules was observed in joints specially prepared by a cylindrical threaded pin profile tool with a 1° tilt angle operating at 800 RPM and a feed rate of 20 mm/min and test was conducted at room temperature. Additionally, it was investigated how process factors affected impact toughness by ANOVA and the results revealed that the tool pin geometry is identified as the most significant process variable on impact toughness, contributing 52.52%, thereafter the tool tilt angles (15.53%), rotating speed (8.80%), and welding speeds (5.84%). The findings showed that, for impact toughness, the tool tilt angle and pin shape were more important than welding speed and tool rotation speed, but the tool pin profile and the welding speed showed governance over rotational speed and angle of tilt in case of hardness. The joints achieved a maximum hardness of 166 VHN at stir zone of the welded specimen made from a threadless taper pin tool for the speed of 1200 rpm, the tool was tilted at 2 degrees while welding at a speed of 40 mm/min. Finally, the effects of process parameters on the microstructure of friction stir welded Aluminum 8006 alloys were addressed and discussed. © 2025 MIM Research Group. All rights reserved.