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RISS 인기검색어
- 검색키워드
- 저자 : Ramana V. Grandhi (검색결과 3 건)
- 무료
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Residual stress behaviors induced by laser peening along the edge of curved models
Jongbin Im,Ramana V. Grandhi,Younghee Ro 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.12
Laser peening (LP) induces high-magnitude compressive residual stresses in a small region of a component. The compressive residual stresses cause plastic deformation that is resistant to fatigue fracture. Fatigue cracks are generally nucleated at critical areas, and LP is applied for those regions so as to delay the crack initiation. Many critical regions are located on the edge of the curved portion of structures because of stress concentration effects. Several investigations that are available for straight components may not give meaningful guidelines for peening curved components. Therefore, in this paper, we investigate residual stress behaviors induced by LP along the edge of curved models. Three curved models that have different curvatures are investigated for peening performance. Two types of peening configurations, which are simultaneous corner shot and sequential corner shots, are considered in order to obtain compressive residual stresses along an edge. LP simulations of multiple shots are performed to identify overlapping effects on the edge portion of a curved model. In addition, the uncertainty calculation of residual stress induced by LP considering laser pulse duration is performed.
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Recep M. Gorguluarslan,Ramana V. Grandhi,최해진,최승겸 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.3
In the design of lattice structures fabricated by additive manufacturing, a multiscale modeling process is usually required to effectively account for fine scale uncertainties. The validation of the multiscale model predictions, on the other hand, is a challenging task. In this research, two prediction assessment approaches, namely the area validation metric and the Kolmogorov-Smirnov test, are presented in a systematic validation pyramid approach with u-pooling method to address this issue. The use of these two approaches are evaluated in terms of being an unbiased decision criterion for the prediction assessment and validation of the multiscale models. The fine scale material and geometry uncertainties are propagated onto homogenized properties using a stochastic upscaling method at each scale of interest. The homogenized model predictions are validated using the experimental data obtained for the lattice structure example fabricated by material extrusion process. The results indicate that the presented approach is capable of effectively validate the predictions of the multiscale models under uncertainty.
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초공동(초공동)하의 수중 주행체 캐비테이터 형상 최적설계
최주호(JooHo Choi),Ramana V. Grandhi 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
When a projectile travels at high speed underwater, supercavitating flow arises, in which a huge cavity is<br/> generated behind the projectile so that only the nose, i.e., the cavitator, of the projectile is wetted, while the<br/> rest of it should be surrounded by the cavity. In that case, the projectile can achieve very high speed due to the<br/> reduced drag. Furthermore if the nose of the body is shaped properly, the attendant pressure drag can be<br/> maintained at a very low value, so that the overall drag is also reduced dramatically. In this study, shape<br/> optimization technique is employed to determine the optimum cavitator shape for minimum drag, given<br/> certain operating conditions. Shape optimization technique is also used to solve the potential flow problem for<br/> any given cavitator, which is a free boundary value problem having the cavity shape as unknown a priori.<br/> Analytical sensitivities are derived for various shape parameters in order to implement a gradient-based<br/> optimization algorithm. Simultaneous optimization technique is proposed for efficient cavitator shape<br/> optimization, in which the cavity and cavitator shape are determined in a single optimization routine.
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