مقالههای Ahmad Assempour
توجه: محتویات این صفحه به صورت خودکار پردازش شده و مقالههای نویسندگانی با تشابه اسمی، همگی در بخش یکسان نمایش داده میشوند.
اطلاعات انتشار: بیستمین کنفرانس سالانه مهندسی مکانیک، سال ۱۳۹۱
تعداد صفحات: ۴
The inverse finite element method was derived from ideal forming to predict the initial blank of sheet forming process and the strain distribution according to the geometry of final product. In this paper an inverse finite element method has been presented to obtain strain and stress distribution in final shape and design initial blank of deep drawing process. The procedure is as following: First, strain distribution in deep drawn part is estimated by kinematics formulations. Then by using Hill’s anisotropic plasticity and according to the associated plastic flow rule, stress distribution is obtained in deep drawn composite part. Finally, initial blank is designed by considering external forces between the sheet and the tools. The accuracy of the present method is evaluated by comparison with ABAQUS for a square cup example. The results are in good agreement with the results of ABAQUS.<\div>
اطلاعات انتشار: دوازدهمین کنفرانس ملی مهندسی ساخت و تولید ایران، سال ۱۳۹۰
تعداد صفحات: ۴
In spite of the fact that the experimental results indicate the significant effect of strain rate on forming limits of sheets, this effect is neglected in all theoretical methods of prediction of Forming Limit Diagrams (FLDs). The purpose of this paper is to modify the most renowned theoretical method of determination of FLDs (M–K model) so as to be able to take into account the effect of strain rate. To achieve this aim, the traditional assumption of preexistence of an initial geometrical inhomogeneity in the sheet has been replaced with the assumption of a preexisting material inhomogeneity. It has been shown that using this assumption, the strain rate would not be omitted from equations; thus it is possible to demonstrate its effect on FLDs. To validate the results, they are compared with some experimental data. The good agreement between the theoretical and experimental results shows capabilities of the proposed method in predicting the effect of strain rate on FLDs.<\div>
۳definition a new dimensionless parameter on geometric ones affecting the chevron crack formation in an extrusion process
اطلاعات انتشار: دومین همایش بین المللی و هفتمین همایش مشترک انجمن مهندسی متالورژی ایران و انجمن ریخته گری ایران، سال ۱۳۹۲
تعداد صفحات: ۶
The central burst defect, also called chevron crack, in the extruded products is analysed by using 2D finite element analysis (FEA) to investigate the effects of affecting parameters on its formation, the three main ones are: cone angle, reduction and friction. By simulating an extrusion process in ABAQUS and changing these variables, some of the results like Von Mises stress, hydrostatic stress and strain in the longitudinal direction are discussed. Due to these results, some curves have been developed to show the safe and dangerous zone to the formation of chevron cracks. The results are also compared with some available experimental data. Also, for reducing the number of variables, a new dimensionless parameter is defined which combine two geometric ones, cone angle and reduction in area. It is suggested that this parameter can satisfy the effects of both of them; it means that as it is increased, whether due to the increasing in the cone angle or decreasing in the reduction in area percentile, the probability of chevron crack formation will be increased.<\div>
اطلاعات انتشار: Journal of Computational and Applied Research in Mechanical Engineering، سوم،شماره۲(پياپي ۶)، Spring ۲۰۱۴، سال ۰
تعداد صفحات: ۱۰
In this work, an inverse finite element formulation was modified for considering material anisotropy in obtaining blank shape and forming severity of deep drawn orthotropic parts. In this procedure, geometry of final part and thickness of initial blank sheet were known. After applying ideal forming formulations between material points of initial blank and final shape, an equation system was obtained in terms of unknown initial positions on the blank sheet. Initial positions of material points were obtained by solving this equation system. In this algorithm, the Hill''s anisotropic plasticity and associated plastic flow rule were used. Strain distribution on the final part was obtained by comparing the initial blank and final part. The method was applied for the simulation of drawing an orthotropic blank to a rectangular cup. Accuracy of the presented method was evaluated by comparing the results with numerical forward method and experiment results.
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