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- 저자 : A. Barata da Rocha (검색결과 2 건)
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P. Teixeira,J.M.A. Cesar de Sa,A.D. Santos,F.M.A. Pires,A. Barata da Rocha 한국소성가공학회 2010 기타자료 Vol.2010 No.6
This article presents an integrated approach for localized necking and failure prediction in sheet metal forming processes, based on the coupling between the anisotropic damage evolution law proposed by Lemaitre [1] and the modified maximum force criterion (MMFC) proposed by Hora et al [2]. To illustrate the essential features of the coupled approach, an aluminum alloy has been selected and numerical predictions have been compared with experimental forming limits, obtained for both linear strain paths evolutions. Numerical results show that the introduction of the softening behavior, caused by the increase of damage, into the necking criterion can play a significant role in triggering local necking, providing an improved prediction of the necking occurrence together with the capability of performing calculations of limit strains when they are governed by fracture rather than by local necking.
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On the Determination of Flow Stress Using Bulge Test and Mechanical Measurement
Abel D. Santos,Pedro Teixeira,A. Barata da Rocha,F. Barlat 한국소성가공학회 2010 기타자료 Vol.2010 No.6
The standard uniaxial tensile test is a widely accepted method to obtain relevant properties of sheet metal materials. These fundamental parameters can be used in numerical modeling of sheet forming operations to predict and assess formability and failure analysis. However the range of strain obtained from tensile test is limited and therefore if one will need further information on material behavior, extrapolation of tensile data is performed. The bulge test is an alternative to obtain ranges of deformation higher than tensile test, thus being possible to obtain non-extrapolated data for material behavior. Several methods may be used to obtain stress-strain data from bulge test, but a common concept is behind them, which needs the measurement of bulge pressure, curvature of bulge specimen, its thickness at the pole and the application of membrane theory. Concerning such measurements, optical methods are being used recently but classical mechanical methods are still an alternative with its own strengths. This paper presents the use and development of a mechanical measuring system to be incorporated in a hydraulic bulge test for flow curve determination, which permits real-time data acquisition under controlled strain rates up to high levels of plastic deformation. Numerical simulations of bulge test using FEM are performed and a sensitivity analysis is done for some influencing variables used in measurements, thus giving some directions in the design and use of the experimental mechanical system. Also, first experimental results are presented, showing an efficient testing procedure method for real time data acquisition with a stable evaluation of the flow curve.
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