MIT2_094S11_luo - Term Project Report of 2.094 Ductile...

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Term Project Report of 2.094 Ductile Fracture Characterization of an Aluminum Alloy Sheet using Numerical Simulations and Tests By Meng Luo Impact and Crashworthiness Lab Department of Mechanical Engineering Massachusetts Institute of Technology Apr 28, 2008
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Term Project Report of 2.094 Contents Abstract . ................................................................................................. 1 1. Introduction. ....................................................................................... 1 2. Numerical Simulations of Four Fracture Calibration Test. ............ 2 2.1 Dog-bone tensile sepcimens . .......................................................................... 2 2.2 Flat specimen with cutouts. ............................................................................. 8 2.3 Flat grooved plane strain specimen. .............................................................. 10 2.4 Punch indentation tests on circular disks. ..................................................... 12 2.5 Ductile fracture calibration using simulation results . ................................... 14 3. Parametric Study of Some Numerical Simulation Parameters. ...16 3.1 Effect of Number of Integration Point through thickness (NIP). .................. 16 3.2 Effect of element type. .................................................................................. 17 3.3 Mesh size effect . ........................................................................................... 19 4. Conclusions. ...................................................................................... 21 I
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Term Project Report of 2.094 Abstract The objective of this project is to characterize the plastic behavior and ductile fracture of the 2mm-thick aluminum alloy sheets. Four different types of tests were conducted all the way to fracture, including tensile tests on classical dog-bone specimens, flat specimens with cutouts and plane strain grooved specimens, as well as a punch indentation test. A comprehensive numerical analysis of these experiments was performed with ADINA. Simulations revealed that the isotropic plasticity model is able to describe, with good accuracy, the plastic response of all four types of tests. Moreover, local equivalent strain to fracture and stress triaxiality parameters were obtained through FE simulations using an inverse engineering method, and a fracture locus of this type of aluminum alloy sheets was determined. In addition, a parametric study was performed to evaluate the effect some variables that will affect numerical simulations, such as number of integration points through thickness, element type, and mesh size. 1. Introduction Prediction of ductile fractures of metals in engineering structures is a topic of great importance in the automotive, aerospace, and military industries. Equivalent strain to fracture ε f (or the fracture strain for short) is widely used to define the material ductility. Many theoretical analyses and experimental results have shown that the material’s fracture strain is not constant but changes under different loading conditions or stress states. The most important fracture controlling parameter is the stress triaxiality η (normalized hydrostatic pressure by Mises equivalent stress, σ = − p ). m Based on the research experience of ICL(Impact and Crashworthiness Lab) at MIT, a Mohr-Coulomb fracture criterion in the space of f and was adopted in this project to determine the fracture locus of the aluminum sheets. For sheet metal, the stress triaxiality range of most interest is 1/3 < < 2/3 . Therefore, four types of tests which can cover this range were designed to calibrate the fracture model.
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This note was uploaded on 02/24/2012 for the course MECHANICAL 2.094 taught by Professor Klaus-jürgenbathe during the Spring '11 term at MIT.

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MIT2_094S11_luo - Term Project Report of 2.094 Ductile...

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