Research Background During my graduate studies at MSU I have worked on multiple projects, some of which are briefly described below: During the initial phase of my research, I have investigated the sheet hydroforming process as a method for improving the formability of aluminum alloy sheets. In this research, I performed experiments using a 4-inch hemispherical punch and verified the results numerically using the FEM code Ls-Dyna. A paper on this subject was published in the International Journal of Mechanical Sciences (IJMS) in 2003 [4].
Next, I studied wrinkling behavior during the forming process of aluminum sheets. First, the accuracy of the material model to be used in the FEM analysis (Barlat YLD96) was established by comparing its ability to simulate wrinkling behavior against experimental data. The developed FEM model was then used to calculate the optimum fluid pressure profile needed for forming deep-drawn hemispherical cups without tearing or wrinkling. Based on the numerically developed pressure profile, it was shown that it is possible to form deep-drawn hemispherical cups without tearing and with minimal wrinkling in the flange and die corner area. Using the FEA, an experimental die was developed and tested where the accuracy of the numerical results was established. A paper on this subject was published in the International Journal of Mechanical Sciences (IJMS) in 2005 [3].
The previously developed hydroforming process for a hemispherical punch was extended for application to complex automotive parts. In this work, the optimum fluid pressure profile to form a deep-drawn complex automotive part was developed. A paper based on this work was presented in the Numiform 2004 conference [8]. A paper is also being prepared for journal publication.
During my PhD study, I investigated the thermo-forming and thermo-hydroforming processes for forming aluminum alloy sheets. The focus of the research was to develop a temperature-dependent anisotropic material model for use in a coupled thermo-mechanical finite element analysis of the forming of aluminum sheets. The research involved material characterization, yield function anisotropy coefficient calculation, UMAT implementation into the FEM code Ls-Dyna, and construction of an experimental setup to test the thermo-forming process. In this research, the importance of using a coupled thermo mechanical finite element analysis with an accurate anisotropic temperature-dependant material model for warm forming process was demonstrated. A two-part paper based on this work is currently under review for publication in the International Journal of Plasticity (IJP) [1, 2].
During my research, I developed capabilities to write and implement User Material Subroutines (UMAT) for the commercial FEM software’s LS-Dyna and Abaqus. The accuracy and speed of these implementations were tested and verified. Some of the material models implemented are: von-Missies Hill 1948 Barlat’s anisotropic yield functions: YLD91, YLD96, YLD2000-2d.
During my past three years of study at MSU, I have been heavily involved in supervising and mentoring graduate students on our research team both in their research and in collaborating on other projects. For the past two semesters (2005), my graduate advisor, Professor Farhang Pourboghrat, has been on a sabbatical leave from MSU. As his senior PhD student, I have taken up the responsibility of supervising the research activities at our labs. I have also supervised most of Dr. Pourboghrat’s other graduate students, helping them towards the completion of their work.
Some other technical projects with which I am involved include: Working with Ideal-Forming process design program to determine the optimum initial blank shape for multiple complex automotive parts. Analyzing tube hydroforming process, numerically and experimentally. Developing and optimizing the fluid pressure profile required to hydroform a complex automotive part by linking the FEM analysis with the optimization code HEEDS (Hierarchical Evolutionary Engineering Design System). Using continuum damage mechanics to predict failure of sheet metals. Developing bulging equipment at our lab at MSU in order to measure thickness stress-strain relations at elevated temperatures. Developing forming limit diagrams (FLD’s) using the M-K model with isotropic and anisotropic material models. Assisting other graduate students in our team with their research, e.g. FEM analysis, building experiments, UMAT development and implementation … etc. Helping to organize the NUMISHEET 2005 conference to be held in Detroit, MI in August 2005. I have designed the conference website, and I am the webmaster for the conference.
From the results of these multiple projects, numerous publications have been submitted and accepted. Some publications are under revision, while others are planned. A list of these and planned publications can be found in the Publications page.
|
