An Improved Zener-Hollomon Parameter and a New Ductile Failure Criterion for Modeling and Predicting Sheet Metal Forming Limit

Sheet metal;Stamping;Hot stamping;Warm forming;Forming limit;Ductile failure;Automotive Systems Engineering;Automotive Systems Engineering, College of Engineering and Computer Science

Sheng, ZiqiangReyes-Villanueva, German ;

University of Michigan

关键词: Sheet metal;    Stamping;    Hot stamping;    Warm forming;    Forming limit;    Ductile failure;    Automotive Systems Engineering;    Automotive Systems Engineering, College of Engineering and Computer Science;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/136078/ZQSheng_Dissertation_final.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Sheet metal forming is an important manufacturing process in the automotive industry. Due to the lightweighting trend, increasing amount of sheet metal materials withhigh strength-to-weight ratios, such as aluminum alloys, magnesium alloys, advanced highstrength steel (AHSS), are being used to make automotive components. However, the roomtemperature formability of those sheet materials is generally inferior to that of conventionally used mild steel. Recent decade has witnessed a fast development of sheetmetal forming technologies at elevated temperatures or so-called warm/hot forming thattake advantage of the enhanced formability at elevated temperatures for those lightweighting sheet materials. Sheng (2102) proposed a Zener-Hollomon (Z) parameter basedforming limit surface (Z-FLS) to model the forming limit at elevated temperatures ofaluminum warm forming. Further development of this concept motivated this PhDdissertation.The current research started with the implementation of Z-FLS for the formabilityprediction of a magnesium alloy under a warm forming condition. It then proposed animproved Zener-Hollomon (Z´) parameter to enhance the capability of representing nonlinearstrain rate effect on the forming limit strain and used the Z´-FLS concept to predict the formability of a boron steel sheet material in a hot stamping condition. Furthermore, itproposed a new ductile failure criterion (DFC) to correctly reflect micromechanicalfindings on critical damage and failure. It also developed methods to predict forming limit curves at room and elevated temperatures by using the proposed DFC and Z´. The proposednew Zener-Hollomon parameter and ductile fracture criterion were validated using published test data on different lightweighting sheet materials. It is shown that the forminglimit predictions match quite well with the experimental observations.