Determining the mechanical constitutive properties of metals as a function of strain rate and temperature: A combined experimental and modeling approach; Progress Report for 2004

Robertson, I. ; Beaudoin, A. ; Lambros, J.

University of Illinois

关键词: Laser Plate Impact Test Facility, Electron Microscopy;    Strain Rate;    Testing;    Laser Plate Impact Test Facility, Electron Microscopy;    Electron Microscopy;   

DOI  :  10.2172/836508
RP-ID  :  DE02NA00072-1
RP-ID  :  FG03-02NA00072
RP-ID  :  836508

美国|英语

来源: UNT Digital Library

【 摘 要 】

Development and validation of constitutive models for polycrystalline materials subjected to high strain rate loading over a range of temperatures are needed to predict the response of engineering materials to in-service type conditions (foreign object damage, high-strain rate forging, high-speed sheet forming, deformation behavior during forming, response to extreme conditions, etc.). To account accurately for the complex effects that can occur during extreme and variable loading conditions, requires significant and detailed computational and modeling efforts. These efforts must be closely coupled with precise and targeted experimental measurements that not only verify the predictions of the models, but also provide input about the fundamental processes responsible for the macroscopic response. Achieving this coupling between modeling and experimentation is the guiding principle of this program. Specifically, this program seeks to bridge the length scale between discrete dislocation interactions with grain boundaries and continuum models for polycrystalline plasticity. Achieving this goal requires incorporating these complex dislocation-interface interactions into the well-defined behavior of single crystals. Despite the widespread study of metal plasticity, this aspect is not well understood for simple loading conditions, let alone extreme ones. Our experimental approach includes determining the high-strain rate response as a function of strain and temperature with post-mortem characterization of the microstructure, quasi-static testing of pre-deformed material, and direct observation of the dislocation behavior during reloading by using the in situ transmission electron microscope deformation technique. These experiments will provide the basis for development and validation of physically-based constitutive models, which will include dislocation-grain boundary interactions for polycrystalline systems. One aspect of the program will involve the direct observation of specific mechanisms of micro-plasticity, as these will indicate the boundary value problem that should be addressed. This focus on the pre-yield region in the quasi-static effort (the elasto-plastic transition) is also a tractable one from an experimental and modeling viewpoint. In addition, our approach will minimize the need to fit model parameters to experimental data to obtain convergence. These are critical steps to reach the primary objective of simulating and modeling material performance under extreme loading conditions. To achieve these goals required assembling a multidisciplinary team, see Table 1, with key collaborators at the National Laboratories. One of the major issues for the team members was to learn about the expertise available and how to communicate across disciplines. The communication issue is a challenging one and is being addressed in part with weekly meetings in which the graduate students present lectures on the fundamentals of their respective areas to the entire group. Breakthroughs in science are presented but these, by necessity, assume a tutorial nature; examples of student led meetings can be found at our website http://hrdg.mse.uiuc.edu/. For example, interpreting electron micrographs and understanding what can be achieved by using electron microscopy is challenging for the modeling expert as is comprehending the input and limitations of crystal plasticity codes for an electron microscopist. Significant progress has been made at dissolving these barriers and the students are able to work across the disciplines.