Seminar Schedule – Fall 2017
Thursday, October 26, 2017
Time: 3:30-5:00 PM
Place: WRW 102
Integrated Computational and Experimental Materials Engineering (ICEME) for Mass Efficient Vehicle Structures
Dr. Raj K. Mishra, General Motors R&D
Automotive industry is embracing ICEME tools to adopt aggressive engineering strategies to meet impending fuel economy and vehicle mass targets in a multi-material framework in a sustainable manner. Computational tools can aid the smart use of current materials and accelerate the development of light metals with enhanced formability, crashworthiness, etc. Successful applications of ICEME requires smart combination of experiments with computation at various length scales, for both calibration and validation of the numerical models. This talk presents multi-scale computational frameworks involving coupled micro-scale and macro-scale numerical models for high strength aluminum alloys, Advanced High Strength Steels (AHSS) and magnesium alloys. For the micro-scale computations, a new 3D finite element analyses based on rate-dependent crystal plasticity theory is developed that incorporates 3D microstructures accurately constructed from 2D electron backscatter diffraction (EBSD) data into finite element analyses. Mechanism based constitutive laws that permit strain hardening and saturation without external adjustment are employed. The macro-scale computations are done with advanced yield functions informed by micro-scale models. Coupling these models with optimization frameworks based on genetic algorithms and neural networks provide a comprehensive ICEME toolset to satisfy design and performance requirements with materials and processes while meeting cost, mass and performance requirements simultaneously. An illustration of this integrated approach for a component level application will be presented.Magnetorheological elastomers (MREs) are ferromagnetic particle impregnated rubbers whose mechanical properties are altered by the application of external magnetic fields. In addition, these composite materials can deform at very large strains due to the presence of the soft polymeric matrix without fracturing. From an unconventional point of view, a remarkable property of these materials is that while they can become unstable by combined magneto-mechanical loading, their response is well controlled in the post-instability regime. This, in turn, allows us to try to operate these materials in this critically stable region. These instabilities can lead to extreme responses such as wrinkles (for haptic applications), actively controlled stiffness (for cell-growth) and acoustic properties with only marginal changes in the externally applied magnetic fields. Unlike the current modeling of hierarchical composites, MREs require the development of finite-strain coupled nonlinear magneto-mechanical models in order to tailor the desired macroscopic instability response at finite strains. As a proof of concept, we study experimentally and theoretically the stability and post-bifurcation of a non-linear magnetoelastic film/substrate block in order to obtain active control of surface roughness. The non-intuitive interplay between magnetic field and elastic deformation owes to material and geometry selection, namely a ferromagnetic particle composite film bonded on a compliant passive foundation. Cooperation of two otherwise independent loading mechanisms�mechanical pre-compression and magnetic field�allows to bring the structure near a marginally stable state and then destabilize it with either magnetic or mechanical fields. We demonstrate for the first time that the critical magnetic field is a decreasing function of pre-compression and vice versa. The experimental results are then probed successfully with full-field finite element simulations at large strains and magnetic fields. The magnetoelastic coupling allows for the reversible on/off control of surface wrinkling under adjustable critical magnetic and mechanical fields. In this view, this study constitutes a first step towards realistic active haptic and morphing devices. Novel auxetic and chiral architected MREs are also proposed as potential candidates for future work.
For further information, please contact Dr. Stelios Kyriakides at skk@utexas.edu or (512) 471-4167.
