CSAR Seminar

SPEAKER: Farid Abed, Louisiana State University

TITLE: Physically Based Multiscale Viscoplastic Model for Metals and Steel Alloys: Theory and Computation

DATE: Wednesday, December 14, 2005
TIME: 10:00 A.M.
PLACE: 2240 DCL
1304 W. Springfield Ave., Urbana, IL

ABSTRACT

The main requirement in large deformation problems such as high-speed machining, impact, and various primarily metal forming, is to develop constitutive relations that are widely applicable and capable of accounting for complex paths of deformation. Achieving such desirable goals for materials such as metals and steel alloys involves a comprehensive study of their microstructures and experimental observations under different loading conditions. In general, metal structures display a strong rate- and temperature-dependence when deformed non-uniformly into the inelastic range. This effect has important implications for an increasing number of applications in structural and engineering mechanics. Physically based vicoplasticity models for different types of metals (body centered cubic, face centered cubic and hexagonal close-packed) and steel alloys are derived in this work for this purpose.

A multi-scale, hierarchical thermodynamic consistent framework for constructing the material constitutive relations for the rate-dependent behavior is adopted. The concept of thermal activation energy, dislocation interaction mechanisms, and the role of dislocation dynamics in crystals are used in the derivation process, taking into consideration the contribution of the plastic strain evolution of dislocation density to the flow stress of polycrystalline metals. It is shown that the model predicted results compare very well with different experimental data over a wide range of temperatures (77K-1000K) and strain rates (10-3--104s-1). Material length scales are implicitly introduced into the governing equations through material viscosity. The proposed framework is implemented into the well-known commercial finite element software ABAQUS. Finite element simulations of material instability problems converge to meaningful results upon further refinement of the finite element mesh due to the successful incorporation of the material length scale in the model formulations.