Session: 16-01-01: Poster Session: NSF-Funded Research (Grad & Undergrad)

Paper Number: 99388

99388 - A Predictive Multisurface Approach to Damage Modeling in Hcp Alloys 

Magnesium alloys are promising candidates for replacing conventional alloys in aerospace and automotive applications. Such lightweight structures require robust damage tolerance procedures, and ductile fracture is essential for for designing fail-safe structures and limiting material waste in manufacturing. Moreover, magnesium alloys are highly anisotropic due to their hexagonal-close-packed crystalline structure, but such anisotropy may be tailored to enhance the performance of advanced materials. Their anisotropy manifest at various scales as it results from low crystal symmetry, strong crystallographic texture, and deformation twinning leading to tension-compression asymmetry. Thus, the plastic flow response is dependent upon orientation and loading mode.

 

On the other hand, voids are observed to mediate failure in a variety of circumstances. Over the past decade, significant progress has been made in understanding fracture processes based on micromechanics. A constitutive theory describing the damage accumulation to failure in ductile materials by void growth and coalescence is developed from the first principles. The new theory of multisurface plasticity accounts for the evolution of the microstructure based on its attributes such as porosity, shape, orientation, and distribution of voids under homogeneous (or void growth) and multiple inhomogeneous yielding (or coalescence-like)  mechanisms. The theory is similar to the continuum crystal plasticity theory; inhomogeneous yielding systems are akin to slip systems. The inhomogeneous yielding systems systems are specified based on the void distribution in the microstructure. Inhomogeneous yielding captures failure by internal necking or by void-sheet coalescence due to plastic flow localization in the inter-void ligament.

 

The interplay between void mediated failure and anisotropic plasticity is not well understood in Magnesium alloys. This is due in part to the lack of comprehensive constitutive formulations for plasticity coupled with damage in this class of materials. Here, progress on two distinct formulations are adopted to predict the ductility and/or strain to failure in magnesium alloys. The first development concerns a two-surface, pressure-insensitive plasticity model to describe the mechanical behavior of damage-free materials. The two surfaces separately account for the primary deformation mechanisms of glide and twinning. The model captures the evolving plastic anisotropy and the tension-compression asymmetry during straining. The second development concerns the effective behavior of porous plastic materials. Two or more surfaces account for one mode of homogeneous yielding (void growth in triaxial tension) and one or more modes of inhomogeneous yielding (void coalescence in triaxial tension and void distortion under severe shear). The model captures failure by internal necking or by void-sheet coalescence quite well. Implementing the new constitutive formulation promises a high-fidelity in high-throughput evaluations of anisotropy dependent failure loci for Mg alloys.

Presenting Author: Vigneshwaran Radhakrishnan Texas A&M University

Presenting Author Biography: Vignesh is a Ph.D. candidate in the Department of Aerospace Engineering, Texas A&M University. He obtained a master's in Aerospace Engineering from the Indian Institute of Technology, Kanpur. He specializes in Materials and Structures, and his research interests are in Structural mechanics, Finite element methods, Plasticity, and Ductile fracture. He has been working with Dr. Amine Benzerga for the past five years toward obtaining a Ph.D.

Authors:

Vigneshwaran Radhakrishnan Texas A&M University
Amine Benzerga Texas A&M University