Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Overview of constitutive laws, kinematics, homogenization and multiscale methods in crystal plasticity finite-element modeling: Theory, experiments, applications

An elasto-viscoplastic formulation based on fast Fourier transforms for the prediction of micromechanical fields in polycrystalline materials

DAMASK – The Düsseldorf Advanced Material Simulation Kit for modeling multi-physics crystal plasticity, thermal, and damage phenomena from the single crystal up to the component scale

The accelerating rate at which new materials are appearing, and transforming the engineering world, only serves to emphasize the vast potential for novel material structure, and related performance. Microstructure-sensitive design (MSD) aims at providing inverse design methodologies that facilitate design of material internal structure for performance optimization. Spectral methods are applied across the structure, property and processing design spaces in order to compress the computational requirements for linkages between the spaces and enable inverse design. Research has focused mainly on anisotropic, polycrystalline materials, where control of local crystal orientation can result in a broad range of property combinations. This review presents the MSD framework in the context of both the engineering advances that have led to its creation, and those that complement or provide alternative methods for design of materials (meaning ‘optimization of material structure’ in this context). A variety of definitions for the structure of materials are presented, with an emphasis on correlation functions; and spectral methods are introduced for compact descriptions and efficient computations. The microstructure hull is defined as the design space for structure in the spectral framework. Reconstruction methods provide invertible links between statistical descriptions of structure, and deterministic instantiations. Subsequently, structure–property relations are reviewed, and again subjected to representation via spectral methods. The concept of a property closure is introduced as the design space for performance optimization, and methods for moving between the closures and hulls are presented as the basis for the subsequent discussion on microstructure design. Finally, the spectral framework is applied to deformation processes, and methodologies that facilitate process design are reviewed.

Microstructure Sensitive Design for Performance Optimization

Hot deformation studies of a newly designed γ + α2 based TiAl alloy of composition Ti–42Al–6Nb–3Cr–0.1B at.% (nominal) realized through ingot metallurgy route using double vacuum arc remelting were carried out. Hot isothermal compression testing was performed in Gleeble™ 3500 at different temperatures ranging from 1123 to 1373 K at 50 K intervals and strain rates of 0.001–1 s−1. Processing maps were developed using an approach of dynamic material modeling of the flow curves to establish the safe hot working regime. Strain rate sensitivity and Zener–Holloman parameters were calculated and constitutive equation was derived. Microstructural investigation revealed dynamic recrystallization and activation of multiple twin systems as the main softening mechanisms operating at optimum hot working conditions. Safe hot working temperature and strain rate regime for the alloy was found to be in the temperature range of 1323–1373 K and strain rate range of 0.001–0.01 s−1.

Hot Deformation Studies on β0 Stabilized TiAl Alloy Made Through Ingot Metallurgy Route

In two phase materials like duplex stainless steels that contain both the phases in nearly equal proportions, the crystallographic texture in the phases is related by special orientation relationship (OR). Most of the studies related to ORs are focused on characterising the type of ORs due to phase transformations and recrystallisation. However, very little is known about the stability of ORs and their role in the texture evolution during deformation. In this work, we present a detailed study on the role of ORs in the texture evolution during rolling in fcc/bcc two phase materials. Three different ORs; Bain, Kurdjumov–Sachs, Nishiyama–Wassermann and two different parent phases; fcc and bcc are considered. Using three-dimensional representative volume element (RVE) based crystal plasticity fast Fourier simulations, we report that the final textures depend strongly on the initial parent phase textures and the existence of an OR, and is independent of the type of the OR. A copper type texture is observed in the fcc phase, when the parent phase is bcc with cube texture. However, a brass type texture is observed when the parent phase is bcc with rotated cube texture. A detailed investigation using a series of bicrystal studies further revealed that even within an OR, the type of Bain variant plays a vital role in the overall texture evolution. It is also observed that there is no marked impact of the initial CRSS ratios and strain hardening on final textures of both the parent and child phases. 

Anand K. Kanjarla

Papers

Hot Deformation Studies on β0 Stabilized TiAl Alloy Made Through Ingot Metallurgy Route

A crystal plasticity investigation on the influence of orientation relationships on texture evolution during rolling in fcc/bcc two phase materials

Quantification of similarity and physical awareness of microstructures generated via generative models

An experimental and crystal plasticity investigation of anisotropic compression behaviour of Mg-Sn-Ca alloy

Bain variant dependent plastic anisotropy and formability in duplex stainless steels