Our research group is interested in modeling and simulation of materials structures and properties. The overall goal of our research is to identify the relationship between microstructure evolution and the macroscopic mechanical response of metals, alloys and advanced structural materials.
Atomistically informed dislocation dynamics (DD) simulations on nanoscale materials
Extensive investigations using atomistic simulations over the past decade provide insight in addressing the unusual high strength, ductility, and damage tolerance of nanoscale materials. A principal component of our current research is developing DD simulation models based on experimental observations and atomic scale simulation results. The DD-interface model can be potentially implemented on nano-twinned systems, nanolayered composites and ultrafine grain materials to improve current knowledge of macroscopic mechanical properties of these systems, and also will fill the gap of materials modeling between atomic-scale models and continuum plasticity models.
Multiscale modeling of crystal plasticity under high strain rate
There are many metallic structures being applied under high strain rate deformation such as high speed machinery, armour systems, high speed transportation vehicles and spacecrafts. To predict the mechanical properties of such structures requires constitutive models that can reflect the underlying dislocation behaviors at these extreme conditions. One of our ongoing research projects is to develop a numerical, hierarchical multiscale modeling methodology that can predict the mechanical response of face-centered cubic (FCC) and body-centered cubic (BCC) materials under different loading conditions.
Dislocation dynamics simulations of mechanical deformation in nickel-based superalloys
Single crystal nickel-based superalloys are a class of high temperature and highly corrosion resistant materials, which are widely used in aerospace, marine and power generation industries. As an important class of structural materials, a fundamental understanding of their constitutive behaviour is essential for safe life and damage tolerance assessment for fracture critical applications. Our 3-D DD simulation program can simulate the mechanical deformation in single crystal Ni-based superalloys with considering the interaction between dislocation and internal microstructure such as precipitates and monitoring dislocation structure and density evolutions. The objective of this work is to improve our current knowledge on the deformation of nickel-based superalloys and help materials design in high temperature materials and collaboration with experimentalists is actively pursued.
Plasticity at small scales
Recently, the ‘smaller-is-stronger’ phenomenon on the nano/micro-compression tests has attracted much attention in materials science field. This challenging problem falls into our areas of interest. Our DD model has captured most key features of nano/micro-compression test, such as image forces from boundary constrains, experiment-like dislocation structures in the test sample and surface truncations of dislocation sources in small samples. In addition, this study has also been extended to polycrystalline thin films. Our work on small scales plasticity, which has been pioneering in the area, supports further investigations on scale-free intermittent flow, dislocation nucleation frequency and strength at small scale materials. Current DD-BEM model can also be used for investigation of the indentation size effect (ISE) at nano and micrometer scales.
Dislocation model for plasticity of supersolid 4He
The observation of softening of the low-temperature shear modulus in solid 4He with increasing temperature around 100 mK has been taken as evidence for anomalous elastic properties tied to supersolidity. For such a new and interesting phenomenon, we have a different perspective from other researchers on its origin and developed a dislocation density-based model to explain the behavior in solid 4He under different temperatures. Our model can successfully predict the decrease of shear modulus of solid 4He with increasing strain and the corresponding dissipation peak caused by dislocation gliding. In future, further detailed microstructural information will be put in this model to check whether the dislocation motion is the fundamental mechanism for anomalous softening in solid 4He.
Reversibility and dynamic phases for driven dislocation assemblies
Colloidal suspensions exhibit both reversible and irreversible behavior under periodic shearing. Both experiments and modeling indicate that particle interactions play an important role in the transition. In crystal materials, plastic flow always arises from motion of collective dislocations that interact with both long-range and short-range forces. An important component of our work is to use 2-D and 3-D DD simulations to investigate the reversibility of dislocation plasticity in crystal materials and identify the critical events that determine the reversible/irreversible response in these systems. At the initial simulations, we have found that driven dislocation assemblies exhibit the same nonequilibrium phases observed in collectively interacting particles systems such as vortices in disordered superconductors. These include a jammed phase analogous to a pinned state, a fluctuating or disordered phase and dynamically ordered or pattern forming states. All of the states are associated with transport signatures such as changes in the transport noise fluctuations as well as features in the dislocation velocity vs applied shear. How these dynamics phases relate to the reversibility of crystal plasticity needs future investigation.