3. Research & grants

Research description

My research deals with the (a) development of continuum mechanics-based constitutive models for solids using (crystal) plasticity theory, (b) modeling of dissipative processes in solids, and (c) usage and development of computational solid mechanics tools. The derived constitutive models are first converted into robust numerical time-integration algorithms and then implemented into a finite-element code through a user-material subroutine interface. We also use physical experimental data available in the literature to verify the developed constitutive models and their numerical implementation.

Some of my areas of research include:

1. Crystal plasticity, twinning and phase transformations

In this work, we develop rate-independent/dependent, thermo-mechanically-coupled, finite-deformation and single-crystal-plasticity-based constitutive equations to describe the superelasticity, variant reorientation/detwinning and shape-memory effect exhibited by single crystal shape-memory alloys. The constitutive theories are derived in a thermodynamically-consistent manner and implemented in the Abaqus finite-element code by writing computationally-robust user-material subroutines. Experiments under uniaxial and multiaxial loading conditions were conducted on commercially-available polycrystalline rod and sheet shape-memory alloy to verify the developed constitutive models and their numerical implementations. We have also developed a phenomenological isotropic-plasticity-based theory to model the deformation behavior of shape-memory alloys under mechanical and/or thermal loading conditions. This model has also been implemented into the Abaqus finite-element program through a user-material subroutine interface.

2. Plasticity in amorphous metals

Here we develop a coupled thermo-elasto-viscoplastic constitutive model for bulk-metallic glasses based on finite-deformation isotropic plasticity theory. The constitutive equations were derived in a thermodynamically-consistent manner aided by microstructural balance laws. The constitutive model has been implemented in the Abaqus finite-element code by writing a user-material subroutine. Several experimental results in the literature conducted on commerically-available bulk-metallic glasses at high homologous temperatures were predicted to be in good accord by the constitutive model and the finite-element simulations. We have also developed a non-local, finite-deformation-based isotropic-plasticity theory to study the length scale effect on the shear localization process in metallic glasses at low homologous temperatures. This constitutive model has also been implemented into our own finite-element code and the Abaqus finite-element program through a user-material subroutine interface.

3. Multiscale modeling of grain growth processes in polycrystalline metals: coupling of finite-element method and phase-field modeling

In this work, a coupled finite-element and phase-field framework is developed to perform multiscale modeling of grain growth processes in polycrystalline metals. The governing equations that model the grain growth process are derived using the fundamental thermo-mechanical balance laws along with the aid of the microstructural balance laws. The constitutive model to describe grain boundary motion is then implemented in the Abaqus finite-element code by writing a user-material subroutine. Representative experimental data in the literature will be used to verify the developed constitutive model and its numerical implementation. The main goal of this project is to control and tailor the microstructure evolution in polycrystalline thin films used in the solar cell industry through computer simulations.

Research grants

• Constitutive equations for martensitic reorientation in shape-memory materials (2004). Awarding body: Faculty Research Council, National University of Singapore. Amount = SGD 179,980. Duration = 36 months. Role: Principal Investigator (PI).
• Bulk-metallic glasses and its applications: constitutive modeling, .finite-element analysis and experimental investigation (2007). Awarding body: Ministry of Science, Technology and Innovation, Malaysia. Amount = MYR 270,180. Duration = 24 months. Role: Joint PI.
• Investigation, development and fundamentals of rechargeable thin .film microbatteries for microelectronics (2008). Awarding body: A.Star Foundation, Singapore. Amount = SGD 761,340. Duration = 36 months. Role: Collaborator.
• Design and optimization of surfaces for auto-manipulation of sessile drops (2010). Awarding body: Faculty Research Council, National University of Singapore. Amount = SGD 110,000. Duration = 24 months. Role: PI.
• Characterization and peridynamic modeling of shape-memory alloy-based self-healing composite aerospace structure (2011). Awarding body: Ministry of Higher Education, Malaysia. Amount = MYR 225,000. Duration = 30 months. Role: Joint PI.
• Advancing novel aerospace materials (2013). Awarding body: Arus Perdana Foundation, UKM. Amount = MYR 100,000. Duration = 24 months. Role: PI.
• Development of reliability analysis for mixed mode loading (2013). Awarding body: Ministry of Education, Malaysia. Amount = MYR 92,000. Duration = 24 months. Role: Collaborator.
• Development of upper limb musculotendon dynamic model for personalized stroke rehabilitation (2014). Awarding body: Arus Perdana Foundation, UKM. Amount = MYR 150,000. Duration = 24 months. Role: Collaborator.
• A fundamental approach in the development of a novel theoretical and computational framework to model polycrystalline grain-growth (2014). Awarding body: Ministry of Education, Malaysia. Amount = MYR 90,000. Duration = 36 months. Role: PI.
• Development of wearable EMG device for post stroke rehabilitation (2014). Awarding body: Ministry of Education, Malaysia. Amount = MYR 30,000. Duration = 24 months. Role: Collaborator.
• Modeling fracture in metallic glass components for use in back contact solar cell applications (2015). Awarding body: Prime Impact Fund, UKM. Amount = MYR 200,000. Duration = 24 months. Role: PI.
• Fundamental Aspects of High Strain Rate Behavior of Carbon Nanotubes enhanced Ultra High-Performance Cementitious Composites (CNT-UHPCC) (2015). Awarding body: Ministry of Education, Malaysia. Amount = MYR 129,000. Duration = 36 months. Role: Collaborator.

Graduated students

Pan Haining (PhD, NUS), Raju Ekambaram (PhD, NUS), Mostafa Jamshidian (PhD, NUS).

Research collaborators

• Prof. FS Chau (NUS). [link to Prof. FS Chau's webpage]
• Prof. N Nikabdullah (University Kebangsaan Malaysia).[link to Prof. Nikabdullah's webpage]
• Prof. Y Li (NUS).[link to Prof. Li's webpage]