Our research focuses on fundamental characterization of advanced material systems. Scope encompasses atomic to bulk experimental investigations and modeling. Current emphasis is on shape memory alloys, microporous metallic foams and polymer nanocomposites.

Polymer Nanocomposites

Nanoparticles, including nanospheroidal particles, nanoplatelets, and nanotubes, have received intense attention and research in the past decade. The addition of nanoparticles into polymer matrix materials has been observed to dramatically change the mechanical, thermal, electrical and diffusion properties of the host polymers, promising a novel class of polymer matrix composite materials with superior properties and added functionalities. These new materials are ideal candidates in many applications, including aerospace, automobile manufacturing, medical devices, and sporting goods. Our research has focused on the synthesis and characterization of low volume fraction nanoparticle reinforced polymers, and the development of multiscale modeling techniques to understand their unique properties and facilitate material design.

The centerpiece of our research on nanocomposites is to understand, and ultimately design, the interphase formed in the vicinity of nanoparticles inside polymer nanocomposites. Our research explores the formation mechanisms of this interphase region and its influence on the overall performance of the composites, aiming towards development of appropriate synthesis methods to control the interphase and tailor the properties of polymer nanocomposites.

• Synthesis and Characterization
• Multiscale Modeling
• Percolation Effects
• Fracture and Toughness
• Bioinspired Nanocomposites
• Model Gel Nanocomposites
• Quantifying Dispersion

Polymers and Composites

Polymers are being increasingly used in advanced structural applications due to their low cost, ease of processibility and ability to tailor their properties by combination of a polymer matrix with fibrous or particulate inclusions to create composites. At the same time, the time, temperature and environmental dependence of polymers makes understanding their long term properties and behavior challenging. Tests developed for metallic structures to assess durability are not valid for polymers and their composites. In our work, we have examined the durability of polymers and composites by focused studies of thermal aging, time-temperature behavior and associated modeling strategies. A large current effort of our group is addressing many of these issues in the realm of polymer nanocomposites as well, as described in a separate section.

• Indentation mechanics for polymers
• Aging of Polymers and Composites
• Impedance Response of Polymers
• Molecular modeling

Shape Memory Alloys

Under the appropriate stress and thermal conditions, Shape Memory Alloys (SMAs) exhibit the ability to fully recover large deformations. The Shape Memory and Superelastic behavior of these alloys are often utilized in unique design applications. For example, the medical field currently utilizes Nickel-Titanium alloys for a surgically implantable stent device that expands to support damaged or weakened arteries. The unique performance of this class of materials is governed by a thermally reversible crystallographic phase transformation (Austenite - Martensite). In our group we perform both constitutive and numerical modeling of the thermomechanical behavior of SMAs and their applications as well as experimental characterization to better understand the nature of the phase transformation. Click on the subtopics to find out more about our current research including self-healing SMA composites, porous SMA for bone implants and thermodynamics based modeling.

• SMA Composites
• SMA constitutive modeling: 1D models, 3D models, Multivariant Model
• Porous SMAs
• Micromechanical characterization

Porous Materials

Part of our research has focused on modeling and characterization of porous materials, with application to bone implants. Due to the huge stiffness mismatch between solid metallic alloys and natural bone, problems with existing bone implants include a poor implant-bone interface and so-called stress-shielding, by which the higher stiffness implant detrimentally bears most of the biological loads, resulting in resorption of the surrounding bone. In collaboration with Professors Dunand and Stupp we have examined porous titanium and porous NiTi (SMA) to help solve these problems for bone implant applications. The bulk of our work has been modeling of the porous materials, creating randomized 2D and 3D microstructures, tackling some of the difficult issues of representative volume elements. Recently we have implemented a robust 3D SMA constitutive law in Abaqus to elucidate the nature of the phase transformation in these porous microstructures.

• Porous Ti
• Porous SMAs