Frank and Ora Lee Marble Professor of Aeronautics and Mechanical Engineering

Research

Our group's interest lies in understanding and modeling the behavior of materials and structures across length and time scales, ranging from atomistic to macroscopic, and over a variety of conditions, from quasistatic to extremes of pressure, temperature and rate of deformation. We are particularly interested in multiscale aspects of material behavior and the structure/property relation, including the development and evolution of microstructure during deformation and its role in shaping the macroscopic response of materials and structures.

We are also interested in understanding the limits of usability of materials, e.g., formability limits, failure mechanisms, fatigue life prediction, plastic deformation, fracture and fragmentation, material and structural instabilities, and others. From a methodological point of view, our group is interested in mathematical and computational methods enabling the application of high-fidelity multiscale material models to engineering systems, with a particular view to predicting their behavior under operational conditions with quantified uncertainties. Modern nonlinear analysis and high-performance computing are two disciplines that we have found particularly useful in that regard and that have provided, and continue to provide, the basis and the focus for much of our work.

  • U.S. Army Research Laboratory through the Materials in Extreme Dynamic Environments Collaborative Research Alliance (University lead PI: K.T. Ramesh). The purpose of this work is to deploy a rigorous methodology of uncertainty quantification in which the requisite uncertainty bounds are supplied by concentration-of-measure (CoM) inequalities. These inequalities exploit the so-called concentration-of-measure phenomenon, which is a non-linear generalization of the law of large numbers.

  • Office of Naval Research: Constitutive Modeling of Glass at Extreme Pressure and Loading Rates. Glass is attractive for armor applications because of its low density (~2.2 g/cm3), high strength (~5-6 GPa), volume expansion following fracture and energy dissipation due to densification. To date, no model exists that predicts these properties of glass, which hampers efforts to evaluate the true potential of glass for armor applications. The proposed work addresses this gap and is concerned with the development of a finite-deformation model of the inelasticity of glass under general multiaxial deformation histories, including irreversible dilation and densification, mixed states and microstructure, hysteresis and dissipation, rate-dependency and thermal softening, for use in terminal ballistics simulations.
  • Office of Naval Research: Unlocking the unexpected behaviors of polyurea. Polyurea exhibits extraordinary behavior at high pressures and strain rates of deformation. However, the root causes of that behavior as still imperfectly understood. The work under the grant is directed at evaluating a number of micromechanical hypotheses and ascertaining their ability to explain the observed anomalous behavior of polyurea under extreme conditions of pressure and rate of deformation. The expected outcome of the research will be a fundamental understanding of the root causes of the unexpected behaviors of polyurea.

  • Caltech Innovation Initiative (CI2) Program: Oncotripsy, Targetting Cancerous Cells Selectively via Resonant Harmonic Excitation. Oncotripsy is a non-surgical cancer therapeutic that selectively targets cancer cells via ultrasound harmonic excitation at their resonance frequency. Current treatment approaches to various forms of cancer require invasive surgical procedures and make use of chemical therapeutics which also induce damage to healthy cells.  Numerical studies performed within the group have revealed the existence of a spectral gap between the natural frequencies and, most importantly, resonant growth rates of healthy and cancerous cells. Cancerous cells can thus be selectively taken to lysis by the application of carefully tuned ultrasound harmonic excitation while simultaneously leaving healthy cells intact. Based on our numerical study results, we are performing in-vitro studies on cancer cell lines. We aim to find a spectral gap in resonance frequencies between cancerous and healthy cells, and to induce lysis of the cancerous cell membranes by means of carefully tuned low-ultrasound harmonic excitation.