Our Research Laboratory focuses on:
- Developing a fundamental understanding of the process-structure-property-function relations in structured materials, and
- Creating innovative structured materials with superior specific properties and novel functionalities for extreme engineering applications.
Hierarchical Materials for Multimodal Energy Absorption and Superior Specific Properties
Materials with superior specific properties such as specific energy absorption, specific modulus, and specific strength are essential for extreme engineering applications, for example, protecting sportsmen and military personnel from high-velocity impacts and vibration, protecting spacecrafts from high-velocity impacts of micrometeorites and space debris, and preventing extreme vibrations in aircrafts and spacecrafts. Hierarchical structuring offers unique opportunities to design materials with superior specific properties due to their structural composition spanning across multiple lengthscales from nanometers to several millimeters that respond in distinct ways to external stimuli of different timescales. A fundamental understanding of the behavior of hierarchical materials over broad length- and timescales is critical to developing superior materials with optimally enhanced mechanical properties, particularly that are often mutually exclusive (e.g. damping and stiffness or strength and toughness). We investigate the key process-structure-property relations in hierarchical and nanostructured materials using experimental and computational approaches to achieve property amplifications that are not usually found in common materials. We focus on understanding the physical and mechanical properties and the geometries of the structural features that makeup the material, the lengthscales at which they are present, how they organize and interact across multiple lengthscales, the effects of mesoscale property gradients, and how those structural features respond to external loading at different timescales–quasistatic compression to harmonic excitation to low and high velocity impacts. We also explore pathways to engineer and exploit nonlinearities that will allow us to control the material behavior in unprecedented fashion.
Nanostructured Metals for Ultrahigh-strength and -Toughness
How can we create metals that are both strong and tough–two mechanical properties that are critical to engineering applications, but are often found to be mutually exclusive? Advances in the nanotechnology over the past two decades have demonstrated that the strength of metals can be dramatically increased by decreasing their grain size to nanoscale. This approach has a caveat that it also makes the nano-grained metals very brittle and prone to catastrophic failure. We use a new approach to create a gradient distribution of grain sizes that has the potential to achieve both strength and toughness optimally through an intriguing gradient plasticity mechanism. We use a laser-induced micro-ballistic (LIMB) apparatus that allows impacting microparticles against a rigid substrate at supersonic velocities to create the gradient-nano-grained (GNG) structure in them. Using in-situ SEM nano-indentation and nano-mechanical testing techniques, we characterize the properties of GNG-structured metals to understand the fundamental process-structure-property relations that will enable us to create ultra-strong and -tough materials.
Non-Hermitian Metamaterials for Controlling Mechanical Wave Propagation
The ability to control sound waves will enable us to create novel engineered materials and devices with exotic phenomena such as acoustic cloaking, acoustic lensing, acoustic rectification, acoustic switching, and Sasing. Phononic crystals, acoustic metamaterials, and SASERS are testaments to our increasing ability to engineer the impedance profile of the materials that propagate sound in desired ways to yield exotic wave phenomena. Recently, exploiting ‘loss’ that is present in materials as a useful ingredient in material design to control sound waves is emerging as a paradigm shift in metamaterials. We study such non-Hermitian metamaterials that incorporate various ‘engineered losses’ and ‘lossy nonlinearities’ to control and direct the mechanical energy transport. We also investigate ways to create ‘gain’ in materials that when balanced with loss, can lead to Parity-Time symmetric materials–a special class of non-Hermitian materials. Acoustic regulators, perfect absorbers, and acoustic limiters are a few of the many potential devices that can be created with non-Hermitian metamaterials.