Project 1.4: Superelastic Granular Materials for Impact Absorption

PIs: Schuh, Radovitzky, Kamrin


Granular and powder materials are well known for their dissipative properties, which are generated from frictional contact interactions between grains. New techniques have enabled the large-scale production of “oligocrystalline” micro-particles whose internal structure provides a secondary mode of dissipation through hysteretic elastic deformation. Project 1.4 seeks to exploit both dissipation mechanisms to produce a new type of energy absorbing media - a granular oligocrystalline (GOC) particulate aggregate - to provide force protection in various battlefield situations. Additionally, GOC media can be sintered into a solid phase, the energy absorption of which during pulverization and fracture permits additional absorption. To explore the GOC concept, advanced discrete and continuum models will be created to simulate the material in order to understand the mechanics of oligocrystalline particle and powder systems. This, combined with experimental testing at the one-particle and many-particle scales, will provide needed inputs to enable full-scale characterization of the large-scale mechanics of these novel materials Manufacturing techniques for production of the GOC particles have been demonstrated and will be further developed. The theoretical, experimental, and numerical efforts proposed could lead to a new class of improved technologies exploiting multi-mode force protection in the battlefield.

This project aims to open scientific exploration at the intersection of two major subfields of materials science, namely granular materials and shape memory materials. By developing the first granular packings of shape memory ceramic materials, a new class of granular materials is proposed that can dissipate mechanical energy through two mechanisms: inter-particle friction and intra-particle martensitic phase transformation. A specific goal of the project is to establish the energy damping properties of shape memory ceramics both as individual particles and as bulk granular materials, and to link those two scales through experiment and modeling. The effect of the intra-particle microstructure — whether single crystal, oligocrystalline, or polycrystalline — will also be investigated to determine its effect on energy dissipation. Granular mechanics will be studied in confined geometries (i.e., die compression), unconfined geometries (i.e., impact and/or impression), and partially confined geometries as well (i.e., encapsulated powder). Research will explore the mechanics of many shape memory particles in these various configurations and connecting each to models at the mesoscale and continuum levels. The overarching goal is to produce a multi-scale model connecting the physics from the single particle level to the continuum level. The resulting knowledge will guide the design of specific product forms for mechanical energy dissipation in force protection applications.



A) Experimental - Compression test on single particles and micro pillars result in characteristic load vs. displacement curves showing superelastic behavior.
B) Single-Crystal Modeling - Using the micro mechanics based constitutive model, we show the orientation dependence of the stress-strain response in single-crystal zirconia.
C) Multi-Particle Modeling - A discrete element method was used to model the interactions between contacting oligocrystalline particles.  This method was tested on a polydisperse system of 10,000 particles.