Dynamic Behavior of an Ordinary Chondrite: the Effects of Microstructure on Strength, Failure and Fragmentation

Article · August 2015with153 Reads
DOI: 10.1016/j.icarus.2015.07.027
Abstract
Knowledge of the relationships between microstructure, stress-state and failure mechanisms is important in the development and validation of numerical models simulating large-scale impact events. In this study, we investigate the effects of microstructural constituent phases and defects on the compressive and tensile strength, failure, and fragmentation of a stony meteorite (GRO 85209). In the first part of the paper we consider the effect of defects on the strength and failure. Strengths are measured and linked with detailed quantification of the important defects in this material. We use the defect statistic measurements in conjunction with our current understanding of rate-dependent strengths to discuss the uniaxial compressive strength measurements of this ordinary chondrite with those of another ordinary chondrite, with a different defect population. In the second part of the paper, we consider the effects of the microstructure and defects on the fragmentation of GRO 85209. Fragment size distributions are measured using image processing techniques and fragments were found to result from two distinct fragmentation mechanisms. The first is a mechanism that is associated with relatively smaller fragments arising from individual defect grains and the coalescence of fractures initiating from microstructure defects. This mechanism becomes more dominant as the strain-rate is increased. The second mechanism is associated with larger fragments that are polyphase and polygrain in character and is dependent on the structural failure mechanisms that are activated during load. In turn, these are dependent on (for example) the strain-rate, stress state, and specimen geometry. The implications of these results are briefly discussed in terms of regolith generation and catastrophic disruption.
    • Spall, and failure in materials are of interest for a wide range of fields applications including ballistic penetration, dynamic fragmentation in hypervelocity particle target interactions, optical, diagnostic equipment hazards in high energy density (HED) facility chambers, and asteroid and meteor dynamics as they enter the atmosphere and break up[61][62][63]. Previous research by the U.S. Army Research Laboratory (ARL) has studied spall in several different metals, in order to provide protection from 'behind-armor debris'. There has been extensive study of spall strength and its mechanisms of dynamic failure in fcc metals.
    [Show abstract] [Hide abstract] ABSTRACT: The use of high-power pulsed lasers to probe the response of materials at pressures of hundreds of GPa up to several TPa, time durations of nanoseconds, and strain rates of 10⁶–10¹° s⁻¹ is revealing novel mechanisms of plastic deformation, phase transformations, and even amorphization. This unique experimental tool, aided by advanced diagnostics, analysis, and characterization, allows us to explore these new regimes that simulate those encountered in the interiors of planets. Fundamental Materials Science questions such as dislocation velocity regimes, the transition between thermally-activated and phonon drag regimes, the slip-twinning transition, the ultimate tensile strength of metals, the dislocation mechanisms of void growth are being answered through this powerful tool. In parallel with experiments, molecular dynamics simulations provide modeling and visualization at comparable strain rates (10⁸–10¹⁰ s⁻¹) and time durations (hundreds of picoseconds). This powerful synergy is illustrated in our past and current work, using representative face-centered cubic (fcc) copper, body-centered cubic (bcc) tantalum and diamond cubic silicon as model structures.
    Article · Feb 2017 · Experimental Mechanics
  • [Show abstract] [Hide abstract] ABSTRACT: Dynamic brittle fragmentation is typically described using analytical and computational approaches for tensile stress-states. However, most fragmentation applications (e.g., impact, blast) involve very large initial compressive stresses and deformations. In this study, the compressive fragmentation of brittle materials is investigated experimentally across a range of materials: silicon carbide, boron carbide, spinel, basalt and a stony meteorite. Analysis of our experimental results suggests that there exists two different regimes in the fragment size distributions, based on two brittle fragmentation mechanisms. The first is a mechanism that produces larger fragments and is associated with the structural failure of the sample being tested. This mechanism is influenced by the loading conditions (rate, stress state) and sample geometry. The second fragmentation mechanism produces comparatively smaller fragments and arises from the coalescence of fractures initiating and coalescence between defects in regions of large stresses and contact forces (e.g., between two fractured surfaces from the larger fragments). A framework is developed for comparing experimental compressive fragmentation results with tensile fragmentation theories. The compressive experimental results are shown to be adequately described by the theories using the new framework.
    Article · Apr 2016
  • File · Data · Apr 2016 · Experimental Mechanics
  • [Show abstract] [Hide abstract] ABSTRACT: Mechanics lies at the heart of many of the underpinnings of modern technological civilization: materials, infrastructure, transportation, health and security. The mechanics of dynamic failure processes also has a major bearing on the potential catastrophes that threaten civilization, including airbursts and major asteroid impacts. Recent events (such as the Chelyabinsk meteoroid) have demonstrated the need to understand major impact and fragmentation events. Many of the fundamental problems of current interest in national security also involve impact and fragmentation, typically studied through large-scale computational simulations. In the Murray lecture, these issues were addressed by describing fundamental high-strain-rate experiments, high-speed visualization, theoretical and computational modeling of failure processes, and simulations of asteroid damage and disruption. This paper focuses on experimental results on meteorites and a basalt.
    Article · Aug 2017
Project
The objective of my current research is to further develop a better understanding of the microstructural aspects of failure, in particular the role of second phase particles in aluminum and magnesi…" [more]
Project
Dynamic fracture of ceramics is important in a range of context such as ballistic impacts and explosive mining. The first few microseconds of impact predetermines material behavior. We employ phase…" [more]
Project
We aim to understand the role of crystallography on the failure processes under general loading conditions. The project will focus on atomistic and crystal plasticity modeling and simulation of fai…" [more]
Project
In this work we study the behavior of ceramics under high-rate loadings, in particular under compressive loading. The primary mechanism of failure is dynamic fracture-related damage.
Conference Paper
February 2014
    In this study, we investigate failure and fragmentation of a meteorite (an L6 chondrite) and basalt for loading rates of 10^-3s^-1 (MTS machine) and 10^+3s^-1 (Kolsky bar). These are representative materials of asteroids and the Moon. Image processing is used to measure the size and shape distributions of the fragments. Distributions are linked to the microstructure. Mass-size distributions... [Show full abstract]
    Conference Paper
    June 2014
      Designing the next generation of armor ceramics will require an improved understanding of how different flaw types contribute to the failure and fragmentation of these novel materials. Currently, quantification of dominant flaw types (e.g., size and orientation distributions) is lacking and the extent of the contributions of these actors to failure and fragmentation is unknown. In this... [Show full abstract]
      Article
      November 2014 · Journal of the American Ceramic Society · Impact Factor: 2.61
        We investigate the rate-dependent compressive failure and fragmentation of a hot-pressed boron carbide, under both uniaxial and confined biaxial compression, using quantitative fragment analysis coupled with quantitative microstructural analysis. Two distinct fragmentation regimes are observed, one of which appears to be more sensitive to the microstructural length scales in the material,... [Show full abstract]
        Discover more