Understanding and Predicting Dynamic Behavior of Materials : Composites and Brittle Materials
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Computational Materials Science and Engineering Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Saryu Fensin, Los Alamos National Laboratory; Avinash Dongare, University of Connecticut; Benjamin Morrow, Los Alamos National Laboratory; Marc Meyers, University of California, San Diego; George Gray, Los Alamos National Laboratory
Thursday 8:30 AM
February 27, 2020
Room: 5A
Location: San Diego Convention Ctr
Session Chair: Jie Chen, Los Alamos National Laboratory
8:30 AM
Micromechanical Methods for Parameterizing Ceramic Failure Models: Daniel Magagnosc1; Andrew Tonge1; 1US Army Research Laboratory
Development of material failure models remains an outstanding challenge particularly for dynamic loading conditions. Brittle materials represent an especially difficult case owing to the inherently stochastic nature of failure. Advanced ceramic material models account for the variability in the local failure strength of the material by assigning a size dependent distribution of failure strengths in each sub-volume of a larger calculation. Historically these strength distributions were fit to macroscale experimental data that can suffer from small sample sizes and a large difference between the specimen and representative element size scales. To circumvent these challenges and interrogate the underlying material properties a micromechanical testing methodology is employed. A series of microscale tension and compression experiments are performed on hot-pressed SiC and B4C. Using these experimental inputs, a framework for parameterizing a dynamic ceramic failure model is developed. The efficacy of the modeling framework is demonstrated through computer simulations of impact loading.
8:50 AM Cancelled
Observation and Analysis of Amorphization-induced Fragmentation in Boron Carbide: Jerry LaSalvia1; C. Marvel1; Kristopher Behler1; M.P. Harmer1; 1ARL (SURVICE Engineering)
Stress-induced amorphization of boron carbide has been extensively studied since its discovery in ballistic fragments almost two decades ago. Numerous issues remain concerning the formation of nanoscale amorphization bands and their impact on damage evolution and fragmentation. In this presentation, fragmentation features in a ballistically-impacted boron carbide were examined by high-resolution STEM. Nanoscale amorphization bands were observed in fragments from these regions. The bands appear to extend from particle-particle contacts. At their tips, the crystal is sheared for some distance, being composed of an array of dislocations. This appears to be a precursor for amorphization. An analysis based on Hertzian contact mechanics and Weibull theory supports the notion that particle fracture is predominately governed by stress-induced amorphization versus bulk flaws below a critical size (dependent upon bulk flaw concentration). This work suggests the importance of stress-induced amorphization in the fragmentation process of boron carbide under compressive stress conditions.
9:10 AM
On the Structural Characterization of Amorphous Phase Recovered from Laser Shock Compression: Shiteng Zhao1; Marc Meyers2; 1University of California, Berkeley; 2University of California, San Diego
Shock induced amorphization has been discovered in laser shock experiments.Due to the presence of strong deviotoric shear stresses, the amorphous phase presented in the shock-recovered materials is intrinsically different from those made by rapid quenching. Using nanobeam electron diffraction, the structure of the amorphous phase can be studied with an unprecendented spatial resolution. The local symmetry as well as radial distribution function of the amoprhous phase can be computed, which can be used to infer the structural difference among the amorphous domains. Two dimensional strain field in the vicinity of the amoprhous bands can be mapped based on the local variation of the lattice constant. Considerable volumeric strain as well as shear strain coexisted, especially along the interface between the amoprhous and crystalline phases.
9:30 AM
Thermodynamics of Pressure-induced Amorphization in Boron Carbide- Unraveling the Mystery through Molecular Dynamic Simulations: Ghatu Subhash1; Amnaya Awasthi1; Matthew DeVries1; 1University of Florida
In 1994 Grady conducted plate impact experiments on boron carbide and noted its anomalous behavior which he described as “dramatic loss in strength,” “near fluid-like response,” “heterogeneous deformation,” “anomalous volume compression,” and “phase-change-like volume collapse.” Despite more than two decades of research, no convincing explanation is available to unravel this mystery. Through molecular dynamics (MD) simulations of high-pressure compression and shock loading of boron carbide, we draw a link between nanoscale thermodynamics to amorphization. For the first time, we generate Rayleigh lines via MD shock simulations and constructed Hugoniot that confirms to the experimental data. Shock-induced temperature in the ceramic exceeds the melting point causing dramatic loss of strength and near fluid like response leading to amorphization. The anomalous volume compression is reflected in Hugoniot being below the hydrostat. By confirming amorphization to be a thermodynamically driven phenomenon, we resolve the scientific issues pertaining to anomalous behavior of boron carbide.
9:50 AM
Sub-surface Observations and Analysis of Indented Polycrystalline Hot-pressed Boron Suboxide (B6O): Kristopher Behler1; Jerry LaSalvia1; C.J. Marvel1; S.D. Walck1; M.P. Harmer1; 1ARL (SURVICE Engineering)
Amorhpization, microcracking and macrocracking have previously been shown in commercially hot-pressed polycrystalline boron carbide (B4C) using Raman spectroscopy combined with mechanical polishing of Knoop and Vickers indents as well as subsurface preparation techniques to observe the microstructure within the inelastically deformed regions. In this current study, polished hot-pressed polycrystalline boron suboxide (B6O) with and without sintering aids (rare earth oxide and/or silica) were indented using Knoop indentation with loads of 0.3 kgf to 2 kgf. The surface of the indents are characterized using Raman spectroscopy. A FIB liftout technique was used to prepare cross-sections of the area under the indent for aberration corrected scanning transmission electron microscopy (AC-STEM), AC-STEM/EDS (x-ray energy dispersive spectroscopy) and transmission electron microscopy (TEM) characterization and analysis. Experimental procedures and the effect of silica and rare earth/silica sintering aids on the microstructure and amorphization are reported.
10:10 AM Break
10:30 AM
Modelling the Effect of Microstructure on Elastic Wave Propagation in Platelet-reinforced Composites and Ceramics: Hortense Le Ferrand1; 1Nanyang Technological University
Ceramics and ceramic-reinforced composites are the gold standard for impact resistance in harsh environments. To improve vibration resistance, the orientation of reinforcing microparticles can be locally controlled to build periodic structures via recent manufacturing strategies based on magnetic manipulation. Here, we propose a modelling tool to select the potentially best microstructure design that would dissipate mechanical energy via elastic wave scattering. This phenomenon has been observed in periodic composite laminates and in biomaterials like the dactyl club of the mantis shrimp. Based on an analytical model, we determine the frequency bandgaps associated to periodic architectures and investigate the influence of microstructural parameters such as inclusion concentration, orientation and pitch. The results are used to define guidelines for the future fabrication of hard bulk ceramic materials that combine traditional ceramic’s properties with high vibration resistance.
10:50 AM
Mechanical Response and Deformation Modes during High-rate Loading of Multiphase Metal Materials: Avery Samuel1; Zachary Levin2; Carl Trujillo3; Saryu Fensin3; Tresa Pollock1; Irene Beyerlein1; Frank Zok4; 1University Of California, Santa Barbara; 2Texas A&M University; 3Los Alamos National Laboratory; 4University of California, Santa Barbara
Multiphase metal materials (M3) have been shown to exhibit enhanced properties over their constituents at quasi-static rates. However, high strain rates change the stress and strain state, potentially altering failure mechanisms. This work aims to elucidate relationships between microstructural inhomogeneities and deformation modes in M3 during dynamic loading. Dynamic deformation behavior of model M3s was investigated via Split-Hopkinson Pressure Bar tests. Results are compared to those from quasi-static tests of similar M3s. Dynamic rates increase flow stresses and exacerbate variations in flow stress that are related to total strain history. The deformation mode is influenced strongly by the orientation of the microstructure relative to the loading direction; significant flow localization occurs for certain combinations of sample/loading orientation.