Understanding and Predicting Dynamic Behavior of Materials : Strength in Metals
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
Tuesday 8:30 AM
February 25, 2020
Room: 5A
Location: San Diego Convention Ctr
Session Chair: Avinash Dongare, University of Connecticut; Garvit Agarwal, Argonne National Laboratory
8:30 AM Invited
Informing Flow Stress Models at High Strain-rates Through In-situ Imaging of Hole Closure under Dynamic Compression: Jonathan Lind1; A.K. Robinson1; M. Nelms1; Nathan Barton1; Mukul Kumar1; 1Lawrence Livermore National Laboratory
The stress at which a material plastically flows depends on the current state of the material, strain-rate, and microstructure among other quantities. Experimental tests at high strain-rates (>103/s) often use measurement of shape change to infer flow stress behavior. Given stress and strain heterogeneities, inferences about flow stress behavior from those observations are facilitated by comparisons with advanced simulations. A new plate-impact experimental test will be described consisting of in-situ x-ray imaging to observe the closure of a cylindrical hole in a sample during the passage of a pressure pulse of controlled amplitude and duration. The rate of hole closure and final hole size are measured through time via multi-frame imaging. The goal being to provide high fidelity data to inform flow stress models at high strain-rates and large strains. We will present experiments on copper that aim to examine the role of starting microstructure. The experimental observations will be compared against predictions from direct numerical simulations using several flow stress models. We will discuss the results, the sensitivity of this new experimental test, and a path forward to informing the models under conditions where data is currently sparse.
9:10 AM
Predicting Dynamic Strain Rate Response using Model Reification: Jaylen James1; Manny Gonzales1; Eric Payton1; Raymundo Arroyave2; Douglas Allaire2; 1Texas A&M University/Air Force Research Laboratory; 2Texas A&M University
Fitting constitutive models of alloy viscoplastic and damage response under dynamic loading conditions remains challenging due to experimental variability, testing costs, and microstructural effects. Experimental variability propagates into model parameters during fitting, and even the ubiquitous Johnson-Cook model lacks microstructural awareness. Combining low fidelity models to yield a new, more accurate model has been successfully applied in weather forecasting and lift calculations for aircraft, and provides one way to address current constitutive model shortcomings. In the present work, a technique called reification is used to fuse the Johnson-Cook (J-C) and Zerilli-Armstrong (Z-A) constitutive models. Parameters are obtained using gradient-based minimization from Kolksy bar testing on the high-strength, low-alloy aerospace steel, AF9628. The reified model is compared with the conventional J-C and Z-A models independently fit to the experimental stress-strain observations. The performance of conventional fitting techniques is compared to the reified model via Spall and Taylor Anvil simulations.
9:30 AM
Calibrating Empirical and Micromechanical Constitutive Models beyond 10^6 s^-1: Xuchen Wang1; Mostafa Hassani1; 1Cornell University
Recent advances in resolving impact-induced deformation of microprojectiles travelling at ~100 m/s to ~1 km/s have opened new and unique opportunities for studies of materials response under dynamic loading in a relatively less explored regime of strain rates, i.e., beyond 106 s-1. This regime is particularly relevant to the conditions experienced in ballistic impacts, impulsive loadings, blasts, as well as some of the kinetic energy-based processes such as cold spray coating. Here we implement a number of constitutive models from empirical to micromechanical into a finite element code and study plastic deformation of spherical metallic microparticles impacting rigid substrates at a few hundred m/s. Linking our finite element simulations to real time observations of plastic deformation through an optimization framework, we show that we can accurately calibrate the constitutive models and discuss the underlying deformation mechanisms in the 106-109 s-1 strain rate regime.
9:50 AM
Effects of Strain Rate on the Mechanical Properties and Fracture Mechanisms of AHSS Dual Phase Steels: Sukanya Sharma1; Shrikant Bhat2; Arun Gokhale1; Naresh Thadhani1; 1Georgia Institute of Technology; 2ArcelorMittal
The quasi-static and dynamic mechanical properties under strain rates of 10-6/s-106/s and resulting fracture response of commercial Dual Phase (DP) steels are described in this work. Formability and crash resistance expose these steels used in automotive applications, to high strain rates, and the required properties and performance are often driven by their two-phase microstructure. DP steels with varying volume fractions and connectivity of the martensite phase were mechanically tested at strain rates spanning twelve orders of magnitude (10-6/s to106/s) using servo-hydraulic machines, Hopkinson bar, and plate impact gas gun experiments. The tensile strength of the steels exhibits a positive strain rate sensitivity with increase in strain rate beyond 103/s, and the strain to fracture is a function of the underlying microstructure. Quantitative fractography at different strain rates reveals sensitivity of operative micromechanisms to strain rate, loading conditions, and intrinsic microstructure.
10:10 AM Break
10:30 AM
Alloying and Strain Rate Effects on the Deformation Mechanisms of CoCrNi MPEAs: John Copley1; Francisco Coury2; Jonah Klemm-Toole1; Yaofeng Guo1; Jinling Gao3; Kester Clarke1; Benjamin Ellyson1; Chandler Becker1; Brian Milligan1; Christopher Finfrock1; Niranjan Parab4; Kamel Fezzaa4; Tao Sun4; Wayne Chen3; Amy Clarke1; 1Colorado School of Mines; 2Universidade Federal de São Carlos; 3Purdue University; 4Argonne National Laboratory
Multi-Principal Element Alloys (MPEAs), which have evolved from studies of High Entropy Alloys (HEAs), are a new and promising class of materials that have potential in structural applications. Some MPEAs, especially those from the CoCrNi family, have shown high toughness, even at cryogenic temperatures. These MPEAs gain their high toughness from deformation mechanisms such as transformation and twinning induced plasticity (TRIP and TWIP, respectively), which increase work hardening and consequently, toughness. Understanding of strain rate effects on toughness-enhancing deformation mechanisms is important for the development of structural materials for use in extreme environments. As the compositional landscape for MPEAs is vast, high-throughput methods for determining the TRIP/TWIP viability of alloys are required. To this end, a series of CoCrNi alloys were prepared and tested across decades of strain rate, including in-situ dynamic testing at the Advanced Photon Source at Argonne National Laboratory, to study the deformation mechanisms exhibited.
10:50 AM
Characteristics of Texture Development in Al-Mg Alloy under High Strain Rate Tension: Srinivasan Nagarajan1; Nilesh Gurao1; Venkitanarayanan Parameswaran1; 1Indian Institute of Technology Kanpur
Understanding the crystallographic texture development in Al-Mg alloys that are widely employed as interior panels of automotive bodies particularly under dynamic loading is indispensable to study their susceptibility to high-speed forming processes, and performance during the crash events. In this work, texture evolution in Al-4%Mg sheet material subjected to dynamic tensile deformation using split Hopkinson tension bar test is studied using X-ray diffraction and compared to the corresponding responses during the quasi-static test for similar strain levels. Using JMAK analysis, this study reveals that although cube and copper components evolve at both the loading rates, the lattice rotation, rotation path, rotation rate, and the strengths of texture components are significantly different at high strain rate. Also, the deformation texture evolution is found to be non-linear at high strain rate and has a direct implication to the characteristics of grain structure, dislocation density, and misorientation evolution measured using electron backscatter diffraction.
11:10 AM
Brittle-ductile Failure Transition of Low-symmetry HCP Metal Beryllium under Dynamic Compression: Nitin Daphalapurkar1; Darby Luscher1; William Blumenthal1; Abigail Hunter1; 1Los Alamos National Laboratory
Uniaxial compression of polycrystalline beryllium (grade S-200F), obtained from quasi-static and split-Hopkinson pressure bar experiments, suggest a significant increase in the failure strain with decreasing rates. In order to predict failure strains, we developed an anisotropic damage model based on A.N. Stroh’s analysis of a crack nucleated by a dislocation pileup. Further, under global compression, the sliding of a Stroh crack induces formation of wing cracks. Kinetic laws for crack growth, dislocation velocity, and dislocation density evolution are physically motivated. Material constants were calibrated using flow stress measurements over a range of strain rates 0.001-5,000 /s. Synergistic with the experimental measurements, we demonstrate the innovative capability of our model to predict trends in the rate-dependence and the temperature-dependence of failure strain. Our model also predicts tension-compression asymmetry and grain-size dependence. Our summary identifies requirements from additional experimental measurements for validation of micromechanical models employed in the proposed theory.