Taylor Impact Tests with Copper Cylinders: Experiments, Microstructural Analysis and 3D SPH Modeling with Dislocation Plasticity and MD-Informed Artificial Neural Network as Equation of State

Abstract

Taylor impact tests involving the collision of a cylindrical sample with an anvil are widely used to study the dynamic properties of materials and to test numerical methods. We apply a combined experimental-numerical approach to study the dynamic plasticity of cold-rolled oxygen-free high thermal conductivity OFHC copper. In the experimental part, impact velocities up to 113.6 m/s provide a strain up to 0.3 and strain rates up to 1.7 × 104 s−1 at the edge of the sample. Microstructural analysis allows us to find out pore-like structures with a size of about 15–30 µm and significant refinement of the grain structure in the deformed parts of the sample. In terms of modeling, the dislocation plasticity model, which was previously tested for the problem of a shock wave upon impact of a plate, is implemented in the 3D case using the numerical scheme of smoothed particle hydrodynamics (SPH). The model includes an equation of state implemented in the form of an artificial neural network (ANN) and trained according to molecular dynamics (MD) simulations of uniform isothermal stretching/compression of representative volumes of copper. The dislocation friction coefficient is taken from previous MD simulations. These two efforts are aimed at building a fully MD-based material model. Comparison of the final shape of the projectile, the reduction of the sample length and increase in the diameter of the impacted edge of the sample confirm the applicability of the developed model and allow us to optimize the model parameters for the case of cold-rolled OFHC copper.

Equation of State for Bismuth at High Energy Densities

“…which provides the value of the sublimation energy E s in the limit of zero density ς → 0 as well as the condition of Equation (5). Satisfying Equations ( 4), (6), and (7) leaves only two free parameters m and n in Equation ( 13).…”

“…Knowledge of the thermodynamic properties of materials in a wide range of highenergy states is required for the analysis of physical phenomena in various processes under intense pulse action on condensed matter [1][2][3]. These processes include high-velocity impact [4][5][6][7], interaction with the material of intense laser radiation [8][9][10][11] or particle flows of high power density [12][13][14], and the electrical explosion of conductors [15][16][17]. For numerical simulations of emerging hydrodynamic flows, it is necessary to know the relationships of the thermodynamic characteristics of the medium in the entire range of realizable states [18][19][20][21][22].…”

Modified Taylor Impact Tests with Profiled Copper Cylinders: Experiment and Optimization of Dislocation Plasticity Model

“…With these profiled head parts of the samples, strain rates up to 10 5 s − 1 and true strains up to about 1 are reached at impact velocities not exceeding 130 m/s, which makes our experimental setup easier and cheaper. It should be mentioned that the dislocation model with the coefficients selected in [ 23 ] for the classical Taylor test failed to describe the results of the modified Taylor tests presented here. This fact confirms the importance of additional tests and motivates us to develop the presented automated algorithm for parameter identification.…”

“…This estimation method was further revisited and improved by a number of authors. Nowadays, Taylor tests are used to study the properties of different materials, including pure metals [ 22 , 23 , 24 ], conventional alloys, and high-entropy [ 25 ] alloys. Various modifications of the classical scheme of experiment were proposed and used, such as the symmetric (rod-on-rod) Taylor test [ 26 ].…”

“…In the experimental part of the present work, we perform modified Taylor tests with various sample shapes cut from a conventional symmetrical cylinder and compare the final shape of the samples with simulation predictions to test and parameterize the dislocation plasticity model [ 30 , 31 ] numerically implemented in a 3D case [ 23 ]. For a more complete verification of a plasticity model and a clearer definition of its parameters, a greater variety of different tests and sample shapes can be advantageous.…”