Experimental Study of the Microhardness and Microstructure of a Copper Specimen Using the Taylor Impact Test

Abstract

One commonly used method for characterizing the dynamic characteristics of materials is the Taylor impact test. This method measures the dynamic yield strength of cylindrical specimens and determines material model constants required for the numerical simulation of the behavior of materials subjected to high-velocity deformation. The purpose of this work is to investigate the microhardness and microstructure of copper specimens at different impact velocities using the Taylor impact test. This paper describes experiments performed on copper specimens (OFHC 99.9%, M1) using a single-stage light-gas gun with impact velocities in the range of 150–450 m/s. After impact, the specimens were cut along the symmetry axis to measure the microhardness and the grain size of the microstructure. Microhardness in the entire area exceeded the initial value for all investigated velocities. The averaged microhardness curves were obtained for each specimen to identify four deformation zones and determine their dimensions depending on the impact velocity. The average grain size in the entire deformed specimen became smaller than in the starting specimen. The study of the microstructure of the specimens has shown that the grain size distribution corresponds to the four deformation zones in the copper specimens.

Optimization of Johnson–Cook Constitutive Model Parameters Using the Nesterov Gradient-Descent Method

“…The parameters of the Johnson-Cook model for OFHC copper were estimated using the experimental data of the Taylor test [41] and well-known experiments on the impact of cylinders with a rigid wall by Gust W.H. [16] and by Wilkins M.L.…”

“…Numerical calculations using the original JC model at an impact velocity of 316 m/s revealed a hardening of ≥5 times due to an increase in equivalent plastic strains, which is 2 times higher than the hardening measured in [41]. In this regard, the JC constitutive model was modified by limiting the maximum value of plastic hardening in terms of the dimensionless factor B max :…”

“…A 3D simulation of a cylindrical projectile impact with a non-deformable target (Taylor test) was performed. The material of the cylindrical sample (oxygen-free high-conductivity copper, OFHC) was chosen to compare the numerical results with the experimental data [41]. Simulations of the experiments [16,43] were conducted for copper specimens with corresponding initial conditions (geometric dimensions, velocity).…”

“…The disadvantage of this model is that an increase in plastic deformation with an increase in the strain rate leads to an unlimited increase in the yield strength, which is not observed in experiments. In particular, Zelepugin S.A. et al [41] showed that OFHC copper in high-velocity impact experiments with plastic strain accumulation demonstrates an increase in microhardness from 900 MPa to ~3000 MPa. Moreover, the JC constitutive model parameters were experimentally determined by the model developers at relatively low strain-rates (up to 10 3 s −1 ).…”

“…A less-reliable measured parameter is the maximum cylinder radius, R f , due to the possible fracture of the cylinder in contact with the rigid wall. It is worth noting that the specimens were partially broken along the external radius at impact velocities of 316 m/s and above [41].…”