Influence of Size Effect on Dynamic Mechanical Properties of OFHC Copper at Micro/Mesoscopic Scale

The dynamic mechanical properties of metallic materials have been extensively investigated at the macro-scale in terms of deformation mechanisms, strain rate strengthening, and fracture mechanisms. However, the dynamic mechanical properties affected by size effects at micro/meso-scales have rarely been investigated. To explore the size effects on the dynamic mechanical properties at micro/meso-scales, the experiments of quasi-static compression and SHPB were carried out using oxygen-free, high-conductivity (OFHC) copper with different geometrical and grain sizes. The experimental results show that the quasi-static and dynamic mechanical properties of OFHC copper are affected by size effects at micro/meso-scales. In particular, OFHC copper exhibits strain rate strengthening effects at the micro/meso-scales, and the presence of micro-cracks was observed in the SHPB experimental specimens. The J-C constitutive model based on the surface layer model is proposed and the analysis of the average relative error of the modified model and the original constitutive model is performed. Finite element analysis was carried out based on the modified J-C model and the original model, and the results show that the modified J-C model was in good agreement with the experimental results.

Investigation of the explosive type on the high strain forming of OFHC copper tube

The paper computationally investigates the explosive forming of the oxygen-free high thermal conductivity (OFHC) copper tube subjected to five different explosives. To investigate the effect of explosive type on the formability of OFHC copper tube, commonly used explosives, including C-4, TNT, HMX, Comp-B, and PBXN, was compared by using the finite element method. To verify the developed finite element model (FEM), the explosive forming experiments were carried out by using C-4. In the simulations, Coupled-Eulerian-Lagrangian (CEL) method to model the large deformations, Jones-Wilkins-Lee (JWL) equations of state (EOS) to define the explosive properties and Johnson-Cook (J-C) strength and damage models to specify the metal’s mechanical behavior were utilized. Besides, Hillerborg’s fracture energy was calculated with the Charpy impact test results and given as input to the FEM. The results of FEM were compared and verified using the results of explosive forming tests considering the mesh density and friction coefficient. The simulations revealed that the explosive type affected both the final shape and also the strain rate of the copper tube. When the simulation results for C-4 was taken as reference, HMX and PBX-N increased the strain rate as 110%, roughly. However, Comp-B and TNT reduced the strain rate by nearly 10% and 22%, respectively. Also, the explosive type changed the final hardness of the metal. OFHC Copper had the lowest hardness (112.7 HV) when the simulations were conducted with TNT. In contrast, the highest hardness value (129.5 HV) was reached when HMX was used in the simulations. In addition, simulations put forth that Hillerborg’s fracture energy criteria could be used in the explosive simulations to predict the damage on the metals.