Structure of Explosively Welded Materials: Experimental Study and Numerical Simulation

Abstract

Purpose: the properties of explosively welded materials to a large extend depend on structure of thin layers which appear near the interface during a high velocity collision of workpieces. The main purpose of this paper was to study formation of materials structure in these layers by simultaneous analysis of numerical simulation results and results of materials characterization. Methods: low carbon steel plates (0.2 wt. %C) were used for explosive welding. The structure of explosively welded material was studied using light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The numerical simulation was carried out using smooth particle hydrodynamic (SPH) method in Ansys Autodyn software. Results and discussion: the most significant structural changes occur in a thin layer near the interface of explosively welded materials. The main part of the sample is just insignificantly deformed and slightly heated. High strain rate deformation in the vicinity of the interface leads to localization of strain and significant heating of materials. The conditions of the deformation during the welding are close to adiabatic. Due to the high temperature diffusivity and large temperature gradients the subsequent transfer of the heat to slightly heated layers occurs with high rates (10(4) ... 10(7) K/s). This leads to formation of metastable structures (in this study, the martensite structures were observed). The structure of the welded plates forms as a result of competition between strain hardening and temperature softening processes. The SPH simulation successfully reproduced wave formation, vortices formation and jetting phenomena. The geometry of the interface predicted by the simulation was in a very good agreement with geometry, observed in metallographic study. The simulation predicts that the strain in a very thin lay er near the interface can exceed epsilon= 6.