Experimental and numerical studies on the expanding fracture behavior of an explosively driven 1045 steel cylinder

Abstract

The expanding fracture of an explosively driven 1045 steel cylinder was studied. The fracture process and the expanding velocity of the cylinder were recorded by a high-speed camera and a Photonic Doppler Velocimetry (PDV) probe in real time. The fragments were recovered and analyzed by metallurgical examinations. The fracture mechanism, expanding velocity and fragment size were analyzed respectively. We found that the adiabatic shear band (ASB) plays a key role in the fracture process of an expanding 1045 steel cylinder. As the deformation of the cylinder increases, multiple ASBs firstly initiate near the inner surface of the cylinder and then propagate outward along the maximum shear stress direction. After the ASBs arrive at the outer surface of the cylinder, all of the plastic deformation is concentrated in the ASBs, and meanwhile the cracks initiate near the outer surface of the cylinder and propagate inwardly along the developed ASBs. The terminal velocity of the cylinder was accurately predicted by the Gurney model and was found to be little influenced by the fracture mode. The width and thickness of the fragments were measured and found to be controlled by the momentum diffusion. Furtherly, we modeled the expanding fracture process of the cylinder. A three dimensional simulation results suggested that the propagation of the shock wave along the radial direction can't be neglected although the cylinder is very thin. At an early stage, the material near the inner and outer surface is in a compressive and tensile state, respectively, and the material in the middle of the cross-section is alternately in a tensile and compressive state due to the propagation of the shock waves. At a late stage, the whole cylinder is in a tensile state. In a two dimensional plane strain simulation, the initiation and propagation of multiple ASBs in the expanding cylinder were successfully replicated.