An investigating on explosive expanding fracture of 45 steel cylinders by SPH method

Abstract

The expanding fracture of ductile alloy cylinder subject to the explosion includes multiple fracture modes, such as tensile, shear, and mixed tensile-shear fracture. The mechanism and the factors influencing the fracture processes are still enigmatic and far from understood. In this paper, the smoothed particle hydrodynamics (SPH) method is used to simulate the explosion experiment of 45 steel cylinders shell with different charges of JOB-9003 and RHT-901. The shear fracture, tension-shear mixed fracture modes and the evolution process of cylindrical shell with different charges are discussed. The simulation results are consistent with the experimental trend. The SPH results show that due to the propagation and reflection of shock wave between the inner and outer surfaces of cylinder during the loading stage of detonation wave, the distribution of equivalent plastic strain on wall-thickness of the cylinder is a convex shape, i.e. the strain in the middle of wall-thickness is larger than that of in the inner and outer walls; when loading by a higher explosive pressure (JOB-9003), the fracture cracks initiate from the middle of wall-thickness, and then develop to the inner and outer walls along the direction of maximum shear in loading stage, showingthe shear fracture mode. However, under the loading caused by charge RHT-901 with relatively low pressure, although the crack still starts from the middle of wall-thickness and propagates along the shear direction, the shear crack could not grow through the section of the wall completely in the loading stage; then the cylinder experiences the stage of free expansion, the stress state of unbroken zone changes into triaxial tensile stress state and the structural instability, similar to “necking” occurs in the unbroken zone. Consequently, the cracks turn from the shear direction to the necking zone along the radial direction, showing the mixed tensile-shear fracture mode. The proportion of tension and shear cracks is related to the occurrence time of structural instability. The results show that the explosion expanding-fracture process of a metal cylinders involves the interaction between shock wave and cylinder structure, and cannot be treated as that of a series of expansion rings.