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Numerical studies of explosion induced cylindrical shell fracture under different detonating modes
Abstract
The explosion induced fracture of metallic cylinder under different detonating modes was simulated. The results show that different detonating modes lead to significant differences on the pressure and apply work history of the cylindrical shell. A semi-decoupling numerical method was proposed to thin the mesh size of the metallic cylinder and to simulate the process of destruction of cylindrical shell under different detonating modes with higher degree of accuracy. Theoretical analysis shows that this method is reasonable. The shear bands appearing during the fracture of metallic cylindrical shell was reproduced using this semi-decoupling method.
... Liu, Mingtao, and Wu, Sisi. et al [9,10] conducted numerical simulations of the shell fracture process under internal and external blast loading in the two-dimensional plane, which to some extent restored the process of the generation of the shell shear zone and the change of the fracture mode. Marinko, Cullis, and Elek et al [11][12][13] conducted numerical simulations of the fragmentation process of a naturally fragmented warhead using the finite element method and counted the parameters of fragmentation characteristics, such as velocity, fragment size, and mass distribution, and demonstrated that some numerical simulation results are in good agreement with experimental data. ...
The fracture process of the metal cylindrical shell under the action of implosion is numerically simulated by AUTODYN finite element software for the expansion of cracks on the surface of the cases under the action of implosion loading. Numerical computations were used to determine the effect law of engineering factors such as the energy density of explosives, shell thickness, and shell material on crack-related parameters. The results show that the shell fracture radius along the axial direction remains nearly constant, and its value is less influenced by the energy density of explosives. The axial crack propagation velocity of the shell from the location of crack initiation to the non-exploding end of the shell shows a trend of change from high to low, fluctuating down. The axial crack propagation velocity and crack circumferential density both increase with the explosive energy density. The fracture density fluctuation range is between 0.4~0.73/mm. The law can be used to study the fracture damage of metal cylindrical shell structures under high impact.
... When the explosion pressure is decreased or the shell thickness is increased, the fracture mode of the shell would change to shear-tensile mixed fracture, and the fracture strain and strain rate would be lower. Through numerical simulation research, Liu et al. [16] also found that different initiation methods of the explosion would affect the fracture of the cylindrical shell because the incident angle of the detonation wave to the inner wall of the cylindrical shell varied under different initiation methods of explosion; the pressure experienced by the inner surface of the cylindrical shell differs greatly. The results show that the peak pressure of the centerline detonation is the maximum, the single-point detonation is the second, and the plane detonation is the minimum. ...
Detonation and fragmentation of ductile cylindrical metal shells is a complicated physical phenomenon of material and structural fracture under a high strain rate and high-speed impact. In this article, the smoothed particle hydrodynamics (SPH) numerical model is adopted to study this problem. The model′s reliability is initially tested by comparing the simulation findings with experimental data, and it shows that different fracture modes of cylindrical shells can be obtained by using the same model with a unified constitutive model and failure parameters. By using this model to analyze the explosive fracture process of the cylindrical shells at various detonation pressures, it shows that when the detonation pressure decreases, the cylindrical metal shell fracture changes from a pure shear to tensile–shear mixed fracture. When the detonation pressure is above 31 GPA, a pure shear fracture appears in the shell during the loading stage of shell expansion, and the crack has an angle of 45° or 135° from the radial direction. When the pressure is reduced to 23 GPA, the fracture mode changes to tension–shear mixing, and the proportion of tensile cracks is about one-sixth of the shell fracture. With the explosion pressure reduced to 13 GPA, the proportion of tensile cracks is increased to about one-half of the shell fracture. Finally, the failure mechanism of the different fracture modes was analyzed under different detonation pressures by studying the stress and strain curves in the shells.
To meet the requirements of an aluminized explosive cylinder test with a longer energy release time, a non-standard cylinder structure with a larger wall thickness was designed, which can not only extend the effective expansion time of detonation products but also avoid a great increase in the test charge mass. The non-standard cylinder was filled with TNT explosives for its relatively stable Gurney energy, and the experimentally generated parameters were compared with those of [Formula: see text]50 and [Formula: see text]100 mm standard cylinders. Based on this, a more accurate Gurney Model for Non-Standard Cylinder (GM-NSC) was proposed taking into account the influence of shell deformation and axial movement of detonation products compared with the traditional Gurney model. The analysis results show that the proposed GM-NSC model curve is suitable for both non-standard and standard cylinders. Finally, the method was applied to DNAN-based aluminized explosives, and the experimental results show that the method can characterize more thoroughly the effect of the detonation product expansion enhanced by the rapid reaction of aluminum powders.
The self-organized shear bands phenomena of cylindrical metal shells driven by sliding explosively loading in either outward or inward direction are discussed. By means of high-speed photograph, the processes of the appearance of initial shear bands and their developments on out and inner surfaces are recorded and the fractured surfaces of recovery specimen are analyzed, showing the longitude shear fracture cell characteristics typical for some metals, such as HR2. The mechanism of the exclusive selection of shear bands orientation remains unexplained about the correlation between the shear bands on a given periphery of cylinder section and between the shear bands along a generatrix of the explosively loaded cylindrical shell with respect to the short time delay before shear bands orientations to be fixed. This uniform selection of shear failure anisotropy from two alternatively groups (45°/135° with respect to the cylinder radii) under explosive loading seems not always related to initial metallurgical texture. It might have some common basic with jet spin phenomenon.
The high-speed photography was applied to observe the expanding fracture of 45 steel cylinder shells driven by detonation. The clear photos of expanding process of steel cylinder shells were obtained. The fracture strains of the expanding steel shells increase with the strain-rate, and decrease when the strain-rate arrived at a certain constant. The plasticity peak during dynamic fracture was experimentally observed. The strain-rate according to the peak of fracture strain is around 7.1 × 104 s-1.
The plastic deformation behavior and modes of fracture exhibited by tubular bomb casings are greatly influenced by the stress state imposed by explosive and inertial forces. These forces combine to produce triaxial compression over a varying inner portion of the tube wall. Noting that compressive hoop stresses would exist over a portion of the wall, Taylor has previously developed a hypothesis for prediction of fracture radius, assuming a radial fracture mode. This paper introduces hypotheses related to the influences of stress state and thermoplasticity upon fracture mode as well as fracture radius. The resulting prediction model closely predicts fracture radius and explains the development of commonly observed shear‐lip fractures. It illustrates why radial fractures are typical only when detonation pressures are relatively low, and why shear fractures are typical when detonation pressures are high.