Study on the Dynamic Evolution of Through-Crack in the Double Hole of Elliptical Bipolar Linear-Shaped Charge Blasting

Seeking the law of through-crack in the double hole of shaped charge can help reveal the rock failure mechanism of directional controlled blasting. Using LS-DYNA numerical simulation analysis, the dynamic mechanical behaviors of double-hole crack development and double-hole crack penetration in elliptical bipolar linear-shaped charge blasting and ordinary blasting were compared and studied. The results showed that it was difficult to form a straight line through the double holes under ordinary blasting, while easy to cause over-under-excavation problems. The blasting of the elliptical bipolar linear-shaped charge had a significant effect on the formation of directional crack. The crack penetrated along the connecting center line of the two holes. The main crack growth form was tensile fracture mode, and the explosion gas was the important driving force for continuous crack growth. The elliptical bipolar linear-shaped charge blasting produced fewer cracks in the nonenergy-accumulating direction, which could effectively reduce the damage of the retained rock mass.

Study on Dynamic Evolution Law of Blasting Cracks in Elliptical Bipolar Linear Shaped Charge Blasting

Based on LS-DYNA numerical simulation analysis and comparison with laboratory tests, the blasting crack development dynamic evolution mechanism of elliptical bipolar linear shaped charge is analyzed. The development law of rock crack and optimal radial decoupling coefficient under different blast hole diameters were studied. The results revealed that the blasting with elliptical bipolar linear shaped charge had a remarkable effect on the directional crack formation, and the maximum effective stress of rock close to the position of shaped charge in the direction of concentrating energy is about 2.3 times of that in the direction of nonconcentrated energy. Moreover, the directional crack could be formed by blasting with elliptical bipolar linear shaped charge with different hole diameters, whilst the length of the main crack was related to the radial decoupling coefficient. Particularly, the main crack reached the longest when the radial decoupling coefficient was 3.36.

A practical review study on shaped charge in the last two decades (2000–2020)

Shaped charges are devices used for cutting or penetrating different aerial, on land, and underwater targets, based on the concentration of the explosion energy to the liner. The purpose of this study is to present a practical review of the studies related to shaped charges in the last twenty years (2000–2020). In this regard, these studies have been reviewed in two different categories for ordinary and advanced shaped charges. In the case of ordinary shaped charges, different aspects including shaped charges against different targets, different types of shaped charges (such as linear shaped charge and explosively formed penetrators), and theoretical advancements are presented. On the other hand, the new kinds of shaped charges developed for a specific purpose are introduced in the case of advanced shaped charges. The survey of the literature indicates that different concepts such as cut-off velocity and theoretical applicability of hydrodynamics theory in shaped charge penetration still Requires effort. Also, few studies have been focused on new shaped charges, such as hyper-velocity shaped charges, annular and dual-mode ones; and the field is still open for further progress. Besides, some of these new shaped-charges, such as double-layer shaped charges, are not realistic enough to be produced for practical purposes or the market.

Analysis of the Cracking Mechanism of an Elliptical Bipolar Linear-Shaped Charge Blasting

This study investigates the cracking mechanism of an elliptical bipolar linear-shaped charge blasting via theoretical analysis, experimentation, and numerical simulation. The results show that in the shaped charge blasting, due to the effect of the shaped jet in the direction of the shaped energy, a certain initial crack length is formed. In the action phase of the stress wave, the energy accumulation direction reduces the load required for crack initiation and propagation. The crack propagation length generated in the energy accumulation direction is greater than the nonenergy accumulation direction. The load value of the initial shock wave in the shaped energy direction is significantly greater, by about 1.64 times than the nonshaped energy direction, and the peak load acting time is earlier than the nonshaped energy direction. A large amount of impact explosion energy is consumed in the area close to the charged energy explosion due to the crushing area, regardless of the charged or noncharged energy direction. In the energy accumulation direction, the shock wave attenuation rate is faster in the near explosion area and the stress wave attenuation rate is slower in the mid and far areas of the explosion. The difference in the explosion load in the mid and far areas is small. In the nonconcentrated direction, owing to the reflected compression wave, the second stress peak appears in the nonconcentrated direction. However, its value is smaller than that of the initial shock wave peak.

Characteristics Study of Mild-Detonating Fuse and Flexible Linear Shaped Charge for Metal Plate Cutting

In many types of spacecraft and missile systems, the vehicle’s skin cutting are carried out by using the mild-detonating fuse (MDF) or the flexible linear shaped charge (FLSC). MDF is a very thin metal tube that filled with explosive charges and has an axisymmetric shape. FLSC is an inverted chevron-shaped flexible tube that generates hypervelocity jet to penetrate or cut thick metal structures. In this study, the characteristics of MDF and FLSC for metal plate cutting are identified. First, the fracture mechanisms due to MDF and FLSC are numerically analyzed in 2-D plane strain using ANSYS AUTODYN, one of commercial hydrocodes. By using proposed numerical scheme, the effects of the cutting methods and the design parameters on cutting performance, fragmentation and backward shock waves are studied; the pros and cons of MDF and FLSC for metal plate cutting are clarified. The numerical method and the results of this study provide the guidelines to select metal plate cutting method and help to establish the design method for optimal metal plate cutting; the number of the expensive explosive experiments can be reduced.

Design of a Novel Linear Shaped Charge and Factors Influencing its Penetration Performance

In this paper, a novel linear shaped charge (LSC), called a bi-apex-angle linear shaped charge (BLSC), has been designed to investigate the improvement of penetration performance. Compared with a traditional single-apex-angle LSC, a BLSC, which consists of a small-apex-angle liner and a large-apex-angle liner, has been investigated by depth-of-penetration (DOP) test. The results show that the penetration depth of BLSC is 29.72% better than that of an ordinary LSC. An Eulerian method is applied to simulate the entire process of jet formation, as well as penetration on a #45 steel target. The effectiveness of the Eulerian model is demonstrated by the good agreement of the computational results with experimental observations. Furthermore, the numerical simulation is developed to investigate the influence of liner thickness, explosive type, combination of small and large apex angle, ratio of small to all apex angle liner, and standoff distance on the penetration performance of BLSCs. The suggested work and results can provide a guide and reference for the structural design of BLSC.