A study on fracture of metal plate under the detonation wave interaction

https://doi.org/10.1016/j.ijimpeng.2020.103665Get rights and content

Highlights

  • The first study using the threshold impact velocity as a criterion to estimate the fracture of metal plate.

  • Experiments of metal plates under the load of detonation waves interaction were conducted.

  • The fracture mechanism of metal plates under explosive load was studied theoretically with a method of micro-element.

Abstract

In this paper, the response of metal plates under the interaction of detonation wave is studied experimentally and numerically. Detonation wave interaction experiments were carried out on metal plates of different materials and thicknesses, and different results such as incision, partial fracture and complete fracture were obtained. ALE algorithm and fluidsolid coupling mode were used to simulate the conditions similar to experiments, and the fracture process and pressure distribution of the metal plate were analyzed. The experimental results were in good agreement with the simulation results. Finally, based on the micro-element fracture theory, the theoretical analysis of the fracture law of the metal plate was carried out, and the fracture criterion based on the threshold impulsive velocity was concluded. It has been verified that this criterion is in good agreement with the simulation and experimental results. It can be used as a basis for estimating the fracture problem of metal plates under explosive load.

Introduction

Since detonation wave reflection phenomenon was discovered, researchers began to study the process of detonation wave propagation by the ways of theoretical analysis, numerical calculations and field tests. The detonation wave interaction process and collision effect are relatively complex three-dimensional processes. Some scholars studied it from the basic theoretical analysis, such as post-wave overpressure, Mach reflection and other key parameters and processes.

Miao Yusong et al. [1]carried out a theoretical analysis of the detonation wave collision process, and explained the generating angles of the normal oblique reflection and Mach reflection of the detonation wave, and calculated the increase multiple of the post-wave pressure separately. In addition, using high-detonation-velocity explosive strip to drive the low-detonation-velocity main charge, the four groups were tested for the explosive-detonation of power. The results showed that the method of detonating at two points on the explosive strip effectively produced the effect of detonation wave collision and energy accumulation. And the detonation velocity of the explosive strip should be 1.15 times or more of the detonation velocity of the main charge. Pan Jian et al.[2] carried out theoretical analysis and numerical simulation on the propagation and interaction process of detonation wave in the separator charge, and explained in detail the regular reflection and irregular reflection after collision. After the partition, the detonation waves on both sides continuously converged toward the center line, and the incident angle continued to increase during the collision. Taking the relationship between the incident angle and the critical incident angle as the criterion, when the incident angle was small, regular reflection occurred, but no Mach rod; when the incident angle was large, Mach reflection occurred, and the height of the Mach rod increased with the incident angle. It could also be found in the simulation process that the pressure peak always appeared on the center line of the detonation wave interaction, namely the collision point, and the convergent detonation wave pressure formed after bypassing the separator was higher. Theoretical studies on this problem show that high-pressure regions will be generated after the detonation wave collides, and the application prospects are relatively extensive.

In order to better characterize the pressure enhancement after the detonation wave collision, some scholars have designed experiments to make the detonation wave interaction effect more obvious. The observation phenomenon or the pressure measurement method was used to verify the post-wave pressure enhancement, and reasonable application directions were proposed. Zhang Chongyu et al.[3] used the optical framing shadow photography and pulse X-ray photography to study the effect of lead fly layer under the head-on collision of two detonation waves. They placed an aluminum fly layer with thickness of 2 mm and a lead fly layer with the same thickness on the PETN cylinder, and set detonators on both sides of the symmetrical column to complete the two-point simultaneous detonation. So that the two synchronously generated detonation waves were propagating toward each other, and the superimposed detonation waves would eventually act on the flying layer. Tests have shown that the detonation wave on the lead fly layer had a phenomenon of advancing protrusion in the collision zone (Fig. 1), and dummyTXdummy-(the height and width of the protrusion would increase with time. The test results were consistent with the superposition and propagation mechanism of the detonation wave. In addition, due to the lead and aluminum used in the test were relatively soft, the process of scattering and atomization phenomenon also appeared in the test. Miao Yusong[4] used LS-DYNA to simulate of detonation wave propagation and collision process. The results showed that the peak pressure of the detonation using the new method could reach 2.42 times higher than that of traditional method, which greatly improved the damage capability of the warhead. Finally, the corresponding experimental verification was carried out, and it was confirmed by X-ray imaging that the results were in good agreement with the numerical simulation results.

Some scholars realized the characteristics of the tube structure in the expansion process to observe easily, and took the metal tube as the effector. The experimental research on the detonation wave collision problem was carried out, and the pressure variation law was summarized by different expansion degrees. Chen Jun et al.[5] designed a detonation wave collision test based on driving a metal tube shell, and recorded the test process by flash X-ray and optical high-velocity framing. The results showed that the normal expansion of the metal tube occurred at the beginning of the explosion, and then the bulge appeared in the middle part of the round tube after the detonation wave collision. Compared with the non-collision area, there was a significant advancement trend. Finally, the metal tube was broken through(Fig. 2). The process was numerically simulated using the fluid dynamics program TTD2C. The results were in good agreement with the test. The two detonation waves collided to increase the pressure and pressure gradient of the detonation product. Zhang Shiwen et al.[6] also carried out a combination research of experiments and simulations on the interaction of detonation waves in metal tubes. In the general simulation calculation, it was difficult to reproduce the historical process of the central bulge of the circular tube. The finite element program was used to process the grid distortion by ALE technology, and the simulation results closer to the experiment were obtained. In addition, the expansion curve of different parts of the circular tube and the expansion velocity curve at a specific position were recorded. Based on all the conclusions, the expansion velocity of the metal tube was distributed in a gradient, and the velocity of the collision zone was the largest, decreasing toward both sides. The reason for the bulge at the center of the collision zone was the difference in expansion velocity.

In addition, in the simulation study of detonation waves, there were many scholars who used a variety of innovative simulation methods to calculate the collision process of detonation waves.

J. K. Clutter[7] used the ignition growth model to simulate the detonation wave interaction, and mainly modified the dynamics-based detonation model. A method of using a polyester sheet to impact a high-velocity explosive and causing it to detonate, driving a metal flyer on the other side of the explosive was applied. The change process of each mechanical parameter in this process, such as detonation pressure, flying piece velocity, etc., was recorded in the simulation software, and the rationality of the model was analyzed. The simulation results showed that the interaction would increase the pressure at the superposition, and the impact initiated detonation process in TNT correctly predicted the formation of stable C-J detonation wave and the velocity of the resulting copper flyer. The model could also correctly simulate the interaction between detonation and compression waves, but has limited applicability to low-velocity deflagration and combustion problems.

Wang Yuxin et al.[8] used a meshless MPM method to simulate the three-dimensional simulation of the detonation wave collision problem. Compared with the general numerical calculation method, this method avoided the re-division of the grid unit, and could more clearly describe the dynamic process of the detonation wave propagation, collision and related interfaces. The simulation and corresponding test results showed that the cylindrical charge with two detonation would produce the energy accumulation effect of the detonation wave collision, and the corresponding high-pressure damage area would be generated on the bottom effect target.

Many scholars used detonation collisions in various interdisciplinary fields to conduct related research. Most of them used the superposition effect of detonation waves to complete relevant experiments and summarize other scientific laws associated with them.

In 1977, Ivanov[9] studied the effect of detonation wave collision on the surface of inert materials, and designed related experiments to verify the phenomenon of detonation wave collision to enhance the explosion effect. Some steel cylinder shells broke along the detonation wave collision line, and some only formed pits on the surface. He believed that in the region with the characteristic thickness of the inert layer, the collision of the detonation wave would lead to the increase of the tensile stress and the destruction of the material. In addition, if the collision on the metal surface did not occur between the detonation waves, but occurred between shock waves of the same intensity, no indentations would form. All experiments have shown that the dent was formed by the interaction of the chemical peaks of the detonation wave, where the pressure was 1.5 to 2 times that of the adjacent region, and the width of the dent was similar to the width of the chemical reaction zone.

Khishchenko[10] studied the detonation collision based on the DT fuel layer. They believed that the efficiency of the DT reaction (symmetric surface reflection) after the collision of the blast wave depended on the spatial uniformity of the thermodynamic function between the reflected detonation wavefronts. In the target ignition model, two plane-propagating plane detonation waves appeared in the fuel. After the collision, a flow occurred at the reflection front. The velocity distribution of the flow was current on the x-axis of the space coordinate, and the thermodynamic function depended on the x-axis. The efficiency of the fusion reaction after collision depended largely on the spatial homogeneity of the combustion rate, and the integral of the Lagrangian particle trajectory determined the magnitude of the local fuel consumption factor.

Miao Yusong[11] used the material point method to establish a three-dimensional model, and numerically calculated the detonation wave collision test, and obtained the scattering process of the explosive and steel sheet, the collision process of the detonation wave, the stress and strain distribution propagating in the lead column. It provided a new method for detonation wave propagation, collision process analysis and explosive violent test. Both the simulation results and the test results showed that there was a high strain region superimposed by detonation waves at the center of the upper surface of the lead column after blasting.

In this paper, the superposition effect of detonation wave is taken as the research content, and the different responses of the metal plate affected by it are emphasized, and the fracture law[12] of the metal plate under the superposition of detonation waves is studied. In the related research content of metal plate fracture, most scholars have studied the quasi-static process of tensile and compressive stress of metal plates, but less on the fracture of metal plates under the combined effects of explosive loads, especially detonation waves interaction[13], [14]. In the 1970s, the plastic dynamic response of the plate structure under blast loading was studied. At that time, the research focused more on the plastic deformation of the plate, and summarized the variation of physical quantities such as deflection and tensile yield stress[15], [16]. Zhou Rui et al.[17] studied the fracture effect of strip explosive load on metal rectangular plate, and summarized the fracture criterion of metal plate based on impulse. But the research content was relatively simple, and the fracture law of metal plates with different thicknesses was not summarized. Hua Zili et al.[18] based on the structural deflection estimation method to theoretically analyze the large deformation of the plate structure, could give an accurate estimation of the deflection of the plate deformation combined with the knowledge of plastic dynamics. But its research purpose was applied to the engineering approximation method. It did not give the fracture law of the plate under explosive load.

Aiming at the above problems, this paper studies the response of the metal plate under the superposition of detonation waves generated by two points of detonation. Regularity conclusions were obtained by two sets of explosion experiments. First, the magnitude of the superimposed pressure of the detonation wave affects the depth of the cuts produced on the surface of the metal plate. Secondly, the fracture of the metal plate under the action of the superposition of detonation waves has a regularity, which is related to the material and thickness of the plate. In the discussion part, firstly, some characteristics of the fracture results of the metal plate were analyzed, and the fracture criterion based on the threshold impulsive velocity was obtained by using the analysis method based on the micro-element fracture theory. It has been verified that this criterion is in good agreement with the experimental and simulation results.

Section snippets

Experiment set-up

As shown in the Fig. 3, the test device is mainly composed of an aluminum two-point detonation network, a TNT cylinder, a circular steel plate and an outer shell. Fig. 3 is a schematic view of the experiment device. The detonator sleeve, the aluminum detonation network, the TNT cylinder, the outer shell and the circular steel plate are placed in a concentric manner from top to bottom. The the aluminum detonation network has a diameter of 99 mm and a thickness of 10 mm. The center of the circle

Further experiments

The material of metal plate, thickness and other factors will affect its response under explosive load. Metal plates of different conditions may have different regular responses under the same explosive load. Therefore, in this group of experiments, the distance between two detonation points is fixed to 30 mm, and the fracture law is observed by changing the bottom metal plates.

In the first set of experiments, the thickness of the steel plate was 5 mm, and the steel plate formed a different

Simulation analysis of three different responses

In the experiments, there were three different responses, dent, partial fracture and complete fracture on the metal plate. In order to analyze the response of the metal plate under the superimposed load of the detonation wave more accurately and intuitively, a simulation model as shown in Fig. 7 was established[20], [21], [22].

The air, the main charge were meshed with the Euler grid, and the metal plate was meshed with the Lagrangian grid. The size, material of the metal plates and detonation

Conclusion

1.The experimental study on the response of the metal plate under the superposition of detonation waves was carried out by using two-point synchronous detonation network. The results showed that the metal plates would produce three kinds of response: indentation, partial fracture and complete fracture, which were related to the thickness and materials of metal plates.

2.The simulation calculation of the experimental conditions was carried out based on ALE algorithm and fluidsolid coupling mode.

Declaration of Competing Interest

We declared that we have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

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