Dongxiao Fu， Rui Zhang， Hu Liu， Fang Li， Zhenhua Du and Hongliang Ma

（1. School of Electrical Engineering, Xi’an Jiaotong University, Xi’an 710049, China；2. State Key Laboratory of Applied Physics-Chemistry, Shaanxi Applied Physics-Chemistry Research Institute,Xi’an 710061, China）

Abstract: Aiming to know the requirement of penetrating the munition semiconductor bridge detonator under the impact overload environment, the impact overload simulation device and the structural finite element software ANSYS/AUTODYN are used to study the variation of the axial dimension, charge and the chip gap of the semiconductor bridge detonator under the impact overload environment. The typical semiconductor bridge detonator is affected by the acceleration, and the strain increases with the increase of the acceleration. The semiconductor bridge detonator shows axial compression, in which the size becomes smaller, and the structural deformation occurs at the output end of the semiconductor bridge detonator. The typical semiconductor bridge detonator is elastically deformed when the acceleration is less than 40 000g. When the acceleration is more than 40 000g, the semiconductor bridge detonator housing is plastically deformed. The gap between the drug column and the chip is divided into three stages with the increase of the acceleration. Initially,with the increase of the acceleration, the gap rises rapidly until the acceleration reaches 43 000g,and when the gap reaches the maximum, the gap decreases rapidly with the increase of the acceleration. When the acceleration reaches 57 000g, the gap tends to be 0 μm in the initial state, and then the gap does not change with the acceleration to keep tending to 0 μm.

Key words: impact overload；semiconductor bridge；detonator；structural damage

The penetration ammunition needs to withstand high-acceleration impact overloads during typical target penetration processes. The detonator used to detonate the warhead is also subjected to impact overload, which requires the detonator to have the capability of resisting high acceleration shock overload[1]. The semiconductor bridge detonator has a right ignition consistency,and it has the ability to prevent radio frequency,the antistatic and stray current is secure, and its synchronism is high[2]. At the same time, it is easy to integrate, making the semiconductor bridge detonator widely used in the ignition device of weapon equipment, and the detonating device[3].

The application of semiconductor bridge detonator in penetrating ammunition has problems such as unclear structural failure law and then no basis for the design. Therefore, we use an air gun combined with a separate Hopkinson pressure bar[4]to carry out impact overload tests on the SCB detonator samples to study the axial dimension variation regularly of the detonator after impact overloads. The variation law of semiconductor bridge detonator column and chip is obtained by using the structural finite element software ANSYS/AUTODYN. The structural damage characteristics of the SCB detonator during impact overloads are obtained to lay the foundation for improving the anti-high acceleration shock overload performance of SCB detonators[5?8].

1 Impact Overload Causes the Axial Dimension Change of the Semiconductor Bridge Detonator

The free Hopkinson pressure bar, the air cannon, and the split Hopkinson pressure bar device are used to simulate the overload of a typical semiconductor bridge detonator[1], and the equivalent acceleration overload method is used to accelerate the equivalent of the split Hopkinson pressure bar. The variation law of acceleration and strain is obtained.

The outer diameter of a typical semiconductor bridge detonator is ?7.0 mm×9.8 mm, and the shell wall thickness is 0.3 mm. Semiconductor bridge detonators are placed in the axial direction. The detonator axis is in the same direction as the movement direction. Under each impact overload condition, 8 detonators are used for testing. The data obtained are average values.

Tab. 1 shows the acceleration and strain change test data, in which the serial numbers 1-4 use the free-style Hopkinson pressure bar for the overload test, the numbers 5-11 use the air gun test for the overload test, and the serial numbers 12-15 use the separate Hopkinson pressure bar for the overload test. After the test, it is transformed to obtain acceleration values correspond-ing to different bullet speeds.

Tab. 1 Acceleration and strain change test data

It can be observed in Fig. 1 that the typical semiconductor bridge detonator is affected by the acceleration. The strain increases with the increase of the acceleration, the semiconductor bridge detonator axial compression appears, the size becomes smaller, and the structural deformation occurs at the output end of the semiconductor bridge detonator (Fig. 2).

Fig. 1 Variation of axial strain with acceleration

Fig. 2 Sample of the semiconductor bridge detonator after the test

When the acceleration is less than 4×104g,the axial strain of the semiconductor bridge detonator is within 0.3%, indicating that the typical semiconductor bridge detonator only undergoes elastic deformation. When the acceleration is more than 4×104g, the semiconductor bridge detonator housing is plastically deformed.

2 Impact Overload Causes the Variation of the Gap Between the Semiconductor Bridge Detonator and the Chip

After subjected to an impact overload, the internal charge of the semiconductor bridge detonator is inevitably subjected to inertia and relative displacements of the semiconductor bridge chip. The relationship between the semiconductor bridge detonator and the chip gap after impact overload is studied by the following numerical simulation(Fig. 3).

Fig. 3 Acceleration less than 5×104g, axial strain law

The finite element software ANSYS /AUTODYN is used to build a typical semiconductor bridge detonator finite element model.The finite element simulation is supposed to achieve high calculation accuracy in less time.Considering the symmetry of the experimental setup, some simplifications were made for the finite element model. The two-dimensional analysis is conducted using an axisymmetric unit. The finite element model includes an electrode plug, a cap, a charge, a insulation ring and a semiconductor bridge chip. Its two-dimensional axisymmetric model and mesh division are shown in Fig. 4. The parameters of the semiconductor bridge detonator in the numerical simulation calculation model are shown in Tab. 2.

Fig. 4 2D axisymmetric model and meshing

In the simulation, the deformation of the semiconductor bridge detonator caused by the impact overload is simulated. Only the yielding of the components of the semiconductor bridge detonator is considered here, and the safety of the detonation of the semiconductor bridge detonator during the deformation process is not considered.

The simulation results are shown in Tab. 3.

Tab. 2 State equations and strength models of various components of semiconductor bridge detonators

Tab. 3 Strain and charge-chip gap simulation results under various accelerations

The simulation results of Tab. 3 are compared with the test results of Tab. 1. As shown in Fig. 5, the simulation results agree well with the experimental results, indicating that the simulation calculations are consistent with the actual test strain results.

Fig. 5 Simulation of acceleration and strain relationship and comparison of test results

During the impact overload process, the axial strain is divided into three stages according to the acceleration increase strain. In the initial elastic phase, the axial strain increases slowly with the increase of the acceleration, and the axial strain is within 0.20%. When the acceleration reaches 4×104g, the axial strain reaches 0.25%.At this time, it enters the plastic deformation stage. At this stage, the axial strain increases rapidly with the increase of acceleration. When the acceleration reaches 6×104g, the axial strain reaches 1.84%. After the axial strain increases with the acceleration, the axial strain increases slowly. At this time, the acceleration has a linear relationship with the strain, as shown in Fig. 6.

Fig. 6 Acceleration and strain, gap change pattern

The charge and chip gap is divided into three stages with the increase of acceleration. Initially, with the increase of acceleration, the gap rises rapidly until the acceleration reaches 4.3×104g, and the gap reaches the maximum,which is 98.26 μm. Then, as the acceleration increases, the gap decreases rapidly. When the acceleration reaches 5.7×104g, the gap tends to be 0 μm in the initial state. After that, the gap does not change with the acceleration and keeps tending to 0 μm. Tab. 4 shows the damage laws and mechanisms of typical semiconductor bridge detonators under different accelerations.

Tab. 4 Damage law and mechanism under different accelerations

3 Conclusions

(1) The variation of the axial dimension of a typical semiconductor bridge detonator under different impact overloads is obtained. When the acceleration is less than 4×104g, the axial strain of the semiconductor bridge detonator is within 0.3%, and the typical semiconductor bridge detonator only undergoes elastic deformation. When the acceleration is more than 4×104g, the semiconductor bridge detonator housing is plastically deformed.

(2) Charge and chip gap are divided into three stages with the increase of acceleration. Initially, with the increase of acceleration, the gap rises rapidly until the acceleration reaches 4.3×104g, there the gap reaches the maximum,and then when the acceleration increases, the gap rapidly decreasing, when the acceleration reaches 5.7×104g, the gap tends to be 0 μm in the initial state, and then the gap does not change with acceleration to keep tending to 0 μm.

(3) The results of this paper can provide essential data support for anti-impact overload semiconductor bridge detonator design, and improve the reliability of semiconductor bridge detonator against impact overload.