Experimental and Simulation Research on the Quasi-dynamic Extrusion Process of the Belt

. The extrusion process of the elastic belt is a process in which the elastic belt and the inner bore of the barrel undergo complex contact and collision, and the rifling gradually penetrates the elastic belt, so that the material of the elastic belt continues to fail and destroy. It has high instantaneous, strong impact, high temperature, high-speed change There is a big gap between the existing theory and the actual squeeze-in process, and it is urgent to carry out research work on this problem. In this paper, a quasi-dynamic test device for the extrusion process of the elastic belt is established. On this basis, the extrusion history of a small-caliber projectile under different belt materials, different extrusion speeds, different extrusion force loading rates and different chamber pressure loading rates is established. The experimental comparison research was carried out. Based on the experimental data, the model calibration was carried out for the simplified chip resistance model of the belt extrusion process, and the calibration model was used to test the extrusion resistance of a newly designed large-caliber and howitzer belt extrusion process. The prediction research is carried out, which provides a reference for the optimal design of internal ballistics and charges, projectiles and barrels, and the coupling design of projectiles, guns and charges in a system.


Introduction
When the artillery automatic weapon is fired, the projectile moves along the barrel under the action of high temperature and high pressure gunpowder and gas, and interacts with the barrel. The extrusion process of the elastic belt has an important impact on the internal ballistic cycle of the barrel weapon. In the classical internal ballistics, friction work and projectile rotational energy are often considered as secondary work and are included in the internal ballistic energy balance equation, and the extrusion process is ignored. When the pressure reaches the starting pressure, the projectile starts to move, which is quite different from the actual situation [1]. The extrusion process of the elastic belt is actually a process of contact and collision between the elastic belt and the inner bore of the barrel, the rifling gradually penetrates the elastic belt, and the material of the elastic belt continues to fail and destroy. The laws of advance resistance and elastic belt deformation are very complex [2][3][4]. Due to many difficulties, there is still a big gap between the existing research theories and the actual extrusion process, and it is urgent to carry out research work on the extrusion process. The importance and complexity of the extrusion process make it a hot and difficult point in the research of launch technology. Many scholars are devoted to the model research of the extrusion process of the elastic belt, such as the Johnson-Cook constitutive model [5]. With the help of three-dimensional simulation analysis software such as ABAQUS studies the large deformation of the elastic band, the plastic deformation flow process of the elastic band material, the shear failure process, and the groove formation process [6], and then study the projectile motion law, extrusion pressure, extrusion resistance change law. However, so far, there is no complete theory about the squeeze-in period in the ballistic literature at home and abroad, and scholars have not reached a consensus on the physical meaning of the squeeze-in pressure value, let alone a satisfactory squeeze-in resistance calculation. Methods [7][8][9]. With the help of 3D simulation software to calculate the intrusion resistance, the modeling process is complex, the number of parameters is large and difficult to determine, and the accuracy of the calculation results is difficult to grasp. In view of the above problems, this paper establishes a quasidynamic test device for the extrusion process of the elastic belt. Based on the experimental data, the simplified chip resistance model of the belt extrusion process was model calibrated, and the calibrated model was applied to the extrusion process of a newly designed large-caliber plus howitzer belt. The intrusion resistance is predicted and researched, which provides a reference for the optimal design of internal ballistics and charges, projectiles and barrels, and the coupling design of projectiles, guns and charges in a systematic way.

Tested Product
The tested items are elastic belts of different structure sizes and materials. The design drawings of standard elastic belts (1#, material brass H96, first top surface width 4mm, chip groove width 2.5mm, belt forward inclination angle 20°) and The physical map is shown in Figure 1, and the material properties of different material elastic belts are shown in Table 1.
(1) Design drawing of the elastic belt (2) Physical drawing of the elastic belt

Participating Products
The test items of this test bench are mainly simulated projectiles, truncated barrels and supports. Among them, the simulated projectile consists of a warhead, a tail and a simulated belt, as shown in Figure 2. When assembling, first put the elastic belt on the end of the warhead from the rear end, and then fasten the tail and the warhead through threads, and at the same time perform the axial positioning of the elastic belt, and then snap the simulated projectile into the rifling barrel as a whole. Since the warhead and the tail are separated and connected by threads, the elastic belts of different materials and different structural parameters can be replaced, and the influence of different material elastic belts and different elastic belt structure sizes on the intrusion resistance can be studied. The truncated barrel is designed according to the structure and size of a small diameter barrel, as shown in Figure 3. The truncated barrel includes a complete sloped bore portion, a rifling start portion and a part of a full rifling portion. When assembling, the simulated projectile is snapped into the truncated barrel as a whole (apply a preload of about 200N). During the squeeze-in test, the design length of the tail should ensure that the notching of the elastic belt is completed and that the elastic belt part of the simulated projectile can completely pass through the truncated barrel. The support body is made of gun steel.
Its function is to provide support for the shortening of the barrel during the extrusion process of the elastic belt, to ensure that the extrusion direction is along the axial direction of the barrel, and to provide a channel for simulating the movement of the projectile and play a soft recovery role. The whole test The physical drawing of the device is shown in Figure 4.

Power Loading Mechanism
The loading mechanism of the intrusion force is a computer-controlled universal testing machine, and its main parameters are: model: 105D; maximum test force: 100KN; displacement resolution: 0.025μm; test force resolution: 1/500000FS; sampling frequency 30HZ.

Test Plan
The experimental protocol is shown in Table 2.   Figure 5 shows the comparison of elastic belts of different materials before and after extrusion. It can be seen from Figure 5 that the elastic belt of nylon Nylon1010 only undergoes elastic deformation of the material before and after extrusion, and no chips are formed; while the duralumin 2A-12 material The hardness is relatively high. Although the chip deformation occurs, the chip material of the elastic belt is not adhered to the elastic belt and the simulated projectile. Soft, copper scraps accumulate in the chip slot after the extrusion is completed, and the copper hanging on the rifling is more serious. When the projectile passes through the fully-rifled barrel, there are obvious traces of copper hanging on the outer wall of the projectile circumference. This phenomenon can also be explained. , using the brass H96 material belt, when designing the charge, the copper remover should be used as the charge accessory.

Comparison of the Extrusion Process of Different Belt Materials
(1) Comparison before and after the brass H96 material belt is squeezed in (2) Comparison of before and after extrusion of duralumin 2A-12 material belt (3) Comparison of nylon Nylon1010 material belt before and after extrusion  Figure 6 is a comparison of the typical extrusion resistance curves of the three elastic belt materials. It can be seen from Figure 6 that the extrusion resistance curve of the standard brass H96 elastic belt is obviously bimodal, and the resistance peak value when passing through the second top surface Higher than the peak value of the first top surface; the extrusion resistance curve of the duralumin 2A-12 elastic belt is single-peaked, and the resistance curve has an inflection point when passing through the first top surface; the extrusion resistance curve of the nylon Nylon1010 elastic belt is double-peaked. And the first peak is higher than the second peak. It can be seen from the three extrusion resistance curves that the peak extrusion resistance is duralumin 2A-12>brass H96>nylon Nylon1010.

Comparison of Extrusion Resistance Curves at Different Extrusion Speeds
Set the extrusion speed to 2mm/s, 4mm/s, 6mm/s, and 8mm/s respectively. Figure 7 shows the comparison of the extrusion resistance curves at different extrusion speeds. It can be seen from Figure 7 that at different extrusion speeds The shape of the extrusion resistance curve is similar, and the peak value of the resistance curve is almost the same, and the difference is only in the completion time of extrusion.  Figure 9 shows the comparison of the intrusion resistance curves when the chamber pressure loading rate increases according to the law of 20MPa/s-40MPa/s respectively. The peak value of the extrusion resistance curve decreased from 37.5KN at 40MPa/s to 28KN at 20MPa/s, a decrease of about 25.3%, and with the decrease of the chamber pressure loading rate, the extrusion process of the elastic belt became more and more unstable, and the extrusion process became more and more unstable. The resistance curve shows obvious oscillation at 20MPa/s, which is consistent with the changing trend under different extrusion pressure loading rates.

Mathematical Model of Contact Stress
Two-dimensional deformation is described by the plastic theory equations: By solving these equations, the contact stress calculation model is obtained: The contact stress is described as follows for different body sections: (1) First slope: (2) Second slope : (3) After entering the cylindrical part of the barrel (IV area), the contact stress is constant, on the negative line, and on the positive line: According to the structural parameters of a small-caliber artillery barrel, projectile, and belt, as well as the material parameters of brass H96 (Table 3-Table 4), the contact area i S between the barrel and the belt can be obtained.
According to the contact area between the elastic belt and the inner bore of the barrel and the contact stress acting on the area, the following contact resistance model is obtained: Among them, BP F is the sum of the embedded resistance.
Assuming that the contact stress on the contact area between the elastic band and the barrel is uniform at the same slope, (10) can be further simplified as: The total embedded resistance is determined by the sum of the stroke resistance of each segment: BP When the insertion section is composed of a smooth groove, a rifling slope and a cylindrical section (of the rifling), the insertion resistance is the sum of three components: the first slope resistance 1

Research on predicition of squeeze-in resistance of a large-caliber howitzer
On the basis of simplifying the calibration of the intrusion model in the chip process, this model is used to study the intrusion resistance of a newly designed large-caliber and howitzer projectile in the intrusion process. The structural parameters and material properties used in the calculation are shown in Table 5. , the calculated contact area changes with the extrusion process are shown in Table 6, and the extrusion resistance and the extrusion component force with the extrusion process are shown in Table 7.     The calculation results of Table 6 and Table 7 are shown in Figure 10. It can be seen that the contact area continues to increase with the extrusion process. At the beginning of the extrusion process, the contact area increases rapidly, and then grows slowly until the end of the extrusion process. , the contact area almost no longer increases, indicating that the extrusion process is completed, and the elastic belts have been embedded in the rifling of the cylindrical part of the barrel; and the extrusion resistance also shows a similar change rule to the contact area, that is, in the early stage of extrusion, the total contact resistance is rapid. Growth, followed by slow growth, to the basic level of the late extrusion curve, indicating that the extrusion resistance is no longer increasing, and the entire belt has entered the cylindrical rifling area. It can also be seen from Figure 10 that the extrusion force F1 in the first groove area is established first, and it is also the main part of the total extrusion resistance in the early stage of extrusion, but when the elastic belt extrusion distance exceeds about 37mm (this distance It is about the sum of the height of the first groove and the width of the elastic belt), and it quickly decays to 0, indicating that the elastic belt has completely passed the first groove area; at this time, the second groove is squeezed into the resistance component F2 and the cylindrical rifling area is squeezed The advancing resistance component force F3 has been established, and the extrusion component force of the second slope bore area only exists in the range of about 20mm to 75mm of the extrusion process, that is, only at this stage, the second slope bore and the bullet have contact stress . The contact stress of the rifling in the cylindrical part of the barrel is established when the extrusion process reaches about 20mm, and it increases continuously with the extrusion process, indicating that the contact area between the elastic belt and the rifling continues to increase. When the extrusion process is completed, the extrusion process is completed. The resistance component F3 basically no longer increases. From the extrusion resistance curve of the entire projectile extrusion process, the bottom pressure converted by the maximum extrusion resistance is 4.81MPa, which is much

Conclusion
In this paper, a quasi-dynamic test device for the extrusion process of the elastic belt is established. On this basis, the extrusion history of a small-caliber projectile under different belt materials, different extrusion speeds, different extrusion force loading rates and different chamber pressure loading rates is established. The experimental comparison research was carried out. Based on the experimental data, the model calibration was carried out on the simplified chip resistance model of the belt intrusion process by using the multivariate parameter regression method. The process intrusion resistance curve was predicted and studied, and the following conclusions were obtained: (1) The material dynamic behavior of elastic belts of different materials is quite different during the extrusion process. The nylon Nylon1010 elastic belt only undergoes plastic deformation, while the duralumin 2A-12 elastic belt produces brittle chips, and the brass H96 elastic belt produces plasticity at the same time. Deformation, brittle chips and viscoplastic deformation, therefore, the phenomenon of copper hanging on the rifling is more serious.
(2) The shape of the intrusion resistance curve is similar at different intrusion speeds, and the peak value of the resistance curve is almost the same, the difference is only in the completion time of the intrusion; with the increase of the intrusion dynamic loading rate, the peak value of the intrusion resistance curve is slightly different. With the decrease of the loading rate of the extrusion force, the extrusion process of the elastic belt becomes more and more unstable, and the extrusion resistance curve shows obvious oscillation; with the increase of the loading rate of the chamber pressure, the peak value of the extrusion resistance curve The peak value of the extrusion resistance curve decreased from 37.5KN at 40MPa/s to 28KN at 20MPa/s, a decrease of about 25.3%, and with the decrease of the chamber pressure loading rate, the extrusion process of the elastic belt became more and more unstable. , the extrusion resistance curve shows obvious oscillation at 20MPa/s.
Under the same working conditions, the extrusion resistance curve is consistent during the extrusion process of the elastic belt, and the peak consistency of extrusion resistance is good, but under different working conditions (when the structural parameters and extrusion force loading methods are different) The resistance curves are quite different.
(4) From the extrusion resistance curve of the entire projectile extrusion process, the bottom pressure converted by the maximum extrusion resistance is 4.81MPa, which is much smaller than the starting pressure defined by the classical inner ballistics 20MPa.