Experimental and Simulation Research of Belt Extrusion Process Based on Simplified Chip Model

. The projectile extrusion process is an extremely important part of the initial trajectory of the artillery launch. The differentiation of the extrusion process brings about the stability problem of the extrusion process, which directly affects the stability and safety of the artillery, ballistic and projectile launching process. sex. Since the simplified chip intrusion resistance model does not pay attention to the projectile movement process and the formation process of the elastic belt groove, and only studies the change law of the intrusion resistance, the model is relatively simple and the parameters are easy to determine. In this paper, a quasi-static test device for the extrusion process of the elastic belt is established. The model is calibrated with the simplified chip resistance model with the intrusion process. Finally, the model is used to calculate the resistance along the process of a large-caliber howitzer projectile extrusion process, and it is compared with the embedded resistance test results of a large-caliber howitzer., the results show that in the whole process of extrusion, the relative error between the calculated value of the total extrusion resistance and the experimental value is basically below 10%, and the maximum relative error is 10.98%, which verifies the accuracy of the model.


Introduction
The squeeze-in period is defined as the time from the start of projectile movement until the tape is fully embedded in the rifling [1]. The squeeze-in process is an extremely important part of the launch trajectory of the artillery. In the process of artillery firing, there are a large number of problems related to the extrusion process, such as projectile initial velocity error, projectile jamming reliability and artillery barrel life. With the development of high-performance launch and new principle technology, the impact of the projectile extrusion process on the entire launch performance has become more and more prominent [2]. For example, due to the increasingly complex firing conditions and requirements of highperformance artillery, the differences in the projectile extrusion process due to different loading parameters will eventually significantly affect the muzzle velocity stability and even cause abnormal chamber pressure; There is a dynamic overlap between the projectile jamming and the extrusion process in new launching principles and technologies such as technology, which makes the extrusion process more complicated. Because the time and stroke of the extrusion process are very short, it is difficult to measure by experiments. Therefore, the classical internal ballistics usually adopts the assumption that the projectile starts to move when the extrusion pressure is reached, and ignores the extrusion process of the elastic belt [3]. However, the research on the extrusion process of the ammunition belt is very important. It is to define the wear relationship between the ammunition belt and the inner bore and the rifling, to check the matching degree of the ammunition belt and the sloped bore, to explore the mechanism of the ballistic peak in the artillery and related to the life of the artillery. The preliminary work on the problems such as the clipping of the bullet belt is indispensable, and it also has an important impact on the shooting density [4]. 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 grooving process [6], and then studies 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 three-dimensional simulation software to calculate the intrusion resistance, the modeling process is complicated, the number of parameters is large and difficult to accurately determine, and the accuracy of the calculation results is difficult to grasp. In view of the above problems, this paper establishes a quasi-static test device for the extrusion process of the elastic belt. Data, the model calibration was carried out on the simplified chip resistance model of the belt extrusion process. The calibration model was used to calculate the resistance along the process of a largecaliber howitzer projectile extrusion process, and compared with the embedded resistance test results of a large-caliber howitzer. By comparison, the results show that in the whole process of extrusion, the relative error between the calculated value of the total extrusion resistance and the experimental value is basically below 10%, and the maximum relative error is 10.98%, which verifies the accuracy of the model.

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 Figure 1 Standard belt diagram

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.

Figure 2
Assembly drawing of the belt and the simulated projectile 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 is a comparison of the typical extrusion resistance curves of the three elastic belt materials. It can be seen from Figure 5 that the extrusion resistance curve of the standard brass H96 elastic belt is obviously doublepeaked, 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 doublepeaked. 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 1010.   Engraving distance(mm) 3 0°2 0° Figure.8 Comparison of intrusion resistance curves of belts with different forward inclination angles It can be seen from Figure 6 that the peak value of the extrusion curve of the first top surface width of 6mm lags behind that of the 4mm elastic belt, which is in line with the structural characteristics of the elastic belt, and the extrusion resistance of the elastic belt with a first top surface width of 6mm The peak value is higher, which is mainly because the width of the first top surface of the elastic band increases, the width of the material chip becomes larger, and the contact area between the elastic band and the rifling increases, so the two peaks of the extrusion resistance curve increase; from Figure 7, it can be seen that It can be seen that there is little difference in the peak resistance of the elastic band with different chip flute widths. The difference is that the second peak resistance of the 3.5mm chip flute width lags behind that of 2.5mm, which is also caused by the different structure of the elastic band; from the figure 8 It can be seen that the peaks of the two resistance curves of different belt forward inclination angles are quite different. The peak value of the resistance curve of the elastic belt with a forward inclination angle of 20° is about 5KN higher than that of the elastic belt with a 30° angle. This is mainly due to the The width of the elastic belt with a forward inclination angle of 20° is larger, and the contact area with the barrel is larger, so the peak resistance value is also larger. It can be seen from Fig. 6-Fig. 8 that when the structural parameters of the elastic band are different, the intrusion resistance curves show an obvious double-peak shape.

Research on simplified chip extrusion resistance model
According to the structural parameters of a small-caliber barrel, projectile, and elastic belt, as well as the material parameters of brass H96 (see Table 3-Table 4), the contact area between the barrel and the elastic belt in different extrusion processes can be obtained. According to the mathematical model of the contact stress, the contact stress acting on the contact area can be obtained. Based on the quasi-static intrusion test data of the elastic belt obtained by the test, the prediction model of the intrusion resistance in the simplified chip process is obtained by multi-parameter fitting: 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 extrusion stage, the formula (1) can be further simplified as: 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 F , the second slope resistance 2 F and the cylindrical section

Research on predicition squeeze-in resistance of a large-caliber howitzer
In order to verify the accuracy of the established simplified chip extrusion resistance model, a large-caliber howitzer was taken as the research object, and the extrusion resistance of the howitzer projectile extrusion process was calculated. The contact area and contact resistance results calculated according to the structural parameters of the howitzer barrel and the projectile are compared with the test results as shown in Table 5. Test Results Calculated R (b) The comparison between the test value and the calculated value of the intrusion resistance Figure 9. Comparison of calculation results and test results of a large-caliber howitzer during the extrusion process

Conclusion
In this paper, a quasi-static test device for the extrusion process of the elastic belt is established. The simplified chip resistance model of the belt extrusion process is calibrated. The recalibrated model is used to calculate the resistance along the path of a large-caliber howitzer projectile extrusion process, and the calculation results are compared with the test results of the embedded resistance. draw the following conclusions: (1) The extrusion resistance curves of different materials are quite different. The extrusion resistance curve of the standard brass H96 elastic belt is obviously doublepeaked, and the peak resistance value when passing through the second top surface is higher than the peak value of the first top surface; The extrusion resistance curve of the duralumin 2A-12 elastic belt has a single peak shape. When passing through the first top surface, the resistance curve has an inflection point; the extrusion resistance curve of the nylon Nylon1010 elastic belt has a double peak shape, and the first peak is higher than the second peak. peak.
(2) The shape of the elastic belts with different structural parameters is not very different after extrusion, the shape of the elastic belt grooves is relatively regular, and the extrusion resistance curves show an obvious double-peak shape, and the extrusion resistance curve of the elastic belt with different structural parameters peak The difference is mainly caused by the structure size.
(3) Under the same working conditions, the extrusion resistance curve is consistent during the extrusion process of the elastic belt, and the peak consistency of the extrusion resistance is better, but the extrusion resistance curves under different working conditions (such as different structural parameters) are quite different. . (4) Using the simplified chip extrusion resistance model established in this paper, in the whole extrusion process, the relative error between the calculated value of the total extrusion resistance and the test value is basically below 10%, and the maximum relative error is 10.98%. the accuracy of the model.