The missile or the carrier rocket stage or the head body is connected by bolts. When separating, the bolts are unlocked by the explosive action of the pyrotechnics to complete the separation of the stages or heads of the missile. The pyrotechnic device releases the explosive energy instantaneously when the unlocking and separating operations are realized, resulting in the release of the strain energy generated by the installation of the pyrotechnic device and the collision between the structural components. The energy instantaneously acts on the separation structure to generate a transient explosion separation shock response, forming an explosion separation impact environment [1-2]. Explosive separation shock as a complex oscillating type impact, the main features are [3-4]: 1 short duration; 2 high acceleration amplitude, but small speed and displacement; 3 high frequency, wide frequency band. A large number of facts show that the explosion separation impact environment has a strong destructive effect on the spacecraft and its electronic system, resulting in spacecraft hardware failure [5]. Therefore, the ground test simulation of the explosion separation impact environment has become the focus of research.
For the simulation test of the ground pyrotechnic device for the explosion separation impact environment, the suspension method is generally adopted, as shown in Figure 1. The upper and lower parts are separated by bolts. After the bolts are unlocked, the lower parts are separated by gravity and separated from the separated upper parts. For ground-based fire-fighting device simulation tests, there are two related test procedures in GJB150.27-2009 [6] and MIL STD-210F [4], that is, simulation with real configuration, simulation with analog or approximate configuration. For the full-scale test, it is expensive to use the full-true configuration test, and may not be able to be carried out under certain restrictions. Therefore, the partial real part approximate configuration test is generally used, which may cause the difference between the pre-tightening force of the connecting upper and lower explosive bolts and the actual situation. The pre-tightening force of the blast bolt is determined by the bolt mounting torque and the quality of the separated lower part. Therefore, it is necessary to analyze its impact on the explosion separation impact environment so that it needs to be changed during the test design.
In [7], the pre-tightening force of the belt in the separation of the star and arrow, the charge of the separation device and the impact response are tested. In this paper, the source of pre-tightening force is generated for the explosion bolts in the interstage or the head body, that is, the tightening torque is installed and the weight of the lower part is separated. The influence of the impact on the explosion separation shock is analyzed by numerical simulation and test, which provides reference for the explosion separation impact test and component design.
Numerical Analysis of a separation installation tightening torque in response to the impact of the explosion
In order to analyze the influence of bolt tightening torque on the impact response, it is convenient for numerical modeling and reducing the calculation scale. Considering the simple structure, the upper and lower separating parts are composed of two conical shells, and the conical shell is connected by explosive bolts. The calculation model is consistent with the literature [8]. As shown in Fig. 2, the upper and lower separating parts are made of aluminum alloy and connected by 6 uniform explosion bolts. The bolt, nut and outer casing material are alloy steel, and the shear pin material is copper. It is modeled by ANSYS/LS DYNA, and the 1/12 finite element model is used for calculation according to the symmetry. In order to apply the pre-tightening force generated by the tightening torque, an axial constraint is applied at the contact between the outer casing of the explosion bolt and the lower part of the cone shell, and a pulling force is slowly applied at the tail end of the bolt (in the case of not causing a significant stress wave effect), when the preload force peak is reached. Suddenly released, the simulated explosion bolt is unlocked. When the tension is applied, the time domain distribution is a triangle, which increases linearly from 0 to a certain value within 2 ms and then mutates to zero. In order to investigate the effects of different tightening torques, it is desirable to calculate the state of the four different tightening torques (20 N·m, 40 N·m, 80 N·m, 120 N·m). In the numerical calculation, only the influence of the tightening torque is considered, and the impact of the explosive explosion, the impact of the bolt separation and the separation of the gravity of the lower part is not considered.
According to the calculation results, the time-domain acceleration peaks under four tightening moments are attenuated as the distance from the explosion bolt increases. See Figure 3. The selected 3 feature points are located on the same busbar of the separated upper part, and the bolts are 2cm, 13cm, and 61cm respectively. The peak value of the analysis is the axial (X-direction) response peak. It can be seen from Fig. 3 that as the distance increases, the acceleration peak shows a tendency to decay, and the attenuation trend gradually changes from violent to moderate. The analysis of the variation of the three characteristic points with the preload force is shown in Fig. 4. According to the literature [9], according to the impact environment intensity and spectral composition, the explosion separation impact environment is divided into near, medium and far field regions. For most point sources, the near field region is within 3 cm from the impact source, and the midfield region is from the impact source 3 ~15cm, the far field area is more than 15cm away from the impact source. 3 feature points are located in the near, middle and far field areas. From the results of 3 feature points, the peak of acceleration increases linearly with the increase of pre-tightening force; the degree of increase of near, medium and far fields is inconsistent, and each has its own difference; as the distance increases, its increasing slope decreases, the near-field slope is the largest, and the far-field is the smallest. That is, the near field response is more sensitive to tightening torque.
2 tightening torque, Experimental Isolation of the change in weight affect the response member
The test piece has a complicated structure, and the separated upper and lower parts are connected by the explosion bolt (Fig. 1). At the same time, the ignition and explosion bolts start the acquisition system to collect the measurement points. According to the influence of the installation tightening torque, the test considers the two torques of 40N·m and 20N·m according to the actual situation; for the influence of the weight of the separated lower part, consider adding the additional weight to change the weight of the separated lower part, that is, separating the lower part itself by 42kg without adding weight An additional 56 kg weight was added and the weight change was 1.3 times. The test is compared with the axial direction (X direction) and the lateral direction (Y-direction acceleration response and shock response spectrum (SRS) of a measuring point. The lateral distance of the measuring point from the center of the explosion bolt is about 13 cm. According to the literature [9], it can be considered The explosion separates the field area in the impact environment.
The comparison of the time domain curve and the shock response spectrum of the two kinds of tightening torque acceleration response is shown in Fig. 5 and Fig. 6. In the figure, "_X" and "_Y" respectively indicate the axial and lateral response of the measuring point acceleration, the same below. The impulse response spectrum of FIG. 6 is obtained by the time domain response data processing calculation of FIG. 5. 5(a) and 6(a) show the X-direction response of the measuring point, and FIGS. 5(b) and 6(b) show the Y-direction response of the measuring point. Although the tightening torque differs by a factor of two, and the time domain curve shows a difference in peak values ​​(X-direction phase difference 9.2%, Y-direction phase difference 29%), the response trend is consistent; in the frequency domain impulse response spectrum, the peak values ​​in the X-direction are 1.3 dB, The Y direction differs by 4.7 dB. According to the GJB150.27-2009 tolerance, the two-phase difference is within the tolerance range, and the two effects can be considered to be consistent. According to the numerical simulation results, the tightening torque is linear with the peak of the acceleration response in the range of 20~120N·m. Combined with the results of this test, the conclusion that the tightening torque changes within 1 time has little effect on the far-field response in the explosion separation shock is consistent with the numerical simulation results. The reason may be that among the three mechanisms for generating explosive separation shock loads, the load generated by the explosion of pyrotechnics is the main factor [8].
The comparison of the time domain curve and the impulse response spectrum of the unweighted and weighted acceleration response is shown in Fig. 7 and Fig. 8. According to the presence and absence of counterweight, the weight difference of the separated pieces is about 1 time. It can be seen from the two figures that the two states in the time domain or the frequency domain are basically the same, indicating that the weight difference of the separated lower parts is within 1 time, and the influence is small. In fact, the X-direction peaks differ by 0.4% in the time domain, and the Y-directions differ by 21.6%; in the frequency domain, the X-direction peaks differ by 1.6 dB, and the Y-direction peaks differ by 0.09 dB. In fact, regardless of the tightening torque or the weight of the separated lower part, it can be attributed to the bolt pre-tightening force. The relationship between tightening torque and bolt preload is Mt=0.2FD(1)
Where: Mt is the tightening torque; F is the bolt pre-tightening force; D is the bolt diameter. The pre-tightening force associated with the weight of the separated lower part can be converted into the weight of the separated lower part. In this test, the 40N·m torque is equivalent to applying 14286N tensile force to the bolt, and the 56Kg weight is applied to the bolt with a pulling force of 548.5N. For comparison, the weight effect is negligible. Consistent with the conclusion of the literature [10], that is, the simulation of the weight does not matter, and the separation can be better achieved.
It is known from the above analysis that the contribution of the lower part is smaller in the pre-tightening force of the explosive bolt, so the bolt tightening torque is superior in the pre-tightening force, and the weight of the separated lower part can be neglected; When the tensile force generated on the bolt is equivalent to the tensile force generated by the tightening torque, the comprehensive influence will need further analysis.
3 conclusions
Through the numerical simulation, test and the impact of the pre-tightening force of the explosive bolt on the impact of the explosion separation shock, the impact of the tightening torque of the explosive bolt and the weight change of the separated lower part on the impact response, the conclusions are as follows:
(1) The tightening torque of the explosive bolt has a linear relationship with the peak value of the acceleration response. The tightening torque has a small influence on the far field response of the explosion separation shock within the range of 1 time. In the actual working range, the tightening torque changes much less than 1 time. Can be ignored.
(2) The quality of the separated lower part is smaller than the bolt preload force in the range of 1 times, and the far field influence in the explosion separation impact environment can be ignored.
(3) The installation torque of the explosive bolts has a small influence on the medium- and far-field impact response within a range of 1 time, and can be applied fuzzy when the loading is difficult; the quality can be ignored when designing the separation of the lower parts.
references
[1] Zhang Xiaoda, Xia Yilin. Standard Research on Explosive Separation Impact Test Method[J]. Aerospace Standardization, 2002(6): 1-5.
[ 2 ] Zhang Jianhua. Overview of Explosive Impact Environment Technology for Aerospace Products[J]. Missile and Space Vehicle Technology, 2005(3): 30-36.
[3] NASA technical standard, Pyroshock testcriteria[s]. NASA STD 9003. NASA, 1999.
[4] Department of defense test method standard. Environmental engineering consideration sand laboratory tests [S]. MIL STD 810F. Department of Defense, USA. 2002: 517. 1-517.
[ 5 ] Moening CJ. Views of the world pyrotechnicshock [J]. S&V Bul, 1986, 56(3): 3-7.
[6] GJB150. 27 2009, Explosive Separation Impact Test [S].
[7] Han Xiaojian, Jiao Anchao, Wang Rui. Impact Test and Data Analysis of Low Impact Device with Tape[J]. Spacecraft Environmental Engineering, 2007, 24(5): 318-321.
[8] Wang Junping, Mao Yongjian, Huang Hanjun. Numerical Simulation of Impact Mechanism of Point Fire Separation Device[J]. JOURNAL OF VIBRATION AND SHOCK, 2013, 32(2): 9-13.
[9] Jin Yushu, Spacecraft Explosion Impact Environment and Its Simulation Test Technology[J]. Environmental Technology, 1993(3): 1-12.
[ 10 ] Pan Ruilin, Wang Yubing. Space System Explosion Separation Impact Data (Volume I), 1975(2): 25-26.
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