The use of pyrodevices in the aerospace industry has been increasing because of their ability to implement separation missions with a small weight, for example, space launchers, spacecrafts, and missiles. During operation, pyrodevices generate pyroshock, which causes failures of electronic devices. Recently, a pyroshock simulation method using laser shock has been developed to evaluate the risk of pyroshock before flight mission. However, depending on the structure, the laser shock showed some difficulty simulating pyroshock in the low-frequency regime accompanying vibration. Therefore, in this study, we developed a hybrid method of numerical modal analysis and laser shock-based experimental simulation to visualize the pyroshock propagation in all the relevant frequency regimes. For the proof of concept of the proposed method, we performed experiments of explosive bolt-induced shock and pyrolock-induced shock in the open-box-type tension joint and compared the hybrid simulation results with actual pyroshock. From the results, we obtained the simulated time-domain signal with an averaged peak-to-peak acceleration difference (PAD) of 11.2% and the shock response spectrum (SRS) with an averaged mean acceleration difference (MAD) of 28.5%. In addition, we were able to visualize the simulation results in the temporal and spectral domains to compare the pyroshock induced by each pyrodevice. A comparison of the simulations showed that the pyrolock had an impulse level of 1/12 compared to the explosion bolt. In particular, it was confirmed that the pyrolock-induced shock at the near field can cause damage to the electronic equipment despite a smaller impulse than that of the explosive bolt-induced shock. The hybrid method developed in this paper demonstrates that it is possible to simulate pyroshock for all the frequency regimes in complex specimens and to evaluate the risk in the time and frequency domain.
Pyrodevices separate a substructure from a main structure via an explosion. Pyrodevices are widely used in the aerospace field because they have the advantages of enabling a separation mission with low weight and small volume [
Pyroshock is divided into point-source pyroshock, linear-source pyroshock, and combined-source pyroshock, depending on the type of the pyrodevice. In addition, pyroshock is divided into three fields according to the magnitude and frequency of the response [
Pyroshock environmental categories: (a) IEST-RP-DTE032 and MIL-STD-810G [
Various simulation techniques have been developed to study pyroshock. Although there have been studies to simulate pyroshock using mechanical shocks, they all have limitations in that they can only be simulated for point-source pyroshock [
To overcome these limitations described above, we developed a hybrid method of modal analysis and laser shock scanning to simulate the pyroshock over the whole frequency regime. In the far field, with low-frequency components less than 3 kHz, because the finite element analysis verified the accurate simulation performance [
The hybrid method developed in this study proves that the pyroshock can be simulated in a complex structure, such as an open-box-type tension joint; thus, the method can be used to evaluate the risk of pyroshock in the temporal and spectral domains.
Figure
Flow chart of the hybrid method of FEM-based modal analysis and laser shock scanning-based simulation (PWPI: pyroshock wave propagation imaging; SRSI: shock response spectral imaging).
A 1/2-inch explosive bolt (Hanwha Corporation), shown in Figure
(a) 1/2-inch explosive bolt, (b) 1/2-inch pyrolock, and (c) measurement setup of pyroshock on the open-box-type tension joint.
Data acquisition condition of pyroshock on the open-box-type tension joint.
Shock source | CF |
|
Filter (kHz) | Number of samples | CFmr (mm/s/V) |
|
Sensing point coordinate |
---|---|---|---|---|---|---|---|
Pyroshock | CF1 = 1.42 |
1 | 0.1∼100 | 30,000 | 1,000 |
|
Point 1–(145, 60) |
Through the pyroshock measurement process, we can observe the characteristics of the pyroshock. However, the point measurement of the actual pyroshock at limited points is not sufficient to understand and analyze the pyroshock that is propagated over the structure. To visualize the propagation of pyroshock in the full field over the structure, we simulate pyroshock using laser shock. The same structure used in the pyroshock measurement was prepared to obtain the laser shock signals. Next, PZT sensors were installed in place of the pyrodevice, as shown in Figure
Laser scanning measurement setup for simulation of pyroshock on the open-box-type tension joint.
Measurement conditions of laser scanning for simulation of pyroshock on the open-box-type tension joint.
Shock source |
|
Filter (kHz) | Number of samples | PRF (Hz) | Scan area (mm) |
---|---|---|---|---|---|
Laser shock | 1 | 0.1∼100 | 8,000 | 50 | Width = 152 |
Because the PZT sensor used to acquire laser shock scanning data is a contact type and broadband sensor of a central frequency of 200 kHz and a bandwidth of 1.2 MHz, the sensitivity differs, depending on the frequency range. However, the PZT has poor sensitivity in the subkilohertz regime. The pyroshock simulation requires shock signal acquisition over a very wide frequency range, and the laser shock-capturing sensor requires very high sensitivity; however, it is difficult to find such a wide-range PZT sensor covering the whole pyroshock analysis range with high sensitivities over the range. In addition, the LDV is not suitable for the simulation because it provides SNR insufficient for measuring laser shock signal. Therefore, we developed the hybrid method involving the finite element analysis method for the low-frequency pyroshock accompanying vibration and the laser scanning method in the high-frequency regime, utilizing the advantages of each of the two simulation methods. Figure
Modal analysis for simulation of pyroshock on the open-box-type tension joint: (a) FEM model, (b) modal analysis results, (c) trained modal analysis data, (d) laser shock data, and (e) reference data.
Modal analysis condition for pyroshock on the open-box-type tension joint.
FEA software | Young’s modulus ( |
Density ( |
Poisson’s ratio | Natural frequency (Hz) | Training point |
---|---|---|---|---|---|
COMSOL | 193 | 8,000 | 0.3 | 1131-first mode |
Point 3–(60, 15) |
Using only two sets of pyroshock data, which were measured at point 1 and point 3, a 1/2-inch explosive bolt-induced pyroshock simulation was performed based on iterative signal decomposition and synthesis. Further information on the iterative signal decomposition and synthesis method can be found in reference [
Simulation results of the 1/2-inch explosive bolt-induced shock at training points: (a) Point 1 and (b) Point 3.
1/2-inch explosive bolt-induced pyroshock propagation evaluation on the open-box-type tension joint: (a) PWPI at 300
Simulation results of 1/2 inch explosive bolt-induced shock at the verification point.
Using only two sets of pyroshock data, which were measured at point 1 and point 3, a 1/2-inch explosive bolt-induced pyroshock simulation was performed based on iterative signal decomposition and synthesis. Figure
Simulation results of 1/2 inch pyrolock-induced shock at training points: (a) Point 1 and (b) Point 3.
1/2-inch pyrolock-induced shock propagation evaluation on the open-box-type tension joint: (a) PWPI at 300
Simulation results of 1/2 inch pyrolock-induced shock at the verification point.
Table
Comparison of the peak-to-peak acceleration between the explosive bolt and the pyrolock.
Peak-to-peak acceleration (g) | |||
---|---|---|---|
Point 1 | Point 2 | Point 3 | |
Explosive bolt | 8,158 | 14,724 | 17,797 |
Pyrolock | 683 | 3,393 | 1,352 |
Simulation similarity result between the real pyroshock and the simulated pyroshock for each experiment.
Training point | Verification point | |||
---|---|---|---|---|
|
|
|
|
|
Explosive bolt | 11.57 | 28.39 | 4.87 | 31.92 |
Pyrolock | 13.30 | 29.11 | 12.6 | 24.12 |
Comparison of the simulation performance between the conventional pyroshock simulation algorithm and the developed algorithm at the verification point: (a) hybrid method and (b) reference [
Evaluation of the pyroshock propagation in temporal and spectral domains on the open-box-type specimen: (a) simulation results of 1/2 inch explosive bolt-induced pyroshock (b) simulation results of 1/2 inch pyrolock-induced pyroshock.
In this study, we developed a hybrid method of modal analysis and laser shock scanning to visualize the pyroshock propagation accompanying vibration according to the boundary condition and to evaluate the risk of pyroshock. The hybrid method predicts the characteristics of pyroshock in the open-box tension joint by combining laser shock and modal analysis where the modal analysis was used to superimpose the low-frequency vibration to pyroshock propagation; Both laser shock and modal analysis results were superposed and reconstructed to the pyroshock using iterative signal decomposition and synthesis. The pyroshock propagation characteristics of the two different pyrodevices, an explosive bolt and a pyrolock, in the open-box-type tension joint were simulated using the developed hybrid simulation method. The time-domain signal was simulated with an averaged PAD of 11.2%, and the SRS was simulated with an averaged MAD of 28.5%. Considering that the repeatability of the pyroshock itself is approximately 20%, the simulation performance was found to be satisfactory. On the contrary, simulation results at point 1 show relatively higher MAD and PAD than the other two points. The reason was that the point 1 showed much more complex response than the other two points since it was the result of measurement near the stiffer boundary. In order to improve the simulation results in this boundary, further investigation of various wave modes seems necessary. We visualized the simulation results in the temporal and spectral domains to compare the pyroshock induced by each pyrodevice. A comparison of the simulations showed that the pyrolock has an impulse level 1/12 in magnitude compared to that of the explosion bolt. In particular, it was confirmed that, in the near field, the pyrolock-induced shock has a smaller impulse magnitude than the explosive bolt-induced shock. The hybrid method developed in this paper demonstrated that it is possible to simulate pyroshock over the entire frequency regime in complex specimens accompanying vibration and to evaluate the risk in time and frequency domains.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
This research was supported by the National Research Foundation of Korea (NRF) Grant funded by the Ministry of Science and ICT (NRF-2017R1A5A1015311) and by the research grant (PMD) of the Agency for Defense Development and Defense Acquisition Program Administration of the Korean government.