Development and verification of a simulation test platform for aerospace pyrotechnic shock environment

In aerospace mechanical environments, pyroshock has garnered significant attention because of its high frequency, high amplitude, and transient broadband behavior. Conducting efficient ground-based pyroshock environment tolerance assessments for aerospace units and components is therefore imperative. To support such assessments, this paper proposes a tunable resonant fixture based on the principle of mechanical impact. This device utilizes a projectile to impact a specific resonant structure (e.g., a beam, plate, or shell) at high speed, thereby converting the impact kinetic energy into a broadband vibration response. By adjusting the structural modal parameters, it achieves envelope control over the target Shock Response Spectrum (SRS), enabling accurate simulation of aerospace pyroshock environments and analysis of product shock resistance.

Built upon classical gas dynamics and incorporating corrections for local corner resistance, variable cross-section losses, and virtual mass effects, an improved internal ballistic equation suitable for a horizontal L-shaped air gun was established. This equation provides a theoretical foundation for the experimental platform. A pyroshock environment simulation test platform was constructed, primarily consisting of an L-shaped air gun excitation device, a resonant plate assembly, test specimen fixtures and supports, and a measurement and control system. The storage chamber pressure is regulated by an automatic pressure regulation device. A pneumatic valve instantaneously releases compressed gas, propelling the projectile to the target speed. This impact on the resonant plate generates a specific shock effect. The resonant plate, leveraging its intrinsic modal characteristics, amplifies or spectrally shapes the shock, thereby establishing a pyroshock simulation environment for the test specimen. A finite element model was established based on the device structure to simulate chamber pressure and projectile velocity. In the context of air gun impact tests, the projectile’s velocity was measured using a high-speed camera. This measurement was then validated against both simulation results and theoretical calculations. Five key variables, including chamber pressure, buffer gasket thickness, projectile length, impact position, and connection method, were systematically studied to ascertain their influence on the SRS. A comparative test case was designed for each parameter type using the controlled variable method. SRS curves at characteristic locations were obtained through testing and compared with finite element simulation results, using simulation data for cross-validation of experimental conclusions.

The device is capable of releasing the projectile at a predetermined target speed. The maximum relative error observed between the measured velocity and the improved theoretical/simulation calculations was 4.57%. The maximum projectile velocity dispersion was observed in three tests, with an average result of 0.224 m/s at 0.6 MPa. In the validation tests of the pyroshock simulation platform, the maximum relative error for the peak value at the knee frequency in three repetitive shock tests was 2.11%. By increasing the chamber pressure, the overall energy level is elevated, while the characteristic frequencies remain largely unaffected. Increasing the thickness of the gasket has been shown to enhance high-frequency attenuation characteristics and mitigate local overloads on the plate system within a certain range. By increasing the projectile length and altering the impact position, it is evident that the participation of the plate system’s dominant modes is noticeably adjusted. This adjustment is accompanied by a high degree of sensitivity to the knee frequency and peak value. The alteration of the connection method and stiffness level results in a modification of the energy distribution among the structural paths, thereby exerting a substantial influence on the response amplitude distribution across the plate surface.

The theoretical calculation model, finite element model, and experimental results established in this paper demonstrate a high degree of agreement, thus achieving high-precision predictions of projectile velocity and the SRS of the resonant plate. The device under consideration enables the precise modulation of projectile impact speed. Through the implementation of parameter control, the configuration of the SRS can be modified to emulate a variety of pyroshock environments. The development of this device is of significant importance for the analysis of shock resistance performance in aerospace products.