Hypervelocity impact response characterization of aluminum plates

Abstract

Hypervelocity impact research is key to the designing of shielding systems to protect structures in Low Earth Orbit with risk of space debris impact. Understanding the physical features contributes to the effective development of impact shielding design. In this study, the impact hole area, lip height, and debris cloud impact radius were investigated for impacts up to around 4km/s for 6061-T6 aluminum panels of 3mm thickness using a 2-stage light gas gun. Image analysis and 3D scanning were employed to measure the geometric features. Numerical analysis was conducted to simulate the experiment cases and the modeling was verified through comparison of the geometric features. The hole area and debris cloud impact radius showed gradually increasing trends with increasing impact velocity. The 3D scan measurements followed the image analysis, and considering the overall similarity between the 3D scan and numerical simulation, the numerical model satisfactorily reproduced and supported the empirical measurements. In order to investigate the hypervelocity impact response of homogeneous 6061-T6 aluminum plates of 3 mm thickness, a 2-stage light gas gun was used to carry out hypervelocity impacts up to 4 km/s and polyvinylidene fluoride(PVDF) piezofilm sensors were used. The acquired impact responses were categorized into non-penetration, hard penetration, fragmented penetration, and debris cloud impact. The frequency domain characteristics of the impact responses were observed and analysis of variance(ANOVA) of the 4 impact categories and correlation analysis with impact velocity were performed using 82 feature parameters with respect to the time, frequency, and time-frequency domains. The ANOVA results revealed that the spectral entropy and the conditional spectral and temporal moments of the time-frequency domain were statistically highly significant in differentiating the impact categories. Using the feature parameters of the third order temporal moment, correlation dimension, and zero crossing rate, accuracy of 91.3% was obtained for the categorization of impact responses into the impact categories, which was further improved to 95.5% by removing outliers. These feature parameters also showed moderate to strong and statistically significant correlation with the impact velocity. Inverse prediction of the impact velocity based on the linear fit for feature parameters with high correlation coefficients resulted in a mean error of 0.0374 km/s using the third order temporal moment minimum. These results indicate the potential of the conditional spectral and temporal moments and other signal energy related feature parameters investigated in this study for post processing and even real time assessment of transient events such as hypervelocity impacts. By using commercial piezofilm sensors and the use of a limited number of preselected feature parameters, the potential of relatively accurately predicting the impact type of an impact response acquired using the piezofilm sensors along with the impact velocity virtually in real time was shown in this study.