Effects of Pre-pressurization on Damage of Blast- Loaded Reinforced Plates

The effects of pre-pressurization on blast-loaded reinforced rectangular aluminum plates were studied experimentally. In this study, small (0.508 x 0.609 x 0.0016 meter) clamped plates with rivet attached reinforcing members were used as a basic model of the fuselage skin of a commercial aircraft. Both un-pressurized and pre-pressurized plates (static pressure of 41.4 kPa (6.0 psi)) were considered to simulate the typical in-flight loads experienced by a commercial aircraft due to cabin pressurization. This work extends previous research on blast loading of pre-pressurized plates to incorporate the effects of reinforcing members. Experimentally, a vacuum vessel system was used to apply a pressure differential to the test plate. Bare spherical explosive charges of C4 were then detonated at fixed distances from the plate. The permanent plate deformations or amount of tearing in the plates were measured for seventeen explosive tests that considered two different blast load intensities. Additionally, a high-speed camera was used to determine the mechanism and time scale of failure propagation in the reinforced panels. For all tests, the high speed camera was found to be an excellent tool to record the consistent failure progression in the reinforced panels. In general, commencing with the onset of panel deformation, the blast-loaded panels exhibited rivet failure in less than 0.5 milliseconds, initiation of tearing in less than 1.0 millisecond, and complete tearing in less than 10.0 milliseconds. A comparison of plate deformations and damage showed two distinct results. For the lowest blast intensity case, both the non-pressurized and pressurized panels deformed but did not tear. In this case, very little effect of pre-pressurization on final panel deformation was noted. For the more intense blast load case, a significant increase in panel damage was observed as static pre-pressurization increased from 0.0 kPa to 41.4 kPa. INTRODUCTION In recent years significant efforts have been made to develop methods for reducing the damage threat posed by internal explosions on-board commercial aircraft. These research efforts have typically focused on protecting aircraft stru As a result of this research, it has been concluded that onboard explosive devices can be particularly damaging to commercial aircraft due to the combined effects of transient explosive forces and normal cabin pressurization [1]. Aircraft compression systems are designed to maintain sea-level atmospheric pressure inside the fuselage up to a given altitude at which a maximum pressure differential is reached. For flights at higher altitudes, a maximum pressure differential in the range of 51.7 to 62.0 kPa (7.5 to 9.0 psi) between the aircraft cabin and the ambient atmosphere is maintained [3]. Of particular interest in the present study is the effect of cabin pressurization on the plastic deformation and damage of a fuselage skin structure under blast loading. Cabin 1 Copyright © #### by ASME pressurization acts as a pre-load on the fuselage and thus may alter the structural response to an internal explosion. Although it would be ideal to utilize full-scale explosive testing on aircraft for this evaluation, the cost and size of such an endeavor are not amenable to a parametric study. For this reason, a square clamped aluminum plate with rivet-attached aluminum stiffeners was selected as a basic model of the skin of a commercial aircraft fuselage. Several recent studies of the blast loading of stiffened plates have provided a useful background for this study. Türkmen and Mecitoglu [2] studied the dynamic response of stiffened laminated composite plates subjected to blast loading. The predicted dynamic plate strains from the finite element method were compared to measured dynamic plate strains under blast loading by the detonation of a fuel-air mixture. Louca and Pan [3] investigated analytical and finite element predictions for the response of blast-loaded steel plates with and without stiffeners. Louca, Punjani, and Harding [4] presented experimental measurements and finite element predictions of tee-stiffened walls under hydrocarbon explosive loading. Rudrapanta, Vaziri, and Olson [5] published the results of finite element damage predictions for blast-loading of stiffened steel plates. Yuen, and Nurick [6] presented the results of a experimental and numerical investigation of the response of uniformly blast-loaded clamped steel plates with various stiffeners. In a closely related study, Langdon, Yuen, and Nurick [7] consider the effects of these stiffened steel plates under localized blast loading. In all these studies, the effects of static pre-pressurization on plate blast response were not directly considered. The present study will build upon previous work to include prepressurization, specifically as experienced by a commercial aircraft fuselage. In addition to the previous studies of stiffened panels, testing and analyses of large-scale, complex fuselage sections has also been conducted. Most notably, a recent research project co-sponsored by the FAA utilizes explosive testing of full-scale sections of the cargo hold of a wide-body aircraft to simulate various terrorist attack scenarios. In this case, a reusable blast test fixture was constructed and used in testing at the Energetic Materials Research and Testing Center (EMRTC) under various pre-pressurization levels [8]. Additional blast testing was conducted on full-size aircraft which has been pressurized to simulate high altitude conditions [9]. Although this large-scale testing is ideal for determining the blast damage response of actual aircraft structural components, these efforts are costly and require elaborate test configurations and analytical methods. This study includes a reasonable degree of structural detail in the modeled fuselage panel, while still allowing a costeffective parametric study of the effects of pre-pressurization on blast damage.