br Flash X ray cinematography

Flash X-ray cinematography set-up A schematic of the measurement set-up for flash X-ray cinematography is shown in Fig. 1. Instead of several separate X-ray tubes one multi-anode 450 kV tube is utilized. In the multi-anode tube eight anodes are arranged on a circle of ≈12 cm diameter. This configuration causes only a relatively small parallax for the projections from the different anodes. The process under observation can be X-rayed at eight different times. The radiation transmitted through the target is then detected on a fluorescent screen. The position of the target is between the multi-anode tube and the fluorescent screen, relatively close to the fluorescent screen. The fluorescent screen converts the radiograph into an image in the visible wavelength range, which is photographed by means of an intensified digital high-speed camera. The maximum frame rate that can be achieved with such a system depends on the decay time of the fluorescent screen, the time characteristics of the intensifier and the camera. Frame rates of 200,000 fps have been achieved with a fast decaying fluorescent screen and have been used in this study.
Materials and experimental configurations The objective of the study was to determine the influence of the SiC-type and the backing on penetration, deformation and erosion of the projectile. For this purpose two commercial SiC grades, EKasic F and EKasic T of 3M Technical Ceramics (formerly ESK Ceramic) and MICASIC (Metal Infiltrated Carbon derived SiC), a C-SiSiC ceramic developed by DLR, have been studied. A compilation of the physical and mechanical properties of the materials is presented in Table 1. The SiC ceramics were tested on three different backing materials: High hardness steel of type ARMOX 500T (Tensile strength 1450–1750 MPa), aluminum 2017 (AlCuMg1, Tensile strength 400 MPa) and Corlight sandwich panels consisting of a NOMEX® T722 meta-aramid honeycomb core of 5.3 mm thickness, covered with one layer of glass fiber in an epoxy matrix on each side. The targets with the sandwich panels consisted of three layers: ceramic, sandwich panel and an aluminum backing plate. Due to the limited penetration capability of the radiation, small targets had to be assembled for the flash X-ray cinematography. On the one hand, in the cinematography set-up a good SBI-0206965 could be achieved with irradiated SiC material thicknesses in the range from 30 to 40 mm. Therefore, the ceramic layer of the targets consisted of single hexagonal tiles with a wrench size (inscribed circle diameter) of 30 mm with EKasic F and T, or 32 mm with C-SiSiC. On the other hand, the size is representative for tiles used in real ceramic armor configurations. The upper and lower lateral surfaces of the tile were surrounded by aluminum caps, which not only provided a confinement of the ceramic but also ensured a homogeneous intensity distribution of the transmitted radiation over the complete width of the ceramic. The photograph in Fig. 2 shows a target consisting of a ceramic on a sandwich panel with aluminum backing on its mounting. The dimensions of the backing plates were 40 mm × 80 mm. The thickness of the ARMOX 500T plates was 8.5 mm, the aluminum backing plates were 8 mm thick. The targets were held by a u-steel with a distance of 80 mm between the support points.
Experimental results Three tests were conducted with C-SiSiC on steel backing. Fig. 3 shows the eight flash radiographs from one of these tests. The radiographs were recorded at a frame rate of 200 kHz, starting with the first frame nominally at 8 µs after impact. The actual times of the X-ray flashes are indicated in the single frames in Fig. 3. The time of impact was determined by means of a thin shortcut trigger foil on the impact side of the ceramic. Due to the high absorption of the X-rays in the steel, the backing plate appears black in the radiographs. It can be recognized from the radiographs that the projectile hardly penetrated the ceramic during the first 20 µs. In particular the radiograph at 18.8 µs illustrates that not only the jacket material but also the core material were moving radially outward along the surface of the ceramic. During this phase of projectile–target interaction the projectile lost mass and its length were significantly reduced. The so-called dwell-phase, where no projectile penetration occurred, was followed by the penetration phase. This is illustrated by the path–time plot in Fig. 4, which shows the position of the projectile tail, tip and the back surface of the steel plate (bulge) for all three tests with the same configuration. Since the tip of the projectile was eroded quickly the term tip position is only used for the sake of simplicity in the following and means the position of the interface between the projectile and the ceramic. The path–time history of the projectile tip (projectile–ceramic interface) is represented in more detail in Fig. 5. The penetration curve could be divided into two sections: During the first 15 µs no significant penetration was observed. A linear regression of the data during this phase yielded an average penetration velocity of 30 m/s. The dwell phase ended after 16 µs and penetration at an average velocity of 192 m/s was then observed until 60 µs after impact. The projectile was stopped since no significant penetration of the steel backing could be noticed after the test.