PSI - Issue 28

N.A. Sazhenkov et al. / Procedia Structural Integrity 28 (2020) 1572–1578 N.A. Sazhenkov et al./ Structural Integrity Procedia 00 (2019) 000–000

1574

3

examined, 7 of them were covered with a layer of polyurea 1.2 ± 0.05 mm thick, 0.069 ± 0.002 Kg in weight, and a areal density of 1.15 kg/m 2 . Tensile strength of the base material (GFRP) has also been found as 353.3 ± 0.5 MPa for the directions [0] and 305.5 ± 4.1 MPa for the directions [90]. The limit strain before failure is 1.78 ± 0.1% and 1.84 ± 0.01% for the directions [0] and [90] respectively. The mechanical properties of the polyurea coating strongly depend on the rate of deformation. The tensile strength and fracture strain at the loading speed of 60 mm/min were 21.7 MPa, and for a loading speed of 3000 mm/min they were 32 MPa and 79%, respectively. 2.2. Experimental setup and procedure. The ballistic experiments was performed on the special test rig (Fig. 2 a) which contains pneumatic gun - 2 (assembled of compressor, receiver, valve and barrel), optical sensor - 3 to measure muzzle velocity of the projectile and two Photron high-speed cameras to capture the impact event from elevated front and plan view at 45,000 frames

a) b) Fig. 2 – (a) Schematic of ballistic setup: 1 – target (sample), 2 - pneumatic gun; 3 – optical sensor; 4 – high speed cameras; 6- PXI system (National Instruments); 7 – PC; (b) Photo of ballistic setup: 1 – target, 2 – barrel, 3 – ballistic chronograph

per second speed. Control of the experiment was preformed via PC - 7 through PXI module of NI system - 6. The specimens - 1 were aligned with the barrel. The presented test rig allows accelerate projectiles up to the speed from 40 to 500 m/s. It is possible use spherical, cylindrical and flat projectiles made of the different materials with that test rig [15-18]. More detailed description of the experiment test-rig is given in the works [19-23]. Solid steel spherical ball was used as a projectile. It has a diameter 23.8 mm and nominal weight 54.7 g. All fiberglass targets were clamped at the bottom end over an area of 50 x 160 mm with the impact point in the centre of the free part of the sample (Fig. 3). Three loading cases were performed during the ballistic tests: (i) a perpendicular impact at the centre of the uncoated free part of the target; (ii) a perpendicular impact at the centre of the target with a polyurea coating on its face; and (iii) impact at the centre of the target with a polyurea coating on the back surface. Four shots were made for each loading case with a stepwise increase in the impact velocity of 8.5 m/s to assess the ballistic limit of the plate with

Fig. 3 – Loading and clamping scheme