PSI - Issue 17

Radek Doubrava et al. / Procedia Structural Integrity 17 (2019) 190–197 Radek Doubrava/ Structural Integrity Procedia 00 (2019) 000 – 000

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The metal test panel was manufactured from sheet aluminium alloy 2024-T3, Kay (2003), with a nominal thickness of 2 mm.

2.2. Projectiles

Ice balls of 1-inch (2.54 cm) and 2-inch (5.08 cm) diameter according to ASTM F320-05 (2005) were used as hail stone impact projectiles (Fig. 3a). The projectiles were accelerated in an air gun barrel using a polystyrene sabot (Fig. 3b)

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Fig. 3. (a) ice ball projectiles and (b) polystyrene sabot with ice ball projectile

2.3. Instrumentation for the measurements

Standard qualitative techniques for high-speed impact analysis, such as high-speed cameras and post-test non destructive techniques (NDT), were used for the analysis of the test results and for verification of the numerical model. A novel technique of dynamic displacement measurement by using a laser triangulation sensor during the impact process was proposed and used for a quantitative analysis and a more precise verification of the data obtained from the numerical model (Fig. 2b). The test specimen deformation during the hail strike was measured using the laser triangulation sensor with a controller for analogue signal output. The measurement range of the laser sensor was 30 mm (from 50 to 80 mm off the sensor). The actual hail impact point was then determined via the high-speed camera record and visual inspection. The measurement data acquisition rate is adjustable over a range from 1.5 to 49.1 kHz and was set at 20 kHz during testing. The resolution of the sensor is 0.3  m. The video images were recorded by two high-speed cameras; the first camera recorded the course of the impact from the front side and the second camera was used to measure the hail speed. The velocity measurement from the high-speed camera was based on the measurement of the time required for the object to traverse a specific distance. The test specimen was attached to the test rig by 20 M10 bolts used to fix a 10 mm thick steel frame. Simulations were conducted for this fixture using boundary conditions (see Fig. 2a). The speed of impactor, and thus the impact energy, was defined based on the following requirements: • For the composite test panel – no fracture was observed, but BVID occurred; • For the metal test panel – obtaining plastic deformation without fracture. Based on the displacement measurement system (chapter 2.3), the maximum displacement for both types of test panels was ±15 mm (due to the setup used the real measurement range was +17 mm and -13 mm). Based on the aforementioned criteria, previous tests and simulation results e.g. Kustron et al. (2018), the next load 2.4. Test boundary condition