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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boundary condition was defined for the tests as: • For the composite test panel - a 50 mm diameter ice ball with an impact speed of approximately 350 km/h; • For the metal test panel – a 25 mm diameter ice ball with an impact speed of approximately 650 km/h. 3. Numerical simulations FE simulations were performed using the ABAQUS (2017) software package. An explicit solver with double precision was used for the analysis with general contact conditions throughout. In terms of the impactor’s (hail) material properties and features, ice is a complex material presenting high degrees of variability. The material density of the ice and hail varies and is subject to a range of factors, such as the weather system(s) in which it was created. Standard ice has a density of 917 kg/m 3 , which may increase slightly as the temperature declines, although it never reaches the density of liquid water. Ice may exhibit two forms of non-elastic behaviour under stress. Under low-velocity deformation, ice exhibits ductile behaviour. However, as the velocity increases, the material becomes brittle (Fig. 4).

Fig. 4. Ice behaviour under stress

The geometry of the projectile (hail) was idealized as 25 and 50 mm diameter spheres (Fig. 3a). The geometry of the hail stone model was meshed using 3,936, C3D8R 8 - node linear brick elements with conversion to particle elements (SPH – Smoothed Particle Hydrodynamics), Doubrava (2013). The S4R shell elements were used for the simulation of the test specimen. The global mesh size of 10 mm was refined to 3 mm at the impact area. From the point of view of the composite material damage analysis the Hashin’s (1981) damage material model was used. The material damping in the composite material was based on the VZLÚ acoustic fatigue experiment, as defined by Běhal (2018). A Johnson-Cook material model, defined by Kay (2003), was used for the metallic test specimen for the simulation of the elasto-plastic and damage behaviour. 4. Results The results from the tests and numerical simulations were determined using: • Qualitative measurements – high-speed camera recordings (speed and fragmentation of the impactor); • Quantitative measurements – dynamic displacement during impact and plastic deformation after impact (metallic test panel).

4.1. Analyses of the high-speed camera measurement

The results from the high-speed camera were analysed based on the point of the impact damage and its position, as well as addressing any uncertainties, such as damage to the impactor before the impact. The second high-speed camera was used to determine the velocity of the impactor.