Empirical relationships for hail impact on rigid targets

• Hailstones with different velocities were impacted onto a rigid wall • Image processing technique was used to obtain displacement, velocity, and acceleration profiles. • Empirical relationships for peak force, contact time, and the time to peak force were obtained • Fitting curves for force-time profiles as a function of hail velocity and diameter were obtained This study employs experimental and numerical methods to investigate the dynamic behavior of hail stones under low-velocity impact. Several experimental tests are conducted to simulate the impact of hail on rigid targets. Hailstones with initial velocities of 10, 12, 15, and 17.5 m/ and a diameter of 45 mm are tested using a gas gun. The motion of the hail is recorded using a high-speed camera, and image processing algorithms are developed to obtain the displacement, velocity, and acceleration of the hail over time. The numerical model utilizes the smoothed particle hydrodynamics (SPH) method to assess the impact of low-velocity hail. This model is developed to analyze hail dynamics for velocities ranging from 10 to 60 m/s and hail diameters varying between 10 and 80 mm. Empirical relationships for peak force, contact time, and the time to peak force are obtained. Moreover, fitting curves for force-time profiles as a function of hail velocity and diameter are obtained. The results demonstrate that the impact force follows a polynomial relationship with both hail diameter and hail velocity. In contrast, the relationship between contact time and the duration needed to reach maximum force is linear with hail diameter, while the relationship with hail velocity is exponential. The method presented in this study for measuring impact force is applicable in various impact dynamics, particularly in studies involving soft impacts. Additionally, the numerical model can be enhanced to address low-velocity impacts from ice. The equations illustrating hail behavior can be utilized in the design of static structures facing hail, such as solar panels, metal roofs, and buildings.