Damage mechanics based analysis of hail impact on metal roofs

Hail is one of the leading causes of annual property damage, that in turn results in economic loss and material waste. The associated risk affects several industries and parties including owners, insurance carriers and building material manufacturers. Due to the lack of detailed understanding of hail impact consequences, damage to building materials due to hail impact is primarily assessed by means of physical (visual) inspection supported by experimental data. Previously presented analytical and numerical models proposed in the literature have not offered a sufficiently robust representation of the damage on building materials due to hail impact. In this study, we present a novel model for hail deformation and impact damage in the hailstorm impact speed range. The proposed hailstone model is based on a strain-rate dependent and pressure-dependent visco-plastic model which allows for the representation of the different deformation regimes that hailstones experience during impact. The model is calibrated based on split-Hopkinson bar experimental results available in the literature. The model is then validated against widely accepted results of hailstone impact on metal sheets. The numerical experiments show that the model successfully captures hail strength, ductility and energy dissipated during impact. Consequently, the validation study shows the capability of the model to represent experimentally observed contact force changes during impact, which is achieved at an accuracy higher than the currently available models. In addition, the modeled response of hailstone deformation and damage is compared qualitatively to high speed camera images available in the literature. Additional parametric studies are performed to investigate the deformation and fracture of metal roofing subject to hail impact. The parametric studies investigate how different impact conditions (e.g. hail size, shape, strength and density, and roof detailing) affect the response and behavior of the metal roofing, associated deformation and potential fracture of the steel material. The proposed numerical modeling framework allows for a more reliable investigation of boundless design variations, while mitigating the labor-intensive costs and material waste associated with physical testing which is widely adopted in the industry right now.