[Retracted] Examining Dent Formation Caused by Hailstone Impact

Abstract

Hailstorms pose significant risk for exposed building cladding materials. Steel sheeting is the most important cladding material used. The understanding of steel sheets behavior under hail impact loading is not sufficient for the manufacturing of hail-resistant sheets. With the purpose-built equipment, artificial hailstones of different sizes were launched to impact at steel sheets of different thicknesses and yield stresses as targets. A theoretical approach for the problem of predicting the dent size due to hailstone impact was developed and compared to the test results. The expressions developed in the theory can predict the dent depth before the impact, assuming the ratio between the dent depth and dent diameter is constant. The expression is not able to predict the depth of dents smaller than 0.75 mm and cannot predict whether the denting will occur or not. All hailstone sizes lead to visible dent on steel sheet of thicknesses 0.35 mm, 0.42 mm, and 0.55 mm. Visible denting was also obtained for the 0.75 mm steel samples with 45 mm and 55 mm hailstones; however, no denting occurred using 40 mm hailstones. It was found that the dent depth was inversely proportional with thickness and yield stress, while the dent diameter was found to be proportional to yield stress. As the yield stress of the steel sheet increased, the dent depth decreased for G300 and G550 steel. The dent diameter however increased as the yield stress increased. When the artificial hailstone shatters on impact, significant energy is lost and less energy is available to cause plastic deformation of the impacted material.

Prediction of Bake Hardening Behavior of Selected Advanced High Strength Automotive Steels and Hailstone Failure Discussion

“…Less known and respectively less published are failure studies, which are related to smaller, non-life-threatening outer damage of sheets due to static and dynamic impacts of small hard objects (up to 100 mm), which reduce aesthetic properties of vehicles and require costly repair. More extensive dent resistance tests were done by [30,31]. A key distinction that is sometimes missing in dent resistance studies is the nature of the dent.…”

“…Mehmet E. Uz [31], simulated the hailstone impact on G300 and G550 steels in laboratory conditions and investigated the dependence of dent size on steel grade, steel thickness, yield strength, and the size, speed, and impact force of ice balls. Experimentation reveals that the dent depth was inversely proportional to thickness and yield strength, while the dent diameter was found to be proportional to yield stress.…”