Experimental study of flat-collared hemispherical shells under shock loading

Hemispherical shells are important structural components that have a wide range of applications due to their high stiffness-to-weight ratio. In blast valves, hemispherical shells are used as part of the closure mechanism. This study aims to investigate the response of flat-collared hemispherical shells under the shock load produced in shock tube experiments. The study is carried out considering flat-collared hemispherical shells with radius of curvature 2r, 3r, and 4r (where r = 50 mm is the circular radius of the hemispherical portion) of four different thicknesses (0.5 mm, 1.0 mm, 1.2 mm, and 1.5 mm), flat circular plates of identical thickness, and a 2.0-mm-thick plate against a driver pressure ranging from 1.5 to 20 bar. The shock loading was produced by a shock tube (diameter of 100 mm) in experimental setup available at DRDO laboratory. The response in terms of radial/meridional and hoop strains at a radial location of 35 mm along with the radial strain at the center (in some cases) for hemispherical shells and circular plates was obtained and compared. Simply supported hemispherical shells were loaded from the front (concave) side. A uniquely designed sample holding mechanism (spring-loaded) held the hemispherical shells in a simply supported manner and released the high-pressure gases just after the loading of the sample. The response of one hemispherical shell with a thickness of 1.5 mm and a radius of 150 mm was simulated on ANSYS Autodyn, and the experimental and numerical results were found in good agreement. Based on the detailed study, it is concluded that the location of meridional normal strain shifts toward the periphery for flat-collared hemispherical shells with decrease in radius of curvature. Further, the meridional strain at r = 35 mm is always greater than the meridional strain at r = 0 with hoop strain (at r = 35 mm) lying between these two values. The variation of meridional strain at r = 35 mm shows the maximum percentage increase with an increase in the radius of curvature. The study shows that the hemispherical shell of 1.5 mm thickness and 150-mm radius of curvature is most suitable (among the shells considered) for blast valve applications with smallest strain values. This study on the investigation of shock response of flat-collared hemispherical shells is carried out for the first time and is the new contribution in comparison with the available literature.