Effect of vent hole size on combustion and explosion characteristics during cook-off tests

Abstract

In this laboratory, a cook-off device was designed and used to analyse combustion and explosion characteristics in fast and slow cook-off tests with different vent hole diameters. Using JO-9C as the experimental material, we measured cook-off reaction temperatures and analysed damage of restraint structures. Through the analysis of the crystal phase of the metal fracture surface, according to the characteristics of the crystal phase fracture surface of different fracture modes, the different conditions and different positions of the shell crushing load are analysed, combined with the change law of the reaction temperature, a reasonable explanation is given to the changing law of the response level. The results showed that the reaction temperature increased continuously with increasing vent hole diameter under fast cook-off conditions, and the reaction temperature difference between the sealed condition and the 7.0 mm vent hole was 45.4 °C. Under slow cook-off conditions, influenced by thermal convection, the diameter of the vent hole had little effect on the reaction temperature. For vent hole diameters that were smaller and larger than 16.0 mm, average reaction temperatures were 272.9 °C and 278.6 °C, respectively. The severity of the reaction first increased and then decreased with increasing vent hole diameter. The fast and slow cook-off reactions were the most violent when the vent diameters were in the ranges of 2.0–4.3 mm and 4.4 mm, respectively. Fragmentation of restraining shells and deformation of upper covers and restraining bolts were comprehensively evaluated. For fast cook-off tests, when the diameter was 5.5 mm, the reaction changed from partial detonation to deflagration. Under slow cook-off conditions, when the vent hole diameter was greater than 16.0 mm, the reaction changed from partial detonation to deflagration. When the vent hole diameter was greater than 20.0 mm, the reaction changed from deflagration to slow combustion.