Investigation on the Post-Processing of Blast Loading Characteristics Along a Convex Structure

Abstract

Interaction between large blast and targets can rarely be studied directly, due to cost and practicality considerations. Blast tests using reduced-scale high explosive charges represent an attractive alternative. The first necessary step consists in studying blast propagation in free-field at the considered reduced-scales. The second step focuses on the determination of the blast load around various types of reference obstacles, in order to provide a critical input for numerical simulation. This approach also aims to build simplified models allowing faster risk assessment processes for government agencies. Since 2017, the French Institute for Radiological Protection and Nuclear Safety (IRSN) and the French-German Research Institute of Saint-Louis (ISL) have been studying blast propagation in free-field and in front of a hemi-cylinder at two different reduced scales using Hexomax ® charges. IRSN developed a significant experience on hemispherical blast effect assessment using 42 g reference Hexomax ® charges detonated in contact to a planar surface supporting a hemi-cylindrical obstacle, both equipped with pressure sensors including two types of technologies: piezo-electric and piezo-resistive. Based on this experience, ISL developed its own outdoor blastpad: 333 g Hexomax ® charges are detonated in a factor two up-scaled version of the IRSN test configuration. Similar sensors are flush-mounted on the pad and the surface of an up-scaled version of the IRSN obstacle. To assess the resulting experiments extensibility, blast characteristics were measured at distances ranging between 0.6 and 3.5 m/kg 1/3 from the different charges with or without obstacle. A classic post-processing methodology identified in the literature was applied to determine all peak overpressure values. The results were consequently compared to the directly determined values in order to propose a unified technique of processing overpressure data for reduced-scale blast tests, including various types of pressure sensors. Finally, this work contributes to the optimization of large scale blast tests designed to evaluate structural response.

Multi-Scale Experimental Study of Blast Propagation Around a Hemi-Cylindrical Barrier

“…The Model S correlation provides a convincing prediction of the 400 g TNT equivalent experimental overpressure evolution on the back side of the upscaled obstacle. Results dispersion at 150° can be explained by the expansion phenomenon itself, the proximity of a welding joint next to the sensor positions as well as the difference in the responses of the pressure gauges [14]. This first inter-scale comparison strengthens the pertinence of the Model S conjecture to predict peak overpressure evolution on the expansion side of a cylindrical target exposed to a blast wave for any d/R ratio and charge mass by defining a reduced shifted direct distance.…”

Towards a model to predict blast propagation around a hemicylindrical barrier

“…An alternative model could also be based on the use of the parameter µ. Based on IRSN blast table [1,2,14,18], ISL modified an existing concrete blast pad seen on Fig. 3 to conduct similar experiments at larger scales: explosive charges with a mass multiplied by 8 are ignited on a factor 2 up-scaled version of IRSN test table.…”