Theoretical and Numerical Analysis of Blasting Pressure of Cylindrical Shells under Internal Explosive Loading

Cylindrical shells are principal structural elements that are used for many purposes, such as offshore, sub-marine, and airborne structures. The nonlinear mechanics model of internal blast loading was established to predict the dynamic blast pressure of cylindrical shells. However, due to the complexity of the nonlinear mechanical model, the solution process is time-consuming. In this study, the nonlinear mechanics model of internal blast loading is linearized, and the dynamic blast pressure of cylindrical shells is solved. First, a mechanical model of cylindrical shells subjected to internal blast loading is proposed. To simplify the calculation, the internal blast loading is reduced to linearly uniform variations. Second, according to the stress function method, the dynamic blast pressure equation of cylindrical shells subjected to blast loading is derived. Third, the calculated results are compared with those of the finite element method (FEM) under different durations of dynamic pressure pulse. Finally, to reduce the errors, the dynamic blast pressure equation is further optimized. The results demonstrate that the optimized equation is in good agreement with the FEM, and is feasible to linearize the internal blast loading of cylindrical shells.

Fitness-for-Service Strategies for Impulsively Loaded Vessels

High-explosive containment vessels are often designed for repeated use, implying predominately elastic material behavior. Each explosive test imparts an impulse to the vessel wall. The vessel subsequently vibrates as a result of the internal blast loading, with amplitude diminishing exponentially in time after a few cycles due to structural damping. Flaws present in the vessel, as well as new flaws induced by fragment impact during testing, could potentially grow by fatigue during these vibrations. Subsequent explosive tests result in new sequences of vibrations, providing further opportunity for flaws to grow by fatigue. The obvious question is, How many explosive experiments can be performed before flaws potentially grow to unsafe limits? Because ASME Code Case 2564-5 (Impulsively Loaded Pressure Vessels) has just been incorporated in Section VIII, Division 3 of the 2019 ASME Boiler and Pressure Vessel Code, evaluation of remaining life and fitness-for-service of explosive containment vessels now draws upon two interrelated codes and standards: ASME Section VIII-3 and API-579/ASME FFS-1. This paper discusses their implementation in determining the remaining life of dynamically loaded vessels that have seen service and are potentially damaged. Results of a representative explosive containment vessel are presented using actual flaw data for both embedded weld flaws and fragment damage. Because of the potentially large number of flaws that can be detected by modern nondestructive inspection methods, three simplifying assumptions and a procedure are presented for conservatively eliminating from further consideration the vast majority of the flaws that possess considerable remaining life.

Blast resistant behaviour of tunnels in sedimentary rocks

The tunnels are being constructed for the faster movement of goods and services from different locations. Therefore, Underground Urban Space (UUS) has evolved as an integral part of metro cities. Critical structures like tunnels have to be designed resistant to the blast due to possible threats and attacks. In the present paper, the efforts are made to analyse and understand the response of rock tunnel for an internal blast loading. The numerical analysis based on the finite element method has been carried out for a 35 m long rock tunnel in a rock mass of longitudinal cross-section 30 m × 30 m. The elastoplastic behaviour of the sedimentary rocks, that is, Sandstone, Mudstone and Silty Sandstone has been incorporated by using a Mohr-Coulomb constitutive material model. The plastic behaviour of the concrete tunnel lining has been incorporated by using concrete damage plasticity model. Moreover, for the Trinitrotoluene (TNT) Jones-Wilkens-Lee (JWL) material model has been considered. Analysis has been performed through the Coupled-Eulerian-Lagrangian (CEL) approach, which incorporates the advantages of both Eulerian and Lagrangian modelling. The present study focuses on the analysis of the tunnels constructed in three different sedimentary rocks, that is, Sandstone, Silty Sandstone and Mudstone. It has been concluded that Mudstone rock is more susceptible to failure due to internal blast load. However, Sandstone rocks were found to be relatively higher blast resistant, hence, may be considered as safer rocks for the construction when compared to other rocks of the present study.