James Dodds & Adam Towse, Assystem UK Ltd.
Assystem UK Ltd were tasked to provide design, simulation, prototyping and verification testing of an encapsulation vessel. The function of the overpack is to contain the product cans thereby providing a protective barrier. It was also required that the overpacks should be able to act as a pressure vessel should the internal can rupture before, during or after postulated impact events. The design of the overpack was driven by the impact analysis results in conjunction with manufacturability, assembly and package space limitations. Additionally, the vessel was designed to comply with the pressure vessel code PD5500 using a design-by-rule approach.
The basic design of the overpack consists of the main vessel body, enclosing the product can, and a cover plate bolted to the vessel body. To create a pressure boundary, metallic seals were present at the interface of the vessel body and cover plate. The overpack also contains an inner restraining device which serves two purposes; one to centralise the enclosed cans during assembly and the second to hold the can away from the overpack inner face during impact.
The analysis of the impacts was carried out using the RADIOSS explicit dynamic software, part of the HyperWorks suite. Additionally, the use of simulation allowed the pressurisation of the overpack at the moment of impact to be performed, which is very difficult to achieve experimentally.
Various drop scenarios of pressurised and non-pressurised Overpacks were simulated to establish the worst case impact orientations using a Design of Experiments approach. During the simulations, the movement of the cover plate seals was monitored along with the integrity of the pressure boundary of the vessel.
Following completion of the design and simulation phase, prototypes were built and tested to verify the engineering design and analysis. The testing showed that simulation driven design was successful in creating a solution for the product can encapsulation