WMG undertook research with Oleo International - an engineering company who design and manufacture energy absorption solutions for the rail, elevator and industrial sectors. The Instron Test Machine is a system which accurately evaluates material properties using flexure, tensile and compression testing which produces results on material quality. The Instrumented Drop Tower system tests small and large structures for crash safety related applications to evaluate the strength and degradation of the material after impact.
Railway vehicles traditionally use hydraulic mechanisms to absorb kinetic energy in day to day operations, such as shunting or general train operation. Hydraulic buffers can absorb a large amount of energy in a fully reversible manner. For more severe impacts it may not be possible to install hydraulic buffers with sufficient stroke to absorb the required energy, due to their relatively long installation length. Other devices need to be added to the vehicle crash energy management system to cope with the increased energy absorption requirements and to ensure the crash energy is absorbed in a controlled manner. The energy absorbing devices also need to keep adjacent vehicles aligned and resist vehicles overriding.
British safety standards (BS EN 15227) require that railway vehicles need to be able to absorb the energy of a crash that occurs at speeds up to 36 km/h. Given the large mass of current railway vehicles, this requirement equates to a need to absorb approximately 1000kJ. This is roughly 20 times more severe than a typical car crash.
This project focused on developing the most efficient energy absorption mechanism for railway vehicles. The objective was to develop an innovative stand-alone energy absorber, which has a good ratio of deforming stroke to installation length and is resistant to vehicle loads. To complying with the requirements of the BS EN 15227 standard it was necessary to demonstrate that the performance of the device is predictable and can be simulated.
Initial work used a decision matrix approach to compare various energy absorbing mechanisms and assess their suitability to railway applications subject to BS EN 15227. It was determined that energy absorption by radial expansion is the most efficient method but due to the non-collapsible nature of expansion tubes, a combination of expansion tube and other collapsible energy absorption mechanisms is being investigated in detail for use as a buffer. The above simulation images show an expansion tube (non-collapsible), a splitting tube (collapsible) and the proposed hybrid solution.
The WMG researcher simulated the performance of the proposed hybrid mechanism using finite element analysis and scale models have been tested. This work has demonstrated the working principles, quantified the benefits over conventional energy absorbers and illustrated the potential application of conventional composite materials to railway energy absorbers.
The research work has produced a simulation model of a compact energy absorber and has verified the stability of the mechanism under transverse loading. Testing of prototypes is expected to be completed by early 2014.