MANAGEMENT OF IMPACT ENERGY AND SHOCK IN RAIL CRASH

Abstract

Passive safety of rail vehicle has attracted increasing attention around the world due to the continuous development of rail transportation, especially the increasing use of high-speed trains and subway vehicles. Rail crash always causes severe occupant injuries, long-term psychological effects and property damage as well as having social impact. The purpose of passive safety is to minimise these effects. The main approach to manage the impact energy and shock resulting from a crash is designing sacrificial crush zones in unoccupied connection areas of rail vehicles. Crashworthiness design of structures and materials in the crush zone has been one of the major topics of research in the rail vehicle engineering. In a crash-stop process, the impact energy and shock are represented by a crash signal, which is generally given by a deceleration-time (or a force-time) history. In this thesis, some fundamental issues associated with the crash signal are identified and characterised from two aspects, i.e. (i) minimisation of head injury index; (ii) physical modelling using single-degree-of-freedom (SDOF) model. Results show that the preferred deceleration-time history (or acceleration-time history in many publications) depends on the selection of the injury (or damage) criterion and the ranges of scenario parameters in the crash-stop problem. To assess the damage of a device based on the crash signal in an impact incident, a method of dual criteria is proposed by combing the maximum acceleration-velocity change (Amax-V) diagram and shock response spectrum (SRS), i.e. the former can offer a lower bound of damage boundary on Amax-V diagram while the latter can define an upper bound of damage boundary on SRS graph. The validation of the dual damage criteria is demonstrated by the numerical simulation examples of cantilever beams. Under the guidance of the crash signal analysis, this thesis moves to more realistic structural optimisation and lattice material design with particular focus on the crush zone of a rail vehicle. In a crush zone, the most critical component is the collapse zone structure, which takes the main role in the management of impact energy and shock. The collapse zone structure is designed with multiple functions, i.e. supporting neighbouring components and attached equipment in normal operation and absorbing impact energy/shock in a crash accident. An efficient procedure through means of implementing conceptual and detailed design is developed to obtain an optimal collapse zone, which exhibits superior crashing performance compared with the conventional one. In addition, regularly-ordered lattice materials are excellent lightweight cellular materials to enhance the crashing performance of a crush zone, thus, improving the management of impact energy and shock. Based on topology optimisation, an advanced lattice material with high energy-absorbing capability is proposed, which is similar to the microstructure of a cuttlefish bone. Furthermore, a functionally graded cuttlebone-like lattice (CLL) material is designed as an energy/shock absorber, which exhibits layer-by-layer deformation and possesses better mechanical properties than the corresponding uniform lattice material. It implies that these newly designed cellular materials can be used to fill the thin-walled components of a collapse zone and an anti-climber (i.e. another element in a crush zone) or as cushion/package materials to protect highly sophisticated facilities in a rail crash. In summary, the management of impact energy and shock in a rail crash is achieved from three main aspects: (i) injury/damage analysis of crash signal to guide the design of crushable structures; (ii) crushable structure design by implementing optimisation methods; (iii) design and characterisation of advanced lattice materials.

Date of Award	31 Dec 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Qing Li (Supervisor) & Jack Wu (Supervisor)