Study Of Structure Durability Analysis Method And Its Application To Rail Vehicle

Due to high-speed operation and haul-heavy loading, structure strength of modern rail vehicle becoming more and more serious. And modern rail vehicle demands not only appropriate static strength and stiffness but also long fatigue life, high reliability and low repairing cost. Based on fracture mechanics, the relationship between fatigue life and initial flaw size as well as crack growth rate is established in the fatigue design method, which is effective to assess structure strength of rail vehicle.However, the original fatigue design method based on fracture mechanics has some limitations, such as the definition and assessment of IFQ (Initial Fatigue Quality), the determination of crack growth rate, which make the method require of a lot of experiment and wreck the applicability of the experiment.Aiming at the limitations, the dissertation focuses on the assessment of IFQ, the determination of crack growth rate, the definition of IFQ and the application of the methods to rail vehicle. The detailed arrangement of this paper stands out as follows:1) Improvement of the assessment of IFQ. Firstly, several different TTCI (Time to Crack Initiation) interpolation methods are compared and the effects of interpolation methods on TTCI distribution and economical life are analyzed. Secondly, based on order reducing and dichotomy, an advanced numerical algorithm is presented for maximum likelihood estimation of three-parameter Weibull distribution. Finally, the improved method of determining TTCI distribution parameters is offered and the new approach to determine the generic parameters of EIFS (Equivalent Initial Flaw Size) distribution is proposed. Results of the numerical calculation indicate that the methods are accurate and depend less on experiment.2) Investigation of the determination of crack growth rate. The relation between S-N (or P-S-N) curve and crack growth rate is deduced. Determination methods of crack growth rate are analyzed under the situation of constant, variable amplitude and stochastic load. Then, the factors on crack growth rate are analyzed. And the determination method of crack growth rate is discussed with other different S-N and P-S-N expression. Experiments and analyses show that the new method of determining crack growth curve with S-N or P-S-N curve is accurate and less depend on experiment. 3) Investigation of the IFQ concept. The demerits of structure IFQ are analyzed and a new concept, IFQ of material, is defined. A new durability method is presented. Being not effected by size, configuration, processing technic and working environment of structure, IFQ of material can be applied to the structures with the same materials and can be used widely.4) Investigation of the application of the durability method to rail vehicle. Aimed at the structure characteristics of rail vehicles, the experiments and analyses of key structure details are carried out, and the durability of the details is assessed, which can find a new way to apply durability method based on fracture mechanics to the design of rail vehicle structure.