Fatigue Analysis And Optimization On The Fixed Frame Of Fully-wrapped Composite Tanks For On-board Storage Of Hydrogen

Since the1990s, China’s automobile industry has grown to become a pillar industry of the national economy. Along with the shortage of energy and the urgency of environmental protection, the development of new energy vehicles is an inevitable choice for the automotive industry. Hydrogen fuel cell vehicles is relatively widely used among various of new energy vehicles. The fully-wrapped composite tanks for on-board storage of high pressure hydrogen which has high specific strength and stiffness is a key components in the hydrogen supply system. Due to the flammable and explosive of hydrogen gas, fatigue life analysis and optimization under random vibration for the components of tanks for on-board storage hydrogen, especially the fixed frame is necessary, because once the fixed frame failed during service, it will result in the collision between the tanks and other parts in the vehicle body, or even cause the explosion of the tanks which is more serious than the conventional fuel vehicles, endangering the safety of the user’s life and property.Fatigue analysis under random vibration on the fixed frame of fully-wrapped composite tanks for on-board storage of hydrogen is a multidisciplinary study which involves structural dynamics, the theory of probability and statistics, fatigue strength theory. This paper is based on random vibration theory and analysis method, using the finite element method to analyze the dynamic response on the fixed frame of tanks for on-board storage of hydrogen under the excitation of the random road spectrum, then evaluate its life according to the fatigue life analysis method, finally optimize the fixed frame. Three specific parts are consisted in this paper as follows.Firstly, the basic theory of structural dynamics and the description of random vibration as well as the power spectrum expression for road roughness are introduced; then the theory of cumulative fatigue, mainly for the linear fatigue cumulative damage theory and its modification, the non-linear fatigue cumulative damage theory are expounded; the random fatigue analysis methods which contains time domain analysis method and frequency domain analysis method, especially the three-interval stress method are discussed followed by.Secondly, the geometric model of the fixed frame and tanks of hydrogen is simplified under the premise of accuracy ensuring and scale controlling, then an appropriate finite element model is built; the structure natural frequencies and the corresponding mode shapes are obtained by modal analysis; the spatial-frequency power spectrum density of road roughness which is from national standards is converted into the time-frequency power spectrum density in the case of considering the effects of speed, on this basis the dynamic response of the structure under the excitation of the random road spectrum is analyzed; fatigue life of the fixed frame on A-level road and D-level road is evaluated according to the results of the analysis combined with linear cumulative damage theory and three-interval stress method.Finally, the strength and stiffness properties of the fixed frame under ultimate toads by two ways mounting to the vehicle body is analyzed with which comes to the conclusion that the mounting way of the lengthwise direction of tanks is perpendicular to the driving direction is better; with the target of longer life, the best ligature spacing for the fixed frame of hydrogen tanks under the excitation of the random road spectrum is obtained, which provides reference for the design of the hydrogen tanks components.