Fatigue Analysis of Fuel Tank Straps Due to Slosh Loads

A great number of investigations on fatigue analysis and liquid sloshing has been carried out in different fields of application such as space vehicles, large ground tanks, cargo ships, and highway truck tankers. A variety of approaches to solve the sloshing problem due to different requirements, tank characteristics, and peculiarities of input disturbance gives different, sometimes contradictory, results which are not directly applied to the car tank system. One of the most important components in the fuel tank system is strap, which has vital role in road safety. Fuel tank strap can be separated due to fatigue during vehicle operation, causing the tank to be unsupported and increasing the risk of fuel leak. Its failure can cause very dangerous accidents. The effect of sloshing load, one of the main applied loads on the tank structure, on life of the strap has not been studied carefully before. This thesis presents the numerical analysis of liquid behaviour in sloshing situation and the fatigue analysis of the fuel tank straps due to slosh loads exerted on the tank walls in an accelerating car. In this study, computational fluid dynamics (CFD) and finite element method (FEM) are employed to simulate transient sloshing of fuel inside the tank and find the location of the critical point of crack initiation and predict the life of the fuel tank strap. Using the volume of fluid (VOF) method, a new developed method in CFD, the range of loads on the walls of the fuel tank is determined for the operational conditions that the vehicle experience. An equivalent mechanical model is developed to verify the CFD sloshing simulation result through the normal impact load applied by the effective mass of a pendulum system. The finite element (FE) is further used to create the virtual model of the strap and perform a static analysis. The stresses and strains from the static analysis are then used as input to locate the critical point and predict the life expectancy of the strap under slosh loading.