Research On Stress Test And Life Assessment Of Locomotive Fuel Tank

With the rapid development of railway industry,in order to adapt to the worse railway operation environment,the design requirements of diesel locomotives have become more stringent.In the process of vehicle service,the locomotive fuel tank will vibrate under the external load,and the internal weld of the fuel tank is prone to fatigue damage.Therefore,it is of great engineering significance to consider the fluid structure coupling effect for the test and simulation fatigue analysis of fuel tank.As the internal weld of fuel tank exists in the closed tank structure,it is impossible to monitor and detect it from the outside in real time.It is very important to evaluate the internal weld accurately through the external dynamic stress test after the fuel tank welding.In this thesis,aiming at the fatigue crack problem of fuel tank,a reasonable fluid structure coupling simulation method and the relationship between the internal and external fatigue damage of fuel tank are derived from the test and simulation.Firstly,the fatigue vibration test of notched specimen is carried out.Design tooling support to divide the samples into two groups: in oil and out of oil and process the test data and count the fatigue life of each sample.According to the experiment,the virtual mass method is used to simulate the fluid structure coupling effect,and through the quasi-static analysis,transient analysis and frequency response analysis,the simulation results are compared with the test results.The results show that the quasi-static analysis based on the virtual mass method cannot simulate the oil action,while the transient analysis can simulate the oil action better than the frequency response analysis.The transient analysis of fatigue life is closer to the test results,and the frequency response analysis is more conservative.Both test and simulation results show that the fatigue life of the sample in the oil is less than that of the sample out of the oil.Secondly,in order to deduce the relationship between the internal and external fatigue damage of the fuel tank,the small scale model of the fuel tank is designed to carry out sweep frequency test and fatigue vibration test respectively.Through sweep frequency test,the accurate damping coefficient is determined and the finite element model verification is provided for the simulation calculation.According to the actual crack direction of the project,the strain gauge is divided into parallel weld direction and vertical weld direction,and different oil state fatigue vibration tests are carried out on different measuring points inside and outside the box.The strain signals were collected and the damage was calculated according to the fatigue characteristics.Finally,the transient analysis method based on virtual mass method is used to simulate the small scale model test of fuel tank.Output the stress response curve in different directions,and calculate the simulated damage of measuring points.Compared with the test results,it is found that the waveform,stress value and damage value of the stress response curve are all in good agreement with the test,which verifies the accuracy of the method again.The addition of oil will increase the weld damage,and have a greater impact on the damage in the direction of vertical weld and a smaller impact on the damage in the direction of parallel weld.The relationship between the internal and external damages of the box in the direction parallel to the weld joint in the empty box state or different height of oil state is the same.The difference between the internal and external damages in the direction of vertical weld in the empty box state is 100 times,while the difference between the internal and external damages in the oil state is 20 times,and the relationship between the internal and external damages in different oil heights is the same.