| In the last twenty years, high pressure water jet has achieved great progress andbeen widely used.One character of high pressure water jet is that the pressure is veryhigh and it is fluctuated greatly and continuously. As a result, many parts worked underthat condition are prone to fatigue damage. As an effective method to improve thefatigue resistance of the ultra-high pressure vessel, autofrettage has been widely used inindustry. The autofrettage process is a process in which a much higher pressure has beenimposed on the internal side of vessel beforehand, which leads to a plastic deformationon the inner wall of the container. Because the plastic deformation is irreversible, thefavorable residual stress distribution is formed on the inner wall of the container afterunloading. It is because of this, the fatigue strength of the parts are significantlyimproved.In order to get some results which can be used in industry directly, a typical partofhigh pressure pump-high pressure cylinder has been selected as the analysis object. Inthe first part of the thesis, autofrettage process has been analyzed from the theoreticalpoint of view. After that, autofrettage process has been farther explored with FEAsoftware. By using different autofrettage pressures, heat treatment conditions and wallthickness of the cylinder, autofrettage process has been simulated. According to thesimulation results, in autofrettage process, large quantity residual compressive stress hasbeen generated in the inner wall of the cylinder. This compressive stress is useful forimproving fatigue strength of cylinder. To further verify the analysis results, a test standhas been built with which a series of cylinders with and without autofrettage processhave been tested. The test results further verified that autofretage process can improvecylinder’s fatigue strength greatly. |
