Research On Fatigue Crack Growth Characteristic Of Titanium Disk With Interior Hard Alpha

Aero-engine airworthiness regulations stipulate that damage tolerance assessments must be performed on life-limited parts.This paper takes the titanium alloy disk as the research object and carries out crack growth research on titanium alloy disk with hard alpha inclusion by crack growth simulation and the disk low-cycle fatigue test with high-speed spin tester.The main research work is as follows:(1)The titanium alloy disk was designed.Preparation methods and burial methods for hard alpha inclusions were proposed and the buried location of inclusions was determined.The finite element analysis method was used to determine the load of low cycle fatigue(LCF)test and the overall stress state of the test article,especially the region which is near the buried inclusions.It is concluded that the circumiferential stress near the location of buried inclusion is the first principal stress,and the radial and axial stresses are relatively low.Therefore,cracks in this region with the crack surface paralleling to axial direction and which expand radially can be approximated as pure Type I crack.(2)The LCF test of the disk was performed in a spin rig facility.By observing the fracture of disk fragment,it can be seen that the fracture belongs to fatigue failure,which is due to the initiation of a crack at the inclusion and growing to critical length.The fracture was observed with an optical microscope to obtain the fracture surface macroscopic morphology,including feature size,area and other information.Scanning electron microscope was used to observe the fracture micro-morphology,including the information of fatigue striation spacing.The fracture analysis was performed to obtain the crack growth life.(3)The 3D crack growth finite element software was used to simulate the crack growth rate of the test article.The initial crack size was determined according to different methods to obtain different crack growth life.Comparing with the fracture reverse life,it is concluded that the initial crack size is determined by using the equivalent area of the inclusion area plus the initiation area,and the simulation results are in good agreement with results of fracture analysis.At the same time,the crack front pattern can be well simulated.At present,the domestic research on the crack growth of titanium alloys disk with hard alpha inclusions is still in its infancy.This paper combines LCF test technology and simulation analysis method to carry out related research in domestic for the first time.It hopes that the research can provide valuable reference for follow-up related research.