Research And Application On Prediction Method Of Notch Tensile Strength Of Typical Disk Material

The analysis of burst speed is an important content of modern aero-engine disk strength design. With the improving of the aircraft engine overall performance level, advanced high strength alloy materials are widely used in the disk, the traditional method of predicting burst speed can not meet the needs of the advanced materials disk design analysis. Research on tensile deformation and failure behavior of high strength disk materials based on notched specimen tensile experiment can effectively reflect the influence of multiaxial stress state in the disk on material deformation and failure behavior. The method of predicting notch tensile strength is established and verified based on the above research foundation, which has an important realistic meaning and engineering value for further development and validation of more reliable method of predicting disk burst speed predict.This article selected the turbine disk common alloy GH4169 as the main study object, experiment and theoretical analysis were studied on the notch tensile failure behavior and the method of predicting ultimate strength, and it wad applied to the analysis of disk burst speed. The main work is summarized as follows:(1)The tensile experiments of notched round bar and plate specimens of GH4169 were carried out, the influence of notch geometry parameters, stress concentration and stress triaxiality were analysed on notch tensile strength and effective fracture strain of GH4169. The results showed that the notch root radius and stress concentration factor had a significant effect on the tensile strength of notched round bar specimen and had a little effect on the tensile strength of notched plate specimen. The local maximum effective fracture strain of notched plate specimen had an approximate linear correlation with stress concentration factor, all the ultimate tensile strength of notched specimen had an approximate linear correlation with the average stress triaxiality of notch root cross section.(2) Subdivision and microscopic observation were conducted on the notched specimen that did not stretched up to fracture at different stage. The results showed that when notch is sharp, before the ultimate load appeared, crack was generated in the specimen surface and extended to interior at the notch root; when notch is blunt, there was no crack founded at the notch root before ultimate strength.(3)Based on the uniaxial tensile data, the nonlinear isotropic hardening constitutive model were established of the material of GH4169 and GH742. Using Hosford yield criterion when it respectively degenerated into Tresca yield criterion and von Mises yield criterion to study the accuracy of large deformation FEM predicting the notched tensile strength of GH4169 and the burst speed of equal thickness disk of GH742. The results show out that the nonlinear isotropic hardening constitutive model that this paper uses could describe the tensile true stress-strain curve well. Compared with the result of von Mises yield criterion, Tresca yield criterion could predict the notched tensile ultimate strength and the tensile curve of GH4169 notched specimen, and the error limit was within 3%.; the predicted result of disk burst speed that used Tresca yield criterion was more close to the experiment result, the error was within 5%.(4) Using Tresca yield criterion and the large deformation FEM, the influence was preliminary studied that the critical geometry characteristic dimension on the predicted result of the burst peed of some sub dimension disk of GH4169. The results showed that radius and thickness of the disk central hole and simulated mortise slit width had a significant influence on the burst speed of the simulated GH4169 disk, the root radius of simulated mortise and web transition radius had a little effect on the burst speed.