A Method for Evaluating Low Cycle Fatigue Life

Abstract

The invention relates to a low-cycle fatigue life evaluating method considering the influences of GH4169 alloy microstructures. The method includes the steps of firstly, carrying out a low-cycle fatigue test of a standard round bar test piece to obtain low-cycle fatigue life data under the GH4169 alloy working conditions; secondly, conducting microstructure observing and representing on the standard piece to obtain the grain size of GH4168 alloy; thirdly, obtaining the content of a delta phase in the GH4168 alloy with the aid of image processing software, and making the delta phase distributedalong crystals equivalent to a crystal interface with a certain width; fourthly, improving an Ostergren life model in terms of energy on the basis of a crystal interface energy expression, and establishing a low-cycle fatigue life predicting model considering the influences of the alloy microstructures; fifthly, predicting the GH4168 alloy low-cycle fatigue life corresponding to different microstructures through the improved Ostergren life model, and evaluating the service life of a corresponding aero-engine part.

Description

technical field [0001] The invention relates to a low-cycle fatigue life evaluation method considering the influence of the microstructure of the GH4169 alloy, which is a low-cycle fatigue life evaluation method capable of considering the influence of the microstructure of the aeroengine GH4169 alloy, and belongs to the technical field of aerospace engines. Background technique [0002] Nickel-based high-temperature alloy H4169 is often used in the preparation of aero-engine turbine disks, high-pressure compressor disks and other disks due to its high yield strength and good plasticity at 650 °C. The working environment of aero-engine discs is very harsh, and low-cycle fatigue failure is prone to occur under the action of repeated loads. However, the disc processing process inevitably leads to differences in the microstructure of different parts of the material, which leads to the dispersion of fatigue life. At present, for the low-cycle fatigue failure of aero-engine discs...

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Problems solved by technology

The working environment of aero-engine discs is very harsh, and low-cycle fatigue failure is prone to occur under the action of repeated loads

However, the disc processing process inevitably leads to differences in the microstructure of different parts of the material, which leads to the dispersion of fatigue life.

At present, for the low-cycle fatigue failure of aero-engine discs, traditional life prediction models rarely consider the influence of microstructure

[0003] The existing literature "Merrick H F. The low cycle fatigue of three wrought nickel-base alloys [J]. Metallurgical Transactions, 1974, 5(4): 891-897" used different heat treatment processes to obtain nickel-base alloys with different grain sizes. Inconel 718 alloy, through the study of its fatigue properties, it is found that the alloy with a larger grain size has a lower low-cycle fatigue life. On the contrary, the alloy with a smaller grain size has a higher low-cycle fatigue life, but the grain size and low cycle are not given. Quantitative relationship between fatigue life, grain size cannot be considered when evaluating low cycle fatigue life

[0004] The existing literature "Zeng Xu. Influence of delta phase on the low-cycle fatigue behavior of nickel-based superalloy GH4169 [D]. Shanghai: East China University of Science and Technology, 2015" obtained GH4169 alloys with different δ phase content and distribution through different heat treatment processes. At low strain amplitude (Δε t / 2=0.5%) standard parts with intergranular distribution and higher δ phase content, the longer the low-cycle fatigue life, but the quantitative relationship between the δ-phase content and fatigue life is not given, when evaluating the low-cycle fatigue life The effect of δ phase content cannot be considered at present

[0005] In a word, when evaluating the low-cycle fatigue life of GH4169 alloy in the prior art, the effects of microstructure such as grain size and δ phase content have not been considered. For GH4169 alloys with different grain sizes or δ phase content, the prior art Limited ability to assess low cycle fatigue life

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