Method for predicting high-low-cycle composite fatigue crack growth life of turbine joggle structure

Abstract

The invention relates to a method for predicting the high-low-cycle composite fatigue crack growth life of a turbine joggle structure, and the method comprises the steps: (1), building a crack growth model giving consideration to a crack closure effect; (2), determining a high-cycle load stress intensity factor model; (3), determining a low-cycle load stress intensity factor model; (4), judging whether a current cycle is a high-cycle load or not: executing step (5) if the current cycle is the high-cycle load, or else executing step (6); (5), calculating a composite fatigue lower crack increment, judging whether a next cycle is a low-cycle fatigue load or not: obtaining the maximum crack tip opening displacement of the current cycle if the next cycle is the low-cycle fatigue load, and executing step (7), or else executing step (8); (6), calculating the variance of the low-cycle load lower crack tip opening displacement; (7), calculating the residual crack tip opening displacement and crack increment according to the results inputted at steps (5) and (6); (8), updating the crack length, repeatedly carrying out the steps (4)-(7) if the maximum stress intensity factor is less than the fracture toughness, or else completing the calculation, and obtaining the crack growth life.

Description

technical field [0001] The invention is a method for predicting the extended life of a high-low cycle composite fatigue crack of an aero-engine turbine mortise joint structure, which is a calculation method capable of high-low cycle coupling, crack closure effect and small time scale, and belongs to the technical field of aerospace engines . Background technique [0002] The turbine disk is one of the few key parts of the aero-engine, and the turbine disk is generally connected with the tenon and tenon of the blade by a fir tree-shaped tenon-and-groove structure. Turbine mortise joints bear low-cycle fatigue loads composed of centrifugal force and thermal load of blades, and small-amplitude and high-frequency high-cycle fatigue loads of blade lateral vibration and self-vibration induced by aerodynamic loads, that is, high-low cycle composite fatigue loads. Due to the dual complexity of structure and loading, not only many types of in-service aero-engines have been troubled ...

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Problems solved by technology

[0003] At present, the prediction method of high-low cycle composite fatigue crack growth life mainly uses the traditional method to calculate the stress intensity factor under high cycle load and low cycle load respectively, and analyzes the crack growth based on the linear cumulative damage theory, which has obvious limitations: ( 1) The coupling effect of high-cycle load and low-cycle load is not considered, so it is difficult to guarantee the prediction accuracy; (2) The traditional method treats high-frequency load as an equal-amplitude static load superimposed on low-cycle load, and does not consider the impact of structural vibration characteristics on high-cycle loads. The influence of hoop stress intensity factor does not reflect the change of structural vibration characteristics with the increase of crack length

[0004] Existing literature Hu D, Yang Q, Liu H, et al.Crack closure effect and crack growth behavior in GH2036 superalloy plates under combined high and low cycle fatigue[J].Int J Fatigue.2017,95:90-103 from the experimental point of view The high-low cycle composite fatigue behavior of GH2036 material was studied, and its crack growth life was predicted, but the research results were only for standard test pieces in the laboratory, without considering the structural characteristics of the turbine tenon joint parts, and did not analyze the turbine tenon joint structure. Transient analysis does not consider the influence of load history on the life of high-low cycle composite fatigue crack growth. The results are relatively single for materials and lack certain applicability.

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