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JP-2026075492-A - Fatigue crack estimation method and estimation apparatus

JP2026075492AJP 2026075492 AJP2026075492 AJP 2026075492AJP-2026075492-A

Abstract

[Problem] To provide a fatigue crack estimation method that can predict the crack propagation rate in the medium temperature range. [Solution] The fatigue crack estimation method includes a confirmation step of confirming the operating conditions of the heat-resistant alloy; a propagation test step of conducting a crack propagation test based on the operating conditions; a relationship formula creation step of creating a first relationship formula between the crack propagation rate and the maximum stress intensity factor K max and a second relationship formula between the amount of crack growth D after unloading and reloading and the stress intensity factor range ΔK based on the results of the crack propagation test; a prediction formula creation step of creating a crack propagation rate prediction formula from the first and second relationship formulas; and an estimation step of inputting the operating conditions into the crack propagation rate prediction formula and estimating the crack propagation rate. [Selection Diagram] Figure 2

Inventors

  • 中原 瞬

Assignees

  • 三菱重工業株式会社

Dates

Publication Date
20260508
Application Date
20241022

Claims (8)

  1. A verification process to confirm the operating conditions of the heat-resistant alloy, A propagation test step in which a crack propagation test is carried out based on the aforementioned operating conditions, Based on the results of the aforementioned crack propagation test, a relational equation creation step is made to create a first relational equation between the crack propagation speed and the maximum stress intensity factor K max , and a second relational equation between the amount of crack propagation D after unloading and reloading and the stress intensity factor range ΔK. A prediction formula creation step is to create a crack propagation velocity prediction formula from the first relation and the second relation, An estimation step is to input the aforementioned operating conditions into the aforementioned crack propagation velocity prediction formula and estimate the crack propagation velocity, A fatigue crack estimation method, including [the following].
  2. The fatigue crack estimation method according to claim 1, wherein the crack propagation velocity prediction formula is an equation obtained by linearly adding the first relation and the second relation.
  3. The fatigue crack estimation method according to claim 1, wherein the tensile strength of the heat-resistant alloy at 800°C is 800 MPa or more.
  4. The heat-resistant alloy is, by mass%, Ni: 26.0% to 55.0%, Cr: 15.0% to 21.0%, Mn: 0% to 0.50%, Mo: 1.30-3.30%, Nb: 0% to 5.50%, Al: 0.20-0.80%, Ti: 0.65-2.15%, C: 0% to 0.08%, Si: 0% to 0.35%, Cu: 0% to 0.30%, Co: 0% to 1.0%, B: 0% to 0.006%, and The fatigue crack estimation method according to claim 1 or 2, wherein the chemical composition consists of Fe and impurities as the remainder.
  5. Based on the behavior of crack propagation under operating conditions for heat-resistant alloys, A relational equation generation unit that generates a first relational equation between crack propagation speed and maximum stress intensity factor K max , and a second relational equation between crack growth amount D and stress intensity factor range ΔK after unloading and reloading, A prediction formula creation unit that creates a crack propagation velocity prediction formula from the first relation and the second relation, An estimation unit that inputs the operating conditions of the heat-resistant alloy into the crack propagation rate prediction formula and estimates the crack propagation rate, An estimation device equipped with the following features.
  6. The estimation device according to claim 5, wherein the crack propagation velocity prediction formula is an equation obtained by linearly adding the first relation and the second relation.
  7. The estimation apparatus according to claim 5, wherein the tensile strength of the heat-resistant alloy at 800°C is 800 MPa or more.
  8. The heat-resistant alloy is, by mass%, Ni: 26.0% to 55.0%, Cr: 15.0% to 21.0%, Mn: 0% to 0.50%, Mo: 1.30-3.30%, Nb: 0% to 5.50%, Al: 0.20-0.80%, Ti: 0.65-2.15%, C: 0% to 0.08%, Si: 0% to 0.35%, Cu: 0% to 0.30%, Co: 0% to 1.0%, B: 0% to 0.006%, and The estimation apparatus according to claim 5 or 6, having a chemical composition in which the remainder consists of Fe and impurities.

Description

This disclosure relates to a fatigue crack estimation method and apparatus. Ni-based alloys are used in aircraft engines and gas turbines due to their excellent high-temperature properties. Accurate life prediction methods are needed because accurately predicting the lifespan of aircraft engines and gas turbines can reduce maintenance costs. Conventionally, as described in Patent Document 1 and Non-Patent Document 1, the remaining life was evaluated using a law (linear addition rule) that states that a linear sum of fatigue damage and creep damage holds true at the temperature at which creep occurs. Japanese Unexamined Patent Publication No. 62-835 Standards for High-Temperature Creep and Creep Fatigue Crack Propagation Tests, High-Temperature Strength Division Committee, Japan Society of Materials Science This is a block diagram showing the configuration of the estimation device according to the embodiment.This is a flowchart of the fatigue crack estimation method according to the embodiment.This figure shows an example of the hardware configuration of the estimation device according to the embodiment.This figure shows the relationship between crack propagation acceleration rate, LCF lifetime reduction rate, creep damage, and temperature.This is a diagram illustrating the test specimen and the direction of the load.This is a diagram showing the loading pattern in a crack propagation test.This figure shows an example of the relationship between crack propagation amount (mm) for each holding time and time or number of repetitions.This figure shows an example of the relationship between the stress intensity factor and crack propagation velocity for each holding time.This figure shows an example of the relationship between the stress intensity factor range for each holding time and the amount of crack propagation D during reloading.This figure shows an example of the relationship between B and retention time.This figure shows an example of the relationship between n and retention time.This figure shows an example of a comparison between estimated and measured values. The inventors conducted a holding-type fatigue propagation test on Inconel® 718, which exhibits the HTC phenomenon, and attempted to predict the crack propagation rate by applying the conventional linear addition rule. However, it was difficult to accurately estimate the amount of crack propagation. Therefore, the inventors diligently investigated the HTC phenomenon in the intermediate temperature range and found that crack propagation in the intermediate temperature range occurs during tensile holding, unloading, and reloading in the fatigue test. Further investigation by the inventors resulted in the creation of relationship equations between the stress intensity factor and the amount of crack propagation during tensile holding and unloading/reloading. By creating a crack propagation rate prediction formula from these relationships, it was found that the crack propagation rate could be predicted with high accuracy. Here, the intermediate temperature range refers to the temperature range where the effect of creep is small, for example, above 1/3 of the melting point (e.g., above 500°C) and below 1/2 of the melting point (e.g., below 600°C). Above 1/2 of the melting point (e.g., 600°C), the effect of creep tends to become significant. (Target substances) The materials targeted by the fatigue crack estimation method and apparatus of this disclosure are, for example, heat-resistant alloys in which the crack propagation velocity increases due to a decrease in grain boundary strength (by exhibiting grain boundary fracture) in the medium temperature range. In other words, the target materials are heat-resistant alloys in which the HTC phenomenon occurs. If the HTC phenomenon does not occur, the lifespan can be predicted by conventional methods. Here, whether a heat-resistant alloy exhibits the HTC phenomenon can be determined by the following method. Measurements are performed according to ASTM E647 (Standard Test Method for Measurement of Fatigue Crack Growth Rates) to obtain the temperature dependence of the crack propagation acceleration rate, the temperature dependence of the LCF (Low Cycle Fatigue) lifetime reduction rate, and the temperature dependence of creep damage. Next, in the medium temperature range, the crack propagation acceleration rate, LCF lifetime reduction rate, and changes in fracture morphology (changes in grain boundary strength and creep phenomena) are checked. If, in the medium temperature range, the crack propagation acceleration rate increases due to a decrease in grain boundary strength (due to grain boundary fracture), the LCF lifetime reduction rate decreases, and creep damage is below a specified value, then it is determined that the HTC phenomenon occurs. Examples of such heat-resistant alloys include those with a tensile strength of 800 MPa or higher at 600°C (preferably 800°C). When a alloy has high tensile strength in