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Forecasting method of material fatigue threshold value under different stress ratios

A prediction method and stress ratio technology, applied in the field of fatigue crack growth, can solve the problems of heavy test workload, complicated measurement procedures, time-consuming, etc.

Active Publication Date: 2014-07-23
EAST CHINA UNIV OF SCI & TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

For the condition of multiple stress ratios, the measurement procedure is complex, cumbersome, and the test workload is large.
In engineering practice, multiple heat treatments are often performed on the same material to meet different performance requirements, and the fatigue threshold test for this type of material is more time-consuming and uneconomical

Method used

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  • Forecasting method of material fatigue threshold value under different stress ratios
  • Forecasting method of material fatigue threshold value under different stress ratios
  • Forecasting method of material fatigue threshold value under different stress ratios

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0043] Example 1 Prediction of Cr-Mo-V Steel Fatigue Threshold for a Certain Rotor

[0044] After quenching a certain rotor with Cr-Mo-V steel, the tempering heat treatment system is 580°×10h. Using compact tensile specimens, the fatigue threshold test at room temperature was carried out by the load-reduction method, and the fatigue crack growth data at R=0.1, 0.3, 0.5, 0.7, and 0.9 were obtained. The specific steps for predicting the fatigue threshold are as follows (see figure 1 ):

[0045] (1) Convert ΔK under various stress ratios to R=0 equivalent stress intensity factor range ΔK (0) , to obtain da / dN-ΔK (0) relationship (such as figure 2 shown). At the same time, calculate da / dN=1×10 -6 α value under high and low R at mm / cyc, where, when R≥0.7, α=α 2 =1.1317×10 -4 ; while for R-4 .

[0046] (2) Fit the C and m values ​​in the Paris formula according to the linear relationship in the log-log coordinates (see Table 1).

[0047] Table 1. C and m values ​​in the Pa...

Embodiment 2

[0055] Example 2 Prediction of Fatigue Threshold Value of Cr-Mo-V Steel for a Certain Rotor After Adjusting Tempering Heat Treatment System

[0056] In order to improve the quenching and tempering properties of the Cr-Mo-V steel used for a certain rotor in Example 1, after quenching the Cr-Mo-V steel used for a certain rotor in Example 1, the tempering heat treatment system was adjusted to 580 ° × 40h, Then predict the fatigue threshold, the specific steps are as follows:

[0057] (1) Carry out the fatigue threshold test under R=0.9 to get the fatigue threshold ΔK th,(0.9) 2.29MPa·m 1 / 2 ; Compared with the original heat treatment, the fatigue threshold increased by 20% after the tempering temperature was increased.

[0058] (2) In the prediction, it is considered that: in ΔK (R) with ΔK (0.9) In the relationship, A(R) and B(R) have little change, that is, the relationship between A(R) and B(R) and R is still:

[0059] A(R)=0.14+0.24R+0.83R 2 ,

[0060] B(R)=0.9-R.

[006...

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Abstract

The invention discloses a forecasting method of a material fatigue threshold value under different stress ratios. A forecasting model of the fatigue threshold value is derived according to fatigue crack propagation data under different stress ratios, and then the fatigue threshold value under any stress ratio is forecasted based on the fatigue threshold value under the stress ratio being 0.9. The forecasting method comprises the following specific steps: (1) converting delta K to deltaK(0) and converting the deltaK under any stress ratio to an equivalent value deltaK(0) under the stress ratio being 0 according to a Kwofie model; (2) fitting parameters, wherein the expression formula is as shown in the specification; (3) determining A(R) and B(R) and establishing relationship between deltaK(R) and deltaK(0.9); and (4) forecasting the fatigue threshold value according to deltaK[th(0.9)]. According to forecasting method, the fatigue threshold value under various stress ratios can be forecasted according to the forecasting model only by obtaining the fatigue threshold value when R is 0.9, the forecasting model is only concerned with the stress ratio, the form is simple, the parameters are few, test materials can be obviously saved, time and cost can be obviously reduced, and the work efficiency can be improved. The model can be used for efficiently forecasting the fatigue threshold value of the same type of material at different process states.

Description

technical field [0001] The invention belongs to the technical field of fatigue crack growth and relates to a method for predicting the fatigue crack growth threshold of materials under different stress ratios. Background technique [0002] In fatigue crack growth research, the fatigue crack growth threshold (ΔK th ) is a measure of whether the crack propagates. In engineering, it is generally stipulated that the fatigue crack growth rate da / dN is 1×10 -7 The corresponding stress intensity range ΔK in mm / cyc is the fatigue threshold. The size of the threshold represents the ability of the material (structure or element) to resist crack propagation. In the structural damage tolerance design, the threshold value is a necessary material performance parameter, which is of great significance to the prediction of the structural life and the optimal design of the structure. GB / T6398-2000 "Metallic Materials Fatigue Crack Growth Rate Test Method" gives the test measurement proced...

Claims

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Application Information

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IPC IPC(8): G01N3/00
Inventor 朱明亮轩福贞杜彦楠李煜佳涂善东
Owner EAST CHINA UNIV OF SCI & TECH
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