Mechanical structure crack expansion rate and crack expansion life span predication method

Abstract

A crack growth rate and crack growth life prediction method for a mechanical structure belongs to a calculation method for fatigue crack growth rate and crack growth length of the mechanical structure. At first, a relationship between S-N and P-S-N curve expressions (power function form) and a crack growth rate curve expression (Paris formula) is built up in the method. A determination method of the crack growth rate under the conditions of block spectrum load, overload hysteresis load and random load is proposed. And a determination method of Paris curve parameters is provided when the S-N and P-S-N curves cannot be expressed in power function form. And a method for improving the prediction precision of the crack growth rate and the crack growth life is proposed. The S-N and P-S-N curves are used by the method to predict the crack growth rate and the crack growth life. Therefore, the method has the advantages of little dependence on tests and high precision and can shorten the product development period and save much manpower, material resources and financial resources.

Description

technical field [0001] The invention relates to a method for calculating the fatigue crack growth rate and crack growth length of a mechanical structure that needs to withstand repeated stress levels during its service life. Background technique [0002] The crack growth rate curve is the basic data for crack growth analysis. However, it is affected by many factors, such as structural form, processing technology, load spectrum type, stress level, etc., and it is difficult to determine, especially the crack growth under variable amplitude loads. rate is more difficult to determine. Generally, the accurate crack growth rate can only be obtained through a large number of crack growth tests. This method has high requirements for test technology, and is time-consuming and laborious, which increases the cost and cycle of product development. [0003] For a long time, people have tried to link the traditional fatigue design method (including the static strength design method) with...

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Problems solved by technology

[0002] The crack growth rate curve is the basic data for crack growth analysis. However, it is affected by many factors, such as structural form, processing technology, load spectrum type, stress level, etc., and it is difficult to determine, especially the crack growth under variable amplitude loads. more difficult to determine

Generally, the accurate crack growth rate can only be obtained through a large number of crack growth tests. This method has high requirements for test technology, and is time-consuming and laborious, which increases the cost and cycle of product development.

[0003] For a long time, people have tried to link the traditional fatigue design method (including the static strength design method) with the durability design method based on fracture mechanics, and establish the relationship between them, such as establishing the fatigue limit σ W and crack growth threshold ΔK th Therefore, some fatigue performance parameters can be used to determine other performance parameters, and the design and test process can be simplified, but they cannot yet establish a relationship with the crack growth rate, and cannot predict the crack growth rate.

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