Method for predicting fatigue crack expanding threshold value under different stress ratios

Abstract

The invention relates to a method for predicting a fatigue crack expanding threshold value under different stress ratios. The method comprises the steps of solving a linear fitting slope and a cross-over point of fatigue crack stable expanding area and near-threshold area data points on a log-log coordinate through the test data of the fatigue crack expanding threshold value under a known stress ratio, i.e. the relation between the fatigue crack expanding rate da / dN and a stress intensity factor range delta K, and executing the calculation under the condition that the maximal stress intensity factor Kmax is equal to delta K / R on the cross-over point of a stable expanding area and a near-threshold area under different stress ratios, so that the fatigue rack expanding threshold value of the unknown stress ratio R can be predicted, and R is more than zero. Compared with the traditional study, the method is not subjected to the limitation of the specific material, and is applicable to the material with uniform tissues and good in universality; moreover, the test workload of the threshold value can be effectively alleviated, and the cost is lowered.

Description

technical field [0001] The invention relates to the field of mechanical properties of a material with a uniform structure, in particular to a method for predicting the fatigue crack growth threshold of a material with a uniform structure under different stress ratios R (R>0). Background technique [0002] The fatigue crack growth threshold reflects the fatigue resistance of materials and is an important index to measure the high cycle fatigue performance of materials. It has important reference significance for the design of long-life and infinite-life components in engineering. However, the test results vary with the change of the stress ratio R, and it is necessary to test the threshold value under different stress ratios R, and the cycle is long and the cost is high. [0003] Existing studies have shown that there is a certain relationship between the threshold of fatigue crack growth and the structure size of the material under a certain stress ratio, and a mathematic...

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Problems solved by technology

However, the test results vary with the stress ratio R, and the threshold value under different stress ratio R needs to be tested, which takes a long period and high cost

[0003] Existing studies have shown that there is a certain relationship between the threshold of fatigue crack growth and the structure size of the material under a certain stress ratio, and a mathematical relationship between the two has been established; however, the threshold of fatigue crack growth under an unknown stress ratio cannot be speculated. And most of them are specific analysis of specific materials, and no general method has been proposed.

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