Model for simulating overload hysteresis effect in fatigue crack propagation

A technology of fatigue crack growth and hysteresis effect, applied in the field of fatigue crack growth life model, it can solve problems such as large error, small overload influence area, and failure to reflect delay and hysteresis phenomenon.

Active Publication Date: 2017-06-23
NORTHWESTERN POLYTECHNICAL UNIV
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Problems solved by technology

[0004] In order to overcome the fact that the existing technology cannot reflect the hysteresis phenomenon, the calculated overload influence area is too small, the calculation of the life of each case other than the small stress ratio and the small tensile overload ratio has a large error, and the consideration of compression overload and the test results Inconsistent deficiencies, the present invention proposes a model for simulating the overload hysteresis effect in fatigue crack growth

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  • Model for simulating overload hysteresis effect in fatigue crack propagation
  • Model for simulating overload hysteresis effect in fatigue crack propagation
  • Model for simulating overload hysteresis effect in fatigue crack propagation

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Embodiment Construction

[0040] This embodiment is a model for simulating the overload hysteresis effect in fatigue crack growth.

[0041] The test piece in this embodiment is 2A12-T4 aluminum alloy M (T) test piece, the test piece width W=100mm, the test piece thickness B=3.74mm, the material yield strength σ s =336MPa, overload cut-off ratio γ S0 =2.62. Material constant in Walker's formula: C=3.8026×10 -11 , p=3.4145, q=0.6586, t=0.1057. Stress Intensity Factor Threshold ΔK th =2.73(1-R) 0.46 . The specimen is subjected to constant amplitude fatigue load, the initial crack length a i =8mm, when the crack length a=13mm, apply overload, then continue to apply constant amplitude fatigue load, terminate the crack length a f = 30mm. Calculate the fatigue crack growth life for the following four types of loading cases.

[0042] (1) Peak value of fatigue load P max =18kN, stress ratio R=0.06, tensile overload ratio γ OL =1.8,2.2;

[0043] (2) Peak value of fatigue load P max = 20kN, stress rati...

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Abstract

The invention discloses a model for simulating overload hysteresis effect in fatigue crack propagation. The model is executed in the following steps of: judging a crack propagation state through the position of a crack tip, and deducing an expression of a hysteresis-free stress intensity factor by adoption of a piecewise function form according to a hysteresis state judgement condition; considering an overload cutoff ratio of a material as a function of a fatigue load stress ratio; and when a weakening function, for hysteresis effect generated by tensile overload, of compressive load is considered, importing a weakening factor to correct a residual stress intensity factor in an overload influence area. Experiments verify that the relative differences between a life value calculated by a model and experiment values are within + / -5%.

Description

technical field [0001] The invention relates to a fatigue crack growth life model, in particular to a fatigue crack growth life model with an overload hysteresis effect. Background technique [0002] For structures subjected to random alternating loads in service, the fatigue crack growth life is affected by the load sequence. In the low-load cycle after high load, the fatigue crack growth rate of the structure decreases, which is significantly lower than that without high load, and the fatigue crack growth life of the structure becomes longer. This phenomenon is called overload hysteresis. The test results have proved that after the tensile overload, the fatigue crack growth rate gradually decreases. After the crack grows for a certain length, the growth rate reaches the minimum value, showing a delay hysteresis phenomenon, and then the growth rate gradually rises, returning to the expansion without overloading. The hysteresis effect disappears at the rate level, and the g...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G06F17/50
CPCG06F30/20
Inventor 郭小华李亚智冯盼盼
Owner NORTHWESTERN POLYTECHNICAL UNIV
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