Fatigue life prediction method for friction stir welded component based on small crack propagation

Abstract

The invention discloses a fatigue life prediction method for a friction stir welded component based on small crack propagation, and belongs to the technical field of fatigue diagnosis and analysis ofmechanical structures. The method comprises the steps that a bone-shaped flat plate sample is prepared, fatigue small crack propagation replica tests under different stress loads and different stressratios are conducted on different areas of a joint, and a secant method is adopted for calculating the propagation rate of small cracks; a New-Raju model is adopted for calculating the stress intensity factor range of the small cracks of the joint; c values in the depth direction and a / 2 values in the vertical direction of semi-arc shapes of fatigue crack propagation zones in fracture shapes of different areas of the joint, and the depth-to-length ratio 2c / a of the cracks is calculated; a curve of the propagation rate of the cracks along with the change of the stress intensity factor range isdrawn; an effective stress intensity factor is calculated; a formula of the propagation rate of the small cracks is determined; an initial crack size a0 and a critical crack size ac are determined; the formula of the propagation rate of the small cracks is integrated to obtain the fatigue life of the welded component. By means of the scheme, the fatigue life of the friction stir welded component can be more easily and accurately predicted.

Description

technical field [0001] The invention relates to a method for predicting fatigue life, in particular to a method for predicting fatigue life of a friction stir welded component based on small crack propagation, and belongs to the technical field of fatigue diagnosis and analysis of mechanical structures. Background technique [0002] For friction stir welded components, the welded joint is the weakest part of the entire structure, and the main failure mode of welded components is fatigue fracture. Fatigue specimens undergo the process of crack initiation, small crack growth and long crack growth. Among them, the initiation and propagation stages of small cracks account for about 70% to 80% of the fatigue life. In most cases, the sample is damaged due to initial microscopic defects such as inclusions, hardened particles, and micro-holes inherent in the material itself, or due to collisions, nicks, and corrosion during processing. For friction stir welded joints, the initiati...

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