Test method for acquiring aluminum alloy plate friction-stir welding head fatigue small crack initiation and extension morphology

Abstract

The invention discloses a test method for acquiring an aluminum alloy plate friction-stir welding head fatigue small crack initiation and extension morphology, and relates to the field of mechanical structural fatigue. The method includes the steps: observing and selecting initial morphologies of characteristic microstructures of four surfaces of a shooting plate under a microscope before fatiguetest; performing continuous fatigue and interrupt fatigue test; performing unloading and shedding on the interrupt fatigue test at regular intervals, observing micro-structural regions of characteristics such as scratches, holes and enhanced particle aggregations in a focused manner, initially confirming a probable initiation point of a small crack once periphery colors of the regions or other regions are deepened and darkened under a 10-time objective lens and sliding belts are generated in the regions or other regions under 40-time objective lens; shooting generated small-crack morphologiesand extension processes; finding out a crack with extension rapider than that of other small cracks, and forecasting a probable main crack; measuring length of the crack, and calculating extension rate according to a secant method; determining the critical size of an aluminum alloy plate fatigue small crack stage according to the extension rate.

Description

technical field [0001] The invention relates to the field of mechanical structure fatigue, and proposes an experimental method for obtaining the initiation and propagation morphology of fatigue small cracks in friction stir welded joints of aluminum alloy plates. Background technique [0002] According to statistical data, for welding, the joint is the weakest link in the whole structure, and the main failure mode of the welded structure is fatigue fracture. Among them, the initiation and propagation stages of small cracks account for about 70% to 80% of the fatigue life. Moreover, for welded joints of aluminum alloy plates, small fatigue cracks may initiate on all four sides of the fatigue plate, especially the side and front. The metal plate goes through the stages of fatigue crack initiation and propagation, and the main crack finally leads to the fracture of the specimen. Since the main crack may not only occur on the front and back, but also easily on the side, and th...

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Problems solved by technology

Since the main cracks may not only occur on the front and back, but also easily occur on the side, and the microscopic characteristics and propagation shape changes of the side cracks are limited by the space of the fatigue testing machine and the size of the sample. It is very difficult to reliably obtain online means.

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