Research On Surface Morphology Of Pure Copper Under Fatigue Loading

At present,all the fatigue control technologies are only applicable to the crack growth stage.For many components,the fatigue initial stage accounts for 90% of the fatigue life,and the fatigue initial stage life depends mainly on the constant consumption of the plastic deformation of the material under cyclic loading.Slip is the main mechanism of plastic deformation,so the plastic deformation experienced by the sample is directly related to the development of the slip zone.This paper hoped to study the evolution law of surface slip band and its influence on component fatigue failure during the process of material fatigue,and explored an actual test method that can describe the material damage characteristics at the initial stage of fatigue and reflect the intricate and complex evolution characteristics of early fatigue life materials,and establish a quantitative understanding of the initial stages of fatigue.In this paper,the fracture mechanism of the fracture mechanism of the sample is found from the static loading test,the notched static load test and the fatigue test at different loading conditions.It is found that the fracture mechanism of the above specimen changes from the ductile fracture of the static load to the fatigue fracture brittle fracture,which indicates that the plastic deformation ability of the specimen in the fatigue process is eliminated.It is consumed.In order to characterize and test the relationship between the consumption of plastic deformation and the fatigue cycle during fatigue,the development and evolution of the slip band and other surface morphology on the surface of the specimen under different fatigue cycles were studied by two methods of direct observation of optical microscope and the SEM test of surface complex.As an exploration of practical testing methods for early damage characteristics of fatigue life,the following conclusions are drawn:1.Fracture analysis shows that the fracture mechanism of pure copper specimens changes from the ductile fracture(ductile fracture and shear)at static load to fatigue fracture brittleness,indicating the plastic deformation capacity of the specimen during fatigue loading.2.The statistical analysis of the surface slip zone in the surface topography image of the pure copper specimen observed by the light microscope shows that the slip line is unevenly distributed on the surface of the sample,and the obtained data can qualitatively reflect the slip of pure copper surface during fatigue.The intensiveness of the belt increases with the increase of the fatigue cycle,which also reflects the non-uniform continuity and anisotropy of the plastic deformation of the material.3.The SEM analysis results of the surface replicas show that,under the same load spectrum,the “twisting lines” of different cycle times have changed from “disorderly” to “already in the same direction”,forming the surface morphology of juxtaposition and gradually increasing in length.4.The surface morphology of pure copper observed on the surface complex does not directly correspond to the slip band on the surface of pure copper,but it increases regularly with increasing fatigue times.As a surface feature,according to the mechanism of metal plastic slip deformation generated on the metal surface,it is expected as a new physical quantity reflecting the degree of fatigue in pure copper fatigue process.5.Due to the appearance of the main crack before the specimen is broken,the stress concentration of the crack tip is increased,that is,the maximum stress triaxiality in the stress field before the fracture increases,which also makes it possible to change the material fracture mechanism from toughness to brittleness.The analysis of stress field before breaking shows that the maximum value of stress triaxiality increases,but it is not yet large enough to make the hole-cutting of cracking machine directly become cleavable brittle fracture,and it can be seen that the consumption of plastic deformation capacity under cyclic loading is still The main cause of fatigue and brittle fracture.