Abstract
To quantitatively investigate the cause of the changes in arithmetic mean roughness Ra and arithmetic mean waviness Wa of austenitic stainless steel under low-cycle fatigue loading, precise observation focusing on persistent slip bands (PSBs) and crystal grain deformations was conducted on SUS316NG. During the fatigue tests, the specimen’s surface topography was regularly measured using a laser microscope. The surface topographies were analysed by frequency analysis to separate the surface relief due to PSBs from that due to grain deformation. The height caused by PSBs and that by grain deformation were measured respectively. As a result, both of the heights rose with the increase of usage factor (UF). The amount of increase in the heights with respect to UF increased with strain range. The trend of development of both heights was similar with the trend of Ra and Wa. A comparison between Ra and the height caused by PSBs showed that these values strongly correlated with each other. A comparison between Wa and the height caused by grain deformation also showed that these values strongly correlated with each other. Consequently, the surface texture parameters Ra and Wa represent the changes in the heights of surface reliefs due to PSBs and grain deformation.
Highlights
When important industrial facilities are subjected to excessive cyclic loadings that lead to deformation, ensuring the structural health of the facilities requires precise damage evaluation from the view-point of material strength
If the changes in the surface topography can be related to the amount of physical damage, it may be possible to estimate the degree of fatigue damage from measuring surface topography
In our previous study [10], we investigated the change in the surface topography under low-cycle fatigue loadings with constant strain range conditions
Summary
When important industrial facilities are subjected to excessive cyclic loadings that lead to deformation, ensuring the structural health of the facilities requires precise damage evaluation from the view-point of material strength. Two mechanisms cause the surface roughening of metallic materials: (a) formation of persistent slip bands (PSBs) [1,2,3,4,5] and (b) deformation of crystal grains [6, 7]. The amount of increase rate in Ra and Wa with respect to UF changes with the strain range It suggested that the applied strain range and the degree of fatigue damage UF could be estimated by measuring Ra and Wa if the strain range condition is constant. It has not been quantitatively investigated whether the changes in Ra and Wa correspond to the evolution of two surface reliefs due to PSBs and grain deformation. To clarify the correspondence between the change mechanisms of surface relief and surface texture parameters, the heights of surface reliefs and surface texture parameters were compared and investigated
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