Abstract: In order to verify the difference effect of roughness in different part of structure, taking a certain type of aluminum alloy as the research object, fatigue test and theoretical analysis are used to analyze the difference of fatigue performance under the combination of different roughness. In the test, emphasis is placed on different surface treatment combinations for corner, face and curved face to find the difference between the effects of the roughness of different parts. In addition, bar specimens and two kinds of thickness plate specimens are designed to illustrate the universality of the test results and two fracture forms of plane fracture (surface fracture) and angle fracture are defined by observing the fracture surface of the specimens In the test results processing. Finite element software is used to analyze the stress distribution characteristics near the micro notch of different parts to quantitatively analyze the difference of the roughness of them. For the particularity of this study, an improved field strength method for stress calculation of micro notch is proposed and effective failure stress and effective stress concentration factor at various micro notches on the specimen surface are calculated by this method. By comparing the experimental results with the theoretical results, it is found that there are significant differences in effective stress concentration coefficient at different locations, which means the concentration coefficient at the corner microgap is obviously higher than that of the face, for the sample with the same surface roughness. This conclusion is reflected in the macroscopic view that the roughness at the corner of the specimen has a greater effect on the fatigue performance of the specimen than the roughness of the specimen surface, which means it is not reasonable to treat them equally in traditional way.

Key words: aluminum alloy, roughness, stress concentration, fatigue test, field intensity method