构件不同部位粗糙度对疲劳性能影响差异分析

Analysis on the Different Effect of Roughness in Different Part of Structure on Fatigue Property

为验证构件不同部位粗糙度影响的差异性,以某型铝合金为研究对象,采用疲劳试验与理论分析相结合的方法分析不同部位粗糙度组合下构件疲劳性能的差异。试验设计中,为区分不同部位粗糙度造成的影响,着重对试样角部、面部和曲面部做不同的表面处理,同时设计棒试样及两类厚度的板试样以说明试验结果的普适性,并在试验结果处理中通过观测试样的断口形貌定义面断裂(曲面断裂)与角断裂两种断裂形式。为进一步定量分析不同部位粗糙度影响差异性的大小,采用有限元软件分析不同部位微缺口附近的应力分布特性,另外,针对本研究的特殊性提出一种适用于微尺寸缺口处应力计算的改进场强法,并采用此方法分别计算试样表面各类微缺口处的有效破坏应力及有效应力集中系数。通过试验结果与理论计算结果对比发现,对于同样表面粗糙度的试样,不同部位微缺口处的有效应力集中系数存在显著差异,即角部微缺口处集中系数明显高于面部,这一结论反映到宏观上表现为试样边角处的粗糙度对试样疲劳性能的影响明显高于试样面部粗糙度的影响,因此传统方法中将两者做等同处理缺乏一定的合理性。

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.