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采用有限元方法,计算了在悬臂弯曲加载方式下,不同载荷作用时板状光滑试样施力点处的挠度;采用成组试验法,通过载荷控制模式,进行了应力比为-1时10CrNiMo钢的S-N曲线试验,并对试样断口进行了观察和分析。结果表明:在试验载荷范围内,所设计试样施力点处的挠度变化,在试验机作动器的有效行程内,可满足S-N曲线试验,通过试验获得了两种常用置信度下10CrNiMo钢的S-N曲线;在大载荷往复作用时,表面裂纹从试样上、下两个表面萌生并扩展所形成的面积基本相当,但在小载荷循环作用下,表面裂纹通常先从试样的一个表面萌生并扩展,当裂纹扩展至一定程度时,试样另一个表面才开始萌生疲劳裂纹,并协同前一表面的裂纹共同扩展至试样断裂。产生这种现象的原因,和不同大小的载荷开动试样上下两个表面材料内部滑移系的数量、材料内部组织的不均匀性,以及裂纹在扩展过程中前缘应力状态的变化有关。
Using finite element method, the deflection at the point of application of plate-shaped smooth specimen under different load is calculated by the method of cantilever bending loading. By using the group test method and the load control mode, the stress ratio is -1 when 10CrNiMo steel SN curve test, and the specimen fracture was observed and analyzed. The results show that within the range of the test load, the deflection of the designed specimen at the point of application of force can meet the SN curve test within the effective stroke of the test machine actuator. Two commonly used 10CrNiMo steels SN curve. When the heavy load reciprocates, the area of the surface crack initiation and expansion from the upper and lower surfaces of the sample is basically the same, but under the action of small load cycle, the surface crack usually starts from one surface of the sample When the crack expands to a certain extent, the other surface of the sample begins to initiate fatigue crack initiation and coalesces with the crack of the previous surface to extend to the fracture of the sample. The reason of this phenomenon is related to the number of slip systems inside and outside the upper and lower surfaces of load-activated specimens of different sizes, the inhomogeneity of the internal structure of the material and the change of the stress state of the leading edge in the crack propagation.