45CrNiMoVA钢的低周疲劳特性和表面疲劳裂纹的在位观测

The Test of Low Cycle Fatigue Characteristics for 45CrNiMoVA Steel and In situ Observation on Surface Crack Propagation

利用 MTS81 0材料试验机对带中心圆孔的 45 Cr Ni Mo VA钢低周疲劳特性进行了研究 ,并借助长焦显微镜和 CCD摄像头对试样表面裂纹的演化规律进行了在位停机观测和在位不停机连续观测尝试 .试验发现 ,裂纹均萌生于与拉伸应力垂直的圆孔边缘 ;疲劳裂纹的萌生与 Lüders形变带密切相关 ,萌生期超过整个疲劳寿命的 70 % .主裂纹的发展既可以共面扩展的方式向前连续延伸 ,也可以裂纹连接的方式向前跳跃传播 .应力控制的低周疲劳条件下 ,疲劳寿命与应力幅存在良好的双对数线性关系 .采用连续光源照明在位停机观测可以得到较好表面形貌图像 。

The low cycle fatigue characteristics of 45CrNiMoVA specimens with central hole were investigated on a MTS810 material testing machine. By means of a long focal distance microscope with CCD camera, the initiation and propagation of surface cracks were observed in both running and stopped states. It was found that in most occasions cracks initiated from the edge of the hole where maximum tension stress occured, and that crack initiation was mainly associated with the Luders deformation bands and covered about 70% of the whole fatigue life. It was also found that cracks could propagate either in a continuous co planar fashion or by jumping extension through coalescence. In the test, a nearly liner logarithmic relationship between fatigue lifetime and stress amplitude was obtained. Continuous illumination and flashing illumination were used respectively for observations in runing and stopped states.