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从抽油杆上截取若干小段制成疲劳试样 ,在疲劳试验过程中 ,每经过一定次数的应力循环之后 ,用降载勾线法得到疲劳裂纹扩展迹线。试样断裂之后 ,观察各条迹线 ,测定所对应的裂纹深度及裂纹形状比a/c,得到 a/c的数值为 0 .7至 0 .8。在每次降载勾线时暂停疲劳试验 ,用超声水浸聚焦方法测定疲劳裂纹的回波高度。将实验结果绘制成回波高度 V与疲劳裂纹深度 a的关系曲线 ,并在裂纹深度为 1 mm至 8mm的范围进行拟合得到一直线关系。除了用超声法对疲劳裂纹进行检测之外 ,还用磁粉法与渗透法对三条疲劳裂纹进行了检测 ,结果是磁粉法和渗透法都未得到缺陷显示 ,只有超声法有缺陷显示。
From the sucker rod interception of a number of small pieces made of fatigue specimens, in the fatigue test process, after a certain number of stress cycles, the load-down line method fatigue crack growth trajectory. After the specimen was broken, the respective traces were observed, and the corresponding crack depth and crack shape ratio a / c were measured to find that the value of a / c was from 0.7 to 0.8. The fatigue test was suspended at each de-hooking of the line, and the echogenic height of the fatigue crack was measured by ultrasonic immersion-focusing method. The experimental results are plotted as the relationship between the echo height V and the fatigue crack depth a, and a linear relationship is obtained by fitting the crack depth in the range of 1 mm to 8 mm. In addition to the fatigue crack detection by ultrasonic method, three fatigue cracks were also detected by the magnetic powder method and the infiltration method. As a result, none of the magnetic powder method and the infiltration method showed any defect, and only the ultrasonic method showed defects.