特殊螺纹接头螺纹根部微动疲劳探究

通过全尺寸疲劳试验，对特殊螺纹油套管连接的疲劳失效模式进行了识别。在某套管外螺纹中，不完全螺纹根部发现了贯穿性裂纹，但裂纹的起始位置取决于应力水平。在应力幅值较大的区域，裂纹起源于应力集中的螺纹圆角处。在应力幅值相对较低的区域，由于微动疲劳，裂纹起源于螺纹根部中间。为了研究特殊螺纹连接的微动疲劳机理，进行了微动疲劳试验。试验表明大滑移条件下螺纹接触面中部会出现微动疲劳失效。

Fretting Fatigue on Thread Root on Premium Threaded Connections

Identification of the fatigue failure mode of the premium threaded connection for Oil Country Tubular Goods pipes was conducted via full-scale fatigue tests. A through-wall crack was found at the imperfect thread root of the male embodiment, but the crack initiation site depended on the stress level. At relatively higher stress amplitude region, the crack originated from the thread rounded corner by stress concentration. At relatively lower stress amplitude region, the crack originated at the middle of the thread root because of fretting fatigue. To investigate the fretting fatigue mechanism in the threaded connection, a fundamental fretting fatigue test was conducted. This test achieved the fretting fatigue failure at the middle of the contact surface under large gross slip condition.