Fatigue cracking machine for circumferential notched tensile specimens

A fatigue cracking machine for circumferential notched tensile (CNT) specimens, comprising:

• a platform;
• a motor securely mounted on the platform, the motor including a motor shaft;
• a bearing support securely mounted on the platform;
• a holding bearing mounted in the bearing support;
• an elongate holding cylinder defining a blind bore, the holding cylinder having a first end coupled to the motor shaft and a second end journaled into the holding bearing, the blind bore having an opening in the second end of the holding cylinder configured for receiving a first end of a CNT specimen into the blind bore;
• a bearing support block securely mounted on the platform;
• a load fork having a pair of tines defining a first end of the load fork and a shaft extending from the tines, the shaft having an end defining the second end of the load fork, the shaft being slidable within the bearing support block;
• a load bearing mounted between the tines of the load fork;
• an elongate load cylinder defining a blind bore, the load cylinder having a first end journaled into the load bearing for rotation therewith in alignment with the holding cylinder, the load cylinder having a second end, the blind bore having an opening defined in the second end of the load cylinder configured for receiving a second end of the CNT specimen into the blind bore;
• an adjustment bolt threadable in and out of the bearing support block to bear against the end of the shaft, the adjustment bolt adjusting displacement of the load fork;
• a support post rigidly mounted on the platform;
• and
• an indicator mounted on the support post, the indicator having a plunger bearing against the load bearing, the indicator being configured to measure displacement of the load bearing;
• wherein the machine forms a crack in the CNT specimen through a plane extending through the circumferential notch when the specimen is supported by the holding cylinder and the load cylinder with the circumferential notch aligned with the second end of the holding cylinder and the motor is activated to rotate the motor shaft and the adjustment bolt is threaded into the bearing support block to displace the load fork to apply a bending force to the CNT specimen, the displacement being measured by the indicator to monitor initiation and propagation of the crack.