Abstract
To substitute for a traditional replication technique, an in-situ fatigue crack observing system for rotating bending testing machine has been newly developed. For verifying performance of this observing system, fatigue tests were carried out by using fatigue specimen having a small artificial defect. It is proved that this system can be detect a small fatigue crack and its propagation behavior.
Highlights
I n the field of the fatigue properties of metallic materials, the assessment of the S-N curve, which consists to the stress level and the number of cycles up to failure, does not give an entire viewpoint of the phenomenon
Unlike the case of pre-cracked specimens used for fracture mechanics experiments, the initiation and the propagation of the conventional fatigue specimens are often investigated by replica methods
This system is composed of (1) the motor and the spindle that is controlling the rotation of the fatigue specimen, (2) the timing gear at opposite side of the specimen is rotated in the same way, (3) the magnetic sensor placed in the vicinity of the gear, (4) the servo-motor, which is introduced here to set the position of the magnetic sensor at any angular position around the gear, (5) the control system that gives the flash directive signal to the LED stroboscope, (6) the high-definition digital video camera, which records at a predetermined interval of time, (7) the long working distance microscope, and (8) the personal computer to record and analyze the data obtained
Summary
I n the field of the fatigue properties of metallic materials, the assessment of the S-N curve, which consists to the stress level and the number of cycles up to failure, does not give an entire viewpoint of the phenomenon. It is necessary to have some experience on the use of this technique, in addition there are cases where the utilization of replica is complex It is the case for fatigue specimens designed for rotating bending tests, with an hourglass shape at the minimum cross section spot. Performances of some optic devices have been improved in the latest years, in the field of: (i) affordable long working distance microscopy, (ii) high-definition video camera, and (iii) high brightness LED components. The combination of these new developments gives the possibility to design a system adapted for fatigue rotating bending tests, and to observe continuously the fatigue crack propagation.
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