Difference between cracks and artificial flaws in ultrasonic testing-ultrasonic testing performed on the smooth part of a 40nm miniature axle specimen

摘要

The accuracy of ultrasonic testing is generally evaluated using artificial flaws made by various methods including the electric discharge method, because it is difficult to make cracks in a specimen with their lengths and depths kept under controlled. The two surfaces of an artificial flaw do not come in contact even at the flaw tip, however, while those of a crack do so at least at the crack tip under a no-load condition. In this study, we choose axles of railway vehicles as the object and perform ultrasonic testing to clarify the difference between cracks and artificial flaws quantitatively. The ultrasonic testing is performed under the condition of tensile and compressive loading using miniature axle specimens cut from a full-scale axle. One of these specimens has a fatigue crack and others have artificial flaws. The echo height shows that the crack opens from half to two-thirds of its depth under the no-load condition, thus, it is possible to judge the crack depth to be half to two-thirds of the actual total depth.