Acoustic evaluation of the endurance of steel specimens and recovery of their serviceability

A study is made of the possibility for evaluation of damage accumulation during fatigue loading by measuring the ultrasound velocity. It is shown that the dependence of the ultrasonic velocity on the number of loading cycles is represented by a three-stage curve and that the ultrasonic velocity decreases at each stage. The most rapid decrease occurs during the final stage of the test, immediately before fracture. It is also shown that the transition to the critical state can be observed on the basis of ultrasonic-velocity measurements. A method of increasing the service life of a specimen that has neared the critical state is proposed. The method involves exposure of the specimen to a series of high-energy pulses of electric current. The treatment increases the service life by 30–40% compared to the initial value.