Nondestructive Evaluation of Metal Fatigue.
Interim scientific rept. Jan-Dec 75,
SOUTHWEST RESEARCH INST SAN ANTONIO TEX
Pagination or Media Count:
The magnetic field perturbation method has been further developed as a nondestructive means for quantitatively characterizing fatigue cracks in high strength ferromagnetic steels in order to assess their fracture criticality supplementary techniques used include ultrasonic surface waves and Barkhausen noise analysis. Rod-type tensile specimens of AISI4340 steel were used in the investigations. Results show the magnetic perturbation signal amplitude to be linearly related to the crack opening displacement and the width of the signal to be correlated with the crack depth. Using a fracture mechanics model, the configuration of the small scale yielding plastic zones adjacent to the crack interface and the monotonic and reversed flow plastic zones in the vicinity of the crack tips were calculated. Measurements were made of the variations in the width of the satellite component of the magnetic perturbation signal for various conditions of applied stress and peak cyclic stress. Comparison of these results to the calculated plastic zones indicate that there may be a relation between the width of the satellite component and the plastic zones around a fatigue crack. Results of Barkhausen noise measurements also show a qualitative correlation with the calculated plastic zones, although refinement of the instrumentation will be needed to better define these relationships.
- Properties of Metals and Alloys
- Test Facilities, Equipment and Methods