Nondestructive Evaluation of Metal Fatigue.
Abstract
Nondestructive evaluation investigations have been conducted of surface entering fatigue cracks in rod-shaped tensile specimens of AISI 4340 and HY 180 steels. To alleviate the need for constant manual monitoring of the fatigue machine for specimens requiring many stress cycles, an automated monitoring capability based on detection of fatigue cracks by surface wave ultrasonics was fabricated. Fatigue cracks up to 0.050-in.-long were studied using magnetic perturbation, surface wave ultrasonics and Barkhausen noise analysis. Results showed the minimum detectable flaw size in HY 180 steel using surface wave ultrasonics to be 2 to 3 times the minimum size detectable in AISI 4340 steel. Also an applied load is necessary to ultrasonically detect fatigue cracks as long as 0.030-in. in HY 180. Extensive magnetic perturbation measurements were made on an AISI 4340 steel specimen cycled near yield. Attempts to interpret the behavior of the signal amplitude with applied static stress in terms of available closure models were not entirely successful. Indications are that the effect of plastic deformation in the vicinity of the crack on the magnetic perturbation signal must be taken into account. The magnetic perturbation signal peak separation was found to depend on crack length in a nonlinear fashion and to be affected by the plastic zones at the crack tips. Other investigations conducted included fractography to study the fracture surfaces and fatigue crack initiation sites in AISI 4340 and HY 180, microhardness measurements of plastic zones, and extension of an analytical model for calculation of magnetic leakage fields from surface entering fatigue cracks. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1977
- Accession Number
- ADA049539
Entities
People
- F. N. Kusenberger
- G. A. Matzkanin
- J. Lankford
- Joshua R. Barton
- Philip H. Francis
Organizations
- Southwest Research Institute