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A laser interferometry technique is described which is capable of resolving crack surface displacements to about 0.2 μm. The method provides continuous measurements of the free surface crack profile in metal specimens without being limited by rigid body displacements. Using the laser interferometry procedure to determine fatigue crack profiles in 2024-T851 aluminum specimens, it was possible to measure the load at which the crack faces completely separate. These opening loads were correlated with peak tensile overloads and subsequent crack retardation. These results are discussed in terms of the Elber concept of fatigue crack closure.
crack propagation, lasers, interferometry, fatigue (materials), measurement, cyclic loads, retarding, stresses, deformation
Professor, Michigan State University, East Lansing, Mich.
Air Force Materials Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio