Factors Affecting Ultrasonic Waves Interacting with Fatigue Cracks

I don\u27t mean to be presumptious and imply that we are going to cover all of the many factors which affect ultrasonic measurements of fatigue cracks, as suggested by the title, but we will attempt to go over some recent work we have been doing at the Materials Lab in this area. We\u27ll be talking about fatigue cracks and what variables, both regarding the fatigue crack itself as an entity and the ultrasonic inspection process, have a significant effect on the results, that are obtained

Kissing Bonds in Diffusion Bonded Parts

The widespread application of diffusion bonding has been hindered, in part, by concerns over kissing bonds. Kissing bonds are generally considered to be conditions where a bond has little or no strength and the concern is that such conditions might escape detection. At Rohr we differentiate between an intimate contact disbond (which has no bond between the surfaces but is detectable by careful ultrasonic testing) and a kissing bond (which also has no bond between the surfaces but is not detectable using current ultrasonic technology). These definitions will be used throughout

Guided and Leaking Interface Waves for NDI/NDE

Last year at this review one of us pointed out that it was theoretically possible to propagate guided elastic waves along the interface between an installed interference-fit fastener and the parts that it joins, and that these waves might be useful for nondestructive inspection and evaluationl. During discussion of that paper, the speaker was asked if experiments were planned, and another questioner wanted to know what would happen if elastic parameters of fastener and part didn\u27t fall in the comparatively narrow ranges for which unattenuated guided waves can propagate. The speaker replied that experiments were indeed planned, and that, hopefully, even when material parameters did not allow guided waves, attenuated interface waves might still propagate and be useful for inspection and evaluation. This report can be viewed as an amplified answer to the two questions. We have carried out experiments. They confirm the existence of both true guided waves, and of leaking or attenuated waves, on interfaces between materials of engineering interest. The theory presented last year, with some extensions, is a useful guide to excitation and reception methods, propagation speeds, and for leaking modes, attenuation factors. Preliminary pulse-echo observations indicate that these waves can be used for indications of flaws in awkward places, such as on a fastener hole in an inner plate

On the variation of fatigue-crack-opening load with measurement location

The work presented here evaluates the vlidity of using the load at the point of linearity on the displacement-load curve, as suggested by Elber, as an experimental measure of the crack-tip-opening load. Displacement-load behavior was investigated for a fatigue-cracked modified compact specimen of a nickel-base superally. Displacements were determined at the notch mouth using a standard clip-on gage, along the crack surface using a laser-interferometric displacement gage and, in the plastic zone ahead of the crack, using an optical-interferometry technique. Acoustic-emission monitoring was employed as a means to detect potential crack extension during measurement-load cycles and to detect physical-crack closure.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43930/1/11340_2006_Article_BF02324983.pd