STP924

    Use of Nondestructive Evaluation Techniques in Studies of Small Fatigue Cracks

    Published: Jan 1988


      Format Pages Price  
    PDF (224K) 14 $25   ADD TO CART
    Complete Source PDF (7.9M) 14 $110   ADD TO CART


    Abstract

    This paper reports progress to date in the development of an ultrasonic surface acoustic wave (SAW) technique to monitor in situ the depth of small cracks as they grow, as well as the stresses required to cause the cracks to begin to open and to fully open.

    Two SAW transducers (transmitter and receiver) are used to monitor crack reflection signals. The surface length is measured by conventional methods. Based on new acoustic theory, the reflection signal and length data are used to infer crack depth below the surface. Acoustically determined depth is compared with that obtained by destructive examination of specimens, and agreement is good.

    The crack opening stress determined acoustically is compared with opening stress determined by scanning electron microscope (SEM) measurements of crack mouth opening displacement versus applied stress. This comparison requires specimens small enough to fit inside an SEM chamber. Preliminary results demonstrate the ability of the acoustic measurements of crack opening to detect behavior below the surface not detected by SEM measurements. Acoustically determined changes in crack opening behavior as a function of constant-amplitude and variable-amplitude stress histories are also presented.

    Keywords:

    nondestructive testing, small crack growth, crack opening stress, closure, load sequence effects, fatigue, acoustic technique


    Author Information:

    Resch, MT
    Research affiliateassociate professorresearch assistantresearch assistant, Stanford University, Stanford, CA

    Nelson, DV
    Research affiliateassociate professorresearch assistantresearch assistant, Stanford University, Stanford, CA

    Yuce, HH
    Research affiliateassociate professorresearch assistantresearch assistant, Stanford University, Stanford, CA

    London, BD
    Research affiliateassociate professorresearch assistantresearch assistant, Stanford University, Stanford, CA


    Paper ID: STP23224S

    Committee/Subcommittee: E08.03

    DOI: 10.1520/STP23224S


    CrossRef ASTM International is a member of CrossRef.