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    STP1236

    Early Stages of Fatigue Damage of Fastener Holes Monitored by Laser Speckle

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    Abstract

    The present work confines itself to the study of the initiation and early propagation of fatigue cracks emanating from simulated fastener holes using a laser speckle method that is a noncontact, nondestructive, and remote sensing technique. When illuminated by a narrow laser beam, the fatigue-induced surface roughness causes the laser beam to diffract into a halo modulated by a random speckle pattern. The fatigue damage information is contained in the speckle diffraction pattern. The half width and cross correlation coefficient of a speckle pattern are chosen to quantify this information. Two kinds of specimens, a thin plate with an open hole in the center and a thin plate with an oversized pin impacted into a central hole, were tested. The fatigue process was monitored by the laser speckle patterns. After crack propagation, the specimens were examined under a scanning electron microscope and their fractographic features correlated with the fatigue process.

    Keywords:

    fatigue, roughness measurement, laser speckle pattern


    Author Information:

    Chiang, F-P
    Chair, leading professor of mechanical engineering, and director, Laboratory for Experimental Mechanics Research, Department of Mechanical Engineering, State University of New York at Stony Brook, Stony Brook, NY

    Du, M-L
    Research assistants, Laboratory for Experimental Mechanics Research, Department of Mechanical Engineering, State University of New York at Stony Brook, Stony Brook, NY

    Li, S
    Research assistants, Laboratory for Experimental Mechanics Research, Department of Mechanical Engineering, State University of New York at Stony Brook, Stony Brook, NY


    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP13052S