SEDL / STP / STP1236-EB / STP13052S

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

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

Pages: 12    Published: Jan 1995

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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.