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Understanding composite failure requires knowledge of the material behavior near the tip of a propagating crack. Microscopy permits examination of small regions of the fracture surface, allowing close study of the crack tip region. This work represents an effort to link visual observations of the crack surface to the mechanical history of the specimen. Scanning electron microscopy examines the fracture surfaces of failed cracked lap shear (CLS) specimens. Quantitative fractography tracks the area fraction of four fracture morphologies as a function of position on the fracture surface. Statistical hypothesis testing determines locations of significant shifts in fracture morphology. These locations are compared to regions of crack arrest during testing, and the correlation is found to be poor. It is suggested that these changes in fracture surface morphology are linked to variations in the thickness of the resin layer along the plane of the crack.
fractography, quantitative fractography, composites, mechanical testing, cracked lap shear (CLS) specimen
Aerospace Engineer, Space Kinetic Impact and Debris Branch, Phillips Laboratory, PL/WSSD, Kirtland AFB, NM
Associate Professor, School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, GA