The objective of the purposed investigation is the introduction of a novel technique for the experimental determination of the stress intensity factors for aluminum specimens. This technique involves the utilization of the optical method of caustics in relation to the method of birefringent coatings. After applying a thin layer of a transparent material on the surface of a pre-cracked aluminum specimen, a coherent light beam emitted from a NE-He laser is employed for its illumination. The stresses that are developed near the crack tip while the specimen is under loading are transferred to the coating and the illumination of the specimen by a laser beam gives rise to a highly illuminated area near the crack tip. The intersection of the light beam by a reference screen leads to the formation of a caustic curve, which separates an inside dark area from an outside bright area. The stress intensity factor at the crack tip is obtained when the characteristic geometrical dimensions of the caustic are measured. Good agreement was found in the stress intensity factors between the experimental data and theoretical results. The aforesaid method can be used to investigate intensity factors of other opaque materials that cannot provide high reflectivity on their surfaces.
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