A STRESS INTENSITY FACTOR TRACER AND ITS APPLICATION TO TIME DEPENDENT FRACTURE TESTING

Abstract

An optical method, so called “Stress Intensity Factor Tracer (SIFT)” (Kim, submitted) has been applied for the measurement of the continuous time history of the stress intensity factor KI(t) of a time-dependent-fracture-testing specimen. This method utilizes the intensity variation of the light impinging on any fixed finite size area γ, that does not include the focal point, in the focal plane on which initially parallel light rays transmitted through the transparent fracture specimen (or reflected from the surface of an opaque specimen) are focused by a converging lens. The light intensity I(t) is related to the stress intensity factor by I(t) = B[KI(t)]473 for KI dominant field, where the constant B is the product of several experimental quantities including a “shape factor” for the sampling area γ, which is a known function of crack velocity for dynamic KI field. An important feature of the method is that I(t) is insensitive to the location of the crack in the specimen plane. The relation for SIFT has been checked experimentally for a DCB specimen and applied to the measurement of the stress intensity factor of the DCB specimen under vibrational loading and of a large Homalite 100 specimen subjected to impulsive loading on the crack faces.