Crack-Tip Principal Stresses by Isochromatic and Isopachic Fringes at a Bi-material Interface

An experimental method of the principal stresses estimation which is based on photoelasticity and isopachic methods is presented. The principal stresses at the bi-material interface crack-tip are theoretically determined using the combination photoelastic and isopachic fringes. The size and the shape of crack-tip isochromatic and isopachic fringes, at a bi-material interface under static load, are studied. When the crack-tip, which is perpendicular to interface, is placed at the interface of the bi-material, the isochromatic and the isopachic fringes depend on the properties of the two materials. Thus, the isochromatic and the isopachic fringes are divided into two branches, which present a jump of values at the interface. The size of the two branches mainly depends on the elastic modulus and the Poisson’ s ratio of the two materials. From the combination of the isochromatic and the isopachic fringes, the principal stresses σ1 and σ2 can be estimated and the contour curves around the crack-tip can be plotted.