Stress Analysis at a Bi-Material Interface Crack-tip

ABSTRACT

The optical methods of Caustics, Photoelasticity and Isopachics for the evaluation of the stress intensity factors and the distribution of the principal stresses at a bi-material interface crack-tip, were proposed. The caustics, isochromatic and isopachic fringes are developed from the stress field which results from a stress function X(r,θ). When the crack-tip, which is perpendicular to interface, is at the interface of the bi-material, the caustics, isochromatic and isopachic fringes depend on the properties of the two materials. So, the caustic, isochromatic and isopachic fringes are divided into two branches, which present a jump of values at the interface. The shape and size of the two branches of caustics, isochromatic and isopachic fringes depend mainly on the elastic modulus and Poisson’s ratio of the two materials. From the caustics the stress intensity factor KI can be calculated, while from the combination of the isochromatic and the isopachic fringes, the principal stresses σ1, σ2 can be theoretically and experimentally calculated. The optical evaluation of the stress intensity factors and the distribution of the principal stresses from isochromatic and isopachic fringes is presented. The stress intensity factors and the principal stresses at the bi-material interface crack-tip, were experimentally determined using the caustics and the combination photoelastic and isopachic measurements. The size and shape of the crack-tip caustics, isochromatic and isopachic fringes, at a bi-material interface under static load, were theoretically and experimentally studied.