Closed interface crack with singular spring stiffness model

The singularity of the stress field at the tip of a partially closed interface crack is discussed based on a non-uniform spring stiffness model that includes an inverse function of the radial distance from the crack edge. The stress singularity is found to be governed by the coefficient of the inverse function, henceforth referred to as “stiffness intensity” due to its resemblance to the well-known stress intensity factor. Two distinct non-oscillatory singular stress fields, corresponding to Modes I and II deformations, respectively, are found to coexist. An oscillatory singularity may also appear, but only when the two stiffness intensities are close to each other. This means that the oscillatory singularity exists when the normal and tangential interactions between the upper and lower crack faces are close.