A 3-D model of wing crack growth and interaction

A simple model of a 3-D wing crack growing in compression from a disk-like initial crack has been developed. At the initial stage of growth the wings aye modeled in vertical cross sections as 2-D cracks wedged at one end by t he displacement produced by the contact area (former initial crack). This d isplacement is evaluated by replacing the contact area with a Mode III crac k of the length equal to the wing width. It is shown that the contribution of the contact area into the crack-generated stress field is at least compa rable with that of the wings. To analyze the possibility of extensive growt h, the crack is modeled by a vertical disk-like crack where the opening (we dging) action of the sliding contact area is simulated by the uniform press ure distributed over a central circular area of the same radius as the init ial crack. It is shown that the continuation of the wing crack growth in su ch a mode would require a considerable increase in the load, which probably explains why extensive (few times the initial flaw size) growth of a singl e 3-D crack has never been observed in experiments. The mechanism of produc ing really large tensile fractures by pairs of 3-D wing cracks has also bee n investigated. On the basis of the dipole (far field) asymptotics, it has been shown that it is the total tensile stresses induced by the wing cracks in the direction perpendicular to the compression direction that could be responsible for the appearance of the tensile fractures. The magnitude of t hese stresses is affected by the crack locations and spacings. (C) 1999 Els evier Science Ltd. All rights reserved.