EFFECT OF RISING ELASTIC-MODULUS IN SURFACE-LAYER ON STRESS INTENSITYAND GRADIENT

The relaxation element method is applied to obtain the stress field ar ound a crack under normal tension. A surface layer is assumed to surro und the crack periphery taken to be in the shape of a narrow ellipse. The elastic modulus within this layer increases from zero to the bulk value of the medium outside. Calculations show that the stresses are f inite at the crack tip; they reach a maximum in the layer and then dec ay to the well known solution of Griffith outside the layer. The influ ence of plastic deformation on the crack front stresses can also be si mulated by the surface layer model. Stress concentration at the crack front is found to be lower when plastic deformation takes place. Sharp decay of stress next to the crack is accompanied by increase of local stress gradients. Severity of the local stress fluctuation depends on the width of the crack surface layer. (C) 1998 Elsevier Science Ltd. All rights reserved.