A laminate composite with a crack normal to the interfaces

Abstract

The redistribution of stresses in a laminate composite due to the presence of a crack or flaw situated normal to the bond lines is studied. The many-layered composite is idealized to the case of a single layer of dissimilar material containing a crack which is sandwiched between two other layers of infinite height. The elastic properties of the two outer layers are assumed to be averaged properties over a large number of layers. Using the integral transform technique, the problem is formulated in terms of integral equations and solved for the singular stress field near the crack tip. The effects of crack size, layer height and the material properties of the composite on the stress-intensity factor are illustrated graphically. Presumably, this factor can be used to characterize the strength of a composite in the same way as it has been applied successfully to the single phase material within the framework of the linear theory of fracture mechanics.Calculations are also carried out for approximating the stress-intensity factors for a crack inclined at an arbitrary position in the sandwiched layer. This is accomplished by taking the two extreme cases of a crack parallel and normal to the interfaces as the upper and lower bound solutions depending upon the relative stiffness of the layers.