Reduction of the concentrated residual stress on the edges of a sandwich plate

Residual stresses exist in a three-layer laminated composite plate. When the middle layer possesses a smaller thermal expansion coefficient than the outer layers, concentrated tensile stress is created on the edges, especially at the corners of a rectangular composite plate, attempting to peel the plate apart into two halves. Providing a set of specific numerical figures on geometry dimensions, material properties and processing conditions, the finite element method (FEM) can determine the magnitude of the resulting stress. Of important interest in this paper is that the stress magnitude at the corner tip of a rectangular composite has been found to be twice the value of that when viewing the plate in the 2D plane-stress condition. For reducing the stress concentration on the edges, two possibilities are analyzed by the FEM using an existing code. The results show that when the sharp corners of the rectangular composite plate are slightly rounded, the original concentrated tensile stress can be reduced by ∼20%, but this technique cannot achieve more than 35%. Another way for reducing the tensile stress concentration is to chamfer the edges. Full chamfering is much more effective than half chamfering, and the greater the chamfering angle is, the better is the effect. Further, full chamfering is also superior to corner rounding.