Stress redistribution as an effect of non-uniform in-plane laminate stresses in laminate composite plates

This paper describes a phenomenon that significantly affects the stress distribution in notched laminate composite structures. Ply-to-ply interactions under non-uniform laminate stress fields induce interlaminar and in-plane stresses that are not described in classical laminate theory. The theory is consist of a power series expansion along the thickness-wise coordinate. The most prominent influence of this effect is a substantial reduction in stress concentrations around notches. This may explain various experimental facts that conflict with classical laminate theory. Although this phenomenon appears to be a derivative of the so-called free-edge effect, it is not based on free-edge boundary conditions. For verification of the theory, this paper also presents finite element analysis cases for 5 mm diameter open hole [90/0]s cross-ply laminate plates. Reductions in stress concentration around hole edges were up to 10% of the far field stress. Insertion of low elasticity layers between 90° and 0° plies, the use of thick plies, or the adoption of ply materials with low transverse shear moduli were identified as effective means of reducing stress concentration around a hole. These findings may enable the application of new design principles to deal with stress concentrations for notched composite structures.