Semi-analytic solution on non-regularized unfolding stress in composite beams employing a series approximation based on legendre polynomilas

Abstract

Unfolding is one of the main causes of failure on composite beams including curved parts in their sections, such as L-beams, T-beams or C-beams, it being in many cases the critical criterion in the sizing of this kind of beams. This failure mechanism is caused by the interlaminar normal and shear stresses. Regularized interlaminar stresses are predicted in a very accurate way with current methods, but typical edge effects make those regularized stresses inaccurate with errors even by 100%. An illustrative example is the joint of a straight and a curved beam, as in the section of L-beams, where the compatibility between the two beams modifies the stress distribution which become significantly different to the regularized stresses. This study presents the fundamentals and the results of a novel semi-analytic method that predicts in a very accurate way the non-regularized stresses in 2D composite laminates of constant thickness and treated as a sequence of several constant-curvature beams. This method is a powerful tool to predict the unfolding failure in composite beams containing curved parts in their sections, with the same or better accuracy than using finite elements.