Semi-analytic model to evaluate non-regularized stresses causing unfolding failure in composites

A novel semi-analytic model is developed to determine interlaminar stresses in laminates including highly curved parts, for obtaining a rapid, accurate and reliable design tool for evaluating the reserve factor of a certain aeronautic composite component prone to unfolding failure. The model assumes plane conditions and is based, firstly, in an approximation of the 2D displacement components by using a series of functional products of separate variables and, secondly, in the use of higher-order moments of the stress components, which allow an enriched beam model to be constructed. The solution is obtained as the sum of products of a set of known functions, written in terms of the eigenvalues and eigenvectors of the matrix governing the model, and a set of integration constants. These constants can be determined with the boundary conditions, in isolated parts, and the continuity conditions, in laminates containing parts with different curvatures. In comparison with an existing analytical method, the present model has the advantage of offering an extremely accurate solution at the zones in which the analytical method may yield errors of even a 100%. In comparison with a detailed finite elements model, the present model obtains a similar accuracy in much lower computational times.