A MIXED FINITE-ELEMENT FOR INTERLAMINAR STRESS COMPUTATION

A mixed finite element method (MFEM) aiming at solving the problem of three-dimensional stress analysis of multi-layer composite laminates with a high accuracy is presented. The approach, which is based on the global-local laminate variational model, proposes a mixed use of a hybrid stress element within a high precision stress solution region in the thickness direction of the laminate and a conventional displacement finite element in the remaining. This results in a reduction of the overall computation time while maintaining the solution precision in the area(s) of interest, normally being certain interface(s) within a laminate. A formulation of a 49 stress parameter hybrid stress element in conjunction with a 42 degree of freedom iso-parametric displacement element is given. The quality of the hybrid stress element is assured by a stiffness matrix eigenvalue analysis. Example computations of laminate cylindrical bending and the classical free-edge problem have shown the feasibility of the MFEM approach and the convergence of the specific 49-beta-42q formulation.