Crippling analysis of composite stringers based on complete unloading method

This paper addresses a nonlinear finite element method for the crippling analysis of composite laminated stringers. Composite stringer is idealized by the nine-node laminated shell element based on the first order shear deformation theory. The stiffness degradation by the local failure is simulated by the complete unloading method. A modified arc-length algorithm is incorporated into the nonlinear finite element method to trace the post-failure equilibrium path after local buckling. Finite element results are compared with those by experiments and show the excellent agreement. A parametric study is performed to assess the effect of the flange-width, web-height, and stacking sequence on the buckling, local buckling, and crippling stresses of stringers.