The FEA To The Propagation Of Delaminated Beams With Through-thickness Reinforcement

Composite materials are widely used in the field of aerospace, sailing, and automobile, etc. Laminated composite materials mainly fail in-plane or on the interlamination (delamination). About 60% failures of laminated composites are attributed to delamination. To avoid delamination and further to prevent delamination propagation, it is proposed to insert enhancing entities (stitches or z-pins) in the thickness direction. Therefore, it is necessary to study the enhancement mechanism of stitches and z-pins to optimize the design of composites.In this paper, a numerical model of delaminated beams with through-thickness reinforcement was proposed by employing a beam element considering the shear deformation combined with a stitching or z-pinning element. The effect of geometrical nonlinearity is taken into account by using the total Lagrange method of finite deformation theory. The enhancement in delamination toughness of DCB (Double Cantilever Beam) due to through-thickness reinforcement was studied numerically. Delamination propagation behavior in the post buckling process of a laminated beam with a symmetrical through-width delamination was also analyzed to investigate the effects of the enhancement entities on delamination propagation. The numerical results show that the enhancement entities can significantly improve the delamination toughness of DCB specimen. The effect of geometrical nonlinearity on the delamination toughness of DCB specimen should be taken into account for the large ratio of open displacement and the delamination crack length. Furthermore, the enhancement entities can effectively prevent delamination propagation for symmetrical buckling of a laminated beam with a symmetrical through-width delamination.