Abstract

The efficiency of the global/local approach using partial hybrid finite elements is examined by the determination of interlaminar stress fields around interior delamination crack tips in composite laminates subjected to out-of-plane loading. The stress field consisting of both in-plane and out-of-plane components around a through thickness edge crack in a laminated composite under uniaxial tension is also studied. The cracked composite laminate is modeled with three types of elements: 20-node three-dimensional sub-laminate partial hybrid elements are used in the local region where the stress gradients are expected to be high; 8-node degenerated partial hybrid plate elements are used in the global region and 15-node transition elements are employed to connect the local and global regions. The results show that the partial hybrid finite element-global/local approach yields accurate solutions with one-third active degrees of freedom, consumption of one third computer space and CPU time as compared with the conventional displacement finite element method. Experiments were performed for cross-ply laminates with mid-plane interior delamination crack subjected to three-point bending. The predicted critical loads by finite element analysis based on both a strength-based criterion and a fracture mechanics approach are in good agreement with the experimental data. It is found that the symmetric notched flexure (SNF) specimen used in the study of interior delamination is quite promising for Mode-II fracture test. In view of having no standard for measuring Mode II fracture toughness of composite laminates, further investigation on SNF is carried out. A finite element analysis was conducted for prediction of the stress distribution around the crack tip to prove that the failure mode is Mode II and this is in excellent agreement with experiment results.