Design For Ply Drop-off In Composite Laminates With Variable Thickness

Ply drop-off in laminated composites structures has been applied abroad in the aircraft industry. The main contents of this paper are summarized as follows:1,A global-local approach for the analysis of tapered laminated composites is presented. A degenerate 2-dimensional (2-D) drop-off element is introduced to carry out the global analysis. At the vicinity of the drop-off where the stress concentration is high a local analysis with a refined mesh is performed with the results of the global analysis. Since a fine mesh is to be adopted only near the drop-off there is substantial economy in the computational effort and time as compared to the conventional analysis models.2,A composite structure with ply drop-off is analyzed by the method of FEM. Through the analysis, the practical distributions of strain and stress of whole structure are obtained especially at the vicinity of the drop-off. The effect of four parameters on the strength of the laminates has been studied. The first one is to observe the effect of dropping many plies off at a single station. The second is the distance between two successive drop-offs (stagger distance) and the third parameter considered is the lay-up of the dropped plies. The last one is to observe the effect of the covering plies.3,A 3-dimensional (3-D) element is used to analysis the drop-off structures. And it bears out that the 2-dimensional element is correct.4,The present investigation aims at developing a few guidelines for the design of tapered laminated composites. Some guidelines for the design of ply drop-off are summarized according to the FEM results in this thesis, and considering the conventional methods。...