| Summary: | 碩士 === 國立中興大學 === 機械工程學系所 === 101 === In recent years, many of the fibrous composite materials have been applied to aircraft structures in order to increase the structural strength and reduce weights. The quality and function of such composites parts become important in aircraft designing/manufacturing fields. The constrained effect in stresses between metallic molds and the composite fibers during curing in autoclave may cause the geometry unexpectedly changed on composites parts. Moreover, the residual stresses may also generate and affect the quality of the fibrous structures. Correct way of predicting the mechanical behavior on such synthetic structures becomes a very important design and manufacturing subject.
In the finite element analysis, the fiber composite material is a layered and very thin shell structure which is usually simulated by general shell/plate elements directly. Alternately, the mold is a very large structure generally simulated by solid brick element. The discrepancy of characteristics of these two elements may cause structural behavior inconsistency while connected. The computational results appear high controversy. In the study, a fiber composite thin shell element has developed which keeps a compatible nodal behavior with the solid elements. The element may be used for analyzing the contraction stress between the fibrous composites structure and molds in cooling process. Thus, the aircraft structure designers can appropriately modify the design of fiber composite parts to ensure structural operational function and safety.
Here, the fundamental theory of fiber thin shell elements is introduced and the corresponding finite element formula is derived. A specifically designed computer program written in F95 is implemented which links to FEAST system, a FEM software system developed by our laboratory. A series of numerical tests are demonstrated to understand the characteristics and ensure the accuracy of such composite structures. A finite element model of molds and composite fiber parts in aero-curing is built and analyzed by the software developed here. The computational results can provide significant information for aero-structure designers and manufacturers and even other related fields.
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