三明治結構套筒之設計與破壞預測

Abstract

套筒為複材三明治結構中常見的金屬嵌入件，用於傳遞接點處的集中力於結構中，避免局部受力過大發生破壞及過大的變形。車輛懸吊接點處的受力，因懸吊型式、幾何、車重等因素對套筒強度有不同負載大小需求。於傳統的設計方法中，多假設套筒及三明治板間完美接合，然而，實驗顯示，其第一破壞模式多為膠合介面剝離，即套筒之負載強度由介面之膠合強度所主導，而不是傳統三明治結構中常見的表材拉斷、心材剪切破壞等，常造成強度的高估。 本研究提出一界定膠合介面性質的方法，將此介面性質以有限元素的膠合元素做模擬，應用於套筒負載強度的預測，改良傳統需完全依靠實驗求得負載強度的設計方法。 在膠合介面性質的界定上，以平板拉伸(flatwise tensile)、單面搭接剪切(single lap shear)的基礎實驗求取其強度、剛性、破壞能等性質，再以同時含有正向力、剪切力效應的剝離試驗(climbing drum peel)進行有限元素模型及材料常數的驗證。 於套筒設計中以有限元素預測各破壞模式下的負載強度，提出三種套筒的設計及材料配置方式，可有效提高負載強度及比負載強度，適用於不同的負載及製程需求，其方法為提高套筒下三明治板剛性以延緩第一破壞模式膠合介面剝離，經由實驗證實，適當的設計，可同時擁有高負載強度及高比強度的特性，達到有效強化及輕量化的目標。

Insert is usually used as a local reinforcement in composite sandwich structure to transfer concentrated load to structure and avoid failure and excess local deformation. Insert load capacity requirement for vehicle suspension connection point depends on suspension type, geometry and vehicle weight. In traditional design method, the interface between insert and sandwich are always under perfectly connected assumption. However, experiments show that the first failure mode is mostly interface peel not face fracture or core shear in traditional sandwich causing load capacity overestimated. In other words, insert load capacity is dominated by interface adhesive strength. In this research, an interface behavior characterizing method is proposed and simulated by finite element cohesive element that is applied to predict insert load capacity and improved the traditional method that wholly depends on experiments. The method of characterizing interface behavior depends on two fundamental experiments, flatwise tensile and single lap shear test, to obtain strength, stiffness and fracture toughness behavior. FEA model is verified by comparing the result with climbing drum peel rest which contains normal and shear force simultaneously on the interface. The load capacity under different failure modes are recorded and predicted by FEA. Three designs and material configurations in revolution successful increased the load and specific load capacity, adapting for different load and manufacturing process requirements. The method was based on increasing sandwich stiffness to prevent interface peel and proofed by experiments; also an adaptive insert design can both have the characteristics with high load and high specific load capacity to reach the target in effective reinforcement and light weight.