複合材料三明治板相對傳統金屬材料，在相同的重量條件之下，能夠擁有較佳的機械性質與強度，然其有一個嚴重的缺陷：其芯材會承受極大的剪應力，以至於整體結構在內部產生裂紋與破壞，這種類型的破壞不僅難以探知，更容易造成整體結構性的失效。

本論文提出以一外部曲面薄膜強化三明治板的方法，藉以降低傳統三明治板中，芯材所承受的剪應力，從源頭上降低芯材受到剪切破壞的可能性，並且在使用曲面薄膜強化後，三明治板的勁度可以更進一步的增加，在相同受力下有較低的位移。

曲面薄膜強化的方法為，將三明治板的上下面板，各減少一部份纖維材料，作為曲面薄膜使用，曲面薄膜在三明治板受力時，會受到向兩側拉應力，此拉應力因為曲面的設計，會有垂直方向的合力，此分力即可抵消部分芯材所受之剪應力。

利用Abaqus進行有限元素static non-linear的分析，以及使用玻璃纖維、PVC發泡芯材製作實體試片進行實驗，皆得以證明此外部曲面薄膜強化三明治板的方法的降低剪應力、增加勁度的效果，在電腦分析中亦可見到，外部曲面薄膜強化三明治板在芯材毀損與脫層的情況，可增強結構損傷耐受性。

雖然外部曲面薄膜強化三明治板在製造上較費時、費工，但它得以解決剪應力帶來的問題，並且更加提升複合材料三明治板的性能，以相同重量達到更佳的表現，或是以較低的重量滿足相同的需求。

關鍵字：有限元素分析、複合材料、三明治板、損傷容限、結構設計、曲面薄膜

SUMMARY

An innovative sandwich concept was proposed by additionally stacking a core and an external curved membrane (reinforcing sheet) on a conventional sandwich panel. The curved face sheet under tension is an efficient means to bear the transverse load and therefore, conduces to the reduction of the shear stress and deformation in the core. The thicknesses of the reinforcing sheets and cores of a proposed panel should be judiciously determined in order to ensure that the proposed panel is not heavier than its traditional counterpart. This study investigated the effect of adding the membrane-like curved face sheet on shear loading in the core material, structural stiffness, and damage tolerance. Three cases were investigated numerically to compare the proposed concept against the conventional: pristine panels, panels with damaged cores that can only sustain loading in the thickness direction, and panels with fully separated sheets. All the compared sandwiches had thin carbon-fiber laminates as the reinforcing sheets. The numerical analyses for the panels without any defect showed that shear strain in the core was reduced by more than 60%, and the structural stiffness was approximately doubled. Regarding the damaged panels, the increase in deflection cast by the internal damages was reduced from about 100% to 10%. The stiffness advantage of the proposed concept of sandwich panel was also confirmed by experiments using specimens consisting of fiber glass laminates and PVC foams.

Key words: finite element method, composite material, sandwich panel, damage tolerance, structural design, curved membrane

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