應變率對纖維複合材料側向抗壓強度影響之探討

Abstract

本論文主要研究應變率對纖維複合材料側向抗壓強度的影響。玻璃纖維/環氧樹脂與碳纖維/環氧樹脂之複合材料在本研究中一併探討。為了證明解應變率的影響，製造完成的複材塊狀試片，將以每秒10-4至 700的應變率，在側向方向測試直到破壞。實驗觀察發現抗壓強度對應變率非常敏感，因而可利用一個半對數函數來描述側向抗壓強度對應變率的靈敏度。並且，將發現試片的主要破壞過程，是由於跟受力方向夾角約32度之平面上的剪力破壞。由此，將抗壓破壞應力籍由莫耳圓之強度分析，可得到沒有側向方向正向力時的面外剪力強度。碳纖維/環氧樹脂的明顯破壞機制為纖維與基材間的剝離，然而，玻璃纖維/環氧樹脂，其破壞機制變成基材的破壞。為提高側向抗壓強度，製造出含有機黏土的玻璃纖維/環氧樹脂奈米複合材料以用於側向方向測試。可以發現複合材料包含有機黏土時，其相對玻璃纖維/環氧樹脂的側向抗壓強度是增大的，其歸因於纖維與基材間界面黏著力的提升。

This research aims to investigate strain rate effect on transverse compressive strength of unidirectional fiber composites. Both glass/epoxy and graphite/epoxy composites were considered in this study. To demonstrate strain rate effect, composite brick specimens were fabricated and tested to failure in the transverse direction at strain ranges from 10-4/s to 700/s. Experimental observations reveal that the compressive strength is sensitive to the strain rates. A semi-logarithmic function was employed to describe the rate sensitivity of the transverse compressive strength. Moreover, it was found that the main failure mechanism of the specimens is the shear failure on the plane with around 32 degree to the loading direction. As a result, the out-of-plane shear strength without the transverse normal stresses was obtained from the compressive failure stress through Mohr’s strength analysis. The dominant failure mechanism for the graphite/epoxy composites is fiber and matrix debonding, however, for glass/epoxy composites, it becomes the matrix failure. To improve the transverse compressive strength, glass/epoxy nanocomposites with organoclay were fabricated, and then tested in the transverse direction. It was found the composites with the presence of the organoclay, the corresponding transverse compressive strength of glass/epoxy is enhanced, which could be attributed to the improved interfacial bonding between the fiber and matrix.