封閉式泡沫鋁材料之剪力機械性質

Abstract

本研究目標在以實驗與模擬之方式，探討封閉式泡沫鋁材料ALPORAS在擬靜態及動態下之剪力機械性質。實驗中透過純扭轉之方式施加純剪力負載，以觀察泡沫鋁材料之扭力響應。實驗包含擬靜態與動態實驗兩種，分別以扭力試驗機與霍普金森扭轉桿進行。擬靜態實驗主要探討試樣相對密度對各機械參數之影響。典型之擬靜態剪應力應變曲線可分為四個區域，分別為線性區、非線性區、剪力破裂區以及材料擠壓區，從中可定義包含剪力模數、剪力強度、剪力強度應變以及能量吸收密度等四個剪力機械參數。實驗結果發現，剪力模數、剪力強度皆隨相對密度增加而提高，剪力強度應變、能量吸收密度與相對密度之關係則較不明顯。動態實驗主要探討剪應變率對各機械參數之影響，討論之剪應變率範圍約在400至600 s-1之間。動態實驗之剪應力應變曲線與擬靜態略有不同，在剪應變0.1後有較大之震盪產生，能量吸收密度之定義較不易，因此只探討剪力模數、剪力強度及剪力強度應變等三項機械參數。實驗結果發現，剪力模數、剪力強度皆隨剪應變率提升而增加，但剪力強度應變並未與剪應變率呈正相關。 數值模擬方面，本研究以三維Laguerre tessellation建立封閉式泡沫鋁材料之數值模型，以有限元素分析軟體ABAQUS模擬泡沫鋁材料之扭轉試驗。擬靜態及動態模擬所得之響應曲線與實驗結果具有相似趨勢，但整體略有高估，推測應為數值模型與實際泡沫材料微觀結構差異所致。

The present study aims to investigate the mechanical shear properties of closed-cell aluminum foam ALPORAS under quasi-static and dynamic loading conditions by means of both experimental and numerical efforts. In quasi-static experiments, the foam specimens with different relative densities were tested using a torsion tester in order to assess the effect of relative density on foam mechanical properties. Experimental results indicated that that the foam mechanical parameters including the shear modulus, the shear strength increased with increasing relative densities. In dynamic experiments, on the other hand, foam specimens with similar relative densities were tested using a Split Hopkinson Torsional Bar (SHTB) under different shear strain rates in order to evaluate the effect of the shear strain rate on foam mechanical properties. It was found that the shear modulus and shear strength increased with increasing shear strain rates whereas the dependence of other parameter remained relatively inclusive. In the numerical simulations, numerical models of were first developed based on three-dimensional Laguerre tessellation algorithm. The finite element analysis software ABAQUS was then incorporated in the numerical simulations. The calculated shear response overestimated the experimental one whereas the overall trends were similar. The discrepancy can be attributed to the difference in detailed microstructural characteristics between the real foam and numerical models.