修改型霍普金森桿應用於封閉式泡沫鋁材料動態力學行為測量之研究

Abstract

本研究目的主要在以實驗與數值模擬方式探討ALPORAS®封閉式泡沫鋁材料之動態力學性質。實驗方面，本研究使用修改型霍普金森桿設備，以進行泡沫鋁材料之動態測試。一般霍普金森桿使用鋁製實心透射桿，但若欲測試對象之阻抗值遠低於鋁時，透射訊號將會相當微弱。為得到適合分析之透射訊號，本研究以空心透射桿取代傳統實心透射桿。由於截面積的不同，空心透射桿之阻抗值低於實心透射桿，因此能有效地放大訊號。實驗結果發現，泡沫材料試體之最大應變與局部最大應力值皆隨著應變率提高而增加，而應變率對楊氏模數之影響則較不明顯。 數值模擬方面，本研究利用有限元素軟體ABAQUS建立霍普金森桿之數值模型。其中桿件假設為線彈性，試體組成律則假設為可壓縮泡沫模型（crushable foam model）。配合適當之負載與邊界條件，模擬結果可準確預測各項實驗結果。

The present study aims to investigate the dynamic response of ALPORAS® closed-cell aluminum foam by means of experimental and numerical efforts. A modified SHPB (Split Hopkinson Pressure Bar) technique was used for the dynamic crushing experiments. Consider that the impedance of the foam specimens was much lower than that of aluminum, the material of the strike and incident bars, a hollow aluminum bar was incorporated to replace the conventional solid transmission bar in order to enhance the transmission signals. Experimental results showed that the maximum strain as well the local maximum stress increased with increasing strain rates while on the other hand the effect of the strain rate on Young’s modulus was found to be insignificant. On the numerical modeling, numerical models were developed using the commercial FE code ABAQUS. The bar material was assumed to be linearly elastic while CRUSHABLE FOAM model was assumed as the constitutive model for the foam specimens. With appropriately chosen loading and boundary conditions, the numerical simulations were able to reproduce experimental results successfully.