封閉式泡沫鋁材料之微觀結構與受壓力學響應

Abstract

本研究主要目的在以實驗及數值模擬方式探討 ALPORAS 封閉式泡沫鋁材料之微觀結構與其受壓力學響應。實驗方面，本研究採用微電腦斷層掃描方式，呈現ALPORAS泡沫鋁材料內部三維結構。利用三維影像重建技巧，量測材料內部包含細胞尺寸、細胞之表面積、細胞之幾何形狀、細胞寬高比與細胞圓球率等幾何特徵。另將材料結構分為支柱與細胞壁面，分別量測其彎曲之最大振幅。 數值模擬方面，本研究使用隨機緊密堆積圓球產生拉蓋爾鑲嵌以建立隨機數值模型，並探討不同圓球參數（產生圓球之體積分布、圓球之體積率與變異係數）對數值模型細胞幾何特徵之影響。此外，加入曲邊、曲面、壁厚變化與缺陷等幾何特徵以建立修正數值模型，分析不同幾何特徵參數對機械性質之影響。最後，進行數值模型完整受壓力學響應之數值模擬，以了解模型結構之變形機制與演進。數值模擬結果發現，相對楊氏模數等機械參數均隨幾何特徵因子增大而降低。而相較於原始隨機模型，修正數值模型模擬結果與實驗結果更為吻合。

The present study aims to investigate the microstructure and compressive response of ALPORAS closed-cell foam by means of both experimental and numerical efforts. Toward this end the micro-CT technique was first adopted to generate the three-dimensional representations of the interior structure of the foam from which the geometrical characteristics of the foam cellular microstructure, including the size, surface area, geometrical shape, aspect ratio, and sphericity of cells were measured. Also the struts and cell walls were separated from the material, so that the maximum amplitude of strut as well as cell wall curvatures can be evaluated. Based on the measured geometric features, Laguerre tessellation type numerical models were developed. The effects of geometric parameters such as probability density functions, sphere volume fraction, and coefficient of variation in sphere volume on the geometrical characteristics of the developed numerical models were examined. In addition, modified Laguerre numerical models were also developed by introducing additional geometric characteristics such as the strut curvature, the cell wall curvature, the cell wall variation and the missing cell walls. Numerical results revealed that the foam Young's modulus and the initiation stress decreased with increasing geometric characteristic factors. Finally both Laguerre as well as modified Laguerre modes were used to simulate the complete compressive response. While Laguerre and modified Laguerre models were capable of reproducing the deformation patterns and deformation revolutions observed in the crushing experiments, the modified Laguerre model outperformed the Laguerre model extensively as compared to the experimental results.