凝膠由許多長鏈分子相互連結成彈性網絡，及存在於網絡孔隙間的大量溶劑分子所構成。溶劑的吸入或排出於孔隙使得彈性網絡產生潤脹或收縮，此現象使得凝膠承受相當大的變形且反應為可逆的。在現今凝膠物理性質的實驗研究中，分析通常以線性孔彈理論為基礎，鮮少有以非線性凝膠理論分析實驗數據之研究。因此，本文以非線性凝膠理論為基礎，提出適用於非線性範疇之方法以量測凝膠參數，並將非線性理論植入有限元素法套裝軟體ABAQUS中，以建立非線性凝膠數值模型，採取以數值方法模擬凝膠於實驗下之情形來驗證本文方法之可行性。本文也針對適用性較高的圓球壓痕實驗，建立非線性凝膠層的瞬態行為預測公式，並探討厚度比的影響，藉以提供實驗分析做依據。

Gels consist of a three-dimensional elastic network which is formed by cross-linked long-chained polymers, and a large quantity of small solvent molecules existing in pores of network. The migration of solvent into or out of pores causes the network to swell or shrink. This makes the deformation of gels considerably large and the response is reversible. In the experimental research of physical properties of gels, the analyses are usually based on linear theory of poroelasticity, and very few data were analyzed by the nonlinear theory of gels. In this thesis, we developed the methods for characterizing the properties of gels from experimental data in large deformation regime, based on the nonlinear theory of gels. We also implemented the nonlinear theory into the finite-element code ABAQUS, and built the numerical model of nonlinear gels. Some numerical experiments were carried out to verify our characterization methods. We also establish the prediction of the short time behavior of a nonlinear gel layer indented by a spherical probe. The effects of layer thickness were discussed and provided for the analysis of spherical indentation test.

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