For high-water content hydrogels in compression, the water inside of hydrogels contributes to the response of hydrogels to external loads directly, but part of the water is expelled from hydrogels in the meantime to change the volume of the hydrogel and reduce the contribution. In order to consider the contribution of the water in the constitution equation, PVA (polyvinyl alcohol) hydrogels with high-water content were used as examples, and compressive experiments were carried out to measure both the stress-strain relation and the change of the volume in the meantime. By considering the effect of the difference of the contribution of water in different directions of the hydrogel, we deduced a new constitutive equation, which can pretty well depict the stress-strain of hydrogels with different water contents. The results showed that the contribution of water to the total stress increases with the compression strain and even exceed that of the polymer, although the expelled water reduces the contribution at the early loading stage, which well explains the difference of elastic moduli of hydrogels in compression and tension.

对于处于压缩状态的高含水量水凝胶，水凝胶内部的水直接有助于水凝胶对外部载荷的响应，但与此同时，一部分水会从水凝胶中排出，从而改变水凝胶的体积并减少其影响。为了考虑水在组成方程中的贡献，以高水含量的PVA（聚乙烯醇）水凝胶为例，并进行了压缩实验以测量应力-应变关系和体积变化同时。通过考虑水在水凝胶不同方向上的贡献差异的影响，我们推导了一个新的本构方程，可以很好地描述不同含水量的水凝胶的应力应变。