免夹持水凝胶材料拉伸试验技术
On the Experimental Technique for Tensile Test of Hydrogel without Clamping

由于水凝胶材料表面非常滑，且内部水分在压力作用下容易流出，从而进一步减小试件表面的摩擦系数，所以该材料在拉伸试验时难以用传统夹具稳固夹持。若夹具施加压力过大又极易造成试件端部破坏，测得的材料拉伸强度并不可靠。本文提出了一种免夹持的水凝胶材料拉伸试验技术，能很好地将水凝胶材料固定于试验机上，且避免试件端部的预先损伤，使试件在中部断裂，从而能够准确地测量出材料的拉伸强度。本文利用该技术测量了多种含水量的聚乙烯醇(polyvinyl alcohol，PVA)水凝胶的拉伸强度，并拟合出了强度随含水量变化的经验公式。
Hydrogel material surface is very slippery, and internal water is easy to flow out under pressure action, resulting in further reduction of specimen surface friction coefficient. So this material is difficult to be firmly clamped by traditional fixture in tensile experiment. If the clamping force is too large, it is easy to cause the failure of specimen, resulting in the uncertainty of measured tensile strength of this material. A new kind of hydrogel material tensile experiment technology is put forward in this paper. Hydrogel material can be fixed on the testing machine without clamping, and pre-damage on specimen ends can be avoided. Thus, the fracture will occur at the middle of specimen, ensuring the accuracy of measured material tensile strength. Tensile strength of polyvinyl alcohol (PVA) hydrogel with different water contents were measured by this technique, and an empirical formula describing the variation of strength with the water content was fitted