Thermal Stresses During Freezing of Biomaterials

在材料的全方位冻结过程中，表面形成冻结的固体外壳，内部冻结引起的体积变化对外壳产生应力。本研究的目的是量化在食品冷冻过程中相变期间生物材料中产生的热应力。冷冻材料的机械性能将在温度控制的Instron机器中测量，使用特别制备的样品，通过从一侧冷冻来最小化残余应力。在典型的冷冻过程中，应力裂纹将在低温显微镜下观察到。观察到的断裂模式将与适当的失效理论预测的断裂模式相关联。这将是第一次定量分析生物材料中由于相变引起的大体积变化而产生的热应力。重要的应用不仅包括食品加工中生物材料的冷冻，还包括器官的冷冻手术和冷冻保存。

During omni-directional freezing of a material, a frozen solid shell forms at the surface, and the volume changes associated with freezing of the interior causes stresses on the outer shell. The objectives of this study are to quantify such thermal stresses developed in a biomaterial during phase change in the context of food freezing. Mechanical properties of frozen materials will be measured in a temperature controlled Instron machine using samples specially prepared to minimize residual stresses, by freezing from one side. Stress cracks during typical freezing processes will be observed under a cryomicroscope. Observed cracking pattern will be correlated to fracture patterns predicted by a suitable failure theory. This will be the first quantitative analysis of thermal stresses in a biomaterial due to large volumetric changes from phase transformation. Important applications include not only freezing of biomaterials as in food processing but also in cryosurgery and cryopreservation of organs.