Ji Donghwan, Im Pilseon, Shin Sunmi, Kim Jaeyun
School of Chemical Engineering, Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea.
Department of Mechanical Engineering, National University of Singapore (NUS), Singapore 117575, Singapore.
Materials (Basel). 2023 Jan 13;16(2):785. doi: 10.3390/ma16020785.
Synthetic tough hydrogels have received attention because they could mimic the mechanical properties of natural hydrogels, such as muscle, ligament, tendon, and cartilage. Many recent studies suggest various approaches to enhance the mechanical properties of tough hydrogels. However, directly comparing each hydrogel property in different reports is challenging because various testing specimen shapes/sizes were employed, affecting the experimental mechanical property values. This study demonstrates how the specimen geometry-the lengths and width of the reduced section-of a tough double-network hydrogel causes differences in experimental tensile mechanical values. In particular, the elastic modulus was systemically compared using eleven specimens of different shapes and sizes that were tensile tested, including a rectangle, ASTM D412-C and D412-D, JIS K6251-7, and seven customized dumbbell shapes with various lengths and widths of the reduced section. Unlike the rectangular specimen, which showed an inconsistent measurement of mechanical properties due to a local load concentration near the grip, dumbbell-shaped specimens exhibited a stable fracture at the reduced section. The dumbbell-shaped specimen with a shorter gauge length resulted in a smaller elastic modulus. Moreover, a relationship between the specimen dimension and measured elastic modulus value was derived, which allowed for the prediction of the experimental elastic modulus of dumbbell-shaped tough hydrogels with different dimensions. This study conveys a message that reminds the apparent experimental dependence of specimen geometry on the stress-strain measurement and the need to standardize the measurement of of numerous tough hydrogels for a fair comparison.
合成坚韧水凝胶受到关注，因为它们可以模拟天然水凝胶的力学性能，如肌肉、韧带、肌腱和软骨。最近的许多研究提出了各种增强坚韧水凝胶力学性能的方法。然而，在不同报告中直接比较每种水凝胶的性能具有挑战性，因为采用了各种测试样品形状/尺寸，这会影响实验力学性能值。本研究展示了坚韧双网络水凝胶的样品几何形状（即缩减部分的长度和宽度）如何导致实验拉伸力学值的差异。具体而言，使用11种不同形状和尺寸的样品进行拉伸测试，系统地比较了弹性模量，这些样品包括矩形、ASTM D412 - C和D412 - D、JIS K6251 - 7以及七种缩减部分长度和宽度各异的定制哑铃形状。与矩形样品不同，由于夹具附近存在局部载荷集中，矩形样品的力学性能测量结果不一致，而哑铃形样品在缩减部分表现出稳定的断裂。标距长度较短的哑铃形样品导致弹性模量较小。此外，还得出了样品尺寸与测量的弹性模量值之间的关系，这使得能够预测不同尺寸哑铃形坚韧水凝胶的实验弹性模量。本研究传达了一个信息，即提醒人们样品几何形状对应力 - 应变测量存在明显的实验依赖性，以及为了进行公平比较需要对众多坚韧水凝胶的测量进行标准化。
