Inelastic zone around crack tip in polyacrylamide hydrogel identified using digital image correlation
Inelastic zone around crack tip in polyacrylamide hydrogel identified using digital image correlation
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DOI：
10.1016/j.engfracmech.2023.109435
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发表时间：
2023-09
影响因子：
5.4
通讯作者：
Yudong Pan;Yifan Zhou;Z. Suo;Tongqing Lu
中科院分区：
文献类型：
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作者：
Yudong Pan;Yifan Zhou;Z. Suo;Tongqing Lu
在断裂之前，聚丙烯酰胺水凝胶的应力-拉伸曲线具有近乎完美的弹性，但有人认为在裂尖周围存在一个非弹性区。然而，在聚丙烯酰胺水凝胶中从未直接观察到这种非弹性区。在这里，我们使用数字图像相关(DIC)来识别非弹性区。我们制备了一种带有预切缝的聚丙烯酰胺水凝胶。当水凝胶样品拉伸时，使用显微镜或相机记录散斑图案，像素大小分别为2.3xμm和22.7xμm。显微镜和相机记录的散斑图案使用DIC软件进行处理，并合并以提供整个样品的变形场。根据Neo-Hookean模型，利用测得的形变场计算能量密度场。当物体是完全弹性时，裂纹尖端周围的能量密度场与离裂纹尖端的距离成反比。实测场和预测的弹性场之间的差异识别非弹性区。测得的非弹性区大小为∼=0.6 mm。进一步证实，当试件比弹性区大得多时，存在一个弹性裂纹尖端场占优势的环。
Prior to fracture, a polyacrylamide hydrogel has a stress-stretch curve of nearly perfect elasticity, but it has been suggested that an inelastic zone exists around a crack tip. This inelastic zone, however, has never been observed directly in a polyacrylamide hydrogel. Here we identify the inelastic zone using digital image correlation (DIC). We prepare a polyacrylamide hydrogel with a precut crack. While a sample of the hydrogel is stretched, the speckle patterns are recorded using a microscope or a camera, with pixel size 2.3 μm and 22.7 μm, respectively. The speckle patterns recorded by the microscope and camera are processed using the DIC software, and merged to provide the deformation field over the entire sample. The measured field of deformation is used to calculate the field of energy density according to the neo-Hookean model. When the body is perfectly elastic, the field of energy density around the crack tip is inversely proportional to the distance from the crack tip. The difference between the measured field and the predicted elastic field identifies the inelastic zone. The measured size of the inelastic zone is ∼ 0.6 mm. We further confirm that, when a sample is much larger than the inelastic zone, an annulus exists, in which the elastic crack tip field prevails.