Application of Digital Image Correlation (DIC) to the Measurement of Strain Concentration of a PVA Dual-Crosslink Hydrogel Under Large Deformation
Application of Digital Image Correlation (DIC) to the Measurement of Strain Concentration of a PVA Dual-Crosslink Hydrogel Under Large Deformation
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DOI：
10.1007/s11340-019-00520-4
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发表时间：
2019-09-01
影响因子：
2.4
通讯作者：
Zehnder, A. T.
中科院分区：
文献类型：
--
作者：
Liu, M.;Guo, J.;Zehnder, A. T.
水凝胶是一种柔软的、高度变形的材料，通过在水中膨胀聚合物链网络而形成。水凝胶具有模拟生物材料的机械性能，经常被建议用于承载生物医学或其他应用，在这些应用中，其变形和破坏性能将是重要的。为了研究这种材料的破坏，除了简单的单轴拉伸试验之外，还需要一种测量变形场的方法。作为一种非接触式的全场形变测量方法，数字图像相关法(DIC)是一种很好的研究方法。本文对DIC在水凝胶中的应用进行了研究，目的是确定DIC在大应变和大应变梯度条件下应用于水凝胶时的准确性。讨论了实验细节，如如何在90%含水的材料上形成持久的散斑图案。DIC用于测量含有中心孔、圆形边缘缺口和尖锐裂纹的拉伸加载试件的应变场。采用非线性、大变形本构模型，用有限元方法对试验进行了模拟。所有三种几何形状的有限元和DIC结果之间的良好一致性表明，即使在裂纹尖端附近存在非常高的应变梯度的情况下，DIC测量的精度也高达10以上的应变。然后应用该方法验证了一个理论预测，即裂纹试件在松弛载荷作用下的变形场，即恒定的外加边界位移，即使应力松弛了三倍，也是时间稳定的。
Hydrogels are a class of soft, highly deformable materials formed by swelling a network of polymer chains in water. With mechanical properties that mimic biological materials, hydrogels are often proposed for load bearing biomedical or other applications in which their deformation and failure properties will be important. To study the failure of such materials a means for the measurement of deformation fields beyond simple uniaxial tension tests is required. As a non-contact, full-field deformation measurement method, Digital Image Correlation (DIC) is a good candidate for such studies. The application of DIC to hydrogels is studied here with the goal of establishing the accuracy of DIC when applied to hydrogels in the presence of large strains and large strain gradients. Experimental details such as how to form a durable speckle pattern on a material that is 90% water are discussed. DIC is used to measure the strain field in tension loaded samples containing a central hole, a circular edge notch and a sharp crack. Using a nonlinear, large deformation constitutive model, these experiments are modeled using the finite element method (FEM). Excellent agreement between FEM and DIC results for all three geometries shows that the DIC measurements are accurate up to strains of over 10, even in the presence of very high strain gradients near a crack tip. The method is then applied to verify a theoretical prediction that the deformation field in a cracked sample under relaxation loading, i.e. constant applied boundary displacement, is stationary in time even as the stress relaxes by a factor of three.