Experimental, fully three-dimensional mechanical characterization of opaque materials with arbitrary geometries undergoing finite deformations is generally challenging. We present a promising experimental method and processing pipeline for acquiring and processing full-field displacements and using them toward inverse characterization using the Virtual Fields Method (VFM), a combination we term MR-u. Silicone of varying crosslinker concentrations and geometries is used as the sample platform. Samples are stretched cyclically to finite deformations inside a 7T MRI machine. Synchronously, a custom MRI pulse sequence encodes the local displacement in the phase of the MR image. Numerical differentiation of phase maps yields strains. We present a custom image processing scheme for this numerical differentiation of MRI phase-fields akin to convolution kernels, as well as considerations for gradient set calibration for data fidelity. The VFM is used to successfully determine hyperelastic material properties, and we establish best practice regarding virtual field selection via equalization.

中文翻译：

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MR-u：使用 3D 位移编码磁共振和虚拟场方法进行材料表征

对具有任意几何形状的不透明材料进行有限变形的实验性全三维力学表征通常具有挑战性。我们提出了一种很有前景的实验方法和处理流程，用于获取和处理全场位移，并将它们用于使用虚拟场方法 (VFM) 进行逆表征，我们将其称为 MR-u。不同交联剂浓度和几何形状的有机硅用作样品平台。样品在 7T MRI 机器内循环拉伸至有限变形。同时，自定义 MRI 脉冲序列对 MR 图像相位中的局部位移进行编码。相位图的数值微分产生菌株。我们为类似于卷积核的 MRI 相场的这种数值微分提供了一种自定义图像处理方案，以及对数据保真度的梯度集校准的考虑。VFM 用于成功确定超弹性材料特性，我们通过均衡建立了有关虚拟场选择的最佳实践。