The Virtual Fields Method (VFM) is an inverse technique used for parameter estimation and calibration of constitutive models. Many assumptions and approximations—such as plane stress, incompressible plasticity, and spatial and temporal derivative calculations—are required to use VFM with full‐field deformation data, for example, from Digital Image Correlation (DIC). This work presents a comprehensive discussion of the effects of these assumptions and approximations on parameters identified by VFM for a viscoplastic material model for 304L stainless steel. We generated synthetic data from a Finite‐Element Analysis (FEA) in order to have a reference solution with a known material model and known model parameters, and we investigated four cases in which successively more assumptions and approximations were included in the data. We found that VFM is tolerant to small deviations from the plane stress condition in a small region of the sample, and that the incompressible plasticity assumption can be used to estimate thickness changes with little error. A local polynomial fit to the displacement data was successfully employed to compute the spatial displacement gradients. The choice of temporal derivative approximation (i.e., backwards difference versus central difference) was found to have a significant influence on the computed rate of deformation and on the VFM results for the rate‐dependent model used in this work. Finally, the noise introduced into the displacement data from a stereo‐DIC simulator was found to have negligible influence on the VFM results. Evaluating the effects of assumptions and approximations using synthetic data is a critical first step for verifying and validating VFM for specific applications. The results of this work provide the foundation for confidently using VFM for experimental data.

中文翻译：

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粘塑性材料模型虚拟场方法中的假设和近似值的研究

虚拟场法（VFM）是一种逆向技术，用于参数估计和本构模型的校准。要使用VFM和全场变形数据（例如来自数字图像相关（DIC）的数据），需要许多假设和近似值，例如平面应力，不可压缩的可塑性以及空间和时间的导数计算。这项工作对这些假设和近似值对304L不锈钢粘塑性材料模型的VFM确定的参数的影响进行了全面的讨论。我们通过有限元分析（FEA）生成了合成数据，以便获得具有已知材料模型和已知模型参数的参考解决方案，并研究了四种情况，其中依次包含更多的假设和近似值。我们发现，VFM可以在较小的样品区域中承受与平面应力条件的较小偏差，并且不可压缩的可塑性假设可用于估算厚度变化，而误差很小。对位移数据的局部多项式拟合已成功地用于计算空间位移梯度。发现时间导数逼近的选择（即，后向差异与中心差异）对计算的变形速率和该工作中使用的速率依赖模型的VFM结果有重大影响。最后，发现从立体声DIC仿真器引入位移数据的噪声对VFM结果的影响可忽略不计。使用合成数据评估假设和近似值的效果是验证和验证针对特定应用的VFM的关键第一步。这项工作的结果为自信地将VFM用于实验数据提供了基础。