Development of an Integrated Materials Testing and High-Resolution Tomography System for Measurement of Three-Dimensional Strain Fields

在材料特性或几何特征使得传统的实验力学方法无法使用或不切实际的情况下，二维数字图像相关技术对于应变场的测量是非常宝贵的。本项目为开发和获取一种仪器提供支持，该仪器将通过数字体积相关方法在三维上提供相同的测量特性。该仪器集材料测试系统和高分辨率x射线断层扫描仪于一体。广泛的复杂结构材料（复合材料，蜂窝固体，天然材料），在几乎任何几何配置，可以研究与该系统。该仪器产生的数据将有助于建立设计标准，揭示基本的微观力学现象，并为材料本构行为模型的验证提供基础。已经证明，数字体积相关方法能够在载荷作用下对整个材料样品内部的完整三维位移向量场进行采样，精度为0.035体素（1.23pm）。位移数据的后处理允许计算整个样品内部的完整三维应变张量场，精度为0.003 （300 ustrain）。这些测量是完全无损的，并且同一样品可以在多种加载条件下进行研究。不需要样品制备或标记。该方法即使在存在高应变梯度和材料屈服的情况下也具有鲁棒性，使其成为研究失效和应变局部化现象的理想工具。在这个项目下，将建造一个综合材料测试和高分辨率x射线断层扫描仪，专门研究复杂材料的载荷。数字体积相关测量能力的全面表征和方法的进一步改进将在工程应用中进行，特别是在层析扫描仪工作范围的高分辨率端，在复合纤维/基体界面应变、裂纹和缺口灵敏度以及层间界面应变等领域将得到发展。这是一项由核磁共振项目支持的设备拨款。

Two-dimensional Digital Image Correlation techniques are invaluable for the measurment of strain fields in situations where material characteristics or geometric features render traditional experimental mechanics methods unusable or impractical. This project provides support for the development and acquisition of an instrument that will provide the same measurement characteristics in three-dimensions through the method of Digital Volume Correlation. The instrument is an integrated materials testing system and high-resolution x-ray tomographic scanner. A broad range of complex structural materials (composites, cellular solids, natural materials), in virtually any geometric configuration, can be studied with this system. Data generated with the instrument will help establish design criteria, reveal basic micromechanical phenomena, and provide a basis for verification of models of material constitutive behavior. It has been demonstrated that the Digital Volume Correlation method is capable of sampling the full three-dimensional displacement vector field throughout the interior of material samples under load to a precision of 0.035 voxels (1.23pm). Postprocessing of the displacement data allows the calculation of the full three-dimensional strain tensor field throughout the sample interior to a precision of 0.003 (300 ustrain). These measurements are completely nondestructive, and the same sample can be studied under multiple loading conditions. There is no sample preparation or marking required. The methodology is robust even in the presence of high strain gradients and material yielding, making it a ideal tool for the study of failure and strain localization phenomena.Under this project an integrated materials testing and high resolution x-ray tomographic scanner dedicated to the study of complex materials under load will be constructed. Full characterization of Digital Volume Correlation Measurement capabilities and further refinement of the methodology will be carried out Engineering applications particularly at the high-resolution end of the tomographic scanner perating range, in the areas of composite fiber/matrix interface strains, crack and notch sensitivities, and interlaminar interface strains will be developed.This is an equipment grant supported under MRI program.