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

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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.