As a practical and effective tool for quantitative in-plane deformation measurement of a planar object surface, two-dimensional digital image correlation (2D DIC) is now widely accepted and commonly used in the field of experimental mechanics. It directly provides full-field displacements to sub-pixel accuracy and full-field strains by comparing the digital images of a test object surface acquired before and after deformation. In this review, methodologies of the 2D DIC technique for displacement field measurement and strain field estimation are systematically reviewed and discussed. Detailed analyses of the measurement accuracy considering the influences of both experimental conditions and algorithm details are provided. Measures for achieving high accuracy deformation measurement using the 2D DIC technique are also recommended. Since microscale and nanoscale deformation measurement can easily be realized by combining the 2D DIC technique with high-spatial-resolution microscopes, the 2D DIC technique should find more applications in broad areas.

https://iopscience.iop.org/article/10.1088/0957-0233/20/6/062001/pdf

Two-dimensional digital image correlation for in-plane displacement and strain measurement: a review

/pdf/high-resolution-x-ray-computed-tomography-in-geosciences-a-3sj7249knj.pdf

High-resolution X-ray computed tomography in geosciences: A review of the current technology and applications

X-ray computer tomography (CT) is fast becoming an accepted tool within the materials science community for the acquisition of 3D images. Here the authors review the current state of the art as CT transforms from a qualitative diagnostic tool to a quantitative one. Our review considers first the image acquisition process, including the use of iterative reconstruction strategies suited to specific segmentation tasks and emerging methods that provide more insight (e.g. fast and high resolution imaging, crystallite (grain) imaging) than conventional attenuation based tomography. Methods and shortcomings of CT are examined for the quantification of 3D volumetric data to extract key topological parameters such as phase fractions, phase contiguity, and damage levels as well as density variations. As a non-destructive technique, CT is an ideal means of following structural development over time via time lapse sequences of 3D images (sometimes called 3D movies or 4D imaging). This includes information nee...

https://www.tandfonline.com/doi/pdf/10.1179/1743280413Y.0000000023

Quantitative X-ray tomography

Comparison of the elastic and yield properties of human femoral trabecular and cortical bone tissue.

http://research.engr.oregonstate.edu/immiscibles/sites/research.engr.oregonstate.edu.immiscibles/files/Papers/Wildenschild_Sheppard_AWR_2012.pdf

X-ray imaging and analysis techniques for quantifying pore-scale structure and processes in subsurface porous medium systems

A three-dimensional extension of two-dimensional digital image correlation has been developed. The technique uses digital image volumes generated through high-resolution X-ray tomography of samples with microarchitectural detail, such as the trabecular bone tissue found within the skeleton. Image texture within the material is used for displacement field measurement by subvolume tracking. Strain fields are calculated from the displacement fields by gradient estimation techniques. Estimates of measurement precision were developed through correlation of repeat unloaded data sets for a simple sum-of-squares displacement-only correlation formulation. Displacement vector component errors were normally distributed, with a standard deviation of 0.035 voxels (1.22 μm). Strain tensor component errors were also normally distributed, with a standard deviation of approximately 0.0003. The method was applied to two samples taken from the thigh bone near the knee. Strains were effectively measured in both the elastic and postyield regimes of material behavior, and the spatial patterns showed clear relationships to the sample microarchitectures.

Digital volume correlation : Three-dimensional strain mapping using X-ray tomography

The impact of boundary conditions and mesh size on the accuracy of cancellous bone tissue modulus determination using large-scale finite-element modeling

Given their specific properties, their natural and renewable sources and their low environmental impact in production, natural fibers offer an opportunity for the development of eco-friendly cement-based composites. The main objective of this experimental work is to evaluate the resistance to the impact load of mortars incorporating natural fibers or polypropylene fibers at 28 days. The assessment was carried out according to an experimental protocol developed in our laboratory. The method consists in dropping a metallic ball on a square shaped specimen of 30x30x2 cm3 to determine the energy supported by each sample. For each specimen, the number of blows required for the first crack initiation and for the total collapse of specimen are detected using a device allowing to measure the speed of ultrasonic waves. The device was fixed on the specimen itself. In order to fulfill the mechanical identity card of the composites, flexural and compression tests were also carried out at 28 days. In this experimental protocol, the pozzolanic binder was considered with different fiber percentages of polypropylene (0.25% and 0.5% by mass of binder) and of natural fibers (0.5% and 1% by mass of binder). All fibers have a length of 12 mm. Results show that natural fiber reinforcement could be considered as an ecological alternative to polypropylene fiber one to improve the resistance of mortars to impact loads.

M. Saad

Papers

Digital volume correlation : Three-dimensional strain mapping using X-ray tomography

The impact of boundary conditions and mesh size on the accuracy of cancellous bone tissue modulus determination using large-scale finite-element modeling

Natural Fibers vs. Synthetic Fibers Reinforcement: Effect on Resistance of Mortars to Impact Loads