The application of digital volume correlation (DVC) to study the microstructural behaviour of trabecular bone during compression.

Abstract

Digital Volume Correlation (DVC) has been emerged recently as an innovative approach to full volume (i.e. internal) displacement and strain field measurement in materials and structures, particularly in conjunction with high resolution X-ray computed tomography (CT). As a relatively novel technique certain aspects of precision, accuracy and the breadth of application are yet to be fully established. This study has applied DVC to volume images of porcine trabecular bone assessing the effect of noise and sub-volume size on strain measurement. Strain resolutions ranging between 70 and 800με were obtained for the optimum sub-volume size of 64 voxels with a 50% overlap for metrological studies conducted. These values allowed the mechanical behaviour of porcine trabecular bone during compression to be investigated. During compression a crushed layer formed adjacent to the boundary plate which increased in thickness as the specimen was further deformed. The structure of the crushed layer was altered to such an extent that it confounded the correlation method. While investigating this factor, it was found that for reliable strain calculations a correlation coefficient of 0.90 or above was required between the sub-volumes in the reference and the deformed volumes. Good agreements between the results and published bone strain failures were obtained. Using the full field strain measurements, Poisson's ratio was identified for each compression step using a dedicated inverse method called the virtual fields method (VFM). It was found that for a given region outside of the crushed zone the Poisson ratio decreased from 0.32 to 0.21 between the first and the final compression steps, which was hypothesised to be due to the bone geometry and its resulting deformation behaviour. This study demonstrates that volumetric strain measurement can be obtained successfully using DVC, making it a useful tool for quantitatively investigating the micro-mechanical behaviour of macroscale bone specimens.