A novel specimen shape for measurement of linear strain fields by means of digital image correlation

High-resolution local trabecular strain within trabecular structure under cyclic loading

Trabecular bone structure is a complex microstructure consisting of rods and plates, which poses challenges for its mechanical characterization. Digital image correlation (DIC) offers the possibility to characterize the strain response on the surface of trabecular bone. This study employed DIC equipped with a telecentric lens to investigate the strain state of individual trabeculae within their trabecular structure by assessing the longitudinal strain of the trabeculae at both the middle and near the edges of the trabeculae. Due to the high-resolution of the used DIC system, local surface strain of trabeculae was analyzed too. Lastly, the correlation between longitudinal trabecular strain and the orientation and slenderness of the trabeculae was investigated. The results showed that the strain magnification close to the edge of the trabeculae was higher and reached up to 8-folds the strain along the middle of the trabeculae. On the contrary, no strain magnification was found for most of the trabeculae between the longitudinal trabecular strain along the middle of the trabeculae and the globally applied strain. High-resolution full-field strain maps were obtained on the surface of trabeculae showing heterogeneous strain distribution with increasing load. No significant correlation was found between longitudinal trabecular strain and its orientation or slenderness. These findings and the applied methodology can be used to broaden our understanding of the deformation mechanisms of trabeculae within the trabecular network.

Damage evolution and fracture behavior of different materials specimens containing a central hole subjected to local loading

The strength of the different materials specimens containing a central hole subjected to varying loading areas constitutes lots of underground engineering such as entry arrangement and mining process. In this study, the failure resulted from micro-fracturing in the specimen, which can be characterized by the crack propagation path if the damage events are monitored by using Digital Image Correlation (DIC), infrared thermal imager and high-speed camera. The experimental results demonstrate that there are three different types of typical failure modes for specimens with central holes according to the loading areas. The evolution of the temperature field is shown for various loading areas, the smaller loading area, the greater the stress concentration, and the more pronounced the thermodynamic features. The temperature field can also be associated with material properties in addition to loading area. Additionally, failure around the hole with redistributed stress has been observed, and strain energy density (SED) can help explain the failure mechanisms. The progressive damage process, which takes into account the heterogeneity in elastic modulus and rock strength characteristic, is demonstrated by developing a constitutive model that uses the uniaxial compression and Brazilian disc tests to parameterize it. By comparison with plastic zone, the proposed constitutive model is used to quantitatively evaluate the accumulation of damage. Failure mechanisms are established based on this work and are anticipated to be extensively utilized in engineering applications.