Being the two primary approaches for full-field kinematics measurements, both subset-based local digital image correlation (DIC) and finite element-based global DIC have been extensively studied. Nowadays, most commercial DIC systems employ local DIC algorithm because of its advantages of straight forward principle and higher efficiency. However, several researchers argue that global DIC can provide better displacement results due to the displacement continuity constraint among adjacent elements. As such, thoroughly examining the performance of these two different DIC methods seems to be highly necessary. Here, the random errors associated with local DIC and two global DIC methods are theoretically analyzed at first. Subsequently, based on the same algorithmic details and parameters during analyses of numerical and real experiments, the performance of the different DIC approaches is fairly compared. Theoretical and experimental results reveal that local DIC outperforms its global counterpart in terms of both displacement results and computational efficiency when element (subset) size is no less than 11 pixels

Cellular microstructures within natural materials enlighten and promote the development of novel materials and structures in the industrial and engineering fields. Characterization of the microstructures and mechanical properties of these natural materials can help to understand the morphology-related mechanical properties and guide the structural optimization in industrial design. Among these natural cellular materials, pomelo peels, having a foam-like hierarchical microstructure, represent an ideal model for developing materials with high energy absorption efficiency. In this work, by combining X-ray tomographic imaging technique and digital volume correlation (DVC), in-situ stepwise uniaxial compression tests were performed to quantify the internal morphological evolution and kinematic responses of pomelo peel samples during compression. Via these experiments, the varying microstructure features and thus diverse resistance to compression from endocarp to exocarp are examined, and the evolution of both bundles bending and large strain domain from endocarp to mesocarp are explored. Based on the experimental results, the microstructure-related mechanical properties of pomelo peels in response to compressive loading that demonstrates nearly linear morphology-mechanics relationship were revealed