Natural rocks belong to the polymineral composite material with complex microstructures. Such a strong heterogeneity of rocks makes it difficult to estimate the effective moduli by traditional models in theory. In the present study, a Mori-Tanaka (MT) model considering the shape and orientation of inclusion minerals obtained by the micro-CT is established, and then it is applied to evaluate the anisotropic parameters of shales. In the MT model, the principal radii and Eulerian angles of the ellipsoidal inclusion are obtained by solving its inertia matrix through the micro-CT. According to these inclusion information, we make statistics on the ratio of average principal radii and the distribution of Eulerian angles of inclusions with different minerals. In what follows, the effective elastic stiffness matrix of shale samples is predicted by the MT model, and the corresponding digital core is input for finite element method (FEM) analysis to verify the accuracy of the theoretical results. It is shown that the anisotropy of the elastic stiffness matrix predicted by the MT model and FEM is consistent under two sizes of representative volume elements. These findings are potential for applications in rock mechanics, civil engineering and oil exploitation, etc.
Soft magnetic robots have attracted tremendous interest owning to their controllability and manoeuvrability, demonstrating great prospects in a number of industrial areas. However, further explorations on the locomotion and corresponding deformation of magnetic robots with complex configurations are still challenging. In the present study, we analyse a series of soft magnetic robots with various geometric shapes under the action of the magnetic field. First, we prepared the matrix material for the robot, that is, the mixture of silicone and magnetic particles. Next, we fabricated a triangular robot whose locomotion speed and warping speed are approximately 1.5 and 9 mm/s, respectively. We then surveyed the generalised types of robots with other shapes, where the movement, grabbing, closure and flipping behaviours were fully demonstrated. The experiments show that the arching speed and grabbing speed of the cross-shaped robot are around 4.8 and 3.5 mm/s, the crawling speed of the pentagram-shaped robot is 3.5 mm/s, the pentahedron-shaped robot can finish its closure motion in 1 s and the arch-shaped robot can flip forward and backward in 0.5 s. The numerical simulation based on the finite element method has been compared with the experimental results, and they are in excellent agreement. The results are beneficial to engineer soft robots under the multi-fields, which can broaden the eyes on inventing intellectual devices and equipment.
Natural rocks belong to the polymineral composite material with complex microstructures. Such a strong heterogeneity of rocks makes it difficult to estimate the effective moduli by traditional models in theory. In the present study, a Mori-Tanaka (MT) model considering the shape and orientation of inclusion minerals obtained by the micro-CT is established, and then it is applied to evaluate the anisotropic parameters of shales. In the MT model, the principal radii and Eulerian angles of the ellipsoidal inclusion are obtained by solving its inertia matrix through the micro-CT. According to these inclusion information, we make statistics on the ratio of average principal radii and the distribution of Eulerian angles of inclusions with different minerals. In what follows, the effective elastic stiffness matrix of shale samples is predicted by the MT model, and the corresponding digital core is input for finite element method (FEM) analysis to verify the accuracy of the theoretical results. It is shown that the anisotropy of the elastic stiffness matrix predicted by the MT model and FEM is consistent under two sizes of representative volume elements. These findings are potential for applications in rock mechanics, civil engineering and oil exploitation, etc.
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