Multilayer interlock three-dimensional (3D) tubular braided composites have been widely used in propeller blades, high pressure pipelines, rocket nose cones and engine nozzles owing to prominent interlaminar shear properties, reliable damage tolerance and outstanding torsion performance. The prediction of the mechanical properties and the design of the fabric structures for the 3D braided composites are dependent on the trajectory distribution of strands and the geometrical model of the braided structure. This paper aims to build theoretical models for the braiding strand trajectories and presents a creative method to establish the parametric geometrical models for the multilayer interlock 3D tubular braided structures. Firstly, mathematical models of braiding strand trajectories are derived based on the analysis for the characteristics of carrier paths, the interlacing and interlocking of braided structures and the motion of braiding strands. The mathematical models are then developed to establish parametric expressions for multilayer interlock 3D tubular braided structures by the advanced development of UG NX®. In addition, the models of corresponding braiding strand trajectories and braiding structures can be obtained automatically in the simulation environment with the modification of design parameters. Finally, the established models are compared with the carbon fiber braided specimen. The results show that the innovative parametric geometric models of the multilayer interlock 3D tubular braided structures accurately describe the key characteristics of the preform.
The properties of anchored surrounding rock may vary considerably under complex geological and stress conditions, especially dynamic loading in deep mining. Therefore, comprehensive study of the reinforced mechanism is required to prevent failures associated with deep mining. In this paper, with sandstone as matrix and steel bar as bolt, the dynamic compression test of reinforced rock was carried out by using a 50 mm rod diameter split Hopkinson pressure bar (SHPB) test device. The mechanical and energy characteristics of reinforced rock under dynamic loading were analyzed. The results show that the dynamic strength of reinforced sample is greater than that of unreinforced sample and increases with the increase of the strain rate. The reflected energy and absorbed energy increase with the increase of incident energy, while the transmitted energy increases slightly. The higher the strain rate, the larger the energy dissipation rate and the higher the degree of fragmentation. It shows that the energy dissipation characteristic reflects the internal damage process to some extent. Compared with the results of unreinforced samples, the reflected energy of reinforced samples significantly increases and the absorbed energy will significantly decrease. It can be seen that the bolt can reduce absorbed energy of surrounding rock, thereby improving the stability of roadway surrounding rock. The results may provide reference for the stability of deep roadway and support design.
As a fundamental mechanical problem in steel and concrete composite structures, the axial compressive behavior of reactive powder concrete (RPC)-filled steel tube stub columns has been a concern of scholars worldwide. At present, the analysis method of RPC-filled steel tube is based on nonlinear finite element method and equivalent uniaxial stress-strain analysis model, but the analysis process is complicated and cannot accurately describe the interaction between the steel tube and RPC. Thus, this study proposed a nonlinear analytical procedure to evaluate the mechanical properties of steel tube and RPC accurately at different compressing stages. The method was employed to predict the load-deformation curves of RPC-filled steel tube stub columns under axial compression. Compressing experiments were conducted on such columns, and the characteristic hoop coefficient was derived. Comparison analysis was performed to verify the accuracy and efficiency of the analytical procedure. Results demonstrate that the characteristic hoop coefficient is a critical value for assessing whether the steel tube yields when columns reach the ultimate bearing capacity. Columns with small hoop coefficient have good ductility, but the material utilization rate of the steel tube is not high. Columns with large hoop coefficient have weak ductility and residual deformation capacity. Moreover, columns with characteristic hoop coefficient can reach good ductility and high material utilization rate. The characteristic hoop coefficient determined by the test analysis in this study is approximately 1.3. The analytical results are generally in good agreement with the experimental results until the starting position of strain hardening or local plastic buckling. The proposed method provides a good prospect for optimizing the design of RPC-filled steel tube columns.
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