Dynamic variation of the dielectric permittivity of elastomers with mechanical constraints

Elastomers are commonly used as insulators or actuators in important fields such as robotics and electronics. The performance of elastomers is strongly influenced by their dielectric permittivity while determining the dielectric permittivity of elastomers appears to be rather challenging. With image processing techniques and a motor-driven biaxial test setup, the dynamic variation of the dielectric permittivity and dielectric loss of elastomers under dynamic mechanical constraints is first examined in this paper. Also, the mechanical rate-dependence and the cyclic behavior of the dielectric permittivity are investigated. At a given mechanical loading rate, the change in the dielectric permittivity is found to follow a cubic polynomial function. The variations of the stress and the dielectric permittivity indicate the mechanical constraints on the polarization of the material. Our experiment setup allows different mechanical loading paths to be applied to the elastomer when simultaneously measuring the dielectric permittivity and the dielectric loss

Spatial-Temporal Sensitivity Analysis of Flood Control Capability in China Based on MADM-GIS Model

To facilitate better implementation of flood control and risk mitigation strategies, a model for evaluating the flood defense capability of China is proposed in this study. First, nine indicators such as slope and precipitation intensity are extracted from four aspects: objective inclusiveness, subjective prevention, etc. Secondly, the entropy weight method in the multi-attribute decision making (MADM) model and the improved three-dimensional technique for order preference by similarity to ideal solution (3D-TOPSIS) method were combined to construct a flood defense capacity index evaluation system. Finally, the receiver operating characteristic (ROC) curve and the Taylor plot method were innovatively used to test the model and indicators. The results show that nationwide, there is fine flood defense performance in Shandong, Jiangsu and room for improvement in Guangxi, Chongqing, Tibet and Qinghai. The good representativity of nine indicators selected by the model was verified by the Taylor plot. Simultaneously, the ROC calculated area under the curve (AUC) was 70%, which proved the good problem-solving ability of the MADM-GIS model. An accurate assessment of the sensitivity of flood control capacity in China was achieved, and it is suitable for situations where data is scarce or discontinuous. It provided scientific reference value for the planning and implementation of China’s flood defense and disaster reduction projects and emergency safety strategies

Finite Element Simulation of NiTiNb Shape Memory Alloy Pipe-Joint Subjected to Coupled Transformation and Plastic Deformation

The assembling process of Ni47Ti44Nb9 alloy pipe joints considering the phase transformation and plasticity was numerically simulated for the first time with a developed constitutive model. The simulated process was based on the experimental material parameters, which were determined with the experimental tensile results of Ni47Ti44Nb9 shape memory alloy (SMA) and steel bars. The results showed that, after assembly, the Mises stress distributed uniformly along the longitudinal direction of the NiTiNb joint, but nonuniformly along the radial direction. The maximum σeq does not appear at the inner wall of the joints due to the coupling effect of the plastic deformation and the recoverable transformation. The contact pressure distributed uniformly along the circumferential direction, but nonuniformly along the longitudinal direction. The sizes of the SMA joint and the pipe should be properly matched to ensure contact during the stage of the rapid reverse phase transformation to obtain stable connection performance. The pull-out force was also computed, and the results were in good agreement with the experimental results. The results obtained can provide available information for the optimization of the design parameters of the high-performance SMA pipe-joint, such as inner diameter and assembly clearance