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To meet the requirement of mobile robots to achieve high mobility and strong obstacle-crossing in complex and variable environment, a design scheme of passive transformable wheel-legged obstacle-crossing robot is proposed. The transformable wheel conversion process of the robot is obtained by external force operation, so no additional driver is required, which reduces the complexity of the mechanism. Firstly, based on the three-dimensional modeling of the whole robot, the structure, principle and force of the transformable wheel are analyzed, and then the structure optimization is carried out by taking the ratio of the triggering torque during the transformation process and radius before and after unfolding as the index. Afterwards, the force condition during the transformable stage of the robot is analyzed and the relevant parameters of the robot platform are adjusted to achieve stable obstacle crossing. Finally, kinematics simulation of transformation and obstacle-crossing process of the robot is carried out by using the Adams software, physical prototype is made and rationality of the structure design of the whole machine is verified by experiment.

Hardness is one of the important mechanical properties of high-temperature structural ceramics and their composites. In spite of the extensive use of the materials in high-temperature applications, there are few theoretical models for analyzing their temperature-dependent hardness. To fill this gap in the available literature, this work is focused on developing novel theoretical models for the temperature dependence of the hardness of the ceramics and their composites. The proposed model is just expressed in terms of some basic material parameters including Young’s modulus, melting points, and critical damage size corresponding to plastic deformation, which has no fitting parameters, thereby being simple for materials scientists and engineers to use in the material design. The model predictions for the temperature dependence of hardness of some oxide ceramics, non-oxide ceramics, ceramic–ceramic composites, diamond–ceramic composites, and ceramic-based cermet are presented, and excellent agreements with the experimental measurements are shown. Compared with the experimental measurements, the developed model can effectively save the cost when applied in the material design, which could be used to predict at any targeted temperature. Furthermore, the models could be used to determine the underlying control mechanisms of the temperature dependence of the hardness of the materials.

The fracture behavior of ultra‐high temperature ceramic matrix composites at high temperature has received increasing attention. However, few studies consider the effect of particle/crack interaction on the high temperature fracture strength of materials. In this work, the effect of particle/crack interaction is introduced into temperature‐dependent fracture strength model of monolithic ultra‐high temperature ceramic matrix composites, which also considers effects of flaw size, grain size, and residual thermal stress. Furthermore, by considering the influence of laminated structure, a theoretical model of the temperature‐dependent fracture strength of laminated ceramic matrix composites is developed. The effect of particle/crack interaction is also included in this model. It should be noted that the predictions of models agree well with the experimental data of both monolithic and laminated materials without using any fitting parameters. The effect of particle/crack interaction is found to have a significant weakening effect on the strength of materials at different temperatures. Highlights: High temperature strength of monolithic and laminated ceramic composites is characterized.Effects of temperature and particle/crack interaction are included in theoretical models.Effects of micro‐laminated structures on high temperature fracture strength are analyzed.Predictions of models agree well with measured data without using any fitting parameters. [ABSTRACT FROM AUTHOR]

Compared with single-phase ceramics, the thermal shock crack propagation mechanism of multiphase layered ceramics is more complex. There is no experimental method and theoretical framework that can fully reveal the thermal shock damage mechanism of ceramic materials. Therefore, a multiphase phase-field fracture model including the temperature dependence of material for thermal shock-induced fracture of multilayer ceramics is established. In this study, the effects of residual stress on the crack propagation of ATZ (Al2O3-5%tZrO2)/AMZ (Al2O3-30%mZrO2) layered ceramics with different layer thickness ratios, layers, and initial temperatures under bending and thermal shock were investigated. Simulation results of the fracture phase field under four-point bending are in good agreement with the experimental results, and the crack propagation shows a step shape, which verifies the effectiveness of the proposed method. With constant thickness, high-strength compressive stress positively changes with the layer thickness ratio, which contributes to crack deflection. The cracks of the ceramic material under thermal shock have hierarchy and regularity. When the layer thickness ratio is constant, the compressive residual stress decreases with the increase in the layer number, and the degree of thermal shock crack deflection decreases. [ABSTRACT FROM AUTHOR]