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2023 Vol. 53, No. 3

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Review

Research on impact response characteristics and damage evolution law of transparent ceramics

HAN Guoqing, ZHANG Xianfeng, TAN Mengting, BAO Kuo, LI Yi

2023, 53(3): 497-560. doi: 10.6052/1000-0992-23-007

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Abstract:
Transparent ceramics excel in light transmission and impact damage resistance, and have good application prospects as superior protective materials in military equipment, aerospace and other national defense fields. It is important to explore the damage evolution process of transparent ceramics and clarify the loading response characteristics of materials under impact load in order to grasp the failure mechanism of materials and improve the elastic performance of transparent ceramic armor. This paper systematically reviews the impact response characteristics of transparent ceramics under static and dynamic loading from the experimental research, including experimental technology, strain rate effect, crack growth rate and material failure characteristics. At the same time, the impact failure mechanism of transparent ceramic materials is elucidated based on the impact failure test of ceramic materials, and thereby the damage model, strength criterion and dynamic constitutive model of impact response of transparent ceramic are elaborated. Finally, this paper analyzes the research status of impact response characteristics and numerical simulation technology of transparent ceramic composite packaging, discusses the development trend of impact response characteristics of ceramic materials, and provides the design of transparent composite targets. In view of the shortcomings of the current research on the impact response of transparent ceramics, this paper also proposes suggestions for future research directions.

Review of numerical simulation methods for hypersonic and high-enthalpy non-equilibrium flow

GAO Zhenxun, JIANG Chongwen, LI Chun-Xuan

2023, 53(3): 561-591. doi: 10.6052/1000-0992-22-051

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High performance simulation of computational fluid dynamics (CFD) can be mutually verified with hypersonic flight tests and high enthalpy ground equipment experiments, and will play a more important role in the research of thermochemical non-equilibrium effects and the development of future hypersonic vehicles. The paper reviews the research progress of CFD method of thermochemical non-equilibrium flow at home and abroad, summarizes the current situation and development trend of related thermochemical models, numerical schemes and development of CFD software, and finally points out the problems that should be paid attention to in basic research, software development, simulation application in the future. (1) In terms of thermochemical models, the commonly used temperature models are not completely accurate. The multi-vibrational temperature model has development potential, but is limited in engineering applications. The state-state models are more accurate but its simulation technology is not yet mature. More accurate thermodynamic transport models, finite-rate chemical reaction models, vibration-dissociation coupling models and surface effect models are important physical models to improve the accuracy of thermochemical nonequilibrium simulation, which are worthy of in-depth study. (2) In terms of numerical methods, multi-physical field coupling simulation is a hot issue and trend in the CFD research of hypersonic thermochemical nonequilibrium flows, which raises higher requirements for the robustness and convergence for CFD methods, and is worthy of special attention and research. In addition, the commonly used numerical schemes need to be remodeled based on the characteristics of thermochemical nonequilibrium flows, and the computational reliability of RANS method in thermochemical nonequilibrium turbulence simulation still needs to be verified and confirmed. (3) In terms of numerical software, the numerical solver based on structured/unstructured hybrid grid is more suitable for the requirements of industrial applications. The future hypersonic numerical software should have stable and robust solver for multidisciplinary multi-physical field coupling solution, and can satisfy the simulation requirements of larger grid scale and large-size complex shapes. (4) The computational efficiency of thermochemical nonequilibrium flow simulation can be improved by comprehensively employing a variety of acceleration techniques. The computational stiffness is a common fundamental problem in the research of thermochemical nonequilibrium numerical simulation method, and the stiffness elimination method still needs further study and develop.

Review on electro-mechanically coupled cyclic deformation and fatigue failure behavior of dielectric elastomers

KANG Guozheng, CHEN Yifu, HUANG Weiyang

2023, 53(3): 592-625. doi: 10.6052/1000-0992-23-009

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The electro-mechanically coupled cyclic deformation and fatigue failure of dielectric elastomers (DEs) has attracted more and more attention in the design and life-assessment of related functional devices. Thus, to prompt the developments of soft robots and other related fields, the progress in the experimental and theoretical researches on the electro-mechanically coupled cyclic deformation and fatigue failure of DEs is reviewed in this work as follows: At first, the cyclic deformation and its evolution feature of DEs presented under the mechanical and electro-mechanically coupled loading conditions are summarized by specifically addressing the cyclic softening, ratchetting, fatigue failure and their electro-mechanical coupling effect; then, the existing constitutive models describing the mechanical and electro-mechanically coupled deformations of DEs are reviewed by discussing the capability of proposed hyperelastic, visco-hyperelastic and visco-hyperelastic-plastic constitutive models to reproduce the cyclic deformation of DEs and its electro-mechanical coupling effect; finally, the progress in the researches on the electro-mechanically coupled failure of DEs is outlined by addressing the low-cycle fatigue failure of DEs subjected to a kind of electro-mechanically coupled large deformation. Based on the comprehensive review on the existing literature, some topics are also recommended in this work for the future research, which are helpful to prompt the development of related fields concerning the DEs.

Advances in verification and validation in computational fluid dynamics

CHEN Jiangtao, XIAO Wei, ZHAO Wei, ZHANG Peihong, YANG Fujun, JIN Tao, GUO Yongyan, WU Xiaojun, CHEN Jianqiang, WANG Ruili, LI Li

2023, 53(3): 626-660. doi: 10.6052/1000-0992-23-012

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Computational fluid dynamics (CFD) has played an increasingly important role in major engineering fields, and its credibility is the key constraint to its further extensive engineering application. It is widely accepted home and abroad that verification and validation is the only way to evaluate and guarantee the credibility of CFD. Through systematic verification and validation, the potential programming errors can be effectively identified, the reliability of numerical solving process can be guaranteed, the adequacy and prediction capability of mathematical models in the intended use can be objectively evaluated and improved when necessary. In this paper, with regard to two key issues, ‘‘what is verification and validation’’ and ‘‘how to perform verification and validation’’, the research progress of verification and validation in CFD is introduced from the aspects including basic concept, implementation processes, main methods, calibration model experiments and platform tools, with focusing on numerical error estimation and uncertainty quantification. At the end, the shortcomings of current research are reviewed and the key research directions are prospected.

Review of mesh adaptation for fluid numerical simulation

TANG Jing, CUI Pengcheng, ZHANG Jian, ZHOU Naichun, WU Xiaojun, GONG Xiaoquan, ZHANG Yaobing

2023, 53(3): 661-692. doi: 10.6052/1000-0992-23-013

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Computational mesh is one of the main source of errors in fluid numerical simulation, which greatly affects the accuracy of flow simulation result. Traditional mesh generation strongly depends on user experience, which increases the difficulty of mesh generation for complicated aircraft and increases the uncertainty of aerodynamic characteristics prediction data. Mesh adaptation is a mesh autonomous optimization technology combined with flow characteristics, which can eliminate numerical errors caused by mesh factors through iterative procedure, and can effectively improve the accuracy of aircraft aerodynamics prediction. In recent years, the successful application of mesh adaptation in the high-lift complicated configuration of transport aircraft shows that the adaptation technology has developed to a relatively mature stage. In this paper, for computational fluid dynamics, first of all, the research progress of three key techniques related to mesh adaptation, including error estimation, mesh editing and geometry shape preservation, is systematically summarized, and their parallel implementation techniques are briefly introduced. Secondly, the main applications of mesh adaptation in mesh correlation analysis, flow detail capture, aerodynamics prediction and unsteady flow simulation are introduced. Finally, the future research direction to tackle the existing problems of mesh adaptation are proposed at the end of the paper.

Thermodynamic strength theory (TST)

WANG Biao

2023, 53(3): 693-712. doi: 10.6052/1000-0992-23-017

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The accurate prediction of structural strength of materials is the key issue to the design and optimization of engineering structures and is one of the core problems in solid mechanics. Traditional strength theories mainly rely on empirical formulas, which are largely limited by the applicable materials and working conditions. To ensure safety, engineering structural design often adopts large safety factors, resulting in a significant waste of materials and still can not eliminate the occurrence of catastrophic accidents. How to break through the empirical shackles of traditional strength theories and develop a new theory of structural strength assessment of materials from universal principles is an urgent scientific and engineering problem to be solved. This article briefly summarizes the problems with traditional strength theories, outlines some methods for predicting the failure behavior of the material structures based on the energy theory, and highlights the thermodynamic strength theory proposed by the author. In this theory we treat the material structure as a thermodynamic systems and establish the relationship between the prediction of the failure strength of a material structure with the thermodynamic stability analysis. In principle, this theory has no restrictions on the failure modes of material structures and is applicable to strength prediction for a wide range of failure modes. Several representative examples are used to demonstrate the correctness and wide applicability of the theory, which reflects excellent prospects for engineering applications.

2023 Vol. 53, No. 3

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