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damage and recovery of fiber Bragg grating under radiation environment

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Chinese Physics B 2018年第9期27卷 230-236页

作者： Shi-Zhe Wen Wei-Chen Xiong Li-Ping Huang Zhen-Rui Wang Xing-Bin Zhang Zhen-Hui He School of Material Science and Engineering Sun Yat-Sen UniversityGuangzhou 510006China State Key Laboratory of Optoelectronic Materials and Technologies Sun Yat-Sen UniversityGuangzhou 510275 School of Engineering Sun Yat-Sen UniversityGuangzhou 510006China School of Physics Sun Yat-Sen UniversityGuangzhou 510275China School of Physics and Astronomy Sun Yat-Sen UniversityZhuhai 519000China Center for Space Technology Sun-Yat Sen UniversityZhuhai 519000China

To develop the application of fiber Bragg gratings as temperature and strain sensors in space environments, it is necessary to understand the effect of high-energy radiation on the performance of the fiber Bragg grating. We performed an experiment involving Co（60）-γ ionizing irradiation with a total dose of 1.01 × 10~6 rad on two Ge-doped single-mode fiber Bragg gratings with central wavelengths of 825 and 835 nm, respectively. We found that, with the increase of radiation dose, the redshift of the peak wavelength of the reflection spectrum of the fiber Bragg gratings indicated the increase of the refractive index and the number of color centers. After irradiation, the refractive index decreased with the decreasing number of color centers. We analyzed the influence of ionizing irradiation on the transmission performance of the fiber Bragg gratings using a color-center model, which explained the experimental results. The proposed model was used to determine the creation rate and annihilation rates of the color center, which are foundational data for using the fiber Bragg gratings in space applications.

关键词： fiber Bragg grating radiation color center refractive index damage recovery annihilation

damage localization effects of the regeneratively-cooled thrust chamber wall in LOX/methane rocket engines

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Chinese Journal of Aeronautics 2018年第8期31卷 1667-1678页

作者： Jiawen SONG Bing SUN School of Astronautics Beihang University

To investigate the damage localization effects of the thrust chamber wall caused by combustions in LOX/methane rocket engines, a fluid-structural coupling computational methodology with a multi-channel model is developed to obtain 3-demensioanl thermal and structural *** and mechanical loads are calculated by a validated finite volume fluid-thermal coupling numerical method considering non-premixed combustion processes of propellants. The methodology is subsequently performed on an LOX/methane thrust chamber under cyclic operation. Results show that the heat loads of the thrust chamber wall are apparently non-uniform in the circumferential direction. There are noticeable disparities between different cooling channels in terms of temperature and strain distributions at the end of the hot run phase, which in turn leads to different temperature ranges, strain ranges, and residual strains during one cycle. With the work cycle proceeding, the circumferential localization effect of the residual strain would be significantly enhanced. A post-processing damage analysis reveals that the low-cycle fatigue damage accumulated in each cycle is almost unchanged, while the quasi static damage accumulated in a considered cycle declines until stabilized after several cycles. The maximum discrepancy of the predicted lives between different cooling channels is about 30%.

关键词： Cyclic plasticity damage Heat transfer Regenerative cooling Rocket engine Service life Thrust chamber

damage and fracture model for eutectic composite ceramics

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Acta Mechanica Sinica 2019年第1期35卷 190-200,I0006页

作者： Jinfeng Yu Xinhua Ni Xiequan Liu Yunwei Fu Zhihong Du Department of Vehicle and Electric Engineering Army Engineering UniversityShijiazhuang 050003China Army Infantry College Nanchang 330000China Xichang Satellite Launch Center Xichang 615000China

Study of damage and fracture models to analyze the fracture mechanism of eutectic composite ceramics is of considerable importance because no accurate fracture models are available for these materials. Eutectic composite ceramics are composed of microcells with random direction. We present herein a model that predicts the damage and fracture of eutectic composite ceramics based on analysis of defect stability and the damage localization band. Firstly, given the microstructure of eutectic composite ceramics, a mesodomain and a microcell model are constructed. The local stress field in the mesodomain is then analyzed based on the interaction direct derivative estimate. Secondly, the stability of a defect around particles in a microcell is analyzed, and the stress intensity factor of an annular defect under the applied stress field and the residual stress field in the particle are calculated. The stress intensity factor of a defect is controlled by the residual stress when the defect extension is small. However, it is controlled by the applied stress when the defect extension is large. Finally, a model for the damage localization band at the crack tip is constructed based on the Dugdale-Barenblatt model. The residual intensity is the important factor affecting the length of the damage localization band. When the damage variables reach their largest value, the residual in ten sity and the length of the damage localization band attain their minimum value. This work provides the theoretical basis for further study of the damage mechanics of eutectic composite ceramics and guides the engineering applications of these materials.

关键词： Microcell Interaction direct derivative estimate Defect stability damage localization band

damage OF A HIGH-ENERGY SOLID PROPELLANT AND ITS EFFECTS ON COMBUSTION

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Acta Mechanica Sinica 2001年第4期17卷 348-353页

作者：张泰华白以龙王世英刘培德 State Key Laboratory of Nonlinear MechanicsLNM Institute of MechanicsChinese Academy of SciencesBeijing 100080China Xi'an Modern Chemistry Research Institute Xi'an 710065China

In order to improve the safety of high-energy solid propellants, a study is carried out for the effects of damage on the combustion of the NEPE (Nitrate Ester Plasticized Polyether) propellant. The study includes: (1) to introduce damage into the propellants by means of a large-scale drop-weight apparatus; (2) to observe microstructural variations of the propellant with a scanning electron microscope (SEM) and then to characterize the damage with density measurements; (3) to investigate thermal decomposition; (4) to carry out closed-bomb tests. The NEPE propellant can be considered as a viscoelastic material. The matrices of damaged samples axe severely degraded, but the particles are not. The results of the thermal decomposition and closed-bomb tests show that the microstructural damage in the propellant affects its decomposition and burn rate.

关键词： propellant damage thermal decomposition tests closed-bomb tests combustion

damage Tolerance Assessment of a Brake Unit Bracket for High-Speed Railway Welded Bogie Frames

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Chinese Journal of Mechanical Engineering 2019年第4期32卷 184-194页

作者： Bing Yang Hao Duan Shengchuan Wu Guozheng Kang State Key Laboratory of Traction Power Southwest Jiaotong University Chengdu 610031 China State Key Laboratory for Strength and Vibration of Mechanical Structures Xi’an Jiaotong University Xi’an 710049 China

The brake unit bracket of a bogie frame is an important load-carrying component, particularly under emergency start/stop conditions. Conventional infinite/safe life approaches provide an over-conservative recommendation for the allowable strength and lifetime, which hinders the lightweight design of modern railway vehicles. In this study, to ensure the reliability and durability of a brake unit bracket, an attempt was made to integrate the nominal stress method and an advanced damage tolerance method. First, a complex bogie frame was modelled using solid elements instead of plate and beam elements. A hot spot stress region on the bracket was found under an eight-stage load spectrum obtained from the Wuhan–Guangzhou high-speed railway line. Based on the probability of foreign damage, a semi-elliptical surface crack was then assumed for residual life assessment. The results obtained by the cumulative damage and damage tolerance methods show that the brake unit bracket can operate for over 30 years. Moreover, even if a 2-mm depth crack exists, the brake unit bracket can be safely operated for more than 2.27 years, with the hope that the crack can be detected in subsequent maintenance procedures. Finally, an appropriate safety margin was suggested which provides a basis for the life prediction and durability assessment of brake unit brackets of high-speed railways.

关键词： Welded bogie frame Fatigue damage accumulation damage tolerance design Residual life assessment High-speed railway vehicle

damage evolution and removal behaviors of GaN crystals involved in double-grits grinding

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International Journal of Extreme Manufacturing 2024年第2期6卷 469-484页

作者： Chen Li Yuxiu Hu Zongze Wei Chongjun Wu Yunfeng Peng Feihu Zhang Yanquan Geng State Key Laboratory of Robotics and System(HIT) Harbin Institute of TechnologyHarbin 150001People’s Republic of China Key Laboratory of Microsystems and Microstructures Manufacturing(HIT) Harbin Institute of TechnologyHarbin 150001People’s Republic of China College of Mechanical Engineering Donghua UniversityShanghai 201620People’s Republic of China Department of Mechanical and Electrical Engineering Xiamen UniversityXiamen 361005People’s Republic of China

Elucidating the complex interactions between the work material and abrasives during grinding of gallium nitride(GaN)single crystals is an active and challenging research *** this study,molecular dynamics simulations were performed on double-grits interacted grinding of GaN crystals;and the grinding force,coefficient of friction,stress distribution,plastic damage behaviors,and abrasive damage were systematically *** results demonstrated that the interacted distance in both radial and transverse directions achieved better grinding quality than that in only one *** grinding force,grinding induced stress,subsurface damage depth,and abrasive wear increase as the transverse interacted distance ***,there was no clear correlation between the interaction distance and the number of atoms in the phase transition and dislocation *** interacted distances between abrasives can decrease grinding force,coefficient of friction,grinding induced stress,subsurface damage depth,and abrasive wear during the grinding *** results of grinding tests combined with cross-sectional transmission electron micrographs validated the simulated damage results,*** atoms,high-pressure phase transition,dislocations,stacking faults,and lattice *** results of this study will deepen our understanding of damage accumulation and material removal resulting from coupling between abrasives during grinding and can be used to develop a feasible approach to the wheel design of ordered abrasives.

关键词： grinding double-grits molecular dynamics damage material removal gallium nitride

damage modeling of ballistic penetration and impact behavior of concrete panel under low and high velocities

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Defence Technology（防务技术） 2021年第1期17卷 202-211页

作者： Chahmi Oucif J.S.Kalyana Rama K.Shankar Ram Farid Abed Institute of Structural Mechanics(ISM) Bauhaus-Universitat WeimarMarienstraße 15D-99423WeimarGermany Department of Civil Engineering BITS Pilani-Hyderabad CampusHyderabad500072India Department of Civil Engineering Vignana Bharathi Institute of TechnologyHyderabad501301India Department of Civil Engineering University of CaliforniaBerkeleyBerkeleyCAUnited States Department of Civil Engineering American University of SharjahP.O.Box 26666United Arab Emirates

This work presents a numerical simulation of ballistic penetration and high velocity impact behavior of plain and reinforced concrete *** paper is divided into two *** first part consists of numerical modeling of reinforced concrete panel penetrated with a spherical projectile using concrete damage plasticity(CDP)model,while the second part focuses on the comparison of CDP model and Johnson-Holmquist-2(JH-2)damage model and their ability to describe the behavior of concrete panel under impact *** first and second concrete panels have dimensions of 1500 mm1500 mm150 mm and 675 mm675 mm200 mm,respectively,and are meshed using 8-node hexahedron solid *** impact object used in the first part is a spherical projectile of 150 mm diameter,while in the second part steel projectile of a length of 152 mm is modeled as rigid *** and scabbing characteristics are studied in the first *** the second part,the comparison results are presented as damage contours,kinetic energy of projectile and internal energy of the *** results revealed a severe fracture of the panel and high kinetic energy of the projectile using CDP model comparing to the JH-2 *** addition,the internal energy of concrete using CDP model was found to be less comparing to the JH-2 model.

关键词： Johnson-Holmquist-2 Concrete damage plasticity Concrete panel damage Impact loads

damage assessment of the target area of the island/reef under the attack of missile warhead

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Defence Technology（防务技术） 2020年第1期16卷 18-28页

作者： Cheng-lin Zhai Xiao-wei Chen State Key Laboratory of Explosion Science and Technology Beijing Institute of TechnologyBeijing 100081China School of Mechatronical Engineering Beijing Institute of TechnologyBeijing 100081China Advanced Research Institute of Multidisciplinary Science Beijing Institute of TechnologyBeijing 100081China

Under the background of vigorously developing facilities of island/reef in the world,the economic value and strategic significance of the island/reef have become increasingly ***,they may easily become the attacking target of missiles in the war ***,aiming at the damage quantification of the targets in the island/reef under the missile attacking,a macroscopic damage assessment model for the target area is proposed in this *** model focuses on the construction of the assessment model ***,the analytic hierarchy process and the grey relational analysis are applied to measure the importance of each target in the region through four indicators of the target hazard,striking urgency,damage advantage and mission relevance,***,based on the damage mechanism of shock wave and fragments to target,the corresponding damage model is established,and the damage grade of each target in the evaluated area is obtained according to the damage criteria and grading ***,the model obtains the overall damage grade of the target area by employing the fuzzy comprehensive evaluation method,with synthesizing the importance and the damage grade of each *** the verification of an example,it demonstrates the certain feasibility of the model and provides a certain basis and reference for the subsequent research.

关键词： Island/reef facilities Shock wave Fragment damage assessment Fuzzy comprehensive evaluation method

damage Simulation for 3D Braided Composites by Homogenization Method

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Chinese Journal of Aeronautics 2010年第6期23卷 677-685页

作者： Dong Jiwei Feng Miaolin Department of Engineering Mechanics School of Naval ArchitectureOcean and Civil EngineeringShanghai Jiaotong UniversityShanghai 200240China

In order to study the failure patterns and strength of 3D braided composites from the microscopic view, the damage propagation under tensile loading steps in three kinds of unit cells is simulated. The homogenization formula of micro-stress and the solving approach of finite element method are given firstly. A criterion is presented to determine the damage and its pattern of each element, and then the stiffness degradation method based on Murakami's geometric damage theory is used to simulate the status of damage under tensile loading steps for three kinds of unit cells. It can be seen that the damage percentage and damage pattern of damaged unit cell are totally different for different kind of unit cells. More damaged elements are observed for face cell and corner cell than that for body cell. It is also observed that the damage firstly occurs at the area of face cell, which agrees well with experimental results. It is verified that considering the effects of face and corner cells are important for the damage and strength analysis of 3D braided composites.

关键词： damage 3D braided composites meso-structure homogenization finite element method