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Measurement of thermal expansion coefficient of nonuniform temperature specimen

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Chinese Optics Letters 2008年第9期6卷 669-672页

作者：戴景民辛春锁何小瓦 department of Automation Measurement and Control Harbin Institute of Technology aerospace Research Institute of Materials and Processing technology

A new technique is developed to measure the longitudinal thermal expansion coefficient of C/C composite material at high temperature. The measuring principle and components of the apparatus are described in detail. The calculation method is derived from the temperature dependence of the thermal expansion coefficient. The apparatus mainly consists of a high temperature environmental chamber, a power circuit of heating, two high-speed pyrometers, and a laser scanning system. A long solid specimen is resistively heated to a steady high-temperature state by a steady electrical current. The temperature profile of the specimen surface is not uniform because of the thermal conduction and radiation. The temperature profile and the total expansion are measured with a high-speed scanning pyrometer and a laser slit scanning measuring system, respectively. The thermal expansion coefficient in a wide temperature range （1000 - 3800 K） of the specimen can therefore be obtained. The perfect consistency between the present and previous results justifies the validity of this technique.

关键词： Environmental chambers Heating Pyrometers Pyrometry Scanning Speed Temperature control Thermal spraying Thermal stress

Dynamic Stability Analysis of Linear Time-varying systems via an Extended Modal Identification Approach

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Chinese Journal of Mechanical Engineering 2017年第2期30卷 459-471页

作者： Zhisai MA Li LIU Sida ZHOU Frank NAETS Ward HEYLEN Wim DESMET School of aerospace Engineering Beijing Institute of Technology department of Mechanical Engineering KU Leuven

The problem of linear time-varying（LTV） system modal analysis is considered based on time-dependent state space representations, as classical modal analysis of linear time-invariant systems and current LTV system modal analysis under the ＂frozen-time＂ assumption are not able to determine the dynamic stability of LTV systems. Time-dependent state space representations of LTV systems are first introduced, and the corresponding modal analysis theories are subsequently presented via a stabilitypreserving state transformation. The time-varying modes of LTV systems are extended in terms of uniqueness, and are further interpreted to determine the system＇s stability. An extended modal identification is proposed to estimate the time-varying modes, consisting of the estimation of the state transition matrix via a subspace-based method and the extraction of the time-varying modes by the QR decomposition. The proposed approach is numerically validated by three numerical cases, and is experimentally validated by a coupled moving-mass simply supported beam exper- imental case. The proposed approach is capable of accurately estimating the time-varying modes, and provides anew way to determine the dynamic stability of LTV systems by using the estimated time-varying modes.

关键词： Linear time·varying systems · Extended modal identification · Dynamic stability analysis · Time·varying modes

A NOVEL THEORY OF EFFECTIVE MECHANICAL PROPERTIES OF CLOSED-CELL FOAM MATERIALS

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Acta Mechanica Solida Sinica 2013年第6期26卷 559-569页

作者： Yuli Ma Xianyue Su R.Pyrz J.Ch.Rauhe The State Key Laboratory for Turbulence and Complex systems (LTCS) and department of Mechanics and aerospace Engineering College of EngineeringPeking University Chinalco Research Institute of Science and technology department of Mechanical and Manufacturing Engineering Aalborg University

In this paper a new theory of effective mechanical properties of foam materials is proposed. A cell volume distribution coefficient is introduced to modify the original Gibson-Ashby equations of effective mechanical properties of foam materials. The constants that influence the effective modulus are replaced by the coeff^cient. Based on the modified distribution coefficient, the yield stress is also recalculated. Using X-ray microtomography, the internal structures of dif- ferent samples of polypropylene-nanoclay foam are obtained. The cell volume distributions of these samples are derived from the experiment by image analysis and the fitting curves are plot- ted. The distribution coefficient is acquired using the parameters from the theoretical model of the distribution curves. The results of the improved theory are compared with the experimental values and show good fitting quality. It was found that the precision of the improved theory is high and the cell volume distribution has an impact on the effective mechanical properties that would lead to the optimization of the synthesis procedure.

关键词： closed-cell foam cell volume distribution distribution coefficient Young's modulus yield stress distribution function

Vibration analysis of foam plates based on cell volume distribution

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Applied Mathematics and Mechanics(English Edition) 2012年第12期33卷 1493-1504页

作者：马宇立陈继伟刘咏泉苏先樾 The State Key Laboratory for Turbulence and Complex systems(LTCS) and department of Mechanics and aerospace Engineering College of EngineeringPeking University Chinalco Research Institute of Science and technology

In this paper, vibration analysis of irregular-closed-cell foam plates is per- formed. A cell volume distribution coefficient is introduced to modify the original Gibson- Ashby equations of effective Young＇s modulus of foam materials. A Burr distribution is imported to describe the cell volume distribution situation. Three Burr distribution pa- rameters are obtained and related to the cell volume range and the diversity. Based on the plate theory and the effective modulus theory, the natural frequency of foam plates is calculated with the change of the cell volume distribution parameters. The relationship between the frequencies and the cell volumes are derived. The scale factor of the average cell size is introduced and proved to be an important factor to the performance of the foam plate. The result is shown by the existing theory of size effects. It is determined that the cell volume distribution has an impact on the natural frequency of the plate structure based on the cell volume range, the diversity, and the average size, and the impact can lead to optimization of the synthesis procedure.

关键词： closed-cell foam plate vibration natural frequency cell volume distribu-tion effective Young's modulus scale factor

Research on film thickness of conductive line formed by laser micro-fine cladding and flexibly direct writing technique

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Chinese Optics Letters 2004年第11期2卷 654-657页

作者：李慧玲曾晓雁李惠芬李祥友陈佚群 State Key Laboratory of laser technology Huazhong University of Science and technology Wuhan 430074 department of Industrial and systems Engineering The Hong Kong Polytechnic University Hung Hom Kowloon Hong Kong

The conventional technology could not fulfill the rapidly growing need for fine conductive lines for its inherent limits. Therefore, in this study laser micro-fine cladding and flexibly direct writing technique is used to obtain conductive lines with high precision and reliability. In the case of different substrates and parameters, film thickness will be different. Film thickness directly influences the reliability and stability of conductive lines with exception of quality and running speed. Therefore, we focus on developing the optimal parameters for the different substrates to achieve expected film thickness and make conductive lines have good performance and quality.

关键词： Cladding (coating) Conductive films Fiber lasers Thickness control

Drop weight impact analysis of GFRP tubes with hollow glass particle-filled matrix

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Defence technology（防务技术） 2023年第11期29卷 1-9页

作者： Daniel Paul R.Velmurugan N.K.Gupta department of aerospace Engineering Indian Institute of Technology MadrasChennaiIndia department of Applied Mechanics Indian Institute of Technology DelhiNew DelhiIndia

Protecting occupants or payloads in crashes and blasts is of utmost importance in both moving and immobile *** way of achieving this is by using a sacrificial energy *** tubes have been studied as potential energy absorbers due to their ability to fail progressively under axial *** this study,the energy absorption capability of these tubes is enhanced by adding hollow glass particles to the ***-weight tests are performed on composite tubes,and a digital image correlation(DIC)-based technique is used to capture their load-displacement *** eliminates the use of electronic data acquisition systems,load cells,and *** load-displacement curves of the tubes are obtained from the DIC-based technique and examined to understand their crushing *** the mean crush load shows a drop,an increase in crush length is *** specific energy absorbed by the tubes improves with an increase in GMB volume *** addition of 0.1,0.2,0.3 and 0.4 vol fractions of GMB results in the specific energy absorption increasing by6.6%,14.7%,24%and 36.6%,respectively,compared to neat glass fibre-epoxy *** examination of the tubes and comparison with tubes subject to quasi-static compression is also performed.

关键词： Composite tubes Syntactic foam Impact Axial compression Digital image correlation

Probing the compound effect of spatially varying intrinsic defects and doping on mechanical properties of hybrid graphene monolayers

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Journal of Materials Science & technology 2020年第15期47卷 44-58页

作者： Kritesh Kumar Gupta Tanmoy Mukhopadhyay Aditya Roy Sudip Dey department of Mechanical Engineering National Institute of Technology SilcharSilcharIndia department of aerospace Engineering Indian Institute of Technology KanpurKanpurIndia

Doping in pristine 2 D materials brings about the advantage of modulating wide range of mechanical properties ***,intrinsic defects(such as Stone-Wales and nanopore) in such hybrid materials are inevitable due to complex manu facturing and synthesis *** that,de fects and irregularities can be intentionally induced in a pristine nanostructure for multi-synchronous modulation of various multi-functional *** the case may be,in order to realistically analyse a doped graphene sheet,it is of utmost importance to investigate the compound effect of doping and defects in such 2 D *** we present a molecular dynamics based investigation for probing mechanical properties(such as Young’s modulus,post-elastic behaviour,failure strength and strain)of doped graphene(C14 and Si) coupling the effect of inevitable *** sensitivity of defect and doping are systematically analyzed considering different rational *** study reveals the effects of individual defects and doping along with their possible compounded influences on the failure stress,failure strain,Young’s modulus and constitutive relations beyond the elastic *** detailed mechanical characterization under the practically relevant compound effects would allow us to access the viability of adopting doped graphene in various multifunctional nanoelectromechanical devices and systems in a realistic situation.

关键词： Defect in graphene Doped graphene Defected 2D material Temperature-dependent mechanical properties Spatial sensitivity of defect and doping

Development of Gravity Theories in the View of TRAPPIST-1e

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Research in Astronomy and Astrophysics 2025年第1期25卷 143-161页

作者： Nan Wang Lu-Yao Lu Hui-Gen Liu An-Dong Chen Tiger Lu Ao-Ran Cui Jun-Kai Wang Marine Science and technology College Zhejiang Ocean University Key Laboratory of Modern Astronomy and Astrophysics Ministry of Education Zhoushan Astronomical Society School of Astronomy and Space Science Nanjing University department of Astronomy Yale University Kuang Yaming Honors School Nanjing University School of Physics Nanjing University

Contrary to the solar system, most exoplanet systems detected hitherto are close-in and compact. One typical system is TRAPPIST-1, which has seven nearly co-planar terrestrial planets all within the orbit of Mercury,including three in the habitable zone. To evaluate the differences in developing sophisticated gravity theories from the solar system, we use N-body integrations to simulate ephemeris and reproduce some important astronomy phenomena observed on the potentially habitable planet TRAPPIST-1e. Retrograde motions of other planets last1–2 orders of magnitude shorter than in the solar system, but occur much more frequently. Transit events of all inner planets can be observed steadily. Except for Kepler's first law, which is hard to notice for low eccentricities of planets, the other two laws can then be precisely verified in 102days, because the areas swept by planets vary by?0.01% and the observed semimajor axes and periods result in constants with theoretical and observation accuracies both ?2%. However, the mean motion correlation implies that the Great Inequality is not always apparent between one pair of planets like Jupiter and Saturn. Furthermore, general relativity can hardly be discovered because it gives rise to perihelion precession of inner planets only ～0.1% of gravity precession, dozens of times smaller than Mercury. Our results support the possibility of developing part of gravity theories by potential exo-civilizations in compact systems like TRAPPIST-1.

关键词： ephemerides extraterrestrial intelligence gravitation planets and satellites: terrestrial planets

Multiresolution state-space discretization for Q-Learning with pseudorandomized discretization

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控制理论与应用（英文版） 2011年第3期9卷 431-439页

作者： Amanda LAMPTON John VALASEK Mrinal KUMAR systems technology Inc.13766 S.Hawthorne BlvdHawthorneCA 90250U.S.A. department of aerospace Engineering Texas A&M University department of Mechanical & aerospace Engineering University of Florida

A multiresolution state-space discretization method with pseudorandom gridding is developed for the episodic unsupervised learning method of *** is used as the learning agent for closed-loop control of morphing or highly reconfigurable *** paper develops a method whereby a state-space is adaptively discretized by progressively finer pseudorandom grids around the regions of interest within the state or learning space in an effort to break the Curse of *** of the method is demonstrated with application to the problem of a morphing airfoil,which is simulated by a computationally intensive computational fiuid dynamics *** setting the multiresolution method to define the region of interest by the goal the agent seeks,it is shown that this method with the pseudorandom grid can learn a specific goal within ±0.001 while reducing the total number of state-action pairs needed to achieve this level of specificity to less than 3000.

关键词： Reinforcement learning Morphing Random grid