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Coupling of quasi-localized and phonon modes in glasses at low frequency

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Chinese Physics B 2024年第5期33卷 564-571页

作者：段军蔡松林丁淦戴兰宏蒋敏强 State Key Laboratory of Nonlinear mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of engineering Science University of Chinese Academy of SciencesBeijing 101408China

Boson peak of glasses,a THz vibrational excess compared to Debye squared-frequency law,remains mysterious in condensed-matter physics and material *** appears in many different kinds of glassy matters and is also argued to exist in damped crystals.A consensus is that boson peak originates from the coupling of the(quasi)-localized non-phonon modes and the plane-wave-like phonon modes,but the coupling behavior is still not fully *** this paper,by modulating the content of localized modes and the frequencies of phonon modes,the coupling is clearly reflected in the localization and anharmonicity of low-frequency vibrational *** coupling enhances with increasing cooling rate and sample *** finite sample size,phonon modes do not fully intrude into the low frequency to form a dense spectrum and they are not sufficiently coupled to the localized modes,thus there is no Debye level and boson peak is *** suggestion remains valid in the presence of thermal motions induced by temperature,even though the anharmonicity comes into *** results point to the coupling of quasi-localized and phonon modes and its relation to the boson peak.

关键词： metallic glasses low-frequency vibrational modes plane wave boson peak

Critical current degradation in an epoxy-impregnated rare-earth Ba_(2)Cu_(3)O_(7-x)coated conductor caused by damage during a quench

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Applied Mathematics and mechanics(English Edition) 2024年第9期45卷 1557-1572页

作者： Donghui LIU Huadong YONG Youhe ZHOU Institute of Superconductor mechanics Lanzhou UniversityLanzhou 730000China Department of mechanics and engineering sciences College of Civil Engineering and MechanicsLanzhou UniversityLanzhou 730000China Key Laboratory of mechanics on Disaster and Environment in Western China Ministry of Education of ChinaLanzhou UniversityLanzhou 730000China

High-temperature superconducting(HTS)rare-earth Ba_(2)Cu_(3)O_(7-x)(REBCO)coated conductors(CCs)have significant potential in high-current and high-field ***,owing to the weak interface strength of the laminated composite REBCO CCs,the damage induced by the thermal mismatch stress under a combination of epoxy impregnation,cooling,and quenching can cause premature degradation of the critical *** this study,a three-dimensional(3D)electromagnetic-thermal-mechanical model based on the H-formulation and cohesive zone model(CZM)is developed to study the critical current degradation characteristics in an epoxy-impregnated REBCO CC caused by the damage during a *** temperature variation,critical current degradation of the REBCO CC,and its degradation onset temperature calculated by the numerical model are in agreement with the experimental data taken from the *** delamination of the REBCO CC predicted by the numerical model is consistent with the experimental *** numerical results also indicate that the shear stress is the main contributor to the damage propagation inside the REBCO *** premature degradation of the critical current during a quench is closely related to the interface shear strength inside the REBCO ***,the effects of the coefficient of thermal expansion(CTE)of the epoxy resin,thickness of the substrate,and substrate material on the critical current degradation characteristics of the epoxy-impregnated REBCO CC during a quench are also *** results help us understand the relationship between the current-carrying degradation and damage in the HTS applications.

关键词： epoxy-impregnated rare-earth Ba_(2)Cu_(3)O_(7-x)(REBCO)coated conductor(CC) quench damage critical current degradation shear stress

Micropillar compression using discrete dislocation dynamics and machine learning

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Theoretical & Applied mechanics Letters 2024年第1期14卷 39-47页

作者： Jin Tao Dean Wei Junshi Yu Qianhua Kan Guozheng Kang Xu Zhang School of mechanics and Aerospace engineering Southwest Jiaotong UniversityChengdu 610031China State Key Laboratory of Nonlinear mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China

Discrete dislocation dynamics(DDD)simulations reveal the evolution of dislocation structures and the interaction of *** study investigated the compression behavior of single-crystal copper micropillars using fewshot machine learning with data provided by DDD *** types of features are considered:external features comprising specimen size and loading orientation and internal features involving dislocation source length,Schmid factor,the orientation of the most easily activated dislocations and their distance from the free *** yielding stress and stress-strain curves of single-crystal copper micropillar are predicted well by incorporating both external and internal features of the sample as separate or combined *** is found that the machine learning accuracy predictions for single-crystal micropillar compression can be improved by incorporating easily activated dislocation features with external ***,the effect of easily activated dislocation on yielding is less important compared to the effects of specimen size and Schmid factor which includes information of orientation but becomes more evident in small-sized ***,incorporating internal features,especially the information of most easily activated dislocations,improves predictive capabilities across diverse sample sizes and orientations.

关键词： Discrete dislocation dynamics simulations Machine learning Size effects Orientation effects Microstructural features

A dispersion-based impact identification method:mechanical model and experimental verification

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Acta Mechanica Sinica 2024年第7期40卷 80-91页

作者： Zishang Liu Tianyu Chen Kun Zhang Yanpeng Wei Yacong Guo Bingchen Wei Key Laboratory of Microgravity(National Microgravity Laboratory) Institute of MechanicsChinese Academy of SciencesBeijing 100190China Center of Materials Science and Optoelectronics engineering University of Chinese Academy of SciencesBeijing 100049China School of engineering Science University of Chinese Academy of SciencesBeijing 100049China Key Laboratory for mechanics in Fluid Coupling Systems Institute of MechanicsChinese Academy of SciencesBeijing 100190China

External transient impact loads widely exist in the service environment of various engineering structures,and urgent engineering and military application requirements call for research on the theory and method of impact *** manuscript proposes a method to identify the impact *** employing the dispersive property of wave propagation through the waveguides,a dispersion-based average power spectral density(PSD)curve for quantitative representation of the dispersion is established,and its evolution law is investigated to apply the identification of impact *** critical parameters of the average PSD curve are obtained by analyzing the response of the structure from the perspective of *** effectiveness of this method is verified through the development of the triple-successive-impact split Hopkinson bar and the triple-successive-impact *** the method proposed in this manuscript,a kind of impact identification under multiple impact loads,which is not convenient to measure directly by the sensor,is realized,especially in the case of highly transient external impact.

关键词： Structural impact Dispersion Structure vibration Waveguides Impact identification

Resolving aging dynamics of a 3D colloidal glass

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Science China(Physics,mechanics & Astronomy) 2024年第3期67卷 110-118页

作者： XiaoJuan Wang Jun Duan Gan Ding YunZhuo Lu Xing Lu LanHong Dai MinQiang Jiang State Key Laboratory of Nonlinear mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Materials Science and engineering Dalian Jiaotong UniversityDalian 116028China School of engineering Science University of Chinese Academy of SciencesBeijing 100049China

Physical aging is an inherent property of glassy matter, but understanding its microscopic mechanism remains a challenge particularly at the particle level. In this work, we use a confocal microscope to in-situ trace the particle trajectories in a 3D colloidal glass for 73000 s, aiming at resolving the aging dynamics. By calculating the mean square displacement of particle motions, we find that the glass aging with time can be divided into three stages: β relaxation, α relaxation and free diffusion. The system's mean square displacement at each aging state is quantitatively resolved into three contributions of particle dynamics modes: vibration within the nearest-neighbor cages, hopping between cages and cooperative rearrangement. We further calculate the particle's free volume and find that the β-to-α transition is accompanied by the temporary increase of the system-averaged free volume due to pronounced hops of particles. Nevertheless, the temporal autocorrelation of the free volume spatial distribution still obeys a monotonically stretched exponential decay with an exponent of 0.76, which is related to the sub-diffusion dynamics of cooperative rearrangements and hops mixed in α relaxation. According to the resolved vibrational displacements,we calculate the vibrational density of states of this 3D glass, and the characteristic boson peak is reproduced at low *** findings shed insight into the particle-level aging dynamics of a real glass under purely thermal activation.

关键词： colloidal glass physical aging particle dynamics free volume boson peak

Concise extraction and characterization of the pore-throat network in unconventional hydrocarbon reservoirs: A new perspective

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Petroleum Science 2024年第3期21卷 1474-1487页

作者： Shu-Heng Du Yong-Min Shi State Key Laboratory of Nonlinear mechanics Institute of MechanicsChinese Academy of SciencesBeijing100190China School of engineering Science University of Chinese Academy of SciencesBeijing100049China School of Earth and Space sciences Peking UniversityBeijing100871China

In this study,a new image-based method for the extraction and characterization of pore-throat network for unconventional hydrocarbon storage and exploitation is proposed.“Pore-throat solidity”,which is analogous to particle solidity,and a new method for automatic identification of pores and throats in tight sandstone oil reservoirs are ***,the“pore-throat combination”and“pure pore”are defined and distinguished by drawing the cumulative probability curve of the pore-throat solidity and by selecting an appropriate cutoff *** the discrete grid set is recognized as a pore-throat combination,Legendre ellipse fitting and minimum Feret diameter are *** the pore and throat grid sets are identified as pure pores,the pore diameter can be directly *** the new method,the analytical results for the physical parameters and pore radius agree well with most prior *** results comparing the maximum ball and the new model could also prove the accuracy of the latter's in micro and nano *** new model provides a more practical theoretical basis and a new calculation method for the rapid and accurate evaluation of the complex processes of oil migration.

关键词： Hydrocarbon exploitation Pore Throat Porous media Identification

Prediction of chemical short-range order in high-/medium-entropy alloys

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Journal of Materials Science & Technology 2024年第2期169卷 115-123页

作者： Pei-Yu Cao Jing Wang Ping Jiang Yun-Jiang Wang Fu-Ping Yuan Xiao-Lei Wu State Key Laboratory of Nonlinear mechanics Institute of MechanicsChinese Academy of ScienceBeijing 100190China School of engineering Science University of Chinese Academy of SciencesBeijing 100049China

Chemical short-range orders(CSROs),as the built-in sub-nanoscale entities in a high-/medium-entropy alloy(H/MEA),have aroused an ever-increasing *** multi-principal elements in an H/MEA to form a complex concentrated solution,a variety of sub-systems of species exist to induce the metastable ordered compounds as candidates for ultimate *** issues remain pending on the origin of CSROs as to how to judge if CSRO will form in an H/MEA and particularly,what kind of CSROs would be stably produced if there were multiple ***,the first-principles method,along with the proposed local formation energy calculation in allusion to the atomic-scale chemical heterogeneities,is used to predict the CSRO formation based on the mechanical stability,thermodynamic formation energy,and electronic *** simulations are detailed in an equiatomic ternary VCoNi MEA with three kinds of potential compounds,i.e.,L1_(1),L1_(2),and B2,in the face-centered cubic *** turns out that L1_(1)is stable but hard to grow up so as to become the final CSRO.L1_(1)is further predicted as CSROs in CrCoNi,but unable to form in FeCoNi and CrMnFeCoNi *** predictions are consistent with the experimental *** findings shed light on understanding the formation of *** method is applicable to other H/MEAs to design and tailor CSROs by tuning chemical species/contents and thermal processing for high performance.

关键词： Short-range order High-entropy alloy Microstructure First-principles calculation Gibbs free energy Local electronic density of states

Multi-Scale-Matching neural networks for thin plate bending problem

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Theoretical & Applied mechanics Letters 2024年第1期14卷 11-15页

作者： Lei Zhang Guowei He The State Key Laboratory of Nonlinear mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of engineering Science University of Chinese Academy of SciencesBeijing 100049China

Physics-informed neural networks are a useful machine learning method for solving differential equations,but encounter challenges in effectively learning thin boundary layers within singular perturbation *** resolve this issue,multi-scale-matching neural networks are proposed to solve the singular perturbation *** by matched asymptotic expansions,the solution is decomposed into inner solutions for small scales and outer solutions for large scales,corresponding to boundary layers and outer regions,***,to conform neural networks,we introduce exponential stretched variables in the boundary layers to avoid semiinfinite region *** results for the thin plate problem validate the proposed method.

关键词： Singular perturbation Physics-informed neural networks Boundary layer Machine learning

A physics-informed neural network for simulation of finite deformation in hyperelastic-magnetic coupling problems

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Applied Mathematics and mechanics(English Edition) 2024年第10期45卷 1717-1732页

作者： Lei WANG Zikun LUO Mengkai LU Minghai TANG Department of engineering mechanics College of Mechanics and Engineering SciencesHohai University School of Mechanical engineering and mechanics Ningbo University

Recently, numerous studies have demonstrated that the physics-informed neural network(PINN) can effectively and accurately resolve hyperelastic finite deformation problems. In this paper, a PINN framework for tackling hyperelastic-magnetic coupling problems is proposed. Since the solution space consists of two-phase domains,two separate networks are constructed to independently predict the solution for each phase region. In addition, a conscious point allocation strategy is incorporated to enhance the prediction precision of the PINN in regions characterized by sharp *** the developed framework, the magnetic fields and deformation fields of magnetorheological elastomers(MREs) are solved under the control of hyperelastic-magnetic coupling equations. Illustrative examples are provided and contrasted with the reference results to validate the predictive accuracy of the proposed framework. Moreover, the advantages of the proposed framework in solving hyperelastic-magnetic coupling problems are validated, particularly in handling small data sets, as well as its ability in swiftly and precisely forecasting magnetostrictive motion.

关键词： physics-informed neural network (PINN) deep learning hyperelasticmagnetic coupling finite deformation small data set O343.5 DEEP LEARNING FRAMEWORK BEHAVIOR MODEL