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Strengthening-softening transition and maximum strength in Schwarz nanocrystals

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Nano Materials Science 2024年第3期6卷 320-328页

作者： Hanzheng Xing Jiaxi Jiang Yujia Wang Yongpan Zeng Xiaoyan Li Center for Advanced mechanics and Materials Applied Mechanics LaboratoryDepartment of Engineering MechanicsTsinghua UniversityBeijing100084China Institute of High Performance Computing(IHPC) Agency for ScienceTechnology and Research(A*STAR)Singapore138632Singapore

Recently,a Schwarz crystal structure with curved grain boundaries(GBs)constrained by twin-boundary(TB)networks was discovered in nanocrystalline Cu through experiments and atomistic *** Cu with nanosized Schwarz crystals exhibited high strength and excellent thermal ***,the grainsize effect and associated deformation mechanisms of Schwarz nanocrystals remain ***,we performed large-scale atomistic simulations to investigate the deformation behaviors and grain-size effect of nanocrystalline Cu with Schwarz *** simulations showed that similar to regular nanocrystals,Schwarz nanocrystals exhibit a strengthening-softening transition with decreasing grain *** critical grain size in Schwarz nanocrystals is smaller than that in regular nanocrystals,leading to a maximum strength higher than that of regular *** simulations revealed that the softening in Schwarz nanocrystals mainly originates from TB migration(or detwinning)and annihilation of GBs,rather than GB-mediated processes(including GB migration,sliding and diffusion)dominating the softening in regular *** analyses of simulation data further showed that compared with those in regular nanocrystals,the GB-mediated processes in Schwarz nanocrystals are suppressed,which is related to the low volume fraction of amorphous-like GBs and constraints of TB *** smaller critical grain size arises from the suppression of GB-mediated processes.

关键词： Schwarz nanocrystal Curved grain boundary Atomistic simulation Grain size effect Maximum strength

Mass-spring model for elastic wave propagation in multilayered van der Waals metamaterials

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Applied Mathematics and mechanics(English Edition) 2024年第7期45卷 1107-1118页

作者： Yabin JING Lifeng WANG Yuqiang GAO State Key laboratory of mechanics and Control for Aerospace Structures Nanjing University of Aeronautics and AstronauticsNanjing210016China

Multilayered van der Waals(vdW)materials have attracted increasing interest because of the manipulability of their superior optical,electrical,thermal,and mechanical properties.A mass-spring model(MSM)for elastic wave propagation in multilayered vdW metamaterials is reported in this *** dynamics(MD)simulations are adopted to simulate the propagation of elastic waves in multilayered vdW *** results show that the graphene/MoS_(2)metamaterials have an elastic wave bandgap in the terahertz *** MSM for the multilayered vdW metamaterials is proposed,and the numerical simulation results show that this model can well describe the dispersion and transmission characteristics of the multilayered vdW *** MSM can predict elastic wave transmission characteristics in multilayered vdW metamaterials stacked with different two-dimensional(2D)*** results presented in this paper offer theoretical help for the vibration reduction of multilayered vdW semiconductors.

关键词： multilayered van der Waals(vd W)metamaterial molecular dynamics(MD) mass-spring model(MSM) dispersion relation transmission characteristic

Quasi-plastic deformation mechanisms and inverse Hall-Petch relationship in nanocrystalline boron carbide under compression

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Chinese Physics B 2024年第8期33卷 405-413页

作者：岳珍李君刘立胜梅海 Hubei Key laboratory of Theory and Application of Advanced Materials mechanics Wuhan University of TechnologyWuhan 430070China

Grain boundaries(GBs)play a significant role in the deformation behaviors of nanocrystalline ***,we investigate the compression behaviors of nanocrystalline boron carbide(nB_(4)C)with varying grain sizes using molecular dynamics simulations with a machine-learning force *** results reveal quasi-plastic deformation mechanisms in nB_(4)C:GB sliding,intergranular amorphization and intragranular *** sliding arises from the presence of soft GBs,leading to intergranular *** amorphization arises from the interaction between grains with unfavorable orientations and the softened amorphous GBs,and finally causes structural ***,nB_(4)C models with varying grain sizes from 4.07 nm to 10.86 nm display an inverse Hall-Petch relationship due to the GB sliding mechanism.A higher strain rate in nB_(4)C often leads to a higher yield strength,following a 2/3 power *** deformation mechanisms are critical for the design of ceramics with superior mechanical properties.

关键词： nanocrystalline boron carbide compression grain boundary sliding amorphization inverse Hall–Petch behavior

Observing strain glass transition in Ti_(33)Nb_(15)Zr_(25)Hf_(25)O_(2)high entropy alloy with Elinvar effect

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Journal of Materials Science & Technology 2024年第1期168卷 16-23页

作者： Kaichao Zhang Kai Wang Bin Wang Chao Lv Jiaxing Zheng Guanqi Li Yu Fu Wenlong Xiao Qingqing Cai Xutao Nie Yingfeng Shao Huilong Hou Xinqing Zhao School of Materials Science and Engineering Beihang UniversityBeijing 100191China China Aerodynamics Research and Development Center Mianyang 621000China State Key laboratory of Nonlinear mechanics Chinese Academy of SciencesInstitute of MechanicsBeijing 100190China Tianmushan laboratory(Zhejiang Provincial laboratory for Aviation) Hangzhou 310000China

Exploring the phase transition of high entropy alloys(HEAs)with multiple major elements is of great importance for understanding the underlying physical *** martensitic phase tran-sition has been frequently reported in HEAs,however,nanoscale microstructural phase evolution has not been investigated to the same ***,we have prepared the Ti_(33)Nb_(15)Zr_(25)Hf_(25)O_(2)HEA and investi-gated the strain glass transition and its associated properties using dynamic mechanical analysis and mi-crostructure *** have found that the elastic modulus in Ti_(33)Nb_(15)Zr_(25)Hf_(25)O_(2)HEA deviates from Wachtman’s equation and observed the Elinvar effect in the form of temperature-independent mod-ulus in the temperature range from 150 K to 450 K and frequency-dependence modulus around 220 *** strain glass transition has been evidenced in Ti_(33)Nb_(15)Zr_(25)Hf_(25)O_(2)HEA by the formation and growth of nano-sized domains during in-situ transmission electron microscopy(TEM)cooling,and substantiated by the broken ergodicity during zero-field-cooling/*** strain glass transition is believed to account for the Elinvar effect,where the modulus hardening of nano-sized domains compensates dynam-ically with the modulus softening of the transformable matrix.

关键词： High entropy alloys Strain glass transition Elinvar effect Microstructural evolution Nanodomains

Analysis of nonlinear multi-field coupling responses of piezoelectric semiconductor rods via machine learning

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International Journal of Smart and Nano Materials 2024年第1期15卷 62-74页

作者： Chuwei Wu Zhengguang Xiao Yuting Guo Chunli Zhang Department of Engineering mechanics Zhejiang UniversityHangzhouZhejangChina Huanjiang laboratory ZhujiChina

Piezoelectric semiconductors(PSs)have widespread applications in semiconductor devices due to the coexistence of piezoelec-tricity and semiconducting *** is very important to conduct a theoretical analysis of PS ***,the present of nonlinearity in the partial differential equations(PDEs)that describe those multi-feld coupling mechanical behaviors of PSs poses a significant mathematical challenge when studying these PS *** this paper,we present a novel approach based on machine learning for solving multi-field coupling problems in PS structures.A physics-informed neural networks(PINNs)is constructed for predicting the multi-field coupling behaviors of PS rods with extensional *** utilizing the proposed PINNs,we evaluate the multi-field coupling responses of a ZnO rod under static and dynamic axial *** results demonstrate that the proposed PINNs exhibit high accuracy in solving both static and dynamic problems associated with Ps *** provides an effective approach to predicting the nonlinear multi-feld coupling phe-nomena in PS structures.

关键词： PS rod multi-feld coupling response machine learning PINNs

Optimizing profile line interval for enhanced accuracy in rock joint morphology and shear strength assessments

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International Journal of Mining Science and Technology 2024年第5期34卷 587-608页

作者： Leibo Song Quan Jiang Shigui Du Jiamin Song Gang Wang Yanting Gu Xingkai Wang Jinzhong Wu School of Civil Engineering Shaoxing UniversityShaoxing 312000China Key laboratory of Rock mechanics and Geohazards of Zhejiang Province Shaoxing UniversityShaoxing 312000China State Key laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan 430071China Institute of Rock mechanics Ningbo UniversityNingbo 315211China

2D profile lines play a critical role in cost-effectively evaluating rock joint properties and shear ***, the interval(ΔI_(L)) between these lines significantly impacts roughness and shear strength assessments. A detailed study of 45 joint samples using four statistical measures across 500 different ΔI_(L)values identified a clear line interval effect with two stages: stable and *** statistical analysis showed a linear relationship between the error bounds of four parameters,shear strength evaluation, and their corresponding maximum ΔI_(L)values, where the gradient k of this linear relationship was influenced by the basic friction angle and normal stress. Accounting for these factors,lower-limit linear models were employed to determine the optimal ΔI_(L)values that met error tolerances(1%–10%) for all metrics and shear strength. The study also explored the consistent size effect on joints regardless of ΔI_(L)changes, revealing three types of size effects based on morphological ***, larger joints required generally higher ΔI_(L)to maintain the predefined error limits, suggesting an increased interval for large joint analyses. Consequently, this research provides a basis for determining the optimal ΔI_(L), improving accuracy in 2D profile line assessments of joint characteristics.

关键词： Rock joint Roughness Shear strength Size effect Profile line interval effect

Friction of graphene on a substrate with a cavity defect

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Science China(Technological Sciences) 2024年第9期67卷 2834-2841页

作者： ZHOU Peng HUO ZhanLei CHANG TienChong Shanghai Institute of Applied Mathematics and mechanics Shanghai Key Laboratory of Mechanics in Energy EngineeringShanghai Frontier Science Center of MechanoinformaticsSchool of Mechanics and Engineering ScienceShanghai UniversityShanghai 200072China The Center for Computational mechanics and Engineering Applications Provincial Mechanics Experimental Teaching Demonstration CenterSchool of Civil EngineeringHebei University of EngineeringHandan 056038China Shanghai Institute of Aircraft mechanics and Control Tongji UniversityShanghai 200092China Joint-Research Center for Computational Materials Zhejiang LaboratoryHangzhou 311100China

The frictional behavior of supported graphene is known to be influenced by the physical properties and surface morphologies of the underlying substrate. However, it is unclear how a surface defect on the substrate affects the friction of supported graphene,and it is even unknown how to define the defect-induced friction force in this context. Here we conduct molecular dynamics(MD) simulations to investigate the friction between a square diamond slider and a graphene sheet supported by a copper substrate with a surface cavity defect. Our results demonstrate that the defect-induced friction exhibits a nonlinear increase with cavity size, while it decreases nonlinearly with slider size. We propose that the definition of defect-induced friction can be linked to the increase in friction work over the length of the slider, and is closely correlated to the defect-induced relative change in indentation depth and the ratio of the cavity area to the contact area. These findings provide a comprehensive evaluation of the impact of a substrate cavity defect on the friction of supported graphene and offer insights that may have broader implications for understanding defect-induced friction in other two-dimensional materials.

关键词： friction graphene underneath substrate cavity defect

Natural vibration and critical velocity of translating Timoshenko beam with non-homogeneous boundaries

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Applied Mathematics and mechanics(English Edition) 2024年第9期45卷 1523-1538页

作者： Yanan LI Jieyu DING Hu DING Liqun CHEN Shanghai Institute of Applied Mathematics and mechanics Shanghai Key Laboratory of Mechanics in Energy EngineeringShanghai Frontier Science Center of MechanoinformaticsSchool of Mechanics and Engineering ScienceShanghai UniversityShanghai 200072China School of Mathematics and Statistics Qingdao UniversityQingdao 266071Shandong ProvinceChina

In most practical engineering applications,the translating belt wraps around two fixed *** boundary conditions of the dynamic model are typically specified as simply supported or fixed *** this paper,non-homogeneous boundaries are introduced by the support *** the translating belt as the mechanical prototype,the vibration characteristics of translating Timoshenko beam models with nonhomogeneous boundaries are investigated for the first *** governing equations of Timoshenko beam are deduced by employing the generalized Hamilton's *** effects of parameters such as the radius of wheel and the length of belt on vibration characteristics including the equilibrium deformations,critical velocities,natural frequencies,and modes,are numerically calculated and *** numerical results indicate that the beam experiences deformation characterized by varying curvatures near the *** radii of the wheels play a pivotal role in determining the change in trend of the relative difference between two beam *** the results unearths that the relative difference in equilibrium deformations between the two beam models is more pronounced with smaller-sized *** the two wheels are of equal size,the critical velocities of both beam models reach their respective *** addition,the relative difference in natural frequencies between the two beam models exhibits nonlinear variation and can easily exceed 50%.Furthermore,as the axial velocities increase,the impact of non-homogeneous boundaries on modal shape of translating beam becomes more *** dealing with non-homogeneous boundaries is challenging,beam models with non-homogeneous boundaries are more sensitive to parameters,and the differences between the two types of beams undergo some interesting variations under the influence of non-homogeneous boundaries.

关键词： translating beam Timoshenko beam non-homogeneous boundary natural frequency critical velocity

Analysis of Piezoelectric Semiconductor Structures Considering Both Physical and Geometric Nonlinearities

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Acta Mechanica Solida Sinica 2024年第1期37卷 72-81页

作者： Zhengguang Xiao Shuangpeng Li Chunli Zhang Key laboratory of Soft Machines and Smart Devices of Zhejiang Province Department of Engineering MechanicsZhejiang UniversityHangzhou 310027China Huanjiang laboratory Zhuji 311816China

Piezoelectric semiconductors(PSs),such as ZnO and GaN,known as the third-generation semiconductors,have promising applications in electronic and optoelectronic devices due to the coexistence and interaction of piezoelectricity and semiconductor *** modeling of PS structures under external loads,such as thermal and mechanical loads,plays a crucial role in the design of PS *** this work,we propose a nonlinear fully coupling theoretical model and investigate the multi-field coupling behaviors of PS structures and PN junctions under thermal and mechanical loads,considering physical and geometric *** electromechanical and semiconducting behaviors of a PS rod-like structure with flexural deformations under different combinations of temperature changes and mechanical loads are *** tuning effect of temperature changes and mechanical loads on multi-field coupling behaviors of PSs is *** current–voltage characteristics of PS PN junctions are studied under different combinations of temperature changes and mechanical *** obtained results are helpful for the development of novel PS devices.

关键词： Piezoelectric semiconductor Nonlinearity Multi-field Coupling Tuning