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stress relaxation properties of calcium silicate hydrate:a molecular dynamics study

Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2024年第2期25卷 97-115页

作者： Zhicheng GENG Shengwen TANG Yang WANG Hubao A Zhen HE Kai WU Lei WANG State Key Laboratory of Water Resources Engineering and Management Wuhan UniversityWuhan430072China Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education School of Materials Science and EngineeringTongji UniversityShanghai200092China College of Materials Science and Engineering Xi’an University of Architecture and TechnologyXi’an710055China

The time-dependent viscoelastic response of cement-based materials to applied deformation is far from fully understood at the atomic *** silicate hydrate(C-S-H),the main hydration product of Portland cement,is responsible for the viscoelastic mechanism of cement-based *** this study,a molecular model of C-S-H was developed to explain the stress relaxation characteristics of C-S-H at different initial deformation states,Ca/Si ratios,temperatures,and water contents,which cannot be accessed *** stress relaxation of C-S-H occurs regardless of whether it is subjected to initial shear,tensile,or compressive deformation,and shows a heterogeneous *** plays a crucial role in the stress relaxation process.A large Ca/Si ratio and high temperature reduce the cohesion between the calcium-silicate layer and the interlayer region,and the viscosity of the interlayer region,thereby accelerating the stress relaxation of *** effect of the hydrogen bond network and the morphology of C-S-H on the evolution of the stress relaxation characteristics of C-S-H at different water contents was elucidated by nonaffine mean squared *** results shed light on the stress relaxation characteristics of C-S-H from a microscopic perspective,bridging the gap between the microscopic phenomena and the underlying atomic-level mechanisms.

关键词： Calcium silicate hydrate(C-S-H) stress relaxation Ca/Si ratio Temperature Water content Atomic simulation

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stress relaxation Behavior of a Nb-Stabilized Austenitic Stainless Steel at 550℃

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Acta Metallurgica Sinica(English Letters) 2023年第12期36卷 2079-2088页

作者： Shuzhan Zhang Xianbo Shi Yuanfei Su Wei Yan Lijian Rong Ke Yang CAS Key Laboratory of Nuclear Materials and Safety Assessment Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China School of Materials Science and Engineering University of Science and Technology of ChinaShenyang 110016China Shi-Changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China

stress relaxation resistance is one of the most significant properties that are critical to the service life of the *** this study,the stress relaxation behavior of a Nb-stabilized austenitic stainless steel was *** was revealed that the homogenization treatment at 1250℃could make more primary NbC particles dissolved back into the matrix and consequently get a great number of nano-sized secondary NbC ***,the stress relaxation resistance will be enhanced due to the effective pinning of such higher density of nano-sized secondary NbC carbides on the dislocation movement.

关键词： Nb-stabilized austenitic stainless steel Homogenization treatment stress relaxation NbC

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New Kinetics Equation for stress relaxation of Semi-crystalline Polymers below Glass Transition Temperature

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Chinese Journal of Polymer Science 2022年第12期40卷 1662-1669,I0010页

作者： Cheng Zhang Li-Hai Cai Bao-Hua Guo Bing Miao Jun Xu Advanced Materials Laboratory of Ministry of Education Department of Chemical EngineeringTsinghua UniversityBeijing 100084China Tsinghua Innovation Center in Dongguan Dongguan 523808China Center of Materials Science and Optoelectronics Engineering College of Materials Science and Opto-Electronic TechnologyUniversity of Chinese Academy of SciencesBeijing 100049China

The stress relaxation of semi-crystalline nylon 1010 cannot be fitted by the Kohlrausch-Williams-Watts formula when the experiments were performed at pre-yielding regime below the glass transition *** study this problem and identify the two-step mechanism of stress *** short time scale,relaxation is fast,dominated by stress biased thermal fluctuation with a fixed short-range length scale(activation volume).At long time scale,relaxation is slow due to the emergence of a cooperative long-range length scale determined by the stress *** cooperative length scale is proportional to the reciprocal of stress and the amplitude of stress fluctuation is the product of stress and activation *** on this two-step mechanism,we propose a new kinetics equation to capture the stress relaxation effectively,where the short time relaxation is described by an Eyring-like local activation and the long-time relaxation is captured by a cooperative excitation process resorting to an extension from the random first order transition *** equation fits the experimental data well and can serve as a model to guide the related experiments of relaxation processes in crystalline solids.

关键词： stress relaxation Semi-crystalline polymers Kohlrausch-Williams-Watts(KWW)equation Random first order transition(RFOT)theory

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Thickness dependence of viscoelastic stress relaxation of laminated microbeams due to mismatch strain

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Applied Mathematics and Mechanics(English Edition) 2022年第4期43卷 467-478页

作者： Xiaosheng CAI Nenghui ZHANG Hanlin LIU Shanghai Institute of Applied Mathematics and Mechanics Shanghai Key Laboratory of Mechanics in Energy EngineeringSchool of Mechanics and Engineering ScienceShanghai UniversityShanghai 200072China

Time-dependent behaviors due to various mismatch strains are very important to the reliability of micro-/*** paper aims at presenting an analytical model to study the viscoelastic stress relaxation of the laminated microbeam caused by mismatch ***,Zhang’s two-variable method is used to establish a mechanical model for predicting the quasi-static stress relaxation of the laminated ***,the related analytical solutions are obtained by combining the differential method and the eigenvalue method in the temporal ***,the influence of the substrateto-film thickness/modulus ratio on the relaxation responses of the laminated microbeam subject to a step load of the mismatch strain is *** results show that the present predictions are consistent with the previous theoretical ***,the thickness dependence of stress relaxation time of the laminated microbeam is jointly determined by the intrinsic structural evolution factors and tension-bending coupling state;the stress relaxation time can be controlled by adjusting the substrate-to-film thickness/modulus ratio.

关键词： laminated structure stress relaxation mismatch strain tension-bending coupling effect analytical method

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Creep deformation and strength evolution mechanisms of a Ti-6Al-4V alloy during stress relaxation at elevated temperatures from elastic to plastic loading

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Journal of Materials Science & Technology 2022年第31期126卷 93-105页

作者： Ying Zhang Dongsheng Li Xiaoqiang Li Xiaochun Liu Shiteng Zhao Yong Li School of Mechanical Engineering and Automation Beihang UniversityBeijing 100191China Institute of Metals College of Materials Science and EngineeringChangsha University of Science&TechnologyChangsha 410004China School of Materials Science and Engineering Beihang UniversityBeijing 100191China

In this study, the stress relaxation(SR) behaviors of a Ti-6Al-4V alloy pre-loaded from elastic to plastic regions and corresponding strength evolution mechanisms at different temperatures were systematically studied. In order to quantitatively analyze the detailed deformation and strength evolution mechanisms during the whole SR tests, which is composed of the loading stage and subsequent SR stage, the evolutions of α/β structures and dislocations have been identified by a series of microstructural observations,i.e., scanning electron microscopy(SEM), electron backscatter diffraction(EBSD), high resolution transmission electron microscopy(HRTEM), energy dispersive spectroscopy(EDS). A great quantity of entangled dislocations in α phase introduced by the plastic loading at temperatures below 800 °C promotes the emergence of SR behavior with a higher creep rate, leading to the much higher SR level with larger pre-load levels. Diffusion is significantly enhanced by dislocations accumulated at interfaces with higher temperatures(> 800 ℃), contributing to a similar SR phenomenon under different initial strain *** strength loss has been observed after SR with high temperatures or pre-loaded to the plastic region, e.g., 94 MPa loss for 800 °C, pre-loaded with a stain of 10% and SR for 2400 s. The strength loss mainly comes from the loading stage where distorted and fragmented β layers occur. The subsequent SR stage facilitates interfacial diffusion and results in a higher fraction of granular β phases, leading to a further decrease in yield strength(YS). This study enhances the understanding on the deformation and strength evolution mechanisms of titanium alloys with lamellar structures in the whole SR process, providing a physical foundation for optimizing the processing parameters for manufacturing titanium alloy components with high accuracy and performance.

关键词： stress relaxation Initial strain Ti-6Al-4V Yield strength Dislocation density

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Analysis of the anelastic deformation of high-entropy Pd_(20)Pt_(20)Cu_(20)Ni_(20)P_(20) metallic glass under stress relaxation and recovery

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Journal of Materials Science & Technology 2022年第12期107卷 82-91页

作者： Y.J.Duan L.T.Zhang T.Wada H.Kato E.Pineda D.Crespo J.M.Pelletier J.C.Qiao School of Mechanics Civil Engineering and ArchitectureNorthwestern Polytechnical UniversityXi’an 710072China Department of Physics Institute of Energy TechnologiesUniversitat Politècnica de CatalunyaBarcelona 08019Spain Institute for Materials Research Tohoku UniversitySendai 980-8577Japan Universitéde Lyon MATEISUMR CNRS5510Bat.B.PascalINSA-LyonF-69621 Villeurbanne CedexFrance

The anelastic deformation behavior of Pd_(20)Pt_(20)Cu_(20)Ni_(20)P_(20) high-entropy metallic glass was probed by monitoring the stress relaxation and recovery processes. The stress relaxation under consecutive strain steps can be described by the Kohlrausch-Williams-Watts(KWW) function. In addition, considering a hierarchy of relaxation processes related to the structural heterogeneity, a constitutive model is proposed in order to describe the whole process of stress relaxation and determine the contribution of different time scales. Moreover, a crossover from stochastic activation to percolation of flow defects with the ultimate strain can be observed during stress relaxation process. The anelastic recovery process after a strain step is studied as a function of the initial strain level and characterized by means of a direct spectrum analysis. The peaks in the recovery time-spectra revealed the evolution of flow defects in Pd_(20)Pt_(20)Cu_(20)Ni_(20)P_(20) high-entropy metallic glass. The understanding of the atomic free-volume zones effect and the anelastic deformation provides important insight into how atomic structural features affect the deformation behavior of high-entropy metallic glasses, and may provide a new avenue into the improvement of their mechanical properties.

关键词： High-entropy metallic glass stress relaxation Anelastic deformation Flow defects Free-volume zones

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stress relaxation of Grouted Entirely Large Diameter B-GFRP Soil Nail

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China Ocean Engineering 2013年第4期27卷 495-508页

作者：李国维倪春裴华富葛万明吴宏伟 Key Laboratory of Ministry of Education for Geotechnique and Embankment Engineering Hohai University Highway and Railway Engineering Institute Hohai University Department of Civil and Environmental Engineering The Hong Kong Polytechnic University Department of Civil and Environmental Engineering The Hong Kong University of Science and Technology

One of the potential solutions to steel-corrosion-related problems is the usage of fiber reinforced polymer （FRP） as a replacement of steel bars. In the past few decades, researchers have conducted a large number of experimental and theoretical studies on the behavior of small size glass fiber reinforce polymer （GFRP） bars （diameter smaller than 20 ram）. However, the behavior of large size GFRP bar is still not well understood. Particularly, few studies were conducted on the stress relaxation of grouted entirely large diameter GFRP soil nail. This paper investigates the effect of stress levels on the relaxation behavior of GFRP soil nail under sustained deformation ranging from 30% to 60% of its ultimate strain. In order to study the behavior of stress relaxation, two B-GFRP soil nail element specimens were developed and instrumented with fiber Bragg grating （FBG） strain sensors which were used to measure strains along the B-GFRP bars. The test results reveal that the behavior of stress relaxation of B-GFRP soil nail element subjected to pre-stress is significantly related to the elapsed time and the initial stress of relaxation procedure. The newly proposed model for evaluating stress relaxation ratio can substantially reflect the influences of the nature of B-GFRP bar and the property of grip body. The strain on the nail body can be redistributed automatically. Modulus reduction is not the single reason for the stress degradation.

关键词： stress relaxation B-GFRP bar soil nail element seamless pipe fiber Bragg grating

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stress relaxation Behaviors of Monocrystalline Silicon Coated with Amorphous SiO_(2) Film:A Molecular Dynamics Study

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Acta Mechanica Solida Sinica 2021年第4期34卷 506-515页

作者： Juan Chen Liang Fang Meng Zhang Weixiang Peng Kun Sun Jing Han State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an710049China School of Materials Science and Engineering Taiyuan University of Science and TechnologyTaiyuan030024China School of Mechanical and Electrical Engineering Xiamen University Tan Kah Kee CollegeZhangzhou363105China School of Mechanical and Electrical Engineering China University of Mining and TechnologyXuzhou221116China

Long-lasting constant loading commonly exists in silicon-based microelectronic contact,as well as the chemical mechanical polishing *** this work,the stress relaxation analysis of single crystal silicon coated with an amorphous SiO_(2) film is performed by varying the maximum indentation depth using molecular dynamics *** is found that during holding,the applied indentation force declines sharply at the beginning and then steadily towards the end of the holding *** stress relaxation amount of bilayer composites increases as the maximum indentation depth *** is also found that the deformation features of SiO_(2) film and silicon substrate during holding are inherited from the loading *** SiO_(2) film during holding is further densified when the maximum indentation depth is equal to or less than a certain value(5.5 nm for the 0.8-nm film).The amount of generated phases and phase distributions of silicon substrate during holding are affected by the plastic deformation of silicon during loading.

关键词： Nanoindentation stress relaxation Single crystal silicon Amorphous SiO_(2)film Molecular dynamics simulation

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stress relaxation of Si/Si_(1-x)Ge_x/Si structure prepared by ion implantation and subsequent annealing process

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Rare Metals 2011年第3期30卷 270-273页

作者： XU Wenting TU Hailing CHANG Qing XIAO Qinghua General Research Institute for Nonferrous Metals Beijing 100088 China GRINM Semiconductor Materials Co. Ltd. Beijing 100088 China

The stress relaxation of 74Ge＋-implanted （100） silicon wafers was investigated. The implantation energy as a function of Si/Si1-xGex/Si struc-ture fluence and two kinds of thermal annealing were reported. The stress and stress relaxation after thermal annealing were calculated on the basis of Raman analysis, and were compared with those obtained from the calculation of virgin Si.

关键词： silicon wafers stress stress relaxation ion implantation annealing

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stress relaxation and Sensitivity Weight for Bi-Directional Evolutionary Structural Optimization to Improve the Computational Efficiency and Stabilization on stress-Based Topology Optimization

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Computer Modeling in Engineering & Sciences 2021年第2期126卷 715-738页

作者： Chao Ma Yunkai Gao Yuexing Duan Zhe Liu School of Automotive Studies Tongji UniversityShanghai201804China

stress-based topology optimization is one of the most concerns of structural optimization and receives much attention in a wide range of engineering *** solve the inherent issues of stress-based topology optimization,many schemes are added to the conventional bi-directional evolutionary structural optimization(BESO)method in the previous ***,these schemes degrade the generality of BESO and increase the computational *** study proposes an improved topology optimization method for the continuum structures considering stress minimization in the framework of the conventional BESO method.A global stress measure constructed by p-norm function is treated as the objective *** stabilize the optimization process,both qp-relaxation and sensitivity weight scheme are *** variables are updated by the conventional BESO *** 2D and 3D examples are used to demonstrate the validity of the proposed *** results show that the optimization process can be stabilized by *** value of q and p are crucial to reasonable *** proposed sensitivity weight scheme further stabilizes the optimization process and evenly distributes the stress *** computational efficiency of the proposed method is higher than the previous methods because it keeps the generality of BESO and does not need additional schemes.

关键词： stress-based topology optimization aggregation function stress relaxation sensitivity weight bi-directional evolutionary structural optimization

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