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Structural Characteristics of Natural Loess in Northwest China and its Effect on Shear Behavior

GEOTECHNICAL AND GEOLOGICAL ENGINEERING 2021年第1期39卷 65-78页

作者： Wang, Yong Yang, Hui Jing, Xu Chinese Acad Sci Inst Rock & Soil Mech Wuhan 430071 Peoples R China Northwest Univ Dept Geol Xian 710069 Peoples R China Northwest Univ State Key Lab Continental Dynam Xian 710069 Peoples R China

This paper presents the results of relationship between structure and shear behavior of natural loess collected from Northwest China. The shear performance was conducted by triaxial tests. Scanning electron microscopy (SEM) in conjunction with MATLAB were used to interpret the microstructure characteristics of soil samples before and after triaxial tests, and mercury intrusion porosimetry (MIP) was performed on investigation of pore size distributions. Based on the MIP results, the pore distribution of natural loess at initial state can be divided into micropore (< 0.03 mu m), fine pore (0.03-5 mu m), medium pore (5-11 mu m) and macropore (> 11 mu m), respectively. The shear behavior during triaxial tests shows that, soil samples exhibit obvious homogenous deformation and yielding hysteresis with the increase of confining pressure, which is well agreement with the microstructure evolution characteristics investigated by means of SEM and MIP. It is found that strength loss of loess soils can be mainly attributed to changes in particle arrangement, breaking up and corresponding pore size variation. Quantitative and qualitative statistics analysis of soil particles and pore types shows that there is a negative relationship between confining pressure and parameters characterizing particle morphology, as well as between pore area and deviating stress. Although the structure of loess differs from region to region, the relationship between structural parameters and confining pressure or deviator stress can be used to estimate the influence of structure on shear behavior.

关键词： Structural characteristics Loess Shear behavior microstructure parameters

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microstructure based analysis and predictive modeling of cast Al7Si1.5Cu0.4Mg alloy mechanical properties

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MATERIALS TODAY COMMUNICATIONS 2022年 30卷

作者： Yan, Kang-jie Huang, Wei-qing Zuo, Zheng-xing Ren, Pei-rong Li, Dong-wei Zhao, Cheng-zhang Song, Jia-nan Zhang, Xiao-bo Beijng Inst Technol Sch Mech Engn Beijing 100081 Peoples R China Beihang Univ Sch Energy & Power Engn Beijing 100191 Peoples R China Air Force Engn Univ Aviat Engn Sch Xian 710038 Peoples R China

The heterogeneity of microstructure leads to non-uniform distribution of mechanical properties, which is also related to strength and reliability degradation of components. Taking diesel engine cylinder heads as an example, this study investigated the relationship between microstructures and tensile mechanical properties of cast Al7Si1.5Cu0.4Mg alloy with different temperatures, including secondary dendrite arm spacing (SDAS), grain size, eutectic silicon morphology. The results indicate that the mechanical properties of cast Al7Si1.5Cu0.4Mg alloy have a strong correlation with the microstructures. Based on the linear regression analysis method, several predictive models were established to quantify the tensile mechanical properties of cast Al7Si1.5Cu0.4Mg alloy with different microstructures. The Hall-Petch model was used to capture the relation between microstructure parameters and yield strength, and a linear relationship model was employed between the hardness and yield strength. The prediction model of ultimate tensile strength was proposed based on the relationship of microstructure and hardness. In addition, considering the error limit of the Hall-Petch relationship, the upper threshold of grain size and SDAS is calibrated. By considering the influence of the material's plastic deformation ability and the material strength on fatigue performance, a novel Tensile-Fatigue Bridge Model was proposed. The model provides a reference for the mechanical properties prediction work of thin-walled small parts and also contributes to the strength evaluation of components with non-uniform microstructures.

关键词： Cast Al7Si1.5Cu0.4Mg alloy microstructure parameters Mechanical properties Hall-Petch relationship Predictive model

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Combined experimental and DFT-TDDFT computational, structural and study effect of inter-diffusion Cu into CdTe thick film by annealing for optoelectronics

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JOURNAL OF MOLECULAR STRUCTURE 2021年 1238卷 130411-130411页

作者： Mahmoud, Safwat A. Al-Hossainy, Ahmed F. Shaaban, Essam R. Northern Border Univ Phys Dept Fac Sci Ar Ar 91431 Saudi Arabia Minia Univ Fac Sci Phys Dept El Minia 111559 Egypt New Valley Univ Fac Sci Chem Dept Al Wadi Al Gadid 72511 Al Kharga Egypt Northern Border Univ Chem Dept Fac Sci Ar Ar 1321 Saudi Arabia Al Azhar Univ Fac Sci Phys Dept PO 71452 Assiut Egypt

In the present study, thermal evaporation techniques were used to prepare Cadmium Telluride (CdTe) films with thickness 1 mu m on a glass substrate (at constant temperature150 degrees C). By immersing these films in a solution Cu(NO3)(2) (1g/1000ml) for 30 min, the prepared films were doped by ion exchange with Cu. Furthermore, the doped films were annealed in vacuum at different temperatures (25, 125, 250, 375, and 500 degrees C) for the diffusion of dopant Cu content, for 30 min. Using the method of Swanepoel, the film thickness as well as the refractive index of films was identified. The density functional theory (DFT-TDDFT) by DMol(3) was used for the optimization of CdTe and Cu:CdTe as an isolated molecule in the gaseous phase. From using the DMol(3)/(GGA-PW91) method with DFT-TDDFT simulation, the HOMO and LUMO values for CdTe and Cu:CdTe isolated molecule are 2.41 eV and 1.66 eV, respectively. The MEP computations and Quantum-chemical calculations properties are computed and combined with the experimental study by using DMol(3)/(GGA-PW91) software. The possible transition in these as deposited and treated films are found to allow direct transition with reduction of the band gap from 1.50 to 1.37 eV with an increase of the temperature of the annealing. Dielectric constant, Energy loss functions (VELF and SELF) for CdTe as deposited and treated were addressed in terms of temperature rise in the annealing. The energy gap is also determined using photoluminescence (PL) and its values the corresponding wavelength peaks correspond roughly to the energy obtained through optical studies. (C) 2021 Elsevier B.V. All rights reserved.

关键词： CdTe:Cu films microstructure parameters DFT-TDDFT Optical constants PL

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Stochastic stability of performance properties for materials with non-deterministic microstructure

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ZAMM-ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND MECHANIK 2021年第6期101卷

作者： Gitman, Inna M. Gitman, Mikhail B. Batin, Sergei E. Boyarshinov, Dmitriy A. Univ Sheffield Dept Mech Engn Sheffield S Yorkshire England Perm Natl Res Polytech Univ Perm Russia

In this contribution an original concept of stochastic stability (P-stability), formulated here to represent realistic stochastic nature of materials, is employed for stability analysis of material performance characteristics. Stochasticity in materials can be related, for example, to manufacturing processes, potential treatment of material, or properties of raw materials. On the other hand, performance characteristics, obtained through the novel fuzzy sets based multi-scale methodology, are also of stochastic nature. The particular strength of this newly developed P-stability, is its ability to analyse not only individual characteristics, but also multiple characteristics simultaneously. This methodology also allows to estimate and quantify an actual accuracy of obtained characteristics.

关键词： fuzzy sets microstructure parameters stochastic stability strength properties

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Influence of cyclic wetting-drying on the mechanical strength characteristics of coal samples: A laboratory-scale study

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ENERGY SCIENCE & ENGINEERING 2019年第6期7卷 3020-3037页

作者： Chen, Shaojie Jiang, Tianqi Wang, Huaiyuan Feng, Fan Yin, Dawei Li, Xiushan Shandong Univ Sci & Technol State Key Lab Min Disaster Prevent & Control Shandong Provence & Minist Sci & Technol Qingdao Shandong Peoples R China Shandong Energy Xinwen Grp Xin Julong Co Ltd Heze Peoples R China Zibo Min Grp Co Ltd Daizhuang Coal Mine Jining Peoples R China

Water-coal interactions have gained much recent attention, although few studies focus on the strength of coal under wetting-drying cycles. This study investigates changes in the microstructure and mechanical strength of coal that are induced by water-coal interactions, at the macroscale and microscale. Fourteen specimens after continuous wetting and fourteen specimens after wetting-drying cycles were tested, indicating that peak stress and elastic modulus decrease with increasing continuous wetting time and number of wetting-drying cycles, while peak strain increases. We analyzed changes in the coal microstructure using a scanning electron microscope (SEM) and the Image Pro Plus 6.0 (IPP 6.0) software. The regression model for cyclic wetting-drying reveals that porosity and pore circularity are the main correlation indicators associated with uniaxial compressive strength. Therefore, different numbers of wetting-drying cycles could induce different degrees of damage to coal, which increases progressively through gradual changes to its microstructure. These findings indicate that wetting-drying cycles have a more significant impact on the stability of coal mass than continuous wetting. Our results are of use in determining the size of coal pillars, and expanding the knowledge base related to the mechanical properties of coal mass, water bursting, water recharge channels, and the stress-crack-permeability evolution law in mines.

关键词： coal cyclic wetting-drying mechanical strength characteristics microstructure parameters Pearson coefficient

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Topology and mechanics of metal rubber via X-ray tomography

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MATERIALS & DESIGN 2019年 181卷

作者： Ma, Yanhong Zhang, Qicheng Wang, Yongfeng Hong, Jie Scarpa, Fabrizio Beihang Univ BUAA Sch Energy & Power Engn Beijing 100191 Peoples R China Univ Bristol Bristol Composites Inst ACCIS Bristol BS8 1TR Avon England

This paper describes the structural characteristics of metal rubber (MR) evaluated by X-ray tomography and skeletonisation at microscopic scale. The parameters used to describe the internal structure of the MR were numerically extracted and compared to assess the effect of different MR manufacturing parameters on the mechanical properties of the material. Quasi-static tests were also performed to obtain the stiffness and damping of the metal porous material and to understand their correlation with the topology defining the samples. A simplified helix cell model was used to interpret the mechanical properties of the MR based on the structural parameters identified in this paper. The transverse isotropic stiffness of the MR observed here is partly caused by the distribution of the metal wires, with more helices oriented along the molding direction resulting in smaller equivalent stiffness. The compression, relative density, helix and wire diameters can influence the structural and mechanical characteristics of the MR in a significant manner. (C) 2019 The Authors. Published by Elsevier Ltd.

关键词： Metal rubber Entangled wire mesh CT scan Topology microstructure parameters Mechanical property

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Multi-scale approach for strength properties estimation in functional materials

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ZAMM-ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND MECHANIK 2018年第6期98卷 945-953页

作者： Gitman, I. M. Klyuev, A. V. Gitman, M. B. Stolbov, V. Yu Univ Sheffield Dept Mech Engn Sheffield S Yorkshire England Perm Natl Res Polytech Univ Perm Russia

A new methodology to obtain metallic functional materials with predefined sets of strength properties has been developed. It has been shown that in order to accurately estimate set of material properties at the macro-level, information from the micro-level needs to be taken into account. As a result a two-level estimation model, based on the theory of fuzzy sets, has been proposed. To demonstrate the developed methodology, a reinforcing steel has been analysed. Using microstructural information, derived from an available set of experimentally obtained digital images of material microsections under different heat treatment conditions, macroscopic strength properties of reinforcing steel have been determined.

关键词： functional materials fuzzy sets microstructure parameters strength properties

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Methodology to estimate the minimum number of experiments and key microstructural parameters in macroscopic strength properties evaluation

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ZAMM-ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND MECHANIK 2019年第3期99卷

作者： Gitman, I. M. Gitman, M. B. Stolbov, V. Yu Batin, S. E. Boyarshinov, D. A. Univ Sheffield Dept Mech Engn Sheffield S Yorkshire England Perm Natl Res Polytech Univ Perm Russia

A novel methodology, based on the theory of fuzzy sets, to obtain materials with pre-defined sets of strength properties has been analysed from the position of identifying the necessary and sufficient number of experiments needed to predict these macro characteristics and establishing which micro parameters significantly influence the macroscale results. The procedure to estimate, with a user-defined degree of accuracy, the minimum number of experiments and significant micro parameters has been tested and verified using experimental data, obtained from digital images of material microsections under different heat treatment conditions while analysing strength properties of reinforcing steel. The results confirm the possibility of using the developed methodologies for the performance properties evaluation of materials based on the minimum number of experiments and identification of the key grain-phase parameters.

关键词： fuzzy sets microstructure parameters strength properties

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microstructure characterization and nano & micro hardness of tri-modal microstructure of titanium alloy under different hot working conditions

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MATERIALS CHARACTERIZATION 2017年 134卷 236-245页

作者： Lei, Zhenni Gao, Pengfei Li, Hongwei Fan, Xiaoguang Cai, Yang Zhan, Mei Northwestern Polytech Univ Sch Mat Sci & Engn State Key Lab Solidificat Proc POB 542 Xian 710072 Shaanxi Peoples R China

In this work, the dependences of tri-modal microstructure parameters and corresponding nano & micro hardness on through-process processing parameters were quantitatively studied during the three-step thermo-mechanical processing of TA15 titanium alloy. It is found that the processing parameters of first step, especially for the deformation temperature and strain rate, mainly affect primary equiaxed alpha (alpha(p)) through the alpha -> beta phase transformation and the competition between dynamic recovery and dynamic recrystallization. The second processing step primarily affects the content and thickness of lamellar alpha (alpha(l)). In the third processing step, compared with low-temperature aging, normal annealing provides sufficient driving force for at and secondary lamellar alpha (alpha(s)) growing, which leads to thicker alpha(l) and alpha(s). As for the nano µ hardness, in one sample undergoing different process, transformed beta matrix (beta(t)) is always harder than alpha(l) and alpha(s) due to the interfacial strengthening effect. In addition, with increasing strain rate of the first step, alpha(p) becomes harder due to the constantly enhanced work hardening effect while the hardness of beta(t), varies little because of the competition between interfacial strengthening and distribution disorder degree. However, the nano hardness of alpha(l) decreases firstly and then increases with strain rate, which presents the same trend with the micro hardness of integrated hardness at different processing conditions.

关键词： Titanium alloy Hot working conditions Tri-modal microstructure microstructure parameters Nano & micro hardness

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Support vector machine model for the relationship between physico-mechanical indexes and microstructure parameters of soft soil

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International Symposium on Geomechanics and Geotechnics - From Micro to Macro

作者： Liu, Yongjian Li, Zhangming Guangdong Univ Technol Inst Geotech Engn Guangzhou Guangdong Peoples R China

ISBN: (纸本)9780415612951

Owing to peculiar geographical and geological conditions, the Pearl River Delta area is mainly made of quaternary soft clays. The mechanical behavior is largely controlled by the internal microstructure of soil. By means of measuring techniques such as Scanning Electron Microscope(SEM) and image processing technique, the paper sheds light on the microstructure characteristics of soft soil of Nansha area. microstructure parameters such as porosity, total area of pores, number of pores, average area of pores, average diameter of pores and pore anisotropy have been obtained. Due to the nonlinear relationship between physico-mechanical indexes and microstructure parameters, Support Vector Machine (SVM), a new algorithm in the field of artificial intelligence, is introduced in this paper. SVM is based on Statistical Learning Theory and owns high generalization capability and can solve the problem of small samples, nonlinear, high dimensions and local minimization. The relationship between microstructure parameters and coefficient of compression, constrained modulus etc. are analyzed, the internal relationship between physico-mechanical indexes and microstructure parameters are established in the paper. Comparison was made between SVM method and Back Propagation neural networks (BP). The results indicate that SVM method can obtain high accuracy and generalization ability, and it can provide an important basis for geotechnical parameters analysis and choice of soft soil engineering.

关键词： Support Vector Machine (SVM) soft soil physico-mechanical index microstructure parameters Back Propagation neural networks (BP)

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