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1.
Applied Mathematics and Mechanics - Mechanical models of residually stressed fibre-reinforced solids, which do not resist bending, have been developed in the literature. However, in some residually... 相似文献
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裂纹前端的断裂过程区是引起岩石非线性断裂及尺寸效应的主要原因。利用数字图像相关技术对砂岩开展了三点弯曲梁实验,获得观测区域高精度的全场位移和应变数据,根据断裂韧带区域水平位移和水平应变的分布特征,结合裂尖岩石颗粒变化的微观分析,提出采用裂纹尖端水平位移波动性和水平应变突变性所得到的波动系数和水平应变突变值,确定断裂过程区形状和临界尺寸的方法。结果表明:砂岩断裂过程区的形状为不规则的狭长带状区域,断裂过程区的临界长度为11~13mm,临界宽度为1.58~2.36mm。断裂过程区区域内形变在趋向裂尖时呈指数增加,但其单位区域内的形变增量呈波动状态。该方法能够更加准确判断岩石断裂过程区的范围,有助于分析岩石的非线性断裂特性。 相似文献
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《Physics letters. A》2020,384(27):126674
A nonlinear molecular structural mechanics (MSM) model is proposed in this paper for studying the tensile properties of microtubules (MTs). In the nonlinear MSM models, the interactions between tubulin monomers in MTs are treated as nonlinear axial and torsional springs, whose stiffness coefficients are extracted from all-atom molecular dynamics simulations. The Young's modulus and fracture properties of MTs under tension extracted from the present nonlinear MSM models are found to agree well with the existing simulation and experiment results, which shows the efficiency and accuracy of the proposed nonlinear MSM models. In addition, the nonlinear MSM models are also extended to investigate the tensile properties including Young's modulus and fracture strain of MTs possessing lattice defects. The results obtained from nonlinear MSM models are utilized to develop a predictive equation for quickly predicting the tensile properties of MTs with different lattice defect levels. 相似文献
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ABSTRACT The present work describes a phenomenological approach to explain the instantaneous behaviour of tungsten heavy alloys (WHAs) in heat-treated and swaged conditions. The strengths and elongation values of heat-treated materials are lower and higher than those of the swaged samples respectively. The heat-treated materials exhibit two slopes in true stress–true plastic strain curves and follow the Ludwigson constitutive equation. On the other hand, swaged materials display a single slope and adhere to typical Swift constitutive equation. The latter reflect the presence of pre-strain in the materials due to swaging deformation. The fracture surfaces in heat-treated materials consist of W-W decohesion along with matrix rupture and W-cleavage, while swaged samples consist of mainly W-cleavage. Both the materials display three typical stages (I, II and III) of work hardening. The second derivatives of true stress–true plastic strain curves of these alloys exhibit a perfect parabola although the nature of true stress–true strain as well as true stress–true plastic strain curves is quite different in heat-treated and swaged materials. This has been observed for the first time in WHAs consisting of matrix and W-grains. The shape of the parabola is simple and easy to fit. The fitting parameters of parabolas have been successfully employed to explain the flow behaviour of a large number of tungsten heavy alloys having two-phase microstructure in different processing conditions. 相似文献
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Molecular dynamics simulations at constant temperature are performed to investigate melting-like transition in Na13K42, Na19K36 and Na26K29 nanoalloys using a second-moment-approximation tight-binding analytic potential to calculate the forces on the constituent atoms. A weighted histogram analysis method is employed to remove non-ergodicity issues due to the complex potential energy surface of these nanoalloys. The heat capacity shows three distinctive steps in melting for Na13K42, while Na26K29 and Na19K36 have two-step and one-step melting transition, respectively. The steepest descent method is used to quench the configurations in a given interval during the simulation and also study the isomerisation processes occurring at different temperatures. Analysing the configuration energies of quenched structures for the entire nanoalloy and the core atoms separately gives more details about the melting mechanism. The Lindemann parameter is also calculated at several temperatures during the simulation which shows a gradual increase for Na13K42 and Na26K29 while a sharp change is observed for Na19K36. These findings are in agreement with the multi-step nature of the phase transition in Na13K42 and Na26K29 and one-step melting of the Na19K36 magic composition. 相似文献
8.
Qiu‐Ying Huang Ming‐Yang Su Xiang‐Ru Meng 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(6):474-478
The combination of N‐heterocyclic and multicarboxylate ligands is a good choice for the construction of metal–organic frameworks. In the title coordination polymer, poly[bis{μ2‐1‐[(1H‐benzimidazol‐2‐yl)methyl]‐1H‐tetrazole‐κ2N3:N4}(μ4‐butanedioato‐κ4O1:O1′:O4:O4′)(μ2‐butanedioato‐κ2O1:O4)dicadmium], [Cd(C4H4O4)(C9H8N6)]n, each CdII ion exhibits an irregular octahedral CdO4N2 coordination geometry and is coordinated by four O atoms from three carboxylate groups of three succinate (butanedioate) ligands and two N atoms from two 1‐[(1H‐benzimidazol‐2‐yl)methyl]‐1H‐tetrazole (bimt) ligands. CdII ions are connected by two kinds of crystallographically independent succinate ligands to generate a two‐dimensional layered structure with bimt ligands located on each side of the layer. Adjacent layers are further connected by hydrogen bonding, leading to a three‐dimensional supramolecular architecture in the solid state. Thermogravimetric analysis of the title polymer shows that it is stable up to 529 K and then loses weight from 529 to 918 K, corresponding to the decomposition of the bimt ligands and succinate groups. The polymer exhibits a strong fluorescence emission in the solid state at room temperature. 相似文献
9.
In this paper, we study the stationary problem for the Lotka–Volterra competition system with cross-diffusion in a spatially heterogeneous environment. Although some sufficient conditions for the existence of positive solutions are obtained by using global bifurcation theory, the information for their structure is far from complete. In order to get better understanding of the competition system with cross-diffusion, we focus on the asymptotic behaviour of positive solutions and derive two shadow systems as the cross-diffusion coefficient tends to infinity, moreover, the structure of positive solutions of the limiting system is analysed. The result of asymptotic behaviour also reveals different phenomena from that studied in Wang and Li (2013). 相似文献
10.
N-acetyl-3,3-dinitroazetidine (ADNAZ) is an important precursor for synthesizing new multinitroazetidine energetic compounds. Its thermal behaviour was studied under a non-isothermal condition by DSC and TG/DTG methods, the results show that there are one melting process and one endothermic decomposition process. The specific molar heat capacity (Cp,m) of ADNAZ was determined by a continuous Cp mode of micro-calorimeter and theoretical calculation, and the Cp,m of ADNAZ was 240.37 J · K−1 · mol−1 at T = 298.15 K. The detonation velocity (D) and detonation pressure (P) of ADNAZ were estimated using the nitrogen equivalent equation according to the experimental density, the value of D and P are (6685.83 ± 3.12) m · s−1 and (18.36 ± 0.02) GPa, respectively. The free radical signals of ADNAZ were detected by electron spin resonance (ESR) technique, which is used to estimate its sensitivity. 相似文献