HU Zhizhong WU Yusheng CAI Heping MA Lihua Xi′an jiaotong University
,
Xi′an
,
China Senior Engineer
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Res.Inst.for Strength of Metals
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Xi′an jiaotong University
,
Xi′an 710049
,
China
金属学报(英文版)
Studies have been made of the torsional fatigue fracture life of notched specimens,the macroscopic fractography and microscopic fracture mechanism of steel 40Cr after various tempering treatments under different stresses,With the increase of stress,the fracture model changes from normal stress fracture to longitudinal shear one,and then transversal shear one. Under same stress,with the increase of strength,the fracture mode transfers from shear to normal stress fracture.The mechanism of normal stress fracture may be:transgranular frac- ture→striation+intergranular fracture→dimple+intergranular fracture,and of shear fracture may be:transgranular fracture→shear trace→dimple.Based on the experimental results,a fracture mechanism map of torsional fatigue has been drawn up.
关键词:
mechanism map
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null
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null
Science in China Series E-Technological Sciences
An analysis model has been established according to the structure feature of high porosity metals, and the mathematical relationship between the tensile strength and porosity for this material has been derived from the model. Moreover, the corresponding theoretical formula has been proved good to reflect the variation law of tensile strength with porosity for high porosity metals by the example experiment on nickel foam.
关键词:
high porosity metal;tensile strength;porosity;foams
Philosophical Magazine a-Physics of Condensed Matter Structure Defects and Mechanical Properties
A first-principles method based on the local-density approximation using discrete variational clusters has been used to study the electronic structure of the hcp metals, Be, Mg, Sc, Y, Ti, Zr, Co, Zn and Cd. The binding energy of these metals was calculated in relation to the volume of a unit cell. The variation in the binding energy with the unit cell volume was obtained by means of a polynomial fit. The theoretical tensile strength and bulk modulus of these metals were estimated from the electronic structure and binding energy calculations. The predicted bulk moduli for these metals are in good agreement with experimental findings and other available theoretical data. A linear relationship between the calculated and the experimental strengths is observed.
关键词:
potentials;density
Nature
In conventional metals, there is plenty of space for dislocations-line defects whose motion results in permanent material deformation-to multiply, so that the metal strengths are controlled by dislocation interactions with grain boundaries(1,2) and other obstacles(3,4). For nano-structured materials, in contrast, dislocation multiplication is severely confined by the nanometre-scale geometries so that continued plasticity can be expected to be source-controlled. Nano-grained polycrystalline materials were found to be strong but brittle(5-9), because both nucleation and motion of dislocations are effectively suppressed by the nanoscale crystallites. Here we report a dislocation-nucleation-controlled mechanism in nano-twinned metals(10,11) in which there are plenty of dislocation nucleation sites but dislocation motion is not confined. We show that dislocation nucleation governs the strength of such materials, resulting in their softening below a critical twin thickness. Large-scale molecular dynamics simulations and a kinetic theory of dislocation nucleation in nano-twinned metals show that there exists a transition in deformation mechanism, occurring at a critical twin-boundary spacing for which strength is maximized. At this point, the classical Hall-Petch type of strengthening due to dislocation pile-up and cutting through twin planes switches to a dislocation-nucleation-controlled softening mechanism with twin-boundary migration resulting from nucleation and motion of partial dislocations parallel to the twin planes. Most previous studies(12,13) did not consider a sufficient range of twin thickness and therefore missed this strength-softening regime. The simulations indicate that the critical twin-boundary spacing for the onset of softening in nano-twinned copper and the maximum strength depend on the grain size: the smaller the grain size, the smaller the critical twin-boundary spacing, and the higher the maximum strength of the material.
关键词:
molecular-dynamics simulation;nanocrystalline materials;mechanical-properties;nanotwinned copper;deformation;plasticity;nanoscale;ductility;crystals;nickel
Cui-Hong Li
,
Qi-Qiang Duan
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Zhe-Feng Zhang
金属学报(英文版)
doi:10.1007/s40195-016-0371-8
A new parameter, i.e., tearing toughness, was employed to characterize the mechanical properties of some ductile metals (Cu, Cu-2 wt% Be, Cu-Al alloys, and some steels) by using three-leg trousers tearing tests. The experimental results demonstrate that their tearing toughness is not a physical constant and shows a close relationship with the materials’ types and microstructures. It can be inferred that the tearing toughness of different ductile metals has their respective variation range, expectantly, and may be represented by the comprehensive mechanical properties of strength and ductility for various ductile materials.
关键词:
Ductile
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metals
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Strength
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Ductility
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Tearing
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toughness
Physical Review B
A first-principles method based on the local-density approximation using discrete variational clusters has been used to study the electronic structure of bcc metals, Li, Na, K, VI Nb, Ta, Cr, Mo, end W. The binding energy of these metals was calculated, and the relationship! between the binding energy and the volume of a unit cell for a given metal was determined. The results show that the contribution of the interaction beyond the third nearest-neighbor atoms to the binding energy is small for transition metals, but large for alkali metals, The theoretical triaxial tensile strength and bull; modulus of these metals were estimated from the electronic structure and binding-energy calculations. The present results of the bulk modulus for Li, Na, K, Nb, Tu, Mo, and W are in good agreement with experiments and other available theoretical data, but the bulk modulus for V and Cr is somewhat overestimated. The theoretical strength obtained in the present work is in good agreement with the results of the linear muffin-tin-orbitals method. [S0163-1879(99)14521-1].
关键词:
density;potentials;accurate;energy
郭立
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吴爱样
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周科平
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姚振巩
中国有色金属学报
基于完全耦合模型解决复杂岩石力学问题的方法论--岩石工程系统理论(RES)的基本原理, 构造了地下工程岩体失稳模式判别的智能预测模型, 并采用具有自学习、非线性映射和数据挖掘功能的模糊自组织人工神经网络模型ANN来实现RES交互作用矩阵的编码.通过一个实例说明这种方法具有良好的实用性.
关键词:
RES理论
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模式判别
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人工神经网络
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岩体稳定性
X.L. Tian C.W. Zhan J.X. Hou X.C. Chen J.J. Sun
材料科学技术（英）
A nanocrystal model for liquid metals and amorphous metals has been developed. With the nanocrystal model, the broadening peak profiles (BPPs) of Cu, Al, Al65Cu20Fe15 alloy, Cu70Ni30 alloy and Fe50Si50 alloy were gained by broadening the X-ray diffraction (XRD) peaks of a crystal lattice. By comparing the BPPs with the XRD intensity curves measured on the liquid metals, it is found that the BPPs are closely in agreement with the XRD intensity curves, respectively, except the Fe50Si50 alloy. Therefore, the nanocrystal model can be used to determine if the atomic cluster structure of the liquid metal is similar to the structure of its crystal lattice.
关键词:
Liquid metal
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Atomic Cluster
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Structure
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Crystal Lattice
Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing
Three-point bending test and acoustic emission technique are used to determine the fracture toughness and fracture process of three types of modified 9Cr-1Mo steel weld metals. Scanning electron microscopy is used to accomplish fractography analysis of fracture specimens. Microstructure of weld metals is investigated using optical microscopy and transmission electron microscopy. The fracture process and factors which affect fracture of the 9Cr-1Mo steel weld metals in post-weld heat treated condition are studied. Experimental results show that the modified 9Cr-1Mo steel weld metals fracture by a quasi-cleavage mechanism at ambient temperature. The microstructure of the weld metals is composed of mainly tempered martensite with M23C6 precipitates. In weld metals, microcracks nucleate from non-metallic inclusions. Fractures develop very quickly when cracks started to propagate. Comparatively, in weld metals with low strength, microcracks initiate at a low stress, but propagation of cracks is limited by plastic deformation. In weld metals with high strength, microcracks nucleate at high stresses, but cracks propagate very quickly and lead to almost immediate fracture of the specimens. As a result, weld metals with the low strength have a higher fracture toughness, while weld metals with higher strengths has a lower fracture toughness. (C) 1999 Elsevier Science S.A. All rights reserved.
关键词:
9Cr-1Mo steel;weld metal;fracture toughness;microstructure;acoustic;emission
B.Q. Li
材料科学技术（英）
Inherent twinnability of face-centered-cubic (fcc) metals was analyzed based on the direct competition between twinning partial dislocation nucleation and trailing partial dislocation nucleation, with which the twinnability of fcc metals can be simply expressed as function of the stacking-fault energy, the unstable stacking-fault energy, and the unstable twinning-fault energy of fcc metals. The predicted twinnability ranking matched well with former experimental results and provided a physical insight to understand twinnability from crystallographic orientation and fault energy parameters.
关键词:
Deformation twinning
