Physical Review Letters
We find that the failure of bulk metallic glassy (BMG) materials follows three modes, i.e., shear fracture with a fracture plane significantly deviating from 45degrees to the loading direction, normal tensile fracture with a fracture plane perpendicular to the loading direction, or distensile fracture in a break or splitting mode with a fracture plane parallel to the loading direction. The actually occurring type of failure strongly depends on the applied loading mode and the microstructure of the material. Extensive evidence indicates that the Tresca fracture criterion is invalid, and for the first time, three fracture criteria are developed for isotropic materials with high strength, such as advanced BMGs or the newly developed bulk nanostructural materials.
关键词:
amorphous-alloys;enhanced plasticity;zr-ti;flow;deformation;composite;strength;microstructure;ribbons;failure
Yiwang BAO(China Building Materials Academy
,
Beijing 100024
,
China)R. W Steinbrech (IWE1
,
Juelich Research Center
,
Germany)
材料科学技术（英文）
The fracture behaviour of glass in biaxial stress state has been investigated. Fracture toughness of disk specimen with a straight-through crack was measured under biaxial tension and uniaxial tension loads respectively. The difference between them and the reasons for the difference are discussed. The influence of the stress parallel to crack on fracture of brittle material was demonstrated in theory and experiments. The results show that plane stress fracture toughness of glass is not a material constant. and that the fracture toughness measured in biaxial tension state is higher than that measured under uniaxial tension. The conventional fracture criterion upon the stress intensity factor is questioned in the case of biaxial stress problem, and the strain dependence of crack growth is discussed.
关键词:
X.H.Song(Centre for Materials Research and Analysis
,
Wuhan University of Technology
,
Wuhan 430070
,
China Manuscript received 6 November 1995
,
in revised form 24 May 1996)
金属学报(英文版)
The theoretical calculation formulas for the plane strain fracture toughness of mode Ⅰand Ⅱcracks of ceramic materials are deduced in this paper by using the nonlocal elasticity theory and maximum tensile stress criterion The deduced formulas, which are independent of crack geometry,bear a relation to material parameters.It is shown through experiment that the theoretical value of fracture toughness is the lower limit of testing value. The theoretical calculation formulas for fracture toughness relate the macro-mechanical performance of materials with the micro-structural parameters and,therefore, are beneficial to fully understanding the physical mechanism of material rupture.
关键词:
:nonlocal elasticity theory
,
null
,
null
材料科学技术（英文）
The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses (BMGs) and their composites. The shear fracture angles of these BMG materials often display obvious differences under compression and tension, and follow either the Mohr-Coulomb criterion or the unified tensile fracture criterion. The compressive plasticity of the composites is always higher than the tensile plasticity, leading to a significant inconsistency. The enhanced plasticity of BMG composites containing ductile dendrites compared to monolithic glasses strongly depends on the details of the microstructure of the composites. A deformation and damage mechanism of pseudo-plasticity, related to local cracking, is proposed to explain the inconsistency of plastic deformation under tension and compression. Besides, significant melting on the shear fracture surfaces was observed. It is suggested that melting is a common phenomenon in these materials with high strength and high elastic energy, as it is typical for BMGs and their composites failing under shear fracture. The melting mechanism can be explained by a combined effect of a significant temperature rise in the shear bands and the instantaneous release of the large amount of elastic energy stored in the material.
关键词:
bulk metallic glasses (BMGs);mechanical properties;shear fracture;failure criterion;plastic deformation;melting phenomenon;supercooled liquid region;fatigue-crack-propagation;nanostructure-dendrite composite;soft-magnetic properties;serrated;plastic-flow;ni amorphous-alloys;ti-based composites;in-situ;formation;cu-be alloy;high-strength
材料科学技术（英文）
A new model of multirange fractals is proposed to explain the experimental results observed on the fractal dimensions of the fractured surfaces in materials. A new explanation to the Williford's multifractal curve on the relationship of fractal dimension with fracture properties in materials has been given. It shows the importance of fractorizing out the effect of fractal structure from other physical causes and separating the appropriate range of scale from multirange fractals. Mechanical alloying process under ball milling as a non-equilibrium dynamical system has been also analyzed.
关键词:
surfaces;interfaces;dimension;growth
Youngsuk Kim
,
Youngmoon Lee
,
Dongyoul Choi
,
Chanil Kim
材料科学技术（英文）
Recently, quasimolecular dynamics has been successfully used to simulate the deformation characteristics of actual size solid materials. In quasimolecular dynamics, which is an attempt to bridge the gap between atomistic and continuum simulations, molecules are aggregated into large units, called quasimolecules, to evaluate large scale material behavior. In this paper, a 2-dimensional numerical simulation using quasimolecular dynamics was performed to investigate laminar composite material fractures and crack propagation behavior in the uniform bending of laminar composite materials. It was verified that under bending deformation laminar composite materials deform quite differently from homogeneous materials.
关键词:
Journal of Physical Chemistry C
Polymer nanocomposites are usually made by incorporating dried narroparticles into polymer matrices. This would easily lead to aggregation of nanoparticles and then would readily bring about opaqueness for narrocomposites based on functionally transparent polymers. In this work, preparation of highly transparent ZnO quantum dots (ZnO-QDs)/epoxy nanocomposites that can emit intense luminescence was reported for the first time by uniformly dispersing ZnO quantum dots in a transparent epoxy resin via a direct dispersion method. The direct dispersion of ZnO quantum dots without drying in the epoxy matrix could effectively avoid aggregation of fine quantum dots and showed a good dispersity of ZnO-QDs in the epoxy matrix. Such materials showed a high transparency in the visible region and exited a broad emission spectrum peaked at 442 nm. On the other hand, in traditional solid state lighting emission diodes, semiconductor quantum dots are used as phosphors that are attached to the die of the lighting emission diode (LED) lamps for emitting luminescence. In this work, the as-prepared ZnO-QDs/epoxy nanocomposites were successfully employed as packaging materials for solid state lighting emission diodes in which conventional phosphors are not required while the nanocomposite encapsulating materials are responsible for emitting luminescence and thus the encapsulated LED lamps have an innovative structure. Consequently, the as-prepared ZnO-QDs/epoxy nanocomposites are promising for use as novel encapsulating materials in LED technology due to the much simplified encapsulating process.
关键词:
polymer nanocomposites;size quantization;zinc acetate;nanoparticles;luminescence;colloids;photochemistry;oxide;particles;diodes
