Y.G. Cao
,
X.Y. Sun
金属学报(英文版)
J-integral and crack opening displacement δ(COD) were important parameters for characterization of fractures in engineering materials. The relationship between J-integral and COD has been investigated for a long time and was enerally represented as J = m σyδ, where σy is the yield strength and m is a function of specimen geometry and material properties. To determine the value of m, extensive studies and experiments have been performed. The method that used the fracture-surface topography analysis (FRASTA) for determining J-integral from fracture surfaces of materials was introduced. On the basis of the relationship between COD and fracture surface average profile, the relationship between J-integral and COD was deduced and compared with the generally used equation. The method was experimentally confirmed to be able to provide a new way to determine the relationship between J-integral and COD.
关键词:
FRASTA
,
null
,
null
QIAO Lijie LIU Rui XIAO Jimei University of Science and Technology Beijing
,
Beijing
,
China
金属学报(英文版)
The effects of stress components on nucleation sites and propagation directions of stress cor- rosion cracks in brass were investigated with specimens under mode Ⅱ and mode Ⅲ loadings. The results indicated that under mode Ⅱ loading,stress corrosion cracks nucleated on the site with maximum normal stress component and propagated along the plane perpendieular to the maximum normal stress,under mode Ⅲ loading,the stress corrosion crack was not evident on the 45°plane due to the general corrosion in aqueous solution with high NH_4OH concentra- tion,while stress corroded in aqueous solution with low NH_4OH concentration, numerous cracks with spacings of 10—150μm were found on the 45°plane with maximum normal stress and no stress corrosion cracks was observed on the plane with maximum shear stress.
关键词:
stress corrosion cracking
,
null
,
null
,
null
Y.G. Cao
金属学报(英文版)
To investigate the causes that led to the formation of cracks in materials, a novel method that only considered the fracture
surfaces for determining the fracture toughness parameters of J-integral for plain strain was proposed. The principle of the
fracture-surface topography analysis (FRASTA) was used. In FRASTA, the fracture surfaces were scanned by laser microscope and the
elevation data was recorded for analysis. The relationship between J-integral and fracture surface average profile for plain strain
was deduced. It was also verified that the J-integral determined by the novel method and by the compliance method matches each
other well.
关键词:
FRASTA
,
null
,
null
Physical Review B
The Hamiltonian for a four-sublattice Heisenberg ferrimagnet or ferromagnet with different exchange constants (J(ab) = J(cd) not equal J(bc) = J(da)) was established. An extended Bogoliubov transformation was developed by solving an equation group, consisting of 20 equations and 20 unknowns. The procedure for solving the equation group was carried out by introducing a simple way of reducing the numbers of the equations and the unknowns. The spin-wave spectra in the present system have been determined by performing the standard Holstein-Primakoff transformation and the Bogoliubov one. It has been found that the spin-wave spectra of the present system depend on the exchange constants and that the degeneracy of the spin-wave spectra remains. The results for a special case (J(ab) = J(bc)) i.e., an antiferromagnet are discussed briefly. The spin-wave spectra of the four-sublattice Heisenberg antiferromagnet are found to be degenerative also and they are linear in k for small k.
关键词:
model
Benlian ZHOU International Centre for Materials Physics
,
Institute of Metal Research
,
Academia Sinica
,
Shenyang
,
110015
,
China
材料科学技术（英文）
A series of superior properties will make composites the most important structural materials in the next century.But they are difficult to design owing to the complexity of structure and processing. Biomaterials had been naturally selected and evolved for millions of years,a great variety of their ra- tional composite structures could be taken as our reference in the biomimetic design of composite materials.There are many difficult problems in the current study on composite materials such as: brittleness of continuous fibers and difficulties in interface design;easy pull-out of short fibers from matrix causing failure in reinforcing;being less easy in selecting the aspect ratio of whiskers and dif- ficulties in finding the way of toughening composites of ceramic matrices as well as the way of heal- ing inner damages.After describing the distinct composite features,the functional adaptability and self-healing ability of biomaterials,several examples o.f biomimetic design of composite materials have been listed in this paper:the optimum design of composites simulating bamboo structure;the fine structure of bamboo fibers;the dumb-bell model simulating animal bone;the model on the pull-out of fiber with fractal-tree structure and some tentative works on the healing of inner damage in composite materials The methodology of biomimetic design and its future have been given at the ast part of this paper.
关键词:
composite material
,
null
,
null
Wear
The abradability of porous seal materials has been evaluated using a single-pendulum scratch device. The results shows that the specific energy e (= E/V) and the tangential dynamic hardness H(T)(= F(T)/A(T)) for small incursion depth are obviously higher than those for greater incursion. The specific energy e and tangential dynamic hardness H(T) have been proposed as two equivalent criteria of abradability of seal materials. The abradability of porous seal materials is dependent on both mechanical properties of the materials and extent of densification. A careful balance between them is the key to a satisfactory seal material.
关键词:
abradability;seal materials;scratch device
