吕忆城
,
M.R.Notis
,
J.I.Goldstein
金属学报
本文研究了淬火冷却过程中Cu:Cu-Al扩散偶α/β界面的逆向迁移,α/β界面的变温扩散模型在Fick第二定律基础上用数值分析法进行了计算.界面逆向迁移的距离和下列因素有关:高温时的原始浓度分布、扩散温度、扩散系数、冷却速率和相图中溶解度曲线的斜率.“界面逆向迁移效应”还影响了浓度分布曲线的形状和界面浓度.
关键词:
吕忆城
,
M.R.Notis
,
J.I.Goldstein
金属学报
用“双套管法”淬火测定Cu:Cu-Al扩散偶中的相平衡,由于该法具有较快的冷却速度,保证了α/β相界面处于局部平衡.传统的淬火方法冷速通常是不够快的,不足以抑制β相的分解.较慢的冷却使界面形貌发生改变;测出的界面浓度是较低温度下的数值.有理由相信,Eifert等实验得到的各温度下都远较平衡浓度为高的α/β相界浓度,是由于实验过程中较慢的冷速所导致.
关键词:
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
null
,
null
金属学报
在工程上,经常由于应力腐蚀开裂和氢脆引起中强度钢结构件发生滞后破坏。这类脆断往往从结构件中预先存在的疲劳或焊接裂纹处开始,因此,运用传统的光滑试样的检验方法不能反映这类破坏的特点。 本文将弹塑性断裂力学中的J积分概念用于滞后破坏的研究,提出用带预制疲劳裂纹的悬臂弯曲试样测定J积分的临界值J_(Ic)和应力腐蚀开裂阈值J_(Iscc)的方法。测定了40CrNiMo钢的J_(Ic)值及其在硫化氢水溶液中的J_(Iscc)值。通过和三点弯曲方法测定的J_(Ic)值的对比,以及和满足线弹性条件时直接测定的应力强度因子K_I值的对比,说明这种方法的可靠性。最后,对悬臂弯曲方法的特点进行了讨论。
关键词:
Physical Review B
The quadratic Holstein-Primakoff spin-wave Hamiltonian for three-sublattice Heisenberg systems with different exchange constants (J(ab)=J(bc)not equal J(ca)) was diagonalized by a three-step procedure. The classical ground state was examined and the effects of quantum fluctuation on the ground state were discussed. The 0 K spin reorientation angles due to quantum fluctuations were found to originate from the asymmetry of the system. As an extended application of the spin-wave study of the multisublattice systems, the spin-wave spectra of a Heisenberg superlattice, which has four or three magnetic atoms or spins, in each magnetic unit cell in the x direction, were solved analytically in terms of creation and annihilation operators. It has been found that the spin-wave spectra of the present superlattice systems depend on the exchange constants J and J(1), and that the degeneracy of the spin-wave spectra remains for the superlattice of four atomic layers and is partially removed for the superlattice of three atomic layers mainly due to the asymmetry of the system. Another type of splitting of the energy level occurs which differs for those levels with different degeneracies. The mixing of the interface and the bulk modes were found for the spin-wave dispersion of the superlattices. It was predicted that even for different superlattices having the same exchange constants (either J or J'), i.e., without the oscillation of the exchange coupling, the asymmetry can lead to the oscillation of magnetic properties, such as magnetization and giant magnetoresistance.
关键词:
ferromagnetic superlattices;reorientation transitions;magnetic;superlattices;modes;temperatures;film
H.P. Chen and Z.J. Deng (State Key Lab. for Mechanical Behavior of Materials
,
Xi'an Jiaotong University
,
Xi'an 710049
,
China)
金属学报(英文版)
The effect of specimen thinkness on JR resistance curve has been investigated using low and middle strength steels. As the J dominance regime is reached, the initial J-integral values, J(i), are definite even if the elastic component Ji(e) and plastic component Ji(p)vary with the thinkness of specimen. The wider the specimen width, the larger the Ji(e)/Ji and the smaller the Ji(p)/Ji. The crack propagation resistance, dJR/da and dJp/da, decreases, while dJe/da increases linearly with increasing specimen thinness.Based on the above experimental results, an empirical formula dJ/da = α+β. B is given, which can be used to evaluate the safety of practical structural components.A modified J-integral is presented, upon which a new view is Put forward that the increase in crack growth resistance is induced mainly by the increase in the plastic J-integral component with the crack propagation,
关键词:
: fracture mechanics
,
null
,
null
,
null
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
平荣刚
原子核物理评论
doi:10.3969/j.issn.1007-4627.2004.02.026
通过J/Ψ→pp-,pN-*,N*N-*衰变,研究了Roper共振态的混杂态结构对衰变角分布和分支比的影响.计算结果表明,如果Roper共振态为纯混杂态,那么J/Ψ→pN-*,N*N-*的角分布几乎相等,而J/Ψ衰变到混杂态的衰变宽度还不到J/Ψ→pp-的1%,给出了Γ(J/Ψ→ N*p-)/Γ(J/Ψ→pp-)和Γ(J/Ψ→ N*N-*)/Γ(J/Ψ→pp-)随混合参数的变化关系,并讨论了在J/Ψ衰变中研究Roper混杂态结构的可能性.
关键词:
Roper共振态结构
,
混杂态
,
J/Ψ
