材料期刊网

SLOW PROPAGATION OF FATIGUE CRACK NEAR THRESHOLD

DENG Rongying ZHOU Aihua JIANG Huaiqing LI Chunxiu Institute of Mechanics , Academia Sinica , Beijing , ChinaZHANG Liqing , SUN Yutian Beijing Institute of Engineering , Beijing , China [Originally published in ACTA METALL SIN(CHINESE EDN)25(3)1989 pp A219—A225 , Associate Profes sor , Institute of Mechanics , Academia Sinica , Beijing , China

金属学报(英文版)

The effect of pearlite interlamellar spacing(d)from 0.31 to 0.77 μm of T8 steel on fatigue crack propagation near threshold has been investigated at different stress ratios(R).The closure stress intensity factor(K_(cl)),the threshold value(ΔK_(th))and crack tip opening dis- placement range(ΔCOD)were measured.The results show that pearlite interlamellar spac- ing in this range has no effect on K_(cl),but has effect on the threshold value in low stress ratio. The threshold value is higher for materials with larger interlamellar spacing.No matter what the stress ratio is,during the propagation near threshold,the propagation rate will be the same,provieded the crack tip opening displacement range is the same. Metallurgical examinations were also carried out to show that the crack propagation path is sensitive to mierostructure.The crack always propagates along either boundary of pearlite colony or ferrite lamellar in pearlite.

关键词: pearlitic steel , null , null , null

EFFECT OF OXIDE LAYER THICKNESS OVER Al AND Al ALLOY POWDERS ON QUALITY OF THEIR EXPLOSIVE COMPACTS

ZHANG Dengxia MA Chenghui CAI Ming Institute of Mechanics , Academia Sinica , Beijing , ChinaAI Baoren ZHANC Jinyuan ZHU Ruizhen LIU Chunlan Central Iron and Steel Research Institute , Ministry of Metallurgical Industry , Beijing , China Associate Professor , Institute of Mechanics , Academia Sinica , Beijing 100080 , China

金属学报(英文版)

Observations of microstructure of explosive compacts made of Al or Al-Li alloy powders by atomization with water,nitrogen or ultrasoic Ar gas were carried out under optical and scanning electron microscopes.The rsults indicate that super quality explosive compact can only be obtained by powders of which the thickness of the oxide layer is less than 30 nm.

关键词: Al powder , null , null , null

EFFECT OF EXPLOSIVE CONSOLIDATION PARAMETERS ON CONSOLIDATION QUALITY

GAO Juxian ZHANG Ke ZHENG Zhemin Institute of Mechanics , Academia Sinica , Beijing , China GAO Juxian Associate Professor , Institute of Mechanics , Academia Sinica , Beijing 100080 , China

金属学报(英文版)

Two-dimension consolidation under the cylindrical converging shock wave has been studied. The major parameters influenced on the explosive consolidation quality are the specific energy,detonation pressure and specific impulse.It seems to be favourable to improving con- solidation quality by a lower but slightly higher than critical detonation pressure and a high specific impulse.

关键词: explosive consolidation , null , null

EFFECT OF TH ETHICKNESS OF SPECIMENS ON THERMAL RESIDUAL STRESSES IN SiCw/Al COMPOSITES

Q. Y. Liu1 , 2) W. D. Fei2) and N. G. Liang1) 1) LNM , Institute of Mechanics , The Chinese Academy of Sciences , Beijing 100080 , China 2) Schoolof Materials Science and Engineering , Harbin Institute of Technology , Harbin 150001 , China

金属学报(英文版)

heinteracteach other among three kindsofthermalresidualstresses were analyzed firstly. Theresultsshown thatthe presenceof microstressandthermal mismatch stresshad noinflu enceon the measurement of macrostress, but macrostress can affect the measured value of thermal mismatch stress. Theeffectofthicknessofspecimen on thermalresidualstresses was discussed. Macrostresscan be neglected in thin specimen, thermal mismatch stressincreased with quenchingtemperatureincreasing, andobtainedtheir maximum valuesat400 ℃,then decreased . Forthethickspecimen, thecompressive macrostressatthesurfaceincreased with the quenching temperature increasing. The changing tendency of thermal mismatch stresswith quenchingtemperature wasquite differentcompared withthethinspecimens, which ob tainedtheir minimum valueat400℃.

关键词: thermalresidualstresses , null , null

FRACTURE MECHANICS ANALYSIS OF THERMAL STRAIN FATIGUE LIFE FOR THE SINTERING MACHINE PALLET

LI Zhenzi and LI Ming (Department of Architectnre Engineering , Central South University of Technology , Changsha 410083 , China)LIAO Fuchang (Shenzhen School of Technology , Shenzhen 518029 , China)Manuscript received 10 August 1995 , in revised form 12 April 1996

金属学报(英文版)

In recent years elastic-plastic fracture mechanics has developed rapidly and is widely used to solve various engineering problems. The application of elastic-plastic fracture mechanics on the pallet of sintering machine is approached in detail for the first time in the present study. The theoretical results were compared with the actual data determined from sintering machine pallet. Results show that good agreement was achieved between the method suggested by the author and the actual data. The basis of determining design of the sintering machine pallet in iron and steel engineering has been provided and it will result in great economic benefits.

关键词: : pallet , null , null , null

THERMAL FATIGUE AND FRACTURE MECHANICS ANALYSIS OF GREY CAST IRON

GUO Chengbi ZHOU Weisheng Dalian Institute of Technology , Dalian , Liaoning , China Professor , Dept.of Shipbuilding , Dalian Institute of Technology , Dalian , Liaoning , China

金属学报(英文版)

The in-phase and out-of-phase thermal fatigue,the C-P type and P-C type isothermal fa- tigue of grey cast iron were experimentally studied.The fatigue life was evaluated analytically by using the elastic-plastic fracture mechanics method(mainly J integral).The results of ex- periments and calculations showed that the lifes of in-phase and C-P type fatigue are longer than that of out-of-phase and P-C type fatigue respectively within the same strain range. This is in contrast to the results of other materials such as low carbon steel.On the other hand, the predicted lifes are consistent with experimental results.This suggests that J integral as a mechanics parameter for characterizing the thermal fatigue strength of grey cast iron and the mechanics model and the calculation method developed here are efficient.A parameter ΔW_1 was proposed from energy aspect to characterize the capacity of crack propagation. The isothermal fatigue life is the same as the thermal fatigue life for identical ΔW_1 values.

关键词: grey cast iron , null , null

Features and states of microscopic particles in nonlinear quantum-mechanics systems

Frontiers of Physics in China

In this paper, we present the elementary principles of nonlinear quantum mechanics (NLQM), which is based on some problems in quantum mechanics. We investigate in detail the motion laws and some main properties of microscopic particles in nonlinear quantum systems using these elementary principles. Concretely speaking, we study in this paper the wave-particle duality of the solution of the nonlinear Schrodinger equation, the stability of microscopic particles described by NLQM, invariances and conservation laws of motion of particles, the Hamiltonian principle of particle motion and corresponding Lagrangian and Hamilton equations, the classical rule of microscopic particle motion, the mechanism and rules of particle collision, the features of reflection and the transmission of particles at interfaces, and the uncertainty relation of particle motion as well as the eigenvalue and eigenequations of particles, and so on. We obtained the invariance and conservation laws of mass, energy and momentum and angular momentum for the microscopic particles, which are also some elementary and universal laws of matter in the NLQM and give further the methods and ways of solving the above questions. We also find that the laws of motion of microscopic particles in such a case are completely different from that in the linear quantum mechanics (LQM). They have a lot of new properties; for example, the particles possess the real wave-corpuscle duality, obey the classical rule of motion and conservation laws of energy, momentum and mass, satisfy minimum uncertainty re-lation, can be localized due to the nonlinear interaction, and its position and momentum can also be determined, etc. From these studies, we see clearly that rules and features of microscopic particle motion in NLQM is different from that in LQM. Therefore, the NLQM is a new physical theory, and a necessary result of the development of quantum mechanics and has a correct representation of describing microscopic particles in nonlinear systems, which can solve problems disputed for about a century by scientists in the LQM field. Hence, the NLQM built is very necessary and correct. The NLQM established can promote the development of physics and can enhance and raise the knowledge and recognition levels to the essences of microscopic matter. We can predict that nonlinear quantum mechanics has extensive applications in physics, chemistry, biology and polymers, etc.

关键词: microscopic particle;nonlinear systems;nonlinear quantum mechanics;basic principle;motion rule;dynamic property;nonlinear Schrodinger;equation

DYNAMIC ASPECTS OF LINEAR ELASTIC FRACTURE-MECHANICS APPLIED TO DIELECTRIC-BREAKDOWN

Journal of Physics D-Applied Physics

The dynamic aspects of linear elastic fracture mechanics applied to dielectric breakdown are studied. In the same direction as the fracture mechanics analogue for dielectric breakdown described previously by some researchers, this paper develops the intrinsic, rate-dependent bond breakdown micromechanism to account for the dynamic process of dielectric breakdown. The formulae of conducting microcrack growth rate and lifetime prediction are derived and applied to the experimental data of SiO2 films.

关键词: sio2-films;oxides

Life prediction of ball grid array soldered joints under thermal cycling loading by fracture mechanics method

Hongyuan FANG , Li WANG , Yiyu QIAN

材料科学技术（英文）

Fatigue crack propagation life of ball grid array (BGA) soldered joints during thermal cycling loading was investigated by fracture mechanics approach using finite element analysis. The relationships between the strain energy release rate (G) acid crack size (a), thermal cycle numbers (N) can be derived. Based on the relationships, fatigue life of the soldered joints was determined. The results showed that crack propagation life was higher than crack initiation life. Therefore, it appears that it is more appropriate to predict the fatigue life of soldered joints using the fracture mechanics method.

关键词:

Electronic structure analysis of self-consistent embedding theory for quantum/molecular mechanics simulations

Physical Review B

The self-consistent embedding theory provides a rigorous framework for quantum/molecular mechanics simulations of materials. By using crystalline aluminum as an example, we present a critical analysis on the accuracy of the embedding theory, focusing on the electronic structure of the primary quantum mechanics region. We examine the influence of embedding potential on the structural energy, local density of states, total electronic density, and electronic states at the Fermi energy of the primary quantum system. The analysis illustrates the success and limitations of the embedding scheme in describing the electronic structure of the primary quantum region.

关键词: aluminium;density functional theory;electronic density of states;Fermi level;pseudopotential methods;energy-density functionals;wave basis-set;molecular-dynamics;metals;systems