铜双晶体循环变形的晶界强化效应

用组合双晶体（ＣＢ）及实际双晶体（ＲＢ）研究平行晶界在铜双晶体循环变形过程中的强化作用，结果表明随双晶体变小，其循环应力升高，晶界作用增强，扫描电镜观察发现晶界附近出现以次滑移为主的晶界影响区，结合双晶体的循环应力－应变响应和晶界影响区，讨论了双晶体的晶界强化机制。     

THE EFFECT OF MODE III LOADING ON FATIGUE CRACK GROWTH IN A ROTATING SHAFT

Abstract— Four particularly pronounced beachmarks have been identified on the fracture surface of a cracked rotor. A correlation has been made between these beachmarks and events in the operational record. Fatigue crack growth calculations have been performed for a chordally cracked shaft subject to alternating self-weight bend stresses. The shaft dimensions and loading used correspond to the position of the crack in the rotor and growth rates were calculated over a range of crack depths spanning the positions of the major beachmarks. The results of the calculations agree with the beachmark correlation if allowance is made for the effect of the torsional loading of the shaft.     

循环荷载水平与加载频率耦合作用下的软粘土特性研究

通过不排水循环三轴试验,并考虑不同循环应力水平及加载频率的影响,研究了软粘土在循环荷载作用下的孔隙水压力及变形特性,分别探讨了这些特性随循环加载时间和加载次数的不同变化规律。研究结果表明,对于相同循环应力水平,相同加载次数下不同加载频率的软粘土特性有所不同,而相同加载时间下不同加载频率的软粘土特性基本相同。此外,无论加载频率为何数值,一旦循环应力水平超过临界值,软粘土破坏必将发生。为了深入研究应力水平和加载频率的耦合作用,该文从应力控制循环加载试验中的应变速率着手,对软粘土的特性进行了分析。结果表明,在应力水平相同的情况下,软粘土在不同加载频率下的应变速率是基本相同的,由此可得对于软粘土在循环荷载作用下特性的影响,应力水平比加载频率更为重要。     

铜单晶体循环应力应变曲线的平台行为的取向效应

系统讨论和总结了单滑移,双滑移和多滑移取向铜单昌体循环形变中呈现的不同平台行为。分析结果表明,晶体取强烈影响双滑移和多滑移铜晶体的循环变行为,平台区的出现与否及平台应力的高低,不仅与闰错反应模式和强度有关。     

晶体取向对铜单晶体循环硬化行为的影响

研究了不同取向铜单晶体的循环硬化行为.结果表明,晶体取向对双滑移和多滑移取向铜单晶体的循环硬化行为有强烈的影响.不同取向铜单晶体的初始循环硬化率θ0.2与晶体中的位错反应模式、强度以及交滑移机会密切相关.临界双滑移晶体在循环硬化初始阶段呈现出独特的应变突发行为.     

THE DEVELOPMENT OF STRESSES AND THEIR DISTRIBUTION IN TWO-PHASE ALLOYS DURING CYCLIC LOADING

A finite element program calculates the cyclic behaviour of the individual component phases of a multiphase material using a master curve observed in uniaxial cyclic stress tests. The fatigue behaviour of the two-phase alloys was characterized by visualizing the evolution of the phase stress (denoted by an average effective stress and an hydrostatic stress) during cyclic loading. The evolution procedure shows a unique fatigue behaviour of the in situ component phases, which differs from that observed in uniaxial or multiaxial fatigue tests of the single phase material. The fatigue damage on a microstructural scale was identified by the distributions of the plastic strain accumulated during cyclic loading and the stress triaxility in the component phases.     

REVERSAL OF CYCLIC CREEP IN MILD STEEL AND COPPER

Abstract— The progressive change of mean strain during the cyclic plastic deformation of a material between fixed stress limits is commonly called cyclic creep. If, in tension-compression testing, the mean stress exceeds a certain critical small compressive value, shortening is to be expected; but, if it is less than this or if it is tensile, lengthening is to be expected. The value of the mean stress decides the eventual direction of cyclic creep but not necessarily the initial direction of cyclic creep. In a pre-strained metal, the form of the tension and compression curves differs because of the Bauschinger effect. This affects the behaviour of the material during the first cycle and also, to a decreasing extent, during subsequent cycles. Thus, if the mean stress tends to cause cyclic creep in a direction opposed to that in which pre-straining has induced initial creep, a reversal of creep can occur. Observations have been made of the phenomena in mild steel (for both directions of pre-strain) and also in high conductivity copper.
It was found that the phenomenon of creep reversal does not depend on the metal undergoing cyclic hardening or softening. However, changes in the strain range and changes in the mean strain caused by cyclic creep itself produced changes in the limits of true stress when cycling was carried out between fixed limits of nominal stress. It was also shown that a reversal of cyclic creep might occur as a result of cyclic hardening or softening of a metal which possesses similar tension and compression characteristics.     

微量硼对铜组织和性能的影响

利用拉伸试验机，定氧仪，电子探针，Ｘ射线衍射、扫描电镜等实验手段，研究了Ｂ脱氧Ｃｕ的组织和结果表明，随着Ｂ的增加，夹杂物Ｃｕ２Ｏ的数量减少，Ｃｕ的强度降低，塑性、韧性提高，同时也提高Ｃｕ的耐蚀性和导电性能。     

THE EFFECT OF ECCENTRIC LOADING ON THE STRESS DISTRIBUTION IN THREAD ROOTS

Abstract Three-dimensional photoelasticity has been used to examine the effect of eccentric loading on the stress distribution along the helix of the roots of threaded fasteners. In the investigation the ratios of axial to bending stress were similar to those found commonly in engineering components. The results showed that, as the level of eccentricity increased, the maximum stress in helix of the thread root did not change significantly, but there was an increase in the length of helix which experienced high stress. This will lead to an increase in the probability of crack initiation and propagation in the presence of eccentric loading.     

THE EFFECT OF MICROSTRUCTURE ON FRACTURE TOUGHNESS OF POLYCRYSTALLINE ALUMINA

Abstract— A study of the dependence of the fracture toughness on the microstructural morphology of polycrystalline materials is presented. The microstructure of several aluminas was characterized by thermal etching and image analysis. The fracture toughness of these materials was then determined by bridge-indentation pre-cracking followed by a four-point bending test procedure. A SEM investigation of the mechanisms of crack propagation was also carried out. The observed microstructure-related fracture toughness responses are discussed.     

EFFECT OF BIAXIAL MEAN STRESS ON CYCLIC STRESS-STRAIN RESPONSE AND BEHAVIOUR OF SHORT FATIGUE CRACKS IN A HIGH STRENGTH SPRING STEEL

Abstract— Biaxial fatigue tests were conducted on a high strength spring steel using hour-glass shaped smooth specimens. Four types of loading system were employed, i.e. (a) fully reversed cyclic torsion, (b) uniaxial push—pull, (c) fully reversed torsion with a superimposed axial static tension or compression stress, and (d) uniaxial push—pull with a superimposed static torque, to evaluate the effects of mean stress on the cyclic stress—strain response and short fatigue crack growth behaviour. Experimental results indicate that a biaxial mean stress has no apparent influence on the stress—strain response in torsion, however a superimposed tensile mean stress was detrimental to torsional fatigue strength. Similarly a superimposed static shear stress reduced the push—pull fatigue lifetime. A compressive mean stress was seen to be beneficial to torsion fatigue life. The role of mean stress on fatigue lifetime, under mixed mode loading, was investigated through experimental observations and theoretical analyses of short crack initiation and propagation. Using a plastic replication technique the effects of biaxial mean stress on both Stage I (mode II) and Stage II (mode I) short cracks were evaluated and analysed in detail. A two stage biaxial short fatigue crack growth model incorporating the influence of mean stress was subsequently developed and applied to correlate data of crack growth rate and fatigue life.     

往复荷载作用下自复位墙受力机理研究

该文以自复位墙作为研究对象,将其简化成一刚体,分别仅考虑自重、考虑预应力筋影响及同时考虑预应力筋和阻尼器的影响,通过理论推导得出了往复荷载作用下的水平力-转角曲线,研究了其在往复荷载作用下的受力机理。研究表明：自复位墙墙体自重和预应力筋共同提供自复位能力,阻尼器提供耗能能力;自复位墙的力学性能与墙体几何尺寸、预应力筋及阻尼器参数有关。     

THE EFFECT OF COMPLEXING AGENTS ON THE PRECIPITATION AND REMOVAL OF COPPER AND NICKEL FROM SOLUTION

This paper addresses the effect of the complexing agents citrate, tartrate, ammonia, phosphate, and EDTA on the removal of copper and nickel from solution using both hydroxide and sulfide precipitation. Both batch and continuous metal sulfide precipitation experiments were performed. Results are presented for the removal of heavy metals and the resulting particle size distributions. The presence of weak complexing agents (citrate, tartrate, ammonia, and phosphate) had a minimal effect on the removal of copper and nickel, while the presence of a strong complexing agent (EDTA) resulted in the residual metal concentration being 1-2 orders of magnitude greater than the case with no complexing agents present. In an open system, the residual nickel concentration increased with increasing reaction time, due to the oxidation of nickel sulfide co nickel sulfate. For copper sulfide precipitation, the presence of complexing agents reduced the precipitate growth rate, nuclei density, and nucleation rate, resulting in a decrease of the dominant particle size (as compared to copper sulfide precipitation with no complexing agents present). The value of the kinetic order, i, decreased, while the kinetic rate constant, kN, increased in the presence of EDTA.     

表面增韧层对层板,夹芯板撞击行为的影响

本文对层板和夹芯板受硬物低速撞击的撞击力进行了计算和测量。本研究的目的是比较层板和夹芯板的耐撞击行为并确定表面增韧层对其低能量撞击行为的影响。     

表面增韧层对层板、夹芯板撞击行为的影响

本文对层板和夹芯板受硬物低速撞击的撞击力进行了计算和测量.本研究的目的是比较层板和夹芯板的耐撞击行为并确定表面增韧层对其低能量撞击行为的影响.     

THE EFFECT OF GRAIN SIZE, STRAIN AND TEMPERATURE ON THE MONOTONIC STRESS-STRAIN BEHAVIOUR OF POLYCRYSTALLINE ALUMINIUM AND AL ALLOYS

Abstract The tensile yield and flow stresses of aluminium, A1-2.63Mg alloy and A1-2.07Li alloy at room temperature are shown to depend on the inverse square root of the polycrystal grain size and are described empirically by the Hall-Petch relation. The same relation describes the flow stress-grain size dependence for A1-2.07Li alloy at temperatures ranging from - 196°C to 400°C. The strain hardening in the friction stress of each material at 20°C is independent of the grain size, is approximately parabolic and is greatest for the precipitation strengthened A1-2.07Li alloy. The grain size contribution to the tensile flow stress is dependent on both the tensile strain and composition. The friction stress, σ₀, and slip band stress intensity parameter, k_ε, at yield, k_y, are both dependent on temperature. Low temperature suppresses dislocation annihilation and recovery processes, leading to planar pile-ups at grain boundaries and a hardening that is linear with strain. Weak hardening is observed at 250°C and 400°C due to extensive annihilation and recovery. The value of k_ε, at all temperatures falls following initial yielding with the generation of freshly unlocked sources.     

周期载荷下聚酯/橡胶复合材料和人造丝/橡胶复合材料的热生成对疲劳行为的影响

以单向帘线增强橡胶复合材料为研究对象,研究了周期载荷作用下橡胶复合材料的热生成对疲劳行为的影响。橡胶复合材料在疲劳过程中伴随较多的热生成,SEM观察表明:热生成温度与断裂表面密切联系。橡胶复合材料的滞后损失并不是全部转换为热,而是其中一部分被内能变化所消耗,不转换为有效热生成的滞后损失与疲劳损伤导致的结构变化有关。在疲劳试验中,直到疲劳破坏所消耗的平均有效能耗与疲劳寿命之间存在定量关系。     

缝合复合材料II型层间断裂特性研究

分别采用测量ENF试样加载点位移与测量其端部剪切位移CSD(Crack Shear Displacement)的试验方法,研究了缝合复合材料层合板的II型层间断裂韧性以及缝合密度,缝合线的直径等缝合参数对于缝合复合材料层合板II型层间断裂韧性和分层模式的影响。结果表明,缝合降低了层合板初始分层韧性G_IIi,但对于分层的扩展有良好的抑制作用。缝合参数对此有较大影响。      

退火处理对紫铜组织和机械性能影响的试验研究

研究退火处理对紫铜组织及机械性能的影响,利用X射线衍射、金相观测、硬度测量、拉伸和疲劳试验以及扫描电子显微镜观测等试验手段,对比分析了退火前后紫铜的金相组织、基本力学性能、疲劳寿命、断口显微形貌和疲劳裂纹扩展行为等。考察了表面形貌对材料试件的疲劳寿命的影响,利用带缺口的试件对疲劳裂纹扩展行为进行了观测,给出了退火前后疲劳裂纹扩展速率及疲劳寿命随表面粗糙度增大而改变的定量结果。结果表明：退火后紫铜主要衍射峰出现窄化,其内部晶粒增大;材料屈服应力、弹性模量、维氏硬度及疲劳性能显著降低。试件疲劳寿命受表面粗糙度影响的敏感性在退火后降低。     

金属材料在拉伸条件下不同屈服形态的原因探讨

金属材料在拉伸的条件下，其载荷－伸长曲线（即Ｐ－Δｌ曲线）通常会出现三种类型的形态，即锯齿形、平台形和渐变形（幂函数形），本文初步分析了产生不同形态屈服的可能原因，并讨论了其产生的物理背景和力学条件。