Ductile fracture in HY100 steel under mixed mode I/Mode II loading

A number of criteria have been proposed which predict the direction of cracking under mixed Mode I/Mode II loading. All have been evaluated for brittle materials, in which a crack subjected to tension and shear propagates normal to the maximum tensile stress (i.e. fracture is of the Mode I type). In a ductile material, however, a notch subjected to mixed Mode I/Mode II loading may initiate a crack in the direction of maximum shear. This paper shows that the profile of the notch tip changes with increasing mixed mode load in such a way that one side of the tip blunts while the other sharpens. Various specimens, subjected to the same mixed mode ratio, were unloaded from different points on the load-displacement curves to study the change in notch-tip profile. Studies under the Scanning Electron Microscope (SEM) have shown that cracks initiate at the sharpened end, along a microscopic shear band. Using a dislocation pile-up model for decohesion of the carbide-matrix interface, a micromechanical model has been proposed for crack initiation in the shear band. It is shown that a theoretical prediction of the shear strain required for decohesion gives a result that is, of magnitude similar to that of the shear strain at crack initiation measured in the experiments.     

Acoustic emission in ferroelectric lead titanate ceramics: Origin and recombination of microcracks

Lead titanate doped with niobium forms solid solutions of the type Pb_1−x/2(Ti_1−xNb_x)O₃ where x = 0.02 and 0.05. The ferroelectric Curie temperature of these solid solutions is around 465°C, compared to 490°C for PbTiO₃ at the cubic-tetragonal phase change. The lattice distortions at and below the Curie temperature generate internal stresses, leading to microcraking. The microcracking in lead titanate ceramics is detected by acoustic emission methods as a function of heating to and cooling from various temperatures upto 800°C. From this study it is concluded that microcracking is primarily triggered by the sudden lattice parameter changes at the Curie temperature on cooling and that it is enhanced by the anisotropic thermal expansion below the transition. The healing of microcracks is a gradual process and escapes direct detection by the acoustic emission methods. An indication of the recombination of microcracks on heating has been obtained by the total number of acoustic emission counts in samples cooled from various temperatures and also from fixed temperatures after different periods.     

Structure and mechanical properties of iron sintered by electric contact heating

Translated from Poroshkovaya Metallurgiya, No. 1(337), pp. 17–22, January, 1991.     

醇–水混合溶剂凝胶注模制备SiC多孔陶瓷的工艺与性能

将SiC陶瓷粉末、醇-水混合溶剂、丙烯酰胺-亚甲基双丙烯酰胺凝胶体系以及堇青石-锂辉石复合烧结助剂配制成料浆,采用凝胶注模成型–烧结工艺制备SiC多孔陶瓷,研究烧结助剂用量和烧结温度对多孔SiC陶瓷的形貌与显微结构、物相组成以及强度、孔径、开孔率与渗透率等性能的影响。结果表明:温度高于1 300℃时,复合烧结助剂熔融形成固溶体,从而实现SiC多孔陶瓷的低温烧结;随烧结助剂用量增加或烧结温度升高,SiC多孔陶瓷的开孔率和气体渗透速率均下降。在料浆中SiC陶瓷粉体体积分数为20%、烧结助剂质量分数为10%、醇水体积比为7:3、锂辉石与堇青石质量比为2:1的条件下,于1 370℃烧结后得到的SiC多孔陶瓷,孔隙率高、孔径分布集中(4~15μm),孔形貌呈均匀的三维无规则贯通结构,抗弯强度为8.5 MPa,开孔率达到67.9%,透气率为280.5 m~3/(m~2·Pa·h)。     

薄板坯连铸连轧工艺制备TRIP钢的力学性能与组织

在实验室条件下模拟薄板坯连铸连轧工艺试制了C-Si-Mn系TRIP钢.拉伸实验表明,实验钢的抗拉强度为610MPa,屈服强度为430MPa,屈强比为0.70,总延伸率为28.4%.组织观察发现,试样组织为铁素体+贝氏体+残余奥氏体的三相组织,实验钢中残余奥氏体的平均含量为5.8%.     

On the variations in the mechanical characteristics of metals under the action of an electric potential

The effect of an electric potential φ ≤ 5 V on the creep and microhardness of a number of metals and alloys is considered. The creep rate and microhardness are shown to vary as an excess electric charge is induced on a surface by applying a potential from a voltage source or due to a contact potential difference. These effects are nonmonotonic and irreversible, and their nature is discussed.     

放电等离子烧结原位制备MoSi_2陶瓷的显微组织与力学性能

以Mo、Si混合粉末为原料,采用放电等离子烧结技术原位制备MoSi_2陶瓷。利用X射线衍射仪、扫描电镜、维氏硬度计、电子万能材料试验机等,研究1 300,1 400和1 500℃下烧结的MoSi_2陶瓷物相组成、微观结构及力学性能。结果表明:MoSi_2陶瓷由MoSi_2和少量Mo_5Si_3/Mo_(4.8)Si_3C_(0.6)及SiO_2组成;随烧结温度升高,第二相Mo_5Si_3/Mo_(4.8)Si_3C_(0.6)含量增多,并发生Mo_5Si_3向Mo_(4.8)Si_3C_(0.6)的相转变;第二相Mo_5Si_3/Mo_(4.8)Si_3C_(0.6)含量增多可细化基体组织,材料沿晶断裂的比例增加,具有一定的强韧化作用;1 500℃烧结的MoSi_2陶瓷综合性能最佳,其致密度为99.5%,维氏硬度为9.8 GPa,抗弯强度和断裂韧性分别为313 MPa和2.9 MPa·m~(1/2)。     

不同原料凝胶注模制备莫来石陶瓷的结构与性能

分别以溶胶-凝胶法制备的莫来石粉末和分析纯级氧化铝/氧化硅混合粉末为原料,经过凝胶注模成形后,在1 400~1 600℃温度下无压烧结,制备莫来石陶瓷,研究原料种类及烧结温度对莫来石陶瓷的显微结构、力学性能和抗热震性能的影响。结果表明:以溶胶-凝胶法制得的莫来石粉末为原料时,随烧结温度升高,陶瓷的密度和抗弯强度都是先升高后降低,烧结温度为1 500℃时,材料的密度和抗弯强度最高,分别为3.13 g/cm~3和155.85MPa,经过5次1 400℃?100℃沸水间热震后抗弯强度保留率达54.99%。以氧化铝/氧化硅混合粉末为原料时,起始烧结温度降低,1 400℃下烧结的陶瓷即具有较高的密度和抗弯强度,分别为3.01 g/cm~3和106.40 MPa,热震后的抗弯强度保留率为77.80%。抗弯强度随烧结温度升高而下降,烧结温度为1 600℃时抗弯强度下降至74.21MPa。     

Control systems of melting electric furnaces in metallurgy and mechanical engineering

The development and improvement of melting electric furnaces and the attendant technological processes are accompanied by development in the field of creating compatible automatic control systems. The automation of the functioning of equipment can also modify the furnaces that operate several decades and can prolong their life.     

Compaction and grain growth in alumina ceramics under microwave sintering

The laws governing the transformations of the porous and grain structures that occur in Al₂O₃-based ceramics during microwave sintering are investigated. These processes are very similar to analogous processes that occur during coherent compaction of powders. Under microwave sintering the ceramic preforms retain a wide range of porosity and microstructure for a long time. As a result strong capillary forces exist throughout the process, causing active compaction. On the basis of the experimental data we suggest that the heating rate and the bulk mode of the heating are not the only factors that accelerate the consolidation of the ceramics under microwave sintering. Institute of Problems in Material Science, National Academy of Sciences of Ukraine, Kiev. Institute of Applied Physics, Russian Academy of Sciences, Nizhnii Novgorod. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 8–13, July–August, 1997.     

Work hardening and mechanical equation of state in some metals in monotonic loading

The work hardening coefficients of Type 316 stainless steel niobium, and 1100 aluminum alloy are measured in tensile tests. It is demonstrated experimentally that in the measured stress, plastic strain rate, and temperature range the work hardening coefficient depends only on the stress and plastic strain rate. The significance of the experimental results is discussed in terms of the concept of the mechanical equation of state for plastic deformation.     

气体雾化Al-Zn-Mg-Cu铝合金粉末的形貌及组织性能研究

利用氮气雾化法制备了Al-Zn-Mg-Cu合金粉末,通过扫描电镜、光学显微镜和X射线衍射仪对粉末的形貌及组织特征进行了研究;检测了粉末热挤压法制备的合金棒材的力学性能,并对其断口进行了分析。结果表明:随着粉末颗粒尺寸减小,颗粒形状由以长条形为主转变为以近球形为主。同时,显微组织中的枝晶臂间距减小,晶粒细化效果明显;合金以α-Al相为主,还有少量η-MgZn2平衡相存在。随粉末颗粒尺寸减小基体过饱和度增加,基体相和MgZn2相衍射峰宽化;粉末粒度减小,挤压合金力学性能提高;挤压合金拉伸断口属于韧性断裂。     

Creep and fracture in model niobium-alumina laminates under shear loading

A simple experimental technique was developed to study the near-interface deformation and fracture behavior in ductile-phase-toughened brittle-matrix laminates subjected to elevated-temperature shear loading. In the study, specimens of Nb-foils bonded to Al₂O₃ blocks were subjected to shear loading parallel to the Nb/Al₂O₃ interfaces. The fracture path was controlled by the applied stress, the temperature and the thickness of the ductile Nb layers. At high shear stresses failure took place by brittle fracture within the Al₂O₃ phase with concurrent shear creep in the Nb, and multiple crack branching/arresting toward the interface. At lower stresses, shear-creep and ductile fracture within the Nb were the dominant damage modes. Shear deformation was found to localize along the mid-plane of the Nb, due to strengthening of the Nb adjacent to the interface via solid solution and precipitation resulting from interdiffusion. With thin 20 μm Nb-layers the fracture energy was low, similar to that found for pure Al₂O₃. Our findings suggest that the ductile-phase toughening of laminated brittle matrix composites depends critically on the thickness of the ductile phase. A concept of brittle-ductile transition to assist in the understanding of the toughness enhancement provided by ductile phase additions into a brittle matrix.     

混联法生产过程中硫的行为及排除方法

混联法生产过程中，随原料、燃料带入系统的硫，长期富集，给熟料窑、蒸发器等设备的操作造成了严重的影响。本从硫积累的成因入手，系统论述了硫的行为，以及国内外氧化铝生产过程排硫的方法，为完善氧化铝生产工艺，提高产品质量，提供了有价值的理论依据。     

煅烧石灰先投料后出灰新工艺的应用

通过对广钢石灰厂竖窑实施“先投料后出灰”创新工艺一年多的实践 ,石灰的产量提高了40 % ,CaO达到 90 %以上 ,活性度达到 30 0ml以上 ,团灰率提高了 8% ,炉衬寿命延长 9个月 ,取得较好经济效益 .     

机械镀锌过程中锌粉的受力及运动分析

采用粒径0.1-8.0μm范围的金属锌粉,在室温下以机械镀方式形成锌镀层。对镀桶内物质运动状态、机械碰撞力及锌粉颗粒之间的相互作用力进行了分析计算。结果表明：表面张力、液桥作用力和气泡团聚力是引起锌粉颗粒聚团的主要原因;分子间作用力、双电层作用力和溶剂化膜作用力对锌粉颗粒的聚团作用影响甚微。锌粉的紧实变形和镶嵌成层主要依靠机械碰撞力。     

Recruitment and proliferative responses of osteoblasts after mechanical loading in vivo determined using sustained-release bromodeoxyuridine

The regulation of cell proliferation or cell death by extracellular factors are the most intensely studied subjects in cell biology. Many conceptual problems remain to be clarified concerning the mechanisms that regulate the programmed cell death. In this work, we focus our attention on the possible role of protein kinase C activation during dimethyl sulfoxide (DMSO)-induced cell death. The present results suggest that the frequency of DMSO-dependent apoptosis of RPMI 8402 thymic lymphoma cells is increased by phorbol ester acetate supplementation. Enhancement of apoptosis can be abolished by cotreatment with the bisindolylmaleimide, a specific PKC inhibitor. The association between PMA and DMSO treatment provokes an early activation of an intracellular signaling mechanism that results, via sustained diacylglycerol elevation, in a possible long-term PKC activation.     

Decomposition of mixed rare earth concentrate by NaOH roasting and kinetics of hydrochloric acid leaching process

A new clean extraction technology for the decomposition of Bayan Obo mixed rare earth concentrate by NaOH roasting is proposed.The process mainly includes NaOH roasting to decompose rare earth concentrate and HCl leaching roasted ore.The effects of roasting temperature,roasting time,NaOH addition amount on the extraction of rare earth and factors such as HCl concentration,liquid-solid ratio,leaching temperature and leaching time on the dissolution kinetics of roasted ore were studied.The experimental results show that when the roasting temperature is 550℃ and the roasting time is 60 min,the mass ratio of NaOH:rare earth concentrate is 0.60:1,the concentration of HCl is 6.0 mol/L,the ratio of liquid to solid(L/S) 6.0:1.0,and the leaching temperature 90℃,leaching time 45 min,stirring speed 200 r/min,and the extraction of rare earth can reach 92.5%.The relevant experimental data show that the process of HCl leaching roasted ore conforms to the shrinking core model,but the control mechanism of the che mical reaction process is different when the leaching temperature is different.When the leaching temperature is between 40 and 70℃,the chemical reaction process is controlled by the diffusion of the product through the residual layer of the inert material.The average surface activation energy of the rare earth element is E_a=9.96 kJ/mol.When the leaching temperature is 75-90℃,the chemical reaction process is controlled by the interface transfer across the product layer(product layer interface mass transfer) and diffusion.The average surface activation energy of rare earth elements is E_a=41.65 kJ/mol.The results of this study have certain significance for the green extraction of mixed rare earth ore.     

Matrix cracking in unidirectional ceramic matrix composites under quasi-static and cyclic loading

Experimental data associated with the development of matrix cracks in unidirectional continuous silicon carbide fibre/calcium alumino-silicate matrix laminates under quasi-static loading are presented, including crack density, residual strain and hysteresis behaviour as functions of applied stress. Simple models are developed, based on an assumption of purely frictional load transfer between the fibre and matrix, which describe reasonably well the quasi-static stress-strain behaviour in the presence of cracks. Under tension-tension mechanical fatigue cycling it is found that the crack density stabilises at a relatively early stage in the test. Based on the quasi-static model, the changes in fatigue hysteresis loops on fatigue cycling are interpreted in terms of a reduction in the effective frictional interfacial shear stress.