The relationship between inert gas wash-out and radioactive tracer microspheres in measurement of bone blood flow: effect of decreased arterial supply and venous congestion on bone blood flow in an animal model

Twenty cases of carpal bone dislocation were encountered during a 7-year period, with an average of 27 months of follow-up. There were ten types of dislocation in this series; the most common type was transscaphoid perilunate dislocation which was seen in nine cases. In addition, there were two scaphoid subluxations; one volar lunate dislocation; one dorsal perilunate dislocation; one scaphoid perilunate dislocation; one hamate and pisiform dislocation; one transhamate pisiform dislocation; one trapezoid dislocation with dislocation of carpometacarpal joints two to five; one dislocation of the trapezium, trapezoid, and carpometacarpal joints two to four; and two trapezium periscapholunate dislocations. Methods of treatment included open reduction, closed reduction, proximal row carpectomy, total wrist arthrodesis, and excision of the lunate. In this series, the patterns of dislocation were different for crushing injuries and dorsiflexion injuries. The clinical results associated with the soft-tissue injuries of the ipsilateral hand were mostly caused by crushing forces. Although carpal instabilities were noted, there was no significant correlation between the clinical and roentgenographic results in some of our cases. Best results invariably relied on a stable anatomic reduction and an adequate period of immobilization. Poor results were demonstrated in the cases with incomplete initial reduction, secondary degenerative arthrosis, or nonunion.     

Effects of hydrogen and carbon on thermally activated deformation in nickel

Deformation experiments were performed to determine the effects of hydrogen and carbon on the activation parameters for dislocation slip in nickel. The techniques used were isothermal stress relaxation and differential temperature measurements. These methods allowed determination of the activation enthalpy and activation area for dislocation motion in nickel and the effects of hydrogen and carbon on these parameters. The results show that hydrogen increases the dislocation mobility in Ni and in NiC alloys by reducing the activation enthalpy for dislocation motion, while carbon reduces the dislocation mobility by increasing the activation enthalpy. Hydrogen solutes decrease the activation area for dislocation motion in both pure Ni and in NiC alloys.     

溶质钒原子与铁的[100](001)位错的相互作用

采用改进分析型EAM模型（MAEAM）研究了溶质钒与铁的[100]（001）位错的相互作用.对铁的[100]（001）位错及掺杂结构用分子动力学方法进行了弛豫.计算了钒在这些掺杂格点上的能量,以及溶质钒与铁的[100]（001）位错缺陷系统的能量,发现在位错芯区域钒的格点能高,随着钒与位错芯之间距离的增加,其格点能降低;溶质钒替代拉伸区位错芯位置的铁原子时,钒与位错的相互作用能最强,缺陷系统的能量最低、结构最稳定.     

强变形过程中铁镍合金的微观结构演化机制

 采用透射电镜观察了铁镍(Fe 32%Ni)合金在形变温度500 ℃(＜05Tm)、形变速率10-2 s-1的变形条件下多轴锻造变形过程中的微观结构演变。结果表明,低温多轴锻造强变形可明显细化晶粒,细化过程为：首先,位错墙、位错缠绕等结构通过大量位错滑移运动在原始晶粒内形成;其次,不同方向的变形导致不同方向的滑移系开动,从而致使不同方向的位错墙互相交叉,将原始粗晶粒细分成小尺寸的胞块结构,当变形量达到一定程度时,位错墙和位错缠绕结构内的位错开始重新排列,形成小角度晶界,导致亚晶粒形成;由于变形量不断增加强迫大量的位错在亚晶界处积聚、重排,同时不同方向的变形造成亚晶发生转动,位错重新规则排列及亚晶转动使小角度的亚晶界转变为大角度晶界,从而形成细小的新晶粒。     

Dislocation evolution in metals during irradiation

Physical models are developed for the evolution of the dislocation density in metals subject to irradiation at elevated temperatures. Two basic processes are shown to account for the experiment observations: the generation of dislocation line length takes place by the Bardeen-Herring mechanisms, whereas dislocation loss can be described in terms of dislocation dipole annihilation. Only two microstructural parameters, namely the mesh length and the bias variance, need to be introduced and adjusted in order to reproduce the experimental observations on dislocation evolution in austemtic stainless steels.     

位错滑移运动与运动阻力辨析

对位错在点阵周期场中运动时需要克服的阻力,以及影响阻力大小的因素作了辨析和讨论.含有位错的晶体变形,确定无疑是位错在外力场作用下滑移运动的宏观结果.对位错在完整晶体中运动分析表明,派-纳力对温度十分敏感.一定温度下,位错并非仅处于某一势能水平.即使外力应力小于派纳力,位错也可以通过扭折侧向运动,且由于热起伏造成的能量隆起,进而侧向扩展,使位错更容易运动.     

The Contribution of Dislocation Density and Velocity to the Strain Rate and Size Effect Using Transient Indentation Methods and Activation Volume Analysis

Constant load indentation creep and load relaxation tests were performed on several FCC Al, Ag, and Ni metals that exhibit indentation size effect (ISE) to examine the coupled relationship between the activation volume V* at specific loads, the dislocation density ρ, and the dislocation velocity (v) from kinetics-based perspective. The influence of the ISE on the dislocation velocity and the activation volume is thoroughly examined using the two independent indentation creep and load relaxation experiments. This study is carried out based on the general experimental and theoretical hypothesis that the ISE is driven by a dislocation mechanism, specifically the increase in the geometrically necessary dislocation density at shallow depth of indentation due to the presence of a large strain gradient. Geometrically necessary dislocations dominate the material’s propensity to work harden when their density exceeds the density of statistically stored dislocations and are primarily considered responsible for the size effects observed in indentation. Based on the preestablished bilinear behavior and the decrease in the activation volume with hardening due to dislocation–dislocation interaction in indentation creep experiments by Elmustafa and Stone, 2003, we demonstrate that the dislocation velocity exhibits a bilinear behavior when plotted vs hardness using the Orowan’s relation. Ag and Ni distinctively depict a bilinear behavior in the dislocation velocity with hardness, whereas Al exhibited a rather linear behavior. This can be explained by the fact that aluminum’s work-hardening rate is higher due to the increase in the rate and intensity of cross-slip and dislocation climbing.

     

In vitro synthesis and characterization of a cartilaginous meniscus grown from isolated temporomandibular chondroprogenitor cells

Between 1984 and 1991, 57 patients with diagnosis of an acute or recurrent patellar dislocation were treated operatively using proximal realignment with vastus medialis transfer and lateral release (Insall operation). A total of 45 patients (15 with acute and 30 with recurrent patellar dislocation) were reviewed at an average follow-up of 6.5 years (2-9.6 years). The average age at injury was 21.5 years, with a predominance of female patients. Follow-up examination included routine knee examination, clinical review using the modified knee scoring scale of Larsen and Lauridsen, sports activity level and subjective satisfaction. Radiographics from 27 patients (60%) were evaluated. One patient from each group suffered recurrence of patellar dislocation. All patients had stable knee joints and a full range of motion. There was no statistical difference in the pre- and postoperative sports activity level in both groups. Three patients (19.9%) with acute patellar dislocation and seven patients (23.3%) with recurrent patella dislocation had excellent results using the Larsen and Lauridsen score scale. Ten patients (66.6%) with acute and 12 (39.9%) with recurrent dislocation had good results. One patient with recurrent patellar dislocation had a fair result. Subjective evaluation revealed the operative result in 93% of cases as very good, good or satisfactory. Patellofemoral osteoarthritis was seen in 11 (40.7%) of 27 patients. Our results show good clinical results for the treatment of acute patellar dislocation in young, active patients with the proximal realignment procedure. The recurrence rate of patellar dislocation can be reduced for acute and recurrent patellar dislocation. Subjective satisfaction with this procedure is rated very good.     

Evolution of dislocation structures and deformation behavior of iron at different temperatures: Part II. dislocation density and theoretical analysis

The evolution of dislocation density in iron deformed at 173 K and at room temperature has been examined by transmission electron microscopy (TEM). At room temperature, the dislocation density in the cell walls increases as the deformation progresses up to large strains, whereas in cell interiors, the density evolves toward a saturation value. A linear relationship exists between the flow stress and the square root of total dislocation density both at 173 K and room temperature. The dependence of deformation behavior on the evolution of dislocation structures is discussed in terms of a model considering the dislocation distribution during deformation. Comparison of the calculated result using this model with the experimental curve at room temperature gives excellent agreement. The changes of deformation behaviors at different temperatures can be described by the effect of temperature on the evolution of dislocation distribution.     

Cyclic evolution of the defect structure in a deformation macrolocalization zone in an HCP Zr-Nb alloy

The microstructure of a Zr-1% Nb is studied in a deformation macrolocalization zone during its transformation into a neck. The related dislocation transformations are found to be cyclic, and this cyclicity is accompanied by oscillatory changes in the volumes occupied by different dislocation substructures, the scalar dislocation density, the subboundary density, and periodic relaxation of internal stresses as a result of the decomposition of low-angle subboundaries and dislocation redistribution.     

Dislocation mobility in heavily doped silicon single crystals

Dislocation mobility has been studied in heavily doped silicon single crystals by kilohertz internal friction measurements. The dopant effect on dislocation mobility previously reported in germanium and silicon under plastic deformation has now been seen in silicon under the influence of much lower applied stresses. The low strains and only moderately elevated temperatures used in the present investigation allow the dislocations to oscillate only slightly about their equilibrium positions. The results from the slight dislocation excursions have led to a unified kink model of dislocation damping in silicon. The dopant effect on dislocation mobility is attributed directly to the surplus electronic carriers in the immediate vicinity of the dislocation kink. The intrinsic carrier concentration in the local vicinity of the dislocation has been found to be 100 times greater than the corresponding bulk value.     

Interfacial dislocation networks strengthening a fourth-generation single-crystal TMS-138 superalloy

The γ/γ′ interfacial dislocation networks in several creep-ruptured superalloys were analyzed. It was found that the morphologies of dislocation networks differ slightly from each other in these alloys. The fourth-generation superalloy has finer dislocation networks and keeps a relatively stable state. Comparatively, the interfacial dislocations in the third-generation superalloy show obvious curved features associated with possible climb or slip. These interfacial dislocation characteristics can be correlated with the creep behavior of these superalloys. The mechanisms of evolution of the interfacial dislocation networks were discussed.     

单晶铜塑性变形的二维离散位错动力学模拟研究

针对亚微米尺度晶体元器件在加工和服役中出现的反常力学行为和动态变形等问题,基于离散位错动力学理论建立了单晶铜塑性变形过程的二维离散位错动力学模型。该模型考虑外加载荷、位错间相互力和自由表面镜像力对位错的作用机制,引入了截断位错速度准则。与微压缩实验对比验证了模型的正确性,并且能够描述力加载描述的位错雪崩现象。应用该模型分析了不同加载方式和应变率下位错演化及力学行为,结果表明:当外部约束为力加载和位移加载时,应力应变曲线分别呈现出台阶状的应变突增和锯齿状的应力陡降,位错雪崩效应的内在机制则分别归结为位错速度的随机性和位错源开动的间歇性;应变率在102～4×104 s?1范围内,单晶铜屈服应力的应变率敏感性发生改变,位错演化特征由单滑移转变为多滑移面激活的均匀变形,位错增殖逐渐代替位错源激活作为流动应力的主导机制。      

Acoustic emission: A probe into dislocation dynamics in plasticity

Acoustic emission (AE) from deforming copper and its dilute alloys was recorded at varied frequencies at room temperature and up to 500°C. All results proved to be compatible with the spurt-like dislocation movement between two bounds being the AE generating event. AE presents a maximum in the beginning of stage II deformation when event lifetimes in the range of microseconds correspond to the recording frequency. Furthermore, AE decreases rapidly with decreasing event size (by work-hardening) resp. decreasing dislocation mobility (by elevated temperature or solute content). In copper viscous dislocation movement achieves some m/s. As event bounds dislocation or cell walls should act. Solution hardening increases the stress exponent in dislocation mobility, but it is demonstrated, that doubt is advisable in some of such results. So AE proves to serve as probe into dislocation dynamics inside the bulk of a work-hardening metal.     

Dislocation structure and deformation in iron processed by equal-channel-angular pressing

The evolution of dislocation structure in pure Fe during equal-channel-angular pressing (ECAP) is investigated. Also, the effect of the formation of this dislocation structure on deformation and fracture behavior is examined. The results show that intensive dislocation cell blocks are present after one pass and even more after subsequent pressings. The low-energy dislocation structures (LEDS) may have changed into the high-energy dislocation structures (HEDS) in the final several pressings. The high-density array of dislocations plays a significant role in strengthening. The HEDS may cause the materials to lose work-hardening ability and show a cleavage morphology of the fracture surface. A proper subsequent annealing treatment will lead to the evolution of HEDS to LEDS while maintaining little grain growth. This change in the nature of dislocation structures allows ultrafine-grained materials to achieve an excellent combination of high strength and high ductility.     

Interfacial ledge structures in Ni3 Al-Ni3Cb eutectic composites

The interfacial structure of Ni₃Al-Ni₃Cb directionally solidified eutectic composites has been investigated by transmission electron microscopy. These interfaces contain at least three distinguishable arrays of features. Two of the arrays, misfit dislocations, have been discussed previously by Nakagawa and Weatherly. The third set, ledges which can fulfill both structural and kinetic growth functions, may interact with the dislocation arrays through strain-energy mechanisms. The interaction is manifested both as a local alteration of the line vector of the dislocation in certain circumstances, and as a change in the response of the dislocation image to ±g electron-microscope image-contrast experiments. A simple model of the strain field of a ledge based on that of an edge dislocation is formulated to rationalize the behavior of a misfit dislocation lying in close proximity to a ledge. The interaction of ledges and dislocation segments is expected to have significance in physical processes of practical interest such as production of matrix slip dislocations, misfit dislocation rearrangement, boundary sliding, and coarsening, and these processes are discussed in some detail.     

Threshold stresses for dislocation climb over hard particles: The effect of an attractive interaction

We present a model for the effect of an attractive interaction between dislocations and hard spherical particles on the process of dislocation bypass by local climb. The interaction is treated by assigning a line tension to the dislocation which is lower in the vicinity of the particle than in the matrix. We find that even for very modest interactions, the strongest barrier to dislocation bypass is no longer provided by the climb obstacle, but rather by the detachment of the dislocation from the particle after climb over the particle is complete. The model provides a possible explanation for some experimentally observed dislocation configurations in crept ODS superalloys and for the creep thresholds which are typical of such alloys.     

Dislocations in continuous filament reinforced W/NiAl and Al2O3/NiAl composites

Continuous filament reinforced W/NiAl and Al₂O₃/NiAl composites (as-processed, annealed, and thermally cycled) have much higher dislocation densities than that of monolithic NiAl. These higher dislocation densities resulted from the relaxation of thermal residual stress, which developed during the cooling of the sample from elevated temperatures and was caused by the difference in the coefficients of thermal expansion between the matrix and the reinforcement. The dislocation density in the region adjacent to the matrix-filament interface was high and decreased only slightly with distance from the interface in the 30 vol pct composites. The as-processed and annealed composites exhibited a rather homogeneous dislocation density in the matrix. After thermal cycling, these composites showed no large difference in the dislocation density and morphology. However, there were local regions of lower dislocation densities. This difference was examined in relationship to filament fracture, surface matrix cracking, and degree of bonding.     

Work Hardening,Dislocation Structure,and Load Partitioning in Lath Martensite Determined by <Emphasis Type="Italic">In Situ</Emphasis> Neutron Diffraction Line Profile Analysis

A lath martensite steel containing 0.22 mass pct carbon was analyzed in situ during tensile deformation by high-resolution time-of-flight neutron diffraction to clarify the large work-hardening behavior at the beginning of plastic deformation. The diffraction peaks in plastically deformed states exhibit asymmetries as the reflection of redistributions of the stress and dislocation densities/arrangements in two lath packets: soft packet, where the dislocation glides are favorable, and hard packet, where they are unfavorable. The dislocation density was as high as 10¹⁵ m^?2 in the as-heat-treated state. During tensile straining, the load and dislocation density became different between the two lath packets. The dislocation character and arrangement varied in the hard packet but hardly changed in the soft packet. In the hard packet, dislocations that were mainly screw-type in the as-heat-treated state became primarily edge-type and rearranged towards a dipole character related to constructing cell walls. The hard packet played an important role in the work hardening in martensite, which could be understood by considering the increase in dislocation density along with the change in dislocation arrangement.