几何尺寸组织定量分析法测量动脉壁静态工作应变

本文利用生物组织固定技术 ,发展了一种直接测量动脉壁内应变分布的方法 :组织定量应变分析法。并用该方法测量了白兔颈动脉壁在 5 0mmHg、10 0mmHg、15 0mmHg、2 0 0mmHg模拟生理载荷状态下的应变分布。将测量结果与应用张开角应变分析法得到的理论应变分布进行了比较。结果表明 :用组织定量应变分析法直接测量的环向应变分布与由理论分析得到的环向应变分布较为一致。这表明组织定量应变分析法是一个可行的直接测量动脉壁内应变的方法。同时 ,本文通过白兔颈动脉环向应变测量结果证明了均匀应变状态的存在。

18Cr2Ni4WA钢的组织特征尺寸与其疲劳极限

研究了１８Ｃｒ２Ｎｉ４ＷＡ钢的奥氏体实际是精度和马氏体束径对其疲劳极限的影响．结果表明，这种钢的疲劳极限σｗ与其原奥氏体晶粒度或马氏体板条束径尺寸ｄ的关系为σｗ＝Ｃ＋ｋｄ（－１／２）（Ｃ，ｋ均为常数）；马氏体束径ｄＭ和原奥氏体晶粒度ｄＡ之间的关系为ｄＭ（－１／２）＝Ｃ＋ｄＡ（－１／２）．通过测量钢的组织特征尺寸估算其疲劳性能．

Ti-22Al-25Nb合金双尺寸板条组织不同温度拉伸性能研究

通过B2相区等温锻造工艺和O+B2相区固溶时效处理获得了Ti-22Al-25Nb合金双尺寸板条组织。研究了双尺寸板条在室温、400、600℃的拉伸性能,分析了断口特征,揭示了在不同温度下的拉伸断裂机制。结果表明:测试温度的变化显著影响双尺寸板条组织的拉伸性能。随温度的升高,双尺寸板条组织的强度下降,塑性提升。室温断裂机制为准解理断裂,断口特征以宏观解理断裂和微观条形刻面加撕裂棱为主;高温断裂机制为韧窝断裂,400℃断口特征以等轴浅韧窝和微孔为主,600℃断口特征呈现明显较大且深的等轴韧窝。

超重力燃烧合成大尺寸织构铁基金属材料

利用超重力结合自蔓延高温合成技术,采用Fe2O3/Al铝热体系,制备出大尺寸织构铁基金属材料,并对其显微组织及相结构进行了分析。结果表明,该金属材料沿离心力方向具有显著择优取向的大尺寸单相晶粒组织,其基体相结构为BCC_B2固溶体型含铝α-Fe;测量了材料的硬度,并对该工艺潜在应用前景进行了探讨。

板条组织Ti-22Al-25Nb合金高温高周疲劳行为

研究了双尺寸板条组织Ti-22Al-25Nb合金在650℃和700℃下的高周疲劳行为,采用升降法测试了合金的高温高周疲劳强度极限。当应力比R=-1,循环周次Nf=107次时,650℃和700℃的疲劳强度极限分别为470MPa和400MPa。由于不同阶段的高周疲劳裂纹在高温条件下暴露的时间不同导致试样断口表面的氧化产物不同,从而使得高温高周疲劳试样的断口上呈现出不同颜色的区域。通过颜色的变化发现疲劳裂纹既可萌生于试样表面,也可萌生于次表面,并且高周疲劳裂纹在次表面形核的试样具有更高的疲劳寿命。此外,研究发现双尺寸板条组织在高温高周疲劳损伤过程中以胞状析出的形式发生B2→β+O相变,形成组织中的不均匀区域,促使疲劳裂纹在此优先形核。

巧用坐标法保证组合体尺寸的完整性

文章针对《机械制图》教材中用形体分析法标注组合体尺寸的局限,通过探索和实践,提出标注组合体尺寸的另一方法——坐标法,解决了各类组合体视图、剖视图尺寸标注的完整性问题。

Combined effects of ECAP and subsequent heating parameters on semi-solid microstructure of 7075 aluminum alloy

The combined effects of equal channel angular pressing (ECAP) and subsequent heating to a semi-solid temperature on the microstructural characteristics of the 7075 aluminum alloy were investigated. The microstructure is influenced by several parameters including the number of ECAP passes, ECAP route, consequent heating temperature, and holding time. The effects of these parameters on the microstructural characteristics including grain size and shape factor of the 7075 aluminum alloy were studied using experimental tests and Taguchi method. The results indicate that five-pass ECAP in route BA and subsequent isothermal holding at 630 °C for 15 min are more appropriate for achieving a semi-solid microstructure. The processing route and holding time have the highest impact on the grain size while the number of ECAP passes and heating temperature have the least impact on the grain size. Meanwhile, the shape factor is significantly influenced by the processing route, holding time and heating temperature while it is less influenced by the number of ECAP passes.

Influence of B4C particle size on microstructure and damping capacities of(B_(4)C+Ti)/Mg composites

To study the influence of B4C particle size on the microstructure and damping capacities of(B_(4)C+Ti)/Mg composites,in situ reactive infiltration technique was utilized to prepare Mg-matrix composites.The microstructure,produced phases and damping capacities of the composites prepared with different particle size of B4C were characterized and analyzed.The results show that the reaction between B4C and Ti tends to be more complete when finer B_(4)C particle was used to prepare the composites.But the microstructure of the as-prepared composites is more homogenous when B4C and Ti have similar particle size.The strain-dependent damping capacities of(B_(4)C+Ti)/Mg composites improve gradually with the increase of strain amplitude,and composites prepared with coarser B4C particles tend to have higher damping capacities.The temperature-dependent damping capacities improve with increasing the measuring temperatures,and the kind of damping capacities of the composites prepared with 5mm B4C are inferior to those of coarser particles.The dominant damping mechanism for the strain-damping capacity is dislocation damping and plastic zone damping,while that for the temperature-damping capacity is interface damping or grain boundary damping.

Numerical simulation of powder effect on solidification in directed energy deposition additive manufacturing

An integrated simulation of powder effects on particle temperature and microstructural evolution in laser directed energy deposition additive manufacturing process was carried out.The spatial distribution of the flying powder particles was simulated by the discrete element method to calculate the energy for the flying powder particles under the laser−particle interaction with electromagnetic wave analysis.Combined with the phase field method,the influence of particle size on the microstructural evolution was studied.The microstructural evolution is validated through comparison with experimental observation.Results indicate that the narrow particle size distribution is beneficial to obtaining a more uniform temperature distribution on the deposited layers and forming smaller equiaxed grains near the side surfaces of the sample.Appropriate powder particle size is beneficial to the conversion of the electromagnetic energy into heat.Particles with small size are recommended to form equiaxed grains and to improve product quality.Appropriate powder flow rate improves the laser energy efficiency,and higher powder flow rate leads to more uniform equiaxed grains on both sides of the cross-section.

Precipitation location of secondary phase and microstructural evolution during static recrystallization of as-cast Ti-25V-15Cr-0.3Si titanium alloy

The microstructural evolution and precipitation location of the secondary phase of an as-cast Ti-25 V-15 Cr-0.3 Si titanium alloy were investigated via isothermal compression experiments and heat treatment. The average aspect（length-to-width） ratio, average area and size of the grains at different heat treatment temperatures and holding time were analyzed and the effects of deformation and annealing time on the grain area and size were considered. It was found that the grain size was strongly influenced by the height reduction and holding time. Grain growth was significant when annealing time increased from 10 min to 2 h at 950 °C and height reduction of 30%; however, grain growth was minimal at annealing time between 2 and 4 h. Many dispersion particles were observed to form in continuous chains; the precipitation location was confirmed to be along initial grain boundaries, and the dispersion particles were identified to be Ti5 Si3 phase by TEM.

Machining characteristics of fine grained AZ91 Mg alloy processed by friction stir processing

AZ91Mg alloy was considered and friction stir processing(FSP)was adopted to achieve grain refinement to investigatethe effect of grain size and secondary phase on machining characteristics during drilling at various speeds and feeds.Super saturatedAZ91Mg alloy was obtained after FSP and the grain refinement was achieved from(166.5±8.7)μm to(21.7±13.5)μm.Surprisingly,hardness reduced for FSP AZ91Mg alloy(88.95±6.1)compared with AZ91alloy(108.2±15.6),which was attributed to the reducedsecondary phase.However,the mean cutting force for FSP-treated(FSPed)AZ91Mg alloy was marginally increased.The edgedamage of the drilled holes was lower for FSPed AZ91Mg alloy compared with unprocessed AZ91Mg alloy.Hence,it can beunderstood that the grain refinement may slightly increase the cutting forces during drilling but better edge finishing can be achievedin machining of AZ91Mg alloy.

Correspondence between low-energy twin boundary density and thermal-plastic deformation parameters in nickel-based superalloy

To deeply understand and even describe the evolutions of the low-energy twin boundary density(BLDΣ3n)in a thermal-plastic deformation process,an improved twin density model as a function of average grain size and stored energy is developed.For Nimonic 80A superalloy,the model is solved based on the EBSD statistical results of grain size and BLDΣ3n in the specimens compressed at temperatures of 1273−1423 K and strain rates of 0.001−10 s−1.The corresponding relationships of BLDΣ3n with stored energy and grain size varying with temperature and strain rate are clarified by the superimposed contour plot maps.It is summarized that BLDΣ3n increases with increasing stored energy and decreasing grain size,and higher BLDΣ3n with finer grains corresponds with lower temperatures and higher strain rates.Such relationships are described by the improved twin density model,and the prediction tolerance of the solved model is limited in 2.8%.

Influence of alloying elements on microstructure and microhardness of Mg-Sn-Zn-based alloys

The phase evolution in （88%-91%）Mg-8%Sn-l%Zn-X （X=A1, Mn and/or Ce） system was analyzed via CALPHAD method and simulations were used in precise selection of the chemical composition. The influence of the addition of different alloying elements such as A1, Mn and Ce on the microstructure and microhardness of Mg-8%Sn-l%Zn-based alloys was investigated. Combined addition of A1 and Mn shows features distinct from separate addition of A1 or Mn. Additions of l%AI and l%Mn to base alloy result in the formation of massive A1-Mn phase in a-Mg matrix grains. Addition of Ce element can refme the second eutectic precipitates and form intermetallic compounds with Sn. Fine rod-like Sn-Ce phase presents mainly on the grain boundaries and plays a role in inhibiting grain growth. The effects of alloying elements on Vickers microhardness and indentation size effect of base alloy were examined.

Political Skill of Narcissistic Leaders

A vast number of researches and studies have been conducted on narcissism, since the term was used to explain a psychological phenomenon in 1898. However, the discussions about narcissists as organization members or leaders have recently become a research topic in the organizational sciences. In this scope, the recent research on narcissism indicates that narcissistic leaders can either cause organizational tragedies or contribute to organizational success by their great vision. In addition to narcissism, another popular leadership feature is political skill which has attracted considerable attentions in recent years, and become one of the important topics of management studies. Moreover, political skill has been asserted to be a positive characteristic which is related to develop vision and team insight as well as to increase in members＇ trust and support; whereas narcissism has both harmful and beneficial effects on organizations. In this study, the relationships between the dimensions of narcissism and political skill are examined via the 16-item Narcissistic Personality Inventory （NPI） and the 18-item Political Skill Inventory. Analysis has shown that the authority, which is the adaptive dimension of narcissism, correlates positively with social astuteness and networking ability dimensions of political skill. Accordingly entitlement, which is one of the maladaptive dimensions of narcissism, correlates significantly and negatively with the networking ability, interpersonal influence and apparent sincerity dimensions of political skill. When political skill is considered as a composite score, the findings indicate that the authority dimension of narcissism has a positive effect whereas, the entitlement dimension has a negative effect on political skill. Besides, implications for future studies are discussed

Microstructure refinement of AZ31 alloy solidified with pulsed magnetic field

The effects of a pulsed magnetic field on the solidified microstructure of an AZ31 magnesium alloy were investigated.The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied to the solidification of the AZ31 alloy.The average grain size of the as-cast microstructure of the AZ31 alloy is refined to 107 μm.By quenching the AZ31 alloy, the different primary α-Mg microstructures are preserved during the course of solidification.The microstructure evolution reveals that the primary α-Mg generates and grows in globular shape with pulsed magnetic field, contrast with the dendritic shape without pulsed magnetic field.The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface, which makes the nucleation rate increased and big dendrites prohibited.In addition, the Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.

Self-organized Criticality in an Earthquake Model on Random Network

A simplified Olami-Feder-Christensen model on a random network has been studied. We propose a new toppling rule -- when there is an unstable site toppling, the energy of the site is redistributed to its nearest neighbors randomly not averagely. The simulation results indicate that the model displays self-organized criticality when the system is conservative, and the avalanche size probability distribution of the system obeys finite size scaling. When the system is nonconservative, the model does not display scaling behavior. Simulation results of our model with different nearest neighbors q is also compared, which indicates that the spatial topology does not alter the critical behavior of the system.

Effect of brazing parameters on fillet size and microstructure of cladded fin-microchannel tube joints

This work concerns the optimization of furnace brazing conditions for joining micro-multiport aluminum tubes and fins made with AA4343/AA3003/AA4343 brazing sheet in mini-assemblies mimicking the core of an automotive heat exchanger.Taguchi method was used for design of experiment,considering five process parameters with two levels of values.The aim was to maximize the fillet size of the brazed joints,which has an important influence on the thermal integrity and mechanical properties.Fillet length measurements of brazed joints were performed with a metallographic microscope.The statistical analysis allowed to obtain the optimum values of process parameters(peak temperature,residence time,heating rate,microchannel tube type and flux).At a 95%confidence level,the variability of fillet length is most significantly affected by the peak brazing temperature(77%),residence time(15%)and heating rate(7%).The predicted maximum fillet length was(152±11)μm,which was corroborated by confirmation trials.The microstructural analysis of tube−fin joints showed that variations in peak temperature and residence time affect only the size of the eutectic zone of fillet formed,but not the nature or composition of the constituent phases.

Microstructure and mechanical properties of AZ31 alloy ingot fabricated by semi-continuous casting

The AZ31 alloy ingot with diameter of 110 mm and length of 3500 mm was fabricated successfully. The compositions and microstructure morphologies of the ingot at different locations were performed, which indicated that the chemical composition distributed homogeneously through the whole alloy ingot and the average grain size increased from the surface to the center. The results of the EDS and element face-scanning illustrated that the eutectic compounds mainly consisted of fl-Mg17Al12 and a small amount of fl-Mgl7（AlZn）12. Furthermore, slight improvements of the strength and ductility were observed from the center to the surface along the axial direction of the alloy ingot, while both the strength and elongation to failure of the samples along the radial direction are higher than that along the axial direction. The fine grain strengthening was the main contributors to the strength of the as-casted AZ31 alloy.

冷速对TC4钛合金组织和性能的影响

对TC4钛合金进行了不同冷速的热处理,得到了不同层次(晶粒、丛域、片层)的显微组织,建立了以片层组织尺寸为基础的Hall-Petch关系。结果表明:随着冷却速率的增加,片层细化,对应的屈服强度和抗拉强度逐渐升高,塑性逐渐降低。片层尺寸和力学性能之间较好地符合Hall-Petch关系,片层尺寸是影响力学性能的主要特征参量。

Microstructural evolution of rolled Mg-5Zn-3Nd(-Zr) alloy

A mini-type rolling machine was employed for multi-passes rolling of a Mg-5Zn-3Nd(-Zr)(mass fraction,%)wrought alloy.For the sake of providing experimental basis for magnesium alloy rolling process,optical microscopy,SEM and TEM observations were used to study the microstructure evolution of magnesium alloys subjected to different rolling reductions before and after annealing.Investigations show that multi-passes can be achieved for this alloy at ambient temperature,but 330℃,15 min annealing was needed for next pass rolling,and total deformation degree was 66%.With the increase in total deformation degree, rolling streams form and the average grain size decreases gradually.The microstructure after rolling is mainly composed of twining, and multiple twining in parallel distribution is also observed.The average grain size in the as-cast condition is about 50μm and decreases to about 10-20μm after rolling,whereas the twinning spacing is limited to 1-2μm.SAED analysis in the twinning area indicates that twinning takes place at{10 1 1}plane.Complete recrystallization can occur in Mg-5Zn-3Nd(-Zr)alloys with various rolling reductions and after 200℃,120 min or 300℃,10 min annealing.Meanwhile,grain growth is apparent under heat treatment at 300℃.