高校学科建设人才引进视角的组织疲劳及规避

高校通过教师劳动力市场引进高层次人才迅速提升学科实力的做法较为常见。鉴于人才引进和使用不当导致的组织疲劳在其他组织管理案例中明确且反复显现,有必要分析高校学科建设中人才引进可能导致的组织疲劳,并寻求规避原则。组织疲劳不能简单等同于组织成员的疲劳,而是人才使用不善导致的组织层面的疲劳。判定组织疲劳的标准包括:人才的引进使用方式透支未来、学科发展水平呈现周期性波动、拔尖人才的带动作用日渐式微、学科内部成员之间的关系日益紧张、优秀团队成员开始离职等。规避组织疲劳不仅要有正确的引人、用人理念,而且还应有必要的制度保障以及不断动态优化的组织形式。

显微组织对TiAl合金冷热疲劳特征的影响

本文对比研究了形变TiAl合金几种不同的起始显微组织对冷热疲劳裂纹形成和扩展特征的影响.结果表明,全片层组织具有较高的抗冷热疲劳阻力,而双态组织和近γ组织具有相似的响应,即都表现为较差的抗冷热疲劳性能.在双态和近γ组织中,裂纹很容易形核并扩展,其扩展路径较平直,而且伴随主裂纹扩展,在其周围还会伴生许多微裂纹.在全片层组织中,裂纹萌生较困难,其裂纹扩展路径较曲折,因此其有效裂纹长度较短,扩展速率较慢.

显微组织对TA15合金疲劳性能的影响

研究了显微组织对TA15合金疲劳性能的影响.片状组织、双态组织的S-N曲线在1×106-2×106寿命处相交.在低循环区域(LCF),双态组织的疲劳强度优于片状组织;在高循环区域(HCF),片状组织的疲劳极限高于双态组织.

资质过剩感对组织公民疲劳的影响研究——基于内部人感知的中介作用

本文基于资源保存理论,探讨资质过剩感对组织公民疲劳的影响机制。研究结果表明:资质过剩感不仅会直接促进员工组织公民疲劳的产生,还会通过员工的内部人身份感知来影响起疲劳感的产生。组织支持感可以减缓资质过剩感所产生的负向影响。

显微组织对Ti-31合金低周疲劳性能的影响

研究了Ti-31合金的显微组织对低周疲劳性能的影响.结果表明:当应变控制在△ε/2=0.6%-1.0%,应变比R=-1时,片状组织和等轴状组织对低周疲劳性能无明显影响,当循环应变次数较低时,基本都表现为循环饱和特征;当循环周次超过100 cyc时,片状组织出现轻度循环软化.等轴状组织的Ti-31合金的过度疲劳寿命略高于片状组织,分别为758和556 cyc.

Microstructural evolution and mechanical properties of duplex-phase Ti6242 alloy treated by laser shock peening

The effects of laser shock peening(LSP)on the microstructural evolution and mechanical properties of the Ti6242 alloy,including the residual stress,surface roughness,Vickers microhardness,tensile mechanical response,and high-cycle fatigue properties,were studied.The results showed that the LSP induced residual compressive stresses on the surface and near surface of the material.The maximum surface residual compressive stress was−661 MPa,and the compressive-stress-affected depth was greater than 1000μm.The roughness and Vickers micro-hardness increased with the number of shocks,and the maximum hardness-affected depth was about 700μm after three LSP treatments.LSP enhanced the fraction of low-angle grain boundaries,changed the grain preferred orientations,and notably increased the pole density ofαphase on the near surface from 2.41 to 3.46.The surface hardness values of the LSP samples increased with the increase of the number of shocks due to work hardening,while the LSP had a limited effect on the tensile properties.The high-cycle fatigue life of the LSP-treated sample was significantly enhanced by more than 20%compared with that of the untreated sample,which was caused by the suppression of the initiation and propagation of fatigue cracks.

TC11钛合金在不同温度下的疲劳断裂分析

借助光学显微镜(OM)、扫描电镜(SEM)和透射电镜(TEM)等研究了TC11钛合金不同温度下高周疲劳断口及断口附近的微观组织形貌。结果表明:TC11钛合金不同温度下的疲劳断口均由疲劳源区、裂纹扩展区和瞬断区3部分组成,裂纹扩展区存在大量的二次裂纹,随着温度的增加,二次裂纹数量逐渐增多的同时其长度与宽度也明显增加,且在二次裂纹附近出现微裂纹,疲劳辉纹的宽度从0.2μm(-30℃)增加到1μm(150℃),相应的疲劳极限也随着实验温度的升高而降低,该实验条件下疲劳极限值从438 MPa(-30℃)降至388 MPa(150℃),温度越高疲劳寿命越短。不同温度下随着循环周次的增加,钛合金内部出现位错或形变孪晶等亚结构来协调变形,低温下变形组织以位错缠结和形变孪晶混合型组织为主,高温下则以位错缠结为主,同时β片层发生明显的断裂现象,在α/β相界面的位错堆积导致的应力集中是疲劳裂纹源形成的主要原因。

TC4钛合金厚板的组织与性能

对新研制的TC4半成品厚板的组织、拉伸性能、断裂韧性、疲劳性能进行了分析,指出厚板生产中的制坯工艺、轧制道次间的变形量控制及退火工艺控制是获得优良组织性能板材的关键.

Ti-6Al-4V合金的疲劳性能

简要综述了Ti-6Al-4V合金的显微组织和织构对其疲劳性能的影响及其机理.

人体脊柱生物力学特性的研究方法及进展

背景:随着脊椎融合术和人工椎间盘植入手术的不断发展,近年来研究者们利用各种医疗仪器设备和研究方法,对脊椎的各项特性展开研究。生物力学研究需要更真实的模拟人体生理环境和运动方式。目的:综述国内外相关文献,从测量主体和测量内容角度总结脊柱生物力学研究方法的优势与不足。方法:以"biomechanical and(properties or study or evaluation),spinal biomechanics,spine mechanical test,spine and(kinematics or motion)"为英文检索词检索PubM ed、Web of Science、Springer数据库,以"生物力学特性,生物力学研究评估,脊柱生物力学,脊柱力学测试,脊柱动力学,脊柱运动"为检索词检索中文期刊全文数据库,纳入脊柱力学、运动学、动力学研究相关文献,主要整理近5年来该领域内的经典文献,排除重复性工作,重点对38篇文献进行分析讨论。结果与结论:近30年来研究者从多个结构细节对脊柱机械特性展开了研究,仿照人体运动研究了基本工况下脊柱的运动形式,掌握了大量脊柱力学与动力学特性。未来还需要对脊柱特性进行更加深入的了解,如力学方面椎间盘的阻尼特性、运动学方面脊柱的空间耦合运动规律等,才能有助于设计性能更加优良的脊椎病治疗产品,更好地修复脊椎疾病。

Effect of wet shot peening on Ti-6Al-4V alloy treated by ceramic beads

Ti-6Al-4V alloy was processed by wet shot peening with ceramic beads. The effects of the shot peened intensity on the microstructure, surface morphology, and residual stress were investigated. A tensile-tensile fatigue test was performed and the fracture mechanism was proposed. The results demonstrate that the surface roughness after wet shot peening is obviously lower than that after dry shot peening. With the increase of the shot peened intensity, the depth of the residual stress layer increases to 250 ktrn, and the maximum stress in this layer increases to -895 MPa. The fatigue strength also increases by 12.4% because of the wet shot peening treatment. The dislocation density of the surface layer is significantly enhanced after the wet shot peening with ceramic beads. The microstructure of the surface layer is obviously refined into ultra-fine grains.

Low cycle fatigue behavior of T4-treated Al-Zn-Mg-Cu alloys prepared by squeeze casting and gravity die casting

Gravity die casting(GC) and squeeze casting(SC) T4-treated Al-7.0Zn-2.5Mg-2.1Cu alloys were employed to investigate the microstructures,mechanical properties and low cycle fatigue(LCF) behavior.The results show that mechanical properties of SC specimens are significantly better than those of GC specimens due to less cast defects and smaller secondary dendrite arm spacing(SDAS).Excellent fatigue properties are obtained for the SC alloy compared with the GC alloy.GC and SC alloys both exhibit cyclic stabilization at low total strain amplitudes(less than 0.4%) and cyclic hardening at higher total strain amplitudes.The degree of cyclic hardening of SC samples is greater than that of GC samples.Fatigue cracks of GC samples dominantly initiate from shrinkage porosities and are easy to propagate along them,while the crack initiation sites for SC samples are slip bands,eutectic phases and inclusions at or near the free surface.

Strength and fatigue fracture behavior of Al-Zn-Mg-Cu-Zr(-Sn) alloys

The strength and fatigue fracture behavior of A1-Zn-Mg-Cu-Zr（-Sn） alloys were studied by performing tensile tests and fatigue crack propagation （FCP） tests. The microstructures of the experimental alloys were further analyzed using optical microscopy （OM）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）; phase analysis of these alloys was conducted with an X-ray diffraction （XRD）. The results show that when Sn is included, growth of the recrystallization grains in the solution-treated A1-Zn-Mg-Cu-Zr alloy is obstructed, the precipitation-free zone （PFZ） of the overaged A1-Zn-Mg-Cu-Zr-Sn alloy becomes narrow, and the grain boundary precipitates are smaller. Consequently, the FCP resistance is higher. In addition, the overaged Sn-containing alloy has considerably higher tensile strength than the alloy without Sn.

Effect of post weld heat treatment on properties of variable polarity TIG welded AA2219 aluminium alloy joints

AA2219 aluminium alloy joints were fabricated by variable polarity tungsten inert gas （VPTIG） welding process and the effects of post weld heat treatment （PWHT） on the tensile properties, microstructure and fatigue behaviour of the welded joints were investigated. The VPTIG welding process was adopted because it could meet the need of cathode cleaning and meanwhile it could reduce the deterioration of tungsten electrode furthest. The welded samples were divided into as-welded （AW） sample and PWHT sample. The PWHT method used on the samples was solution treatment （535 ℃, 30 rain）, water quenching and artificial aging （175 ℃, 12 h）. The experimental results show that, compared with the AW samples, the microstructure characteristics and mechanical properties of the AA2219 joints after PWHT were significantly improved. The improvement of yield strength, ultimate tensile strength, and fatigue strength are 42.6%, 43.1% and 18.4%, respectively.

Effect of annealing treatment on microstructure and fatigue crack growth behavior of Al–Zn–Mg–Sc–Zr alloy

Al-Zn-Mg-Sc-Zr alloy samples were annealed to four different states （under-aging, peak-aging, over-aging and double-aging） and then thoroughly investigated by means of electron backscatter diffraction （EBSD）, transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, tensile and fatigue crack growth rate tests to explore the influence of annealing treatment on microstmcture and fatigue crack growth behavior. The results indicate that Al3（Sc,Zr） particles can effectively refine grains and enhance tensile properties and fatigue properties. After annealing treatment, the under-aged sample and double-aged sample obtained average grain sizes of 4.9473 and 4.1257 μm, and the maximum value of yield/tensile strength （561 MPa/581 MPa） was obtained in peak-aged state. In the Paris region, fatigue crack growth rate, crack deflection and bifurcation, crack blunting and inter/trans-granular propagation were discussed based on data fitting and Laird model and Griffith theory. And the results show that the under-aged sample possesses the best resistance to fatigue crack propagation and the most tortuous and bifurcated crack path. For all samples, the fatigue crack growth rate in the rupture region was inversely proportional to yield strength.

Fatigue strength and microstructure evaluation of Al 7050 alloy wires recycled by spray forming,extrusion and rotary swaging

Recycled high-strength aluminum alloys have limited use as structural materials due to poor mechanical properties. Spray forming remelting followed by hot extrusion is a promising route for reprocessing 7 xxx alloys. The 7050 alloy machining chips were spray formed, hot extruded, rotary swaged and heat-treated in order to improve mechanical properties. Microstructures, tensile properties and fatigue strength results for a 2.7 mm-diameter recycled wire are presented. Secondary phases and precipitates were investigated by XRD, SEM, EBSD, TEM and DSC. As-swaged and heat-treated(solution and aging) conditions were evaluated. Mechanical properties of both conditions outperformed AA7050 aerospace specification. Substantial grain refinement resulted from the extensive plastic deformation imposed by rotary swaging. Refined micrometric and sub-micrometric Al grains, as well as coarse and fine intermetallic precipitates were observed. Subsequent solution treatment resulted in a homogeneous, recrystallized and equiaxed microstructure with grain size of 9 μm. Nanoscale GP(I) zones and η′ phase precipitates formed after aging at 120 ℃, imparting higher tensile(586 MPa) and fatigue(198 MPa) strengths.

High cyclic fatigue performance of Al-Cu-Mg-Ag alloy under T6 and T840 conditions

High cyclic fatigue(HCF)behavior of an AA2139alloy belonging to Al-Cu-Mg-Ag system in T6and T840conditionswas examined.The T840treatment involving cold rolling with a40%reduction prior to peak ageing provides an increase in tensilestrength compared with the T6condition.However,fatigue lifetime for two material conditions was nearly the same since there isweak effect of thermomechanical processing on micro-mechanisms of crack initiation and growth.

Study on damages constitutive model of rocks based on lognormal distribution

The damage constitutive relation of entire rock failure process was established using the theory of representative volume element obeying the Iognormal distribution law, and the integrated damages constitutive model of rock under triaxial compression was established. Comparing with triaxial compression test result, it shows that this model correctly reflects the relationship of stress-strain. At the same time, according to the principle of the rock fatigue failure that conforms to completely the static entire process curve, a new method of establishing cyclic fatigue damage evolution equation was discussed, this method form is simple and the physics significance is clear, it may join preferably the damage relations of the rock static entire process curve.

Microstructure evolution of 55Ni−23Cr−13Co nickel-based superalloy during high-temperature cyclic deformation

The cyclic deformation behavior and microstructure evolution of the 55Ni−23Cr−13Co nickel-based superalloy were studied at 750℃ under the strain amplitudes from 0.35%to 0.6%.Coffin−Manson−Basquin and Smith−Watson−Topper relationships were employed,which satisfactorily predicted the fatigue life of the alloy under various strain amplitudes.The superalloy showed an initial cyclic hardening as a result of the interaction between the dislocations and the precipitates,and following cyclic softening behavior mainly due to the shearing of theγ′phase by dislocations and dislocations recovery under all strain amplitudes.Microstructure analyses showed that the M_(23)C_(6) carbides exhibited a continuous-chain distribution at lower strain amplitudes,while they showed a discontinuous distribution at higher strain amplitudes.As the strain amplitude increased,the size of theγ′phase decreased as the consequence of repeated shearing by dislocations.Fracture mechanisms were analyzed.Under higher strain amplitudes,cavities preferred to form around grain boundaries.

Effects of microstructural heterogeneity on fatigue properties of cast aluminum alloys

Cast Al alloys are widely employed for engine components,structural parts,gear box,chassis,etc.and subjected to mechanical cyclic load during operation.The accurate fatigue life prediction of these alloys is essential for normal operation as fatigue cracks initiated during operation induce the lubrication oil leak and serious safety hazard.Microstructural heterogeneity,including shrinkage/gaspores and secondary phase particles,is the most detrimental factor that affects fatigue life of cast Al alloys.The approximate fatigue life cycles could be estimated based on the size distribution and locations of shrinkage pores/defects.The relationship between crack population and stress was reported by statistical distributions and the cumulative probability for cast Al alloys fail at a certain stress could be predicted by combination of Paris law and pore size distribution.Pore depth was found to dominate the stress field around the pore on the surface and the maximum stress increases sharply when the pore intercepted with the surface at its top.The microstructure of cast Al alloys usually is composed of primary Al dendrites,eutectic silicon,Fe-rich particles and other intermetallic particles are dependent upon alloy composition and heat treatment.The coalescence of microcracks initiated from the fractured secondary phases was clearly found and can accelerate the initiation and propagation of the fatigue cracks.A link between defect features and the fatigue strength needs to be established through a good understanding of the fatigue damage mechanisms associated with the microstructural features under specific loading conditions.This paper reviews the influences of shrinkage/gaspores and secondary phase particles,formed during casting process,on the fatigue life of Al-Si-Mg cast Al alloys.