机车弹簧失效分析

通过OM、SEM、X射线应力测试仪等测试手段对断裂失效弹簧进行了夹杂物、金相、脱碳层和断口形貌的表征及晶粒度、硬度、残余应力和残留奥氏体的检测。结果显示,各项性能均在正常范围内,晶粒等级为10.5级,较为细化但有混晶现象。弹簧表层存在脱碳和挤压压痕,脱碳层厚度约为180μm。断口分析表明,弹簧失效形式为疲劳失效,原因是弹簧圈之间相互挤压产生的表面压痕引起应力集中,改变了表层应力状态,同时脱碳层和部分脱碳层之间的过渡区易于产生微裂纹,导致了疲劳断裂。     

汽车冲压模具弹簧的失效分析

为了寻找某一汽车零件冲压模具弹簧的失效原因,对弹簧断口部位进行了化学成分、金相组织、硬度、断口SEM扫描等测试。检验的结果表明,失效是由于在高交变应力作用下,弹簧丝在内侧表面附近区域形成了疲劳裂纹源,并最终导致弹簧早期疲劳断裂。     

铁路机车用51CrV4弹簧失效分析

采用化学成分分析、组织观察和硬度测试等分析方法,对铁路机车用51CrV4弹簧进行失效分析。结果表明:断簧的化学成分、非金属夹杂物级别和金相显微组织均符合技术规范要求。但弹簧的强度、断口处硬度及疲劳源附近残余压应力值偏低,且存在全脱碳层。此外,弹簧支撑圈和工作圈间因反复接触产生的压痕破坏了表面完整性,易于引发应力集中而导致弹簧疲劳裂纹萌生。在这几个因素综合作用下,弹簧在高频交变应力作用下产生裂纹导致早期疲劳断裂失效。     

城轨机车螺旋弹簧断裂分析

对断裂失效的城轨机车螺旋弹簧采用扫描电镜、金相检验、强度和硬度测试等方法进行。结果表明:该弹簧的断裂方式为疲劳断裂,显微组织、晶粒度和非金属夹杂物水平均正常,造成其断裂失效的主要原因是弹簧表面脱碳缺陷深度过大(>0.2mm),从而降低表面强度。基体组织的洛氏硬度和强度检测结果表明,其硬度和强度偏低,导致弹簧疲劳寿命显著降低而出现断裂失效。     

60Si2CrVA弹簧钢断口及断裂原因分析北大核心CSCD

60Si2Cr VA弹簧在服役状况下,运行寿命不到设计寿命的1/3,发生了断裂。为了分析弹簧的断口和断裂原因,根据该弹簧钢的制造和服役状况,对断口宏观形貌、SEM照片进行了分析;并对弹簧钢的应力分布、化学成分、组织和硬度进行了分析。发现了弹簧断裂为疲劳断裂,其失效起源于表面缺陷和最大切应力的共同作用,且弹簧内部组织有石墨化现象,硬度高,韧性降低,导致了整个工件的断裂。提出了该弹簧在加工过程、检测过程及热处理过程中的一些改进的措施。     

60Si2CrVA弹簧钢断口及断裂原因分析

60Si2Cr VA弹簧在服役状况下,运行寿命不到设计寿命的1/3,发生了断裂。为了分析弹簧的断口和断裂原因,根据该弹簧钢的制造和服役状况,对断口宏观形貌、SEM照片进行了分析;并对弹簧钢的应力分布、化学成分、组织和硬度进行了分析。发现了弹簧断裂为疲劳断裂,其失效起源于表面缺陷和最大切应力的共同作用,且弹簧内部组织有石墨化现象,硬度高,韧性降低,导致了整个工件的断裂。提出了该弹簧在加工过程、检测过程及热处理过程中的一些改进的措施。     

55SiCr汽车悬挂弹簧早期失效分析

某厂生产的55SiCr汽车悬挂弹簧在车辆行驶5 000 km后发生断裂,为寻找弹簧早期失效原因,验证同批次弹簧安全性,并寻找防止断裂的预防措施,使用扫描电镜和金相显微镜等分析设备进行断裂弹簧试样失效分析,发现断口上存在明显的疲劳弧线,断裂起源部位存在机械损伤。检测分析结果表明,该弹簧断裂属于疲劳断裂,疲劳源为弹簧材料内弯表面机械损伤。     

喷丸强化的基本原理与调控正/切断裂模式的疲劳断裂抗力机制图

20世纪90年代前,汽车上使用的各种圆柱螺旋弹簧(以下称弹簧)承受较低的扭转疲劳载荷,在交变正应力作用下,绝大多数发生的是宏观正断型疲劳断裂,其形貌呈45°斜断口。因为喷丸强化弹簧表层引入的残余应力与外施交变正应力间存在交互作用,所以都利用喷丸强化工艺中的"应力强化机制"提高其疲劳断裂抗力。但21世纪伊始,随着轿车结构的迅速发展,设计者迫切要求弹簧承受的扭转疲劳载荷水平与日俱增,由此导致喷丸强化的弹簧除正断型的疲劳断裂外,时而出现纵向或横向切断型的疲劳断裂,由此引发疲劳断裂抗力发生显著下降,以往很少出现这种难以理解的现象。目前从事喷丸强化工艺技术的弹簧制造行业很少有文献关注这类问题。文中通过逻辑思维对弹簧的受力分析得出的诠释发现:在切断模式下,喷丸引入的残余应力与外施交变切应力之间不存在交互作用,表明"应力强化机制"在改善切断型疲劳断裂抗力中的强化作用已经基本消失。根据作者提出的喷丸强化工艺原理,喷丸同步引入弹簧表层的是由残余应力与循环弹塑性变形改性的组织结构组成的一对"孪生",通过分析作者发现,"孪生"中改性的显微组织结构形成的"组织结构强化机制"取代"应力强化机制"起到了改善切断型疲劳断裂抗力的作用。研究结果还表明,优化的喷丸强化工艺必须同时具备"组织结构强化机制"和"应力强化机制",才能够起到改善正断型和切断型疲劳断裂抗力的作用。     

摩托车刹车毂失效分析

运用宏观分析、显微组织检查、断口分析、化学成分与硬度测试等手段对摩托车上的刹车毂进行了失效分析,结果表明摩托车刹车毂断裂是由弹簧最先断裂引起,而硬度过高,表面质量差,是导致该弹簧早期疲劳断裂的主要原因。     

冷轧机轴承的失效分析

冷轧机使用一段时间后第四滚子组的销子发生断裂失效现象。采用扫描电镜、金相、硬度、化学成分测试对失效件进行了综合分析。结果表明,滚子与外圈不良接触导致其接触部位产生磨损,滚子内的固定销承受较高的扭转应力并使其发生疲劳断裂。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

THERMODYNAMICS STUDY ON THE DECOMPOSITION OF CHROMITE WITH KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

INFLUENCE OF HEAT TREATMENT ON DAMPING BEHAVIOUR OF THE MAGNESIUM WROUGHT ALLOY AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

新型的治疗阿尔茨海默氏症药物(1-二甲基磷酰基-2,2,2-三氯)-乙基-1-醇烟酸醋对体外神经细胞的作用

目的: 观察本实验室合成的一种治疗阿尔茨海默氏症(AD)的药物(1-二甲基磷酰基-2, 2, 2 -三氯)-乙基^-1-醇烟酸醋(NMF),对体外培养的皮层神经细胞活性的影响以及对海人藻酸(KA)所致的神经损伤的保护作用。方法: 采用体外培养皮层神经元的方法,解剖分离 15 d胚胎小鼠皮层神经细胞, 接种于 96孔板,48 h 后加药并培养 72 h,以 MIT 法 观察 NMF 对小鼠皮层神经细胞活性的影响;同时将接种于 24 孔板的细胞预先给予 NMF,d 3 时加或不加KA处理后,以台盼蓝染色鉴别并计数死、活细胞,可得出细胞的存活率。结果: NMF 明显促进胎鼠皮层神经元活性,其中 NMF1、0. 1、10nmol·L^-1促进神经元活性增殖率分别高达 34.7%、37.4%、36. 7%, NMF 明显促进正常胎鼠皮层神经元存活卒,与对照组比较,10nmol·L^-1 NMF 对皮层神经元的存活率分别提高 39.3%、73.5%。 NMF能显著 对抗 KA 所致的神经元损伤,与 KA 损伤组相比, NMF0.1、10、10nmol·L^-1对损伤皮层神经元的保护率分别为 77.30%、80.10%、84.15%。结论: NMF 明 显促进胎鼠皮层神经元的洁性、提高正常皮层神经元,的存活卒,并能有效地保护KA所致的神经元损伤,提示 NMF 是一种很有潜力的治疗 AD 的药物。     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Three-Dimensional Growth of Coherent Ferrite in Austenite: A Molecular Dynamics Study

Coherent second phase often exhibits anisotropic morphology with specifi c orientations with respect to both the second and the matrix phases. As a key feature of microstructure, the morphology of the coherent particles is essential for understanding the second-phase strengthening eff ect in various industrial alloys. This letter reports anisotropic growth of coherent ferrite from austenite matrix in pure iron based on molecular dynamics simulation. We found that the ferrite grain tends to grow into an elongated plate-like shape, independent of its initial confi guration. The fi nal shape of the ferrite is closely related to the misfi t between the two phases, with the longest direction and the broad facet of the plate being, respectively, consistent with the best matching direction and the best matching plane calculated via the Burgers vector content(BVC) method. The strain energy calculation in the framework of Eshelby's inclusion theory verifi es that the simulated orientation of the coherent ferrite is energetically favorable. It is anticipated that the BVC method will be applicable in analysis of anisotropic growth and morphology of coherent second phase in other phase transformation systems.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.