可拆卸卡箍断裂原因分析

飞机发动机引气预冷系统导管固定卡箍服役后发生断裂,通过外观观察、断口宏微观观察、金相组织检查、硬度试验、化学成分分析等方法对卡箍断裂原因进行了综合分析,结果表明:断裂卡箍为高周疲劳断裂;导管设计布局在发动机舱,断裂卡箍处位于导管安装有波纹管端附近,在发动机运转中产生振动,如果卡带与支架装配过程中装配应力过大,会导致外表面边角处应力较大,同时在振动应力作用下,在外表面边角应力集中处形成裂纹并扩展,降低支架的边缘和卡带表面处的应力集中,消除卡带边缘的残余应力,可有效防止卡箍的疲劳断裂。     

扭杆弹簧的早期断裂和预防措施

45Cr NiMoVA钢扭杆弹簧发生早期断裂。通过断口分析、化学成分、金相检验和硬度检测分析了扭杆弹簧断裂的原因。结果表明,扭杆弹簧的花键齿表面存在脱碳现象,使断裂韧度和疲劳强度降低,在交变载荷作用下,在花键齿根萌生疲劳源,最终导致扭杆弹簧早期疲劳断裂。预防扭杆弹簧早期断裂的措施是避免扭杆花键齿表面脱碳和适当提高淬火后的回火温度。     

合金钢支架断裂失效分析

利用体视显微镜、扫描电镜、直读光谱仪和金相显微镜研究了合金钢支架的断口形貌、化学成分和微观组织。结果表明:支架的化学成分和显微组织符合技术要求。裂纹源位于断口的表面位置,且断口只有常见的Fe、C、O、Cr、Mn、Mo、Si元素,没有其它的夹杂物,断口属于疲劳断裂。在试验过程中,应力过大导致支架表面出现裂纹源,然后扩展成裂纹导致断裂。     

5A06铝合金钣金支架的振动断裂原因分析

以某箭体使用的5A06铝合金钣金支架为研究对象,对振动失效区域进行了静载强度有限元仿真计算。采用OM、SEM、EDS对断口裂纹表面进行了分析和显微硬度测试。结果表明:裂纹源起始于钣金支架折弯处外侧面,折弯过程承受的高速冲击与大塑性变形在支架外侧引起了表层微裂纹,在振动过程交变动态载荷持续叠加,折弯边进入塑性状态,在峰值应力作用下产生断裂破坏。     

汽车发动机进油管支架疲劳断裂分析

利用超景深三维光学显微镜、金相显微镜、直读式光谱仪、碳硫分析仪、扫描电镜等,研究分析发动机进油管支架断口形貌特征、金相组织、化学成分等,确定其断裂性质及产生原因。结果表明:平台试验时支架折弯处的U型豁口呈显著的应力集中状态;在周期性振动应力作用下,该处折叠类表面缺陷处萌生疲劳裂纹,裂纹发生扩展,并最终导致断裂失效;通过优化结构设计与控制加工表面质量,支架的使用性能得到改善,避免发生早期疲劳失效。     

装甲车辆扭杆裂纹的声发射检测

采用常规的无损检测手段检测装甲车辆悬挂系统扭杆裂纹损伤比较困难。为了方便地检测扭力轴上的裂纹缺陷,提出了利用声发射技术在扭杆加载状态下,检测裂纹损伤的方法。为此基于虚拟仪器的原理,采用便携式工控机、高速数据采集卡、高灵敏传感器、手动液压加载装置构建了扭杆检测硬件系统,并编制了专用的检测定位软件。通过实际应用试验,成功地检测到了被测装备扭杆上的损伤。通过对比分析可得,基于声发射技术的动态检测方法是解决扭杆裂纹静态检测的有效办法。     

中缸体焊接接头断裂行为的有限元分析

液压支架中缸体是以焊接方式连接,那么焊缝位置的选择对于中缸体的使用寿命具有重要的影响。这样笔者分析了不同位置焊接接头的受力特点、应力强度因子以及与其相关的裂纹扩展速率(寿命评估)等断裂参数。通过不同位置焊接接头的有限元分析可知:焊接接头在中缸体中间时对压力的敏感性较强。应力强度因子的计算结果表明:对两种位置焊接接头的应力强度因子值的比较可以发现,焊接接头在中缸体中间时其应力强度因子值小于在中缸体端部时的应力强度因子值,说明了焊接接头在中间位置时抗疲劳和断裂能力较强。裂纹扩展速率试验结果表明:热影响区裂纹扩展速率大于焊缝的裂纹扩展速率,因此裂纹扩展沿着熔合线扩展的可能性更大。     

发动机散热器支架断裂原因分析

某型发动机钛合金散热器支架发生断裂故障。通过对故障件进行外观检查、断口分析、表面微观检查、材质分析、工艺对比分析,以查找确定支架的断裂性质和产生原因。结果表明:支架断裂性质为高周疲劳断裂,导致支架过早发生疲劳断裂的主要原因是支架棱角尖锐造成了应力集中以及表面电加工重熔层中存在微裂纹。通过对2种电加工工艺试件的表面状态进行对比研究,有效避免了此类故障的发生。     

扭杆表面材料本构关系及滚压仿真分析研究

扭杆表面的应力状态是扭杆使用寿命以及运行可靠性的关键因素,滚压工艺参数对扭杆表面应力状态有重要的影响。通过对扭杆建立材料本构关系模型,基于此本构关系模型,对三维滚压过程进行了有限元仿真分析,得到压入量、工件转速和进给速度对表面轴向残余应力的影响规律。结果表明:工件转速和压入量的增加都会增大扭杆表面轴向残余应力;进给速度的增加使扭杆表面轴向残余应力先增大后减小。     

应力比对Mg-3Al-2Sc合金疲劳行为的影响

在不同应力比条件下对热挤压变形的Mg-3Al-2Sc合金进行了疲劳试验,分析了应力比对合金裂纹扩展行为和断裂机制的影响。结果表明:在应力幅Δσ=60 MPa时,随应力比的增加,Mg-3Al-2Sc合金疲劳寿命显著降低,裂纹扩展速率提高。在裂纹萌生区和扩展区疲劳断裂机制主要表现为解理断裂,而在瞬断区主要表现为准解理和沿晶断裂的复合断裂机制。     

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.     

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).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

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.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。