冲压过程中冲压速度对声发射信号幅度的影响

冲压速度对冲压成形工艺影响很大,为此利用声发射技术来检测不同速度下的冲压过程。以不同速度下的冲压过程产生的声发射信号幅度为研究对象,研究两者之间的关系。结果表明,冲压速度对冲压成形过程中产生的声发射信号幅度影响非常大。即随着速度的增大,声发射信号幅度随之增大。     

镁合金筒形件热拉深变压边力工艺研究

以镁合金筒形件作为研究对象,利用Dynaform软件模拟不同变压边力加载曲线下的拉深成形过程。通过比较不同变压边力加载曲线下筒形件拉深的成形质量,得出压边力随凸模行程增加的方式能够较好改善筒形件成形质量,其中线性增加变压边力加载曲线的成形质量最好。同时以压边力加载曲线、冲压速度、摩擦系数为试验因素设计正交试验,得出最优参数组合为:变压边力加载曲线5、冲压速度2 500mm/s、摩擦系数0.150。     

挤压速度对铝合金挤压过程中摩擦声发射能量信号的影响

采用声发射技术,监测铝合金挤压过程中坯料与工模具之间的动态摩擦过程,采集分析了金属坯料在不同挤压速度下与工模具之间的摩擦声发射能量信号,研究了挤压速度对摩擦声发射能量信号的影响。研究结果表明:在挤压温度和摩擦条件基本不变的情况下,声发射能量信号随挤压速度增加而增加,摩擦声发射能量信号对挤压速度非常敏感。挤压速度为10mm/min,声发射能量平均值为123.89m V·μs,挤压速度为40mm/min,声发射能量平均值为1672.5m V·μs。     

基于声发射技术检测镁合金挤压过程动态摩擦研究

研究了镁合金在挤压过程中的坯料与工模具接触表面的摩擦状态。采用声发射技术对AZ91镁合金在不同挤压速度下挤压成形过程摩擦信号进行采集分析,研究挤压速度对摩擦声发射信号的影响,并分析了挤压型材的组织和力学性能。结果表明,镁合金在挤压过程中声发射信号振幅和能量随滑动速度增加而增加,不同挤压速度下声发射振幅信号平均值为64.4 d B。声发射振幅与声发射能量具有对应性;挤出型材抗拉强度和屈服强度随挤压速度的增加而增加,当挤压速度为10 mm/min时,声发射信号振幅为56.3 d B,抗拉强度为350 N/mm2,平均晶粒尺寸为63.2μm;当挤压速度为40 mm/min时,声发射信号振幅为72.3 d B,抗拉强度为达405 N/mm2,平均晶粒尺寸为53.7μm。为采用声发射技术的实时波形和声发射信号参数的平均值监测金属挤压成形时的摩擦状态提供了试验依据。     

大坝混凝土动态弯拉声发射特性试验

为了研究大坝混凝土在不同加载速率下的弯拉声发射特性,并进一步理解不同加载速率下混凝土的损伤发展过程,在MTS试验机上以四种不同的加载速率进行了无开口湿筛混凝土梁的三弯点试验。结果表明,随着加载速率的提高,声发射撞击累计数减少,而撞击率峰值增加,低振幅（35-40 dB）的声发射信号所占比例有所增加,声发射振铃数、信号能量和持续时间的平均值都有提高的趋势;在低加载速率时,混凝土在破坏过程中产生较少数的微裂缝,其破坏机制受少数主要裂缝（跨中位置）控制,而在高加载速率时,微裂缝分布在较宽的范围之内。     

1050铝合金箔材微拉深成形工艺试验研究

微成形工艺是高质、高效、低成本的有效微细加工手段。以50μm厚的1050为试验合金,利用电子万能实验机和扫描电子显微镜等,研究了不同退火工艺和压边力对拉深力、拉深比、制耳和起皱的影响规律。结果表明,聚乙烯薄膜润滑,拉伸速度为0.05 mm/s、拉深比2.1时,顺利成形出质量良好、内径为1 mm的微小杯形件;增加压边力,有助于抑制起皱的发生,但增加了破裂的倾向;退火处理能够增加拉深比、降低成形力和减弱凸耳缺陷。     

方盒形件拉深成形变压边力加载规律优化

选择方盒形非轴对称件为模拟研究对象,分析了方盒形件拉深成形的工艺特点和常见的失效形式及判定标准,通过专业CAE分析软件DYNAFORM,研究分析了方盒形件在不同典型压边力加载模式下的拉深成形性能和极限拉深比(LDR),确定了V型或者类似于V型的变压边力加载状态下坯料的成形效果和LDR最优。建立了方盒形件成形过程中变压边力加载规律的径向基(RBF)神经网络智能预测模型,并完成预测模型的训练和性能检验,对比发现预测结果与模拟结果吻合较好,而且RBF神经网络预测变压边力加载时板料拉深成形质量更好,也更趋近实际生产状态。最后对神经网络预测结果进行多项式拟合优化,获得了成形效果较为理想的变压边力加载曲线。     

SPCC钢动态摩擦与塑性变形声发射信号对比分析

金属板材在塑性加工中不可避免产生摩擦。利用声发射技术检测塑性加工的摩擦状况。以SPCC钢在单向拉伸与相对运动速度为100mm/min、正压力为7.5 kg的动态摩擦过程产生的声发射信号为研究对象,采用参数关联分析方法对两种信号进行了对比分析。试验结果表明,在相同采集的条件下有①摩擦声发射幅度与拉伸声发射幅度相差不大。②幅度相同时的摩擦声发射能量值比拉伸过程产生的声发射能量值要大得多;而摩擦声发射振铃计数值却小于拉伸声发射振铃计数值。③动态摩擦过程产生的声发射信号的持续时间在从很低到8 000μs这一范围;而拉仲过程声发射信号的持续时间一般低于5 800μs,仅当出现裂纹或断裂时才出现更高的持续时间的声发射信号。     

基于DEFORM-2D的304奥氏体不锈钢拉深过程应力应变的数值模拟

不锈钢板材在拉深成形过程中应变硬化严重,影响因素复杂,易出现起皱、破裂、黏模等现象.运用DEFORM-2D的有限元软件,对不同拉深工艺条件下304奥氏体不锈钢圆筒件的拉深成形过程进行了数值模拟,分析了不同工艺条件下的应力应变情况.结果表明:工件凸缘处的摩擦因数越大,拉深成形极限高度hmax越小;提高拉深速度或降低摩擦因数,拉深成形极限高度hmax增大.通过几种不同条件下的模拟分析发现,在模拟实验条件范围内,304奥氏体不锈钢圆形件拉深成形的最佳成形条件为:凸模圆角rp=3mm、凹模圆角rd=3mm、凸缘处的摩擦因数μ=0.08、拉深速度v拉=30mm/s.这与实际生产中的情况相吻合,产生破裂的部位也与实际一致.     

起重机箱形梁结构表面裂纹扩展的声发射特性

采用声发射技术监测带有表面焊接裂纹的箱形梁结构的三点弯曲试验。分析了箱形梁试件受载弯曲过程中裂纹扩展的声发射信号特征,比较了加载过程中不同载荷水平下定位源信号的声发射参数特征。研究发现,表面裂纹扩展的声发射信号为突发型信号,其幅度主要为45～60dB,频率主要分布在100～450kHz。试验结果表明,线定位方法可以对箱形梁试件中的裂纹缺陷进行准确定位。     

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。