熔石英磨削的残余应力层深度预测研究

目的磨削后工件表面残余应力处于裂纹层下方其位置隐蔽、不易检测,使用过程中受到应力作用易扩展成裂纹,影响后续工艺参数设计和工件使用寿命。因此,研究磨削后表面残余应力层深度有助于确定后续工艺加工余量,提高工件使用性能。方法本文采用离散元法建立单颗磨粒磨削熔石英的离散元模型,研究磨粒粒径对工件亚表面损伤深度的影响。采用角度抛光法和差动腐蚀法测量熔石英亚表面裂纹层和损伤层深度,计算残余应力层深度并验证模型。结果当磨粒粒径分别为7、14、28、40μm时,仿真得到的裂纹层深度分别为2.53、3.02、4.07、7.39μm,残余应力层深度分别为0.75、1.00、1.34、2.33μm;实验测得的裂纹层深度分别为2.51、3.14、4.65、8.16μm,残余应力层深度分别为0.86、0.93、1.31、1.87μm。由此可见,随着磨粒粒径的增大,工件表面的脆性去除愈加明显,表面质量变差,亚表面裂纹层深度和残余应力层深度增大。仿真预测裂纹层深度与实验值偏差小于15%,残余应力层深度偏差小于25%,残余应力层深度约为裂纹层深度的1/4~1/3,随磨粒粒径增大,比例逐渐减小。结论离散元仿真可有效预测熔石英磨削后的残余应力层深度,为其磨削工艺的制定提供参考。

高压过滤器壳体喷丸残余应力技术研究

零件经过喷丸处理后,其表层的残余应力分布发生了变化,因此,通过对喷丸后材料表层残余应力的测量,就可以知道喷丸处理对零件的强化效果,通过测量不同喷丸工艺参数下的零件、标准试片的残余应力大小获得残余应力大小-残余应力层深关系,根据残余应力大小-残余应力层深关系评估受喷零件的喷丸效果,最终总结出一套适用于内螺纹牙底喷丸效果能够量化检测的有效方法。

异种材料扩散连接接头残余应力的分布特征及中间层的作用

利用有限元方法 ,模拟分析了异种材料扩散连接接头残余应力的分布特征。分析表明 ,对接头有害的较大的残余应力区域分布在膨胀系数较小母材靠近焊缝附近的地带 ,而残余应力的最大值出现在其界面脆性相及焊缝附近靠近接头边缘的微小区域 ,降低连接温度、减少连接时间有利于减小接头残余应力 ,优化接头的界面应力状态。提出了中间层残余应力因子Rf 和中间层厚度因子Tf 概念 ,考虑到中间层的接触强化影响及被焊金属表面物理接触的形成要求 ,当选择中间层时 ,为降低接头的残余应力 ,应尽量选择 |Rf|、Tf 较小的中间层 。

激光诱导残余应力的试验

对激光诱导残余应力的机理进行了分析研究．用波长1．06μm、脉宽23ns,功率密度10^8～10^9W／cm^2的脉冲激光冲击外形尺寸为30mm×30mm×5．5mm的LY12CZ试样，研究了激光能量密度和冲击次数对残余应力分布的影响，并将激光诱导的残余应力与传统的机械喷丸形成的残余应力进行比较．结果表明：残余压应力随着激光能量密度的加大而加大，残余压应力层的深度随着冲击次数的增加而增加，激光诱导的残余压应力层的深度是传统机械喷丸形成的3～4倍．

层间残余应力对带夹层复合板组织性能影响

利用层间真空涂覆技术在不锈钢复合板间添加充型夹层会产生层间残余应力,在后续热轧成形过程中可能受层间残余应力影响导致复合板组织与力学性能发生变化。不锈钢复合板层间残余应力由充型夹层凝固过程中层间热应力与相变应力共同作用产生,拟通过轧前热处理对层间残余应力进行消除,采用数值模拟与试验验证相结合的方法制定轧前热处理工艺,通过层间真空压差涂覆、轧前热处理及热轧试验制备消除与未消除层间残余应力的2种不锈钢复合板,利用金相观测、硬度测试、界面能谱扫描及拉伸、剪切等表征及性能测试试验分析层间残余应力对复合板组织性能的影响。研究结果表明,在保证基层、夹层、复层组织不变的情况下,消除层间残余应力的轧前处理工艺为加热至400℃,保温3.5h,缓慢冷却;经过轧前处理,层间残余应力消减了96.3%;相较于未消除层间残余应力的复合板,消除层间残余应力复合板轧后夹层应力显著增强,晶粒细化81.7%,同时,消除层间残余应力能够提升复合板剪切强度13.3%、拉伸强度3.9%、断后伸长率4%及夹层界面显微硬度3.5%。研究内容通过消除层间残余应力提升了带充型夹层复合板的整体性能,可为相关铸造成型构件性能的提升提供理论指导,为工艺进一步推广应用拓展了新思路。

阳逻大桥钢锚箱焊缝超声冲击降低焊接残余应力工艺试验研究

基于超声冲击消除焊接残余应力机理及特点,利用磁致伸缩效应方法,对在超声冲击后焊缝区域不同深度残余应力有不同变化的系列试验进行测试,结果表明,超声冲击后表面塑性变形层深度内残余拉应力可以大幅降低、甚至产生一定压应力。试验结果的数据分析对超声冲击方法消除焊缝残余应力的工艺研究与工艺制定具有较大的实用价值。

玻璃纤维增强树脂/镁合金叠层板的成型性能数值分析

采用ABAQUS软件对基于热压成型制备的玻璃纤维增强树脂/镁合金叠层板成型后的层间残余应力和变形位移进行了模拟分析。结果表明:叠层板的粘接类型不同,其成型后的层间残余应力和变形位移分布存在明显差异,其中直接粘接叠层板的最大等效应力约为85.5 MPa,其层间残余应力和变形位移主要分布于叠层板边缘,并向层板中心呈梯度递减;而间接粘接叠层板的最大等效应力约为74.2 MPa,其层间残余应力和变形位移主要集中于沿x轴和y轴的中心地带,且呈十字形分布。两种粘接类型叠层板的等效变形位移量相近,数值较小,呈微米级。

7050铝合金的激光喷丸强度表征

分析了激光喷丸强度的表征机制,采用不同厚度的试片的弧高和表面残余应力对7050铝合金进行激光喷丸强度表征研究。弧高表征采用如下方法:试片冲击面尺寸(长×宽)为93 mm×10 mm,厚度分别为2.4、3.0、4.0、5.0 mm,吸收层采用铝箔,约束层采用流水,光斑的搭接率为30%,以激光作用在靶材的有效区域进行计算,夹持试片一端并采用U字形喷丸路径对试片中间规定区域进行喷丸。试验结果表明,激光喷丸强度可用试片弧高进行表征;不同厚度试片适合表征不同范围的激光喷丸强度,对于5～20 J的激光喷丸条件,选用2.4 mm试片较为合适;在能量为20～40 J激光喷丸条件下,4.0 mm试片应作为表征激光喷丸强度的优先选择;残余应力可以辅助试片弧高来表征激光喷丸强度。研究工作为7050铝合金激光喷丸强度表征提供了有效的方法,对激光喷丸质量控制具有重要的工程意义。

激光冲击强化技术原理及研究发展

激光冲击强化技术(LSP)是一种新型的激光应用表面处理技术。与传统表面改性技术相比,激光冲击强化技术能给材料带来更深的残余应力层,使材料表层晶粒细化甚至出现纳米晶,同时大幅提高材料的疲劳寿命。利用高能激光辐照约束层材料(黑漆、黑胶带或铝箔),约束层材料在瞬间熔融气化并产生高温高压的等离子体。等离子体冲击波是一种爆轰波,可以通过C-J模型计算冲击波的峰值压力。等离子体冲击波在约束层(水、光学玻璃)的约束下向材料内部传播,其压力远远超过了材料的弹性屈服极限,材料经历了弹性-塑性变形,最终材料表面形成稳定的残余应力场并发生微弱的塑性变形。本文介绍了激光冲击强化技术的研究发展历程,在此基础上对该技术发展方向进行了展望。

Effect of annealing temperature on joints of diffusion bonded Mg/Al alloys

To study the effect of annealing temperature on the joints between magnesium and aluminum alloys, and improve the properties of bonding layers, composite plates of magnesium alloy（AZ31 B） and aluminum alloy（6061） were welded using the vacuum diffusion bonding method. The composite specimens were continuously annealed in an electrical furnace under the protection of argon gas. The microstructures were then observed using scanning electron microscopy. X-ray diffractometry was used to investigate the residual stresses in the specimens. The elemental distribution was analyzed with an electron probe micro analyzer. The tensile strength and hardness were also measured. Results show that the diffusion layers become wide as the heat treatment temperature increases, and the residual stress of the specimen is at a minimum and tensile strength is the largest when being annealed at 250 ℃. Therefore, 250 ℃ is the most appropriate annealing temperature.

Debonding phenomenon of TiO_2 nanotube film

Curvature method was used to measure the residual stress and substrate straining tensile test was carried out to study the debonding behavior of TiO2 nanotube film. The results indicate that the internal residual stress is -54 MPa. The strains of debonding initiation of TiO2 nanotube films without annealing, with 250 °C annealing and with 400 °C annealing are 2.6%, 5.1% and 8.6%, respectively, and the average radii of the debonding patches with debonding initiation are 27.5, 17.1 and 19.4 μm, respectively. The true critical debonding stresses of TiO2 nanotube films without annealing, with 250 °C annealing and with 400 °C annealing can be estimated as 220.4, 394.5 and 627.9 MPa, respectively. Interfacial shear lag model is modified and polynomial fitting equation of the interfacial shear strength of TiO2 nanotube film is demonstrated under debonding conditions. The modification and polynomial fitting are reliable since good agreement of the interfacial shear strengths after fitting is obtained compared with those results from the crack density analysis.

激光体能量密度对选区激光熔化成形的有限元分析

建立Ti-6Al-4V合金三维有限元模型,探究低功率密度下不同的激光体能量密度对选区激光熔化多层沉积成形过程热行为及热应力演变的影响。本模拟采用热−结构间接耦合的方式计算应力场,利用Sqarse/PCG自动求解器增加其收敛性。结果表明:随着低功率密度下激光体能量能量密度从37.04 J/mm^(3)增加至74.07 J/mm^(3),温度分布具有相似的变化趋势,熔池深度及宽度先增大后趋于平稳,实验熔宽与模拟结果基本一致。随着激光体能量密度的增加,整体残余应力呈减小趋势,降幅6.30%。表面应力呈“条带状”周期性分布,应力集中处于扫描轨道的搭接区域,基板层边缘处应力较大。通过对比模拟与实验层间残余应力结果,可见随着体能量密度的增加两者具有相同的变化趋势,最大偏差6.28%。在能量密度为37.04~74.07 J/mm^(3)范围内,经线性拟合后,模拟/实验层间残余应力与硬度值呈反比关系。

Evaluation of residual stress and corrosion behaviour of electroless plated Ni-P/Ni-Mo-P coatings

Single Ni-P and Ni-Mo-P coatings as well as duplex Ni-P/Ni-Mo-P coatings with the same compositions were prepared by electroless plating.The residual stresses of the coatings on the surface and cross sections were measured by nanoindentation and AFM analysis,and the corrosion behaviour of the coatings in10%HCl solution was evaluated by electrochemical methods,to establish the correlation between the residual stresses and corrosion behaviour of the coatings.The results showed that the single Ni-P and duplex Ni-P/Ni-Mo-P coatings presented residual compressive stresses of241and206MPa respectively,while the single Ni-Mo-P coating exhibited a residual tensile stress of257MPa.The residual compressive stress impeded the growth of the pre-existing porosity in the coatings,protecting the integrity of the coating.The duplex Ni-P/Ni-Mo-P coatings had better corrosion resistance than their respective single coating.In addition,the stress states affect the corrosive form of coatings.

Influence of methane on hot filament CVD diamond films deposited on high-speed steel substrates with WC-Co interlayer

Diamond films were deposited on high-speed steel substrates by hot filament chemical vapor deposition （HFCVD） method. To minimize the early formation of graphite and to enhance the diamond film adhesion, a WC-Co coating was used as an interlayer on the steel substrates by high velocity oxy-fuel spraying. The effects of methane content on nucleation, quality, residual stress and adhesion of diamond films were investigated. The results indicate that the increasing methane content leads to the increase in nucleation density, residual stress, the degradation of quality and adhesion of diamond films. Diamond films deposited on high-speed steel （HSS） substrate with a WC-Co interlayer exhibit high nucleation density and good adhesion under the condition of the methane content initially set to be a higher value （4%, volume fraction） for 30 min, and then reduced to 2% for subsequent growth at pressure of 3 kPa and substrate temperature of 800 ℃.

Structure design of gradient hard coatings on YG8 and their residual stress analysis by ANSYS

A structure of gradient hard coatings( Ti,TiN,TiCN and TiAlN) is designed,and residual stress is simulated by a finite element method with ANSYS. The influence of the realistic situation including load and temperature on the residual stress of the coatings is investigated. Simulated results show that the realistic situation strongly affects the residual stress. To be specific,i) The main residual stress concentrates on the coatings prepared on YG8 substrate,and the residual stress and its gradient of the coatings are bigger than that of the substrate; ii) TiAlN and TiCN coatings have better resistance compression than that of TiN coatings in the same condition; iii) The improved multilayer structure of the gradient hard coatings produces weaker residual stress but higher anti-pressure of the substrate.

Analysis of Differences in Inductance of Ni-Cu-Zn Ferrite Chip Inductors during the Plating Process

Although plating is a necessary process for SMT components, it alters the magnetic characteristics and inductance level of Ni-Cu-Zn ferrite components. The results of this work show that the following three factors in plating affect these components, and the effects are different for Ni- and Sn-plating： （1） Plating layers exert stresses and react with the residual stress of components to change the inductance level, and the effect of the tin layer is greater than that of the nickel one; （2） The plating current induces a magnetic field inside the components directly and indirectly, and this remains as remanence inside the components and reduces the inductance level, and the effect level of Ni-plating is greater than that of Sn-plating; （3） The plating solution corrodes the interface of the termination and ferrite core of the components to release the residual stress, and causes an increase in inductance, and the effect of Sn-plating is greater than that of Ni-plating. In addition, the inductance level is the result of the net effect of these three factors, and if the sintering temperature is increased to change in the type of residual stress, the net effect will be changed.

30CrMoA车轴材料超声表面挤压强化技术研究

为了提高车轴疲劳强度,本文基于超声挤压强化技术,研究了其对列车专用30CrMoA车轴钢加工表面的影响.对比分析了超声挤压强化前后工件表面外观、表面粗糙度、残余应力等特征的变化,绘制了残余压应力沿层深分布的曲线.结果表明:超声强化后的试件表面达到了很好的镜面效果,表面光滑且具有光泽,消除了前道工序残留的环状纹路;表面粗糙度得到改善,粗糙度数值由原来的3.746μm降低到0.2μm左右,在前道工序的基础上下降了95%左右;原来的残余拉应力可以被调节成为压应力,残余压应力层的深度可以达到近2mm,阻止了疲劳裂纹的萌生和扩展,有利于提高金属材料的疲劳强度和使用寿命.

A composite insulation structure for silicon-based planar neuroprobes

Silicon-based planar neuroprobes are composed of silicon substrate,conducting layer,and insulation layers of SiO 2 or SiN membrane.The insulation layer is very important because it affects many key parameters of neuprobes,like impedance,SNR(signal noise ratio),reliability,etc.Monolayer membrane of SiO 2 or SiN are not good choices for insulation layer,since defects and residual stress in these layers can induce bad passivation.In this paper a composite insulation structure is studied,with thermal SiO 2 as the lower insulation layer and with multilayer membrane composed of PECVD SiO 2 and SiN as the upper insulation layer.This structure not only solves the problem of residual stress but also ensures a good probe passivation.So it's a good choice for insulation layer of neuroprobes.

Simulation of residual stresses and their effects on thermal barrier coating systems using finite element method

Thermal barrier coating(TBC)systems are widely used in industrial gas-turbine engines.However,premature failures have impaired the use of TBCs and cut down their lifetime,which requires a better understanding of their failure mechanisms.In the present study,experimental studies of isothermal cycling are firstly carried out with the observation and estimation of microstructures.According to the experimental results,a finite element model is established for the analysis of stress perpendicular to the TBC/BC interface.Detailed residual stress distributions in TBC are obtained to reflect the influence of mechanical properties,oxidation,and interfacial roughness.The calculated results show that the maximum tensile stress concentration appears at the peak of TBC and continues to increase with thermal cycles.Because of the microstructural characteristics of plasma-sprayed TBCs,cracks initialize in tensile stress concentration(TSC)regions at the peaks of TBC and propagate along the TBC/BC interface resulting in the spallation of TBC.Also,the inclusion of creep is crucial to failure prediction and is more important than the inclusion of sintering in the simulation.

Residual stress of physical vapor-deposited polycrystalline multilayers

An extended one-dimensional stress model for the deposition of multilayer films is built based on the existing stress model by considering the influence of deposition conditions. Both thermal stress and intrinsic stress are considered to constitute the final residual stress in the model. The deposition process conditions such as deposition temperature, oxygen pressure, and film growth rate are correlated to the full stress model to analyze the final residual stress distribution, and thus the deformation of the deposited multilayer system under different process conditions. Also, the model is numerically realized with in-house built code. A deposition of Ag-Cu multilayer system is simulated with the as-built extended stress model, and the final residual stresses under different deposition conditions are discussed with part of the results compared with experiment from other literature.