基于马尔可夫链的飞机结构腐蚀状态预测

腐蚀损伤是最常见的飞机结构损伤形式之一,会降低结构的剩余强度和耐久性。针对在役民用典型机型飞机易腐蚀结构,首先将腐蚀状态划分为5个等级;其次拟合遭受腐蚀的飞机结构剩余厚度递减函数,给出腐蚀状态转移概率矩阵,建立马尔可夫状态预测模型。最后收集某型飞机后货舱隔框腐蚀数据作为算例,预测了隔框结构在潜伏期之后的腐蚀状态。结果发现使用26个月之后,沿海地区飞机隔框结构腐蚀已达到三级状态。预测结果与工程实践相符,说明马尔可夫模型适用于飞机结构腐蚀状态预测。     

基于无偏灰色马尔可夫链组合模型的管线腐蚀剩余寿命预测

压力管线腐蚀剩余寿命预测研究对防止管线泄漏和制定管线的合理检验策略具有重要意义。针对压力管线腐蚀检测数据量少且随机性大的特点,基于传统灰色GM(1,1)模型建立无偏灰色GM(1,1)模型提高预测精度,之后以此为基础构建无偏灰色马尔可夫链组合模型进行腐蚀剩余寿命预测。最后通过对某海洋油田原油处理系统管线腐蚀数据的算例分析,验证所建立模型精度并预测管线腐蚀剩余寿命。预测结果表明:该管线在使用8a左右将达到5级泄漏腐蚀状态,需进行大型检修,无偏灰色马尔可夫链组合模型的预测精度高于94%,预测精度符合工程问题的精度要求,说明此模型可用于中长期存在随机扰动的管线腐蚀剩余寿命预测。     

基于PSO-GRNN模型的埋地管道腐蚀剩余寿命预测

目的 构建埋地管道腐蚀深度预测模型,预测腐蚀管道的剩余使用寿命。方法 依据ASME B31G剩余强度评价标准,给出管道的最大允许腐蚀深度计算方法,引入广义回归神经网络（GRNN）,构建埋地管道腐蚀深度预测模型,采用粒子群算法（PSO）优化GRNN的网络参数,结合管道腐蚀发展趋势预测方法,对埋地薄弱管道进行腐蚀剩余寿命预测。以陕西省某埋地输油管道为例,选取8个主要外腐蚀因素,构建外腐蚀指标体系,借助Pycharm编程仿真,结合埋片试验,对该模型预测结果进行验证分析,并预测各腐蚀管段剩余使用寿命。结果 与BP模型相比,PSO-GRNN模型的管道腐蚀深度预测结果最大相对误差控制在13.77%以内,平均相对误差仅为6.63%。寿命预测结果显示,部分管段的剩余使用寿命未能达到其预期服役寿命。结论 所建模型预测性能要明显优于BP模型,预测精度更高,能够较好地预测埋地管道的最大腐蚀深度和未来的腐蚀发展规律,剩余寿命预测结果贴近实际,为管道的维修和更换提供了指导依据,在实际工程中,具有一定的应用价值。     

数控车床主轴回转精度寿命的灰色预测

将数控车床主轴回转精度的过去及现在已知的或非确知的情况,视作一个灰色系统。通过定期检测5台同一型号数控车床主轴的径向跳动误差、轴向窜动误差和卡盘端面跳动误差值,构成原始等间隔数据序列。据此建立灰色系统GM(1,1)模型,求解灰色系统的微分方程。结果表明:通过残差模型的修正提高了计算精度;修正后的GM(1,1)模型可用来预测数控车床的主轴回转精度寿命,为数控车床的后期检修周期、更换主轴轴承、恢复机床精度提供了依据。     

应用灰色系统理论预测沥青涂层在土壤模拟液中的寿命

目的基于灰色系统理论预测模型建立涂层腐蚀寿命的预测模型,利用该模型计算不同厚度的无溶剂环氧煤焦沥青涂层在滨海氯盐土模拟液中的涂层寿命。方法采用电化学方法,测定不同厚度无溶剂环氧煤焦沥青涂层涂覆的碳钢在滨海氯盐土模拟液中的交流阻抗值。基于灰色系统理论GM(1,1)模型将滨海氯盐土模拟液中测试的无溶剂环氧煤焦沥青涂料的低频阻抗模值和浸渍时间关系,建立涂层腐蚀寿命的预测模型。结果三种不同厚度无溶剂环氧煤焦沥涂层试样在侵蚀性溶液中浸泡240 d时,低频阻抗模值仍保持在8.3×10~8Ω·cm~2以上,应用预测公式计算的滨海氯盐土模拟液中三种无溶剂环氧煤焦沥涂层低频阻抗模值的实测值与预测值的相对误差小于6.0%,C0.35,P=1,该模型的预测精度好。涂层厚度为200μm的无溶剂环氧煤焦沥青层预测寿命t=781 d,涂层从浸泡初期阶段进入中期阶段。随着涂层厚度的增加,涂层寿命愈长,当涂层厚度为600μm时,其预测寿命达到2926 d。结论所建涂层腐蚀寿命的预测模型表现出较好的拟合精度和预测可靠度。     

基于灰色神经网络模型的强力旋压连杆衬套屈服强度预测

强力旋压连杆衬套的力学性能与旋压参数之间的关系复杂,难以用较为系统的数学公式进行表达。为科学准确预测连杆衬套的屈服强度,采用灰色系统理论,选取旋压工艺参数作为系统相关因素,建立预测连杆衬套屈服强度的GM(0,3)模型,经过后验差检验,模型精度二级,平均相对误差为3.25%。为提高模型精度,利用RBF神经网络对预测残差进行修正后,将模型精度提高为一级。在将外来数据回代检验时,GM(0,3)+RBF模型预测结果相对误差在1%左右。研究结果表明:利用灰色理论建立的GM(0,3)+RBF模型能够较精确的预测连杆衬套屈服强度,且预测能力较强,建模简单快速。     

结构腐蚀损伤定量预测方法对比研究

用BP人工神经网络(artificial neural简称ANN)算法分别对飞机结构材料、lCrl7不锈钢腐蚀损伤数据进行学习训练，建立了腐蚀损伤与环境条件的映射模型，并预测腐蚀损伤值。分析了三种预测方法的预测精度。得到了ANN预测的精度比灰色GM(1，1)模型及Logistic模型的预测精度高，且对数据有较好的适应能力的结论；采用ANN技术定量预测飞机结构腐蚀损伤是一种较好工程方法。     

基于灰色理论的数控机床故障预测的研究

针对数控机床可靠性故障间隔预测模型过程中数据采样难度大、成本高、数据量小、常规数据拟合和预测方法误差较大、数据难以处理等问题,提出一种基于传统灰色预测模型,将灰色残差优化模型和BP神经网络模型相结合的预测方法。在预测过程中该模型首先根据灰色理论建立主轴可靠性故障模型,再用BP神经网络训练并优化灰色理论的残差,最后用文献的主轴故障数据验证预测精度。通过不同的算法对数控机床主轴故障的试验数据验证,证明了灰色神经网络模型在主轴可靠性故障间隔工作时间的预测上优于单一算法及GM(1,1,P)模型,验证了灰色神经网络模型的可行性及有效性。     

基于VB/GM(1,1)模型的腐蚀管道剩余寿命预测分析

腐蚀管道剩余寿命预测是管道完整性及安全性评价的重要组成部分。针对开展管道剩余寿命预测没有分析软件的情况,本文以灰色理论GM(1,1)模型为基础,利用VB编写管道剩余寿命预测程序。输入原始腐蚀值可得到预测值、精度检验等级等数据;输入任意两个年份的腐蚀测量数据,得到平均腐蚀速率。程序界面整洁,操作方便,是进行腐蚀管道剩余寿命预测分析的有效工具,为管道腐蚀检测周期确定提供理论依据。     

灰色神经网络模型在海水腐蚀预测中的应用

根据实际海水材料腐蚀数据,将灰色预测模型GM(1,1)与径向基(Radial basis function,RBF)神经网络预测模型结合,建立预测碳钢、低合金钢在实际海水环境中平均腐蚀速率的灰色神经网络模型.结果表明,灰色RBF网络建模优于传统灰色预测模型,符合海水腐蚀的特点.     

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.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.