某型航空发动机涡轮叶片服役微观损伤研究

涡轮叶片是航空发动机工作条件最为恶劣的热端部件,其工作性能的优劣决定着整机能否高效、安全、可靠工作。涡轮叶片在服役过程中不可避免地形成各类损伤,由于涡轮叶片制造复杂、造价昂贵,因此对涡轮叶片的服役损伤进行分析和梳理,使涡轮叶片得到安全可靠且充分有效的使用,具有重要的经济价值。利用金相观察、SEM分析和EDS分析等方法对某型航空发动机第一级高压涡轮叶片在服役过程中产生的微观损伤进行分析。结果表明该型航空发动机涡轮叶片的微观损伤以强化相的粗化和筏化为主。以此为基础建立了一套以强化相尺寸为指标的涡轮叶片服役微观损伤表征方法。对服役涡轮叶片开展了硬度测试试验,结果发现随着微观组织的退化,叶片各个部位的维氏硬度出现不同程度的下降。随后,对热暴露预损伤涡轮叶片材料薄壁试样在850℃/810MPa考核条件下开展了低周疲劳试验。结果表明随着微观组织的退化,合金的低周疲劳性能出现了不同程度的下降,说明服役微观损伤降低了涡轮叶片材料的抗疲劳性能。     

压力容器断裂韧度要求的预测

在弹塑性断裂双参数分析方法的基础上，导出了预测压力容器等重要工程结构断裂韧度ＣＴＯＤ要求的理论表达式。只要在实际结构服役条件下，材料断裂韧度高于该表达式要求的韧度值，就可防止结构的弹塑性断裂失效。同时，在该表达式中考虑了应力集中及焊接残余应力的影响，并表明断裂韧度要求随作用应力及板厚的增加而增加。最后给出了两个实例，以考核该理论表达式的实用性。     

断裂韧性JIC及JR阻力曲线的试验研究（一）—对现有标准与规范的消化吸收

本文论述了Ｊ积分和Ｊ阻力曲线作为表征材料断裂韧性特征的过程，介绍了国际上现有的测试ＪＩＣ和ＪＲ曲线的各种标准。对标准中的几个关键问题：延性断裂韧度ＪＩＣ的确定方法，Ｊ控制裂纹扩展条件，斜化线斜率的确定和对试样几何型式与尺寸要求进行了分析与讨论。     

球墨铸铁断裂韧度测试技术研究进展

断裂韧度是材料重要的抗断指标.总结了平面应变断裂韧度、弹塑性断裂韧度、裂纹尖端张开位移和动态断裂韧度测试技术的研究概况及在球墨铸铁材料上的应用,介绍了温度、显微组织、试样尺寸对球墨铸铁断裂韧度的影响规律,探讨了球墨铸铁断裂韧度试样中的裂纹长度测试问题,介绍了基于J-Q(J积分-三轴性应力因子)理论的球墨铸铁断裂韧度测试方法;认为基于J-Q理论的多参数断裂韧度测试是未来研究的重点,并且若要使断裂韧度真正用于工程安全评定,必须在测试时综合考虑实际服役时的加载模式及环境.     

预应变对管线钢低温断裂韧度影响研究

油气管线无论是在安装还是在服役过程中,都会不可避免地产生大塑性应变(即预应变).为了研究预应变对材料力学性能和断裂韧度的影响,对X80管线钢原材料和塑性变形材料分别进行不同温度下的拉伸试验和断裂韧度试验,并对试样断口形貌进行分析.试验结果表明,温度对管线钢的断裂韧度具有显著作用,钢材的断裂韧度随着温度的降低显著减小,断裂方式也由延性断裂转变为脆性断裂;拉伸预应变因工作硬化提高了钢材的屈服强度与抗拉强度,而压缩预应变因包申格效应降低了钢材的屈服强度与抗拉强度,但两者都降低了钢材的塑性及断裂韧度,进一步增加脆性断裂发生的概率.因此,在管道设计、选材、安全分析及评定时,应充分考虑温度和预应变对管线钢断裂行为的影响.     

轴流压缩机叶片断裂分析

轴流压缩机累计运行443天后动叶叶片断裂。通过宏观断口检验和金相分析、力学性能测试、扫描电镜显微分析以及宏观和微观的成分检测等方法对断裂叶片进行了分析。结果表明,叶片在服役过程中承受了复杂的交变应力,叶片材料中有呈带状分布的夹杂物和材料晶界上产生了磷元素偏聚,这些缺陷的存在会使叶片的疲劳寿命显著降低,造成叶片的早期疲劳断裂。     

基于声发射的电化学充氢时间对X100管线钢力学性能和断裂韧度的影响

X100在海洋石油领域具有广泛应用前景,服役过程中不可避免受到氢的影响。以API X100管线钢为研究对象,通过电化学试验和声发射监测等试验方法,研究不同电化学充氢时间对管线钢力学性能和断裂韧度的影响;结合微观形貌,探究充氢时间与X100管线钢作用机理。结果表明：管线钢本身具有良好的强韧性,电化学引入氢后,材料的屈服强度和抗拉都会降低,且随着充氢时间的增加,性能恶化加剧。充氢后,材料性能的恶化,主要归因于引入的氢会扩散到材料的应力集中缺陷处,与缺陷处组织发生交互,最终导致材料性能变化。研究结果可为高强钢服役时的性能劣化预测及开裂监控提供依据。     

焊接接头在预应变下断裂性能试验研究

以常用建筑结构钢Q345为研究对象，进行了母材与焊缝在预应变下的冲击、拉伸和断裂韧度试验。结果表明，预应变下，母材和焊缝的冲击韧度均有所降低，韧一脆转变温度有所提高，109／6预应变后的焊缝其韧一脆转变温度低于室温(20℃)，仍可在室温下安全使用，随预应变增加，材料的屈服强度与抗拉强度均有所提高，脆性断裂危险性增加。研究发现，为建立客观的材料韧度指标及进行更有效的安全分析时，预应变应作为一个考虑因素。     

CrWMn钢制冷冲具的强韧化处理

我厂生产的增压器上的喷嘴叶片冲模(材料1Cr18Ni9Ti,厚度1.5mm),使用寿命只有几百到两千件,很多模具在使用中发生脆性崩刃现象。模具修磨使用二三次后即报废,使用寿命成为必须解决的问题。 图1所示为喷嘴叶片冲模结构。工作中主要承受拉应力和冲击力作用,刃口受到强烈的摩擦和挤压。致使模具的服役条件恶劣。因此,要求模具具有足够的强度、硬度、耐磨性及一定的韧度。为提高模具的     

球墨铸铁断裂韧度的可靠性分析

通常球墨铸铁与其他铸铁材料一样被认为属于脆性材料，断裂韧度应该用线弹性力学理论进行研究。本文发现由于球墨铸铁中的石墨呈球状，当裂纹通过石墨时，裂纹扩展机理将发生相应的变化，结果显示用弹一塑性理论来研究球墨铸铁的断裂韧度是适应和有效的。对可靠度为95％球墨铸铁断裂韧度的区间估计进行分析，以便对工程中的断裂韧度提供相关的数据。     

面向小偏置碰的轮毂断裂模拟研究

为准确地模拟轮毂的碰撞断裂失效行为,开展了AlSi7(铸铝)材料的断裂力学试验,基于CrachFEM失效准则研究了材料特性参数拟合方法.根据轮毂的准静态和动态试验与仿真对比分析,提出了适用于轮毂断裂模拟的有限元建模规则和材料失效参数调整方法,使轮毂碰撞断裂模式的仿真结果更贴合试验结果.研究结果表明:利用所提建模规则与方...     

Thermal shock/fatigue evaluation of FGM by AE technique

This study has been carried out to analyze the thermal shock and fatigue characteristics of functionally gradient material (FGM). The thermal shock/fatigue tests were conducted at a specific temperature and fracture patterns were studied by SEM and AE. Also, thermal fracture behavior of plasma-sprayed FGM and conventional coating material (NFGM) was examined by acoustic emission technique under heating and cooling. Furnace cooling and air cooling tests were used to examine the effect of temperature change under various conditions. The conventional and FGM coatings were compared to heat-resistant property and fracture surface of these materials for each temperature history. Based on these results, some critical temperature at the onset of coating failure can be evaluated to characterize the thermal resistance of the materials. It turned out to be that FGM gives higher thermal property compared with NFGM by AE signal and fracture surface analysis.     

小冲杆试验方法评价1.25Cr0.5Mo珠光体钢的蠕变性能

对1．25Cr0．5Mo珠光体钢的小冲杆蠕变试验结果和传统蠕变试验结果进行比较。试验结果表明小冲杆蠕变试验所获得的中心挠度变形曲线与传统蠕变试验的应变变形曲线是相似的。同时也发现在相同的断裂时间下,小冲杆蠕变试验中所施加的载荷值与传统蠕变试验的应力值的比值在一定载荷范围内为一恒量。在本次研究中,一些在传统蠕变试验中常用的经验公式如Larson—Miller法则、Dorn方程、Monkman-Grant关系式等被用束分析小冲杆蠕变试验。所得结论与传统蠕变试验的结论是相近的。综上所述,小冲杆试验方法可以用于高温下服役材料蠕变性能的评价。     

高锰钢晶界微观应力状态的有限元计算

通过对高锰钢晶粒内部和晶界偏聚硬壳层区域的有限元应力模拟计算,获得了不同偏聚程度条件下的应力状况。计算结果表明,晶界应力集中程度随晶界Ｍｎ偏聚浓度和偏聚层厚度的上升而显著提高,由于晶界偏聚而导致的晶界区域硬壳层对高锰钢的断裂性能是非常有害的。从模拟计算这一角度证实了晶界应力集中是高锰钢产生脆断的主要原因,这与宏微观结构成分和力学性能试验所得到的结果吻合。     

Prediction model and simulation of cutting force in turning hard-brittle materials

The removal mechanism of hard-brittle material was studied in this paper. The shear strain and specific shear work of brittle material cutting were analyzed. The cutting force model of hard-brittle material was developed based on the fracture mechanics. Johnson-Cook model was modified and applied to finite element simulation of hard-brittle material cutting. The cutting force of machinable ceramics was predicted by BP neural network. The turning experiments of machinable ceramics were carried out. The influence of processing parameters on cutting force was investigated. The results show that the modified constitutive model well reflects the fracture removal process of brittle material. The simulation results are in well agreement with experimental data and theoretical data. The effects of cutting depth and feed speed on cutting force are larger than those of cutting speed and tool cutting edge angle.     

基于A350锻件各向异性材料的小冲杆试验研究

通过小冲杆试验对锻造A350各向异性材料沿着轴向和周向两个方向进行了试验研究,并对所做的小冲杆试验数据和试样金相和断口形貌进行了分析。结果表明小冲杆试验可以有效地应用于评价各向异性材料的力学性能,对常规拉伸材料和小冲杆试样的断口对比分析,发现它们具有相同的断裂机理,为小冲杆试验与常规拉伸试验相关联提供了事实依据,同时也观察到试验中的尺度效应,小冲杆试样断口形貌韧窝尺寸要大于常规力学拉伸试样断口韧窝尺寸,本试验尺度下的小冲杆试样仍能够与常规力学试验数据有效地经验关联。     

某型飞机典型疲劳关键件加速腐蚀条件下 C-T曲线的测定

针对某型飞机典型疲劳结构模拟件开展加速环境谱及加速腐蚀试验技术探索性研究.根据腐蚀损伤等效原则,给出试验室加速环境下与外场使用环境下的腐蚀当量关系,对预腐蚀不同时间后的模拟件进行载荷谱疲劳试验,获得了腐蚀影响系数C随地面停放年限T的变化曲线,为确定该结构日历寿命提供依据.     

Fracture Assessment for Electron Beam Welded Damage Tolerant Ti-6Al-4V Alloy by the FITNET Procedure

Fracture assessment of the cracked structures is essential to avoiding fracture failure.A number of fracture assessment procedures have been proposed for various steel structures.However,the studies about the application of available procedures for titanium alloy structures are scarcely reported.Fracture assessment for the electron beam(EB) welded thick-walled damage tolerant Ti-6Al-4V(TC4-DT) alloy is performed by the fitness-for-service(FFS) FITNET procedure.Uniaxial tensile tests and fracture assessment tests of the base metal and weld metal are carried out to obtain the input information of assessment.The standard options and advanced options of FITNET FFS procedure are used to the fracture assessment of the present material.Moreover,the predicted maximum loads of compact tensile specimen using FITNET FFS procedure are verified with the experimental data of fracture assessment tests.As a result,it is shown that the mechanical properties of weld metal are inhomogeneous along the weld depth.The mismatch ratio M is less than 10% at the weld top and middle,whereas more than 10% at the weld bottom.Failure assessment lines of standard options are close to that of advanced option,which means that the standard options are suitable for fracture assessment of the present welds.The accurate estimation of the maximum loads has been obtained by fracture assessment of standard options with error less than 6%.Furthermore,there are no potential advantages of applying higher options or mismatch options.Thus,the present welded joints can be treated as homogeneous material during the fracture assessment,and standard option 1 can be used to achieve accurate enough results.This research provides the engineering treatment methods for the fracture assessment of titanium alloy and its EB welds.     

EFFECT OF DYNAMIC LOADING ON FRACTURE BEHAVIOR OF WELDED JOINTS OF STRUCTURAL STEEL

To investigate the effect of dynamic loading on fracture behavior of welded joints of structural steel Q23SB and 16Mn in common use and compare the earthquake resistances of the two kinds of materials, dynamic tension and fracture toughness tests are carried out at room temperature. On the basis of the tests, the stress-strain fields near the crack tip of the compact specimens are analyzed by three-dimensional finite element model. The test results and finite element analysis results show that, the fracture toughness of welds and base metal of 16Mn steel increases with the increment of loading rate. Compared with 16Mn steel, Q235B steel is more sensitive to dynamic loading. The fracture toughness of welds of Q235B is comparatively low under static loading and dynamic loading at room temperature. Compared with the static loading, the fracture toughness of Q235B parent metal under dynamic loading decreases by about four times. Therefore, it can be concluded that compared with 16Mn steel, the earthquake re     

Mechanical behaviour of brittle materials under hydrostatic pressure (on torsion of chalk cylinders)

Torsion tests were carried out on black-board chalk under hydrostatic pressures of up to 4·0 kgf/mm² in order to investigate the pressure effect on the deformation and fracture of brittle materials. Chalk, which is very weak (the tensile strength is about 0·1 kgf/mm²), was chosen as test material because the ratio of the applied hydrostatic pressure to the tensile strength of the material could be easily raised to high values.It is shown that there is a distinct difference in the characteristics of deformation and fracture between specimens under a pressure which is higher than a critical value of 0·3 kgf/mm² and those under a pressure less than that value. It is also shown that under relatively high pressure a macroscopic crack is formed around the twist angle yielding the maximum torque and thereafter it propagates helically with increase of twist angle.