考虑应变路径的多轴低周疲劳寿命预测模型

通过分析材料在多轴非比例加载下产生附加强化的机理,该文以拉扭薄壁管试件为研究对象,分析了临界平面上的应变状态,并在此基础上以塑性应变能为控制参数定义表征多轴低周疲劳寿命对应变路径依赖性的非比例度。基于多轴疲劳临界损伤面原理,应用von-Mises 准则和本文定义的应变路径非比例度参数建立起能反映应变路径对非比例附加强化影响的多轴低周疲劳寿命预测模型。利用该模型预测08X18H10T 不锈钢、Ti-6Al-4V合金、S460N 钢和2.25Cr-1Mo 钢这4 种材料的多轴疲劳寿命,并与试验值进行比较。结果表明:该模型的预测结果与试验结果吻合良好,能同时适用于比例与非比例加载,预测精度较高,便于工程应用。     

基于塑性应变能的多轴低周疲劳寿命预测模型

在分析多轴疲劳损伤机理的基础上,提出一个新的多轴低周疲劳寿命预测模型。此模型以临界平面上的塑性应变能作为疲劳损伤参量,分析了临界平面的特点并给出了损伤参量的计算过程。利用该模型预测了不同加载路径下的304不锈钢试件的疲劳寿命,并与试验值进行比较。结果表明,该损伤参量具有明确的物理意义,能够适用于多轴比例与非比例等各种复杂的加载情况。     

AZ91D室温环境棘轮及其低周疲劳行为

通过AZ91D室温环境应力控制下的低周疲劳试验,对铸造镁合金棘轮及其低周疲劳行为进行了研究,讨论了室温环境下材料的应力循环特性、棘轮行为、塑性应变范围、全应变范围等疲劳参量随载荷水平和加载历史的变化规律,同时基于平均应力修正对材料的应力-寿命曲线进行了讨论。研究结果表明:AZ91D在室温环境下的应力循环呈循环硬化,材料的棘轮行为和塑性应变范围、全应变范围等疲劳参量依赖于载荷水平和加载历史,另外考虑平均应力修正后的应力-寿命曲线预测效果有明显改观。     

一种基于临界平面法的多轴疲劳寿命预测模型

在多轴交变应力作用下,由于非比例循环附加强化效应导致疲劳寿命降低。针对这一问题,以薄壁圆管疲劳试件为研究对象,在分析临界平面上剪应变和正应变随相位角变化特征的基础上,引入了一个新的有效循环变量———临界平面上的等效应力,提出了一种新的多轴疲劳预测模型。新的损伤参量不含经验常数,便于工程实际的运用。通过和铝合金7075-T651多轴疲劳实验数据比较,结果表明,所提出的多轴寿命预测模型具有更好的预测精度,适用于比例与非比例加载条件。     

在多轴载荷下45钢的循环特性

通过多轴疲劳试验，研究了在多轴加载条件下45钢的循环特性变化规律，分析了非比例附加强化、多轴循环软化/硬化特性及疲劳寿命对加载路径参数的依赖性，结果表明，相位角主要影响非比例附加强化程度，幅值比主要影响多轴循环软化/硬化特性，二者都影响多轴疲劳寿命。     

基于有限元法的16MnR缺口件疲劳寿命预测方法

以16MnR钢缺口棒状试样为研究对象,基于有限元分析方法,提出了一个缺口构件疲劳寿命预测方法。以一种能描述材料非Masing特性的A-F类循环塑性理论为基础,用有限元方法分析了缺口棒状试样在比例与非比例加载下的多轴应力-应变状态。比例与非比例加载工况通过理想的试验控制路径和半寿命时的试验实际路径来实现加载。基于有限元应力-应变结果,运用一个基于临界面概念的多轴疲劳损伤准则预测了缺口构件的疲劳启裂位置和寿命。分析结果表明:提出的疲劳寿命预测方法能很好地预测缺口构件在比例与非比例加载下的疲劳寿命。     

一种新的多轴高周疲劳模型

将疲劳强度以上加载等效为塑性应变,建立了塑性应变与加载应力呈线性关系的表达式,由此得到循环加载的塑性应变能。该塑性应变能使材料微观组织结构发生不可逆变化而引起等效宏观应力。假定该应力符合一种特定的分布函数,导出其最大应力与外加应力叠加达到材料本征断裂应力时的裂纹成核寿命,从而并由微裂纹引起上述两部分应力变化,得到继续加载直至宏观裂纹出现的疲劳寿命。所建立的多轴疲劳寿命公式由3个材料参数表达,并通过单轴疲劳试验数据确定。初步研究表明：该模型对所引用的多轴疲劳试验数据有很好的预测能力。     

基于单轴缺口试样的一种低周疲劳测试方法与应用

对于漏斗式小曲率半径的缺口圆棒与缺口薄片试样提出了一种采用轴向测量应变的低周疲劳测试方法.通过有限元分析建立小曲率半径的漏斗式缺口圆棒或薄片试样的轴向测试应变到缺口根部Tresca等效应变的应变转换模型,并由疲劳损伤等效假设建立基于缺口试样疲劳实验数据的材料低周疲劳寿命估算模型;完成了大曲率半径漏斗光滑试样和小曲率半径缺口试样的Ti-4Al-2V合金低周疲劳试验,基于缺口试样的疲劳试验所建立的材料低周疲劳寿命估算模型与基于大曲率半径漏斗试样的低周疲劳寿命估算模型有良好的符合度.新方法也方便应用于N18锫合金缺口薄片试样的材料高温单轴低周疲劳行为试验研究,可推荐于材料低周疲劳测试规范修订采用.文中获得的Ti-4Al-2V合金和N18锆合金的不同温度下单轴低周疲劳行为试验数据与寿命估算模型有宜于工程应用.     

多轴低周载荷下钛合金BT9疲劳损伤的微观机理

应变控制比例及非比例载荷低周疲劳试验结果表明,非比例载荷下钛合金BT9附加强化程度很小,而疲劳寿命降低明显.采用透射电镜(TEM)对钛合金BT9的疲劳位错亚结构进行了观测和分析,结果表明,钛合金BT9比例、非比例载荷下出现的多滑移位错亚结构都呈条块状;位错密度随等效应变强度、相位角的增加而增加,且分布极不均匀;非比例载荷下钛合金BT9中的局部高密度位错是其低周疲劳损伤程度加剧及寿命降低的主要因素.     

镍基单晶合金低周机械疲劳寿命模型评述

航空发动机叶片等先进动力推进系统涡轮叶片长期服役于高温、高压、高离心力的工作环境,对叶片材料的性能有很高的要求。普通多晶合金材料存在晶界,晶界处较为脆弱,裂纹易滋生于晶界并沿晶界扩展。采用定向凝固工艺的镍基单晶合金消除了晶界组织,具有较高的高温强度、良好的蠕变与疲劳抗力、优异的热稳定性,长久以来一直作为涡轮叶片材料使用。镍基单晶材料的疲劳损伤是直接影响叶片服役时间的一个重要因素,疲劳损伤的评估依赖于合理有效的疲劳寿命模型。镍基单晶材料的疲劳模型涉及范围很广泛。一方面,材料的工作环境复杂,涉及的疲劳问题包括机械疲劳、热疲劳、热机械疲劳以及蠕变疲劳等。另一方面,单晶材料本身的各向异性带来了疲劳性能的各向异性,取向偏离这一铸造缺陷决定了单晶材料的实际使用取向并非材料性能的择优取向。目前,研究者们主要从复杂环境带来的复杂疲劳状态和单晶本身的各向异性方面进行疲劳寿命模型的探究。针对复杂的疲劳状态,目前的疲劳模型从基本机械疲劳出发,向各个侧重探究方向延伸,尚没有广泛适用且机理清晰的模型。机械疲劳模型的探究仍处于前列。在针对材料本身各向异性的研究方面,学者们提出了不同的各向异性疲劳性能的处理方式,如基于单晶体弹性模量各向异性的取向因子类模型,这类模型因操作简单而适合工程应用,但其预测能力缺乏评估。由于复杂疲劳状态涉及范围太广,本文立足于低周机械疲劳,分类整理了其疲劳模型,按照疲劳损伤参量的定义思路将模型分为宏观损伤参量模型和微观损伤参量模型两大类,论述了各类模型的建模原理。同时收集了五种镍基单晶材料的11组疲劳试验数据,对典型模型进行了评估,以期为进一步探究镍基单晶的疲劳寿命模型提供参考。     

Application of a combined high and low cycle fatigue life model on life prediction of SC blade

A combined high and low cycle fatigue life prediction model for nickel-base single crystal (SC) has been presented to analyze the low cycle fatigue (LCF) and high cycle fatigue (HCF) life of SC blade. In the paper, a power law function of life model based on crystallographic theory is adopted to predict the LCF life. A power law function based on elastic analysis is adopted to predict the HCF life. Furthermore, the LCF and HCF experiments at different temperature are carried out to obtain the model parameters. The predicted results show that the model is reasonable for LCF and HCF. The linear life model introduced in the paper satisfies the combined high and low cycle fatigue life prediction of nickel-base single crystal superalloy. Special attention is put on the combined high and low cycle fatigue life of SC turbine blade. The resolved shear stress and first-order vibration stress are analyzed by the crystallographic rate dependent finite element analysis (FEA) and orthotropic elastic FEA, respectively. It is shown that the prediction model can be well used in the fatigue life prediction of SC blade.     

Investigation on low cycle fatigue of nickel‐based single crystal turbine blade in different regions

Low cycle fatigue experiments of nickel‐based single crystal superalloy miniature specimens were carried out at 760 °C/1000 MPa and 980 °C/750 MPa. According to testing results, low cycle fatigue life is dependent on sampling position of turbine blade under same test conditions. Fracture surface morphology and longitudinal profile microstructure indicated that the fracture mechanism transformed from cleavage fracture to ductile fracture with the changing of medium temperature to high temperature due to the particle cutting at yield stress intensity. The scanning electron microscopy observation of original material demonstrated that the smaller precipitate size of samples have a shorter fatigue life. Meanwhile, the constitutive model considering size effect was built based on the crystal plastic theory. The finite element analysis demonstrated that the smaller precipitate size could dramatically reduce the plastic deformation suffering the same cycle loading.     

Crystal plasticity finite‐element modelling of cyclic deformation and crack initiation in a nickel‐based single‐crystal superalloy under low‐cycle fatigue

Nickel‐based single‐crystal superalloys are predominantly used for turbine blades in aircraft engines and land‐based gas turbines. Understanding and predicting the fatigue failure of Ni‐based single‐crystal superalloys are critical to ensure the safety of these components during operation. In this paper, low‐cycle fatigue experiments were carried out to investigate cyclic deformation of a nickel‐based single‐crystal superalloy MD2, recently developed by GE Power, with different crystallographic orientations. Specialty in situ scanning electron microscope (SEM) tests were also conducted to study the slip‐controlled initiation of short cracks under low‐cycle fatigue. In particular, the stress–strain response for both [001] and [111] orientations was used to calibrate a crystal plasticity model, which allowed us to simulate the activation of crystallographic slip systems and predict the initiation of short fatigue crack. Using the accumulated shear strain as a criterion, the simulations confirmed that the slip system with the maximum accumulated shear strain appeared to control the crack initiation. The location and direction of slip traces and short cracks, captured by the crystal plasticity finite‐element simulations, agreed with the in situ SEM observations. The modelling tool will be valuable for assessing the structural integrity of critical gas turbine blades.     

TA17合金薄片材料毫小试样疲劳性能研究

关键工程结构、小尺寸零部件和焊接区的疲劳寿命评估中往往无法采用传统大试样进行疲劳试验,因此本文提出了一种采用毫米级别薄片试样获取材料循环本构关系和低周疲劳寿命的新方法。在Care原位试验机上完成毫米级别薄片漏斗试样的加载工装和低周疲劳试验的基础上,通过变幅对称循环试验和等辐循环试验分别实现了材料循环本构关系和低周疲劳性能的获取。该文提出了一种对不同幂律材料和不同几何尺寸构型均具有良好普适性的材料循环本构关系预测模型,并通过有限元实现了模型准确性的正反向预测验证。将循环本构关系用于有限元计算中,给出了薄片漏斗试样漏斗两侧名义应力、名义应变和漏斗根部真实应力、真实应变的转换方程,进而预测材料的低周疲劳寿命。该文完成了TA17合金等直圆棒试样和1.2 mm厚度薄片漏斗试样的对称变幅循环试验和多级等辐循环试验。由模型预测获得的TA17合金循环本构关系与等直圆棒试样的试验结果比较表明:两种曲线的弹性段和0.009 mm/mm~0.011 mm/mm应变段吻合良好,在弹塑性过渡段（0.004 mm/mm~0.009 mm/mm）模型预测结果最大相对误差小于9%。根据两组应力和应变转换方程获得的漏斗试样材料代表性体积单元疲劳寿命和Manson-Coffin寿命预测模型与等直圆棒试样试验结果均吻合良好。     

微量Hf对大角度晶界含Re双晶合金高温持久性能的影响

采用籽晶法制备含有大角度晶界(约20°)的双晶试板,通过分析不同Hf含量(质量分数:0%,0.4%)的含Re合金晶界处析出相、γ/γ′组织、晶界成分及1100℃/100MPa横向持久性能,研究Hf对晶界组织及高温力学性能的影响。结果表明:Hf显著提高了铸态合金大角度晶界处共晶和碳化物体积分数;热处理后,Hf显著抑制了晶界胞状再结晶组织的形成,含Hf合金的1100℃/100MPa横向持久寿命均显著提高。晶界持久性能与晶界析出相种类、形貌、含量和成分密切相关,而Hf元素在晶界未发现显著的偏聚。本研究对先进镍基单晶合金中晶界缺陷的评价及Hf元素晶界强化作用机制的认识具有一定的指导意义。     

A comparative study on thermomechanical and low cycle fatigue failures of a single crystal nickel-based superalloy

The cyclic deformation and lifetime behaviors of a single crystal nickel-based superalloy CMSX-4 have been investigated under out-of-phase thermomechanical fatigue (OP TMF) and isothermal low cycle fatigue (LCF) conditions. OP TMF life exhibited less than a half of LCF life although smaller inelastic strain range and lower mean stress level during OP TMF were observed compared to those during LCF. During OP TMF cycling, the maximum tensile strain at the minimum temperature was found to accelerate the surface crack initiation and propagation. Additionally, the multiple groups of parallel twin plates near crack provided a preferential path for crack propagation.     

Thermal—Mechanical Fatigue Behavior and Life Analysis of Cast Ni—base Superalloy K417

In-phase(IP) and out-of-phase(OP)thermal-mechanical fatigue(TMF) behavior of cast Ni-base superalloy K417 was studied.All experiments were carried out under total strain control with temperature cycling between 400-850℃.Both in-phase and out-of-phase TMF specimens exhibited cyclic hardening followed by cyclic softening at the minimum temperature.Besides,they cyclically hardened in the early stage of life followed by cyclic softening at the minimum temperature.Besides,they cyclically hardened in the early stage of life followed by cyclic softening at the maximum temperature.OP TMF life was longer than of IP TMF.Various damage mechanisms operating in different controlled strain ranges and phasing were discussed.A few life prediction methods for isothermal fatigue were used to handle TMF fatigue and their applicability to superalloy K417 was evaluated.The SEM analysis of the fracture surface showed that transgranular fracture was the principal cracking mode for both IP and OP TMF.Oxidation was the main damage mechanism in causing shorter fatigue life for IP TMF compared with OP TMF.     

考虑循环塑性修正的薄片材料低周疲劳试验方法

对N18锆合金和SAPH440板材采用薄片漏斗试样进行了室温下的等幅低周疲劳试验,基于局部应力、应变相等的疲劳损伤等效原理,建立了用于估算N18和SAPH440材料疲劳寿命的Manson-Coffin模型和循环应力-应变方程。对于符合Masing律的材料,提出了一种获得循环本构关系的新方法,用转子材料B65A-S在300℃高温下的低周疲劳试验进行了验证。通过基于标定循环本构关系的有限元分析,建立了两种材料薄片漏斗试样平均应力到漏斗根部轴向应力、测试应变到漏斗根部轴向应变的转换模型。完成了SAPH440材料等直圆棒试样的低周疲劳试验,证明了采用薄片漏斗试样的低周疲劳测试新方法具有较高的精度。     

一种镍基单晶高温合金的热处理工艺研究

研究了一种镍基单晶高温合金的热处理工艺。采用差热分析法和金相测试法确定合金的初熔温度在1280℃左右;利用光学金相显微镜观察了合金在不同固溶处理后的微观组织,测试了合金的持久性能。结果表明,合金的最佳热处理工艺为1245℃/2h,AC+1275℃/4h,AC+1100℃/2h,AC+850℃/24h,AC。采用该工艺处理后的单晶高温合金具有优异的持久性能,在980℃、235MPa的条件下持久寿命达159.35h。     

Effects of Rhenium on Creep Rupture Life of a Single Crystal Superalloys

1.Intr0ductionSince1980'stheturbinebladefabrication0fsinglecrystalsuperall0yshasbeenone0fthesignificantkeytechnol0giesofaeroengine.Atpresentsinglecrystalsuperalloysarebeingusedtofabricatethebladesofaeroengineswithpushweightrati01O,suchasaer0-engineFll9(U.S.A.),Fl2O(U.S.A.),GE90(U.S.A.),EJ200(England,Germany,ItalyandSpain),M88-2(France)andP2000(Russia).Thesinglecrystalsuperalloysofthefirstgenerati0n,secondgenerati0nalldthirdgenerationhavebeenstudiedandappliedt0thebladesandvanesofaeroe…