柴油机铝合金活塞疲劳寿命预测

针对某高强化柴油机活塞,基于温度分布测试结果,运用有限元软件ABAQUS的热分析功能计算得到热应力分布.考虑材料性能的温度效应,并施加按正弦波规律简化的燃烧压力,采用疲劳分析软件FE-FATIGUE进行活塞热-机械载荷复合疲劳寿命预测,经对比,软件预测与台架试验结果吻合.     

多轴低周疲劳寿命预测软件

通过Visual Basic6.0各种控件和算法的运用，编制的“多轴低周疲劳寿命预测软件（MLCFP1.0）”，涉及多种疲劳寿命预测方法，特别适用于结构中出现非比较、多轴应力状态的情况，为多轴疲劳下的寿命预测提供了解决的有力工具。本软件还留有新模型的嵌入接口，数据处理过程实现多文件操作。后处理绘图软件LCF FIGURE1.0，能给出标准的疲劳寿命预测图形，其保存文件形式多样。     

K403合金高温低周应变疲劳寿命预测方法研究

对材料K403进行700℃应变控制的低周疲劳试验.用Manson-Coffin方程进行数据处理,并对该材料700℃时的低周疲劳寿命进行预测.针对在用Manson-Coffin方程进行数据处理时出现负的塑性应变和寿命预测结果不理想的情况,提出一种基于应力疲劳和Manson-Coffin方程的等温低周应变疲劳寿命预测方法,并用该方法对材料K403在700℃时的低周疲劳数据进行处理,得到寿命预测方程.通过寿命预测发现,该方法得到的寿命预测方程不仅使试验数据得到充分的利用,而且寿命预测能力较Manson-Coffin方程的寿命预测能力有明显提高.     

内燃机铝合金活塞疲劳寿命预测研究

以内燃机铝合金活塞弹塑性有限元计算为基础，研究了高温蠕变影响下铝合金活塞寿命的预测方法，给出了寿命宏观预测公式。针对一具体的高强化柴油机铝合金活塞，计算预测了其寿命，并将计算结果与活塞台架试验及发动机整机可靠性试验数据进行了比较，证明了预测公式及预测方法的可靠性。     

某乘用车催化器总成低周疲劳寿命预测

鉴于目前SUS441铁素体不锈钢催化器总成应用低周疲劳寿命预测经验通用公式精度低的不足,对SUS441材料进行高温拉伸试验数据采集,拟合修正了Manson-Coffin公式疲劳寿命预测参数;通过STAR-CCM+软件和ABAQUS软件建立基于体映射法的流-固-热耦合模型,分析了催化器总成在4个工作循环后的热负荷,对SUS441催化器总成进行低周疲劳寿命估计。结果表明,温度场仿真结果与试验数据在误差范围内,模型可信度高;利用修正公式得到应变-低周疲劳寿命曲线,进行寿命预测,通过发动机台架冷热冲击耐久试验证明修正公式比经验通用公式更准确,该结果可为催化器总成设计开发提供指导。     

低周疲劳下45钢的寿命预测

选取带有V型缺口45钢试样,通过控制加载过程中的应变幅,研究缺口对试样疲劳寿命的影响.并应用低周疲劳寿命预测理论,提出了修正的Manson寿命预测模型,用来预测带有V型缺口中45钢的低周疲劳寿命.模型的预测结果和试验结果吻合很好.     

非比例载荷下304不锈钢低周疲劳寿命预测

在拉扭疲劳试验机上完成了一系列非比例加载下对304不锈钢的低周疲劳试验,对目前常用的几种多轴疲劳寿命预测模型进行了分析比较。结果表明,以单轴疲劳寿命分析方法为基础的等效应变法,不能预测多轴非比例加载下的低周疲劳寿命,以临界面法为基础的Socie剪切模型对非比例加载下304不锈钢材料的疲劳寿命预测较好。     

应用当量应变法预测多维高温低周疲劳寿命

采用铝合金材料三维缺口试件进行300℃下高温低周疲劳断裂试验，借助ADINA程序计算试件缺口周围的三维应力和应变场，根据von Mises当量理论对疲劳寿命进行预测。预测结果表明，当量应变范围与疲劳断裂寿命的数学关系不受试件缺口型式的影响，说明当量应变范围方法用作评价三维结构高温低周疲劳寿命的力学参量是有效的。     

低循环疲劳寿命预测的幂指函数模型

从塑性应变幅与疲劳失效反向数在双对数坐标系下的二次曲线特征及残差稳定化两个角度出发,基于幂变换法,构造低周疲劳寿命预测的幂指函数模型。给出一些材料的幂变换指数p值,并对模型寿命预测能力进行检验,结果表明,幂指函数模型对低周疲劳寿命预测具有良好的精度。并指出Manson-Coffin方程实际是幂指函数模型在双对数坐标系下的一阶线性近似,它对应于p=1的情况。由于幂指函数模型非线性的增强,使其对寿命的预测能力大大提高,而通过幂变换方法,模型参数回归仍采用线性回归方法,保持了模型应用的简便性。     

疲劳失效准则在钛合金BT9低周疲劳寿命估算中的应用

在应变控制条件下对钛合金 BT9进行了单轴拉 -压、纯扭及拉 -压与扭转比例加载的低周疲劳试验 ,得到了相应的试验结果。讨论了几种寿命预测准则及其寿命预测精度。在分析 Brown- Miller理论及 Makinde-Neale广义疲劳失效准则的基础上 ,提出了 Makinde-Neale广义疲劳失效准则的变异方程。应用所提出的方程对钛合金 BT9进行了多轴应变条件下的寿命预测 ,并得出了更为符合试验结果的预测结果     

轮盘低循环疲劳寿命可靠性分析方法

疲劳寿命呈现异方差特性,其标准差随弹性应变幅和塑性应变幅的减小而增大,因此在Manson-Coffin公式中引入标准正态变量斗和线性标准差σe、σp,将ε-N曲线参数表示为随机变量μ的函数,建立了低循环疲劳寿命的概率模型。在低循环疲劳试验数据的基础上应用异方差回归分析方法获得了该模型的参数,通过蒙特卡洛模拟验证了模型的精度。应用该模型进行等厚空心轮盘的低循环疲劳寿命可靠性分析,得到了轮盘中心孔危险点的疲劳寿命分布。由于没有事先假设疲劳性能参数的分布特性,参数均由试验数据分析得到,并且采用异方差回归分析能够充分利用数据信息,在提高分析精度的同时能够节约疲劳试件,因此该分析方法具有较好的工程应用前景。     

活塞销疲劳寿命预测的研究

疲劳破坏是活塞销的主要失效形式。对活塞销进行了载荷分析、利用APDL语言建立了有限元分析模型。理论计算了活塞销的疲劳安全系数。基于有限元结果结合Goodman单轴、Sinse多轴修正的名义应力算法,计算预测了活塞销的疲劳寿命。进一步利用FE-SEFE软件进行了单轴、多轴两种方法的疲劳寿命预测,验证该活塞销满足疲劳设计要求,理论验证了FE-SEFE软件在预测高周疲劳寿命的可行性。     

Fretting fatigue life estimations based on fretting mechanisms

Generally the fretting fatigue S-N curve has two regions: one is the high cycle (low stress) region and the second is the low cycle (high stress) region. In a previous paper we introduced the fretting fatigue life estimation methods in high cycle region by considering the wear process; with this estimation method the fretting fatigue limit can be estimated to be the crack initiation limit at the contact edge. In this paper we estimate the low cycle fretting fatigue life based on a new critical distance theory, modified for a high stress region using ultimate tensile strength σ_B and fracture toughness K_IC. The critical distance for estimating low cycle fretting fatigue strength was calculated by interpolation of the critical distance on the fretting fatigue limit (estimated from σ_w0 and ΔK_th) with critical distance on static strength (estimated from σ_B and K_IC). By unifying this low cycle fretting fatigue life estimation method with the high cycle fretting fatigue life estimation method, which was presented in the previous paper, we can estimate the total fretting life easily. And to confirm the availability of this estimation method we perform the fretting fatigue test using Ni-Mo-V steel.     

Evaluation method of multiaxial low cycle fatigue life for cubic single crystal material

The coupling effect of normal stress and shear stress on orthotropic materials happens when applied loading deflects from the directions of the principal axes of the material coordinate system. By taking account of the coupling effects, formulas of equivalent stress and strain for cubic single crystal materials are cited. Using the equivalent strain and equivalent stress for such material and a variable k, which is introduced to express the effect of asymmetrical cyclic loading on fatigue life, a low cycle fatigue (LCF) life prediction model for such material in multiaxial stress starts is proposed. On the basis of the yield criterion and constitutive model of cubic single crystal materials, a subroutine to calculate the thermo elastic-plastic stress-strain of the material on an ANSYS platform was developed. The cyclic stress-strain of DD3 notched specimens under asymmetrical loading at 680°C was analyzed. Low cycle fatigue test data of the single crystal nickel-based superalloy are used to fit the different parameters of the power law with multiple linear regression analysis. The equivalent stress and strain for a cubic single crystal material as failure parameters have the largest correlation coefficient. A power law exists between k and the failure cycle. The model was validated with LCF test data of CMSX-2 and DD3 single crystal nickel-based superalloys. All the test data fall into the factor of 2.5 for CMSX-2 hollow cylinder specimens and 2.0 scatter band for DD3 notched specimens, respectively.     

High-temperature low cycle fatigue, creep–fatigue and thermomechanical fatigue of steels and their welds

High-temperature low cycle fatigue (LCF) is influenced by various time-dependent processes such as creep, oxidation, phase transformations and dynamic strain ageing (DSA) depending on test conditions of strain rate and temperature. In this paper, the detrimental effects of DSA and oxidation in high-temperature LCF are discussed with reference to extensive studies on 316L(N) stainless steel and modified 9Cr–1Mo steel. DSA has been found to enhance the stress response and reduce ductility. It localizes fatigue deformation, enhances fatigue cracking and reduces fatigue life. High-temperature oxidation accelerates transgranular and intergranular fatigue cracking in modified 9Cr–1Mo steel and during long hold time tests in austenitic stainless steel. In welds, microstructural features such as presence of course grains in the HAZ and formation of brittle phases due to transformation of δ ferrite during testing influence crack initiation and propagation and fatigue life. Thermomechanical fatigue (TMF) studies are suggested as more closer to the actual service conditions. In 316L(N) stainless steel, TMF lives under out-of-phase cycling are found to be lower than those under in-phase conditions in the low-temperature regimes, while the converse holds good when the upper temperature encompassed the creep-dominant regime.     

一种新的汽车全生命周期评价指标

在考虑了汽车生命周期成本、排放、行程和载重的情况下,提出了一种新的汽车全生命周期评价指标—汽车生命周期行程载重成本。给出了该指标的定义,并以小客车为案例,给出了该指标的计算方法。通过分析给出了提出这一新指标的意义,并指出提高汽车的生命周期行程,提高额定载重,降低成本,减少排放都会有利于降低汽车的生命周期行程载重成本,从而提高汽车的整体表现。该新指标的建立有利于今后更客观全面地评价汽车产品的综合表现,适用可持续发展的需要。     

基于虚拟仪器的减振器活塞杆侧向弯曲疲劳试验系统

结合LabVIEW软件和NI公司的数据采集设备,开发出基于虚拟仪器的活塞杆侧向弯曲疲劳试验系统.在该系统中,驱动电机带动曲柄连杆滑块双弹簧机构对活塞杆施加正弦激振力,数据采集系统检测激振力波形,并记录弯曲疲劳寿命.试验结果表明,该试验系统具有使用方便、测试精度稳定的特点,能满足直径不大于32mm的活塞杆弯曲疲劳试验.     

应变曲线在零件疲劳寿命设计时的应用

首先对零件产生低周疲劳的原因及其特点进行了简要叙述,说明了应用σ-N曲线无法描述零件低周疲劳寿命的变化规律.在工程设计应用中通常采用σ-N曲线来反映零件低周疲劳的实际寿命变化的规律.扼要论述了通过实践验证及对多种不同静强度的材料进行等应变幅疲劳试验,归纳出适用于零件低周疲劳的通用公式.并用实例验证了其估算过程,对计算结...     

车轮径向疲劳试验有限元仿真及疲劳寿命估算

采用有限元分析方法,建立汽车车轮有限元模型,模拟车轮径向疲劳试验施加合理的载荷及边界条件.通过分析车轮试验过程中的应力变化情况,得出高应力集中区域及其各主应力值,运用疲劳寿命计算理论及ANSYS软件估算车轮的疲劳寿命.通过与车轮径向疲劳试验结果进行比较,结果表明高应力集中区域与实际裂纹位置吻合,预估的疲劳寿命与车轮实验寿命基本吻合,验证了有限元方法预估车轮寿命的有效性,为以后对车轮进行结构改进起指导作用.     

A comparative life cycle assessment of the manufacture of base fluids for lubricants

A comparative life cycle assessment (LCA) study of three types of base oils used in the manufacture of hydraulic fluids has been carried out, and is reported here. The fluid types investigated are a mineral oil, a synthetic ester, and a rape seed triglyceride oil. The applications chosen for the finished lubricants are in mobile hydraulic systems in forestry operations, some of which are almost 100% total loss applications. The scope and limitations of the LCA model are discussed, and conclusions drawn concerning the application of LCA models as evaluation tools for the development of environmentally adapted lubricants. The methodology used is compatible with the ISO 14000‐type industrial standard.