Contact stress and residual stress in the nose rail of a high manganese steel crossing due to wheel contact loading

Fatigue failure of a high manganese steel crossing is related to its internal crack initiation and growth, which is affected significantly by the magnitude and distribution pattern of contact stress and residual stress in the crossing. Considering the actual service conditions of a crossing and the accuracy requirement for numerical calculation, a whole model of wheel/crossing/ties and a partial model of wheel/crossing are established using elastic‐plastic finite element method. The distributions of contact stress fields and residual stress fields due to wheel contact loading are studied. The effect of train speed on the residual stress in the nose rail is discussed. The contact stress field shows regular contours in the cross‐section of nose rail and decreases remarkably with increasing distance of the wheel‐crossing contact position. The maximum contact stress is located at the contact surface between wheel and crossing. The maximum residual stress is located at a position of 1.5‐2.0 mm below the surface of the nose rail, rather than at the contact surface of wheel and crossing. In a failed high manganese steel crossing, the dense cracks mainly were observed neither at the position of maximum contact stress (the contact surface between the wheel and the crossing), nor at the position of maximum residual stress (1.5‐2.0 mm below the surface of the nose rail), but around the depth of 0.8‐1.0 mm from the worn surface, which is between the position of maximum contact stress and the position of maximum residual stress. It indicates that the combined effects of the maximum contact stress and the maximum residual stress play important roles in fatigue crack initiation in the nose rail. The size of high residual stress region increases with the increase of the train speed. The maximum residual stress in the nose rail increases remarkably with the increase of the train speed.     

碳酸饮料瓶爪瓣式瓶底结构力学性能研究

目的研究碳酸饮料瓶爪瓣瓶底几何形状参数对瓶底应力开裂现象的影响规律。方法通过加速应力开裂测试观察瓶底的应力开裂现象;通过单因素试验分别分析凹槽底部圆弧直径、凹槽侧壁张角、凹槽深度以及爪瓣数量对最大主应力最大值的影响规律;通过全因素实验研究对比4个几何参数对最大主应力最大值影响的显著性。结果通过单因素试验,发现随着凹槽侧壁张角、凹槽底部圆弧直径以及爪瓣数量的增大,最大主应力的最大值均呈现下降的态势,而表示凹槽深度4个数据的分析结果则呈现虽深度增加但最大主应力的最大值均增加的态势。全因素实验证实这4个参数中只有槽底圆弧直径、凹槽数量以及凹槽深度对瓶底最大主应力的最大值有显著的影响。另外,凹槽深度、凹槽数量分别与槽底圆弧直径的交互效应呈现出显著影响。最后拟合了瓶底最大主应力的最大值与影响显著的几何参数之间的回归方程。结论在厚度均匀的前提下研究了几何结构的相关参数对应力开裂的影响及规律,厚度变化及厚度分布的变化对应力开裂的影响还需进一步研究。     

THE EFFECTS OF STRESS RATIO, COMPRESSIVE PEAK STRESS AND MAXIMUM STRESS LEVEL ON FATIGUE BEHAVIOUR OF 2024-T3 ALUMINIUM ALLOY

Abstract— Fatigue crack growth behaviour of 2024-T3 aluminium alloy is investigated as a function of stress ratio, compressive peak stress and maximum stress level. It is found that as the stress ratio and the magnitude of the compressive peak stress are increased, the threshold stress intensity range decreased linearly. Intermediate and near threshold growth rate data are analysed with different formulae for effective stress intensity range. The data covered different values of stress ratio, compressive peak stress and maximum stress level. A formula for the crack opening stress level is introduced as a function of stress ratio, compressive peak stress and maximum stress level. The formula permitted a good correlation between crack growth data for both positive stress ratio and negative compressive peak stress values. Using the new formula, intermediate and near threshold crack growth data for the 2024-T3 aluminium alloy yielded a unique crack growth rate vs effective stress intensity range curve for all stress ratio and compressive peak stress values investigated. This suggests that for the 2024-T3 aluminium alloy the crack growth rate vs effective stress intensity range curve does not depend on stress ratio, compressive peak stress, or maximum stress level. The significance of the new equation and the crack growth rate versus effective stress intensity range curve is that they allow a designer to find crack growth rate vs stress intensity range data for the 2024-T3 aluminium alloy in both intermediate and near threshold regions for the particular stress ratio, compressive peak stress and maximum stress level conditions of the component under investigation.     

1Cr18Ni9Ti不锈钢单轴棘轮本构模型研究

对1Cr18Ni9Ti不锈钢进行了室温单轴棘轮试验,研究了平均应力、峰值应力和棘轮历史对饱和棘轮应变的影响规律.结果表明,当平均应力大于一定范围后,饱和棘轮应变与峰值真应力之间存在单调函数关系,先前低峰值应力的棘轮历史,对后继高峰值应力的饱和棘轮行为无影响.给出了用于室温饱和棘轮应变预测的模型和用于棘轮应变演化预测的模型.模型的预测结果与试验结果基本吻合.     

Elastic–plastic finite element analysis of the effect of compressive loading on crack tip parameters and its impact on fatigue crack propagation rate

The effects of applied compressive stress on the crack tip parameters and their implications on fatigue crack growth have been studied. Four center-cracked panel specimens with different crack lengths are analysed using finite element method. The results show that under tension–compression loading the local crack tip parameters are determined by two loading parameters. The two loading parameters are the maximum stress intensity and the maximum compressive stress in the applied stress cycle. Predictions of fatigue crack propagation behaviour based on the maximum stress intensity and maximum compressive stress agree well with experimental observations.     

FATIGUE UNDER OUT-OF-PHASE BENDING AND TORSION

Test data on fatigue under out-of-phase bending and torsion has been reanalysed. For the materials tested failure has been found to be consistent with the plane of maximum range of maximum range of maximum principal stress, as for the in-phase case. The critical shear planes are assumed to be those associated with this principal stress plane. A multiaxial fatigue damage parameter based on the maximum range of shear stress on the critical shear plane allowing for the effect of the range of normal stress occurring on this plane has been used to develop a proposed set of design curves for in-phase bending and torsion which are conservative for the long life out-of-phase case.     

基于有限元法的缓冲材料力学性能分析

目的基于有限元法对发泡聚乙烯(EPE)缓冲包装材料的力学性能进行分析。方法基于有限元法研究缓冲材料的厚度、压板的施压速度对EPE缓冲包装材料的应力分布及应力应变曲线的变化情况。结果随着缓冲材料厚度的增加,最大应力从1.646 kPa逐渐减小到0.624 kPa,材料屈服点的应力从41.700 Pa逐渐降低到14.727 Pa。随着施压速度的增加,压板与EPE接触边缘的最大应力由1.646 kPa逐渐增大到8.617 kPa,应力上升开始点的应力从23.497 Pa逐渐增大到144.978 Pa。结论应力主要分布在压板与缓冲材料接触边缘。随着缓冲材料厚度的增加,最大应力逐渐减小。随着施压速度的增加,压板与EPE接触边缘最大应力逐渐增大,且EPE缓冲材料内部受力区域逐渐增大。     

MSP试验法评价PZT陶瓷的循环疲劳寿命

采用小样品力学性能试验方法(Modified Small Punch Tests,简称MSP)对Pb(Zr,Ti)O3陶瓷(PZT)实施了不同大小应力下的循环疲劳实验,循环应力越大,样品的残余强度和压电常数衰减越快,这是由应力循环过程中大量微裂纹的产生和扩展所致.通过最大强度值与疲劳寿命的对应关系求得100 Hz循环疲劳下该样品的裂纹扩展指数n为395,由此推测了PZT陶瓷样品的使用寿命,在循环应力的最大值不超过79.1 MPa的条件下,该样品的连续使用寿命可达5年以上.     

45冷轧钢在拉应力作用下的力-磁效应

在不同的最大拉应力作用下反复加载-卸载过程中,测量了45冷轧钢试件表面某确定点漏磁场随拉应力的变化关系。结果表明,当最大拉应力〈610MPa时,磁感应强度随应力的变化关系为线性关系;当最大拉应力处于610MPa与屈服点653MPa之间时,磁感应强度随应力的关系为折线关系,并且折线极值点的位置由较小应力处迅速移向较大应力位置。当最大拉应力大于屈服点时,磁感应强度的变化量保持恒定,折线极值点的位置也保持不变。从而证实了可以通过磁信号的特征对试件的安全性做出评估。     

45冷轧钢拉应力作用的力-磁效应研究

在不同的最大拉应力作用下，反复加载．卸载，测量了45冷轧钢试件在加载和卸载过程中试件表面某确定点漏磁场随拉应力的对应关系。试验结果表明，当最大拉应力＜610MPa时，磁感应强度随应力的变化关系为线性关系。当最大拉应力处于610MPa与屈服点653MPa之间时，磁感应强度随应力的关系由直线关系变为折线关系，并且折线极值点的位置由较小应力处迅速变为较大应力处位置。在极值点位置向高应力方向移动过程中，磁感应强度的变化量迅速增大。当最大拉应力大于屈服点时，磁感应强度的变化量保持较大的状态，折线极值点的位置基本保持不变。得到了试件在拉应力作用下的磁化关系，同时证实了可以通过磁信号的大小对试件的安全性做出评估。     

A multiaxial high-cycle fatigue life evaluation model for notched structural components

A model for multiaxial high-cycle fatigue life evaluation of notched structural components is proposed, which considers the impact of the stress field on fatigue life by utilizing the Theory of Critical Distances (TCD) and Finite Element Method (FEM). The maximum shear stress range plane is defined as the critical plane, and the damage parameters are the maximum effective shear stress amplitude and the maximum effective normal stress, which are obtained by averaging the stress in the hemisphere volume around the maximum stress point. To validate the accuracy of the model, multiaxial fatigue tests are carried out for both smooth and notched specimens of Aluminum–Silicon alloy. The results indicate that the evaluated life and experimental life have a good agreement.     

钛合金多向锻造数值模拟

目的研究TC4钛合金在多向锻造过程中的变形行为。方法基于Deform-3D模拟软件平台,对钛合金的多向锻造变形过程进行有限元模拟分析,研究不同工艺参数(锻造温度、锻造速度、锻造工步)下合金最大主应力、等效应变和载荷最大值的变化规律。结果多向锻造的每工步锻造为典型的镦粗过程,坯料中心部位一直受压应力作用,鼓肚处则出现最大拉应力。随着锻造温度的升高和锻造速度的减小,最大压应力和拉应力均减小,多工步锻造之后合金主应力场分布更加均匀。随着锻造工步的增加,坯料等效应变增大且中心大变形区域体积分数增加。最大载荷随锻造温度的升高和锻造速度的降低而减小,相同参数下不同锻造工步的载荷最大值变化不大。结论锻造温度、锻造速度、锻造工步对TC4钛合金多向锻造变形行为有显著的影响,适当选择多向锻造工艺参数,可以降低载荷并获得均匀性较好的坯料。     

TiC-Ni梯度功能材料的优化设计

对ＴｉＣ－Ｎｉ梯度功能材料在制备过程中的残余热应力进行了计算机有限元模拟,考察了梯度组成分布指数对热应力大小,最大热应力发生的位置以及纯陶瓷ＴｉＣ侧热应力状态的影响,综合分析了热应力的大小和分布,得到了缓和制备热应力的梯度组成分布指数Ｐ＝１．０的优化设计结果。     

SPAR平台立管相互碰撞的有限元分析

以SPAR平台中立管与立管碰撞为研究对象,采用三维有限元模拟碰撞过程,并采用显示动力求解结构的最大碰撞力及最大碰撞应力,计算且讨论了内压、碰撞时立管之间的夹角、碰撞时立管速度之间的夹角及摩擦对立管碰撞的影响。结果表明一定的内压值可以使立管在径向更不容易破坏,对于带有保护层的立管,不同角度碰撞对立管碰撞的影响相对较少,当碰撞角度为45度,最大碰撞应力比较小,摩擦对立管碰撞影响不是很大。     

Numerical Simulation of Brazing TiC Cermet to Iron with TiZrNiCu Filler Metal

The maximum thermal stress and stress concentration zones of iron/TiC cermet joint during cooling were studied inthis paper. The results showed that the shear stress on iron/TiC cermet joint concentrates on the interface tip andthe maximum shear stress appears on the left tip of iron/TiZrNiCu interface. Positive tensile stress on TiC cermetundersurface concentrates on both sides of TiC cermet and its value decreases during cooling. Negative tensile stresson TiC cermet undersurface concentrates on the center of TiC cermet and its value increases during cooling. Brazingtemperature has little effect on the development and maximum thermal stress.     

Investigation on crystallographic behaviors of nickel‐base single crystal alloy cooling holes with different spanwise injection angles

Film cooling as an important thermal protection technology is widely used in aviation and ground gas turbine blades. But film cooling holes reduce the strength of blade seriously, which have become a key region of crack nucleation. In this paper, the plastic behaviors of nickel‐base single crystal alloy turbine cooling holes in spanwise injection angles range from 0° to 40° are investigated on basis of crystallographic constitutive theory. The results show that there are both higher stress regions and lower stress regions around multi‐column cooling holes, where suffer stress interference. The maximum Mises stress occurs at the hole in the center column. The places where the maximum resolved shear stresses occurs change with load and spanwise injection angle. The maximum Mises stress around holes with injection angle of 0° is lowest. With the injection angle increases, the maximum Mises stress increases until injection angles up to 30°. In all the slip systems, the resolved shear stress of hexahedral slip system is most sensitive to the changing of spanwise injection angle and load.     

基于Ansys的不同截面密封圈密封性能仿真分析

目的对"凸"形、矩形和"Y"形截面密封圈的密封性能进行对比分析,为端面静密封形式的密封圈选型和结构设计提供参考。方法基于Ansys的大变形接触有限元分析,对3种不同截面密封圈进行应力和接触压力仿真分析,并对结果进行比较。结果 "凸"形截面密封圈在压缩过程中最大应力和最大接触压力变化均匀,最大接触压力面较宽;矩形截面密封圈最大应力变化均匀,最大接触压力在密封圈压缩量超过18%后呈现陡增现象;"Y"形截面密封圈最大应力和最大接触压力在密封圈压缩量超过18%后均呈现陡增现象,而且最大接触压力面狭窄。结论对于特定密封圈槽的端面静密封形式,"凸"形截面密封圈密封性能最优。     

A new effective method to estimate the effect of laser shock peening

The paper focuses on the influencing parameters to the plastically affected depth and maximum residual stress of the metallic target after laser shock peening. Firstly, by using a new coupling analysis method, the shock pressure characteristics including peak pressure and pressure duration are given. Secondly, based on the deduced pressure profile, dimensional analysis method is employed to find the controlling parameters, and the relationships of plastically affected depth, maximum residual stress versus peak pressure, pressure duration and laser spot size are given. Thirdly, a two dimension axisymmetric finite element model based on LS-DYNA package is built, and the dynamic responses of metallic target subject to laser shock processing are computed with different input parameters. The result shows that the plastically affected depth is proportional to pressure duration, whereas the maximum residual stress is independent with it; the plastically affected depth and the maximum residual stress are not affected by laser spot size within a certain range, whereas have approximate linear relationships with peak pressure after reaching to a certain level; maximum residual stress and plastically affected depth increase significantly for a thin target configuration in laser shock peening system.     

Long-life torsion fatigue with normal mean stresses

Relatively simple fatigue tests have been performed on two common engineering materials, cast ductile iron and low-carbon steel, using two stress states, cyclic torsion and cyclic torsion with static axial and hoop stresses. Tests were designed to discriminate between normal stress and hydrostatic stress as the most suitable mean stress correction term for high cycle fatigue analysis. Microscopy shows that cracks in low-carbon steel nucleate and grow on maximum shear planes, while for cast iron pre-existing flaws grow on maximum normal stress planes. The data illustrate that tensile normal stress acting on a shear plane significantly reduced fatigue life and is an appropriate input for fatigue analysis of ductile materials. Static normal stresses did not significantly affect the fatigue life for the cast iron because the net mean stress on the maximum normal stress plane was zero. Mean torsion significantly reduced the fatigue strength of the cast iron. A critical plane long-life parameter for nodular iron which accounts for both stress state and mean stress is proposed, and is found to accurately correlate experimental data.     

Analysis of Critical Stress for Subsurface Rolling Contact Fatigue Damage Assessment Under Roll/Slide Contact

As one of the main failure modes of component operated under rolling contact loading, the rolling contact fatigue is classified into two types: subsurface initiated and surface initiated. Different stresses such as orthogonal shear stress, maximum principle shear stress, and octahedral shear stress have been applied as the critical stresses for the assessment of the subsurface cracks’ initiation due to rolling contact fatigue. The influences of friction on distributions of the ranges of orthogonal shear stress, maximum principle shear stress, and octahedral shear stress in subsurface were analyzed with reference to the results of the reference articles. The results show that friction does influence the subsurface distributions of these stresses to a certain extent. However, the upper limits of both the maximum principle shear stress and octahedral shear stress are smaller than that of range of orthogonal shear stresses under the rolling contact conditions of usual steel components. Hence, it is more appropriate that the orthogonal shear stress be selected as the critical stress for the assessment of subsurface rolling contact fatigue.