焊接残余应力对2024铝合金薄板疲劳寿命的影响

对搅拌磨擦焊、TIG焊和激光焊进行数值模拟,得到焊接残余应力场.将残余应力场施加到线弹性断裂力学模型之中,运用J积分方法计算残余应力强度因子,并计算裂纹扩展速率,通过与试验结果和虚拟裂纹闭合法计算结果进行对比,验证了文中所使用方法的正确性.研究发现,残余应力强度因子的分布与残余应力分布形式相似.残余应力的引入,对应力比有较大影响,但随着应力比的增大,残余应力对应力比的影响逐渐减弱.焊接残余应力的引入缩短了焊接构件的使用寿命,当裂纹长度较小时,TIG焊接构件使用寿命比搅拌摩擦焊接构件和激光焊接构件使用寿命短.     

GH4169疲劳试样加工残余应力的表征及其对低周疲劳寿命的影响

为了探究GH4169合金低周疲劳试样加工过程中表面残余应力的变化及残余应力对低周疲劳性能的影响，采用X射线衍射法对“车 磨 抛”不同加工工艺的试样表面残余应力进行表征及对成品试样进行残余应力层深度测试，通过中子衍射法对试样内部进行残余应力测试。采用电液伺服万能试验机进行了低周疲劳试验。结果表明：GH4169合金低周疲劳试样加工表面残余应力随着切削量的增加由表面残余压应力变为残余拉应力。根据残余应力层深度测试，机加工对试样表面造成残余应力层深度小于0.01 mm，内部残余拉应力减小；根据疲劳试验结果，GH4169合金疲劳寿命与表面轴向残余压应力呈正相关关系。     

GH4169疲劳试样加工残余应力的表征及其对低周疲劳寿命的影响

为了探究GH4169合金低周疲劳试样加工过程中表面残余应力的变化及残余应力对低周疲劳性能的影响,采用X射线衍射法对“车 磨 抛”不同加工工艺的试样表面残余应力进行表征及对成品试样进行残余应力层深度测试,通过中子衍射法对试样内部进行残余应力测试。采用电液伺服万能试验机进行了低周疲劳试验。结果表明：GH4169合金低周疲劳试样加工表面残余应力随着切削量的增加由表面残余压应力变为残余拉应力。根据残余应力层深度测试,机加工对试样表面造成残余应力层深度小于0.01 mm,内部残余拉应力减小;根据疲劳试验结果,GH4169合金疲劳寿命与表面轴向残余压应力呈正相关关系。     

残余应力对涂覆WC-17Co涂层的Ni718合金弯曲疲劳寿命的影响

利用超音速火焰喷涂技术在Ni718合金表面制备WC-17Co涂层,对喷涂后的试样进行150℃? h 和300℃? h 保温热处理,利用Almen试片曲率法计算不同热处理条件下涂层中的残余应力,利用反复弯曲试验测试试样的疲劳寿命,分析残余应力对试样疲劳寿命的影响。结果表明在疲劳循环过程中,裂纹在涂层中萌生并向涂层/基体界面处扩展,最后扩展至基体内部形成最终断裂。涂层中的残余压应力能够抑制疲劳裂纹的产生和扩展。当经过保温处理后涂层中的残余压应力降低,导致试样的疲劳寿命随热处理的温度上升而下降。     

The effect of residual stress in HVOF tungsten carbide coatings on the fatigue life in bending of thermal spray coated aluminum

One factor that affects the suitability of tungsten carbide (WC) coatings for wear and corrosion control applications is the fatigue life of the coated part. Coatings, whether anodized or thermal spray coated, can reduce the fatigue life of a part compared to an uncoated part. This study compares the fatigue life of uncoated and thermal spray coated 6061 Al specimens. The relation between the residual stress level in the coating and the fatigue life of the specimen is investigated. Cyclic bending tests were performed on flat, cantilever beam specimens. Applied loads placed the coating in tension. Residual stress levels for each of the coating types were determined experimentally using the modified layer removal method. Test results show that the fatigue life of WC coated specimens is directly related to the level of compressive residual stress in the coating. In some cases, the fatigue life can be increased by a factor of 35 by increasing the compressive residual stress in the coating.     

焊接残余应力对Invar钢疲劳寿命影响分析

利用有限元软件MSC.Marc计算了液化石油天然气船液舱Invar钢薄膜的焊接温度场和残余应力场,并计算了焊接残余应力与液体晃荡压力耦合条件下焊缝处的疲劳寿命.结果表明,焊缝表面中心线上的节点的纵向残余应力可达298.1 MPa左右,焊缝纵向残余应力的峰值可达328.3 MPa左右,高于Invar钢的室温屈服强度280.1 MPa.由于焊接残余应力的存在,Invar钢薄膜焊缝的疲劳寿命约由2.1×106降低到1.7×105.     

Effects of coating thickness and residual stresses on the bond strength of ASTM C633-79 thermal spray coating test specimens

Wire-arc-sprayed nickel-aluminum is widely used in the aircraft industry for dimensional restoration of worn parts and as a bond coat for thermal barrier coatings and other top coats. Some repair applications require thick coatings, which often result in lower bond strength. A mechanism being investigated to ex-plain this decrease in bond strength is the free edge effect, which includes both coating residual stresses and coating thickness. The layer-removal method was used to determine experimentally the residual stresses in wire-arc-sprayed nickel-aluminum coatings of different thicknesses. Bond strength evalu-ations were performed using an improved ASTM C 633-79 test specimen. Finite-element analysis and fracture mechanics were used to investigate the effects of coating thickness and residual stress state on coating bond strength.     

Numerical and experimental investigation on the fatigue life evaluation of butt-welded joints

In many applications, welded components are subjected to complicated states of stress and strain due to complex loading and welding residual stresses. Fatigue under these conditions, termed multiaxial fatigue, is an important design consideration for reliable operation of welded components. This investigation develops an effective procedure to predict fatigue life in the weldments by combining the thermo-elasto-plastic theory, multiaxial fatigue theory, and finite element methods. The proposed procedure, which followed the conventional strain-based method (maximum principal strain and von Mises effective strain) to predict the fatigue life of the butt-welded joints, was fairly sensitive to welding residual stress. Furthermore, fatigue tests of steel butt welds having tensile residual stresses were conducted to verify the proposed procedure. Comparative results demonstrate that fatigue life estimates made using the novel procedure closely approximate experimental results.     

考虑残余应力的激光搭接焊接头拉伸和疲劳试样宽度标准化

抗剪强度和疲劳强度是激光搭接焊接头性能的两个最重要指标。关于激光搭接焊接头的拉伸和疲劳试样的宽度选取,目前还没有相应的标准进行规定。以不锈钢薄板激光搭接焊接头为研究对象,通过残余应力数值与试样宽度变化关系的测定,确定了考虑和不考虑残余应力影响的拉伸和疲劳试样合理宽度,比较了有无残余应力试样抗剪强度的区别。结果表明,残余应力通过改变焊接接头受力状态和微观变形均匀性降低了薄板激光搭接焊接试样的抗剪强度。     

超高强度钢喷丸表面残余应力在疲劳过程中的松弛规律

对超高强度钢23C014Ni12Cr3MOE进行了喷丸强化，采用X射线衍射应力分析方法研究了旋转弯曲疲劳过程中喷丸表面残余应力的松弛变化规律。结果表明，在疲劳循环过程中，残余应力的松弛主要发生在疲劳的初始循环100周次内，疲劳循环100周次后残余应力基本稳定在某一个应力水平上，而且其中的大幅度松弛发生在疲劳的初始循环10周次内。对比不同应力水平下的松弛行为，在疲劳极限以上的应力水平下，残余应力松弛的幅度和速率都较大。对喷丸后的试样在疲劳试验前先进行200℃／2h的保温提前应力松弛处理，然后再进行疲劳试验，200℃／2h的保温处理可降低残余应力松弛的幅度和速率甚至在低于疲劳极限的应力水平时只发生小的松弛或不发生松弛。但由于喷丸强化试样疲劳裂纹往往从次表层萌生，表面残余应力的松弛只能作为评价材料疲劳性能的一个参考数值，在工程应用时不能只依据表面残余应力来判定材料的疲劳性能。     

X射线衍射测试PDC表面残余应力的实验研究

作者采用DIMAX2500型X射线衍射仪,通过对入射光狭缝尺寸进行调整,使X射线的照射光斑尺寸缩小为1.5×5 mm,从而实现了对PDC表面沿径向的四个不同位置的应力测量.测量采用sin2ψ法,不但测出了PDC表面不同位置的残余应力,还由此得到了PDC表面应力沿径向的分布规律,而且这一测试结果与通过有限元分析计算出的应力分布趋势基本吻合.作者还对测试值与有限元分析计算值出现偏差的原因从测试方法、有限元分析参数取值及样品表面加工方式等几方面进行了分析讨论.     

基于神经网络的喷丸25CrMo合金疲劳寿命及残余应力松弛行为预测研究

首先,本文采用BP神经网络建立了喷丸25CrMo车轴钢疲劳寿命预测模型。然后,在此基础上采用遗传算法（GA）对BP神经网络的预测精度进行了优化。此外,还采用了径向基神经网络（RBF）进行建模分析,并与以上两种模型的预测结果进行对比,结果表明：遗传算法优化的BP神经网络（GA-BP）相比于BP和RBF神经网络具有更高的预测精度,其中训练集和测试集的平均预测精度分别为91.5%和85.4%。然后,基于GA-BP神经网络模型的连接权值矩阵和Garson方程进行了灵敏度分析,从而进一步量化了输入影响因素对喷丸25CrMo车轴钢疲劳寿命的相对影响比重;最后,还采用GA-BP神经网络预测了喷丸25CrMo车轴钢表面残余压应力的松弛行为,结果表明：测试集的平均预测误差仅为3.4%,表明了该神经网络预测性能良好。综上所述,本文采用神经网络建模分析了喷丸25CrMo车轴钢的疲劳性能和残余压应力松弛行为,显著降低了传统疲劳试验所需的成本,并且还保证了较高的准确性。     

激光冲击工艺对钛合金疲劳寿命的影响

研究激光加工工艺对Ti6A14V航空钛合金叶片表面粗糙度和残余应力的影响，并分析影响表面质量的激光加工工艺参数；探讨表面粗糙度和表面残余应力对叶片疲劳寿命的影响。结果表明，采用激光冲击航空叶片，叶片表面残余压应力大大增强，从而使得其抗疲劳破坏能力增强，而表面粗糙度减小；在激光脉冲功率允许的范围内，选择合适的冲击参数能有效降低叶片表面粗糙度，而表面残余压应力对疲劳寿命的影响起主导作用。     

残余应力对高速列车A7N01铝合金焊接接头疲劳行为的影响

研究了残余应力在疲劳加载过程中的应力松弛行为,采用预拉伸、表面喷丸等表面预制残余应力的方法预制了表面残余应力,并研究了焊接接头的疲劳性能. 结果表明,在经过1×105周次循环载荷后,各个部位残余应力发生较大松弛,在经过2×105周次后,应力松弛较1×105周次时松弛幅度降低. 在2×105周次后,应力松弛不再明显,最终残余应力分布在拉应力20～40 MPa之间. 当引入残余应力后,各种条件下的实际应力循环比发生了明显的变化,当应力比R≥0时,随着R的增大,平均应力增大,试样的疲劳周次显著下降. 残余压应力会使裂纹萌生的周期缩短,同时加快疲劳裂纹扩展速率.     

Nondestructive test of weld residual stresses by acoustoelastic technique

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A-100钢开缝衬套孔挤压强化残余应力场研究

为研究A-100钢开缝衬套挤压工艺,提高孔的疲劳性能,使用X射线衍射方法和中间开孔的板状试样,研究开缝衬套挤压过盈量、挤后铰削量和保温温度对残余压应力场的影响。研究表明,由于孔受挤压发生弹塑性变形而引入切向残余压应力(σ_h),σ_h值随开缝衬套挤压过盈量(I_ce)增加而显著增大,当I_ce =0.4mm时,σ_h值可达-500MPa以上。未铰削的挤压试样,孔边缘残余压应力最大,可达到-680MPa,随着铰削量(R)的增大,σ_h降低,而当R=0.7mm时,σ_h仅剩余28%。保温10小时后,各点σ_h值均明显降低, 350℃下孔边缘σ_h仅存14%。     

Measurement of heat treatment induced residual stresses by using ESPI combined with hole-drilling method

In this study,residual stresses in heat treated specimen were measured by using ESPI(Electronic Speckle-Pattern Interferometry)combined with the hole-drilling method.The specimen,made of SUS 304austenitic stainless steel,was quenched and water cooled to room temperature.Numerical simulation using a hybrid FDM/FEM package was also carried out to simulate the heat treatment process.As a result,the thermal stress fields were obtained from both the experiment and the numerical simulation.By comparision of stress fields,results from the experimental method and numerical simulation well agreed to each other,therefore,it is proved that the presented experimental method is applicable and reliable for heat treatment induced residual stress measurement.     

7075铝合金残余应力与机械载荷交互作用的试验研究

振动时效是一种能有效降低残余应力的工艺技术,但是工件在振动时效过程中微观组织和宏观力学性能都会发生变化。通过激振器和试验机两种装置研究7075高强铝合金板的振动时效发现,残余应力的松弛也伴随着材料力学性能的下降。断口扫描电镜分析表明,杂质相和第二相粒子造成的组织缺陷是疲劳性能降低的主要原因,但两种情况下略有不同。结果认为振动时效除了应合理选择动应力,激振频率对材料残余应力松弛与力学性能也有重要影响,疲劳累积损伤理论是另一重要影响因素。