一般应力比时焊接结构S—N曲线的预测方法

本文考虑了焊接结构的几何形状，受载形式，应力比，残余应力，尺寸效应以及材料等因素对疲劳寿命的影响，利用Ｐｅｔｅｒｓｏｎ公式和极值疲劳切口系数概念，建立了一般应力比时焊接结构Ｓ－Ｎ曲线的预估模型，文中对几类典型的焊接结构的Ｓ－Ｎ曲线进行了预测，预测值与实验结果符合较好，本文方法可以大量减少疲劳实验，具有一定的工程实用价值。     

确定铝合金P—S—N曲线的一种简便方法

根据作者提出的应力疲劳公式，建立了确定铝合金Ｐ－Ｓ－Ｎ曲线的简便方法，如果循环应力下材料的疲劳发布已知，且与高循环应力相比，试件在低循环应力下个有更长的疲劳寿命和更同的寿命分散度，则有可能用本文的方法确定材料的疲劳强度分布和Ｐ－Ｓ－Ｎ曲线表达式。     

基于当量名义应力的耐久性分析的特征应力法

本文建立了一种基于当量名义应力的新的结构耐久性分析的特征应力法。该方法首先给出了用结构细节特征应力表征的ａ－Ｓ－Ｎ曲线，然后利用Ｎｅｕｂｅｒ法求得载荷谱中名义应力对应的结构应力集中部位的局部应力应变，再将其转换当量名义应力。并根据ａ－Ｓ－Ｎ曲线，等寿命曲线和累积损伤理论确定谱载下的（ａｋ，ｔｋ）数据，最后利用（ａｋ，ｔｋ）数据确定结构细节的当量初始缺陷分布，并给出裂纹超越娄级结构损伤度的估算。     

Ti_(3)Al基合金的高温蠕变－疲劳行为EI

本文测试了两种热处理状态下的Ｔｉ_３Ａｌ（ＮｂＭｏｖ）合金在７００℃时保持最大应力恒定、改变最小应力１Ｈｚ梯形波加载条件下的疲劳断裂寿命。结果表明，随平均应力增高将导致蠕变损伤加重，致使Ｓ－Ｎ曲线反向。在相同应力幅时，于β相区固溶的样品比在两相区固溶的样品具有较高的蠕变－疲劳抗力。最后发现，这些宏观性能的变化与稳态应变速率和微观断裂特征是密切相关的。     

Ti_3Al基合金的高温蠕变－疲劳行为

本文测试了两种热处理状态下的Ｔｉ_３Ａｌ（ＮｂＭｏｖ）合金在７００℃时保持最大应力恒定、改变最小应力１Ｈｚ梯形波加载条件下的疲劳断裂寿命。结果表明，随平均应力增高将导致蠕变损伤加重，致使Ｓ－Ｎ曲线反向。在相同应力幅时，于β相区固溶的样品比在两相区固溶的样品具有较高的蠕变－疲劳抗力。最后发现，这些宏观性能的变化与稳态应变速率和微观断裂特征是密切相关的。     

Ti—25Al—10Nb—3V—1Mo合金的高周疲劳性能及断裂特征

实验测定了Ｔｉ－２５Ａｌ－１０Ｎｂ－３Ｖ－１Ｍｏ合金６５０℃下高周疲劳Ｓ－Ｎ曲线及热暴露后合金的疲劳性能。结果表明，Ｔｉ－２５Ａｌ－１０Ｎｂ－３Ｖ－１Ｍｏ合金具有较高的疲劳强度，可以满足转子零件的要求。对比光滑和缺口试样的高周疲劳性能，可以看出该合金缺口敏感程度高，且随着应力水平的增加而增大。     

金属材料疲劳规律的预测理论研究

本文对Ｓ－Ｎ曲线的特征进行了描述，并对目前所采用的多种对Ｓ－Ｎ曲线及疲劳极限的近似预测方法进行了评述，并由此提出了新的预测方法。实验表明：提出的方法有较高的预测精度，通用性强，有一定的实用价值。     

腐蚀环境和孔挤压强化对300M超高强度钢疲劳性能的影响

研究了３．５％ＮａＣｌ盐水环境和孔挤压强化对３００Ｍ超高强度钢疲劳性能的影响。实验结果显示，在ｆ＝１０Ｈｚ下挤压件在盐水环境中和未抗日压件在空气环境中的Ｓ－Ｎ央线之间存在一相交点。应力水平高于该要交点强化效果起主导作用；低于该点，环境效应起主导作用。     

具有应力集中的钢结构的低周疲劳分析

根据材料静力参数，估算其疲劳参数，利用实验加以修正，获得了循环σ－ε曲线和εｕ－２Ｎｆ曲线，进而把非线性有限元法和局部应力应变分析结合在一起计算两个试件疲劳寿命，同时，针对这两个试件进行了低周疲劳实验研究，理论结果和实验结果作了比较，从而证明了本文提出了分析方法是行之有效的。     

炭分子筛的空分性能与比表面积的实验关系

实验测定了炭分子筛的ＣＯ２比表面积和Ｎ２比表面积。结果表明,炭分子筛ＣＯ２比表面积和Ｎ２比表面积的差值（ＳＣＯ２－ＳＮ２）可反映炭分子筛有效微孔的数量,比值（ＳＣＯ２－ＳＮ２）／ＳＣＯ２可定性表征炭分子筛有效微孔的相对含量和空分性能,比值（ＳＣＯ２－ＳＮ２）／ＳＣＯ２（记为Ｘ）和炭分子筛空分性能Ｎ２％（记为Ｙ）之间存在近似定量关系Ｙ＝９７．０３－１１．９９Ｘ＋１５．１２Ｘ２。     

THE EFFECT OF UNDERCUT, MISALIGNMENT AND RESIDUAL STRESSES ON THE FATIGUE BEHAVIOUR OF BUTT WELDED JOINTS

Abstract— A mathematical model is developed to predict the effect of weld toe undercut, misalignment and residual stresses on the fatigue behaviour of butt welded joints subjected to zero-to-tensile loading. Linear Elastic Fracture Mechanics (LEFM), Finite Element Analysis (FEA) and superposition approaches have been used for the modelling. It has been found that an undercut at the toes of welded joints is one of the most important weld geometry parameters. The reduction of fatigue strength of welded joints with a weld toe undercut is at least twice that of joints without an undercut in comparison with flush-ground welded plate. A misalignment of 5% of plate thickness and an undercut of 2% of plate thickness are fairly representative for the lower boundary of S-N curves of butt joints. The improvement of fatigue limits by means of surface treatments is shown to be effective for both undercut and misaligned joints. This approach is practical for a "Fitness-for-Purpose" assessment of welded joints subject to fatigue conditions.     

基于缺口应力法的焊接接头疲劳分析

等效缺口应力法作为焊接疲劳分析的一种局部方法,不仅克服了焊接结构名义应力难以确定和焊根结构应力无法定义的困难,而且能够反映焊接局部后处理对焊接接头疲劳强度的影响,因此近年来备受关注。该文建立了典型焊接接头的三维缺口应力模型,对焊趾根部的缺口应力集中系数进行了求解;通过对对接接头和纵向角接头在焊后未处理(AS-weld)和超声喷丸处理(UPT)两种状态下的疲劳试验数据进行分析处理,获得了两种焊接接头在缺口应力系统下统一的S-N曲线,并与目前国际焊接学会所推荐的具有相同存活率的疲劳寿命曲线(IIW:m=3,FAT=225)进行比较,结果表明,该曲线具有更高的疲劳等级和更低的斜度。     

A structural stress definition and numerical implementation for fatigue analysis of welded joints

A mesh-size insensitive structural stress definition is presented in this paper. The structural stress definition is consistent with elementary structural mechanics theory and provides an effective measure of a stress state that pertains to fatigue behavior of welded joints in the form of both membrane and bending components. Numerical procedures for both solid models and shell or plate element models are presented to demonstrate the mesh-size insensitivity in extracting the structural stress parameter. Conventional finite element models can be directly used with the structural stress calculation as a post-processing procedure. To further illustrate the effectiveness of the present structural stress procedures, a collection of existing weld S-N data for various joint types were processed using the current structural stress procedures. The results strongly suggests that weld classification based S-N curves can be significantly reduced into possibly a single master S-N curve, in which the slope of the S-N curve is determined by the relative composition of the membrane and bending components of the structural stress parameter. The effects of membrane and bending on S-N behaviors can be addressed by introducing an equivalent stress intensity factor based parameter using the structural stress components. Among other things, the two major implications are: (a) structural stresses pertaining to weld fatigue behavior can be consistently calculated in a mesh-insensitive manner regardless of types of finite element models; (b) transferability of weld S-N test data, regardless of welded joint types and loading modes, can be established using the structural stress based parameters.     

各种平均应力下高周疲劳极限间的定量关系

疲劳极限是材料工程应用中的一个重要特性参数,但它并不是材料常数。在不同循环载荷作用下,材料会有不同的疲劳极限值。疲劳极限值很大程度上依赖于循环载荷中的平均应力或最大应力幅值,两者之间的关系是材料自身固有的特性关系。因为在接近疲劳极限的低循环应力幅下,S-N曲线受疲劳极限控制,所以在工程应用中对其定量关系有迫切的需求,但现有的经典经验关系只能对其进行非常粗略的估算,不能满足工程应用中有关寿命设计的需要。现状是只能通过大量的实验,得出其实验关系。该文提出了一种函数形式的关系式,该关系式可以足够精确地描述各种材料的疲劳极限和平均应力之间的关系,且只包含三个材料常数。只要这三个材料疲劳特性常数被事先确定,则任意疲劳载荷下的疲劳极限值,都可由该关系式估计得到,因此可以作为材料本身固有的疲劳强度的状态关系式使用。     

FATIGUE DESIGN CRITERION FOR WELDED STRUCTURES

Abstract— For continuously welded structures subjected to cyclic loading, the highly stressed zones where cracks initiate and lead to failure are usually located at weld toes. At these critical points, called hot-spots, the very local stress states are difficult to determine so that standard fatigue criteria are very difficult to apply for fatigue life prediction.
This work presents a fatigue design criterion for continuously welded thin sheet structures, based on a unique S-N curve. The approach, which refers to the hot-spot stress concept, defines the design stress S as the geometrical stress amplitude at the hot-spot.
In practice, the geometrical stress state is calculated by means of the finite element method (FEM) using thin shell theory. Meshing rules for the welded connection, which can be applied methodically to any welding situation, allow the hot-spot location, and therefore the design stress of any structure, to be determined.
Experimental data and FEM calculations show that a unique S-N curve can be obtained whatever the geometry of the welded structure and the loading mode.     

Comparison of fatigue properties between friction stir welds and TIG welds

对比分析了搅拌摩擦和氩弧焊两种工艺方法对铝合金焊接接头疲劳性能的影响,建立了焊接接头的S-N曲线,结果表明：在相同的载荷条件下,搅拌磨擦焊接接头的疲劳性能优于氩弧焊接头。搅拌摩擦焊接头疲劳寿命N=106次的疲劳强度值约为59~65MPa之间。对焊接接头显微组织的分析表明：搅拌摩擦焊接接头具有比氩弧焊接头更为细小的晶粒和狭窄的焊接热影响区,阻碍了滑移带的形成和裂纹的扩展,从而提高了接头的疲劳性能。TIG焊接接头疲劳端口分析显示,焊接缺陷是主要的疲劳裂纹源。     

搅拌摩擦与氩弧焊铝合金接头疲劳性能的比较

建立了铝合金焊接接头的S-N曲线,对比分析了搅拌摩擦和氩弧焊两种工艺对其焊接接头疲劳性能的影响,结果表明:在载荷相同的条件下,铝合金搅拌磨擦焊接接头的疲劳性能优于氩弧焊接头,搅拌摩擦焊接头的疲劳寿命N=106次的疲劳强度为59-65 MPa,搅拌摩擦焊接接头具有比氩弧焊接头更为细小的晶粒和狭窄的焊接热影响区,阻碍了滑移带的形成和裂纹的扩展,从而提高了接头的疲劳性能,铝合金焊接接头的缺陷是主要的疲劳裂纹源.     

Fatigue assessment of arc welded automotive components using local stress approaches: Application to a track control arm

The applicability of the structural and notch stress approach is examined on the basis of arc welded and dynamically loaded steel structures, taken from the automotive sector. In detail, this is a transverse control arm. Components and specimens with critical regions of failure are tested under cyclic loading with constant and variable amplitudes. With the help of strain gauges, the crack initiation is determined. The specimens are the basis for the application and evaluation of the different approaches for the assessment of fatigue life. The numerical determination of the nominal, structural and notch stresses is performed with finite-element models. Finally the experimental and computational results allow the derivation of structural and notch Woehler S-N curves.     

Unique fatigue threshold and growth properties of welded joints in a tensile residual stress field

The fatigue threshold and high growth rate region properties were investigated on several kinds of welded joints. These properties became unique in spite of the variation of steels (ferrite-pearite, martensite, austenite), welding method, heat input and stress ratio. It was revealed that the unique properties occurred from the fully opened fatigue crack due to the tensile residual stresses. Based on these results, the equation of the fatigue crack growth curve for the design and inspection of welded structures was proposed. It is also suggested that the inducement of compressive residual stress at the fatigue critical zone is effective in improving the fatigue properties of welded structures.     

EFFECT OF RESIDUAL STRESSES OF SHOT PEENING ON THE FATIGUE BEHAVIOUR OF A HIGH STRENGTH STEEL*

Abstract— The effects of shot-peening residual stresses on bending fatigue behaviour of welded plate and surface-flawed plate were investigated. The results show that shot peening residual stresses may significantly increase fatigue strength as well as the threshold stress- intensity factor range of a surface-flawed plate. This paper presents a simple analytical method for determining the residual stresses. The calculated values are essentially in agreement with the experimental results.