带人工裂纹的焊接钢结构梁柱节点有限元应力分析

近年来,日、美两国地震经验表明,焊接钢结构的脆断往往发生在焊接缺陷和应力集中共同作用的区域。由于梁翼缘的平坡口焊缝垫板结构存在,梁翼缘焊缝根部融合不良而形成“人工”裂纹。本文用有限元方法研究在承受梁端弯曲载荷情况下,梁柱节点的应力分布,以及翼缘焊缝根部的“人工”裂纹造成的应力集中。从断裂力学的观点来分析计算焊根部裂纹尖端的应力强度因子,计算表明底梁翼缘焊根部的应力强度因子值明显大于顶梁翼缘焊根部的应力强度因子值,这与实际地震时脆断更容易发生在底梁翼缘焊缝情况非常吻合。     

桥式起重机主梁焊缝有限元计算子模型

桥式起重机主梁焊缝是易产生应力集中和疲劳裂纹的部位。采用板单元的主梁整体模型中焊缝高度尺寸比板单元尺寸小很多，其计算结果不能反映焊缝的应力分布状况。运用“板到体子模型”法，精确得出主梁跨中焊缝处的应力分布状况，计算结果与实际情况相符，表明子模型法是分析结构局部应力集中的有效手段。     

桁架结构K形节点焊缝应力分布规律的研究

由于K形管焊缝周围的应力分布受载荷形式影响,首先针对履带起重机臂架中K形管的受力特点,对K形管常用的几何参数进行分析,建立了45个适应于履带起重机桁架臂几何参数的K形管有限元模型。其次,采用热点应力法并考虑K形管的弯曲次应力,得出了K形管焊缝周围应力集中系数随几何参数的分布规律。通过分析可知,在履带起重机典型载荷形式下,K形管焊缝周围的应力集中系数受几何参数影响,最大应力集中系数出现在跟点处,且冠点处与跟点处应力集中系数接近,而鞍点处最小,为履带起重机的抗疲劳设计提供了重要的数据参考。     

球形容器接管环带区的应力集中系数研究

本文对球形容器接管环带区的应力及应力集中系数分布进行了研究:认为球形容器接管环带区的峰值应力及最大的应力集中系数位于离焊缝较近的球壳侧。从实测的接管环带区应力集中系数数据出发,对斜插接管环带区的应力集中系数进行了数值分析,提出了一个可为工程实际应用的估算公式。     

白光散斑法用于K型管接头模型应力分析

介绍了白光散斑法用于承受面外弯曲载荷K型管接头模型的应力分析。试验得到了较大尺寸三维模型的全场条纹图,采用逐点法确定它的条纹级数,对四种模型进行了应力分析,确定热点位置和应力集中系数大小,研究焊缝趾部对应力集中系数的影响。试验结果与电测、有限元计算结果进行比较的一致性证实试验结果是可靠的,试验方法是行之有效的;焊缝趾部使主、支管应力集中系数有不同程度的下降。     

补强圈的设计与制造

采用补强圈补强是常用的压力容器开孔补强结构，制造方便，造价低廉，使用经验成熟，能有效地降低开孔接管根部的峰值应力。1补强圈厚度壳体焊上补强圈后，使该处的容器壳体刚性变大，对接管与壳体的角焊缝的冷却收缩起较大的约束作用，容易在焊缝处造成裂纹。在补强圈外围因外形尺寸突变，引起不连续应力，造成新的应力集中，使其焊缝脚趾处易于开裂。补强圈越厚，这种可能性越大。所以笔者认为，补强圈的厚度一般不应超过开孔处壳体的厚度，GB150－89《钢制压力容器》63．2条关于“补强圈的厚度应小于或等于1．5δn（δn为壳体厚度）；”…     

基于有限元法的桁架节点搭接接头应力集中分析

应力集中对桁架节点处疲劳寿命影响显著,焊缝处几何形状不规则,易产生应力集中,可能导致结构破坏。为了研究结构的几何尺寸和焊缝的几何形状对焊缝处应力集中系数的影响,将总应力集中系数分解为焊缝几何应力集中系数和热点应力集中系数的乘积形式。用有限元方法分析焊缝长度、焊缝熔深、弦杆厚度和焊脚尺寸对几何应力集中系数和热点应力集中系数的影响,并拟合经验公式。结果表明:弦杆厚度对应力集中影响不大,焊缝截面形状和焊缝长度对应力集中有一定影响。     

冲击值与金属材料其他力学性能关系的研究

通过试验研究与理论分析,确定缺口应力集中系数,找出缺口应力集中系数和应力强化系数之间的关系;通过40CrMnSiMoA数字化冲击试验数据分析结果,找出冲击值与材料缺口敏感性的关系、冲击裂纹形成功与疲劳裂纹形成寿命之间的关系;从而得出结论:对于高强度和超高强度材料,冲击功值对缺口试样疲劳裂纹形成寿命影响更大,且冲击功值较高的材料比冲击功值较低的材料在等应力条件下疲劳寿命长。     

计算切口应力集中系数的无限相似单元法

在边界条件和其他几何条件相同时,可以通过切口的应力集中系数求得相应裂纹问题的应力强度因子。边界条件比较复杂时,应力集中系数较难求得,而应力强度因子可以通过无限相似单元方法求得,提出了计算平面切口应力集中系数的无限相似单元方法。该方法适应性好、精度高、使用方便。用该方法对几个问题进行了计算。     

起重机金属结构裂纹的复合修复方法

针对起重机金属结构在长期疲劳交变载荷作用下易产生疲劳裂纹的问题，采用碳纤维复合材料（CFRP）加固止裂孔的方法对裂纹进行复合修复。建立不同载荷下止裂孔、CFRP以及复合修复的有限元模型，分析计算应力应变状态和应力集中系数；建立止裂孔打偏情况下复合修复的有限元模型，研究CFRP加固对止裂孔修复的影响；通过静拉伸强度试验，研究复合修复方法对损伤构件的修复效果，并与仿真结果进行对比，验证了CFRP与止裂孔复合修复这一技术的可行性。结果表明，复合修复方法相比于止裂孔及CFRP修复效果，不仅可以消除裂纹尖端的奇异性，减小名义应力，提高试件的承载能力，还可以弥补钻止裂孔修复焊缝裂纹的不足，为工程维修提供了参考。     

Three-dimensional finite element analysis for estimation of the weld residual stress in the dissimilar butt weld piping

Numerous dissimilar metal welds are used to connect carbon steel and stainless steel in nuclear power plants. Recently, some cracks have occurred in the dissimilar metal welds, and welding residual stress is considered as a contributing factor to the cracks. In this study, welding residual stresses in dissimilar butt weld piping were evaluated by the 3-dimensional (3-D) finite element method. Welding residual stresses along the circumference of heat affected zones as well as weld regions were obtained through the analysis, which could not be obtainable with 2-dimensional (2-D) analysis. The differences between 2-D analysis and 3-D analysis are presented in this paper.     

Three-dimensional weld toe magnification factors for various welded joints

To effectively calculate the stress intensity factors in welded components, a weld toe magnification factor is introduced here that will allow for the influence of geometrical effects. This factor was derived from the data obtained in a parametric study performed by FEM. Several sets of weld toe magnification factor solutions have been presented, but these are applicable only to non-load-carrying cruciform or T-butt joints, due possibly to the requirement of very complicated calculations. In the majority of cases for various welded joints such as cruciform, cover plate and longitudinal stiffener joints, the currently used weld toe magnification factors do not adequately describe the behavior of weld toe cracks. In the present study, the weld toe magnification factor solutions with exponents and fractions that have polynomial functions in terms of a/c and a/t ?? i.e., crack depths normalized by corresponding crack lengths and specimen thickness ?? were developed through a parametric study using 3-dimensional finite elements for the above mentioned three types of welded joints. These weld toe magnification factor solutions showed a tendency to increase at a/t < 0.2. Meanwhile, for 0.2 < a/t < 0.7, the effect of the attachment on the weld toe magnification factor decreased asymptotically. When the a/t ratio exceeded this range, the weld toe magnification factor became almost one of unity. The fatigue crack propagation life was evaluated by using the proposed weld toe magnification factor and by considering the propagation mechanisms of multiple-surface cracks, and it showed good agreement-to within a deviation factor of 2-between the experimental and calculated results for the fatigue crack propagation life for all welded joint.     

马氏体不锈钢大拘束度结构焊接裂纹及防止措施

马氏体不锈钢常温组织为硬脆的马氏体组织,它的导热性较碳钢差,焊接残余应力较大,使得在焊后冷却时容易产生裂纹。从力学、金属学两方面分析了产生裂纹的原因,并通过更改焊接材料、优化焊接参数等解决了约束型马氏体不锈钢产生焊接裂纹的问题。     

发电厂主蒸汽管道开裂分析

介绍了某机组主蒸汽管道水压试验隔离阀焊口开裂的情况,通过分析指出管道的一次应力过大是导致管道失效的主要原因。说明对高温高压管道进行改造时,必须重视管道应力分析的重要性。     

基于Ansys的起重机焊缝初始裂纹仿真计算

起重机金属结构中大量存在焊缝,在焊缝中不可避免会存在初始裂纹,初始裂纹的大小决定了焊缝的疲劳寿命,但初始裂纹的测量一直是工程上的一大难点。采用Ansys对带有初始裂纹的起重机典型焊缝试件进行仿真,通过对仿真结果的数据拟合获得裂纹强度因子的表达式,由此可计算该焊缝试件的初始裂纹。该计算方法可为带初始裂纹的起重机焊缝的疲劳寿命预测提供依据和手段。     

Effect of welding heat input on fatigue life of quenched boron steel and FB steel lap joint

The effect of welding heat input on the fatigue life of a quenched boron steel and ferrite-bainite (FB) steel lap joint was investigated. Boron steel was quenched and welded with FB steel in heat input ranging from 0.29 to 0.67 kJ/mm. Boron, which can increase hardenability, affected the microstructure and hardness of the weld metal and heat affected zone (HAZ). The hardness of the weld metal and HAZ increased with decreasing welding heat input, and the high hardness of the weld metal and boron steel HAZ prevented the initiation of cracks in the stress concentration area around the bead. The bead width increased with increasing heat input, and the results of finite element method (FEM) showed that the maximum stress in the notch of the weld joint decreased when the bead width was increased. That is to say, the fatigue life increased when the weld joint had wider bead width. Finally, while the fatigue life was affected by the residual stress, the variation of the welding heat input used in this study had hardly any affect on the residual stress distribution.     

Fatigue strength depending on position of cracks for weldments

This is a study of fatigue strength of weld deposits with transverse cracks in plate up to 50 mm thick. It is concerned with the fatigue properties of welds already with transverse cracks. A previous study of transverse crack occurrence, location and microstructure in accordance with welding conditions was published in the Welding Journal (Lee et al., 1998). A fatigue crack develops as a result of stress concentration and extends with each load cycle until fatigue occurs, or until the cyclic loads are transferred to redundant members. The fatigue performance of a member is more dependent on the localized state of stress than the static strength of the base metal or the weld metal. Fatigue specimens were machined to have transverse cracks located on the surface and inside the specimen. Evaluation of fatigue strength depending on location of transverse cracks was then performed. When transverse cracks were propagated in a quarter-or half-circle shape, the specimen broke at low cycle in the presence of a surface crack. However, when the crack was inside the specimen, it propagated in a circular or elliptical shape and the specimen showed high fatigue strength, enough to reach the fatigue limit within tolerance of design stresses.     

Welding residual stress in roots between deck plate and U-rib in orthotropic steel decks

Fatigue cracks have recently been observed at weld roots between the deck plate and U-rib in orthotropic steel decks. Some cracks initiated from the weld roots and then propagated through the deck plate. The welding residual stress at the root appears to have a considerable influence on crack initiation and propagation. However, the stress has not yet been efficiently clarified in previous studies. In this study, the residual stress of model specimens with or without weld penetration and root gap were measured using the cutting method and magnetostriction method. In addition, thermo-elastic-plastic finite element analyses were carried out on parametric models of actual welded joints.     

蒸压釜的工作特点及失效模式

蒸压釜使用过程中承受交变应力,循环载荷。主要应力有:薄膜应力、弯曲应力、不连续应力、峰值应力、局部应力、温差应力等。常见失效模式主要有:釜体法兰与釜体、釜盖法兰与釜盖的连接焊缝裂纹,蒸压釜固定支座与釜体连接处裂纹,活动支座与釜体的连接部位裂纹,蒸压釜现场组焊环焊缝裂纹,釜体底部腐蚀、釜体法兰失圆、安全联锁装置失效、内表面损伤等。     

游梁式抽油机悬绳器焊接裂纹的探讨

对游梁式抽油机悬绳器焊接裂纹产生原因进行了分析.结果表明:由于钢淬硬以后,焊缝在氢的诱发和促进下发生脆化,并在拘束应力的作用下而形成了裂纹;铸件焊缝熔合线开裂是因为铸件热处理不完善所致,为此采用了"先E4303焊条打底,后E5016焊条进行第二层焊接"的工艺方法,有效地解决了该悬绳器焊缝冷裂纹的产生.