焊接吊车梁疲劳裂缝及加固试验的研究

文章对包钢棒材厂钢坯跨重级工作制钢吊车梁腹板上部裂缝进行了全面的检测与评估,并将一根损伤有代表性的吊车梁在实验室进行了疲劳模拟实验和研究,发现疲劳裂缝多出现在小车频繁移动的区域；轨道偏离导致卡轨严重的区域及轨道接头处产生冲击荷载区域.得出卡轨力、冲击力、偏心荷载是影响吊车梁疲劳破坏的主要因素的结论.     

重级工作制直角突变式钢吊车梁突变处疲劳性能分析

本文从近年发生的直角突变式吊车梁疲劳破坏分析入手,采用有限元计算与传统手册计算对比,分析了突变点疲劳破坏的原因,提出了突变点插板的应力集中系数、疲劳类别以及提高特重级工作制吊车梁的欠债效应的等效系数等建议,供特重级工作制吊车梁设计参考使用。     

450／80t钢吊车梁突变支座改进设计

通过对450／80t钢吊车梁圆弧式突变支座及直角式突变支座应力及疲劳破坏的分析比较,决定在实际设计中采用直角式突变支座并进行了改进。     

轻型钢结构吊车梁设计方法及节点构造

通过分折和研究单层门式刚架轻型钢结构厂房中的吊车梁设计，总结了轻型钢结构吊车梁的设计方法和节点连接构造，对合理设计吊车梁，降低用钢量提出了设计建议。     

钢吊车梁加固的一种简便处理方法

厂房由于生产工艺改造要求，加大吊车吨位后，对钢吊车梁系统进行检测鉴定与加固设计的实际工程，介绍了一种在不停产情况下采用钢斜撑方案加固在用钢吊车梁的一种方法。     

变截面钢吊车梁挠度计算的近似公式

对于变截面钢吊车梁,一些设计手册中仅给出了一种变截面形式的梁在特定条件下的挠度计算公式、。本文利用共轭梁法提出现有各种开荒为截面钢吊车梁挠度计算的一般公式,同时论证了吊车梁挠度计算的一般公式只能是近似式。     

钢吊车梁裂缝分析与处理

以实际工程为背景,对钢吊车梁裂缝产生的原因进行了分析,提出解决措施,以供类似工程处理参考。     

钢吊车梁设计中应注意的几个问题

阐述了钢吊车梁设计的一般规定,即吊车动力系数与荷载的确定,挠度的容许值,实腹式焊接梁翼缘板和腹板的连接,吊车梁垂直支撑和横向加劲肋的设置等。     

钢吊车梁的裂缝及其维修

吊车梁结构的整体性、稳定性是确保工业生产正常运行的关键一环。本文通过对吊车梁运行过程中出现的裂缝现象,原因认定和分析,提出设计、检修、维护措施。     

大跨距钢吊车梁的制作

介绍了大跨距钢吊车梁制作过程中,在下料、厚板焊接、构件组装、钢梁焊接、矫正、翻身等方面所采取的技术措施,使吊车梁的施工质量满足规范和设计要求.     

新型扭杆弹簧用高强度马氏体钢疲劳性能研究

利用旋转弯曲疲劳试验研究新型扭杆弹簧用N1钢和45CrNiMoVA钢的疲劳性能,并通过对2种试验钢组织、硬度、强度、夹杂物类型及大小、疲劳裂纹扩展速率以及氢含量的对比,探讨影响扭杆弹簧用钢旋转弯曲疲劳性能的因素及其疲劳失效机制.结果表明,推荐热处理制度的45CrNiMoVA钢和N1钢旋转弯曲疲劳极限强度分别为892和9...     

Failure Diagram and Chemical Driving Forces for Subcritical Crack Growth

Kitagawa-Takahashi diagram that is modified for fatigue is now extended to the subcritical crack growth behavior under stress-corrosion crack growth. The analogy with the fatigue helps us to identify several regimes of interest from both the point of understanding of the material behavior as well as quantification of the failure process for structural design of components that are subjected to stress-corrosion and corrosion fatigue crack growths and failure. In particular, the diagram provides a means of defining the mechanical equivalent of chemical stress concentration factor and the chemical crack-tip driving forces to crack growth or its arrest. In addition, threshold stresses, crack arrest, and nonpropagating crack growth conditions can be defined, which help in developing sound design methodology against stress corrosion and corrosion fatigue. Chemical crack driving forces under corrosion fatigue can be similarly defined using the inert behavior as a reference.     

汽车齿轮轴用钢SCM440H扭转疲劳寿命及断裂特征分析

通过试验测定汽车齿轮轴用钢SCM440H经淬火和高温回火后的扭转疲劳寿命,并采用扫描电镜(SEM) 对疲劳断口进行观察、分析。结果表明,显微组织为回火索氏体的SCM440H齿轮轴用钢,在106的循环周次下,扭转疲劳强度约为253MPa;不同切应力幅下的扭转疲劳断口呈现韧性断裂特征,疲劳断口裂纹源处没有明显的析出物。     

Fatigue crack propagation in Ni-base superalloy single crystals under multiaxial cyclic loads

The effects of crystallographic orientation and stress state on the multiaxial fatigue behavior of MAR-M200* single crystals were examined. Using notched tubular specimens subjected to combined tension/torsion cyclic loads, crack growth rates were determined at ambient temperature as functions of stress intensity range, the shear stress range-to-normal stress range ratio, and crystallographic orientation. Comparison of crack growth data at the same effective ΔK reveals a weak dependence of the crack growth rate on both the tube axis and the notch orientation. For a given set of tube axis and notch orientation, the crack growth rate might or might not vary with the applied stress state, depending on whether roughness-induced crack closure is present. In most cases, subcritical cracking occurs either along a single 111 slip plane or on ridges formed with two 111 slip planes. Neither fracture mode is altered by a change in the applied stress state. This complex crack growth behavior will be discussed in terms of the crack-tip stress field, slip morphology, and crack closure. Formerly with Southwest Research Institute     

温度与应力比对6061铝合金疲劳裂纹扩展行为的影响

为了研究温度与应力比对航空铝合金疲劳裂纹扩展行为的影响,利用电液伺服疲劳试验机对6061铝合金材料开展了不同温度(室温、-70、150 ℃)、应力比(0.1、0.5)条件下的疲劳裂纹扩展速率试验,获得不同条件下的疲劳裂纹扩展速率曲线,揭示温度与应力比对疲劳裂纹扩展的影响规律。结果表明,在相同应力比下,室温与高温150 ℃下的疲劳裂纹扩展速率曲线(da/dN-ΔK)基本一致,低温-70 ℃下的疲劳门槛值与疲劳裂纹扩展速率明显提高,这表明低温环境下6061铝合金材料具有较高的抗疲劳裂纹扩展性能;在相同温度下,随着应力比的增大,疲劳门槛值降低,疲劳裂纹扩展速率升高。讨论了温度与应力比对疲劳裂纹扩展行为影响的可能原因。     

Fatigue Crack Growth Analysis Under Spectrum Loading in Various Environmental Conditions

The fatigue process consists, from the engineering point of view, of three stages: crack initiation, fatigue crack growth, and the final failure. It is also known that the fatigue process near notches and cracks is governed by local strains and stresses in the regions of maximum stress and strain concentrations. Therefore, the fatigue crack growth can be considered as a process of successive crack increments, and the fatigue crack initiation and subsequent growth can be modeled as one repetitive process. The assumptions mentioned above were used to derive a fatigue crack growth model based, called later as the UniGrow model, on the analysis of cyclic elastic–plastic stresses–strains near the crack tip. The fatigue crack growth rate was determined by simulating the cyclic stress–strain response in the material volume adjacent to the crack tip and calculating the accumulated fatigue damage in a manner similar to fatigue analysis of stationary notches. The fatigue crack growth driving force was derived on the basis of the stress and strain history at the crack tip and the Smith–Watson–Topper (SWT) fatigue damage parameter, D = σ_maxΔε/2. It was subsequently found that the fatigue crack growth was controlled by a two-parameter driving force in the form of a weighted product of the stress intensity range and the maximum stress intensity factor, ΔK ^p K _max ^1?p . The effect of the internal (residual) stress induced by the reversed cyclic plasticity has been accounted for and therefore the two-parameter driving force made it possible to predict the effect of the mean stress including the influence of the applied compressive stress, tensile overloads, and variable amplitude spectrum loading. It allows estimating the fatigue life under variable amplitude loading without using crack closure concepts. Several experimental fatigue crack growth datasets obtained for the Al 7075 aluminum alloy were used for the verification of the proposed unified fatigue crack growth model. The method can be also used to predict fatigue crack growth under constant amplitude and spectrum loading in various environmental conditions such as vacuum, air, and corrosive environment providing that appropriate limited constant amplitude fatigue crack growth data obtained in the same environment are available. The proposed methodology is equally suitable for fatigue analysis of smooth, notched, and cracked components.     

Fatigue Fracture of Concrete Subjected to Biaxial Stresses in the Tensile C–T Region

In this paper cyclic quasi-static and constant amplitude fatigue responses of concrete subjected tensile compression–tension (C–T) biaxial stress are presented. In the tensile C–T region within the biaxial stress space, magnitude of the principal tensile stress is larger than or equal to that of the principal compressive stress. An experimental program consisted of subjecting hollow, cylindrical concrete specimens to torsional loading. Failure in both quasi-static and fatigue is due to crack propagation. It is shown that the crack propagation resulting from the biaxial loading can be predicted using Mode I fracture parameters. The fatigue crack growth is observed to be a two-phase process: an acceleration stage that follows a deceleration stage. The crack length where the rate of crack growth changes from deceleration to acceleration is shown to be equal to the crack length at the quasi-static peak load. Analytical expressions for crack growth in the deceleration and acceleration stages are developed in terms of the mechanisms that influence quasi-static crack growth. The model parameters obtained from uniaxial fatigue tests are shown to be sufficient for predicting the biaxial fatigue response. Finally, a fracture-based fatigue-failure criterion is proposed, wherein the fatigue failure can be predicted using the critical Mode I stress intensity factor.     

Fatigue studies on piping components including fatigue-ratchetting interaction

A component test programme was initiated to address the applicability of leak-before-break to Indian PHWRs. After completing the tests with constant amplitude loading under air environment, the interactive nature of fatigue was addressed. The parameters considered the present studies are:

• Water environment and constant amplitude loading
• Loading due to bending and torsion
• Fatigue ratchetting

This paper describes the results of the effect of above parameters on the fatigue crack growth behavior of the piping components of Indian Power Reactors. Water environment accelerates the fatigue crack growth rate in case of both carbon steel and stainless steel. Similarly, the presence of torsion has the effect of inducing higher crack growth rate. But the final aspect ratio is not affected by these interactions and the leak-before-break argument remains valid. The results of the fatigue-ratchetting tests address a new phenomenon. The test data has necessitated a modification to the Coffin-Basquin equation to account for the triaxiality and the ductility exhaustion due to strain accumulation resulting from ratchetting. The modified equation gave a very good match to the fatigue life observed during the tests.     

起重机械承力构件应力集中分析

以双梁桥式起重机为例,通过对承力构件的应力分析计算,探讨起重机械中存在的应力集中现象,以及由此引起的疲劳裂纹。分析计算表明,正常情况下,主梁的弯曲正应力及弯曲剪应力均满足要求,但由于主梁有仓门处的形状突变及表面粗糙,应力集中度大,不满足剪切疲劳强度要求。因此,承力构件出现的裂纹是应力集中引起的疲劳裂纹。建议对在用的起重机械承力构件进行应力集中分析,及时消除安全隐患。     

Fatigue crack initiation and propagation in a quenched and tempered niobium bearing HSLA steel

The fatigue crack initiation and propagation behavior of a niobium bearing HSLA steel heat treated to give two tempered martensitic microstructures presumably with and without fine niobium carbides has been studied by light microscopy, electron microscopy, and strain gage measurements of plastic zone deformation. The high cycle, stress controlled fatigue life of the steel in both heat treated conditions was quite similar with the steel presumably containing the fine niobium carbides having slightly better resistance at low stress amplitudes. This slightly better high cycle resistance is associated with better resistance to fatigue crack initiation for this heat treatment. The fatigue crack propagation behavior of the steel was the opposite. The steel presumably containing the fine niobium carbides exhibited a much faster fatigue crack growth rate than that without them. The difference in growth rates is explained in terms of the plastic work expended during the propagation of the fatigue crack.