FPSO典型焊接接头残余应力释放及其对疲劳强度的影响

为了在估算结构疲劳强度时计及残余应力释放的作用,合理地解释在以往焊接接头疲劳试验中不能解释的试验结果,借助三维弹塑性有限元法,研究了FPSO典型焊接接头在任意变幅循环载荷作用下的残余应力释放规律,建立了在任意变幅循环载荷作用下残余应力释放大小与残余应力和外载荷大小之间的计算公式,从而定量地分析了残余应力的释放,提高了疲劳强度估算的准确性和可靠性。     

残余应力释放影响FPSO疲劳强度的研究综述

浮式生产储油卸油船(FPSO)服役前常经历过较大的静载荷,会使焊接接头处较高的残余应力产生释放,船舶结构还承受着不断变化的波浪载荷。在估算FPSO等船舶结构典型焊接接头的疲劳强度时,需考虑残余应力释放的影响。介绍了国外学者对该方面的研究动态、发展趋势和研究成果。详细描述了基于残余应力释放的FPSO疲劳强度需重点关注的一些问题。     

FPSO典型焊接接头在疲劳载荷下的残余应力释放数值模拟

为了保证FPSO典型焊接结构的安全可靠性,较准确地预测残余应力在疲劳载荷下的释放状况,采用了三维弹塑性有限元方法．首先分析了在有预载荷情况下,FPSO典型焊接接头的残余应力释放大小,并用试验数据进行验证,然后分析了该结构在疲劳载荷下的残余应力释放行为．计算结果表明,残余应力释放是与初始残余应力和外载荷的大小密切相关的．     

残余应力对水下耐压结构典型焊接接头疲劳强度的影响

水下耐压结构典型焊接接头模型常采用高强度钢建造,对焊接残余应力较为敏感,因此有必要针对残余应力对其疲劳强度的影响进行相关研究。采用ANSYS的APDL语言编程,通过数值模拟分析得到典型焊接接头的焊接残余应力;并基于局部应力—应变法,对水下耐压结构典型焊接接头考虑与不考虑残余应力这2种情况下结构的疲劳寿命进行数值分析。研究发现:典型焊接接头在凹锥面焊缝附近其残余应力最大,寿命最短;其寿命周期为104,属低周疲劳范围;随着外载荷的增加,疲劳寿命最小值也随之减小;残余应力的存在会明显降低典型焊接接头的疲劳寿命。     

变幅载荷作用下焊接接头疲劳寿命预测方法

船舶与海洋结构物在其服役过程中受到波浪等载荷的交变作用而引起结构的疲劳损伤.检测结果表明船舶及海洋结构的疲劳热点部位大多数是在构件相互连接的焊缝焊趾处.因此,研究典型接头表面裂纹应力强度因子统一计算方法以及变幅载荷作用下表面裂纹扩展规律对船舶与海洋结构物的寿命预测是十分重要的.本文讨论了裂纹闭合及开口比的计算,在Newman有效应力强度因子计算方法的基础上,提出了考虑因素更全面的有效应力强度因子幅计算式以及变幅载荷作用下船舶与海洋结构物典型焊接接头疲劳裂纹扩展寿命预测模型.     

AH36船用高强钢焊接残余应力释放的数值模拟与试验分析

为了解焊接残余应力及其释放规律,基于顺序耦合热力学有限元方法对ABAQUS软件进行二次开发,模拟平板对接焊的焊接过程,计算焊接残余应力分布及其在0.8σ_s循环拉伸载荷作用下的释放情况,同时开展相应的试验研究,验证有限元计算方法的有效性。讨论循环载荷大小对残余应力释放的影响,计算3种不同水平载荷下焊接残余应力释放情况,得出AH36钢对接焊平板残余应力释放计算公式,通过对比有限元计算结果与试验结果,表明残余应力释放公式具有较好的计算精度,可以用于估算不同载荷作用后焊接残余应力的释放。     

考虑焊接残余应力释放的结构疲劳寿命分析方法研究

焊接残余应力对于焊接结构的疲劳寿命产生很显著的影响,同时循环载荷作用下焊接残余应力会出现释放现象,因此有必要对焊接件疲劳寿命预测方法进行研究.基于改进的McEvily疲劳裂纹扩展速率模型,同时结合课题组研究得到的AH36钢对接焊平板残余应力释放计算公式,提出考虑焊接残余应力释放的结构物疲劳寿命计算方法.随后,以潜艇锥柱耐压壳的疲劳为例,详细阐述了本文提出的疲劳寿命分析方法的计算流程.考虑耐压壳焊接顺序影响,分析了含半椭圆表面裂纹的锥柱耐压壳疲劳寿命.对比文献的试验结果,表明焊接结构疲劳寿命计算公式有较好的预测效果,可以用于评估带表面裂纹焊接件在拉伸循环载荷作用下的疲劳寿命.     

一种复杂载荷作用下船舶结构疲劳裂纹扩展预报方法

风暴模型是Tomita等提出的用来评估船舶结构疲劳强度的一种随机波浪载荷简化模型,它能表达波浪载荷是与时间相关的随机过程。文中介绍了风暴模型及波浪诱导应力短期分布的基本特征。将风暴模型和裂纹扩展率单一曲线模型及焊趾表面裂纹应力强度因子的计算方法结合起来,探讨了复杂载荷作用下船舶结构疲劳裂纹扩展预报方法。并用权函数法计算了给定残余应力分布的表面裂纹应力强度因子。预报了对接焊接接头焊趾处表面裂纹在风暴波浪载荷作用下的疲劳裂纹扩展行为,结果表明风暴的大小、顺序,初始裂纹尺寸及残余应力对裂纹扩展行为影响明显。合理的风暴模型参数及初始裂纹尺寸的确定对船舶结构的疲劳寿命预报是非常重要的。     

焊接速度对AH36船用高强钢焊接残余应力及其释放的影响

基于ABAQUS软件二次开发,建立平板对接焊试件焊接残余应力及其释放的有限元模型,利用顺序耦合热力学数值仿真计算3种焊接速度下的焊接残余应力分布,并研究了3种焊接速度下初始焊接残余应力在3种拉伸循环载荷作用下的释放情况。随着焊接速度的增加,沿试件深度方向的初始横向焊接残余应力明显下降。在相同外载荷作用下,随着焊接速度的降低,焊接残余应力释放水平提高、释放量增加。随着焊接速度的增加,第一次循环残余应力的释放量占循环50次后残余应力释放总量的比例增加。     

焊接速度对AH36船用高强钢焊接残余应力及其释放的影响

焊接件由于焊接速度不同,焊接残余应力分布存在很大差异,焊接残余应力在循环载荷作用下会产生释放现象,焊接残余应力存在对于结构安全性和稳定性有很大影响,有必要开展焊接速度对于焊接残余应力及其释放影响研究。基于ABAQUS软件二次开发建立平板对接焊试件焊接残余应力以及释放有限元模型,利用顺序耦合热力学数值仿真计算三种焊接速度下的焊接残余应力分布,并开展三种焊接速度下初始焊接残余应力在三种拉伸循环载荷作用下的释放情况研究。     

一种基于累积损伤理论和裂纹尖端弹塑性应力场的裂纹扩展预测方法

文章提出了一种预测疲劳寿命的应力循环叠加和损伤循环叠加的双重叠加方法。该方法依据累积损伤理论,通过分析变幅载荷下裂纹尖端的应力场,采用应力循环叠加的方法反映残余应力的影响;同时利用SWT应力应变和寿命的关系,循环叠加裂尖损伤。该方法能够很好地反映过载时裂纹扩展的迟滞效应,适合变幅载荷下疲劳寿命的评估分析。     

随机载荷作用下的疲劳裂纹扩展

船舶等许多工程结构在服役过程中的受载荷历程是一个随机过程.而变幅载荷下的载荷相互作用对疲劳裂纹扩展寿命将产生显著的影响.因此研究随机载荷作用下的裂纹扩展及定量计算对船舶结构的疲劳寿命预测的可靠性是十分重要的.该文提出了一个基于有效应力强度因子,以应力比和裂纹尖端塑性区尺寸为主要参数的随机载荷作用下疲劳寿命预测模型.该模型用于预测几种载荷谱作用下的裂纹扩展试验,结果表明预测结构和实验结果符合得很好.     

循环荷载波形变化对天津滨海软土刚度软化特性的影响

为研究循环荷载波形对结构性软土刚度软化的影响,以天津滨海新区天津港保税区海积软土为研究对象,对其施加不同波形、不同幅值的循环荷载。试验结果表明:当循环荷载应力幅值较小时,软土刚度软化速率慢,不同波形循环荷载对软土刚度软化影响差别不大;当循环荷载较大时,软土刚度软化速率加快,荷载波形变化对结构性软土刚度软化速率影响明显,其中方波循环荷载作用下软土刚度软化的速率最大,正弦波次之,三角波最小。通过对比分析不同波形、不同应力幅值荷载作用下软土软化指数衰减曲线,得到综合考虑荷载波形和应力幅值的软化指数经验公式。     

Full-scale fatigue tests of ship structures to validate the S–N approaches for fatigue strength assessment

Ships belong to those welded structures which are prone to fatigue due to high cyclic loads. Different approaches exist for the fatigue strength assessment which are varying between the industrial sectors. Therefore, deeper fatigue strength investigations were performed in Germany within an industry-wide joint research project aiming at the harmonization of the approaches. Regarding ship structures, two types were selected for full-scale tests. The first concerned web frame corners being typical for roll-on/roll-off ships (ro/ro) ships, from which three models were tested under constant amplitude loading. The second type was the intersection between longitudinals and transverse web frames, which recently showed fatigue failures in containerships. Five models were tested, three under constant and two under variable amplitude loading. All tests showed a relatively long crack propagation phase after first cracks had appeared, calling for a reasonable failure criterion. For the numerical analysis, the structural hot-spot stress as well as the effective notch stress approach have been applied. The latter allows the consideration of the weld shape which could partly explain differences in the observed and calculated failure behaviour. Another factor is the distribution of welding-induced residual stresses, which obviously affected the failure behaviour in the web frame corner as well. Insofar the investigations give a good insight into the strength behaviour of complex welded structures and into current problems and opportunities offered by numerical analyses.     

交变载荷下厚板对接焊残余应力的松弛行为

对于承受交变载荷的焊接构件,焊接残余应力的存在对于结构的疲劳寿命影响巨大。由于焊接残余应力形成机理的复杂性,当交变载荷作用时,焊接残余应力的松弛演变具有不确定性,导致该领域的研究难度相当大。迄今为止,鲜有文献就交变载荷下的厚板焊接残余应力松弛行为进行深入报道。采用低周疲劳试验,利用X射线残余应力测试仪,对试件表面焊接残余应力的松弛演变行为进行追踪研究,通过在试件表面近焊缝区布置网状测点,采集测点的横向及纵向焊接残余应力进行数据拟合,在试验对比修正的基础上,最终建立焊接残余应力的松弛演变模型。结果表明：在交变载荷作用下,焊接残余应力会发生松弛,并且,应力松弛量的大小与交变载荷的特征值大小紧密相关。     

半潜式钻井平台用钢DH36安定行为试验研究

为了给半潜式钻井平台的安全性和寿命评价提供可靠试验依据,在室温下对半潜式钻井平台用钢DH36钢进行了考虑加载波形、加载速率和应力比影响的多工况单轴棘轮安定试验。结果表明:循环硬化速率随循环周次的增加快速下降,在低于某一值的循环应力作用下,应变将最终趋于棘轮饱和状态;正弦应力波比三角波更快地趋于安定,采用较低的加载速率可以加速材料趋向饱和棘轮状态;峰值应力固定不变时,棘轮应变对应力比历史无明显的记忆性;波形和加载速率对饱和棘轮应变的影响有限,饱和棘轮应变随着应力峰值的增加而增大。     

Numerical investigation on the ultimate strength of stiffened cylindrical shells considering residual stresses and shakedown

In this paper, the effects of residual stresses on the ultimate strength of stiffened cylinders are numerically investigated with an emphasis on shakedown which might occur during the service of these structures. Residual stresses caused by two types of actions, namely, cold bending and welding, are simulated with simplified approaches in numerical analysis. Cold bending stresses are simulated by simulating cold rolling and elastic springback until the desired curvature for cylindrical shell is obtained. Welding is simulated by applying cooling down to a certain temperature on the elements adjacent to stiffener-shell joints to obtain weld-shrinkage with realistic magnitudes. Six small-scale externally pressurized ring-stiffened cylinder models are utilized to evaluate the appropriateness of the method for inclusion of welding residual stresses in numerical analysis by comparing the experimental and numerical results. Ultimate strength analyses are then performed for a reference ring-stiffened cylinder model under radial pressure and stringer-stiffened cylinder under axial loading. To assess the effect of shakedown, after applying cyclic compressive loading to the ring-stiffened cylinder model, the level of stress relief and the change in the ultimate strength are evaluated.     

A simplified life estimation method for the spherical hull of deep manned submersibles

Creep and fatigue are involved in the loading of deep manned submersible, which is a rather complex variable amplitude pattern. Dwell effects resulting in lower life than pure fatigue are observed in the prior experimental research while no proper prediction methods are available to explain the phenomenon. Recently, the authors proposed a modified crack growth rate model to explain the creep effect under the cyclic loading which is validated for the crack growth of some titanium alloys under cyclic creep loading, however, its application is restricted to the condition where lots of parameters have to be determined based on many experiments and it is not very convenient in the material selection and primary design stage of a component. In this paper, a simplified prediction model for the load pattern of constant amplitude cyclic loading is proposed aiming at one of the most applicable materials for the pressure hull of submersibles, Ti–6Al–4V ELI. The method can be easily used to estimate the life of the pressure hull based on two series of basic mechanical properties of the material and validated by the modified crack growth rate model with parameters determined by large amounts of experimental data.