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Fatigue strength analysis of offshore tubular welded joints under constant amplitude loading: Local strain and fracture mechanics approach.

机译：恒定振幅载荷下海上管状焊接接头的疲劳强度分析：局部应变和断裂力学方法。

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摘要

The main components of steel offshore structures, whether fixed or floating, are generally tubular members. Large stress concentrations arise due to the abrupt geometric dicontinuities at the intersections of these welded tubular members, called joints or nodes. The varying environmental loads acting on these joints cause fatigue crack initiation, growth and their final catastrophic failure. This thesis presents a numerical study of the total fatigue life of offshore tubular welded joints under the action of axial, in-plane and out-of-plane bending loads, using local stress-strain and linear elastic fracture mechanics approaches. The study includes the development of a computer program for the automatic generation of meshes for tubular joints and a contact program for the prevention of crack surface penetration.;Stress analysis to determine the possible location of the crack initiation on the tubular joint has been carried out using eight noded degenerate isoparametric shell elements. The influence of geometric parameters on the stress distribution around the joint as well as through the joint thickness has been investigated, and the results obtained therein compared with experimental results; they also have been compared with established parametric equations. Good comparisons have been obtained with the experimental values.;The local stress-strain approach, using the Manson-Coffin rule, is utilized for the study of the crack initiation. Using experimental investigations on crack initiation life of tubular welded T-joints, fatigue strength exponent b and fatigue ductility exponent c have been determined empirically and used to compute crack initiation life of the tubular joints analyzed in this study.;The weld toe crack influence on the through thickness and surface stress distribution has been studied using the line spring element in conjunction with the degenerate eight node shell elements to model the crack. The stress intensity factors determined, from this study, were compared with available theoretical studies and found to give good results.;Using the stress intensity factors obtained from the line spring model, the through-thickness crack propagation lives of the tubular joint under consideration were predicted using Paris crack growth law. The propagation lives for each loading conditions were predicted, on an incremental cycle basis, up to 90% of the chord thickness cracking. The estimated fatigue lives were compared with experimental investigations carried out at Memorial University of Newfoundland St. John's (for axial loading) and University of Waterloo (for in-plane loading) under the Canadian Cooperative Offshore Tubular Joint Program and found to give good results.
机译：海上钢结构的主要部件，无论是固定的还是浮动的，通常都是管状构件。由于在这些焊接的管状构件（称为接头或节点）的相交处突然出现几何不连续性，因此产生了很大的应力集中。作用在这些接头上的变化的环境载荷会导致疲劳裂纹的萌生，扩展以及最终的灾难性破坏。本文利用局部应力应变和线性弹性断裂力学方法，对轴向，面内和面外弯曲载荷作用下的海上管状焊接接头的总疲劳寿命进行了数值研究。该研究包括开发用于自动生成管状接头网格的计算机程序和用于防止裂纹表面渗透的接触程序。;已经进行了应力分析，以确定裂纹在管状接头上的可能位置。使用八个节点的简并等参壳单元。研究了几何参数对接头周围应力分布以及贯穿接头厚度的影响，并将所得结果与实验结果进行了比较；它们也已与已建立的参数方程式进行了比较。与实验值取得了很好的比较。局部应力-应变方法，使用曼森-科芬（Manson-Coffin）规则，被用于裂纹萌生的研究。通过对管状焊接T形接头的裂纹萌生寿命进行实验研究，通过经验确定了疲劳强度指数b和疲劳延性指数c，并用于计算本研究中分析的管状接头的裂纹萌生寿命。使用线弹簧单元和退化的八个节点壳单元对裂纹进行建模，研究了贯穿厚度和表面应力分布。通过这项研究确定的应力强度因子与现有的理论研究进行比较，并得出了良好的结果。；使用从线弹簧模型获得的应力强度因子，可以考虑所考虑的管状接头的全厚度裂纹扩展寿命使用巴黎裂缝增长定律预测。在递增循环的基础上，预测了每种载荷条件下的传播寿命，最高可达弦厚裂纹的90％。将估计的疲劳寿命与在加拿大合作海上管状接头计划下在纽芬兰圣约翰纪念大学（轴向载荷）和滑铁卢大学（平面载荷）进行的实验研究进行了比较，结果显示出良好的效果。

著录项

  • 作者

    Nwosu, Daniel Iheanacho.;

  • 作者单位

    Memorial University of Newfoundland (Canada).;

  • 授予单位 Memorial University of Newfoundland (Canada).;
  • 学科 Engineering Civil.;Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 1993
  • 页码 361 p.
  • 总页数 361
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 普通生物学;
  • 关键词

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