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An investigation of residual stresses in tubing.

机译：调查管中的残余应力。

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摘要

Residual stresses fall naturally into two categories; macrostresses and microstresses. An indication of the origins of both, types is given. The presence of residual macrostresses in a body can be recognized by the occurrence of distortions on making cuts in the body. In bodies of regular geometry, the distortions which occur on gradual removal of uniform layers from one surface can often be used to assess the magnitude of the residual stresses in the removed material. Over the years, many techniques based on this principle have been developed. The Sachs method (ref.5) for the determination of triaxial axisymmetric residual stresses in solid bars, hollow cylinders and tubes, is one such technique, A brief account of the method and the assumptions on which it is based is presented, A number of important refinements are described. The residual stresses in thin-walled cylinders and tubing have been the subject of many experimental investigations, Although some studies of quenching and machining stresses have been carried out, the residual stresses produced during tube-drawing have attracted the most attention. Recent work on this topic is briefly reviewed, and the origins of residual stress in drawn tubing are discussed. Although it has long been realised that tubing drawn under commercial conditions almost always exhibits some degree of eccentricity, only Knights (82) has suggested that this should be taken into account when determining residual stresses in such tubing. The same author has also suggested that significant circumferential variations of the residual stresses may occur in drawn tubing, possibly associated with plastic bending at entry or exit from the drawing die. The present work was carried out to determine whether circumferential variations of residual stress existed in drawn tubing, to establish the effect of eccentricity on the determination of residual stress by the Sachs method, and to evaluate the bending deflection method (which is the usual alternative to the Sachs technique) in the presence of eccentricity and possibly suggest some improvements. The results obtained from an experimental investigation of the longitudinal and circumferential variation of the deformations produced on cutting drawn tubing to length suggest the presence of additional residual stresses not previously reported. The terms 'type A' and 'type B' residual stresses are introduced to distinguish between normal residual stresses and the additional residual stresses. 'Type B' longitudinal residual stresses exist as alternate regions of tension and compression round the circumference of drawn tubing and 'type B' circumferential residual stresses exist as opposing bending stresses in adjacent lengths. Both appear to be completely relieved in what are normally regarded as 'long' specimens (i,e, for the tubing used, in specimens with length/diameter ratios less than 5). 'Type B' longitudinal residual stresses may possibly be associated with imperfect lubrication during drawing. The origin of 'type B' circumferential residual stresses is not clear. The determination of circumferential and radial 'type A' residual stresses in a uniform cylinder by the Sachs technique is based on the assumption that the relief of these stresses in part of the cylinder (by layer removal) is equivalent to the application of a uniform pressure to the remainder. Since the application of a uniform pressure to an eccentric cylinder produces circumferential variations of stress on both boundaries, the Sachs technique cannot readily be applied where eccentricity is appreciable. Experimental results suggest that the Sachs technique can be applied in practice to determine the circumferential and radial 'type A' residual stresses over about 80% of the wall thickness of drawn tubing with I.D./O.D. =0.941 and an initial wall thickness variation less than +/-6% provided that these residual stresses do not vary circumferentially, Where the circumferential stresses applied by layer removal are compressive, the procedure may be complicated by the occurrence of elastic pre-buckling deformations of a circumferential lobar form, and a stage may even be reached at which plastic buckling takes place, The determination of longitudinal 'type A' residual stresses in the presence of eccentricity is complicated by the development of longitudinal shear stresses as the variation of wall thickness is increased by layer removal. The possibility of applying a simple modification of the Sachs analysis which takes account of wall thickness variation, but not shear stresses, is examined. The limitations of the Sachs method in the presence of eccentricity are discussed. Although the bending deflection method has certain advantages over the Sachs technique for the determination of 'type A' longitudinal residual stresses in the presence of eccentricity, its usefulness is restricted since no satisfactory method of determining the coexistent circumferential residual stresses is available, A method which incorporates a recently developed technique for the determination of local residual stress (91,100), is proposed and is shown to have considerable advantages.
机译：残余应力自然分为两类：宏观压力和微观压力。给出了两种类型的起源的指示。人体中残留的宏观应力可以通过在人体上切开时出现变形来识别。在规则几何体中，从一个表面逐渐去除均匀层时发生的变形通常可用于评估去除后的材料中残余应力的大小。多年来，已经开发了许多基于此原理的技术。用于确定实心棒材，中空圆柱体和管材中三轴轴对称残余应力的萨克斯方法（参考文献5）就是这样一种技术，简要介绍了该方法和所基于的假设，描述了重要的改进。薄壁圆筒和管材中的残余应力一直是许多实验研究的主题，尽管已经进行了淬火和机加工应力的一些研究，但在拉管过程中产生的残余应力引起了最大的关注。简要回顾了有关该主题的最新工作，并讨论了抽油管中残余应力的起源。尽管人们早已认识到在商业条件下抽出的油管几乎总是表现出一定程度的偏心率，但只有Knights（82）建议在确定此类油管的残余应力时应考虑到这一点。同一作者还提出，在拉制管材中可能会发生残余应力的明显周向变化，这可能与拉制模头进入或退出时的塑性弯曲有关。目前的工作是确定抽油管中是否存在残余应力的周向变化，建立偏心率对通过Sachs方法确定残余应力的影响以及评估弯曲挠度方法（这是通常的替代方法）。 （Sachs技术）在偏心的情况下，可能会提出一些改进。从对拉长的油管切割成一定长度后产生的变形的纵向和周向变化进行实验研究的结果表明，存在先前未报道的其他残余应力。引入术语“ A型”和“ B型”残余应力以区分正常残余应力和其他残余应力。 “ B型”纵向残余应力存在于拉伸管周围的拉伸和压缩交变区域，而“ B型”纵向残余应力存在于相邻长度的相反弯曲应力中。在通常被认为是“长”样本的情况下（例如，对于所使用的管道，在长度/直径比小于5的样本中），两者似乎都被完全消除了。 “ B型”纵向残余应力可能与拉拔过程中的润滑不良有关。 “ B型”圆周残余应力的起源尚不清楚。通过Sachs技术确定均匀圆柱体中的周向和径向“ A型”残余应力的假设是，假设这些应力在圆柱体的一部分中的释放（通过去除层）等效于施加均匀的压力其余的。由于向偏心圆柱体施加均匀的压力会在两个边界上产生应力的周向变化，因此，Sachs技术无法轻易应用于偏心率较高的地方。实验结果表明，可以在实践中应用Sachs技术来确定周向和径向``A型''残余应力超过内径/外径的拉伸管壁厚的80％。 = 0.941且初始壁厚变化小于+/- 6％，前提是这些残余应力不会沿周向变化。如果通过去除层施加的周向应力是压缩性的，则过程可能会因发生弹性预屈曲变形而变得复杂圆周叶形，甚至可以达到发生塑性屈曲的阶段。由于壁厚的变化，纵向剪切应力的发展使确定存在偏心的纵向“ A型”残余应力变得复杂通过去除层来增加。研究了对Sachs分析进行简单修改的​​可能性，该修改考虑了壁厚的变化，但没有考虑剪应力。讨论了在存在离心率的情况下Sachs方法的局限性。尽管在偏心存在的情况下，弯曲挠度法相对于Sachs技术具有确定“ A型”纵向残余应力的某些优势由于尚无令人满意的确定共存的圆周残余应力的方法，因此其用途受到限制。提出了一种结合了最新开发的确定局部残余应力的技术的方法（91,100），该方法具有明显的优势。

著录项

  • 作者

    Simpson, George Bleet.;

  • 作者单位

    University of Glasgow (United Kingdom).;

  • 授予单位 University of Glasgow (United Kingdom).;
  • 学科 Mechanical engineering.
  • 学位 Ph.D.
  • 年度 1976
  • 页码 349 p.
  • 总页数 349
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 海洋工程;
  • 关键词

  • 入库时间 2022-08-17 11:51:45

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