Residual stresses and ductile fracture

残余应力和延性断裂

• 批准号: 2648429
• 金额: --
• 依托单位: University of Manchester
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2648429
• 关键词: Residual; stresses; ductile; fracture

EDF are interested in starting a PhD examining the impact of residual stresses on ductilefracture, specifically on ductile tearing resistance up to about 2mm of growth.This problem has been examined using a number of different approaches in the past, so it isworth reviewing the state of the art briefly before defining a new project.Experimental evidenceHere we have the problem of the limit load. If crack initiation occurs close to Lr=1then it is difficult to identify any impact of residual stress since the predicted effectsare both small and masked by experimental scatter.Brittle fracture occurs at low values of the crack driving force, and it is relativelystraightforward to design and perform small-scale tests where fracture occurs at lowLr where there is little plasticity-induced relaxation in the residual stress field (forexample see [1]). It is also possible to test over a range of Lr to examine the effectsof plasticity.Most ductile materials of direct relevance to the nuclear sector have high fracturetoughness and relatively modest yield strength, and the crack growth resistance risesas tearing proceeds. It is difficult to design small-scale tests that do not undergoinitiation and tearing at the limit load in engineering steels (for example, see [2]).Thus, any effects of residual stress are masked by the usual experimental scatter.The STYLE project performed a single large-scale fracture test on an Esshete 1250 pipecontaining a repair weld, where the residual stresses were high enough to have ameasurable effect on crack initiation and the early stages of tearing, since initiationoccurred at Lr<0.5 [3]. This however was a single, complex, expensive test, whichperhaps should be regarded as a validation benchmark rather than a basis for ascientific investigation.Sherry and co-workers have approached the problem by using a model material: alow toughness aluminium alloy that still fails by micro-void coalescence. This class ofmaterial allows the use of small specimens and standard testing machines.The methods used to introduce residual stresses are varied. Making accurateestimates of their magnitude and distribution is often not straightforward, and caremust be taken that the introduction method does not alter the properties of thematerial being tested (or that any property changes are well understood).

EDF感兴趣的是开始PHD测试残余应力对韧性断裂的影响，特别是对高达2 mm的韧性撕裂阻力的影响。这个问题在过去已经用许多不同的方法进行了研究，所以在定义新项目之前，有必要简单回顾一下最新技术的现状。实验证据我们有极限载荷的问题。如果裂纹萌生接近Lr=1，则很难识别任何残余应力的影响，因为预测的影响都很小，并且被实验散射所掩盖。在裂纹驱动力的低值时发生脆性断裂，并且在低Lr处发生断裂的小规模试验相对容易设计和执行，在那里残余应力场中几乎没有塑性引起的松弛(例如，见[1])。也可以在一系列LR上进行测试，以检查塑性的影响。大多数与核部门直接相关的延性材料具有高的断裂粗糙度和相对适中的屈服强度，裂纹扩展阻力随着撕裂的进行而上升。在工程钢中，很难设计在极限载荷下不发生起裂和撕裂的小规模试验(例如，参见[2])。因此，任何残余应力的影响都被通常的试验散布所掩盖。Style项目在一条包含修复焊缝的Esshete 1250管道上进行了一次大规模断裂试验，其中残余应力足够高，足以对裂纹起裂和撕裂的早期阶段产生一定的影响，因为起裂发生在LR&lt；0.5[3]。然而，这是一种单一的、复杂的、昂贵的测试，它可能应该被视为验证基准，而不是科学研究的基础。Sherry和他的同事们通过使用一种模型材料来解决这个问题：仍然通过微孔结合而失效的低韧性铝合金。这类材料允许使用小试件和标准试验机。用于引入残余应力的方法有多种。对它们的大小和分布做出准确的估计往往不是一帆风顺的，必须注意引入方法不会改变被测试材料的性质(或者任何性质的变化都被很好地理解)。