Mechanical properties of buckled pipe materials

在役管道的机械屈曲是一个重要的技术问题。管道在施工后可能会经历复杂的加载路径，原因包括地震事件、永久冻土融化造成的土壤移动，甚至是重型设备在埋地管道上的移动。因此，有必要建立模型来预测在役管道的材料特性，如屈服应力和初始加工硬化特性。这里，有几个重要的冶金现象是相关的。首先，定性地知道，当加载方向改变时，这会影响屈服应力(经典地称为包辛格效应)。在这种情况下，相关的情况是，成型管道期间的变形方向可以与管道在使用中经历的弯曲应变垂直。其次，人们还知道，在塑性变形后和常温下的静态阶段，由于碳原子偏析到晶体位错，可能会产生“屈服点”。然而，缺乏对基本机制的了解，预测这种行为的能力仅限于质量值。 这项工作的目标是：i)通过精心设计的一系列实验和建模活动来解决这一知识差距；ii)培养1名博士生和1名博士后研究员；iii)将这些知识传授给TransCanada管道有限公司的工程师。

The in-service mechanical buckling of pipelines is an important technological problem. The pipeline can experience complex loading paths after construction due to seismic events, soil shifting due to melting of permafrost or even the movement of heavy equipment over the buried pipeline. Thus, it is necessary to have models to predict the material behaviour of the pipe in service, such as the yield stress and the initial working hardening behaviour. Here, there are several important metallurgical phenomena which are relevant. First, it is qualitatively known that when the direction of the loading changes, this can affect the yield stress (classically known as the Bauschinger effect). In this case, the relevant scenario would be that the direction of deformation during forming the pipe can be orthogonal to bending strains that the pipe experiences in-service. Second, it is also known that the after plastic deformation and a static period at ambient temperatures, a "yield point" can be produced due to segregation of carbon atoms to crystal dislocations. However, there is a lack of knowledge on the basic mechanisms and the ability to predict this behaviour is limited to qualitative values. The objectives of this work are i) address this knowledge gap by a carefully designed set of experiments and modelling activities, ii) educate 1 Ph.D. student and 1 postdoctoral fellow and iii) to transfer this knowledge to engineers at TransCanada Pipelines Ltd.