Test-based fracture criteria for pipeline steels

钢管作为加拿大重要的基础设施，经常暴露在各种地质和环境条件下，导致管壁出现裂缝、凹痕、沟槽等缺陷，从而导致管道断裂，影响管道的整体功能，造成重大的经济损失、环境问题甚至死亡。预测断裂能力的方法有多种，包括实验测试、分析方法和先进的数值方法。采用计算机程序实现的固定断裂应变准则，由于大应变的集中，可能无法正确预测裂纹的扩展路径。此外，忽略裂纹尖端约束并依赖于用于获取断裂指标的试样类型的断裂准则可能导致预测结果不一致。有必要开发和实施更有效和准确的断裂标准，具体到管材，作为裂纹尖端约束的函数，独立于所用试样的类型和预裂的大小。本研究项目旨在开发基于数值的断裂准则，用于预测钢管道中的裂纹扩展。本项目制定的标准将考虑到各种加载条件下裂纹尖端的限制，并将适用于用于制造管道的各种钢种，为加拿大管道行业提供一种评估和设计管道的增强方法。

Steel pipelines, as key Canadian infrastructure, are often exposed to various geological and environmental conditions that cause defects such as cracks, dents, and gouges in the pipe wall, which can lead to pipe fracture in pipelines, compromising the entire functionality of pipelines and resulting in significant economic losses, environmental issues or even fatalities. There are several methods to predict the fracture capacity, including experimental testing, analytical approaches, and advanced numerical methods. The application of the fixed fracture strain criterion implemented in the computer programs may not appropriately predict the crack propagation path because of the concentration of large strains. Furthermore, fracture criteria that ignore the crack tip constraints and depend on the type of test specimens used to obtain fracture indices may lead to inconsistent predictions. There is a need to develop and implement more efficient and accurate fracture criteria specific to pipe steel as a function of crack tip constraints, independent of the type of specimens used and the size of pre-cracking. This research project aims at developing calibrated numerical-based fracture criteria for predicting the crack propagation in steel pipelines. The criteria developed in this project will take into consideration the constraints at the crack-tip specific to various loading conditions and will be applicable to various steel grades used to manufacture pipes, providing the pipeline industry in Canada with an enhanced method to assess and design pipelines.