Assessment of Crack Arrest Behaviour in Modern Structural Steels

基于断裂力学的工程结构适用性评估通常基于失效准则，即在特定温度下脆性断裂或韧性撕裂引发裂纹扩展。裂纹止裂背后的原理是，如果裂纹在高应力或局部脆化区域开始，它将在周围材料中被止裂，以防止整个结构的破坏。确保裂纹止裂的基本、简单的想法是，材料必须具有足够的裂纹止裂韧性，以确保在低韧性和/或高应力区域开始的快速扩展的裂纹在走出临界区域后被止裂。显然，在船舶、管道和某些特定压力容器的设计阶段，裂缝止裂分析是至关重要的。温度的影响是另一个需要考虑的因素，在评估裂纹止裂过程中或在设计抗裂纹止裂时。本项目的主要目的是推导经验模型，该模型可用于从小试件（即Charpy试验）中定义裂纹止裂韧性。还提出了研究和量化两种钢的裂纹起裂韧性和止裂韧性之间的差异，并根据材料微观结构解释这种差异。有限元建模技术也将被纳入了解裂纹止裂行为，通过分析裂纹尖端条件与特定加载条件下的特定微观结构的关系。

Fracture mechanics based Fitness-For-Service (FFS) assessment of engineering structures is normally based upon the failure criterion, which is the initiation of crack extension by brittle fracture or ductile tearing at specified temperatures. The philosophy behind crack arrest is that if a crack initiates in a region of high stress or local embrittlement, it will be arrested in the surrounding material to prevent failure of the entire structure. The basic, simple idea for ensuring crack arrest is that the materials must have sufficient crack arrest toughness to ensure that fast propagating cracks, initiated in regions of low toughness and/or high stress, are arrested after they emerge from the critical zone. Obviously, during the design stage of ships, pipelines and some specific pressure vessels, analysis of crack arrest is of vital importance. The effect of temperature is another factor that needs to be taken into account in the course of the assessment of crack arrest or during design against crack arrest. The main aim of this project is to derive empirical models, which can be used to define crack arrest toughness from small test specimens (i.e. Charpy tests). It is also proposed to investigate and quantify the differences between the crack initiation and arrest toughness of two types of steels and explain the differences based on material microstructure. Finite Element modelling techniques will also be incorporated to understand crack arrest behaviour by analysing crack tip conditions in relation to a particular microstructure under specified loading condition.