Assessment of Crack Arrest Behaviour in Modern Structural Steels

基于断裂力学的工程结构适用度评估通常基于失效准则，即在特定温度下由脆性断裂或延性撕裂引起的裂纹扩展。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萌生，它将被阻止在周围的材料中，以防止整个结构的破坏。确保止裂的基本、简单的想法是，材料必须具有足够的止裂韧性，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出现在临界区后被止住。显然，在船舶、管道和某些特定压力容器的设计阶段，止裂分析是至关重要的。温度的影响是在止裂评估过程中或在防止裂设计过程中需要考虑的另一个因素。该项目的主要目的是建立经验模型，可以用来从小的试验试件(即Charpy试验)中确定止裂韧性。还建议研究和量化两种钢的起裂和止裂韧性的差异，并从材料微观组织的角度解释这种差异。还将结合有限元建模技术，通过分析特定加载条件下与特定微观结构相关的裂纹尖端条件来了解裂纹止裂行为。

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.