School of Metallurgy and Materials, The University of Birmingham, Birmingham, UK
Philos Trans A Math Phys Eng Sci. 2015 Mar 28;373(2038). doi: 10.1098/rsta.2014.0126.
This paper describes characteristics of transgranular cleavage fracture in structural steel, viewed at different size-scales. Initially, consideration is given to structures and the service duty to which they are exposed at the macroscale, highlighting failure by plastic collapse and failure by brittle fracture. This is followed by sections describing the use of fracture mechanics and materials testing in carrying-out assessments of structural integrity. Attention then focuses on the microscale, explaining how values of the local fracture stress in notched bars or of fracture toughness in pre-cracked test-pieces are related to features of the microstructure: carbide thicknesses in wrought material; the sizes of oxide/silicate inclusions in weld metals. Effects of a microstructure that is 'heterogeneous' at the mesoscale are treated briefly, with respect to the extraction of test-pieces from thick sections and to extrapolations of data to low failure probabilities. The values of local fracture stress may be used to infer a local 'work-of-fracture' that is found experimentally to be a few times greater than that of two free surfaces. Reasons for this are discussed in the conclusion section on nano-scale events. It is suggested that, ahead of a sharp crack, it is necessary to increase the compliance by a cooperative movement of atoms (involving extra work) to allow the crack-tip bond to displace sufficiently for the energy of attraction between the atoms to reduce to zero.
本文描述了结构钢中穿晶解理断裂的特点，从不同的尺度进行了观察。首先考虑的是结构及其在宏观尺度上所承受的服务职责，强调塑性失效和脆性失效。接下来的部分描述了使用断裂力学和材料测试进行结构完整性评估。然后，注意力集中在微观尺度上，解释了如何将缺口棒材中的局部断裂应力值或预制裂纹试样中的断裂韧性值与微观结构的特征相关联：加工材料中的碳化物厚度；焊接金属中氧化物/硅酸盐夹杂物的大小。简要讨论了中观尺度上“不均匀”的微观结构的影响，涉及从厚截面中提取试样以及将数据外推到低失效概率的问题。局部断裂应力值可用于推断局部“断裂功”，实验发现该值比两个自由表面的断裂功大几倍。在关于纳米尺度事件的结论部分讨论了原因。有人认为，在尖锐裂纹之前，有必要通过原子的协同运动（涉及额外的功）来增加柔度，以使裂纹尖端键合足够地位移，以便原子之间的吸引力能量降低到零。
