![]() A ductile failure has a dull gray appearance. 5.Ī brittle fracture is distinguishable from a ductile failure by the lack of deformation at the edge of the tear, and its bright granular appearance. ![]() The metallurgical properties of the steel plate. ![]() There is a temperature above which brittle fracture will not occur. The subject is too complex to be dealt with in detail in this text, but it is known that the following factors influence the possibility of brittle fracture and are taken into consideration in the design and material selection of modern ships: 1.Ī sharp notch is present in the structure from which the fracture initiates. Mild steel used extensively in ship construction is particularly prone to brittle fracture given the conditions necessary to trigger it off. Fracture occurs instantaneously with little warning and the vessel’s overall structure need not be subject to a high stress at the time. Any applied external loading and stress concentrations in the structure's design also contribute to the risk of brittle fracture.īrittle fracture occurs when an otherwise elastic material fractures without any apparent sign or little evidence of material deformation prior to failure. This makes the ‘stress’ corner of the triangle in Figure 5.1 of particular concern, and the requirement for post-weld heat treatment (PWHT) of welded structures to reduce the residual stresses is therefore very important for brittle fracture avoidance. An example of this occurred in some of the Liberty ship failures where ships fractured after fabrication without leaving dry dock. However, a welding defect in such a plate may initiate brittle fracture with no external load, because of the effect of the welding residual stress alone. In a thick plate containing a butt weld, if it is left alone, the butt weld will not exhibit a ductile failure because it cannot deform and yield without an external applied load. Philippa Moore, Geoff Booth, in The Welding Engineer�s Guide to Fracture and Fatigue, 2015 5.3.2 Weld stressīrittle fracture is perhaps of most concern in welded structures because a residual stress alone (see Chapter 3) is sufficient to propagate a brittle fracture, without any external loading. ![]()
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