Fatigue and fracture are important potential failure modes for ships and offshore structures. With regard to fatigue, marine structures are in general designed for finite life, requiring detailed knowledge of fatigue strength of the different parts of the structure. Fracture properties are in particular important for structures that are subjected to large strain, for example pipelines during laying operations, and for structures exposed to arctic temperatures where steel materials may become brittle. The course addresses analysis and design methods for welded structures with respect to fatigue and fracture. Emphasis is placed on providing knowledge of materials characterisation and design principles laid down in the most relevant codes and guidelines for design against fatigue and fracture given by NORSOK, DNV, British Standards Institution and American Society for Materials and Testing (ASTM). The theory is illustrated with exercise problems on realistic structures.
Basic materials technology and mechanics of solids.
After completion of the course the students will have a thorough understanding of the governing physical phenomena of fatigue and fracture and be able to establish simple calculation models for fatigue and fracture of components in marine structures. The students will be able to:
- Describe the fundamental principles of linear-elastic and elastic-plastic fracture mechanics.
- Understand the theory for analysis of unstable fracture in materials.
- Describe the fracture properties of structural materials, the ductile-to-brittle temperature transition for Carbon steels and the criteria for material characterisation to avoid unstable fracture.
- Understand the failure assessment diagram and be able to use the diagram for quantitative analysis of fracture.
- Understand and use the guideline for fracture design given by BS 7910, Levels 1 and 2.
- Understand the basic mechanisms of fatigue crack initiation and growth in metals.
- Understand and apply fracture mechanics to calculate fatigue crack growth, understand the relationship between SN diagram and the crack growth properties of materials.
- Understand the technological factors that may affect fatigue capacity of welded structures.
- Understand the phenomenon of stress corrosion cracking (SCC), and how materials are characterised with respect to SCC.
- Understand the effect of marine environment and cathodic protection on fatigue initiation and crack growth, and how the effects are accounted for in design.
- Understand the basic theory of cumulative damage, and to calculate fatigue life for structures subjected to stochastic loading.
- Understand and use the guidelines for fatigue design of planar and tubular joints.
- Understand the mechanisms of weld-improvement methods, and the potential and limitations of these methods.