TWI Industrial Member Report Summary 752/2002
A Muhammed and J B Wintle
This report describes an improved probabilistic fatigue crack growth method for the assessment of offshore and other structures subjected to variable amplitude loading. Existing approaches form the basis of the method, but these normally assume the loading spectrum can be fitted to a standard statistical distribution. The method significantly enhances these approaches by allowing for fatigue crack growth and the threshold effect when a structure is subject to variable amplitude loading that does not follow a standard distribution. As this is normally the case with loading on offshore and many other types of structure, the development is of practical importance.
Flaw acceptance criteria or remaining life assessments are generally based on fracture mechanics analyses or workmanship criteria. In most cases, the analysis is deterministic and based on worst-case assumptions of every input parameter. Probabilistic fatigue analyses can provide a more rational means for making these assessments providing that the data is available and a target probability can be specified and justified.
- Develop a probabilistic fatigue analysis method for structural components subjected to variable amplitude loading that does not necessarily conform to a standard statistical distribution.
- Verify the method by checks and comparisons.
- Explore through example calculations the potential for practical applications in setting weld flaw acceptance criteria.