A fracture mechanics analysis of the fatigue reliability of tubular welded joints

[摘要] Fatigue failure is generally the result of crack initiation at a surface followed by stable crack propagation leading finally to unstable fracture. The total fatigue life is often a random variable due to the randomness of fatigue loading. the variability of material properties and the final failure conditions. Fracture mechanics provides a rational description of fatigue based on which an analytical method has been developed for assessing the reliability of components under random loading. This method can be used for predicting the distribution of crack lengths after a given number of fatigue cycles have been applied to a initial crack; the distribution of the number of cycles needed to grow a crack to a specific length; or the distribution of fatigue lives terminated at a random final crack length. In order to assess the fatigue reliability of tubular welded joints, the stress intensity factors of surface cracks have been determined by shell analysis with the cracked section modelled by line springs. The surface cracks are generally subjected to mixed mode loadings and the line spring method allows the stress intensity factor for individual modes to be assessed separately. The applicability of the line spring method to stress concentration areas has been verified in plane strain T joints, which has provided the confidence to apply this method to tubular welded joints. The calculations are compared with available experimental data. The fatigue life distributions of a tubular welded T joint for three loading modes have been predicted based on an assumed initial crack length. The S-N curve produced from the analytic prediction compares favourably with experimental data in terms of an equivalent hot spot strain range. In the cases studied, the hot spot strain range is seen to be a reasonable but not very accurate parameter for determining fatigue life. In conclusion, fracture mechanics has been demonstrated to be a valid and important method for predicting the residual fatigue life of damaged tubular welded joints.

[发布机构] University:University of Glasgow;Department:School of Engineering

[关键词] TA Engineering (General). Civil engineering (General)