Research On Assessment For Remaining Fatigue Life Of Steel Structure

Many steel structures have been served in our country, and some of them have various fatigue cracks. For safe service of them, it is necessary to estimate their remaining fatigue life. Today, elastic fracture mechanics approach is the dominant method of estimating remaining fatigue life. At small fatigue loading, the remaining fatigue life of steel structure could be estimated by elastic fracture mechanics approach, and the estimating result is well. But, if the steel structure is at big fatigue loading, and it has smaller crack or faster growth crack rate, the assessment for remaining fatigue life of them must be done by elastic-plastic fracture mechanics approach. In this paper, some research on assesment for remaining fatigue life by elastic-plastic fracture mechanics is done.The application range of elastic fracture mechanics and the reason for the constraint application of elastic-plastic fracture mechanics are analysised in this paper. The theory of J-A₂ three-term solution and how to resolve constraint parameter A₂ are introduced.The J-R curves and elastic-plastic crack growth rote of engineer structure are different from these of specimen. It is also difficult for engineer structure to get the J-R curves and elastic-plastic crack growth rate by test directly. But, they are more important for their assessment for remaining fatigue life. For attaining J-R curves and elastic-plastic crack growth rate closing to structure, improving the accuracy of estimation, J-A₂ methodology is applicated to the assessment for remaining fatigue life of steel structure in this paper.Elastic-plastic crack growth rate of engineer structure is predicted by J-A₂ methodology. Combining this with EPRI, a caculating formula of estimating remaining fatigue life of structure is founed. So, the method of assesment for remaining fatigue life of structure is set up in this paper. Meanwhile, combining J-A₂ methodology with crack expension loading graph, a new caculating method of the residual strength of structure is gived out also in this paper.In this paper, the application of J-A₂ methodology to assesment for remaining fatigue life of structure is a new creation.At the end of the thesis, the end loading and remaining fatigue life of engineer pipe are estimated by the approachs provided in this paper.