Abstract
The failure assessment diagram (FAD) method has been widely accepted to evaluate the extent to which cracks may affect structural safety. The usage of this FAD method has been validated and included in [1]-[3]. The structure under investigation, described in four fully welded T-joint (BCC5) specimens, where these welded joints are a source of stress concentration and defects from which fatigue cracks can grow. The four specimens were modeled under different displacement loading using a finite element analysis program Ansys and SolidWorks software. In this work, the application of a FAD (Lr, Kr) using maximum stress, cumulative stress ranges, and the last half-cycle stress range was investigated. The results are showing that all the points were lying outside the FAD curve except for the BCC5D specimen point was inside FAD when using maximum stress.
 Conclusions made that the cumulative stress gives Lr and Kr are extremely large and hence predict failure too early. With the Crack Tip Opening Displacement (CTOD) of the test specimen assumed to be about 1mm rather than 0.1mm it was found that, if a FAD is to be used to indicate failure, then both Lr and Kr should be based on the maximum stress. It appears that the FAD methodology does help to predict the final failure (which is the usual application in such cases). This represents more effectively the structural behavior and would be more easily used by designers.
Highlights
During the last 40 years, various assessment methods were developed based on fracture mechanics
With the Crack Tip Opening Displacement (CTOD) of the test specimen assumed to be about 1mm rather than 0.1mm it was found that, if a failure assessment diagram (FAD) is to be used to indicate failure, both Lr and Kr should be based on the maximum stress
Aims and Objectives This research work carried out by the author is aimed at studying the Application of Failure Assessment Diagram (FAD) for steel welded connection based on British Standard BS7910 and pipeline assessment method DET NORSKE VERITAS DNV-RP-F108 using four fully welded T-joint specimens
Summary
During the last 40 years, various assessment methods were developed based on fracture mechanics. Two mechanisms of failure were identified; brittle fracture and plastic collapse, which are described in [1], [2], [6]-[8]. The X-axis and Y-axis of the failure assessment diagram curve use the plastic collapse ratio (Lr) and the brittle fracture ratio (Kr) respectively. The points under the failure assessment diagram curve indicate acceptable cracks (providing suitable safety factors being applied). The evaluation points which fall outside the FAD curve represent unacceptable cracks that indicate a structural failure. This can be useful to determine the predicted critical crack sizes. Aims and Objectives This research work carried out by the author is aimed at studying the Application of Failure Assessment Diagram (FAD) for steel welded connection based on British Standard BS7910 and pipeline assessment method DET NORSKE VERITAS DNV-RP-F108 using four fully welded T-joint specimens
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