Current defect assessment procedures assume all flaws to be sharp, a conservative assumption that can lead to pessimistic structural integrity assessment of structures and under-estimation of their safety margin against fracture. This study has developed an engineering assessment procedure for predicting cleavage fracture resistance of structures containing non-sharp defects. The new procedure can be incorporated into existing defect assessment methods via a modification of the Failure Assessment Diagram (FAD). The new procedure was developed and validated using a combination of testing and finite element analysis. A heat-treated structural steel formed the basis for the experimental work. A large test programme of 135 Single Edge Notch Send SEeS) specimens with sharp cracks and U-notches was used to quantify the increase in apparent toughness that occurs with increasing notch root radius p. The Weibull stress-based toughness scaling model was used to predict the increase in cleavage fracture resistance that occurs with increasing p up to a notch radius of 2mm. In the new assessment procedure several new parameters are utilised that are analogous to parameters used in existing constraint correction methods. The notch tip loading severity is described by the elastic notch tip stress ON , analogous to the use of the elastic T-stress used to quantify crack tip constraint in constraint correction. The notch geometry is measured using a loadindependent non-dimensional parameter {3N analogous to the {3r parameter used in constraint correction. Material parameters r and I define the sensitivity of the material toughness to the notch effect; these are analogous to the material parameters a and k used for constraint correction. The parameters r and I can either be obtained from test data or from a series of look-up tables developed using the Wei bull stress-based toughness scaling model. The study also showed that for a given level of constraint defined by the T-stress, the notch and constraint effects are independent of each other. This enables the toughness benefit due to the notch to be applied in conjunction with existing constraint correction methods, e.g. for the assessment of blunt, shallow flaws.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:515092 |
| Date | January 2010 |
| Creators | Horn, Anthony John |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.001 seconds