Abstract
Residual and thermal stresses have a considerable effect on the process of brittle fracture. In addition to this, the effect of these stresses on elastic-plastic fracture is known to be significant. This is accounted for in structural integrity assessment methodologies such as R6 Rev 4 and BS 7910:2013 by introducing factors representing the interaction between primary and secondary stresses (those that do and do not contribute towards plastic collapse, respectively).
The initiation of ductile tearing in a ferritic pressure vessel steel was studied experimentally. Energy-dispersive X-ray diffraction was used to determine lattice strains in the vicinity of a crack tip in modified compact tension specimens at incremental loading steps until the initiation of ductile tearing. The X-ray diffraction measurements allowed the stress field to be evaluated with a high spatial resolution. At the same time, the pattern of total strain at the surface of the specimen was observed using digital image correlation. Prior to the experiment, two samples were subjected to localised out-of-plane compression ahead of the crack tip to introduce a residual stress field and hence significant crack loading in the absence of external load. Stress and strain field data for cracked specimens, with and without a pre-existing residual stress field, indicated significant differences in the development of plastic strain up to the point of tearing initiation. It is shown that this can only be explained when both residual stress and prior material hardening are taken into account.
The initiation of ductile tearing in a ferritic pressure vessel steel was studied experimentally. Energy-dispersive X-ray diffraction was used to determine lattice strains in the vicinity of a crack tip in modified compact tension specimens at incremental loading steps until the initiation of ductile tearing. The X-ray diffraction measurements allowed the stress field to be evaluated with a high spatial resolution. At the same time, the pattern of total strain at the surface of the specimen was observed using digital image correlation. Prior to the experiment, two samples were subjected to localised out-of-plane compression ahead of the crack tip to introduce a residual stress field and hence significant crack loading in the absence of external load. Stress and strain field data for cracked specimens, with and without a pre-existing residual stress field, indicated significant differences in the development of plastic strain up to the point of tearing initiation. It is shown that this can only be explained when both residual stress and prior material hardening are taken into account.
| Original language | English |
|---|---|
| Title of host publication | Proceedings of the ASME 2016 Pressure Vessels & Piping Conference |
| Subtitle of host publication | Volume 6a: Materials and Fabrication |
| Publisher | American Society of Mechanical Engineers (ASME) |
| Number of pages | 9 |
| ISBN (Print) | 9780791850428 |
| DOIs | |
| Publication status | Published - 21 Jul 2016 |
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Coules, H., Horne, G., Peel, M., Oliver, S., Van Gelderen, D., & Connolley, T. (2016). Direct observation of elastic and plastic strain fields during ductile tearing of a ferritic steel. In Proceedings of the ASME 2016 Pressure Vessels & Piping Conference: Volume 6a: Materials and Fabrication [PVP2016-63345] American Society of Mechanical Engineers (ASME). https://doi.org/10.1115/PVP2016-63345