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Dissertation
Large deformation stress: strain response in low stacking fault energy FCC metals
Doctor of Philosophy (Ph.D.), Drexel University
Jun 1998
DOI:
https://doi.org/10.17918/00000713
Abstract
A detailed study on the strain hardening and microstructural evolution in simple compression in a group of low SFE fcc alloys that are known to twin revealed four distinct and almost identical regimes of strain hardening when plotted on suitably normalized plots. Stage A, in which the hardening rate dropped in a manner similar to stage III in medium and high SFE metals, came to an arrest at a strain of 0.1. Stage B, where the hardening rate was constant, had a value in the range of.02G to 0.03G (G is the shear modulus) for all materials studied and was correlated with the onset of twinning. Stage C, where the hardening rate started to drop again, was interrupted by a constant plateau. Stage D, was in the range of 0.007 to 0.01 G for all materials studied, was correlated with twin intersections. Important conclusions were drawn about the commonality of normalized strain hardening rates in these group of low SFE alloys. In contrary to the belief that twinning is mainly controlled by SFE, we found in this work that the dislocation density is the major controlling parameter in the process of deformation by twinning for a given slip length. The higher strain hardening (higher dislocation density) associated with low SFE and the fact that low SFE metals maintain the original slip length over a larger period of deformation allows for the criteria for twin nucleation to be satisfied. The strain hardening of low and medium SFE metals was studied in different stress states (plane strain compression and simple shear). Detailed study on the evolution of texture was conducted and the results support the idea that the copper to brass texture transition is largely attributable to the formation of shear bands and not to twin initiation as previously assumed. Strain path change test (simple shear to simple compression) revealed that there is a strong geometrical effect behind the low flow stress levels and the lower hardening rates in simple shear. The accuracy of isotropic plasticity model to predict yield strength in a non-homogeneously deformed sample was also evaluated. Finally the secondary hardening phenomenon in MP35N (Co-Ni alloy) was characterized.
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Details
- Title
- Large deformation stress
- Creators
- Ehab Adel El-Danaf
- Contributors
- Surya Kalidindi (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xvii, 176 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Materials (Science and) Engineering (Metallurgical Engineering) [Historical]; College of Engineering (1970-2026); Drexel University
- Other Identifier
- 991014970339104721