Why Fracture?– NanoNomology
Event details
| Date | 12.11.2013 |
| Hour | 13:15 › 14:15 |
| Speaker |
Prof. William Gerberich, University of Minnesota, USA Bio : The research careers of Professor Gerberich and his students have spanned 9 orders of magnitude time (s) and 9 orders of magnitude scale (nm). As a graduate student at Berkeley, he was tagged as someone to help investigate a construction mishap at about the 50th story level of the World Trade Center as it was being built. Who could have known that 40 years later a former student of his from the National Institute of Standards and Technology (NIST) would be called to investigate the same steel after 9/11. Still at Berkeley and shortly afterwards at the University of Minnesota, he and his graduate students made the first measurements of the fracture resistance of transformation induced plasticity (TRIP) steels. For thin sheet this produced 1.5 GPa yield strength steels with a fracture toughness of 300 MPa-m1/2, properties ultimately attracting the interest of Belgian researchers. With less-expensive alloys, high-end automobile companies incorporated TRIP steel as a side-impact safety feature some 30 years later. In the 70s and 80s, understanding of high toughness and resistance to hydrogen embrittlement culminated with discretized dislocation studies matched to transmission microscopy (TEM) observations in the 90s. For studies at the nm scale, both nanosphere and nanopillar studies of single crystal silicon were studied in the early 00s using AFM, SEM and TEM microscopies. These were among the first in situ experiments showing that theoretical strengths could be achieved in compression even after plastic deformation of small sized objects in the vicinity of 100nm.Subsequently for silicon, it was demonstrated with others that the brittle to ductile transition could be lowered to room temperature by decreasing size alone. To summarize why fracture develops in high strength materials, and how one might avoid it, the research is unfinished as a combination of dislocation nucleation, dislocation shielding and impurity modified thermally-activated processes clearly hold the keys to future advances. |
| Location | |
| Category | Conferences - Seminars |
Abstract : In any science “nomology” seeks the principles governing phenomena. To apply that to fracture with origins at the scale of interatomic spacings requires a nanobot with a portable nanoscope and a picohammer. With no science fiction available, studies at the nm scale of nanosphere and nanopillar single crystal silicon were conducted in the early 00s using AFM, SEM and TEM microscopies. We were fortunate to produce in situ experiments showing that theoretical strengths could be achieved in compression even after plastic deformation of small sized objects in the vicinity of 40-100nm. Subsequently for silicon, it was demonstrated with others that the brittle to ductile transition could be lowered to room temperature by decreasing size alone. Taking it to the next level really requires such length scales coupled to the appropriate temporal and temperature scales to develop sufficient “nomology”. What is meant by sufficient are those measures also accessible to computational materials science for producing mutually validating results.
To summarize why fracture develops in high strength materials and how one might avoid it: -- not possible as such research is zeroth order. A combination of dislocation nucleation, dislocation shielding and impurity modified thermally-activated processes holds the keys to future advances.
To summarize why fracture develops in high strength materials and how one might avoid it: -- not possible as such research is zeroth order. A combination of dislocation nucleation, dislocation shielding and impurity modified thermally-activated processes holds the keys to future advances.
Practical information
- General public
- Free
Organizer
- IGM
Contact
- Géraldine Palaj