*********************************
There is now a CONTENT FREEZE for Mercury while we switch to a new platform. It began on Friday, March 10 at 6pm and will end on Wednesday, March 15 at noon. No new content can be created during this time, but all material in the system as of the beginning of the freeze will be migrated to the new platform, including users and groups. Functionally the new site is identical to the old one. webteam@gatech.edu
*********************************
MSE Ph.D. Proposal - Wade R. Lanning
Date: Tuesday, December 2, 2014
Time: 1:00 PM
Location: Love 295
Committee
Prof. Christopher Muhlstein (Advisor, MSE)
Prof. David McDowell (MSE, ME/MSE)
Prof. Richard W. Neu (ME)
Prof. Hamid Garmestani (MSE)
Prof. Arun Gokhale (MSE)
Title: Crack Growth Resistance and Surface Layer Toughening of 2D Ductile Metal Nanosheets
Abstract
2D metal nanosheets (free-standing films ~100 nm thick) are an important component of MEMs, flexible-substrate electronics, optical coatings and more, but have fracture toughness orders of magnitude lower than their bulk counterparts. This project explores the possibility of engineering nanosheets to have higher fracture toughness. Preliminary experiments on 120 nm thick wrought Au sheets have revealed a low fracture toughness consistent with the literature, but also signs of significant plastic thinning at the crack tip consistent with geometry-controlled toughness. Furthermore, evolving R-curve behavior during stable crack growth and large (as much as 20 µm) crack tip process zones demonstrate that large-area 2D nanosheets reveal aspects of crack growth not captured by previous work using micro-scale specimens. Ductile metal sheets with geometry-controlled toughness present an intriguing opportunity: by increasing the stress necessary to develop the process zone, the work necessary to grow a crack may also be increased. Because the sheet thickness is smaller than the spacing of in-plane barriers to dislocation motion (grain boundaries, dislocation arrays, etc.), we propose to engineer the yield stress and fracture toughness of 2D Au nanosheets with surface treatments. This project will use thermal processing and deposition of Pt and Ru nanolayers to determine the relative effectiveness of in-plane defects and surface layers (respectively) toughening strategies. By developing methods to characterize and improve the fracture toughness of 2D metal nanosheets, we can both improve existing thin-film devices and enable the creation of new devices via assembly of free-standing 2D nanosheets.
