Northwestern Events Calendar

May
27
2014

Todd Hufnagel: Deformation and Fracture of Metallic Glasses

When: Tuesday, May 27, 2014
4:00 PM - 5:00 PM CT

Where: Technological Institute, L211, 2145 Sheridan Road, Evanston, IL 60208 map it

Audience: Faculty/Staff - Student - Public - Post Docs/Docs - Graduate Students

Contact: Department Office   (847) 491-3537

Group: Department of Materials Science and Engineering (MatSci)

Category: Lectures & Meetings

Description:

The Department of Materials Science and Engineering welcomes you to its 2014 Spring Colloquium Series. 


Tuesday, May 27th 
Tech L211, 4:00pm

Abstract: Amorphous metallic alloys combine some of the advantageous mechanical properties of metals, such as high strength and (in some alloys) toughness, with the processing flexibility associated with materials capable of undergoing a glass transition into a supercooled liquid state. The disordered structure of metallic glasses implies that the mechanisms of deformation and fracture in these novel materials are different from those of conventional crystalline alloys.

In this talk we will review the mechanical behavior of metallic glasses and discuss several recent experiments that shed new light on mechanisms of elastic deformation, plastic deformation, and fracture. In the case of elastic deformation, high-energy x-ray scattering experiments and molecular dynamics simulations both indicate that an apparent length-scale dependence of the elastic strain is associated with localized non-affine atomic displacements that may be related to the operation of shear transformation zones (STZs). Stress-strain data recorded with high temporal resolution reveal that both scaling and dynamics of load drops during plastic flow are in excellent agreement with a simple mean-field model describing these events as avalanches of individual STZ operations. These avalanches are manifested as shear bands, and experiments designed to measure the heat released during shear band operations show that they can occur without significant heating. Finally, we show how high-energy x-ray scattering can be used to map the elastic strain state locally around crack tips in fracture specimens, and that a loss of fracture toughness at low temperature is associated with a reduction in the size of the plastic zone around the crack tip. We propose that the difference in behavior is associated with changes in the flow stress and elastic constants, which influence the number density of shear bands in the plastic zone and thus the strain required to initiate fracture on an individual band.

Biography: Todd Hufnagel is Professor of Materials Science and Engineering and Mechanical Engineering at Johns Hopkins University. He has received an NSF CAREER Award and an ARO Young Investigator Award. His current research emphasizes the use of x-ray scattering and imaging to study dynamic processes in materials.
He received his B.S. degree in Metallurgical Engineering from Michigan Tech, and M.S. and Ph.D. in Materials Science and Engineering from Stanford.

 

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