טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentZev Lovinger
SubjectMultiple Adiabatic Shear Bands in a Collapsing Cylinder -
Failure Characterization and Microstructural
Effects
DepartmentDepartment of Mechanical Engineering
Supervisors Full Professor Rittel Daniel
Dr. Zvi Rosenberg


Abstract

Shear bands formation in collapsing thick walled cylinders occurs in a spontaneous manner. The advantage of examining spontaneous, as opposed to forced shear localization, is that it highlights the inherent susceptibility of the material to adiabatic shear banding without prescribed geometrical constraints. The Thick-Walled Cylinder technique (TWC) reported in the literature uses an explosive cylinder to create the driving force, collapsing the cylindrical sample. In this research we developed an electro-magnetic set-up using a pulsed current generator to provide the collapsing force on the cylindrical specimens. This new experimental set-up has been established as a controllable and repeatable technique to create and study multiple adiabatic shear bands. The main diagnostics is post-mortem: The collapsing cylinders, which come to a stop at the end of the experiment, are sectioned and polished to reveal the spatial distribution of shear bands. Using this platform we examined the shear band evolution at different stages of formation in 7 metallic alloys, spanning a wide range of strength and failure properties. To examine microstructural effects, we conducted systematic tests on materials with different grain sizes. 2D numerical simulations were carried out to explore the complex dynamics of shear band evolution in this geometry, with a failure criterion based on a strain energy density approach. The numerical results provide a reliable description of the shear bands distribution and spacing, thus paving the way for predictive work. Calibration of the failure model for the different materials, led to a good quantitative comparison with the experimental results, for the first time. The results also indicate that, whereas, potential localization sites are similar for all the studied materials, shear band growth is controlled by the plastic deformation micro-mechanisms. The results of this work are discussed and compared to explosively driven collapsing TWC results in the literature and to existing analytical models for spontaneous adiabatic shear localization.