On the observations of autowaves and avalanches in an aluminum magnesium alloy

The present study attempts to answer the question of what the local deformation characteristics look like in a dynamically strain aging material before the onset of macroscopic instability. A solution strengthened aluminum magnesium alloy was tested in a work hardened condition in uniaxial tension under a constant applied displacement rate. In situ digital image correlation captured the 2D spatial strain field which was differentiated to find the local strain rate field. Propagating waves in the local strain rate were observed in an extended elastoplastic transition during macroscopically uniform deformation before the onset of the Portevin-Le Chatelier effect. The formation of the synchronous oscillations suggests a reduction in dimensionality in the system. These waves eventually transition into intermittent plastic behavior which is attributed to dislocation avalanches. The strain magnitudes for these autowaves and dislocation avalanches are much lower than would be observed for a plastic burst developed from the Portevin-Le Chatelier effect. Fourier analysis on the global load signal confirms the observed intermittency spans multiple scales, which is consistent with the behavior of various materials. Also, wavelet analysis provided a method of quantifying transitions in the deformation behavior in both the time and frequency domains and reveals a period doubling transition in both the global and local signal.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Mudrock, Rebecca N.

Contributors dc:contributor

• Beaudoin, Armand J.

• Plasticity
• Dynamic Phenomena
• Dynamic Strain Aging
• Aluminum Alloys
• Image Analysis

Statement dc:rights

• Copyright 2011 Rebecca N. Mudrock

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/24188

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/24188