The Constitutive Behavior of Copper at High Strain Rate as Determined by the Free Expansion Ring Test

Study of deformation of materials at high strain rate is important to many industries. Several techniques exist to characterize materials at high strain rates but all of them have their limitations. The ring expansion technique is explored in this thesis. This technique can augment the scope of research in this field. The introduction of Photonic Doppler Velocimetry (PDV) offered measurement of the velocity of the ring in this technique with higher temporal resolution, reliability and portability. But quantitative analysis of the data from the PDV was a problem, which has been addressed in this thesis. A MATLAB code is developed which analyzes the signal from PDV with minimum user intervention and generates stress-strain plots from the experiments and saves the required data automatically. Extraction of the signal frequency from the raw PDV data is done by taking discrete time short time fourier transform (STFT) of the data and then fitting a Gaussian curve to the power spectral density sub-matrix at each time step. Fitting of the velocity-time graph is necessary to calculate acceleration of the ring to obtain flow stress in the ring. Power law of second degree, linear fit, quadratic fit and cubic fit were tried and power law fit was finally used in the code.OFHC copper is tested using the ring expansion technique with aluminum wire and urethane as actuator. Results from the experiments are presented and it can be shown that stress increases with increasing strains. It can also be shown that high stresses are obtained if higher peak velocities are achieved. But it is difficult to comment about the strain rate sensitivity of the material at this stage. Johnson Cook and Zerilli Armstrong constitutive models are fitted to the experimental data and it can be concluded that one constitutive law is unable to describe the nature of the material in the conditions present in this technique.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor dc:publisher

The Ohio State University

Year dc:date

2013

Author dc:creator

• Gupta, Shweta

Contributors dc:contributor

• Daehn, Glenn
• Luscher, Anthony

• Engineering
• Materials Science
• Mechanical Engineering

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=osu1366200117

OAI identifier oai:identifier

oai:etd.ohiolink.edu:osu1366200117