Date of Award:

8-2011

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Mechanical and Aerospace Engineering

Committee Chair(s)

Leijun Li

Committee

Leijun Li

Committee

Robert E. Spall

Committee

Barton Smith

Committee

Brent Stucker

Committee

Wei Ren

Abstract

A systematic experimental and numerical combined study of the thermomechanical bonding mechanisms in the ultrasonic welding (UW) process was conducted. A fully coupled thermomechanical finite element model has been built to fully understand the evolution and coupling between the in-process thermomechanical variables. The severe, localized, plastic deformation at the bond region is believed to be the major phenomenon for bond formation in ultrasonic welding. The influences of substrate dimensions on bond formation were studied and explained with an analytical vibration model. The formation of banded and cyclic stress-strain maxima in the substrate was found to be caused by superposition of vibrations. A push-pin type, combined experimental and numerical, method has been developed, validated, and applied to quantitatively determine the bond strength of UW parts. The best bond strength produced using the set of process parameters in this study was 75% of the ultimate tensile strength of the base material (Al3003-H18). Effects of UW parameters (normal pressure, vibration amplitude, and travel velocity) on bond strength have been characterized. Due to the weak vertical bond strength of UW parts, the pressurized post-weld heat treatment (PWHT) approach is originally proposed to improve the bond strength. The results show that the modified bond strength, up to 96% of the strength of the base material, can be achieved under the optimum parameters of 2.5 MPa pressure, 450 ◦C temperature, and 1.5 h time.

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Comments

This work made publicly available electronically on September 2, 2011.

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