Date of Award

Spring 2021

Project Type

Dissertation

Program or Major

Mechanical Engineering

Degree Name

Doctor of Philosophy

First Advisor

Brad Kinsey

Second Advisor

Glenn Daehn

Third Advisor

Pierre L’Eplattenier

Abstract

There is a growing interest in creating light weight structures in various industries such as automobile, electronics, and aerospace in order to reduce energy consumption. One means to achieve mass reductions is to join or weld dissimilar materials to create lightweight structures. However, traditional fusion welding processes cannot be used for such dissimilar materials applications due to differences in material characteristics and the tendency to form brittle intermetallic compounds. One approach to join dissimilar materials is through high speed impact welding. With appropriate process parameters, a wavy interfacial morphology is commonly obtained at the interface of the two impact welded partners in high speed impact welding.

In this dissertation research, effects of several process parameters on the interface morphology were investigated through two different impact welding processes, Magnetic Pulse Welding (MPW) and Vaporized Foil Actuator Welding (VFAW). Effects of impact velocity, target thickness, and supporting mandrel inclusion were investigated through the welding of tubular parts Al6060T4 (flyer) to Cu-ETP (target), by MPW. The influence of flyer thickness and impact angle were investigated in VFAW using a material combination of Al1100-O and 1018 Steel. The target material properties’ effects were also examined by MPW through the joints between Al1100-O and various target materials. In addition, numerical analyses were used to verify the afore-mentioned experimental observations. The traditional Lagrangian Finite Element Analysis (FEA) method is not feasible to model high speed impact welding due to excessive element distortions at the interface. Alternatively, Smoothed Particle Hydrodynamics (SPH) and Arbitrary Lagrangian-Eulerian (ALE) methods were used to numerically investigate the interface morphology as well as the influence of process parameters for the material combinations mentioned above. Both experimental and numerical results indicated that the interfacial wavelength increased with both increasing flyer thickness and impact angle for the mateiral combination of Al1100-0 and 1018 steel. Increasing impact velocity and target thickness, and inserting a mandrel into a tubular thin target, resulted in wavelength growth for the Al6060T4 and Cu-ETP material system. Vortices can also be obtained for this material combination with appropriate impact velocity (larger than 300 m/s) and a well-supported target. Finally, low yield strength of the target material led to a wavy interface for the material system of Al1100-O and copper alloys.

In order to further understand the science behind high speed forming and welding processes as well as benefits of various numerical simulation methodologies, SPH and Eulerian methods were utilized to simulate the CP-Ti/Cu110 bimetallic system. Several process parameters calculated by both methods were in a good agreement, and the accuracy of the results was corroborated by comparisons with experimental observations.

Lastly, as a part of this dissertation research, a coupled electromagnetism-structural numerical analysis was conducted to accurately capture the material deformation in Electromagnetic Forming (EMF) for sheet metals using a coil design called a Uniform Pressure Actuator (UPA). The inclusion of relative motion between the workpiece and outer channel allowed accurate predictions of displacements and velocities of the workpiece. A simplified analytical model was derived to predict the forming pressure and shell theory for mechanical deformation. Velocity and the final deformed part shape are compared between the numerical, analytical, and experimental methods.

Available for download on Thursday, June 23, 2022

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