Abstract

The goal of this dissertation is to fabricate wires made of Cu/CNT and Al/CNT composites with good mechanical strength and super thermal/electrical conductivities using powder compaction and wire extrusion manufacturing processes. Powder compaction was studied using both test and simulation. Cold compaction, hot compaction and vibration assisted (cold) compaction tests were conducted to achieve different density ratios. Hot compaction tests improved about 6% compared with cold compaction under the same compression pressure. Although the relative density ratio does not obviously improve at vibration assisted (cold) compaction, the strength of the specimens made under vibration loading is much better than those of cold compaction. Additionally, finite element models with well calibrated Drucker Prager Cap (DPC) material constitutive model were built in Abaqus/Standard to simulate powder compaction processes. The results of finite element model have excellent correlations with test results up to the tested range, and finite element models can further predict the loading conditions required in order to achieve the higher density ratios of the materials. Two exponential formulas for predicting density ratio were obtained by combining the test data and the simulation results. A new analytical solution was first time developed to predict the axial pressure versus the density ratio for powder compaction according to DPC material model. The results between analytical solution and simulation model have an excellent match. Extrusion method was adopted to produce wires of aluminum (Al), copper (Cu) and copper/carbon nanotubes (Cu/CNTs) composites. A new analytical solution was developed to predict magnitude of extrusion force, where friction effects between die and sample were considered. The analytical solution achieved a much better result than the classical slip line theory and other existing analytical solutions. Extensive finite element (FE) models were built to validate the analytical solution under different extrusion conditions. FE simulation cases were run for different die angles (including 30°, 45° and 60°) and different extrusion area ratios (including 16:1 and 4:1). The comparison results showed a good match between analytical solutions and finite element models. Both Eulerian and Lagrangian methods were set up and compared in finite element models in order to predict the extrusion force during the extrusion process. Four wire extrusion tests of metals and metal/CNTs composites were successfully conducted under elevated temperatures ranging from 300°C to 703°C. Test results further validated the accuracy of the analytical solution.

Notes

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Graduation Date

2021

Semester

Summer

Advisor

Bai, Yuanli

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Degree Program

Mechanical Engineering

Format

application/pdf

Identifier

CFE0008762;DP0025493

URL

https://purls.library.ucf.edu/go/DP0025493

Language

English

Release Date

August 2021

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

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