Date of Award

2022-08-01

Degree Name

Doctor of Philosophy

Department

Engineering

Advisor(s)

Roger V. Gonzalez

Second Advisor

Joshua T. Green

Abstract

Multi-material (M2) manufacturing with functional gradients and local composition control (LCC) is an emerging technology with high demand in numerous industries. This research investigated multi-material technology that has potential impact to joint implants, synthetic joints, and damage resistant parts. Novel manufacturing subsystems within established selective laser sintering (SLS) additive manufacturing processes were pioneered to enable printing M2 parts with LCC and functionally graded materials. Powder bed fusion (PBF) material blends consisting of low temperature thermoplastics, low temperature thermoplastic elastomers (TPE), carbon fibers (CF), and hydroxyapatite (HA) particulates were explored to match the designed and tested M2 SLS prototype. M2 sintering, material blending, and M2 parts demonstrated the feasibility of sintering material gradients using Polyamide 12 (PA12) as a matrix material mechanically blended with TPE, CF, and HA. Various PA12/CF blends were characterized via tensile tests to investigate the potential of tuning material properties based on the CF blend ratio. Printing and characterization of Single Edge Notch Tensile (SENT) specimens with binary and gradient material interfaces were performed to study the effects of functional material (fiber) gradients in polymer PBF and to validate the novel M2 SLS subsystems developed in this research. A joint implant conceptual prototype consisting of a PA12 matrix with functional binary gradients of CF and HA was printed to demonstrate the possible impact of tri-material parts. The combination of the M2 SLS prototype, mechanical material blending, and binary gradient tests demonstrated the capability to customize and tune multiple material properties throughout a single part while increasing overall part ultimate tensile strength, yield stress, and crack energy absorption. However, the results also showed the potential to use the methods developed in this research to stabilize and functionalize material blends (e.g., high CF or TPE blends) through M2 PBF that may otherwise be unprintable with single material PBF. However, inconsistencies between two sets of SENT tests highlighted the importance of continued research and testing under numerous environments and damaged states to fully understand sintered PA12/CF composites before â??as printedâ?? parts containing these material blends can be used in most applications. The combination of all results in this research has revealed this type of M2 manufacturing may have a broader impact in biomedical, aeronautical, and other evolving industries.

Language

en

Provenance

Received from ProQuest

File Size

348 p.

File Format

application/pdf

Rights Holder

Jonathan James Slager

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