Date of Award

2025-05-01

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

Advisor(s)

Yirong Y. Lin

Abstract

Section 1.1. Abstract This chapter investigates the use of direct ink write (DIW) additive manufacturing to control grain orientation in non-toxic barium titanate (BTO) ceramics by blending spherical and platelet-shaped particles in the ink. A series of inks containing 0–40 wt.% BTO platelets were formulated with poly(vinyl alcohol), polyethylene glycol, poly(acrylic acid-co-maleic acid), and ammonium hydroxide to ensure printability and homogeneous dispersion. Cylindrical specimens (20 mm × 3 mm) were printed using a Hyrel 30M DIW system and subjected to de-binding (650 °C, 2 h) followed by a two-step sintering schedule (T₁: 1200–1350 °C; T₂: 700–850 °C; 24 h dwell). Relative density peaked at 85.9 % for 0 wt.% platelets (1300 °C/800 °C) and decreased with increasing platelet content due to inhibited grain-boundary diffusion. SEM and XRD analyses confirmed platelet alignment parallel to the build plate, with Lotgering factors (F₂₀₀) rising from 0.00 (0 wt.%) to 0.63 (40 wt.%). This texturization produced a 29.6 % enhancement in dielectric constant compared to randomly oriented ceramics. The results demonstrate that DIW-induced shear alignment coupled with optimized thermal processing can tailor microstructure and functional performance of BTO ceramics for sensor and energy-storage applications. Section 2.1. Abstract This chapter presents the development of multifunctional lattice structures fabricated from a novel PEEK–carbon fiber (CF)/carbon nanotube (CNT) composite filament for fused filament fabrication (FFF). An optimized melt-blend extrusion process produced filaments with 11.6 wt.% CF and 12 wt.% CNT, yielding uniform dispersion and robust interfacial bonding. Two lattice geometries—truncated octahedron and re-entrant auxetic—were selected to exploit plateau stress regions (5–15 % strain) for decoupling piezoresistive and thermoresistive responses. Printed specimens exhibited surface roughness as low as ~20 µm Ra, compressive strengths up to 60 MPa, and electrical conductivities reaching 0.067 S/m. Cyclic loading under controlled temperatures (25–100 °C) confirmed stable resistance during plateau stress and a positive temperature coefficient of resistance with < 0.3 % variation, achieving 99.7 % repeatability. These results demonstrate that lattice architecture, combined with tailored composite formulation, enables selective force and temperature sensing in a single-material system. Section 3.1. Abstract This chapter introduces Hybrid PIZCAL, a multi-material lattice architecture enabling programmable directional piezoelectric sensing via fused filament fabrication (FFF). Using an ABS–BaTiO₃ composite filament with 20 vol.% ceramic loading co-printed alongside pure PLA, we create geometrically anisotropic lattices that concentrate mechanical strain along the Z-axis while passivating the X–Y planes. Thermal poling (3 kV/mm at 85 °C) aligns dipoles in the active regions, yielding a Z-axis voltage-per-mass output of 13.7 mV/g—293 % higher than a monolithic piezoelectric cube—while suppressing transverse responses by >20 %. Finite-element simulations confirm compliance contrasts exceeding 5× between axes, and SEM micrographs demonstrate homogeneous BaTiO₃ dispersion within the ABS matrix. The Hybrid PIZCAL thus combines topological control with material zoning to deliver high-fidelity, single-axis sensing in a single-step AM process, paving the way for advanced wearable, robotic, and structural-health-monitoring applications.

Language

en

Provenance

Received from ProQuest

File Size

50 p.

File Format

application/pdf

Rights Holder

Alexis Lopez

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