Date of Award

2018-01-01

Degree Name

Master of Science

Department

Mechanical Engineering

Advisor(s)

David Espalin

Abstract

Additive manufacturing (AM - most commonly known as 3D printing) is a fabrication method and aims to increase production efficiency while lowering costs of constructing quality components for industry application when compared to traditional machining. In addition to this, AM possesses capabilities that far exceed machining as complex geometries are achievable through an array of technologies in a wide variety of materials. The AM process begins with a computer aided design (CAD) which creates a design path for a 3D printer to follow. By following this path, components are built from bottom to top in a layer by layer fashion. Binder jetting (BJ) is an AM process that adheres each layer of the constructed object together with a liquid binder solution jetted through a print head. Once fabricated, components are subjected to heat treatments to further adhere particles within each layer to achieve higher densities. What separates BJ from other methods of AM are its capabilities to fabricate utilizing materials that normally require casting such as sands and ceramics. In addition to this BJ also possesses the capability to fabricate a variety of metals and alloys, such as copper and Inconel alloys.

Recently in the field of energy harvesting, micro electrical mechanical sensors (MEMS) have garnered substantial interest due to the growing demand for green energy production from self-sufficient systems. A proposed method for the production of these self-sufficient sensors uses piezoceramic materials, which produce electrical charges upon excitation. Harvesting benign energy via piezoelectric materials is a cost effective alternative to batteries normally utilized in these wireless sensors as batteries often require replacement and routine maintenance. The challenges with implementation of these wireless MEMS within energy generating systems is the small amount of energy produced from material excitation and whether this energy supply will sustain a sensor for an extended period of time. The research conducted aims to produce AM fabricated piezoceramics capable of producing adequate energy outputs from several variants of excitation via a custom test set up.

BJ is selected as the AM technology utilized for component fabrication as this technology allows for the fabrication of piezoceramics without diminishing the piezoelectric characteristics of materials throughout the manufacturing process. Throughout this component fabrication process, several variants of piezoelectric materials were investigated as high energy output and high density from components were desired due to the nature of the harsh environment MEMS are subjected to in the fossil energy industry. Pure barium titanate (BTO), pure lithium niobate (LiNbO3), pure lead zirconate titanate (PZT), a mixture of PZT & BTO, and a mixture of LiNbO3 & graphene oxide (GO) were all iterations of piezoelectric materials that were printed on the ExOne M-Lab BJ printer for this work. Prior to implementing these materials within the printer, the feasibility of each iteration of material was tested via pellet fabrication. These samples were fabricated by depositing the powder material and binder in a casting to simulate a printed component. From this, the mixture was packed together using 3000N of compressional force from a hydraulic press which provided a high density green body component. Heat treatments applied to these samples achieved high density (in the range of 57% to 94% full theoretical density) for each material iteration, thus producing a target density for AM fabricated components to attain. Furthermore, contact angle measurements were also performed prior to printing which determined the wettability of the binder solution when applied to the piezoelectric material. From this test the contact angle of pure and doped binder solution revealed that binder with weight concentrations of up to 1% GO maintain hydrophilic qualities, therefore allowing all iterations of binders to be investigated in the AM process.

To harvest a sufficient supply of energy for the proposed MEMS, the feasibility of subjecting a piezoelectric material to combined excitations for producing doubled amounts of power was tested on a solid PZT-5A sample purchased from a manufacturer. The pyroelectric and piezoelectric characteristics of this material allow for energy production from mechanical and thermal excitation. Therefore a custom test setup to implement thermal and mechanical stress upon the material simultaneously was designed and utilized to determine the energy yield produced from coupled excitation. The setup consisted of a parallel synchronized switch harvesting on the inductor (SSHI) rectifying circuit to harvest energy produced, a custom load frame fixture compatible with an INSTRON 8801 load frame to apply compressional stress, and 60 W resistive heating cartridges for thermal stress application upon the sample. To ensure the feasibility of this energy harvesting investigation a total of five test parameters were assessed. Cyclical compression-compression loadings of 3500N were applied to the sample for a pure mechanical test and cyclical thermal loadings fluctuating in the range of 50°C-60°C were applied to the sample for pure thermal testing. The sample was then secured within the fixture with 2500N of compressional force and subjected solely to 50°C for a pure thermal test and then repeated at a temperature of 60°C to determine if higher temperatures yielded more power production. Finally the sample was subjected to 3500N of cyclical mechanical loading simultaneously with thermal fluctuations between 50°C-60°C for combined energy harvesting. This investigation revealed although combined energy harvesting is feasible, pure thermal stress applications were dominant when coupled with mechanical stress frequencies. Pure mechanical loadings yielded powers in the range of 200 nW whereas pure thermal loadings yielded powers in the range of 500 nW. Furthermore, the investigation proved that increased pure thermal stress concentrations yield the highest power amongst other test iterations.

From these preliminary investigations the feasibility of additively manufacturing piezoceramics was confirmed and parameter development for fabrication ensued. Due to correlations between mechanical strength and parameters such as high binder saturation, low layer thickness, and low powder roller speed, each iteration of material was subjected to processing parameters that would produce relatively higher density components. Once fabricated, each material also possessed specific heat treatment parameters to avoid material oxidation or melting while pursuing full density. Regardless of these specific parameters, full density was not attainable from AM fabricated components, with the highest recorded density belonging to the PZT & BTO iteration of powder, the porous component achieved 58% of the full theoretical density. Other materials such as pure LiNbO3 and pure BTO yielded densities such as 39.4% and 57.9%, respectively.

The low density of components did not allow for piezoelectric property measurement, however the PZT & BTO was an exception. After being thermally poled at 120°C in a non-conductive silicon oil with a static electric field of 1.2 kV/mm, the d33 measurement was 3 E-12C/N (pico-newton). In comparison to a pellet sample comprised of this mixture yielding 70 pico-newton, and a pure PZT pellet sample yielding 500 pico-newton, the piezoelectricity of the AM fabricated sample was low. This was attributed to high porosity of the AM fabricated components. In the pursuit of a higher density from these components to produce higher piezoelectric characteristics, further process parameter development in the BJ stage was executed.

Language

en

Provenance

Received from ProQuest

File Size

92 pages

File Format

application/pdf

Rights Holder

Victor Fernando Elicerio

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