Structures and Materials Commons^™

Mechanical Properties Of Nanomodified Hybrid Gfrp Composite Materials, Micah Rop Kimutai

College of Graduate Studies: Theses & Dissertations

The mechanical behavior of the nanomodified hybrid epoxy matrix was investigated in glass fiber reinforced plastics (GFRP). In this study, five nanocomposites enriched with as received halloysite, nanomer I.28E, HNT-APTES, and the hybrid combinations of the two HNTs with the nanomer I.28E were successfully fabricated. To evaluate the effects and morphological characteristics of the individual fillers and the hybrid configurations on the epoxy resin matrix, TGA, DSC, and DMA were analyzed. To understand the effect of the five configurations on the neat GFRP laminate, mode I interlaminar fracture toughness, tensile, and vibration properties were investigated. Electron microscopy testing techniques were …

Analysis Of After Impact Characteristics And Structural Optimization Of Cfrp Composite Plate, Zhennan He

Doctoral Dissertations and Master's Theses

Low-velocity impact (LVI) on composites may cause Barely Visible Impact Damage (BVID), which is one of the most common damage types and may result in a decrease in strength of the composite. The objectives of this research were (a) to identify the characteristics of a carbon/epoxy composite plate after low-velocity impact, (b) to create a validated model to simulate the impact process and progressive failure, and (c) to perform sizing and shape optimization of the laminate for improving the damage resistance of the plate. As a part of this thesis, composite plates were fabricated using carbon fiber reinforced polymer (CFRP) …

Parametric Analysis Of Particle Spreading With Discrete Element Method, Yuxuan Wu

Doctoral Dissertations and Master's Theses

The spreading of metallic powder on the printing platform is vital in most additive manufacturing methods, including direct laser sintering. Several processing parameters such as particle size, inter-particle friction, blade speed, and blade gap size affect the spreading process and, therefore, the final product quality. The objective of this study is to parametrically analyze the particle flow behavior and the effect of the aforementioned parameters on the spreading process using the discrete element method (DEM). To effectively address the vast parameter space within computational constraints, novel parameter sweep algorithms based on low discrepancy sequence (LDS) are utilized in conjunction with …

Experimental Analysis Of Heat Generation In Carbon, Mounisha Ganesan

Doctoral Dissertations and Master's Theses

The purpose of this research is to study a novel non-covalent functionalization technique of single-walled carbon nanotubes (SWCNTs) and to examine the feasibility of using carbon nanotube films as thin film heaters. We developed a unique methodology to synthesize a well dispersed, environmentally friendly solution of CNTs that could be easily spin coated as well as spray coated on different substrates based on the application. Using the produced solutions, thin films of SWCNTs were fabricated on a glass substrate. Two sets of experiments were conducted to study the influence of polyaromatic moiety and the pH on the electro thermal characteristics …

Laser-Based Interfacial Patterning Enables Toughening Of Cfrp/Epoxy Joints Through Bridging Of Adhesive Ligaments, Ran Tao, Xiaole Li, Arief Yudhanto, Marco Alfano, Gilles Lubineau

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The ability to prevent catastrophic failures in secondary bonded CFRP adhesive joints is important for reliable automotive and aerospace structures. In a previous study, we proposed an innovative damage-tolerant interfacial design concept for adhesively bonded composite joints, which relied on the extrinsic dissipation of bridging adhesive ligaments enabled by controlling the adhesion at CFRP/epoxy interfaces. In this work, we experimentally validate this strategy by combining laser processing and mechanical testing using double cantilever beam (DCB) joints. Mechanical tests indicate that the pattern geometry, i.e., number and spacing of the areas with different adhesion, controls the formation of either single or …

Hexakis Icosahedron Frame-Skin Vacuum Lighter Than Air Vehicle, Brian Cranston, Anthony N. Palazotto

AFIT Patents

A vacuum lighter than air vehicle (VLTAV) includes a rigid frame of rods connected together to form a hexakis icosahedron. A membrane skin covers the rigid frame and defines therewith a vessel configured to hold an internal vacuum that allows the vessel to float in the air. The plurality of rods and membrane skin have weights and dimensions that result in a neutral and/or positive buoyancy for the vessel while preventing geometric instability.

Effect Of Cold Work Expansion On The Fatigue Life Of Pre-Cracked Al 2024-T3, Christopher Leirer

Doctoral Dissertations and Master's Theses

No abstract provided.

Enhancement Of Fracture Toughness In Secondary Bonded Cfrp Using Hybrid Thermoplastic/Thermoset Bondline Architecture, A. Yudhanto, M. Almulhim, F. Kamal, R. Tao, L. Fatta, M. Alfano, G. Lubineau

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Structures made of carbon fiber-reinforced polymer (CFRP) can be assembled using adhesive bonding. However, such bonding is prone to brittle delamination, and a method to improve delamination resistance is desirable. Here, we propose a technique to introduce crack-arrest features that increase the R-curve response by engineering the adhesive bond line/interface. We specifically designed a wavy net-like thermoplastic insert that was embedded into the thermoset adhesive bond line where the new mechanisms of energy dissipation were generated. We demonstrate that the technique is effective at improving mode I fracture toughness of secondary bonded carbon/epoxy by more than 400%. The hybrid thermoset/thermoplastic …

Inkjet-Printed Ti3c2tx Mxene Electrodes For Multimodal Cutaneous Biosensing, Abdulelah Saleh, Shofarul Wustoni, Eloise Bihar, Jehad K. El-Demellawi, Yizhou Zhang, Adel Hama, Victor Druet, Arief Yudhanto, Gilles Lubineau, Husam N. Alshareef, Sahika Inal

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Among the existing two-dimensional materials, MXenes, i.e. transition metal carbides, nitrides and/or carbonitrides, stand out for their excellent electrochemical properties. Due to their high charge storage capacity, metal-like conductivity, biocompatibility as well as hydrophilicity, Ti3C2Tx MXene-based inks hold great potential for scalable production of skin conformable electronics via direct printing methods. Herein, we develop an aqueous MXene ink and inkjet-print MXene films on freestanding, flexible, and conducting polymer-based substrates. These skin-adherent MXene electrodes detect electrocardiography signals with high signal-to-noise ratio while exhibiting preserved electrical performance after 1000 cycles of bending with a 50 d long shelf life in ambient conditions. …

Characterizing And Modeling The Progressive Damage Of Off-Axis Thermoplastic Plies: Effect Of Ply Confinement, Ditho Pulungan, Arief Yudhanto, Gilles Lubineau

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Although the mechanisms of degradation are, overall, quite similar between thermoset and thermoplastic composites, thermoplastic laminates exhibit a higher ductility. Because of that, classical models developed for thermosets fail in predicting accurately the response of thermoplastic-based laminates. Here, we demonstrate that simulations based on the properties identified on isolated thermoplastics unidirectional plies, as usually done for thermosets, result in large errors. This is explained by the significant load-bearing capacity of the ply in the transverse direction that remains even after the first-ply failure, as a result of the confinement provided by adjacent plies. This effect also exists in thermosets, but …

On The Effect Of Interfacial Patterns On Energy Dissipation In Plastically Deforming Adhesive Bonded Ductile Sheets, Arturo Pascuzzo, Arief Yudhanto, Marco Alfano, Gilles Lubineau

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Toughening of brittle adhesive joints is a topic of great interest for the fabrication of layered structures. Recent experimental work by the authors indicated that spatially varying interface properties (i.e., patterned interfaces obtained using laser irradiation) could tune energy dissipation in plastically deforming adhesive joints. In this study, we use a cohesive zone approach to ascertain the interplay between fracture process zone size and pattern geometry on the overall work of separation. The analysis is carried out in the context of the elasto-plastic peeling response of adhesive bonded ductile thin sheets. The mating surfaces of the adherents feature alternating strips …

Improving Mode Ii Fracture Toughness Of Secondary Bonded Joints Using Laser Patterning Of Adherends, A. Wagih, R. Tao, A. Yudhanto, G. Lubineau

Mechanical and Aerospace Engineering Faculty Research & Creative Works

We improve mode II fracture toughness of secondary bonded joints based on the laser treatment of adherend surfaces. We applied CO₂ Laser treatment to adherend surface alternatively with low and high energy, resulting in a repeated pattern of rough and smooth surfaces. We used ENF test to characterize mode II fracture toughness, GII, of the bonded CFRP substrates. The results demonstrated that our proposed pattern arrested the crack propagation and triggered new damage mechanisms, such as adhesive cracking, adhesive failure and crack migration to the other interface. These additional mechanisms, some of them were non-local in nature, resulted in …

Piezoresistive Hybrid Nanocomposites For Strain And Damage Sensing: Experimental And Numerical Analysis, Audrey Jean-Miche Gbaguidi

Doctoral Dissertations and Master's Theses

Carbon nanomaterials such as carbon nanotubes (CNTs) and graphite nanoplatelets (GNPs) demonstrate remarkable electrical and mechanical properties, which suggest promising structural and functional applications as fillers for polymer nanocomposites.

The piezoresistive behavior of these nanocomposites makes them ideal for sensing applications. Besides, hybrid nanocomposites with multiple fillers like carbon nanotubes (CNTs) and graphite nanoplatelets (GNPs) are known to exhibit improved electrical and mechanical performance when compared to mono-filler composites.

To comprehensively understand the mechanisms of electrical percolation, conductivity, and piezoresistivity in hybrid nanocomposites, the author develops a two-dimensional (2D) and a three-dimensional (3D) computational Monte Carlo percolation network models for …

Topology Optimization And Analysis Of Thermal And Mechanical Metamaterials, Lee Alacoque

Doctoral Dissertations and Master's Theses

To take advantage of multi-material additive manufacturing technology using mixtures of metal alloys, a topology optimization framework is developed to synthesize high-strength spatially periodic metamaterials possessing unique thermoelastic properties. A thermal and mechanical stress analysis formulation based on homogenization theory is developed and is used in a regional scaled aggregation stress constraint method, and a method of worst-case stress minimization is also included to efficiently address load uncertainty. It is shown that the two stress-based techniques lead to thermal expansion properties that are highly sensitive to small changes in material distribution and composition. To resolve this issue, a uniform manufacturing …

Development Of High-Density Propulsion System Technologies For Interplanetary Small Satellites And Cubesats, Morgan Andrew Roddy

Graduate Theses and Dissertations

The goal of this research was to support the development of a novel propulsion system for small satellites (<180 kg) and CubeSats. This was pursued by conducting a collection of studies that were designed to provide engineering data that would be critical in designing a functional prototype. The novel propulsion system was conceived by the author to provide best-in-class performance for the small satellite and CubeSat families of spacecraft. This context presents specific design requirements that the presented technology attempts to satisfy. The most critical among these is high density; the propellant was designed to be stored with high density and the thruster was designed to be as compact as possible. The propulsion system is composed of two primary elements, a propellant generator and a thruster. The propellant generator works by sublimating a solid crystal into vapor and then using this vapor to etch a dense metal. The resulting gaseous byproducts of this reaction are the propellant. This dissertation used xenon difluoride (XeF2) vapor to etch tungsten (W) which react to form xenon gas (Xe) and tungsten hexafluoride (WF6). This approach gave a theoretical propellant storage density 5.40 g/cm3; and 5.17 g/cm3 was demonstrated. The sublimation dynamics of the XeF2 were studied as a function of surface area and temperature and it was found to be suitable for the intended application due to its high effluence rate; that is, it sublimates fast enough to be useful. The sublimation rates are on the order of 10’s of µg/s. The etch rate of XeF2 on W was also studied and found to be suitably fast to provide useful amounts of reactants for use as a propellant, again on the order of 1’s of µg/s. The thruster is an electrostatic radio frequency (RF) ion thruster design and is manufactured with Low Temperature Co-Fired Ceramic (LTCC) materials system and manufacturing technology. Manufacturing samples of the thruster were built at the University of Arkansas in July 2015 and tested at NASA’s Marshall Space Flight Center in May 2018. Testing validated the viability of the LTCC thruster and provided valuable information on how to improve the thruster’s design.

How The Spatial Correlation In Adhesion Properties Influences The Performance Of Secondary Bonding Of Laminated Composites, Xiaole Li, Ran Tao, Arief Yudhanto, Gilles Lubineau

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Spatial heterogeneity of adhesion properties is known to result in bridging during debonding of secondary bonded composite joints. The ligaments that bridge both substrates have crack-arrest features and thus significantly enhance the fracture resistance of joints. We have investigated the effect of randomly distributed adhesion properties between the adhesive layer and each composite substrate in previous works; however, the spatial correlation of adhesion heterogeneity within or between the substrates and how it effects the failure of secondary bonded composites is still poorly understood. In this current work, we assume that the spatial heterogeneity of adhesion follows a log-normal distribution. The …

Filament Winding Composite Airframes For Sounding Rockets, Eric Ford

Student Works

This study’s objective was to determine the feasibility of manufacturing carbon fiber cylinders using an X-Winder filament winder for a structural airframe in sounding rockets. Multiple carbon fiber tubes were manufactured using the X-Winder and tested. The results of this testing successfully demonstrated that tubes manufactured with the X-Winder are capable of performing as an airframe for small sounding rockets. Five tube samples were destructively tested in compression, and the average maximum compressive strength of the tubes was 9,854 lbf. One of the tubes was used as the airframe in a small sounding rocket which flew to 4,042 feet above …

Vibration Isolation System, Bradley Y. Kwan, Bailey Groh, Max Wu, Nicole Yen

Mechanical Engineering

The Vibration Isolation System Senior Project is a collaborative group project between its sponsor, Maxar Technologies, and a team of students from Cal Poly - SLO to effectively design, manufacture, and test a structural assembly for satellites, isolating vibrations during launch and orbit conditions. After initial sponsor contact, requirements and needs were set which dictated deliverables for the senior project group. The group performed analyses to validate all design decisions, including a modified concept and design direction, selection of a prototype viscoelastic damping material, preliminary testing to validate design specifications, and detailed design and analysis toward a finalized design. Instead …

Miniaturized Ultraviolet Imager Phase Iii, Bradley D. Albright, Nicolas A. Armenta, Colin W. Harrop

Mechanical Engineering

This document details the work to date, June 9, 2020, done by the Cal Poly Mechanical Engineering senior project team, Miniaturized Ultraviolet Imager: Phase III (MUVI III), sponsored by the University of California, Berkeley – Space Sciences Laboratory (UCB SSL). MUVI III is the third senior project team of an ongoing design, MUVI: the prototype of a 2U sized CubeSat intended to capture aurora images in the ionosphere. The first team, MUVI I, finished development of the UV imager. The second team, MUVI II, designed the mirror mounting and deployable door mechanisms. The goal of MUVI phase III is to …

Design, Validation, And Verification Of The Cal Poly Educational Cubesat Kit Structure, Nicholas B. Snyder

Master's Theses

In this thesis, the development of a structure for use in an educational CubeSat kit is explored. The potential uses of this kit include augmenting existing curricula with aspects of hands on learning, developing new ways of training students on proper space systems engineering practices, and overall contributing to academic capacity building at Cal Poly and its collaborators. The design improves on existing CubeSat kit structures by increasing accessibility to internal components by implementing a modular backplane system, as well as adding the ability to be environmentally tested. Manufacturing of the structure is completed with both additive (Fused Deposition Modeling …