The Appearance of Platelet-Polymer Composite Coatings: Microstructural Characterization, Hybrid Modeling, and Predictive Design.

The appearance of a platelet-containing polymer composite coating is governed by the microstructure and optical properties included scattering particles and platelets. Many models attempt to predict the coating's appearance, but do not utilize the complete 3D-microstructure, reducing their predictive utility. In this thesis, laser scanning confocal microscopy was used to measure the effect of platelet orientation on angle-dependent lightness, and quantify the spacing between platelets, from which a new microstructural property, the gap factor, was determined. The gap factor is a measure of the average gap size between platelets per unit material surface length. It ranged from 0 to 2 for the systems studied in this thesis. An increase in gap factor of about 0.1, keeping the orientation similar, reduced the near-specular lightness of the physical samples by more than 20%. A 3D hybrid-simulation was created using wave-optics to simulate the bidirectional-reflection-distribution-function (BRDF) for individual platelets. This was combined with ray-tracing to quantify the scattering behavior of a platelet array. This model more accurately predicted the lightness of a silver paint sample than an orientation-based microfacet-model, and was used to study how the surface roughness of the platelets influences lightness. The lightness at 15 degrees off-specular was about 130 when the root-mean square of the amplitude of the roughness, sigma(RMS), was much less than the wavelength of light. Lightness reduced to about 80 when sigma(RMS) was about equal to the wavelength of light. This effect of sigma(RMS) on lightness was found to be more significant with decreases in the roughness correlation length. The hybrid model was also used to study how width, thickness, and volume concentration of the platelets change the near-specular and backscattered lightness. The observed reduction in near-specular lightness with gap factor was verified. However, the resultant 2nd-order exponential decay was weaker than observed. This was attributed wave-scattering by faces and edges, behavior not included in the current model, but may be added in the future. This hybrid model can be used in the future to design unique microstructures to produce new and novel visual or functional effects using manufacturing techniques such as 3D-printing.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133404/1/cseubert_1.pd

Investigation on the effect of low-pressure plasma treatment on the adhesion properties of different carbon-fiber-reinforced-polymer materials for structural adhesive bonding

This three-part study, developed with the collaboration of the Istituto Italiano di Tecnologia (IIT), reports a systematic and quantitative evaluation of the effects induced by various low-pressure plasma (LPP) treatments on the adhesive properties of Carbon Fiber Reinforced Polymer (CFRP) substrates. In particular, Part A of this work was focused on the surface activation of CFRP substrates, made via traditional vacuum-bag technique, which was performed using several combinations of LPP parameters. From the comparison with conventional pre-bonding preparations, it was possible to quantify the effectiveness of LPP in increasing the performance of adhesively-bonded CFRP joints. Further measurements of roughness and wettability were performed, and analyses via x-ray photoelectron spectroscopy (XPS) were also carried out, allowing identification of the morphological, physical and chemical phenomena involved in the treatments. Then, a quantitative evaluation of the aging behavior of the adhesively-bonded joints was the topic of the subsequent Part B. Four significant sets of LPP-treatment conditions were selected, and then subjected to accelerated temperature-humidity aging. To assess the durability of the CFRP-adhesive system under severe aging conditions, tensile shear strength (TSS) testing and wedge cleavage test (WT) were performed in parallel. The experimental findings showed that LPP treatment of the CFRP substrates results in increased short-term quality of the adhesive joint as well as in enhancement of its durability even under severe aging conditions. The last part of the work (Part C) was inspired by the recent developments in additive technologies for the manufacturing of structural thermoplastic-composite parts. In this context, the mechanical and failure behavior were investigated of continuous carbon-fiber (CCF) composite materials built via Fused Filament Fabrication (FFF) technology when used as substrates for bonded joints. Notably, the experiments were focused on verifying how the additively-manufactured substrates respond to adhesive bonding when the interface interactions are increased by preparing the surface with LPP treatment. This approach allowed detection of those criticalities that might limit the application of adhesive bonding to 3D-printed composite parts, with respect to that observed using traditional CFRP materials

New advances in vehicular technology and automotive engineering

An automobile was seen as a simple accessory of luxury in the early years of the past century. Therefore, it was an expensive asset which none of the common citizen could afford. It was necessary to pass a long period and waiting for Henry Ford to establish the first plants with the series fabrication. This new industrial paradigm makes easy to the common American to acquire an automobile, either for running away or for working purposes. Since that date, the automotive research grown exponentially to the levels observed in the actuality. Now, the automobiles are indispensable goods; saying with other words, the automobile is a first necessity article in a wide number of aspects of living: for workers to allow them to move from their homes into their workplaces, for transportation of students, for allowing the domestic women in their home tasks, for ambulances to carry people with decease to the hospitals, for transportation of materials, and so on, the list don’t ends. The new goal pursued by the automotive industry is to provide electric vehicles at low cost and with high reliability. This commitment is justified by the oil’s peak extraction on 50s of this century and also by the necessity to reduce the emissions of CO2 to the atmosphere, as well as to reduce the needs of this even more valuable natural resource. In order to achieve this task and to improve the regular cars based on oil, the automotive industry is even more concerned on doing applied research on technology and on fundamental research of new materials. The most important idea to retain from the previous introduction is to clarify the minds of the potential readers for the direct and indirect penetration of the vehicles and the vehicular industry in the today’s life. In this sequence of ideas, this book tries not only to fill a gap by presenting fresh subjects related to the vehicular technology and to the automotive engineering but to provide guidelines for future research. This book account with valuable contributions from worldwide experts of automotive’s field. The amount and type of contributions were judiciously selected to cover a broad range of research. The reader can found the most recent and cutting-edge sources of information divided in four major groups: electronics (power, communications, optics, batteries, alternators and sensors), mechanics (suspension control, torque converters, deformation analysis, structural monitoring), materials (nanotechnology, nanocomposites, lubrificants, biodegradable, composites, structural monitoring) and manufacturing (supply chains). We are sure that you will enjoy this book and will profit with the technical and scientific contents. To finish, we are thankful to all of those who contributed to this book and who made it possible.info:eu-repo/semantics/publishedVersio

A microgripper for single cell manipulation

This thesis presents the development of an electrothermally actuated microgripper for the manipulation of cells and other biological particles. The microgripper has been fabricated using a combination of surface and bulk micromachining techniques in a three mask process. All of the fabrication details have been chosen to enable a tri-layer, polymer (SU8) - metal (Au) - polymer (SU8), membrane to be released from the substrate stress free and without the need for sacrificial layers. An actuator design, which completely eliminates the parasitic resistance of the cold arm, is presented. When compared to standard U-shaped actuators, it improves the thermal efficiency threefold. This enables larger displacements at lower voltages and temperatures. The microgripper is demonstrated in three different configurations: normally open mode, normally closed mode, and normally open/closed mode. It has-been modelled using two coupled analytical models - electrothermal and thermomechanical - which have been custom developed for this application. Unlike previously reported models, the electrothermal model presented here includes the heat exchange between hot and cold arms of the actuators that are separated by a small air gap. A detailed electrothermomechanical characterisation of selected devices has permitted the validation of the models (also performed using finite element analysis) and the assessment of device performance. The device testing includes electrical, deflection, and temperature measurements using infrared (IR) thermography, its use in polymeric actuators reported here for the first time. Successful manipulation experiments have been conducted in both air and liquid environments. Manipulation of live cells (mice oocytes) in a standard biomanipulation station has validated the microgripper as a complementary and unique tool for the single cell experiments that are to be conducted by future generations of biologists in the areas of human reproduction and stem cell research

Design, Synthesis and Study of Thermomechanically Active Polymer Networks Based on Latent Crosslinking of Semicrystalline Polymers

Demand has arisen rapidly for smart materials in the world of the need to develop and understand new functional products like plastics, rubber, adhesives, fibers, and coatings. Such products are essentially composed of polymers, large molecules of high molecular weight with homogeneous or various repeating units, which researchers term “macromolecules” that engender specific structural, morphological, and physical and mechanical properties. Those polymers with the capacity to change their configuration in accordance with environmental alteration are specifically referred to as shape memory polymers (SMPs), attracting much interest of study both academically and industrially. Herein, this dissertation aims at design, fabrication, and characterization of novel crosslinkable semicrystalline polymeric materials utilizing different techniques and mechanisms in order to explore their special thermomechanical features as well as the possibilities for potential industrial application based on shape memory (SM) effects. Key aspects include use of modern polymer synthesis to tailor thermal and shape memory properties and the adoption of electrospinning processing techniques to form continuous, fine fibers that allow unique molecular modifications, study of enzymatic degradation behavior involving physical form and microstructural state, and unprecedented approaches of making new kinds of shape memory assisted self-healing (SMASH) materials and thermal-responsive self-reversible actuators that require no human intervention. In the following is described the dissertation scope and organization. Chapter 1 goes over background relating to material science within the scope of SM material, self-healing (SH) material, and actuators. Chapter 2 outlines research conducted to achieve new compositions of matter and post-synthesis process, along with supporting characterization for the development of novel SMP materials with featuring tunable reversible actuation capability under ambient stimulus. We prepared a family of crosslinkable (unsaturated), semicrystalline cyclooctene (CO)-based copolymers with varying second monomer and composition via ring opening metathesis polymerization (ROMP). The unsaturation enables covalent crosslinking of polymer chains, in the presence of select thermal initiator through compression molding, allowing subsequent formation of a temperature-responsive network that shows a reversible two-way shape memory (2WSM) effect, indicative of crystallization-induced elongation upon cooling and melting-induced contraction upon heating when a constant, external stress is applied. Molecular, thermomechanical, and SM experiments were performed to investigate and tune the reversible actuation of aforementioned copolymers for the purpose of yielding quantitative guidelines for tailoring material and actuation performance through variations in composition and process. Chapter 3 seeks a latent-crosslinkable, mechanically flexible, fully thermoplastic shape memory polymer. Towards this end, we have developed a simple but effective macromolecular design that includes pendent crosslinking sites via the chain extender of a polyurethane architecture bearing semicrystalline poly(ε-caprolactone) (PCL) soft segment. This new composition was used to prepare fibrous mats by electrospinning and films by solvent casting, each containing thermal initiators for chemical crosslinking. Relevant to medical applications, in vitro enzymatic degradation experiments were carried out to understand the effect of crosslinking state and crystalline structure on degradation behavior of the materials. Chapter 4 builds upon the results of Chapter 3, reporting on the design, fabrication and characterization of a novel, electrospun SMASH polymer blend that incorporates the aforementioned latent-crosslinkable polyurethane. This unique blend system has been unprecedentedly developed by employing a solution in which crosslinkable polyurethane and linear polyurethane are mixed homogeneously for electrospinning. After preparing a family of blends with varying compositions, comprehensive characterizations and various healing tests were done to determine optimal healing performance. Further, the effect of different damage types and molecular anisotropy (nanofibers aligned in high speeds during electrospinning process) were studied for their effect on healing performance. Chapter 5 continues along the line of Chapter 3, presenting the fabrication and testing of novel, electrospun SMP composites that were designed to exploit molecular and geometric anisotropy in reversible actuation under external stress-free condition upon change in ambient temperature. More specifically, the SMP composites consist of two electrospinnable constituents, one being the aforementioned latent crosslinkable polyurethane that serves to shape fixing and recovery (SM properties), and the other being a thermoplastic elastomer known as Pellethane that provides the internal stress field needed for 2WSM to occur. Multiple designs were developed and investigated in this chapter, in particular, including uniaxial actuator, bending actuator, and twisting actuator along with their bench demonstration of self-reversible actuation. Chapter 6 discusses the overall dissertation conclusions, followed descriptions of suggestions for future work, some of which are sub-sectioned at the end of this dissertation

Multifunctional Nanocomposites For High Damping Performance

Composite structures for aerospace and wind turbine applications are subjected to high acoustic and vibrational loading and exhibit very high amplitude displacements and thus premature failure. Materials with high damping or absorbing properties are crucially important to extend the life of structures. Traditional damping treatments are based on the combinations of viscoelastic, elastomeric, magnetic, and piezoelectric materials. In this work, the use of carbon nanofibers (CNFs) in the form of interconnected self-supportive paper as reinforcement can significantly improve damping performance. The interfacial friction is the primary source of energy dissipation in CNF paper based nanocomposites. The approach entailed making CNF paper by filtration of well-dispersed nanofibers under controlled processing conditions. The CNF paper was integrated into composite laminates using modified liquid composite molding processes including Resin Transfer Molding (RTM) and Vacuum Assisted Resin Transfer Molding (VARTM). The rheological and curing behaviors of the CNF-modified polymer resin were characterized with Viscometry and Differential Scanning Calorimetry (DSC). The process analysis in mold filling and pressure distribution was conducted using Control Volume Finite Element Method (CVFEM) in an attempt to optimize the quality of multifunctional nanocomposites. The mold filling simulation was validated with flow visualization in a transparent mold. Several tests were performed to study the damping properties of the fabricated composites including Dynamic Mechanical Analysis (DMA) and piezoceramic patch based vibration tests. It was found that the damping performance was significantly enhanced with the incorporation of carbon nanofibers into the composite structures

Design, Modeling, and Testing of a Novel Inductor for Electric Vehicles: Iron Nitride Soft Magnetic Composites

New technology for electric vehicles (EVs) must meet the requirements of higher energy usage, lower costs, and more sustainable source materials. One promising material for EV power system components is iron nitride (IN) soft magnetic composites (SMCs) because of their competitive magnetic properties and high abundance of the source materials. As part of an ongoing program at Sandia National Laboratories, this project focused on using computer modeling to optimize the prototyping process for an iron nitride SMC toroidal inductor to reach a target inductance of 600 μH. Four inductors with different combinations of wiring (26 AWG and 20 AWG) and vol% loading of iron nitride (65 vol% and 50 vol%) were fabricated at Cal Poly and characterized using an LCR meter. These inductors were also modeled using COMSOL Multiphysics™ with the Magnetic Fields module. The inductance data from the experiment and the model show that the 65 vol% IN prototypes and models agree with about 8% difference, while the 50 vol% IN samples show about a 9% difference between the prototype and the model. These results suggest that the model can predict inductance with both accuracy and precision with low confidence for the given sample size of four. An additional parameter of AC resistance is studied but the AC resistance results from the inductors and from the model generally do not agree closely, suggesting that the current model used in the project does not fully capture the mechanisms behind AC resistance of the inductor. With the focus of the project on inductance, the percent difference results of less than 9% across the four inductors that were tested increases confidence in the model’s predictive capabilities for inductance only. Using the inductance results from both the model and experiment, the final suggested inductor design is a 65 vol% core with 150 windings of 20 AWG wire that is 8 cm across and 1.5 cm tall to reach the inductance goal of 600 μH based on analysis using the optimized COMSOL™ model

4D Microprinting Based on Liquid Crystalline Elastomers

Two-photon laser printing (2PLP) is a disruptive three-dimensional (3D) printing technique that can afford structural fabrication at the submicrometer scale. Apart from constructing static 3D structures, research in fabricating dynamic ones, known as "4D printing”, is becoming a burgeoning field. 4D printed structures exhibit adaptability or tunability towards their environment through the control of an external stimulus. In contrast to the rapid growth in macroscale fabrication, progress in microprinted actuators has only been scarcely reported. Liquid crystal elastomer (LCE) stands out among the promising classes of smart materials for fabricating microrobotics or microactuators due to its distinct anisotropic property, which enables the printed structures to exhibit automated reversible movements upon exposure to stimuli without environmental limitations. Nevertheless, the use of 2PLP for the manufacture of 4D printed LCE microstructures with high versatility and complexity have presented some challenges, limiting their implementation in final applications. This thesis aims to overcome two main obstacles faced in this regard: first, the limitation of two-photon printable stimuli-responsive materials; and second, the lack of a facile approach for aligning liquid crystal (LC) within three dimensions. The first part of this thesis aims on expanding the library of materials used for implementing light responsiveness into LC microstructures, as light provides a higher degree of temporal and spatial control compared to other stimuli. The initial approach has involved incorporation of acrylate-functionalized photoresponsive molecules, such as azobenzene and the donor-acceptor Stenhouse adduct (DASA), into a LC ink using a conventional synthetic method. However, several challenges, such as compatibility with the LC ink, have prevented the achievement of 4D printing via 2PLP. The second approach is based on post-modifying printed LC structures and successfully fabricated microactuators with five different photoresponsive features by individually incorporating each light-absorbing molecule. Furthermore, LC microactuators that exhibit distinct actuation patterns under different colors of light were fabricated by simultaneously implementing orthogonal photoresponsive molecules. The second project presented in this thesis focuses on developing a new strategy to induce alignment domains in a more flexible manner, with the aim of spatially tailoring the LC topology of the 3D printed microstructures. This is achieved by microprinting 3D scaffolds based on polydimethylsiloxane (PDMS) to manipulate the alignment directions of LC molecules. Taking advantage of 2PLP to fabricate arbitrary scaffolds, LC alignments, including planar and radial patterns, could be introduced freely and simultaneously in three-dimensional space with varying degrees of complexity. The applicability of this alignment approach was demonstrated by fabricating responsive LC microstructures within different PDMS environments, and distinct actuation patterns were observed. Overall, these two breakthroughs have unveiled a wide array of new potentials for the utilization of responsive LC microsystems with tunable functionalities and customizable actuation responses, that can be applied across various domains and applications