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In most application to date reinforced carbon fiber composites have been used in relatively smaller thickness, less than 10mm thick and essentially for carrying in-plane loads. As a result, design and testing procedures were developed which reflected the need to understand the in-plane response of the material. recently, engineers and designers have begun to use reinforced carbon fiber composites in thicker sections, where an understanding of the through-thickness response is of para-mount importance in designing reliable structures, particularly where the through-thickness strength has a controlling influence on the overall structural strength of the component. In this thesis tests will be done on carbon fiber non-crimp fabric (NCF) which will be loaded in compression and shear and elastic moduli and strength will be evaluated. In characterizing the through-thickness mechanical properties of a composite, the objective is to produce a state of stress in the test specimen which is uniform and will repeatedly measure the true properties with accuracy. In this study, specimens were machined from two blocks of thick (~20 mm) laminates of glass/epoxy and NCF carbon fiber infused with vinylester and tested in compression, and shear.

This research investigated effect of submicron glass fiber modification on mechanical performance of short carbon fiber reinforced vinyl ester resin. Firstly, the mixture of resin and glass fiber was made by mixing submicron fiber into resin in a homogenizer at the speed of 5000 rpm in 30 minutes. Then, this modified resin was reinforced by short carbon fiber at the length of 1 mm, 3mm and 25 mm. The modifying effects were accessed by evaluating mechanical properties such as: bending, tensile, impact test as well as dynamic mechanical analysis. To explain some manners of material caused by adding glass fiber into resin, some techniques were also used (IFSS, SEM, laser microscope scanner, ultrasonic S-scan, X-ray ...). / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University

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This research demonstrated the fabrication, flexural testing, and analysis of nominally 5 ft (1.5 m) 6-bay and 10 ft (3 m) 12-bay carbon/epoxy IsoBeam™ structures. The rectangular cross-section was 5 in (12.7 cm) wide by 10 in (25.4 cm) high. The IsoBeam structure is a composite lattice structure that is a geometric derivative of the IsoTruss® structure. Modifying the geometry to yield a rectangular cross-section provides additional applications for these beams as structural elements in buildings, aircraft, vehicles, and other structures. The diameters of the constituent members of the IsoBeam, namely the longitudinal and diagonal members, were sized such that the IsoBeam could hold the design load of a 10K1 steel joist 550 plf (818.5 kg/m). Three IsoBeam structures were manufactured: two 5 ft (1.5 m) long and one 10 ft (3 m) long. The IsoBeam structures were manufactured with carbon/epoxy composite tows comprised of T700SC-12K-50C carbon fibers and UF3369-100 pre-impregnated (pre-preg) epoxy resin. The pre-preg tows were positioned on a modified pin-mandrel under tension using a combination of hand and machine filament winding in an interwoven pattern to create the complex geometry of the IsoBeam structure. Each member was circumferentially wrapped with 1 in (2.5 cm) wide strips of Dunstone Hi-Shrink Tape (polyester) to consolidate the tows during the manufacturer’s recommended curing process. Microscopic measurements after testing established that these careful manufacturing techniques produced high-quality specimens with an average void ratio of 0.72% and an average fiber volume fraction of 69.5%. The average compression stiffness and strength were 18.7 ksi (129 GPa) and 115.1 ksi (793 MPa), respectively.Each IsoBeam was loaded in four-point bending to failure, with other tests performed in the linear-elastic range to study load path behavior of the IsoBeam. Strain, deflection, and load data were collected to provide a detailed understanding of the behavior of individual members under load and their corresponding stresses. The 6-bay IsoBeam structures experienced failure at 8055 lbs (35.8 kN) and 11224 lbs (49.9 kN), in compression initiated by buckling. The longer 12-bay IsoBeam structure failed in a similar manner at 8035 lbs (35.7 kN) but also exhibited delamination, due to insufficient interweaving.Experimental results were compared to the predicted strength of the IsoBeam based on a linear finite element model (created using SAP 2000) and hand calculations. Validation of the design through the comparison of experimental and predicted values gave insight on design techniques and overall understanding of the performance of the IsoBeam in bending, with excellent correlation in the linear range. The assumption that longitunals are primarily responsible for bending strength and diagonals primarily carry shear was validated, indicating a strong correlation between manufacturing quality and performance of IsoBeam structures.

Composite lattice structures known as the IsoBeam™ made with unidirectional carbon/epoxy were manufactured and tested in shear-dominated bending. The manufacturing process consisted of placing tows of carbon fiber pre-impregnated with epoxy resin onto a pin-type mandrel to create members with interwoven joints. The members were consolidated with a half spiral aramid sleeve. The IsoBeam structure consists of two main types of members: longitudinal and diagonal members measuring nominally 0.4 in. (10.2 mm) and 0.2 in. (5.1 mm) in diameter, respectively. The hand-manufactured specimens measured nominally 6 in. (152.4 mm) high by 3 in. (76.2 mm) wide by 2 ft (0.61 m) long with 4 bays, each 6 in. (152.4 mm) long. The beams weighed between 1.82-1.86 lbs (8.09-8.27 N). A finite element analysis of the IsoBeam was compared to the experimental results. The IsoBeam specimens were tested in four-point or three-point bending but were dominated by shear due to short-beam bending because of the low length/height aspect ratio. After testing to failure, individual members that were lightly loaded and appeared to be undamaged were removed and tested in axial compression. The void percentage and fiber volume fraction were also measured. The average maximum strength of the IsoBeam structure was 4.11 kips (18.3 kN), yielding an equivalent shear of 2.06 kips (9.15 kN) and bending moment of 20.2 kip-in (2.29 kN-m). This strength was lower than expected and is attributed primarily to low material quality, insufficient consolidation of members, and inadequate tension on the tows during manufacturing. The structure exhibited ductile behavior absorbing considerable energy after initial failure, as well as exhibiting damage tolerance due to the inherent structural redundancy. The inner diagonal members which are inherently stiffer exhibited higher strains than the side outer diagonal members after initial failure. The members removed and tested exhibited an average compression strength of 86.9 ksi (599 MPa) and compression modulus of 17.8 Msi (122 GPa) which are both lower than observed in members tested in past research. The diagonal members had a higher strength of 111 ksi (767 MPa) than the longitudinal member's compression strength of 62.5 ksi (431 MPa). Most members were seen to have a high percentage of voids with an average of 4.3% for diagonal members and 6.4% for longitudinal members. The average fiber volume fraction content of members was very low at 38%. The linear finite element analysis of the IsoBeam structure predicted failure at a load of 34 kips (151 kN). Without considering buckling, the first member predicted to fail was a vertical outer diagonal. This research demonstrates that increasing the manufacturing quality should yield an IsoBeam structure that is strong, ductile and damage tolerant.

Due to enhanced properties such as large surface area-to-volume ratio, metal nanoparticles are often employed as catalysts for various applications. However, most studies involving nanoparticle catalysts have been conducted on collections of particles rather than single nanoparticles. Results obtained for ensemble systems can be difficult to interpret due to variations in particle loading and interparticle distance, which are often challenging to control and characterize. In this study, two immobilization strategies for incorporating gold nanoparticles (AuNPs) on carbon fiber ultramicroelectrodes (UMEs) were compared with the goal of extending these techniques to nanoelectrodes for studies of single AuNPs. Both layer-by-layer deposition of AuNPs on natural carbon fiber UMEs and direct reduction of AuNPs on nitrided carbon fiber UMEs were explored. Although both methods proved feasible, the direct reduction method seemed to be more effective and should better enable direct comparisons of bare and capped AuNPs.

Due to their unique properties, carbon fiber reinforced polymers (CFRP) are becoming ever more prevalent in today's society. Unfortunately, CFRP suffer from a wide range of failure modes and structural health monitoring methods are currently insufficient to predict these failures. It is apparent that self-sensing structural health monitoring could be advantageous to protect consumers from catastrophic failure in CFRP structures. Previous research has shown that embedded nickel nanostrand nanocomposites can be used to instantaneously measure strain in carbon fiber composites, but these methods have been severely limited and can induce high stress concentrations that compromise the structural integrity of the carbon fiber structure. In this research the strain sensor material and the connective circuitry to the sensor are analyzed to improve the practicality of in situ strain sensing of carbon fiber structures. It has been found that the use of nickel nanostrands embedded directly onto carbon fiber as a strain sensor material has no advantages over a carbon fiber strain sensor alone. Additionally, it has been shown that the circuitry to the strain sensor plays a critical role in obtaining a strong, consistent piezoresistive signal that can be related to strain. The use of nickel coated carbon fiber in the circuitry has been evaluated and shown to reduce the noise in a piezoresistive signal while allowing for remote strain sensing from greater distances away from the strain location. The piezoresistive strain sensing utilized in the tested sensor designs relies on electrons tunneling through an insulting barrier between two conductors. This phenomenon is known as quantum tunneling. Two factors - tunneling barrier height and gap distance - affect the probability of quantum tunneling occurring. Thus, to accurately model and predict the piezoresistivity of nanocomposites these two parameters must be known. Through the use of dielectric spectroscopy the gap distance can be determined. Using nanoindenting, the barrier height for various polymers was also determined. The measured values can be used, in future work, to improve the modeling of nickel nanostrand nanocomposite.

The automotive industry faces the challenge to manufacture vehicles with reduced material usage and climate impact. To achieve this the industry has begun using other materials such as carbon fibre composite than materials such as steel and aluminium which are normally used for the manufacturing of automobile parts. Because its anisotropic structure gives the manufacturer increased opportunity to selectively use the material for the part’s stability and ability to withstand loads However Carbon fiber has drawbacks, the material is time-consuming to work with and expensive, because such automobile parts are either made by hand or with precisio nmolding equipment that requires experienced and educated personnel to produce parts with satisfactory quality. A car component whose weight reduction is crucial is the car rim. The car rims and tire’s weight determines the wheel shaft’s torque needed for steering which makes it an important component of the car. This work examines a manufacturing technology with the potential to reduce material use and the climate impact of car rims manufacturing. The manufacturing technology involves a robotic system that weaves carbon fiber threads on a winding frame that sits on a rotary table. The work’s purpose is to derive a theoretical model which describes the following characteristics: Production time, material usage, how the carrim and winding frame are to be adapted to one another to ensure the car rim can withstand loads to which it can be expected to be subjected.The objective is to generate data which describes these characteristics. To derive a theoretical model and generate data which describes the manufacturingstechnology’s characteristics, the work was split into two parts; In the first part, a theoretical formula was derived to relate material usage with the used length of a carbon fibre thread. Simulations are made to relate material usage and production time with theory for a PID-regulator.In determining the weaving pattern, material technology’s theory for anisotropy is used. The second part involves using theory from solid mechanics to derive theoretical equations which describes how the winding frame and car rim’s dimensioning are to be adapted to one another, with regards to the car rim’s critical parameters. Which in this work is the car rim’s stiffness and carbon fibre’s yield strength. To test the mechanical performance of the car rim, Finite-element-method(FEM) simulations are made and the validation of the simulation is done with the derived theoretical equations. In simplifying the work, winding frame, weaving pattern, and car rim are visualized using Computer-aided-design(CAD) tools. The conclusion from the results is that while the theoretical model showcases the manufacturing technology’s potential but further work is needed to improve it and adapt it to car rim’s industrial standards.

Carbon ber composites have become popular in aerospace structures and applications due to their light weight, high strength, and high performance. Recently, scientists have begun investigating hybrid composites that include fibers and particulate fillers, since they allow for advanced tailoring of mechanical properties, such as improved fatigue life. This project investigated a hybrid carbon ber reinforced polymer (HCFRP) that includes carbon fiber and additional alumina nanoparticle fillers, which act as embedded nano stress-sensors. Utilizing the piezospectroscopic e ect, the photo-luminescent spectral signal of the embedded nanoparticles has been monitored as it changes with stress, enabling non-contact stress detection of the material. The HCRFPs stress-sensitive properties have been investigated in-situ using a laser source and a tensile mechanical testing system. Hybrid composites with varying mass contents of alumina nanoparticles have been studied in order to determine the e ect of particle content on the overall stress sensing properties of the material. Additionally, high resolution photo-luminescent maps were conducted of the surfaces of each sample in order to determine the particulate dispersion of samples with varying alumina content. The dispersion maps also served as a method of quantifying particulate sedimentation, and can aid in the improvement of the manufacturing process. The results showed that the emitted photo-luminescent spectrum can indeed be captured from the embedded alumina nanoparticles, and exhibits a systematic trend in photo-luminescent peak shift with respect to stress. The stress maps showed a linear increase in peak shift up to a certain critical stress, and matched closely with the DIC strain results. Therefore, the non-contact stress sensing results shown in this work have strong implications for the future of structural health monitoring and nondestructive evaluation (NDE) of aerospace structures.