Traditionally it was thought that the unidirectional strength in the fiber direction of fiber dominated composites was not influenced by the matrix material. As long as the fiber was not affected then the strength would remain. However this thesis will challange that belief. The unidirectional strength in the fiber direction of fiber dominated composites is influenced by the matrix material. The object of this study was to examine the quasi-static tensile strength of unidirectional polymer composites, and then use current analytic models to predict the experimental results. The different matrix materials were polyphenylene Sulfide (PPS), vinyl ester with two different fiber-matrix interface materials, and polyether ether ketone (PEEK). / Master of Science

Ultramicroelectrodes (UMEs) have gained considerable attention over the few past decades due to the important roles they play in electrochemical studies. Electrodes with dimension less than 25 mm can generally be classified as UMEs. These electrodes exhibit enhanced electrochemical properties as their dimensions get smaller hence making nanoelectrode (production of electrodes with limiting dimensions less than 100 nm) a continuing area of interest in research. Nanometer size electrodes have advantages of high sensitivity which enables them to be used in fields such as single particle characterization and single cell analysis, and fast electron and mass transport which permits use for studying short-lived and transient electrochemical reactions such as those involved in neurochemistry. Nanoelectrodes can be fabricated via a few different strategies which include but are not limited to electrochemically etching a thin metal wire down to a cone shape or flame-etching a carbon fiber, and chemical vapor deposition of carbon in nanopipette. This work seeks to employ the use of the laser-assisted pulling method to fabricate carbon fiber electrodes sealed in glass capillary tubes. Effects of various pre- and post- treatment techniques on electrode size and stability are explored. Key words: Electrodes, Electrochemical, carbon fiber.

Carbon fiber composites are continually seeing increased use in aerospace applications. It is necessary to understand their failure modes in order to properly design and perform analysis on structures constructed primarily from them. This thesis studies woven carbon fiber composites with and without double-edge notches in a series of static and fatigue tests performed on an Instron 8801 servo-hydraulic testing system. Specimens were constructed of Advanced Composites Group product # LTM45EL woven carbon fiber pre-preg/epoxy and were cut to approximately 9-inch in length and 1-inch in width. Notches were cut into some of the specimens using a slitting saw blade of 0.006-in. thickness. Ultimate strength, Young’s modulus and Poisson’s ratio for specimens were determined to be 119,418 psi, 7,149,000 psi and 0.05, respeictively. Fracture stress for specimens with notch depths of 0.10, 0.15, 0.20, 0.25, 0.30 and 0.35 was determined to be 93,481 psi, 88,193 psi, 86,968 psi, 81,112 psi, 84,197 psi and 81,955 psi, respectively. The results from these tests showed that the specimens followed Griffith’s model for brittle failure. Average number of cycles to failure was determined to be 6,600, 37,200, 94,300 and 293,400 for fatigue tests with maximum stresses of 72.5%, 75%, 77.5% and 80% of the ultimate strength. Fatigue tests performed on notched specimens produced data that was too scattered from which to draw a statistically significant result. Numerical modeling in Abacus showed comparable results to experimental tests for stress and strain.

This is a practice-based design research project in the fields of glass blowing and knitting. It takes its starting point in trying to combine these two crafts with an experimental approach, using carbon fiber. The main focus has been to explore how I, as a designer, together with experts in their respective fields, could drive this collaboration and offer another angle on the two crafts. The outcome of my project is a series of experiments collected in an object library, showcasing the crossbreed of the two crafts.

Carbon Fiber Reinforced Polymer (CFRP) composites exhibit exceptional specific stiffness and strength properties. However, their use in structural applications is often constrained with high safety margins out of concern for their brittle and sudden failures. This study proposes manipulating the tensile failure mechanism by utilizing a discontinuous overlapped architecture, which has been demonstrated in the literature to non-linearize the tensile stress-strain response of CFRP laminates. Continuous Carbon fiber 3D-printing provides freedom in building complex morphologies and adjusting the resin content, enabling intricate discontinuous patterns for further tuning the stress-strain response. This study characterizes the constituents and tensile properties of 3D-printed continuous UD laminates. Then, an investigation is conducted on the mechanical tensile response of a 3D-printed discontinuous laminates design and the effect of discontinuity pattern length, and post-processing.

Carbon fiber composite cryogenic fuel tanks are very attractive to the aerospace industry. More information is needed on micro-cracking and how different composite formulations perform at cryogenic temperatures. In this study a cryogenic bulge test fixture was developed to rapidly screen small scale composite samples that are easily formulated in the laboratory. The design goal was to develop a simple fixture that induced thermal and mechanical strains in the same fixture. The pressure decay rate of helium gas through the composite sample after cryogenic operation gives a measure of the amount of micro-cracking induced. Uncertainty analysis techniques were employed to determine the resolution of the pressure decay determined from the bulge test.

No description available.

A lightweight carbon fiber reinforced polymer (CFRP) c-channel beam was previously designed using analytical theory and finite element analysis and subsequently manufactured through a pultrusion process. Physical testing revealed the prototype did not meet the bending and torsional stiffness of the beam model. An investigation revealed that the manufactured prototype had lower fiber content than designed, compacted geometry, an altered ply layup, missing plies, and ply folds. Incorporating these changes into the beam model significantly improved model-experiment agreement. Using what was learned from the initial prototype, several new beam designs were modeled that compare the cost per weight-savings of different composite materials. The results of these models show that fiberglass is not a viable alternative to CFRP when designing for equivalent stiffness. Standard modulus carbon was shown to have slightly lower cost per-weight savings than intermediate modulus carbon, although intermediate modulus carbon saves more weight overall. Core materials, despite potential weight savings, were ruled out as they do not have the crush resistance to handle the likely clamp loads of any attaching bolts. Despite determining the ideal materials, the manufactured cost per weight-savings of the best CFRP beam design was about double the desired target. / Graduation date: 2013 / Access restricted to the OSU Community at author's request from Oct. 5, 2012 - Oct. 5, 2014

When using Finite Element Analysis (FEA) to model notched composite panels, the values of certain material properties can have a great effect on the outcome of the simulation. Progressive damage modeling is used to model how a composite structure will fail, and how that failure will affect the response of the structure. Many different progressive damage models exist, but the formulation known as Hashin damage is used to model failure in tension and out-of-plane bending in this study. This model has ten different material properties that are used to define the damage response of the material. Each of these material properties must be calculated experimentally in a time consuming and expensive process. A method of determining which properties will have the greatest effect on the model, and therefore, which to spend the most money on accurate tests, is a factorial analysis sensitivity study. Studies of this nature have been used in many different situations regarding material properties testing and optimization. The work presented in this study uses several factorial analysis designs to perform a sensitivity study on the ten Hashin damage parameters in a variety of situations. Five different ply layups are used in modeling specimens that are loaded in tension and out-of-plane bending. The results of this study show that the significant factors depend on the ply layup and loading scenario, but there are generally less than three factors that play a significant role in modeling the failure of the panels. This means that in most cases, rather than spending substantial money on finding ten different material properties, the time and money can be focused on a small subset of the properties, and an accurate model can still be achieved. While the results of the scenarios presented may not apply to all scenarios, the methods presented can be used to perform a similar study in other specific scenarios to find the significant factors for that case. / Graduation date: 2013

Submitted in fulfillment of the requirements of the Degree of M.Tech.: Mechanical Engineering, Durban University of Technology, 2017. / Fatigue crack initiation and propagation behaviour of CFRP have been of great importance because such composites are often used in engineering components that are subjected to continuous cyclic loading. The objective of this thesis work was to investigate the damage characteristics of the fatigue properties of CFRP composites by the modification of the polymer matrix with nanoclay addition. Carbon fibre reinforced epoxy was produced via vacuum assisted resin infusion moulding method (VARIM) with nanoclay concentrations of 0wt%, 1wt%, 3wt% and 5wt%. Tension-tension fatigue tests were conducted at loading levels of 90%, 75% and 60%. The frequency that was used was 3Hz with R value of 0.1. The results showed that at nanoclay percentages of 0wt%, 1wt% and 3wt% there was a consistent trend, where the number of cycles increased in fatigue loading percentages of 90%, 75% and 60%. At 5wt% nanoclay percentage the number of fatigue cycles dropped significantly at the 90% fatigue loading. The brittle nature of the 5wt% laminate became dominate and the sample fractured early at low fatigue cycle numbers. At the 75% fatigue loading, the number of cycles increased and at 60% fatigue loading the 5wt% nanoclay sample exceeded the number of cycles of all the nanoclay percentages by 194%. This was due to the intercalated arrangement of the nanoclays favouring the slow rate of surface temperature increase, during fatigue testing, at low fatigue cycle loading. The Crack Density analysis was performed and showed that at the same time in the fatigue cycle life, the 1wt% had 55 cracks, 3wt% had 52 cracks and the 5wt% had 50 cracks, for the 60% fatigue loading. This proved that it took longer for the cracks to initiate and propagate through the sample as the nanoclay percentage increased. Impact and hardness testing showed that the 5wt% exhibited brittle behaviour, which contributed to the results above. Scanning electron microscopy examination highlighted that the agglomeration of nanoclays delayed the crack initiation and propagation through the specimen and that the extent of fatigue damage decreased as the nanoclay percentage increased. A fatigue failure matrix was developed and showed that delamination, fibre breakage and matrix failure were the predominate causes for the fatigue failure. / M