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A small gas gun, capable of accelerating a projectile 1m long by 25.4mm diameter to about 50 m/s, and an extended split Hopklnson bar apparatus have been designed and constructed for the tensile impact testing of fibre reinforced composite specimens at strain rates of the order of 1000/s. Elastic strain measurements derived from the Hopkinson bar analysis are checked, using strain gauges attached directly to the specimen and the validity of the elastic moduli determined under tensile impact is confirmed. Epoxy specimens reinforced with plain-weave fabrics of either carbon or glass or with several hybrid combinations of the two in various lay-ups, giving five different weight fractions of reinforcement from all-carbon to all-glass, have been tested in tension at three strain rates, nominally, ~10^-3/s, ~10/s and ~10³/s. The effect of both hybrid composition (volume fraction of carbon reinforced plies) and applied strain rate on the tensile modulus, the tensile strength and the strain to fracture is determined and a limited hybrid effect is observed in specimens with a carbon volume fraction in the approximate range 0.6 to 0.7 where, at all three strain rates there is an enhancement of the failure strain over that for the all-carbon plies and an increased failure strength, most marked in the impact tests, over that predicted by the rule of mixtures. The fracture surfaces of specimens are examined by optical and scanning electron microscopy and the failure process in the hybrid composites is related to that found in the all-carbon and the all-glass specimens. The classical laminated plate theory and the Tsai-Wu strength criterion are used to predict the stiffness and strength of the hybrid composites from the elastic and strength properties of the constituent plies. Analytical predictions are in good agreement with experimental measurements.

The role of the interphase in fiberglass reinforced composites was studied by a combination of theoretical analysis, mechanical tests, and several high-resolution analytical techniques. The interphase was varied in composition by using epoxy and polyester matrix polymers with and without added coupling agents, as well as four fiber surface modifications. Different coupling agents on the fibers were shown to change the fiber tensile strength markedly. Filament wound unidirectional composites were tested in short beam "shear." Corresponding samples were fabricated by embedding one to seven fibers in the center of polymer dogbone specimens that were tested in tension to determine critical fiber lengths. Those values were used in a new theoretical treatment (that combines stress gradient shear-lag theory with Weibull statistics) to evaluate "interfacial shear strengths". The fact that results did not correlate with the short beam data was examined in detail via a combination of polarized light microscopy, electron microscopy (SEM) and spectroscopy (XPS or ESCA) and mass spectroscopy (SIMS). When the single fiber specimens were unloaded, a residual birefringent zone was measured and correlated with composite properties, as well as with SIMS and SEM analysis that identified changes in the locus of interphase failure. Variations in the interphase had dramatic effects upon composite properties, but it appears ·that there may be an optimum level of fiber-matrix adhesion depending upon the properties of both fiber and matrix. Fiber-fiber interactions were elucidated by combining tensile tests on multiple fiber dogbone specimens with high-resolution analytical techniques. In general, this work exemplifies a multidisciplinary approach that promises to help understand and characterize the structure and properties of the fiber-matrix interphase, and to optimize the properties of composite materials. / Master of Science

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

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A variety of retrofitting methods are used to upgrade existing structures. For example, steel plates and Fiber Reinforced Polymer (FRP) jackets are externally bonded to members to increase their capacity in flexure and shear. However, due to the issue of corrosion these strengthening systems may lose their efficiency with time. FRP materials have been used to strengthen many structural components of different shapes and types. FRP jackets, FRP Strips, and FRP rods have commonly been used to rehabilitate existing structural components. The many advantages of using FRP as strengthening materials have made this material an attractive alternative: advantages such as lightweight, high strength, and ease of setting up. Among the many applications using FRP, Near Surface Mounted -- Fiber Reinforced polymer (NSM-FRP) is a promising technique used to strengthen concrete members. However, de-bonding issues have to be overcome to make this technique efficient and reliable. The NSM-FRP technique consists of making a groove along the surface of the concrete member to be retrofitted with depth less than the cover of the member. After cleaning the groove, epoxy paste is used to fill two-thirds of the groove's depth. The FRP element is then mounted in the groove. Finally, the groove is filled with epoxy and the excessive epoxy is leveled with surface of the concrete. This technique makes the FRP material completely covered by epoxy in the cover of the concrete. This method can be used for strengthening both the positive and negative moment regions of girders and slabs. Groove size, paste, concrete, and rods properties are the main variables that control the efficiency of the NSM-FRP rods. The main objective of this research project is to determine the behavior of reinforced concrete beams that are strengthened with NSM-CFRP reinforcement bars. In this research project, the bond characteristics of NSM-CFRP reinforcement bars are first determined from pullout tests. Then, NSM-CFRP rods are installed in reinforced concrete beams and the beams are tested. Loads, strains, and deflections are measured and theoretical and measured capacities are compared. Finally, the reliability and efficiency of using NSM-CFRP rods technique in retrofitting existing structures is observed.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, October 2017 / This research looks into the manufacturing process of complex geometries using continuous fibre reinforced thermoplastics (CFRTP). The purpose of this work was to develop methods that will enable the production of defect free complex components. This was achieved by investigating the key process parameters in the CFRTP manufacturing process, and optimizing them in order to improve the quality of components. The investi- gations were performed with the aid of software making use of the finite element method, and this was found to be instrumental in predicting the formability of geometries. The re- search showed that the formability of complex geometry is largely determined by the ability of the laminate to be draped into the required geometry. The forming mechanisms that take place during the draping process can be linked to the formation of defects where draping is unsuccessful. The study also showed that the quality of the drape can be influenced by blank and tool design factors. It was also shown that the blank can be manipulated using a restraint mechanism to improve the formability of geometries. The effect of processing parameters such as forming speed, forming pressure and tool temperature were also investigated. The research resulted in the formulation of guidelines to follow when manufacturing CFRTP components. The developments that were made were successfully implemented to improve the formability of a complex component that had previously been difficult to form without defects. / MT2018

ABSTRACT The repair and strengthening of concrete bridge members with CFRP has become increasingly popular over recent years. However, significant research is still needed in order to develop more robust guidelines and specifications. The research project aims to assist with improving design prosedures for damaged concrete members with the use of CFRP. This document summarizes the analysis and testing of full-scale 40’ foot long prestressed concrete (PSC) bridge girders exposed to simulated impact damage and repaired with carbon fiber reinforced polymers (CFRP) materials. A total of five AASHTO type II bridge girders fabricated in the 1960’s were taken from an existing bridge, and tested at the Florida Department of Transportation FDOT structures lab in Tallahassee, Florida. The test specimens were tested under static loading to failure under 4-point bending. Different CFRP configurations were applied to each of the girders. Each of the test girders performed very well as each of them held a higher capacity than the control girder. The repaired girders 5, 6 and 7 surpassed the control girder’s capacity by 10.88%, 15.9% and 11.39%. These results indicate that repairing laterally damaged prestressed concrete bridge girders with CFRP is an effective way to restore the girders flexural capacity.