Fiber-reinforced concrete (FRC) is nowadays extensively used in civil engineering throughout the world due to the composites of FRC can improve the toughness, flexural strength, tensile strength, and impact strength as well as the failure mode of the concrete. It is an easy crazed material compared to others materials in civil engineering. Concrete, like glass, is brittle, and hence has a low tensile strength and shear capacity. At present, there are different materials that have been employed to reinforce concrete. In our experiment, nanostructures iron oxide was prepared by electrodepostion in an electrolyte containing 0.2 mol/L sodium acetate (CH3COONa), 0.01 mol/L sodium sulfate (Na2SO4) and 0.01 mol/L ammonium ferrous sulfate (NH4)2Fe(SO4)2.6H2O under magnetic stirring. The resulted showed that pristine Fe2O3 particles, Fe2O3 nanorods and nanosheets were synthesized under current intensity of 1, 3, 5 mA, respectively. And the pull-out tests were performed by Autograph AGS-X Series. It is discovering that the load force potential of nanostructure fibers is almost 2 times as strong as the control sample.

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

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 73-77). Also available on the World Wide Web.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 170-175). Also available via the Internet.

Excellent properties of Carbon Fiber Reinforced Polymer (CFRP) composites are usually obtained in the direction at which carbon fibers are embedded in the polymeric matrix material. The outstanding properties of this material such as high strength to weight ratio, high stiffness and high resistance to corrosion can be tailored to meet specific design applications. Despite their excellent mechanical properties, application of CFRPs has been limited to more lucrative sectors such as aerospace and automotive industries. This is mainly due to the high costs involved in manufacturing of this material. Machining, milling and drilling, is a critical part of finishing stage of manufacturing process. Milling and drilling of CFRP is complicated due to the inhomogeneous nature of the material and extreme abrasiveness of carbon fibers. This is why CFRP parts are usually made near net shape. However, no matter how close they are produced to the final shape, there still is an inevitable need for some post machining to obtain dimensional accuracies and tolerances. Problems such as fiber-matrix debonding, subsurface damage, rapid tool wear, matrix cracking, fiber pull-out, and delamination are usually expected to occur in machining CFRPs. These problems can affect the dimensional accuracy and performance of the CFRP part in its future application. To improve the efficiency of the machining processes, i.e. to reduce the costs and increase the surface quality, researchers began studying machining Fiber Reinforced Polymer (FRP) composites. Studies into FRPs can be divided in three realms; analytical, experimental and numerical. Analytical models are only good for a limited range [0° – 75°] of Fiber Orientations , to be found from now on as “FO” in this thesis. Experimental studies are expensive and time consuming. Also, a wide variety of controlling parameters exist in an experimental machining study; including cutting parameters such as depth of cut, cutting speed, FO, spindle speed, feed rate as well as tool geometry parameters such as rake angle, clearance angle, and tool edge/nose radius. Furthermore, the powdery dust created during machining is known to cause serious health hazards for the operator. Numerical models, on the other hand, offer the unique capability of studying the complex interaction between the tool and workpiece as well as chip formation mechanisms during the cut. Large number of contributing parameters can be included in the numerical model without wasting material. Three main objectives of numerical models are to predict principal cutting force, thrust force and post-machining subsurface damage. Knowing these, one can work on optimization of machining process by tool geometry and path design. Previous numerical studies mainly focus on the orthogonal cutting of FRP composites. Thus, the existing models in the literature are two-dimensional (2D) for the most part. The 2D finite element models assume plain stress or strain condition. Accordingly, the reported results cannot be reliable and extendable to real cutting situations such as drilling and milling, where oblique cutting of the material occurs. Most of the numerical studies to date claim to predict the principle cutting forces fairly acceptable, yet not for the whole range of fiber orientations. Predicted thrust forces, on the other hand, are generally not in good agreement with experimental results at all. Subsurface damage is reported by some experimental studies and again only for a limited FO range. To address the lack of reliable force and subsurface damage prediction model for the whole FO range, this thesis aims to develop a 3D finite element model, in hope of capturing out-of-plane displacements during stress formation in different material phases (Fiber, Matrix and the Interface bonding). ABAQUS software was chosen as the most commonly used finite element simulation tool in the literature. In present work a user-defined material subroutine (VUMAT) is developed to simulate behavior of carbon fibers during the cut. Carbon fibers are assumed to behave transversely isotropic with brittle (perfectly elastic) fracture. Epoxy matrix is simulated with elasto-plastic behavior. Ductile and shear damage models are also incorporated for the matrix. Surface-based cohesive zone technique in ABAQUS is used to simulate the behavior of the zero-thickness bonding layer. The tool is modeled as a rigid body. Mechanical properties were extracted from the literature. The obtained numerical results are compared to the experimental and numerical data in literature. The model is capable of capturing principal forces very well. Cutting force increases with FO from zero to 45° and then decreases up to 135°. The simulated thrust forces are still underestimated mainly due to the fiber elastic recovery effect. Also, the developed 3D model is shown to capture the subsurface damage generally by means of a predefined dimensionless state variable called, Contact Damage (CSDMG). This variable varies between zero to one. It is stored at each time step and can be called out at the end of the analysis. It was shown that depth of fiber-matrix debonding increases with increase in FO. / Graduate

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

The concept of reinforcement was developed in late 20th century and since then till the recent past there are many works carried out on the effect of fibers in imparting strength and stiffness to the soil. Experimental investigations on fiber reinforced soils showed an increase in shear strength and reduction in post peak loss of strength due to the reinforcement. Analytical/mechanistic models are developed to predict the stress-strain response of fiber reinforced soil (under discrete framework, energy dissipation methods, force equilibrium methods etc). Numerical investigations are also carried out, and it was observed that the presence of random reinforcing material in soils make the stress concentration diffuse more and restrict the shear band formation. Soil properties vary from point to point at micro level and influence stress mobilization. Hence, there is a need to carry out probabilistic analysis to capture the effects of uncertainties and variability in soil and their influence on stress-strain evolution. In the present thesis an attempt has been made to propose a mechanistic model that predicts the stress-strain response of fiber reinforced soil and also considers the effect of anisotropy of fibers. A stochastic/probabilistic model is developed that predicts the stochastic stress-strain response of fiber reinforced soil. In addition, probabilistic analysis is carried out to observe the effect of number of fibers across the shear plane in imparting shear resistance to soil. The mechanistic model and stochastic models are validated with reference to the experimental results of consolidated undrained (CU) triaxial tests on coir fiber reinforced red soil for different fiber contents. The entire thesis is divided into six chapters. Chapter-wise description is given below. Chapter one presents a general introduction to the works carried out on fiber reinforced soils and also the investigations carried out on probabilistic methodologies that takes into account the soil variability. Thus, the chapter gives an outline of the models developed under mechanistic and probabilistic frameworks in the thesis. The objectives and organization of the thesis are also presented. Chapter two presents a detailed review of literature on the role of fibers in fiber reinforced soil. The details of experimental investigations carried out and models developed are explained briefly. Also, the literature pertaining to the role of variability in soil on its engineering behavior is presented. Based on the literature presented in this chapter, concluding remarks are made. Chapter three presents the details of a new mechanistic model developed based on modified Cam-clay model. This model considers the effect of fiber content and also the effect of anisotropy due to fibers. The predictions from the mechanistic model are compared with the experimental results. Under anisotropic condition, as angles of inclination of fiber vary from 0° to 90° with the bedding plane, it is observed that the strength increment in the reinforced soil is not as significant as that observed in isotropic case. Horizontal fibers turn out to be most effective since they are subjected to maximum extension thereby inducing tensile resistance which in turn contributes for strength increase in fiber reinforced soil. Chapter four presents a new approach to predict the stochastic stress-strain response of soil. Non-homogeneous Markov chain (multi-level homogeneous Markov chain) modeling is used in the prediction of stochastic response of soil. The statistical variations in the basic variables are taken into account by considering the response quantities (viz. stress at a given strain or settlement at a given load level) as random. A bi-level Homogeneous Markov chain predicts the stochastic stress-strain response efficiently. The predicted results are in good agreement with the experimental results. An illustration of this model is done to predict the stochastic load-settlement response of cohesionless soil. A simple tri-level homogeneous Markov chain model is proposed to predict settlements of soil at a given load for an isolated square footing subjected to axial compression. A parametric study on the effect of correlation coefficient on the prediction of settlements is performed. Chapter five presents the results of probabilistic analysis carried out to determine the effect of number of fibers across the shear plane in improving the shear strength of soil. It is observed that as the percentage of fibers in the specimen increases, the probability of failure of specimen under the same stress condition reduces and thus the reliability of the fiber reinforced soil system increases. In Chapter six, a summary of the important conclusions from the various studies reported in the dissertation are presented.

Use of fiber reinforced polymer (FRP) material has been a good solution for many problems in many fields. FRP is available in different types (carbon and glass) and shapes (sheets, rods, and laminates). Civil engineers have used this material to overcome the weakness of concrete members that may have been caused by substandard design or due to changes in the load distribution or to correct the weakness of concrete structures over time specially those subjected to hostile weather conditions. The attachment of FRP material to concrete surfaces to promote the function of the concrete members within the frame system is called Externally Bonded Fiber Reinforced Polymer Systems. Another common way to use the FRP is called Near Surface Mounted (NSM) whereby the material is inserted into the concrete members through grooves within the concrete cover. Concrete beam-column joints designed and constructed before 1970s were characterized by weak column-strong beam. Lack of transverse reinforcement within the joint reign, hence lack of ductility in the joints, and weak concrete could be one of the main reasons that many concrete buildings failed during earthquakes around the world. A technique was used in the present work to compensate for the lack of transverse reinforcement in the beam-column joint by using the carbon fiber reinforced polymer (CFRP) sheets as an Externally Bonded Fiber Reinforced Polymer System in order to retrofit the joint region, and to transfer the failure to the concrete beams. Six specimens in one third scale were designed, constructed, and tested. The proposed retrofitting technique proved to be very effective in improving the behavior of non-ductile beam-column joints, and to change the final mode of failure. The comparison between beam-column joints before and after retrofitting is presented in this study as exhibited by load versus deflection, load versus CFRP strain, energy dissipation, and ductility.

Master of Science / Department of Architectural Engineering and Construction Science / Kimberly W. Kramer / Reinforced concrete is a common building material used for blast resistant design. Adding fibers to reinforced concrete enhances the durability and ductility of concrete. This report examines how adding steel fibers to reinforced concrete for blast resistant design is advantageous. An overview of the behavior of blasts and goals of blast resistant design, and advantages of reinforced concrete in blast-resistant design, which include mass and the flexibility in detailing, are included in the blast resistant design section. The common uses for fiber-reinforced concrete, fiber types, and properties of fiber reinforced concrete varying with fiber type and length, and concrete strength are discussed in the fiber-reinforced concrete section. Two studies, Very High-Strength Concrete for Use in Blast-and-Penetration Resistant Structures and Blast Testing of Ultra-High Performance Fiber and FRP-Retrofitted Concrete Slabs, are reviewed. Lastly, the cost, mixing and corrosion limitations of using steel fiber-reinforced concrete are discussed. Reinforced concrete has been shown to be a desirable material choice for blast resistant design. The first step to designing a blast resistant reinforced concrete structure is to implement proper detailing to ensure that structural failures will be contained in a way that preserves as many lives as possible. To design for the preservation of lives, a list of priorities must be met. Preventing the building from collapse is the first of these priorities. Adding steel fibers to concrete has been shown to enhance the concrete’s post-crack behavior, which correlates to this priority. The second priority is reducing flying debris from a blast. Studies have shown that the failure mechanisms of steel fiber reinforced concrete aid in reducing flying debris when compared to conventional reinforced concrete exposed to blast loading. The major design considerations in designing steel fiber reinforced concrete for blast resistant design include: the strength level of the concrete with fiber addition, fiber volume, and fiber shape. As research on this topic progresses, the understanding of these factors and how they affect the strength characteristics of the concrete will increase, and acceptance into the structural design industry through model building codes may be possible.