Indiana University-Purdue University Indianapolis (IUPUI) / This study represents a cost-effective method to advance the physical and mechanical properties of carbon fiber-reinforced polymer (CFRP) prepreg composite materials, where electrospun multiwalled carbon nanotubes (CNTs)/epoxy nanofibers fabricated and deposited in between the layers of traditional CFRP prepreg composite. CNT-aligned epoxy nanofibers were uniformly formed by an optimized electrospinning method. Electrospinning is considered one of the most flexible, low-cost, and globally recognized methods for generating continuous filaments from submicron to tens of nanometer diameter. Nanofilaments were incorporated precisely on the layers of prepreg to accomplish increased adhesion and interfacial bonding, leading to increased strength and enhancements in more mechanical properties. As a result, the modulus of the epoxy and CNT/epoxy nanofibers were revealed to be 3.24 GPa and 4.84 GPa, leading to 49% enhancement. Furthermore, interlaminar shear strength (ILSS) and fatigue performance at high-stress regimes improved by 29% and 27%, respectively. Barely visible impact damage (BVID) energy improved considerably by up to 45%. The thermal and electrical conductivities were also increased considerably because of the highly conductive CNT networks present in between the CFRP layers. The newly introduced approach was able to deposit high content uniform CNTs at the ply interface of prepregs to enhance the CFRP properties, that has not been achieved in the past because of the randomly oriented high viscosity CNTs in epoxy resins.

This study represents a cost-effective method to advance the physical and mechanical properties of carbon fiber-reinforced polymer (CFRP) prepreg composite materials, where electrospun multiwalled carbon nanotubes (CNTs)/epoxy nanofibers fabricated and deposited in between the layers of traditional CFRP prepreg composite. CNT-aligned epoxy nanofibers were uniformly formed by an optimized electrospinning method. Electrospinning is considered one of the most flexible, low-cost, and globally recognized methods for generating continuous filaments from submicron to tens of nanometer diameter. Nanofilaments were incorporated precisely on the layers of prepreg to accomplish increased adhesion and interfacial bonding, leading to increased strength and enhancements in more mechanical properties. As a result, the modulus of the epoxy and CNT/epoxy nanofibers were revealed to be 3.24 GPa and 4.84 GPa, leading to 49% enhancement. Furthermore, interlaminar shear strength (ILSS) and fatigue performance at high-stress regimes improved by 29% and 27%, respectively. Barely visible impact damage (BVID) energy improved considerably by up to 45%. The thermal and electrical conductivities were also increased considerably because of the highly conductive CNT networks present in between the CFRP layers. The newly introduced approach was able to deposit high content uniform CNTs at the ply interface of prepregs to enhance the CFRP properties, that has not been achieved in the past because of the randomly oriented high viscosity CNTs in epoxy resins.

No description available.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18586号 / 工博第3947号 / 新制||工||1607(附属図書館) / 31486 / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 北條 正樹, 教授 北村 隆行, 教授 琵琶 志朗 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19412号 / 工博第4128号 / 新制||工||1636(附属図書館) / 32437 / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 北條 正樹, 教授 北村 隆行, 教授 琵琶 志朗 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

No description available.

In this thesis, a fully nonlinear finite element study of the flexural behavior of doubly reinforced concrete beams strengthened using different Carbon Fiber Reinforced Polymer (CFRP) composite strengthening configurations has been carried out. Prior to the study, a total of six beams were constructed, pre-cracked, strengthened and tested to failure under a four-point loading condition (Zhao and O'Riordan-Adjah, 2004). Then, for the purpose of this thesis work, detailed three dimensional finite element models were created not only to correlate the results obtained from the experiments, but also to predict the load capacity, failure modes and crack pattern of reinforced concrete (RC) beams strengthened using Fiber Reinforced Polymer (FRP) composites. Knowing the behavior for each of the materials that compose the beam (concrete, steel, bonding material or interface, and FRP laminates) and how to get their properties, an accurate and representative finite element model can be created. Tests and analytical (FE) results showed that the strengthened configuration plays an important role in the overall strength, failure mechanisms, and, more significantly, the ductile behavior of the beams. Considerable increases in the load-carrying capacity of the RC beams were observed. Increases that range from 12% (using FRP only on the bottom of the beam) to 35% (FRP on the bottom + 45 degrees sides' configuration as explained later) compared to the control beam before ultimate failure were obtained. Failure modes were also affected since the beam with only FRP on the bottom failed completely by debonding of the laminate while the beams with side FRP anchorage strips failed by a combination of composite debonding on the sides and concrete crushing. Finally, ductile behavior of the beams was greatly improved due to the application of the strengthening material on the side of the concrete beams, serving as an anchorage to the bottom fabric. The accuracy of the model has been validated comparing the results obtained from the six beam tests to the ones determined using the FE approach. Good agreement between the two has been found.

About 77,600 bridges throughout the United States in the Federal Highway Association (FHWA) bridge database are listed as structurally deficient. This has created a need to either replace or strengthen bridges quickly and efficiently. Due to high costs for total replacement of deficient bridges, strengthening of existing bridges is a more economical alternative. A technique that has been developing over the past two decades is the strengthening of bridges using carbon fiber reinforced polymer (CFRP) sheets. The CFRP sheets are attached to the bottom of the bridge girders using structural adhesives so that the CFRP becomes an integral part of the bridge and carries a portion of the flexural loading. The CFRP sheets allow for an increase in the capacity of the bridge with minimal increase in the weight of the structure due to CFRP having a low density. Because the CFRP is expected to be an integral component and carry some of the long-term loading it is important to understand the long-term durability of the composite section. This thesis is part of a larger project, in which the long-term durability of the CFRP composite on concrete beams is investigated experimentally. The CFRP strengthened beams are exposed to fatigue testing and thermal-humidity cycling followed by failure testing. The testing scheme for this experiment allows for the investigation of the individual effects of fatigue and thermal-humidity loading as well as to explore the effects from combined fatigue and thermal-humidity loading. The investigation of the combined effects is a unique aspect of this experiment that has not been performed in prior studies. Results indicate that a polyurethane-based adhesive could provide a more durable bond for the CFRP-concrete interface than possible with epoxy-based adhesives.

yes / This paper presents test results of six concrete beams reinforced with longitudinal carbon fiber reinforced polymer (CFRP) bars and without vertical shear reinforcement. All beams were tested under a two-point loading system to investigate shear behavior of CFRP reinforced concrete beams. Beam depth and amount of CFRP reinforcement were the main parameters investigated. All beams failed due to a sudden diagonal shear crack at almost 45°. A simplified, empirical expression for the shear capacity of FRP reinforced concrete members accounting for most influential parameters is developed based on the design-by-testing approach using a large database of 134 specimens collected from the literature including the beams tested in this study. The equations of six existing design standards for shear capacity of FRP reinforced concrete beams have also been evaluated using the large database collected. The existing shear design methods for FRP reinforced concrete beams give either conservative or unsafe predictions for many specimens in the database and their accuracy are mostly dependent on the effective depth and type of FRP reinforcement. On the other hand, the proposed equation provides reasonably accurate shear capacity predictions for a wide range of FRP reinforced concrete beams.

No / This paper presents a numerical method for estimating the curvature, deflection and moment capacity of hybrid FRP/steel reinforced concrete beams. A sectional analysis is first carried out to predict the moment-curvature relationship from which beam deflection and moment capacity are then calculated. Based on the amount of FRP bars, different failure modes were identified, namely tensile rupture of FRP bars and concrete crushing before or after yielding of steel reinforcement. Comparisons between theoretical and experimental results of tests conducted elsewhere show that the proposed numerical technique can accurately predict moment capacity, curvature and deflection of hybrid FRP/steel reinforced concrete beams. The numerical results also indicated that beam ductility and stiffness are improved when steel reinforcement is added to FRP reinforced concrete beams. (C) 2015 Elsevier Ltd. All rights reserved,