Papers by Keyword: CFRP

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Authors: Hugo Biscaia, João Cardoso, Carlos Chastre
Abstract: The bonding between two different materials or between same materials is a quite popular method. Unlike fastener joints, it avoids undesirable stress concentrations and doesn't demand an intrusive application to ensure the good performance of the joint. However, depending on the configuration of the adhesively bonded joint, its performance responds differently and the choice (if possible to make) on the best configuration, i.e. the configuration that originates the highest strength and/or stiffness, may be hard to make. Within this context, several configurations of aluminium-to-aluminium bonded joints unstrengthened and strengthened with fiber reinforced polymers (FRP) were modelled using a commercial finite element code. The linearity and nonlinearity of the FRP composite and the aluminium were considered, respectively, and the adhesively bonded joints were subjected to a regular displacement that intended to simulate a tensioning load. Also, the nonlinearities of the interfaces were considered in the form of nonlinear cohesive adhesive laws. The fracture Modes I and II were defined trough a bond-slip relation with a bi-linear shape and the Mohr-Coulomb failure criterion is used for the coupling of the cohesive adhesive laws of the interface when the debonding process of the bonded joint configuration implies the interaction between both fracture modes, i.e. the joint is under a mixed-mode (Mode I+II) situation. The results are presented and discussed and the configurations of the bonded joints are all compared through bond stress distributions and load-slip responses. The study herein presented is, therefore, a contribution to the analysis of the structural integrity of bonded joints between FRP composites and aluminium substrates, helping also on the choice of the most adequate bonded joint configuration and corresponding reinforcement to be used and applied in practice.
Authors: Woo Tai Jung, Moon Seoung Keum, Sung Yong Choi, Jae Yoon Kang, Jong Sup Park
Abstract: The anchoring of CFRP tendon can be performed by wedging, bonding or compressing. The wedge type anchor, used for PS steel tendon, is inappropriate for direct application to the CFRP tendon due to its low lateral stiffness. Since the bond performance of the CFRP tendon depends on the anchor performance, the bond type anchor presents the problem of requiring long steel sleeve in case of low bond performance or high tensile performance. Compared to the bond type anchor, the compressing type anchor offers better applicability but necessitates the development of a sleeve fitted to the dimensions of each CFRP tendon. This study intends to examine the anchoring characteristics of the compressed sleeve for the temporary anchorage of a CFRP tendon with diameter of 10 mm. To that goal, the properties of the 10 mm-diameter CFRP tendon were assessed using the bond type anchor and the corresponding anchor performance is compared to that of the compressed anchor. The test results revealed that the use of spacers in the compressed anchor provided lower anchor performance due to the characteristics of the spacers. For the specimen without spacer, the micro-deformations formed inside the sleeve were seen to compress the CFRP tendon by gearing directly the tendon and to provide anchor performance reaching about 72% of the tensile strength of the CFRP tendon. Further study shall develop a sleeve with increased compress force on the CFRP tendon so as to improve the anchor performance of the compressed sleeve. Moreover, solution shall also be provided to introduce a uniform compress force.
Authors: Jonas Huether, Robert Maertens, Oleg Saburow, Elisa Seiler, Theresa Aicher, Kay André Weidenmann
Abstract: The increasing demand for composites leads to a growing amount of end-of-life materialand production waste. The latter consists of a large fraction of unimpregnated fibre waste which is notsufficiently reprocessed using conventional textile processing procedures as they are either too expensiveor their mechanical performance is too low. Using pieces of dry non-crimp fabrics (patches) ina Bulk Moulding Compound process (BMC) displays a straightforward approach of fabric recycling.Adding fillers to the mixture not only offers the opportunity to modify mechanical and electrical propertiesas well as the costs but also a chance for a more holistic approach of dry fibre recycling, whenconventional fillers like chalk are replaced by ground recycled carbon fibres. In this way, all kindof dry fibre wastes can be reused in one process: Larger offcuts are chopped to smaller rectangularpatches whereas waste fractions of small offcuts are processed to carbon fibre powder as filler andprocessed together with resin to produce BMC materials. Mechanical investigations reveal that thepresented approach shows higher specific properties than the conventional filler without compromisingthe process and material quality.
Authors: Kun Xian Qiu, Ya Xing Bie, Sheng Qin, Qing Long An, Ming Chen
Abstract: High strength carbon fiber reinforced polymers (CFRP) with unidirectional laminate structure have gradually developed into major materials in load-bearing aerospace components, and the cutting demand of CFRP is increasing. In this work, orthogonal cutting tests were conducted on T700 high-strength CFRP laminates to get the mechanistic force model of special cutting tools. Also cutting force coefficients were obtained when cutting T700 high-strength CFRP laminates under different fiber orientations. Experimental results showed that the lowest cutting force was obtained when fiber orientation was between 120° and 150°.
Authors: Anna Trauth, Pascal Pinter, Kay André Weidenmann
Abstract: Failure of fiber reinforced polymers is a complex interaction of different microstructural mechanisms. In order to assign those mechanisms to the macroscopic material response, in-situ methods as acoustic emission can be applied. This allows for the detection of initiation and growth as well as for the localization of damage in mechanically loaded materials. In this study, mechanical material testing of continuous and discontinuous fiber reinforced polymers was coupled with acoustic emission. Results have shown that different failure mechanisms resulting from different reinforcement architectures can be distinguished due to their acoustic emission signal. Based on experimentally captured acoustic emission signals, machine learning algorithms were applied to differentiate various failure mechanisms. This offers the possibility to investigate damage of hybrid continuous-discontinuous Sheet Molding Compounds exposed to bending loads.
Authors: Woo Tai Jung, Moon Seoung Keum, Jae Yoon Kang, Jong Sup Park
Abstract: Despite of their outstanding axial strength, CFRP tendons necessitate special anchorage due to their low lateral shear strength. In order to cope with such CFRP tendon, the conventional bond type anchor needs to be improved. The results of bond tests executed on 10-mm diameter CFRP tendons coated with sand and oxide revealed that, even if the average bond strength increases by 3 times compared to the non-coated bare tendon, the coated CFRP tendon still requires excessively long anchored length for bonding. Therefore, this study applies a method enabling to shorten the bonded length and improving further the bond performance compared to sand or oxide coating. The improvement of the bond characteristics is achieved by splitting the ends of the CFRP tendon so as to widen the bonded area by 3.5 times. The test results showed that the anchor performance of the CFRP tendon reaches 95% of its tensile strength making it applicable for the bond type anchor.
Authors: Kyoung Bong Han, Doo Yong Cho
Abstract: In the recent construction industry, Fiber reinforced polymers (FRPs) have been considered to be an innovative material to repair and strengthen damaged structures. It is because FRPs have many beneficial characteristics, such as corrosion resistance, a high tensile strength-to-weight ratio, non-conductivity and design flexibility. As a demand of FRPs has increased, many researches on behavior of the structures which were externally strengthened with FRPs have been conducted. However, researches on time-dependant behavior of the structures have not been conducted yet. In order to provide improved serviceability to reinforced concrete (RC) members, the behavior of the RC members strengthened with FRPs under sustained loads should be investigated. This paper presents a series of long-term experiments and deformation-recovery experiments. For the long-term experiments, three RC beams were fabricated and two of the beams were strengthened with a carbon fiber reinforced polymer (CFRP) plate and a glass fiber reinforced polymer (GFRP) plate respectively. The beams were placed under sustained loads for about 550 days. After the 550 days, all of the beams were unloaded for the measurement of deformation recovery. The deflection and strains of rebar and FRP reinforcements were measures for about 60 days. As the result of long-terms experiment, the beams strengthened with CFRP plate showed a better performance in terms of deflection and strains of rebar and CFRP plate. Moreover, the beam with CFRP plate showed a higher deformation recovery and residual strength than the other beams.
Authors: Shu Han, You Hong Gong, Ni Hong Yang, Sheng Chao Han
Abstract: Carbon Fiber Reinforced Plastic (CFRP) is widely used in aerospace field as an advanced composite material. Recently, more and more studies are focused on milling of CFRP with its increasing applications. In this paper, three different milling tools were chosen, and a systematic analysis on cutting force, surface quality and tool wear has been carried out to evaluate the tools. Experimental results indicate that the multi-flute tool with diamond coating has a better performance than the double spiral compression tool and the multi-tooth tool with AlTiN coating, with a lower cutting force, a better surface quality and a higher tool life than others, which would be a better tool for cutting of CFRP.
Authors: Woo Tai Jung, Moon Seoung Keum, Jae Yoon Kang, Jong Sup Park
Abstract: This study evaluates the bond performance of the CFRP tendon through pull-out test and investigates experimentally the strengthening performance according to the eventual surface treatment of the tendon on concrete beams strengthened by near-surface mounted (NSM) tendon. The pull-out test revealed that the bond strength was improved by 3 times when surface treatment was applied to the tendon. In addition, similar improvement of the bond performances was observed regardless of the execution time of the surface treatment being manually on site or at the factory during the production of the tendon. The flexural test showed that the surface treatment of the CFRP tendon improved the strengthening performance by 13%. Consequently, when using the CFRP tendon featured by low bond strength, it appears that structural reinforcement can be improved by executing beforehand surface treatment of the tendon on site.
Authors: Ying Jun Zhao, Christoph Beisteiner, Sandra Gschossmann, Martin Schagerl
Abstract: Carbon fiber-reinforced polymer (CFRP) composites are lightweight, durable, and corrosionresistive materials that are popular for constructing automotive bodies and aircraft structures. However, their heterogeneous composition and anisotropic mechanical behavior make design of their service lives challenging. To address challenges in monitoring CFRP’s structural behavior, a cheap, weightless, and reliable sensor shall be developed for CFRPs to monitor their damage-to-failure mode. In this study a carbon nanotube (CNT)-embedded thin film is inkjet-printed onto a flexible substrate and applied over a tensile testing coupon. Coupled with the algorithm of electrical impedance tomography, the sensor with 16 electrodes is able to reconstruct the strain distribution of a surface under 8 sec. Non-uniform strain distribution can also be reconstructed at strain levels down to 0.001%.
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