• Steel and Composite Structures
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• v.29 no.5
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• pp.635-645
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• 2018

Beam-column joints play a significant role in static and dynamic performances of reinforced concrete frame structures. This study contributes a numerical approach of topologically optimal design of carbon fiber reinforced plastics (CFRP) to retrofit existing beam-column connections with crack patterns. In recent, CFRP is used commonly in the rehabilitation and strengthening of concrete members due to the remarkable properties, such as lightweight, anti-corrosion and simplicity to execute construction. With the target to provide an optimal CFRP configuration to effectively retrofit the beam-column connection under semi-failure situation such as given cracks, extended finite element method (X-FEM) is used by combining with multi-material topology optimization (MTO) as a mechanical description approach for strong discontinuity state to mechanically model cracked structures. The well founded mathematical formulation of topology optimization problem for cracked structures by using multiple materials is described in detail in this study. In addition, moved and regularized Heaviside functions (MRHF), that have the role of a filter in multiple materials case, is also considered. The numerical example results illustrated in two cases of beam-column joints with stationary cracks verify the validity, benefit and supremacy of the proposed method.

• Corrosion Science and Technology
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• v.19 no.2
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• pp.75-81
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• 2020

To reduce structural weight, light metals, including aluminum and magnesium alloys, have been widely used in various industries such as aircraft, transportation and automobiles. Recently, composite materials such as Carbon Fiber Reinforced Plastics (CFRP) and Graphite Epoxy Composite Material (GECM) have also been applied. However, aluminum and its alloys suffer corrosion from various factors, which include aggressive ions, pH, solution temperature and galvanic contact by potential difference. Moreover, carbon fiber in CFRP and GECM is a very efficient cathode, and very noble in the galvanic series. Galvanic contact between carbon fiber composites and metals in electrolytes such as rain or seawater, is highly undesirable. Notwithstanding the potentially dangerous effects of chloride and temperature, there is little research on galvanic corrosion according to chloride concentration and temperature. This work focused on the effects of chloride concentration and solution temperature on AA7075T6. The increased galvanic corrosion between CRFP and AA7075T6 was evaluated by electrochemical experiments, and these effects were elucidated.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.3
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• pp.125-132
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• 2007

The purpose of present paper is to investigate a fracture characteristics of the finite-width single-edge-notch(SEN) carbon fiber/epoxy reinforced plastics(CFRP) plates by using an acoustic emission(AE). Uni-directionally oriented 10 plies CFRPs specimen which had different notch length were prepared for monotonic tensile test. Matrix cracking appeared over whole testing process and fiber breaking appeared later on mainly Load distribution factor of the matrix confirmed that increased according as increases of plate width ratio. The amplitude distribution of AE signal from a specimens is an aid to the determination of the different fracture mechanism such as matrix cracking, disbonding, interfacial delamination, fiber pull-out, fiber breaking, and etc. In the result of AE amplitude distribution analysis, matrix cracking, fiber disbonding or interfacial delamination, and fiber pull-out or fiber breaking signal correspond to <65dB, <75dB, and <90dB respectively, Also, changes of the slope of cumulative AE energy represented crazing phenomena or degradation of materials.

• Composites Research
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• v.30 no.3
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• pp.215-222
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• 2017

The effect of a multi walled carbon nanotubes (MWNCT) on the adhesive properties and thermal properties of epoxy were studied by double lap-shear tests. Epoxy/MWCNT resins were prepared from a different amount of the MWCNT incorporated into the epoxy resins (araldite 2011). Steel plates and carbon fiber reinforced plastics (CFRP) were chosen as materials. Mechanical tests were performed by a universal testing machine (UTM). The analysis of thermal properties were conducted by a thermogravimetric analyzer (TGA) and a differential scanning calorimetry (DSC). The fracture surface morphology was examined using a scanning electron microscopy (SEM) and optical microscope. Compared to neat epoxy, it was found that the mechanical properties of epoxy/MWCNT resins are increased.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.110-113
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• 2004

Aluminum and CFRP tube is light-weight material representatively but collapse mechanism is different under axial loading. Aluminum tube absorbs energy by stable plastic deformation under axialloading. While CFRP(Carbon Fiber Reinforced Plastics)tube absorb synergy by unstable brittle failure but its specific strength and stiffness is higher than that of aluminum tube. In this study, for complement of detect and synergy effect by combination with the advantages of each member, the axialcollapsetests were performed for combined aluminum CFRP tubes which are composed of aluminum tubes wrapped with CFRP out side aluminum square tubes. Collapsecharacteristics were analyzed for combined square tubes which have different CFRP orientation angle and thickness. Test results were compared with that of aluminum tubes and CFRP tubes.

• Journal of the Korean Society of Safety
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• v.16 no.4
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• pp.47-51
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• 2001

The carbon fiber reinforced plastics(CFRP) have been widely used in aircraft and spacecraft structures as well as sports goods because it has high specific strength, high specific stiffness and low coefficient of thermal expansion. Machining of CFRP poses problems not frequently seen for metals due to the nonhomogeneity, anisotropy, and abrasive characteristics of CFRP. Delamination is a common problem faced while drilling holes in CFRP using conventional drilling. Therefore, AE characteristics related to drilling damage process of unidirectional and [0/90/]s crossply laminate composite was studied. Also drilling damage like the delamination was observed by video camera in real time monitoring technique. From the results, we basically found the relationships between the delamination from drilling and AE characteristics for CFRP composites.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.4
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• pp.243-246
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• 2017

In this study, flexible fixtures and end effectors are conceptually designed for the holding of thin-walled carbon-fiber reinforced-plastic (CFRP) workpieces in machining processes. Firstly, the fixture scenarios and system requirements for the conceptual designs of flexible-fixture and core units are proposed, including the propounding of the workpiece-holding mechanism and the core-unit requirements. A ball-joint pneumatic system is determined as a locking mechanism of the flexible-fixture system for the machining of thin-walled components. Secondly, conceptual designs of the core units are suggested with the driven requirements from the fixture scenarios. A self-tilting mechanism and an end-effector return mechanism are also proposed. Finally, the prototypes of the core units are manufactured, and the workpiece-holding capacity of each prototype is measured.

• Composites Research
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• v.26 no.3
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• pp.195-200
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• 2013

This study aims to detecting and analyzing the defects of damaged carbon fiber reinforced composites after impacts, particularly focusing on barely visible impact damages. The impact test was progressed by a drop-weight machine and applied to introduce simulated damages on laminated composites used in aircrafts. Various nondestructive testing (NDT) techniques were applied to identify the defects on the specimens with different levels of impact energies. Based on the measurements data, the levels of the barely visible impacts, and the applicability and effectiveness of the detection methods were discussed. Generally, the results demonstrated that their inner damages contained bigger footprints than those on the surfaces. However, when the damage energy was low, it was found that the inner damage size could be smaller than those appeared on the surfaces.

• Steel and Composite Structures
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• v.10 no.3
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• pp.281-295
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• 2010

An experimental and a non linear finite element investigation on the behavior of steel-concrete composite beams stiffened in hogging moment region with Carbon Fiber Reinforced Plastics (CFRP) sheets is presented in this paper. A total of five specimens were tested under two-point loads. Three of the composite beams included concrete slab while the other two beams had composite slabs. The stiffening was achieved by attaching CFRP sheets to the concrete surface at the position of negative bending moment. The suggested CFRP sheets arrangement enhanced the overall beam behavior and increased the composite beam capacity. Valuable parametric study was conducted using a three dimensional finite element model using ANSYS program. Both geometrical and material nonlinearity were included. The studied parameters included CFRP sheet arrangement, concrete strength and degree of shear connection.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.6
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• pp.566-576
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• 2003

Carbon-fiber reinforced plastics (CFRP) composite laminates often possess strong in-plane elastic anisotropy attributable to the fiber orientation and layup sequence. The layup orientation thus greatly influences its properties in a composite laminate. It could result in the part being rejected or discarded if the layup orientation of a ply is misaligned. A nondestructive technique would be very beneficial, which could be used to test the part after curing and to require less time than the optical test. In this paper, ultrasonic scanners were set out for different measurement modalities for acquiring ultrasonic signals as a function of in-plane azimuthal angle. The motorized scanner was built first for making transmission measurements using a pair of normal-incidence shear wave transducers. Another scanner was then built fer the acousto-ultrasonic configuration using contact transducers. A ply-by-ply vector decomposition model has been developed, simplified, and implemented for composite laminates fabricated from unidirectional plies. We have compared the test results with model data. It is found that strong agreement are shown between tests and the model developed in characterizing cured layups of the laminates.