• 한국정밀공학회지
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• 제34권4호
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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.

• Smart Structures and Systems
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• 제28권6호
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• pp.737-744
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• 2021

In this study, structural health monitoring (SHM) methods of carbon fiber reinforced plastics (CFRPs) were investigated using electrical resistance. The developed sensing technique monitored electrical resistance in accordance with the impact damage of a CFRP. The changes in electrical resistances with multiple electrode sets enabled SHM without extra sensors so that this technique can be called self-sensing. Moreover, this study proposed electrodes only at peripheral side of a structure to minimize the number of electrodes compared to those in an array which has square number of sensors as the sensing area increases. For the intensive investigation, electromechanical sensitivity in terms of electrode distance was analyzed and optimized under drop weight impact testing. Then, SHM methods with electrodes in an array and electrodes in peripheral edges were comparatively investigated. The developed methods successfully localized impact damages into 2D coordinates. Furthermore, damage severity can be shown with a damage map by calculating electrical resistance change ratio. Therefore, structural health self-sensing system using electrical resistance was successfully developed with the minimum number of electrodes.

• Structural Engineering and Mechanics
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• 제58권1호
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• pp.143-161
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• 2016

Utilization of mineral and chemical admixtures in concrete technology has led to changes in the formulation and mix design in recent decades, which has, in turn, made the concrete stronger and more durable. Lightweight concrete is an excellent solution in terms of decreasing the dead load of the structure, while self-compacting concrete eases the pouring and removes the construction problems. Combining the advantages of lightweight concrete and self-compacting concrete is a new and interesting research topic. Considering its light weight of structure and ease of placement, self-compacting lightweight concrete may be the answer to the increasing construction requirements of slender and more heavily reinforced structural elements. Twenty one laboratory experimental investigations published on the mix proportion, density and mechanical properties of lightweight self-compacting concrete from the last 12 years are analyzed in this study. The collected information is used to investigate the mix proportions including the chemical and mineral admixtures, light weight and normal weight aggregates, fillers, cement and water. Analyzed results are presented in terms of statistical expressions. It is very helpful for future research to choose the proper components with different ratios and curing conditions to attain the desired concrete grade according to the planned application.

• Computers and Concrete
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• 제22권2호
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• pp.209-220
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• 2018

In order to evaluate the effect of hybrid fibers on the flexural performance of tunnel segment at room temperature, twelve reinforced self-consolidating concrete (SCC) symmetric inclination beams containing steel fiber, macro polypropylene fiber, micro polypropylene fiber, and their hybridizations were studied under combined loading of flexure and axial compression. The results indicate that the addition of mono steel fiber and hybrid fibers can enhance the ultimate bearing capacity and cracking behavior of tested beams. These improvements can be further enhanced along with increasing the content of steel fiber and macro PP fiber, but reduced with the increase of the reinforcement ratio of beams. The hybrid effect of steel fiber and macro PP fiber was the most obvious. However, the addition of micro PP fibers led to a degradation to the flexural performance of reinforced beams at room temperature. Meanwhile, the hybrid use of steel fiber and micro polypropylene fiber didn't present an obvious improvement to SCC beams. Compared to micro polypropylene fiber, the macro polypropylene fiber plays a more prominent role on affecting the structural behavior of SCC beams. A calculation method for ultimate bearing capacity of flexural SCC symmetric inclination beams at room temperature by taking appropriate effect of hybrid fibers into consideration was proposed. The prediction results using the proposed model are compared with the experimental data in this study and other literature. The results indicate that the proposed model can estimate the ultimate bearing capacity of SCC symmetric inclination beams containing hybrid fibers subjected to combined action of flexure and axial compression at room temperature.

• Earthquakes and Structures
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• 제13권2호
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• pp.165-176
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• 2017

Multi-Axial Testing System (MATS) is a 6-DOF loading system located at National Center for Research on Earthquake Engineering (NCREE) in Taiwan for advanced seismic testing of structural components or sub-assemblages. MATS was designed and constructed for a large variety of structural testing, especially for the specimens that require to be subjected to vertical and longitudinal loading simultaneously, such as reinforced concrete columns and lead rubber bearings. Functionally, MATS consists of a high strength self-reacting frame, a rigid platen, and a large number of servo-hydraulic actuators. The high strength self-reacting frame is composed of two post-tensioned A-shape reinforced concrete frames interconnected by a steel-and-concrete composite cross beam and a reinforced concrete reacting base. The specimen can be anchored between the top cross beam and the bottom rigid platen within a 5-meter high and 3.25-meter wide clear space. In addition to the longitudinal horizontal actuators that can be installed for various configurations, a total number of 13 servo-hydraulic actuators are connected to the rigid platen. Degree-of-freedom control of the rigid platen can be achieved by driving these actuators commanded by a digital controller. The specification and information of MATS in detail are described in this paper, providing the users with a technical point of view on the design, application, and limitation of MATS. Finally, future potential application employing advanced experimental technology is also presented in this paper.

• 접착 및 계면
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• 제23권3호
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• pp.59-69
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• 2022

섬유강화 복합재료에서 가장 중요한 부분은 섬유와 수지간의 계면 접착특성이다. 본 총설에서는, 섬유강화 복합재료의 계면특성을 평가하기 위해 사용되는 미세역학 시험법에 대해 역사적 초점을 두어 서술하고자 한다. 미세역학 시험법은 섬유 한 가닥과 기지재료 간의 계면 접착특성을 전단력평가로 관측하는 재료자체의 변수만이 고려되는 평가법으로써 계면에 대한 보다 정량적인 접착특성 및 감지능을 고찰할 수 있다. 미세역학시험법을 이용한 이전의 연구와 비교적 최근 연구동향을 본 총설에서 비교 논의하며, 미세역학 실험법에 대한 응용과 앞으로의 발전을 설명하고자 한다.

• Computers and Concrete
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• 제32권4호
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• pp.351-363
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• 2023

Reducing the self-weight of reinforced concrete structures problem is discussed in this paper by using two types of self-weight reduction, the first is by using lightweight coarse aggregate (crushed brick) and the second is by using styropor block. Experimental and Numerical studies are conducted on (LWAC) lightweight aggregate reinforced concrete slabs, having styropor blocks with various sizes of blocks and the ratio of shear span to the effective depth (a/d). The experimental part included testing eleven lightweight concrete one-way simply supported slabs, comprising three as reference slabs (solid slabs) and eight as styropor block slabs (SBS) with a total reduction in cross-sectional area of (43.3% and 49.7%) were considered. The holes were formed by placing styropor at the ineffective concrete zones in resisting the tensile stresses. The length, width, and thickness of specimen dimensions were 1.1 m, 0.6 m, and 0.12 m respectively, except one specimen had a depth of 85 mm (which has a cross-sectional area equal to styropor block slab with a weight reduction of 49.7%). Two shear spans to effective depth ratios (a/d) of (3.125) for load case (A) and (a/d) of (2) for load case (B), (two-line monotonic loads) are considered. The test results showed under loading cases A and B (using minimum shear reinforcement and the reduction in cross-sectional area of styropor block slab by 29.1%) caused an increase in strength capacity by 60.4% and 54.6 % compared to the lightweight reference slab. Also, the best percentage of reduction in cross-sectional area is found to be 49.7%. Numerically, the computer program named (ANSYS) was used to study the behavior of these reinforced concrete slabs by using the finite element method. The results show acceptable agreement with the experimental test results. The average difference between experimental and numerical results is found to be (11.06%) in ultimate strength and (5.33%) in ultimate deflection.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2010년도 추계학술대회 논문집
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• pp.336-337
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• 2010

In the underwater veicle self-noise from the propeller reduces the sensor sensitivity. To increase the sensor sensitivity SNORE ring(Self-noise reduction ring) has been used. In this paper to calculate the effectiveness of the SNORE ring and de-coupeler numerical simulation is conducted. Based on the simulation results CRP(Carbon reinforced plastic)and SNORE ring reduced noise and vibration.

• The Korean Journal of Ceramics
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• 제4권3호
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• pp.171-175
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• 1998

$Al_2O_3$-TiC composites were prepared from aluminum, titanium oxide, and carbon fibers by self-propagating high-temperature synthesis(SHS). After the SHS reaction, the TiC phase in the sample was found either fibrous or non-fibrous shape. The fraction of the fibrous TiC phase varied with the amount of $Al_2O_3$ diluent addition. The optimum amount of diluent to make fibrous carbide was determined to be 30%. The fibers were hollow inside and made of multiple grains with a composition of titanium carbide. The hollow fiber formation mechanism was suggested and discussed. The synthesized powders were consolidated to dense composites by hot pressing at $1750^{\circ}C$ under 30 MPa.

• Structural Engineering and Mechanics
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• 제88권5호
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• pp.481-492
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• 2023

The past earthquakes revealed the importance of the design of moment-resisting reinforced concrete framed structures with ductile behavior. Due to seismic activity, failures in framed structures are widespread in beam-column joints. Hence, the joints must be designed to possess sufficient strength and stiffness. This paper investigates the effects of fibers on the ductility of hybrid fiber reinforced self-compacting concrete (HFRSCC) when subjected to seismic actions; overcoming bottlenecks at the beam-column joints has been studied by adding low modulus sisal fiber and high modulus steel fiber. For this, the optimized dose of hooked end steel fiber content (1.5%) was kept constant, and the sisal fiber content was varied at the rate of 0.1%, up to 0.3%. The seismic performance parameters, such as load-displacement behavior, ductility, energy absorption capacity, stiffness degradation, and energy dissipation capacity, were studied. The ductility factor and the cumulative energy dissipation capacity of the hybrid fiber (steel fiber, 1.5% and sisal fiber, 0.2%) added beam-column joint specimen is 100% and 121% greater than the control specimen, respectively. And also the stiffness of the hybrid fiber reinforced specimen is 100% higher than the control specimen. Thus, the test results showed that adding hybrid fibers instead of mono fibers could significantly enhance the seismic performance parameters. Therefore, the hybrid fiber reinforced concrete with 1.5% steel and 0.2% sisal fiber can be effectively used to design structures in seismic-prone areas.