• Composites Research
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• 제22권6호
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• pp.1-6
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• 2009

탄소나노튜브 고분자 복합체는, 외력에 의한 변형에 따라 전기적 저항이 변화하는 피에조저항(piezoresistivity) 거동을 나타낸다. 피에조저항은 고분자 모재 내에서 탄소나노튜브가 형성하는 전기전도망(conductive network)의 변화에 의해서 발현된다. 피에조저항 낮은 탄소나노튜브 함유량에서 더 현저하게 나타난다. 탄소섬유, 카본블랙 등 타 탄소기반 소재에 비해 전기전도도와 길이 대 직경비(aspect ratio)가 월등히 우수하기 때문에, 낮은 탄소나노튜브의 함유량에서도 스트레인 센싱시스템을 구현할 수 있다. 본 연구에서는, 구조물에 부착 또는 임베드 시켜서 구조물의 건전성을 실시간을 진단할 수 있는 탄소나노튜브 고분자 복합체 기반 센싱시스템을 개발하였다. 센서는 열가소성 수지와 다중벽 탄소나노튜브를 사용하여 필름 형태로 제조되었으며, 센싱 성능은 나노복합체를 구조물에 부착한 후 인장, 굽힘, 압축 등의 다양한 형태의 하중을 가하면서 평가하였다.

• Composites Research
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• 제19권6호
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• pp.23-31
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• 2006

나노허니컴 구조물의 영률, 굽힘 탄성 계수. 공칭파괴강도를 구하였다. 양극산화 알루미늄은 잘 정렬된 나노허니컴 구조물의 일종으로서 공정이 간단하고, 높은 종횡비, 자가 정렬된 기공구조를 가지고 있고, 기공의 크기를 조절할 수 있다. 원자현미경으로 외팔보 굽힘 시험을 수행하였고 나노-UTM을 이용한 3점 굽힘 실험결과와 비교하였다. 또한 나노-UTM으로 인장시험을 수행하였다. 나노허니컴 구조물의 한쪽 면은 막혀 있어서, 일반적인 샌드위치 구조물의 면재에 비유될 수 있다. 하지만 이러한 막힌 면은 굽힘 강도 증가에 영향을 끼치지 못하고 균열선단으로 작용한다는 것을 알 수 있었다. 본 연구로 나노허니컴 구조물을 설계하는데 기초적인 물성을 제공하고자 한다.

• Steel and Composite Structures
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• 제42권5호
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• pp.617-631
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• 2022

To study the eccentric compressive performance of the basalt-fiber reinforced recycled aggregate concrete (BFRRAC)-filled circular steel tubular stub column, 8 specimens with different replacement ratios of recycled coarse aggregate (RCA), basalt fiber (BF) dosage, strength grade of recycled aggregate concrete (RAC) and eccentricity were tested under eccentric static loading. The failure mode of the specimens was observed, and the relationship curves during the entire loading process were obtained. Further, the load-lateral displacement curve was simulated and verified. The influence of the different parameters on the peak bearing capacity of the specimens was analyzed, and the finite element analysis model was established under eccentric compression. Further, the design-calculation method of the eccentric bearing capacity for the specimens was suggested. It was observed that the strength failure is the ultimate point during the eccentric compression of the BFRRAC-filled circular steel tubular stub column. The shape of the load-lateral deflection curves of all specimens was similar. After the peak load was reached, the lateral deflection in the column was rapidly increased. The peak bearing capacity decreased on enhancing the replacement ratio or eccentric distance, while the core RAC strength exhibited the opposite behavior. The ultimate bearing capacity of the BFRRAC-filled circular steel tubular stub column under eccentric compression calculated based on the limit analysis theory was in good agreement with the experimental values. Further, the finite element model of the eccentric compression of the BFRRAC-filled circular steel tubular stub column could effectively analyze the eccentric mechanical properties.

• 한국식생활문화학회지
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• 제25권6호
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• pp.779-787
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• 2010

The principal objective of this study was to determine the optimal mixing conditions for three amounts of onion powder, sugar, and butter to prepare onion powder cookies. The experimental design was based on the central composite design methodology of response surface, which included 16 experimental points including two replicates for onion powder, sugar, and butter. The mechanical and sensory properties of the cookies were measured, and these values were applied to the mathematical models. A canonical form and perturbation plot showed the influence of each ingredient on the mixed final product. The results of the spread ratio did not show significant results, but hardness increased with increasing quantities of onion powder and sugar but decreased with butter (p<0.01). The color lightness "L" value increased with increasing quantities of sugar and butter but decreased with added onion powder. In contrast, the redness color "a" value increased with increasing quantities of onion powder and sugar. Sugar did not affect the yellowness color "b" value, but the color b value increased with increasing onion powder and sugar. The results of a sensory evaluation using the predicted model showed significant values for flavor (p<0.01), texture (p<0.05), taste (p<0.05), and overall quality (p<0.01). As a result, the optimum formulation by numerical and graphical methods was calculated as 12.58 g onion powder, 35 g sugar, and 52.38 g butter.

• Steel and Composite Structures
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• 제49권4호
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• pp.457-471
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• 2023

To make up for the performance weaknesses of recycled aggregate concrete (RAC), expand the application range of RAC, and alleviate the environmental problems caused by excessive exploitation of natural coarse aggregates (NCA), this study proposes a basalt fiber-reinforced recycled aggregate concrete (BFRRAC)-filled square steel tubular columns that combines two modification methods of steel tube and fiber, which may greatly enhance the mechanical properties of RAC. The axial compression performance for BFRRAC-filled square steel tubular columns was reported during this study. Seven specimens with different replacement ratios of recycled coarse aggregate (RCA), length-diameter ratios, along with basalt fiber (BF) contents were designed as well as fabricated for performing axial compression test. For each specimen, the whole failure process as well as mode of specimen were discovered, subsequently the load-axial displacement curve has obtained, after which the mechanical properties was explained. A finite element analysis model for specimens under axial compression was then established. Subsequently, based on this model, the factors affecting axial compression performance for BFRRAC-filled square steel tubes were extended and analyzed, after which the corresponding design suggestion was proposed. The results show that in the columns with length-diameter ratios of 5 and 8, bulging failure was presented, and the RAC was severely crushed at the bulging area of the specimen. The replacement ratio of RCA as well as BF content little affected specimen's peak load (less than 5%). As the content of BF enhanced from 0 kg/m³ to 4 kg/m³, the dissipation factor and ductility coefficients increased by 10.2% and 5.6%, respectively, with a wide range.

• Composites Research
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• 제36권6호
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• pp.402-407
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• 2023

Activated carbon fibers (ACFs) are fibrous form of activated carbon (AC) with higher mechanical strength and flexibility, which make them suitable for building modules for applications including directional gas flow such as air and gas purification. Similarly, ACFs are anticipated to excel in the efficient capture of CO₂. However, due to the difficulties in fabricating monofilament carbon fibers at a laboratory scale, most of the studies regarding ACFs for CO₂ capture have relied on electrospun carbon fibers. In this study, we fabricated monofilament carbon fibers from PAN-based monofilament precursors by stabilization and carbonization. Then, ACFs were successfully prepared by chemical activation using KOH. Different weight ratios ranging from 1:1 to 1:4 were employed in the fabrication of ACFs, and the samples were designated as ACF-1 to ACF-4, respectively. As a function of KOH ratio, increase in surface area could be observed. However, the CO₂ adsorption trend did not follow the surface area trend, and the ACF-3 with second largest surface area exhibited the highest CO₂ adsorption capacity. To understand the phenomena, nitrogen content and ultramicropore distribution, which are important factors determining CO₂ adsorption capacity, were considered. As a result, while nitrogen content could not explain the phenomena, ultramicropore distribution could provide a reasoning that the excessive etching led ACF-4 to develop micropore structure with a broader distribution, resulting in high surface area yet deteriorated CO₂ adsorption.

• Korean Circulation Journal
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• 제53권8호
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• pp.550-562
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• 2023

Background and Objectives: To identify the factors associated with adverse outcomes following surgery for functional insufficiency of the mitral valve (MV) or tricuspid valve (TV) associated with atrial fibrillation (AF). Methods: We evaluated 100 patients (age, 66.5±10.0 years; 47 males) who consecutively underwent surgery for functional insufficiency of the MV or TV associated with AF between January 2000 and December 2020 at our center. The primary outcome was a composite endpoint of all-cause death, valve reoperation, congestive heart failure (CHF) requiring rehospitalization, and stroke. Results: During follow-up (532 patients-years [PYs]), adverse events included death in 16 (3.0%/yr), MV reoperation in 1 (0.2%/yr), CHF in 14 (2.6%/yr), and stroke in 5 (0.9%/yr) patients, demonstrating a 5-year rate of freedom from the primary endpoint of 69.5%. The rate of postoperative AF was high even in those who underwent AF ablation (n=92), with cumulative rates of 48.1% at 1 year and 60.2% at 5 years. In multivariable analyses, the primary outcome was significantly associated with age (adjusted hazard ratio [aHR], 1.06; 95% confidence interval [CI], 1.02-1.10; p=0.005), chronic kidney disease (aHR, 7.76; 95% CI, 2.28-26.38; p=0.001), left atrial appendage exclusion (aHR, 0.35; 95% CI, 0.16-1.78; p=0.010), and postoperative AF as a time-varying covariate (aHR, 3.33; 95% CI, 1.50-7.40; p=0.003). Conclusion: Among patients undergoing surgery for functional atrioventricular insufficiency associated with AF, a significant proportion showed recurrence of AF over time after concomitant AF ablation, which was significantly associated with poor clinical outcomes.

• Steel and Composite Structures
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• 제50권4호
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• pp.383-401
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• 2024

The research comprehensively studies the axial compression performance of T-shaped concrete-filled thin-walled steel tubular (CTST) long columns after fire exposure. Initially, a series of tests investigate the effects of heating time, load eccentricity, and stiffeners on the column's performance. Furthermore, Finite Element (FE) analysis is employed to establish temperature and mechanical field models for the T-shaped CTST long column with stiffeners after fire exposure, using carefully determined key parameters such as thermal parameters, constitutive relations, and contact models. In addition, a parametric analysis based on the numerical models is conducted to explore the effects of heating time, section diameter, material strength, and steel ratio on the axial compressive bearing capacity, bending bearing capacity under normal temperature, as well as residual bearing capacity after fire exposure. The results reveal that the maximum lateral deformation occurs near the middle of the span, with bending increasing as heating time and eccentricity rise. Despite a decrease in axial compressive load and bending capacity after fire exposure, the columns still exhibit desirable bearing capacity and deformability. Moreover, the obtained FE results align closely with experimental findings, validating the reliability of the developed numerical models. Additionally, this study proposes a simplified design method to calculate these mechanical property parameters, satisfying the ISO-834 standard. The relative errors between the proposed simplified formulas and FE models remain within 10%, indicating their capability to provide a theoretical reference for practical engineering applications.

• Structural Engineering and Mechanics
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• 제89권6호
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• pp.557-570
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• 2024

Due to interfacial ageing, chemical action and interfacial damage, the interface debonding may appear in the interfaces of composite laminates. Particularly, the laminates display a side-dependent effect at small scale. In this work, a three-dimensional (3D) and anisotropic thick nanoplate model is proposed to investigate the effects of imperfect interface and nonlocal parameter on the bending deformation, vibrational response and buckling stability of one-dimensional (1D) hexagonal quasicrystal (QC) layered nanoplates. By combining the linear spring model with the transferring matrix method, exact solutions of phonon and phason displacements, phonon and phason stresses of bending deformation, the natural frequencies of vibration and the critical buckling loads of 1D hexagonal QC layered nanoplates are derived with imperfect interfaces and nonlocal effects. Numerical examples are illustrated to demonstrate the effects of the imperfect interface parameter, aspect ratio, thickness, nonlocal parameter, and stacking sequence on the bending deformation, the vibrational response and the critical buckling load of 1D hexagonal QC layered nanoplate. The results indicate that both the interface debonding and nonlocal effect can reduce the stiffness and stability of layered nanoplates. Increasing thickness of QC coatings can enhance the stability of sandwich nanoplates with the perfect interfaces, while it can reduce first and then enhance the stability of sandwich nanoplates with the imperfect interfaces. The biaxial compression easily results in an instability of the QC layered nanoplates compared to uniaxial compression. QC material is suitable for surface layers in layered structures. The mechanical behavior of QC layered nanoplates can be optimized by imposing imperfect interfaces and controlling the stacking sequence artificially. The present solutions are helpful for the various numerical methods, thin nanoplate theories and the optimal design of QC nano-composites in engineering practice with interfacial debonding.

• Steel and Composite Structures
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• 제51권2호
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• pp.185-202
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• 2024

In this research paper, and for the first time, wave propagations in sigmoidal imperfect functionally graded material plates are investigated using a simplified quasi-three-dimensionally higher shear deformation theory (Quasi-3D HSDTs). By employing an indeterminate integral for the transverse displacement in the shear components, the number of unknowns and governing equations in the current theory is reduced, thereby simplifying its application. Consequently, the present theories exhibit five fewer unknown variables compared to other Quasi-3D theories documented in the literature, eliminating the need for any correction coefficients as seen in the first shear deformation theory. The material properties of the functionally graded plates smoothly vary across the cross-section according to a sigmoid power law. The plates are considered imperfect, indicating a pore distribution throughout their thickness. The distribution of porosities is categorized into two types: even or uneven, with linear (L)-Type, exponential (E)-Type, logarithmic (Log)-Type, and Sinus (S)-Type distributions. The current quasi-3D shear deformation theories are applied to formulate governing equations for determining wave frequencies, and phase velocities are derived using Hamilton's principle. Dispersion relations are assumed as an analytical solution, and they are applied to obtain wave frequencies and phase velocities. A comprehensive parametric study is conducted to elucidate the influences of wavenumber, volume fraction, thickness ratio, and types of porosity distributions on wave propagation and phase velocities of the S-FGM plate. The findings of this investigation hold potential utility for studying and designing techniques for ultrasonic inspection and structural health monitoring.