Stretchable and transparent electrodes based on in-plane structures

Kim, Kukjoo,Kim, Joohee,Hyun, Byung Gwan,Ji, Sangyoon,Kim, So-Yun,Kim, Sungwon,An, Byeong Wan,Park, Jang-Ung The Royal Society of Chemistry 2015 Nanoscale Vol.7 No.35

<P>Stretchable electronics has attracted great interest with compelling potential applications that require reliable operation under mechanical deformation. Achieving stretchability in devices, however, requires a deeper understanding of nanoscale materials and mechanics beyond the success of flexible electronics. In this regard, tremendous research efforts have been dedicated toward developing stretchable electrodes, which are one of the most important building blocks for stretchable electronics. Stretchable transparent thin-film electrodes, which retain their electrical conductivity and optical transparency under mechanical deformation, are particularly important for the favourable application of stretchable devices. This minireview summarizes recent advances in stretchable transparent thin-film electrodes, especially employing strategies based on in-plane structures. Various approaches using metal nanomaterials, carbon nanomaterials, and their hybrids are described in terms of preparation processes and their optoelectronic/mechanical properties. Some challenges and perspectives for further advances in stretchable transparent electrodes are also discussed.</P>

Evaluation of Internally Cured Concrete Pavement Using Environmental Responses and Critical Stress Analysis

Kukjoo Kim,Sanghyun Chun 한국콘크리트학회 2015 International Journal of Concrete Structures and M Vol.9 No.4

Three full-scale instrumented test slabs were constructed and tested using a heavy vehicle simulator (HVS) to evaluate the structural behavior of internally cured concrete (ICC) for use in pavements under Florida condition. Three mix designs selected from a previous laboratory testing program include the standard mixture with 0.40 water-cement ratio, the ICC with 0.32 water-cement ratio, and the ICC mixture with 0.40 water-cement ratio. Concrete samples were prepared and laboratory tests were performed to measure strength, elastic modulus, coefficient of thermal expansion and shrinkage properties. The environmental responses were measured using strain gages, thermocouples, and linear variable differential transformers instrumented in full-scale concrete slabs. A 3-D finite element model was developed and calibrated using strain data measured from the full-scale tests using the HVS. The results indicate that the ICC slabs were less susceptible to the change of environmental conditions and appear to have better potential performance based on the critical stress analysis.

Enhanced photoluminescence from zinc oxide by plasmonic resonance of reduced graphene oxide

Kim, Kukjoo,Min Lee, Seong,Seon Do, Yun,Il Ahn, Sung,Cheol Choi, Kyung American Institute of Physics 2013 JOURNAL OF APPLIED PHYSICS - Vol.114 No.7

Effect of Dowel Bar Arrangements on Performance of Jointed Plain Concrete Pavement (JPCP)

Kukjoo Kim,Sanghyun Chun,Sangyoung Han,Mang Tia 한국콘크리트학회 2018 International Journal of Concrete Structures and M Vol.12 No.4

A full-scale jointed plain concrete pavement (JPCP) with two different dowel bar arrangements, namely, standard and special method, was constructed and evaluated under actual traffic-environmental condition in Florida. For standard dowel bar arrangement, dowel bars spaced at 304.8 mm (12 in), while three dowel bars spaced at 304.8 mm (12 in) only within the wheel paths were installed for special dowel bar arrangement. Field performance evaluation was conducted in terms of longitudinal crack, transverse crack, corner crack, spalling, and load transfer efficiency (LTE). Also, a three-dimensional (3-D) finite element (FE) model was developed to evaluate change in structural response characteristics due to different dowel bar arrangements under the critical loading condition. The developed FE model was used to perform a parametric analysis to determine the effects of different dowel bar arrangements. Results indicated that no significant changes in pavement structural responses, including the slab stresses and deflections, were predicted between two dowel bar arrangements that may result in no significant difference in expected performance for the test slabs evaluated, and this matched well with results of field performance evaluation. Also, it was indicated that the base modulus plays an important role on the dowel-joint behavior and stiffer base condition could significantly improve the dowel-joint performance. Therefore, when the base layer is stiff enough to support the slab deflection and resist erosion (e.g., AC layer), special dowel bar arrangement could provide similar performance as compared to standard dowel bar arrangement that result in significant cost savings without any negative effects on expected pavement performance.

RAP 콘크리트의 비선형 응력-변형률 특성이 강성포장 구조해석에 미치는 영향

Kim, Kukjoo,Chun, Sanghyun,Park, Bongsuk,Tia, Mang 한국도로학회 2017 한국도로학회논문집 Vol.19 No.1

PURPOSES: This study is primarily focused on evaluating the effects of the non-linear stress-strain behavior of RAP concrete on structural response characteristics as is applicable to concrete pavement. METHODS : A 3D FE model was developed by incorporating the actual stress-strain behavior of RAP concrete obtained via flexural strength testing as a material property model to evaluate the effects of the non-linear stress-strain behavior to failure on the maximum stresses in the concrete slab and potential performance prediction results. In addition, a typical linear elastic model was employed to analyze the structural responses for comparison purposes. The analytical results from the FE model incorporating the actual stress-strain behavior of RAP concrete were compared to the corresponding results from the linear elastic FE model. RESULTS : The results indicate that the linear elastic model tends to yield higher predicted maximum stresses in the concrete as compared to those obtained via the actual stress-strain model. Consequently, these higher predicted stresses lead to a difference in potential performance of the concrete pavement containing RAP. CONCLUSIONS : Analysis of the concrete pavement containing RAP demonstrated that an appropriate analytical model using the actual stress-strain characteristics should be employed to calculate the structural responses of RAP concrete pavement instead of simply assuming the concrete to be a linear elastic material.

지하시설내 드론전투체계 운용을 위한 요구능력 도출 연구

김국주(Kim, Kukjoo),이영주(Lee, Youngju),이선호(Lee, Sunho),박영준(Park, Youngjun) 한국방재학회 2020 한국방재학회논문집 Vol.20 No.2

본 연구의 목적은 지하시설내 대량살상무기제거 작전에 드론전투체계를 운용하기 위한 요구성능을 도출하는데 있다. 연구방법은 델파이기법을 사용하였으며, 30명의 드론전투체계 기술개발 및 WMD 제거작전과 관련 있는 전문가 그룹을 구성하였다. 1차 설문은 드론전투체계의 요구성능에 관한 개방형 질문을 통해 고려요소를 도출하였고, 2-4차 설문은 고려요소에 대한 전문가의 합의여부를 통계적으로 분석하였다. 채택된 전문가의 의견에 대해 요인분석을 실시한 결과, 총 8개의 요인으로 요구성능이 도출되었음을 확인하였다. This research aimed to derive the required operational capability considerations of the drone combat system to carry out CWMD operations in underground facilities. The Delphi technique was used for this study and the survey was conducted among 30 experts in the fields of drone combat systems and CWMD operations, and in the military and civilian sectors. The first questionnaire investigated the required operational capabilities by using open-ended questions, and the second to fourth questionnaires statistically analyzed the agreement of the experts on each required capability. As a result of the factor analysis, a total of eight factors were derived.

고강도 콘크리트의 구속폭발저항성능에 관한 실험적 평가

김국주(Kim, Kukjoo),박상우(Park, Sang-Woo),백장운(Baek, Jang-woon),박영준(Park, Young Jun) 한국콘크리트학회 2020 한국콘크리트학회 학술대회 논문집 Vol.32 No.2

건물의 EMP 감쇠특성을 고려한 EMP 방호등급 결정 방안

김국주(Kim, Kukjoo),박영준(Park, Young-Jun) 대한건축학회 2021 대한건축학회 학술발표대회 논문집 Vol.41 No.2

The primary purpose of this study was to classify electromagnetic pulse (EMP) protection levels and determine various protection measures. The numerical analysis was conducted to determine the attenuation characteristics of building materials and geometry designs. The natural attenuation effect of soil, concrete and reinforcement of building materials. was confirmed for structures installed underground. For instance, the attenuation effect of wet soil for underground facility was up to 30dB. Therefore, EMP shelters can be constructed by applying the differential protection level scheme applying more effective EMP protection measures such as light-weight film, fabric, paint and wall papers.

4.75 mm 공칭 최대 골재 치수 아스팔트 혼합물의 효과적인 포장 시스템 적용을 위한 공용성 특성 평가 연구

Chun, Sanghyun,Kim, Kukjoo,Park, Bongsuk 한국도로학회 2016 한국도로학회논문집 Vol.18 No.1

PURPOSES : This study primarily focused on evaluating the performance characteristics of 4.75-mm nominal maximum aggregate size (NMAS) asphalt mixtures for their more effective implementation to a layered flexible pavement system. METHODS: The full-scale pavements in the FDOT’s accelerated pavement testing (APT) program, including 4.75-mm mixtures at the top with different thicknesses and asphalt binder types, were considered for the faster and more realistic evaluation of the rutting performance. The results of superpave indirect tensile (IDT) tests and hot-mix asphalt fracture mechanics (HMA-FM) based model predictions were used for cracking performance assessments. RESULTS: The results indicated that the rutting performance of pavement structures with 4.75-mm mixtures may not be as good as to those with the typical 12.5-mm mixtures, and pavement rutting was primarily confined to the top layer of 4.75-mm mixtures. This was likely due to the relatively higher mixture instability and lower shear resistance compared to 12.5-mm mixtures. The energy ratio (ER) and HMA-FM based model performance prediction results showed a potential benefit of 4.75-mm mixtures in enhanced cracking resistance. CONCLUSIONS : In relation to their implementation, the best use of 4.75-mm mixtures seem to be as a surface course for low-trafficvolume applications. These mixtures can also be properly used as a preservation treatment that does not necessarily last as long as 12.5-mm NMAS structural mixes. It is recommended that adequate thicknesses and binder types be considered for the proper application of a 4.75-mm mixture in asphalt pavements to effectively resist both rutting and cracking.

Wearable, wireless gas sensors using highly stretchable and transparent structures of nanowires and graphene

Park, Jihun,Kim, Joohee,Kim, Kukjoo,Kim, So-Yun,Cheong, Woon Hyung,Park, Kyeongmin,Song, Joo Hyeb,Namgoong, GyeongHo,Kim, Jae Joon,Heo, Jaeyeong,Bien, Franklin,Park, Jang-Ung The Royal Society of Chemistry 2016 Nanoscale Vol.8 No.20

<P>Herein, we report the fabrication of a highly stretchable, transparent gas sensor based on silver nanowire-graphene hybrid nanostructures. Due to its superb mechanical and optical characteristics, the fabricated sensor demonstrates outstanding and stable performances even under extreme mechanical deformation (stable until 20% of strain). The integration of a Bluetooth system or an inductive antenna enables the wireless operation of the sensor. In addition, the mechanical robustness of the materials allows the device to be transferred onto various nonplanar substrates, including a watch, a bicycle light, and the leaves of live plants, thereby achieving next-generation sensing electronics for the 'Internet of Things' area.</P>