http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Review of State-of-the-Art Sensor Applications Using Mechanoluminescence Microparticles
Suman Timilsina,김지식,김재환,김기우 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.9
The term mechanoluminescence (ML) refers to the light emission from various organic and inorganic materials in response to mechanical stimuli such as friction, tension, fracture, and compression. Recently, this interesting luminescence phenomenon has enabled us to explore various advanced sensor applications. In this review article, the overall ML mechanism that arises under different experimental conditions is discussed thoroughly. The recent research achievements of state-of-the-art sensors based on ML microparticles such as SrAl2O4:Eu,Dy (SAO), ZnS:Cu, and ZnS:Mn are then reviewed. As a new functional smart material, SAO ML microparticles can be used in possible substitutive and substantial methods for structural health monitoring (SHM) systems, owing to their relative simplicity but effectiveness in detecting arrested or propagating crack tips, and in assessing the in-situ structural state by means of fracture parameters such as stress intensity factors. The applicability of ML paint and thin films on various types of ceramics and concretes as fracture sensors is reviewed. The research on sensors based on different ML microparticles such as noncontact torque sensors based on ZnS:Cu, flexible pressure sensors and impact sensors using ZnS:Mn is also reviewed in this article. Potential applications using ML microparticles are also briefly discussed.
조민영,Suman Timilsina,노종욱,Walter Commerell,신호근,권용남,김지식 대한금속·재료학회 2021 대한금속·재료학회지 Vol.59 No.5
A photo-rheological fluid (PRF) is a smart fluid which exhibits different viscosity under UV irradiation. A PRF is comprehensively presented in this work, with particular focus on its responses under UV off/on conditions. The isomeric conversion from SP to MC and vice versa under UV off and on, respectively, showed unequal rates of transformation. As a result, a complex non-linear hysteretic response was observed. To be used indifferent types of sensors and actuators which can exploit its rheological properties, it is essential the PRF have linearized hysteresis behavior. To minimize the asymmetric non-linear hysteresis characteristics under UV on and off conditions, the well-known long-lasting phosphor SAO (SrAl2O4:Eu2+, Dy3+) was incorporated. The incorporation of SAO in the PRF improved the linearity of the PRF response, although the conversion rate was not identical under UV off/on conditions. The SAO particles were observed to settle over time due to phase splitting, undermining the usefulness of the SAO-PRF composite. Instead of improving the PRF response by further adjusting the PRF composite, a software approach based on Long Short-Term Memory Recurrent Neural Networks (LSTM RNN) was employed to model and compensate the asymmetric non-linear hysteresis response, ensuring the realization of sensors and actuators that exploit PRF as hardware.
이상수,TIMILSINA SUMAN,최선두,신호근,장성민,이영선,권용남,김지식 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.5
Superplastic forming (SPF) is a promising approach used for manufacturing parts with complex geometries, especially in the automotive, aerospace, and marine industries. However, the wider use of this method is limited by issues of low forming rate, high-temperature requirement, non-uniform thickness distribution, and expensive base materials. The two-stage hybrid forming (HF) method, in which hot-punch forming is executed before the SPF, was introduced to overcome these limitations. In this study, a conventional non-superplastic grade 5052 aluminum (AA5052) alloy with an average grain size of 70 μm was used to evaluate the applicability of two-stage HF for manufacturing parts with complex geometries from coarse grain alloys. Before implementing the two-stage HF, the optimal experimental conditions for hot drawing and hot blowing were first determined. The optimum HF conditions were identified, as follows: a hot-punching temperature of 400oC, punch depth of 35 mm, punching speed of 150 mm/min, blow forming temperature of 500oC, and gas pressure of 2.5 MPa. The HF results were also verified using the finite element method. The finite element analyses results for thickness distribution and optimal process condition were compared with the experimental results for one-stage and two-stage forming, and showed acceptable similarity.
Evaluation of the elasto-plastic crack tip singularities via mechano-luminescent effects
Basnet, Ramesh,Timilsina, Suman,Lee, Kwang Ho,Kim, Ji Sik Elsevier 2018 International journal of engineering science Vol.123 No.-
<P><B>Abstract</B></P> <P>New techniques to directly evaluate the plastic singularity of elasto-plastic crack under a mixed mode from the plastic J field, as well as indirectly from an elastic K field, have been suggested using Mechano-luminescence (ML) in SrAl<SUB>2</SUB>O<SUB>4</SUB>:Eu,Dy. For this purpose, the ML of a plastic core, Hutchinson–Rice–Rosenberg (HRR), field in the vicinity of a physical crack tip during four-point shearing was visualized and analyzed. Plastic stress intensity factors (SIFs) of K M P measured at 829 and 872 N directly from the ML-HRR field showed proper agreement with those of K M P e that were predicted indirectly from elastic SIFs with deviations of less than 11%. An imaginary crack tip within the plastic zone and a propagating angle with the plastic zone size under transient cracking were evaluated separately to verify use of ML technique for considering elasto-plastic crack in Structural Health Monitoring (SHM).</P>
조민영,김지식,Jo, Min-Yeong,Timilsina, Suman,Kim, Ji-Sik 한국정보디스플레이학회 2016 인포메이션 디스플레이 Vol.17 No.2
압광 기술의 발전으로 인하여 압광 소재가 형광 페인트나 박막 형태로 제조되어, 응력을 받고 있는 소재의 표면에 적용됨으로써 실시간으로 가해지는 응력과 변형의 정도 및 그 변화를 가시적으로 표시 하고자 하는 센서 기술이 지난 10 여 년간 비약적으로 발전하였다. 이러한 성과를 바탕으로 본 기술 특집 원고에서는 압광 및 형광 기반의 스마트 센서 개발과 관련된 분야에 특화된 내용을 중점적으로 요약 소개 하였다.
이중 인공지능을 이용한 Al 7075 합금에서의 압광 균열 진단 연구
박태오,신윤우,이승환,좌비오,권용남,Suman Timilsina,장성민,조철우,김지식 대한금속·재료학회 2023 대한금속·재료학회지 Vol.61 No.12
The phenomenon of mechanoluminescence (ML) refers to the emission of light induced bymechanical stimulation applied to mechano-optical materials for example SrAl2O3:Eu,Dy (SAO). Numeroustechnologies on the basis of ML have been presented to visualize the stress or strain in various structures forthe applications including structural health monitoring. As a result, extensive attention has been devoted tothe design, synthesis, characteristics, optimizations, and applications of ML materials. However, challengesstill remain in the standardization of ML measurement and evaluation, thereby commercially viable MLapplications are currently unavailable. To overcome these difficulties, present study proposes ML measurementand evaluation techniques employing the ML fracture mechanics, finite element method, and dual deeplearnings. For the effective normalization of visualized ML images under fixed initial ML intensity condition,continuous UV irradiation above the critical ML power density has been subjected to tensile and compacttension (CT) specimens. Therefore, Plastic Stress Intensity Factor (SIF) as well as crack tip stress field havebeen extracted successfully from normalized ML images based on ML fracture mechanics. To complement andverify the ML analysis, numerical FEM simulation and analytical ASTM calculation have been also provided. Finally, a double deep learning consists of Generative Adversarial Networks (GAN) and Convolutional NeuralNetworks (CNN) has been trained and tested for the standard evaluation of in-situ ML images.
Cho, Min-Young,Lee, Jeong Heon,Kim, Seong-Hoon,Kim, Ji Sik,Timilsina, Suman American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.12
<P>Here, we describe the utility of a carbon fiber (CF) electrode that is inexpensive, simple, and flexible and can be embedded with elastomeric nanocomposite piezo-resistive sensors fabricated from silicone rubber (Ecoflex) blended with carbon nanotubes (CNTs) and various wt % of silicone thinner to tune the sensitivity and softness range. The performance of the CF electrode was evaluated on the basis of piezo-resistive responses from the sensors subjected to dynamic sinusoidal compressive strains at different levels and frequencies. The responses were positive-pressure effects with rate-dependent asymmetric nonlinear hysteresis characteristics. Developing a mathematical model to describe the rate-dependent asymmetric nonlinear hysteresis behavior is technically impossible; therefore, we employed artificial intelligence-based hysteresis modeling, long short-term memory recurrent neural network, to describe the hysteresis nonlinearity. The debonding strength of the CF electrode was determined in the pull-off testing and was found to be much higher than that of a copper wire electrode. The debonding mechanism was further elucidated via an in situ resistance profile. The importance of a robust conductive interface between a CF electrode and a nanocomposite was experimentally demonstrated. It was found that the inherent piezo-resistance of the CF was negligible compared with the piezo-resistance of the sensor; therefore, the signals from the sensor were free of interference. We believe CF-embedded tunable piezo-resistive sensors could be used in biomedical devices, artificial e-skins, robotic touch applications, and flexible keyboards where the required stretchability of the electrode can be introduced via an appropriate geometrical design.</P> [FIG OMISSION]</BR>