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Timilsina, S.,Lee, K.H.,Jang, I.Y.,Kim, J.S. Elsevier Science 2013 ACTA MATERIALIA Vol.61 No.19
The use of mechanoluminescence (ML) has enabled a new technique for the determination of the mode I stress intensity factor (SIF) in SrAl<SUB>2</SUB>O<SUB>4</SUB>:Eu<SUP>2+</SUP>,Dy<SUP>3+</SUP> (SAO). The stress rate fields and its cumulative isostress contour patterns in terms of ML in the vicinity of a crack tip during compact tension were evaluated based on the two different stress criteria of the hydrostatic and deviator in triggering the trap-releasing processes of the ML mechanism. The magnitude and shape of the crack tip stress field predicted by the deviator stress criterion rather than by the hydrostatic stress criterion showed good agreement with the experimental ML evidence in a determination of the SIF from the ML intensity. The analysis derived from the deviator stress criteria not only allowed the possibility of characterizing the fracture toughness in a range of modes under static and dynamic crack propagation, but also provided a better understanding of the ML mechanism of the trap-releasing process in SAO.
Timilsina, S.,Bashnet, R.,Kim, S.H.,Lee, K.H.,Kim, J.S. IPC Science and Technology Press ; Elsevier Scienc 2017 International journal of fatigue Vol.101 No.1
<P>Mechano-luminescent (ML) paint consisting of SrAl2O4:Eu2+,Dy3+ powders and transparent epoxy resin could reveal the complex crack initiation and propagation evolved from the Brazilian test of conventional concrete. ML paint also showed excellent fatigue resistance in terms of mechanical strength and optical ML durability, even in weatherproof. Although the intensity of emitted photons from ML paint has been reduced as the number of repetitive stress cycles increased, however, the deterioration of ML intensity with the variation of additive stress cycle was less than 5% in the cases of high cycle failure. Consequently, the life time reproducibility of ML paint allows the possibility to characterize the longterm integrity of various concrete structures. (C) 2017 Elsevier Ltd. All rights reserved.</P>
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.
Rockfall Impact Energy and Trajectory Study for Rockfall Hazard Mitigation in Nepal
( Manita Timilsina ),( Ranjan Kumar Dahal ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2
Low-cost slope mitigation practices are usually well practiced in Nepal. Among them, gabion and stone masonry retaining walls are very much common mitigation practices for landslide in Nepal. Such protection systems are good for shallow soil slope failure and erosion control only, Suitable system for rockfall protection is not well practiced till date. Some initiatives have been started in recent years. Design of rockfall protection measures requires data for two basic parameters of rockfall impact energy and trajectory. Basically, information is required on the mass and velocity of falls to determine the required energy capacity, and on impact locations and trajectory paths to determine the optimum location and dimensions of the rockfall protection barrier or fence. Development of these design parameters requires the collection of relevant site data, followed by the analysis of energies and trajectories and then selection and design of the appropriate protection system. This paper describes and discusses new technologies for rockfall mitigation in the Nepalese slopes. It highlights the importance of impact energy and trajectories to find best suitable rockfall barrier system and describe how impact energy and trajectories are fixed for particular project. Some case studies will be highlighted in the presentation.
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.
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.
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>