점용접 열영향부의 동적 물성특성에 관한 연구

하지웅(Jiwoong Ha),송정한(Junghan Song),허훈(Hoon Huh),임지호(Jiho Lim),박성호(Sungho Park) 한국자동차공학회 2008 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

This paper propose a methodology to identify the dynamic material properties of the HAZ near the base metal in a resistance spot weld at various strain rates. The mechanical properties of the HAZ of SPRC340R were obtained by fabricating thermal simulated HAZ specimens which have similar hardness and microstructure as the actual weld HAZ near the base metal. The thermal simulated HAZ specimens are fabricated using the Material Thermal Cycle Simulator (MTCS). Then, dynamic tensile tests are performed at various strain rates of 0.001 /sec to 100 /sec. Finite element analysis of tensile-shear tests were done under the static and dynamic loading conditions to verify the validity and effectiveness of thermal simulated HAZ properties. Load and displacement curves were obtained with and without applying the material properties of HAZ. The curves are compared to the experimental data. The amount of errors between the analysis and experiment were reduced when the material properties of thermal simulated HAZ were applied to the HAZ. The comparison demonstrates that the dynamic material properties obtained from thermal simulated HAZ specimens are valid for the analysis of spot welded specimens.

Available P as a Soil Indicator Controlling the Spatial Variability of Soil Chemical Properties in the Orchard Farming Systems of Chungcheong Province, Korea: Revealed by Data Binning Method

Pros Khok,Kyoungyoung Kim,Yong gook Kim,Park Jee won,Gwang Hyun Han 한국토양비료학회 2021 한국토양비료학회 학술발표회 초록집 Vol.2021 No.11

Soil properties vary spatially at all level of observation within a field to a larger regional scale and the causes of the variation can be both natural and anthropogenic factors. Knowledge of spatial variability in soil properties is important for effective nutrient management plan in crop production. One integrated test by compiling several soil properties together may provide growers with one number that represents as overall spatial variabilities. Therefore, understanding the functional relationship between soil properties is necessary. The objective of the study was to characterize a soil indicator that can be used to estimate the overall spatial variability of selected soil properties in orchard farming systems. We have selected and analyzed eight soil chemical parameters, including pH, EC, SOC, available N, available P, and exchangeable cations such as K, Ca, and Mg of the individual 126 soil samples collected randomly from 42 orchard farms across Chungcheong province. The median of each soil parameters was similar or lower than the mean, which indicates that the effects of abnormality on sampling value were not high. Coefficient of variation (CV) indicated that soil parameters except pH varied from medium to high in heterogeneity (CV > 20%). Available P had the most variability (MRD = 31.8) and soil pH had the least variability (MDR = 0.89) among of all soil properties. Apparently, the dynamic interrelations were observed between soil properties and the higher amount of statistical significant correlations (p ≤ 0.05 and p ≤ 0.01) belong to available P, and all of exchangeable cations, respectively. We confirmed these apparent correlations using discrete binning method and regression. Result showed that the higher amount of statistical significant correlation belong available P, so we concluded that available P is a major soil indicator can be used to predict the spatial variability of all selected soil parameters in this study. The high significant relationship were found between available P and all of selected soil chemical properties in orchard farming systems of Chungcheong province, suggesting that the large spatial variability was associated with the application of inorganic, organic, and animal by-product fertilizers. Data binning is a wide diverse analysis tool for indicating the relationship of soil properties with high spatial variability.

시각 차단과 불안정한 지지면을 이용한 불가리안 스플릿 스쿼트 운동 시 동적 균형 능력과 근속성의 비교

양진현,이교현,박경호,박수경 대한정형도수물리치료학회 2023 대한정형도수물리치료학회지 Vol.29 No.1

Background: Bulgarian split squat (BSS) is beneficial to improve dynamic balance ability and muscle activity of lower extremities, however its effects have not been fully investigated. Therefore, this study aimed to compare changes in dynamic balance ability and muscle properties according to various modifications of BSS exercises. Methods: Thirty healthy male volunteers participated in this study, and they were randomly divided into three different groups. The subjects performed the BSS exercise either on a stable surface with the eyes opened (n=10) or eyes closed (n=10), and on an unstable support plane with eyes opened (n=10) conditions, respectively. Dynamic balance ability was measured via Biodex balance system under the eyes-opened and closed conditions. Additionally, muscle properties of the rectus femoris (RF), vastus medialis (VM) and vastus lateralis (VL) were evaluated. Results: Dynamic balance ability did not show the significant differences among the groups that performed the BSS exercises. However, in the Unstable group, there were significant differences in the overall stability index and anterior posterior stability index under the eyes-closed condition between pre-exercise and post-exercise. In comparison of muscle properties according to the groups, RF muscle showed a significant difference in amount of change of elasticity (p=.038). Additionally, there were significant changes in post measurements of VM muscle tone (p=.016), stiffness (p=.012) and elasticity (p=.002). VL muscle, however had no significant differences in muscle properties. Conclusion: These results indicate that BSS exercises could induce the alteration of RF and VM muscle properties, in particular VM muscle which is susceptible to weakness. Thus, BSS could be applied in various ways as an effective rehabilitation exercise.

국유재산의 상시관리체계에 관한 연구

임형택(Lim, Hyung-Taek),장교식(Jang, Kyo-Sik) 한국토지공법학회 2015 土地公法硏究 Vol.72 No.-

국유재산을 유지·보수하던 종래의 소극적 관리에서 적극적 관리로 세계적 패러다임이 전환되면서, 우리나라에서도 이를 수용하기 위한 법제의 변화가 있었다. 그러나 법제의 변화에도 불구하고 현실적으로 국유재산의 적극적 관리는 실현되고 있지 않다. 본래 국유재산의 적극적 관리를 위해서는 정확한 실태조사를 기초로 올바른 계획을 수립하고 그 계획을 성실히 실행하는 3단계의 과정이 유기적으로 결합하여야 한다. 특히 국유지의 실태조사와 관련해서는 시시각각 변동하는 무단점유나 유휴지의 방치 등의 문제가 발생하기 때문에 이를 정기적으로 조사하는 정태적 관리뿐만 아니라 상시적으로 이를 조사할 수 있는 동태적 관리를 필요로 한다. 그러나 국유지를 총괄 관리하는 기획재정부의 관련 인원은 약 30여명에 불과하며 예산 역시 충분히 확보되어 있지 않아 국유지의 실태 파악조차 어려운 상황이다. 이러한 문제를 해소하기 위해서는 기획재정부의 관련 인원을 대폭 확충하는 방안이나 또는 실태조사에 전문성이 있는 기관과의 협력적 거버넌스 체계를 구축하는 방안을 생각해 볼 수 있다. 이중 기획재정부의 관련 인원을 대폭 확충하는 방안은 공무원 조직의 비전문성, 의사결정의 지연, 경제적 비효율 등으로 대표되는 정부의 실패라는 문제를 야기할 위험이 있다. 따라서 국유지 실태조사를 위한 조직의 확충문제는 국유지 관리에 전문성이 있는 기관과의 협력적 거버넌스를 통해 상시관리체계를 구축하는 것이 보다 바람직할 것이다. 이러한 상시관리체계를 통해 향후 국유재산의 효율적 활용을 위한 기초 토대가 굳건히 구축될 수 있을 것으로 기대한다. There has been a shift of paradigm in the repair and maintenance of state-owned properties from passive to active management around the world. As a result, South Korean government also attempted to amend its legal system. Despite change in the legal system, however, active management of state-owned properties hasn’t been implemented. To manage national properties in an active manner, in general, it is needed to establish a proper plan based on a proper survey and systematically combine a 3-stage process which is needed to carry out the plan. According to a survey on state-owned properties, in particular, a certain problem (ex: The occupation of state property without permission, abandonment of idle land, etc.) can occur. In terms of the management of state-owned properties, therefore, dynamic management which examines them regularly as well as static management which checks them occasionally is required. In the Ministry of Strategy and Finance, however, only about 30 people are now in control of national properties. Furthermore, it is hard to examine their current conditions due to lack of budget. To solve these problems, the government body might be able to increase the staff or establish a cooperative governance system with professional organizations. However, the former suggestion can cause a government organization’s non-professionalism, delay in decision-making process and economic inefficiency. Therefore, it would be more desirable to establish a regular management system through cooperative governance with an organization which is specialized in the management of state-owned properties. It appears that this kind of a regular management system would strengthen the ground for the efficient utilization of state-owned properties.

Bio-Composites Reinforced with Natural Fibers: Comparative Analysis of Thermal, Static and Dynamic-Mechanical Properties

Rajesh Mishra,Jakub Wiener,Jiri Militky,Michal Petru,Blanka Tomkova,Jana Novotna 한국섬유공학회 2020 Fibers and polymers Vol.21 No.3

In the present study, flax, jute and glass woven fabric samples were developed as reinforcement for compositeswith bio-epoxy resin. Flax fabrics were developed with plain weave, twill weave (different areal densities) and unidirectional(UD) structure. Jute fabrics were woven with three different structures i.e. plain, matt and twill respectively. For comparisonpurpose, glass woven fabric with plain weave and 3D orthogonal weave were used in this study. Static mechanical propertieslike flexural strength and impact resistance were studied. Dynamic mechanical properties were investigated by DMA 40XTRMI equipment.. Thermal conductivity has been studied for all composite samples. It is observed that the static mechanicalproperties of glass fabrics reinforced composites are superior but the flax & jute fabric reinforced composites are moreflexible. The specific flexural strength as well as specific impact strength of the flax & jute fabric reinforced composites arecompetitive. The dynamic mechanical properties are comparable to that of glass fabric reinforced composites. They can beused in relatively lower load bearing applications as they are a sustainable source of materials for bio-composites whichreduce the environmental burden and reduce the manufacturing cost.

Stochastic dynamic instability response of piezoelectric functionally graded beams supported by elastic foundation

Shegokara, Niranjan L.,Lal, Achchhe Techno-Press 2016 Advances in aircraft and spacecraft science Vol.3 No.4

This paper presents the dynamic instability analysis of un-damped elastically supported piezoelectric functionally graded (FG) beams subjected to in-plane static and dynamic periodic thermomechanical loadings with uncertain system properties. The elastic foundation model is assumed as one parameter Pasternak foundation with Winkler cubic nonlinearity. The piezoelectric FG beam is subjected to non-uniform temperature distribution with temperature dependent material properties. The Young's modulus and Poison's ratio of ceramic, metal and piezoelectric, density of respective ceramic and metal, volume fraction exponent and foundation parameters are taken as uncertain system properties. The basic nonlinear formulation of the beam is based on higher order shear deformation theory (HSDT) with von-Karman strain kinematics. The governing deterministic static and dynamic random instability equation and regions is solved by Bolotin's approach with Newmark's time integration method combined with first order perturbation technique (FOPT). Typical numerical results in terms of the mean and standard deviation of dynamic instability analysis are presented to examine the effect of slenderness ratios, volume fraction exponents, foundation parameters, amplitude ratios, temperature increments and position of piezoelectric layers by changing the random system properties. The correctness of the present stochastic model is examined by comparing the results with direct Monte Caro simulation (MCS).

생활한복지의 동적 드레이프성

박정환(Park Jeong-Whan),배진화(Bae Jin-Hwa),안승국(An Seung-Kook) 한복문화학회 2008 韓服文化 Vol.11 No.2

Drape is the one of the important factors influencing to the aesthetics and functionality of fabrics. In this study, the behaviours of the static and dynamic drape of woven fabrics for Saeng-hwal Hanbok have been analyzed according to the fabric structural parameters such as the weft density and weave structure. The static drape properties have effects on the bending properties and shear properties. And also the dynamic drape coefficients have great effects on the bending properties and shear properties at the lower speed of dynamic drape speed. But there is less effect at (with) the higher speed of dynamic drape tester.

On-Orbit Estimation of Dynamic Properties for STSAT3

Sungwook Yang,Dong-Ik Cheon,Sangchul Lee,Hwa-Suk Oh 제어로봇시스템학회 2008 제어로봇시스템학회 국제학술대회 논문집 Vol.2008 No.10

Reliable and efficient attitude control requires the accurate dynamic properties. On orbit, the mass and inertia values are to be changed by some activities such as the propellant use, the solar panel deployment, etc. To obtain the accurate mass properties, the estimation should be performed. For the initial on-orbit estimation of the mass properties, the gyro-based attitude data is applied for the batch method. The gyro-based attitude data includes the noise, which affects the estimation accuracy. We suggested several filtering methods including the extended Kalman filtering algorithm to obtain the well-conditioned attitude data. Applying the proper filters, we can obtain the reliable estimation result of the mass properties of STSAT3.

Mechanical properties of thin films of graphene materials: A study on their structural quality and functionalities

Velram Balaji Mohan,Hamid Souri,Krishnan Jayaraman,Debes Bhattacharyya 한국물리학회 2018 Current Applied Physics Vol.18 No.8

Several studies have been done on physiochemical properties of thin films of graphene materials, but less on their mechanical properties. The mechanical properties such as tensile and storage modulus of films of graphene oxide (GO), different reduced graphene oxides (rGO), functionalised reduced graphene oxide (frGO) and a few layers graphene (graphene) were analysed in this study. During syntheses processes, a range of variations occurs due to different reducing agents and functionalising components used; this affects or changes the mechanical properties of the materials. In addition, it has become vital to comprehend the mechanical properties of these films as the potential applications such as sensor and electrodes demand extended life cycles or lifetime. It has been found that the ultimate tensile strength (UTS), tensile modulus, and storage modulus vary across all the samples that highly depend on nature/efficiency of reducing agent used, amount of impurities such as oxygen functional groups and defect density such as discrepancies/holes in the aromatic structure. The highest UTS and modulus have been identified with a few layers graphene and with hydroiodic acid reduced GO among the rGOs. The frGO shows almost similar properties to that of graphene.

Investigation of Dynamic-Mechanical-Thermal Analysis of Innovative Hybrid Carbon/Glass Fibers Reinforced by GNPs and Al2O3 for Marine Structures

Mohamed Abu‑Okail,Metwally Abdel Ghafaar,Abou Bakr Elshalakany,Mohamed S. Shiba,Ahmed Abu‑Oqail,Mohammed Gamil 한국섬유공학회 2023 Fibers and polymers Vol.24 No.11

Marine structural applications face numerous challenges related to environmental load, corrosion, and fatigue under varying time and temperature conditions. One of the major challenges faced by marine structural applications is dynamic mechanical thermal analysis (DMTA). In this study, innovative hybrid carbon/glass fibers (CGF) reinforced with different contents (1.5 wt. % and 3 wt. %) of dual nano-powders, including graphene nanoplatelets (GNPs) and aluminium oxide (Al2O3), were developed as reinforcements inside the epoxy matrix. The nanocomposites were fabricated using a hand lay-up technique, resulting in a nanocomposite sheet with dimensions of 300 mm length, 200 mm width, and 2.3 mm thickness. DMTA test specimens were prepared with dimensions of 50 mm length, 10 mm width, and 2.3 mm thickness. To ensure accuracy, three replicates were conducted for each condition, and the average values were calculated for analysis. Before DMTA, the prepared nanocomposites were analyzed using optical microscopy (OM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDAX) to compare the influence of incorporating dual nano-powders. DMTA was carried out at different temperature values (ranging from 10 °C to 105 °C) and times (ranging from 5 to 575 min) at 1 Hz frequency with a heating rate of 4 °C/min and a nitrogen flow rate of 20 ml/min. The main objective of this study was to investigate the influence of incorporating dual nano-powders such as GNPs and Al2O3 on various dynamic mechanical properties including storage modulus, loss modulus, damping factor (DF), and glass transition temperature (Tg) of the hybrid carbon/glass fiber-reinforced epoxy composites. The fabricated hybrid CGF composite with 1.5% wt. GA nanoparticles exhibited higher values for the DF of 0.68 and the Tg of 73.4 °C. However, increasing the nanoparticle content to 3% wt. GA led to a deterioration in the DF (0.54) and a reduction in Tg (27.8 °C) due to decreased bonding between the carbon fibers (CF) and glass fibers (GF) caused by the higher nanoparticle concentration. The complex modulus (E*) values demonstrated expected trends with temperature and time for the CGF-1.5% wt. GA composite, indicating acceptable behaviour. In contrast, the CGF-3% wt. GA composite exhibited lower E* values, indicating a decrease in stiffness and mechanical properties compared to the CGF-1.5% wt. GA composite. Microstructural observations after DMTA revealed a uniform scattering of nanoparticles in the CGF-1.5% wt. GA sample, while the CGF-3% wt. GA sample demonstrated improved scattering of Al2O3 nanoparticles on the surface. The microstructural analysis further indicated a brittle nature with high resistance to crack initiation and propagation in the CGF-1.5% wt. GA composite.