• Geomechanics and Engineering
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• 제22권1호
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• pp.81-95
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• 2020

Measurement of the unconfined compressive strength (UCS) of the rock is critical to assess the quality of the rock mass ahead of a tunnel face. In this study, extensive field studies have been conducted along 3,885 m of the new Nagasaki tunnel in Japan. To predict UCS, a hybrid model of artificial neural network (ANN) based on genetic algorithm (GA) optimization was developed. A total of 1350 datasets, including six parameters of the Measurement-While- Drilling data and the UCS were considered as input and output parameters respectively. The multiple linear regression (MLR) and the ANN were employed to develop contrast models. The results reveal that the developed GA-ANN hybrid model can predict UCS with higher performance than the ANN and MLR models. This study is of great significance for accurately and effectively evaluating the quality of rock masses in tunnel engineering.

• 정보처리학회논문지C
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• 제14C권7호
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• pp.603-610
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• 2007

이동 중인 사용자에게 연속성 있는 서비스 제공을 위해서는 효과적인 핸드오버 결정 기법이 필요하다. 본 논문에서는 측정된 수신 신호 강도를 이용한 핸드오버 결정 방법의 성능을 늦은 통보와 오보율 측면에서 평가하기 위한 분석 모델을 제안한다. 제안 모델은 핸드오버 결정 기법의 성능에 영향을 미치는 사용자의 이동성, 핸드오버 프로토콜 메시지 교환 지연, 셀 크기 및 안정적인 수신 신호 강도 측정을 위한 수신 신호 강도 측정 주기를 모두 고려한다. 또한 본 논문에서는 제안한 분석 모델을 통해 각 인자들의 영향을 정량적으로 고찰하여 효과적인 고속 핸드오버 시작 시점 결정을 위한 연구 방향을 제시한다.

• 마이크로전자및패키징학회지
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• 제20권2호
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• pp.11-15
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• 2013

The wafer bonding process becomes a flexible approach to material and device integration. The bonding strength in 3-dimensional process is crucial factor in various interface bonding process such as silicon to silicon, silicon to metals such as oxides to adhesive intermediates. A measurement method of bonding strength was proposed by utilizing AFM applied CNT probe tip which indicated the relative simplicity in preparation of sample and to have merit capable to measure regardless type of films. Also, New Tool was utilized to measure of tip radius. The cleaned $SiO_2$-Si bonding strength of SPFM indicated 0.089 $J/m^2$, and the cleaning result by RCA 1($NH_4OH:H_2O:H_2O_2$) measured 0.044 $J/m^2$, indicated negligible tolerance which verified the possibility capable to measure accurate bonding strength. And it could be confirmed the effective bonding is possible through SPFM cleaning.

• 통합자연과학논문집
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• 제11권2호
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• pp.113-120
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• 2018

This study was planned to prepare the high strength hydrogel ophthalmic lens containing isocyanate group and nanoparticles. HDI with carbon nanoparticles were used as additives for the basic combination of HEMA, MA and MMA, and the materials were copolymerized with EGDMA as the cross-linking agent and AIBN as the initiator. The mixture was heated at $100^{\circ}C$ for an hour to produce the high performance hydrogel ophthalmic lens by cast mold method. Measurement of the physical characteristics of the produced material showed that the refractive index was in the range of 1.4027~1.4600, water content 25.21~44.01%, contact angle $54.18{\sim}72.94^{\circ}$, visible light transmittance 53.03~92.09%, and tensile strength 0.1024~0.2359 kgf and breaking strength was 0.0872~0.2825 kgf. The results showed an increase of refractive index while the decrease in water content. And also, the breaking strength was highest when the addition ratio of HDI was 5%(wt). As a result of the absorbance measurement, no significant difference was observed in all the samples, so it can be judged that the stabilization of nanoparticles in the polymer was maintained.

• 한국전문물리치료학회지
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• 제26권3호
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• pp.11-22
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• 2019

Background: Sling exercises are frequently used for the rehabilitation process of patients with shoulder joint injuries, but research on the significant frequency intensity and appropriate treatment duration for sling exercises with local vibration stimulation is lacking. Objects: The aim of this study was to investigate the effects of sling exercise with vibration on shoulder range of motion (ROM), muscle strength, pain, and dysfunction in patients with a medical diagnosis of shoulder joint injury. Methods: Twenty-two patients were randomly assigned to the experiment and control groups. Six sling exercises with and without 50 Hz vibrations were applied in the experiment and control groups, respectively. Each exercise consisted of 3 sets of 5 repetitions performed for 6 weeks. The assessment tools used included shoulder joint range of motion, muscle strength, pain level, and shoulder pain and disability index for functional disability. We conducted re-evaluations before and 3 and 6 weeks after intervention. The changes in the measurement variables were analyzed and compared between the two groups. Results: The ROM of the external rotation of the shoulder joint had a significant interaction between the group and the measurement point (F=3.652, p<.05). In both groups, we found a significant increase in external rotation angle between the measurement points (p<.05). The flexor strength of the shoulder joint significant interaction between the group and the measurement point (F=4.247, p<.05). Both the experiment (p<.01) and control groups (p<.05) showed a significant increase in shoulder flexor strength at the measurement points. After 6 weeks of the interventions, both the groups showed significantly improved VAS (p<.01), SPADI (p<.01), and orthopedic tests (p<.01). However, there was no significant difference between the group and the measurement point in terms of the clinical outcomes observed. Conclusion: The sling exercise with local vibration of 50 Hz affected the external rotation of the shoulder range of motion and improved shoulder flexor strength in the patients with shoulder injuries. Therefore, we propose the use of the sling exercise intervention with vibration in the exercise rehabilitation of patients with shoulder joint injuries.

• 한국정밀공학회지
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• 제21권8호
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• pp.89-96
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• 2004

Micro-tensile testing system, consisting of a micro tensile loading system and micro-ESPI(Electronic Speckle Pattern Interferometry) system, has been developed for measurement of micro-tensile properties of thin micro-materials. Micro-tensile loading system had a load cell with the maximum capacity of 50N and micro actuator with resolution of 4.5nm in stroke. The system was used to apply a tensile load to the micro-sized specimen. During tensile loading, the micro-ESPI system acquired interferornetric speckle patterns in the deformed specimen and measured the in-plane tensile strain. The ESPI system consisted of a CCD-camera with a lens and the window-based program developed for this experiment. Using this system, stress-strain curves for 4 kinds of electrolytic copper foil 18$\square$m thick were obtained. From these curves, tensile properties, including the elastic modulus. yielding strength and tensile strength, were determined and also values of the plastic exponent and coefficient based on Ramberg-Osgood relationship were evaluated.

• 한국세라믹학회지
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• 제33권6호
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• pp.709-717
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• 1996

Design parameter of Si3N4 for engineering part could be calculated through the measurement of tensile strength with cylindrical specimen($\Phi$=7.15, ι=110mm) Relative densities of Si3N4 test specimen prepared by pressure-less sintering (PLS) and sinter/HIP were 98.5 and 99.2% respectively. Tensile strength of Si3N4 was 378 MPa for PLS and 509 MPa for sinter/HIP. By the Weibull statistic Design parameter such as Weibull modulus m=8-12 could be calcuated. Fracture strength of Si3N4 related to volume could be effectively pridicted by using Weibull theory.

• 대한기계학회논문집
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• 제18권7호
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• pp.1664-1673
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• 1994

As a fundamental study on effects of thermal-cycles on residual stress of ceramics/metal joints, residual stresses in $Si_3N_4$/SUS304 joint specimens were measured before and single thermal-cycle by X-ray diffraction method and finite element method(FEM). The residual stress was found to increase after single thermal-cycle, which was agreeable with the results of residual stress measurement by X-ray diffraction method and residual stress analysis by finite element method. After the residual stress measurement, 4-point bending tests were performed. The relationship between the bending strength, the thermal-cycle temperature and hold time was examined. The bending strength was found to decrease with the increase of residual stress in linear relation.

• 소성∙가공
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• 제12권8호
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• pp.718-723
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• 2003

Tn order to develop springback control technology for high-strength steel sheets, several studies have been conducted: dome stretching test, stepped s-rail forming and springback measurement, and optimally shaped initial blank design. First, to find out the formability of TRIP60, dome stretching test was performed. Next, the stepped s-rail die, which was designed to form a channel type panel with large twist and wall curl, was manufactured and used to evaluate the effect of controlling forming variables, such as blank holding force and flange amount on the springback. Furthermore, new measurement method of the springback was introduced to define wall curl and twist in geometrically complex panels. Finally, the optimally shaped initial blank was employed to verify one of the best ways to control the springback in channel type. high-strength sheet panels.

• Computers and Concrete
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• 제28권5호
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• pp.521-532
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• 2021

Present paper focuses on the modeling of size effect on the compressive strength of normal concrete with the application of Discrete Element Method (DEM). Test specimens with different size and shape were cast and uniaxial compressive strength test was performed on each sample. Five different concrete mixes were used, all belonging to a different normal strength concrete class (C20/25, C30/37, C35/45, C45/55, and C50/60). The numerical simulations were carried out by using the PFC 5 software, which applies rigid spheres and contacts between them to model the material. DEM modeling of size effect could be advantageous because the development of micro-cracks in the material can be observed and the failure mode can be visualized. The series of experiments were repeated with the model after calibration. The relationship of the parallel bond strength of the contacts and the laboratory compressive strength test was analyzed by aiming to determine a relation between the compressive strength and the bond strength of different sized models. An equation was derived based on Bazant's size effect law to estimate the parallel bond strength of differently sized specimens. The parameters of the equation were optimized based on measurement data using nonlinear least-squares method with SSE (sum of squared errors) objective function. The laboratory test results showed a good agreement with the literature data (compressive strength is decreasing with the increase of the size of the specimen regardless of the shape). The derived estimation models showed strong correlation with the measurement data. The results indicated that the size effect is stronger on concretes with lower strength class due to the higher level of inhomogeneity of the material. It was observed that size effect is more significant on cube specimens than on cylinder samples, which can be caused by the side ratios of the specimens and the size of the purely compressed zone. A limit value for the minimum size of DE model for cubes and cylinder was determined, above which the size effect on compressive strength can be neglected within the investigated size range. The relationship of model size (particle number) and computational time was analyzed and a method to decrease the computational time (number of iterations) of material genesis is proposed.