• Computers and Concrete
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• 제4권3호
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• pp.207-220
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• 2007

In this paper, hybrid fibers including high elastic modulus steel fiber and low elastic modulus synthetic macro-fiber (HPP) as two elements were used as reinforcement materials in concrete. The flexural toughness, flexural impact and fracture performance of the composites were investigated systematically. Flexural impact strength was analyzed with statistic analyses method; based on ASTM and JSCE method, an improved flexural toughness evaluating method suitable for concrete with synthetic macro-fiber was proposed herein. The experimental results showed that when the total fiber volume fractions ($V_f^a$) were kept as a constant ($V_f^a=1.5%$), compared with single type of steel or HPP fibers, hybrid fibers can significantly improve the toughness, flexural impact life and fracture properties of concrete. Relative residual strength RSI', impact ductile index ${\lambda}$ and fracture energy $G_F$ of concrete combined with hybrid fibers were respectively 66-80%, 5-12 and 121-137 N/m, which indicated that the synergistic effects (or combined effects) between steel fiber and synthetic macro-fiber were good.

• Composites Research
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• 제12권1호
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• pp.68-75
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• 1999

본 연구에서는 저속 충격에서 충격 속도에 따른 금속복합재료의 동적 거동을 연구하였다. 시험에 사용된 재료는 모재로 AC8A와 보강재로 알루미나($Al_2O_3$)와 탄소를 사용하였으며 용탕 주조법을 이용하여 금속복합재료를 제조하였다. 금속복합재료에는 15%의 부피분율을 가진 알루미나 예비성형체와 알루미나와 탄소를 각각 12%와 3% 사용한 혼합 에비성형체가 사용되었다. 제조된 금속복합재료는 인장 시험과 진동 시험을 통해 인장 강도와 탄성계수를 구하였으며, 저주파 여파기(low pass filter)와 계장화 충격 시험기를 이용하여 충격 속도에 따른 금속복합재료의 충격 거동을 연구하였다. 저주파 여파기를 이용함으로써 충격 속도에 관계없이 안정적인 실험치를 확보할 수 있었다. 충격 속도의 증가에 따라 모재와 금속복합재료의 충격에너지는 증가하였으나, 동적인성치는 일정한 값을 보였다. 충격 속도가 증가할수록 충격에너지 중 균열전파에너지의 향상이 두드러졌으며, 재료의 변형량이 증가하였다. 충격에너지 중 균열개시에너지와 동적파괴인성치의 관계를 설명하기 위하여 변형율 에너지와 노치에서의 응력 분포를 이용하여 간단한 모델을 제시하였으며, 이로부터 균열개시에너지는 동적 파괴 인성치의 자승에 비례하고 탄성계수에 반비례하는 것을 보였다.

• 한국전문물리치료학회지
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• 제23권3호
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• pp.29-39
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• 2016

Background: In the treatment of temporomandibular joint (TMJ) disorder, the goals of traditional physical therapy are not only to reduce the inflammatory process leading to pain, but also to decrease joint overload and muscle hyperactivity. To achieve those goals, physical therapists generally use a photo-therapy, joint mobilization, and massage. Objects: To examine the impact of an unloading technique using non-elastic taping on the pain, opening mouth, functional level, and quality of life in patients with TMJ disorder. Method: Twenty patients with TMJ disorder were included in this study and randomly divided into the experimental ($n_1$=10), and control ($n_2$=10) groups. Traditional physical therapy including massage and stretching for 30 min was performed in both groups. Non-elastic taping was performed in the experimental group after traditional physical therapy, and they were recommended to keep the tape attached for 12 hours. Outcomes for pain, functional level, and quality of life were measured using a survey. The opening mouth was measured using a general ruler. Result: Significant differences were observed in the pain level, opening mouth, functional level, and quality of life after the intervention and on follow-up in both groups. However, we found that while the levels of all parameters were maintained throughout the follow-up period in the experimental group, the functional status level was not maintained throughout the follow-up period in the control group. Conclusion: Our unloading technique using non-elastic tape results comparable to those achieved by traditional physical therapy in the treatment of TMJ. However, the unloading taping method using non-elastic tape is more effective than traditional physical therapy in maintaining the impact of intervention.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 추계학술대회 논문집 전기물성,응용부문
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• pp.128-130
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• 2003

As toughness-investigation to improve brittleness of existing epoxy resin, elastic-factor of elastic epoxy using TMA (Thermomechanical Analysis), DMTA (Dynamic Mechanical Thermal Analysis) and FESEM (Field Emission Scanning Electron Microsope) for structure-images analysis were investigated. A range of measurement temperature of the TMA, DMTA was changed from -20[$^{\circ}C$] to 200[$^{\circ}C$]. When modifier was ratio of 0[phr], 20[phr], 35[phr], glass transition temperature (Tg) of elastic epoxy was measured through thermal analysis devices. Also, it was investigated thermal expansion coefficient ($\alpha$), modulus and loss factor through DMTA. In addition, it was analyzed structure through FSSEM and made sure elastic-factor of elastic epoxy visually. As thermal analysis results, 20[phr] was superior than 30[phr] thermally and mechanically. Specially, thermal expansion coefficient, modulus, damping properties were excellent. By structure-images analysis through FESEM, we found elastic-factor of elastic epoxy that is not existing epoxy, and proved high impact.

• Structural Engineering and Mechanics
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• 제26권5호
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• pp.499-516
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• 2007

An experimental method denoted as Impulse Method is proposed as a cost-effective non-destructive technique for the on-site evaluation of concrete elastic modulus in existing structures: on the basis of Hertz's quasi-static theory of elastic impact and with the aid of a simple portable testing equipment, it makes it possible to collect series of local measurements of the elastic modulus in an easy way and in a very short time. A Hypothesis Testing procedure is developed in order to provide a statistical tool for processing the data collected by means of the Impulse Method and assessing the possible occurrence of significant variations in the elastic modulus without exceeding some prescribed error probabilities. It is based on a particular formulation of the renowned sequential probability ratio test and reveals to be optimal with respect to the error probabilities and the required number of observations, thus further improving the time-effectiveness of the Impulse Method. The results of an experimental investigation on different types of plain concrete prove the validity of the Impulse Method in estimating the unknown value of the elastic modulus and attest the effectiveness of the proposed Hypothesis Testing procedure in identifying significant variations in the elastic modulus.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2011년도 춘계학술대회 논문집
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• pp.1237-1238
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• 2011

• 한국산학기술학회논문지
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• 제6권6호
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• pp.542-546
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• 2005

연성 크랙의 발생 평가를 위한 J-적분이 충격 하중을 받는 탄소성 3점 굽힘 시험편들에 대하여 연구한다. J-적분을 측정하고 평가하는 실험적인 방법이 연구되었으며 이 결과가 유한 요소법을 이용한 탄소성 이론 해석을 한 값들과 비교하여 거의 일치함을 보였다. 이론적인 수치 해석으로서도 본 연구의 유한 요소 모델로서 J-적분값을 계산할 수 있으며 삼점 굽힘 시험편의 동적 비선형 파괴 실험에 있어서 크랙 입구 개구 변위 (CMOD)에 의하여 J-적분값의 단순 계산이 가능함을 입증하였다. 탄소성 재료의 특성이 여러 가지의 충격 속도들에서 고려된다. J-적분은 충격 실험 동안 얻어진 사진들로부터 직접적으로 측정된 크랙 입구 개구 변위로부터 예측될 수 있다.

• 대한기계학회논문집
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• 제16권9호
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• pp.1615-1626
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• 1992

본 연구에서는 배플이 없는 사각단면을 가진 양단자유의 탄성보에 강구가 횡 방향으로 충돌할 때 발생되는 음압을 M.Sakata와 M.Horii의 방법을 적용하여 구하였으 며, 보의 가속도는 모우드 해석기법을 적용하여 구하였다. 그리고 충돌시 발생되는 충격격과 접촉시간은 허즈(Hertz)접촉이론을 이용하였다.그리고 실험을 통하여 이 론으로 구한보의 가속도, 접촉시간, 방사음압의 결과와 비교하였다. 기존의 연구내 용을 기반으로한 본 논문의 기여부분은 hertz 접촉이론을 본 연구의 시스템에 적용하 여 접촉시간을 실험적으로 검증하였으며 모우드 해석기법을 이용하여 구한 보의 진동 을 실험과 비교하였고, 시스템을 탄성보로하여 M.Sakata의 방법을 적용하여 발생되는 음압을 실험으로 검증한 것이다.

• KIEE International Transactions on Electrophysics and Applications
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• 제4C권5호
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• pp.230-235
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• 2004

In this paper, epoxy elasticity factors were investigated by TMA (Thermomechanical Analysis), DMTA (Dynamic Mechanical Thermal Analysis) and FESEM (Field Emission Scanning Electron Microscope) to improve toughness and reduce brittleness of existing epoxy resin. Dumbbell shaped specimens were made and tested at rates of 0, 20 and 35phr (part per hundred resins). TMA temperatures ranged from -2$0^{\circ}C$ to 20$0^{\circ}C$. Tg (glass transition temperature) of elastic epoxy was measured by thermal analysis. Also investigated were thermal expansion coefficient ($\alpha$), modulus and Tan$\delta$ (loss factor). And we analyzed structure through FESEM, could find elastic-factors of elastic epoxy that is not existing-epoxy. In addition, we measured permittivity and Tan$\delta$ for investigation of the electrical properties of elastic epoxy. Permittivity and Tan$\delta$ depend on elastomer composition. Namely, permittivity and Tan$\delta$ increase according to the elastomer contents. For experimental analysis results, 20phr was considered an excellent specimen.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.33-40
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• 2005

Impact-echo test, a kind of simple and economical method to evaluate the integrity of drilled piles has some limitations to use because the stress wave can be generated only on the head of a pile and the wave propagation in the pile with surrounding soils are very complicated. Numerical analyses and model tests in the laboratory have shown that both the ratio of length to diameter of a pile and the stiffness ratio of pile to soil have influence on the resolution of testing results. Full scale testing piles which have artificial defects were used to verify the capability of impact-echo technique as a tool for the pile integrity evaluation. Behaviour of the reflected signal of stress wave was investigated according to the type of defects. Elastic modulus of the pile was calculated using the wave velocity in the pile and the unconfined strength of concrete specimen. Influences of the stiffness difference between the pile and the ground on the characteristics of a wave signal were also examined.