• Elastomers and Composites
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• 제48권1호
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• pp.18-23
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• 2013

용융상태에서 nylon 12 elastomer에 소량의 dicumyl peroxide (DCP) 와 triallyl cyanuate (TAC)를 첨가하여 nylon 12 elastomer를 부분적으로 가교시켰으며, 이에 따른 nylon 12 elastomer의 기계적, 동적기계적 그리고 유변학적 특성을 tensile test, DMA, small amplitude oscillating rheometer를 이용하여 각각 알아보았다. TAC의 함량이 증가함에 따라 인장탄성률과 영률은 증가하고, 파단신율은 감소하였다. DMA 측정결과, DCP로 부분적으로 가교시킨 nylon 12 elastomer의 PTMG상의 유리전이온도는 순수한 nylon 12 elstomer에 비해 증가하였고, storage modulus는 nylon 12상의 용융온도 이상에서도 거의 일정한 값을 나타내었다. 부분적으로 가교시킴에 따른 유변학적 특성의 변화는 TAC의 함량이 증가함에 따라 solid like behavior와 shear thinning behavior가 점점 뚜렷하게 나타남을 알 수 있었다. 이로부터 nylon 12 elastomer를 용융상태에서 부분적으로 가교시킴으로써 용융가공성을 저하시키지 않으면서, 기계적 물성은 효과적으로 향상시킬 수 있었으며, 특히, nylon 12 elastomer의 사용가능 온도범위를 증가시킬 수 있었다.

• Advances in concrete construction
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• 제13권 2호
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• pp.123-132
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• 2022

This paper aims to adapt Multilinear regression (MLR) to predict the strength and toughness of SIFCON containing various pozzolanic materials. Slurry Infiltrated Fibrous Concrete (SIFCON) is one of the most common terms used in concrete manufacturing, known for its benefits such as high ductility, toughness and high ultimate strength. Assessment of compressive strength (CS.), flexural strength (F.S.), splitting tensile strength (STS), dynamic elasticity modulus (DME) and impact energy (I.E.) using the experimental approach is too costly. It is time-consuming, and a slight error can lead to a repeat of the test and, to solve this, alternative methods are used to predict the strength and toughness properties of SIFCON. In the present study, the experimentally investigated SIFCON data about various mix proportions are used to predict the strength and toughness properties using regression analysis-multilinear regression (MLR) models. The input parameters used in regression models are cement, fibre, fly ash, Metakaolin, fine aggregate, blast furnace slag, bottom ash, water-cement ratio, and the strength and toughness properties of SIFCON at 28 days is the output parameter. The models are developed and validated using data obtained from the experimental investigation. The investigations were done on 36 SIFCON mixes, and specimens were cast and tested after 28 days of curing. The MLR model yields correlation between predicted and actual values of the compressive strength (C.S.), flexural strength, splitting tensile strength, dynamic modulus of elasticity and impact energy. R-squared values for the relationship between observed and predicted compressive strength are 0.9548, flexural strength 0.9058, split tensile strength 0.9047, dynamic modulus of elasticity 0.8611 for impact energy 0.8366. This examination shows that the MLR model can predict the strength and toughness properties of SIFCON.

• 대한치과기공학회지
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• 제37권2호
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• pp.57-62
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• 2015

Purpose: This study was performed to investigate mechanical properties of the porous Ti implants according to porosity. Porous Ti implant will be had properties similar to human bone such as microstructure and mechanical properties. Methods: Porous Ti implant samples were fabricated by sintering of spherical Ti powders(below $25{\mu}m$, $25{\sim}32{\mu}m$, $32{\sim}38{\mu}m$, and $38{\sim}45{\mu}m$) in a high vacuum furnace. Specimen's diameter and height were 4mm and 40 mm. Surface and sectional images of porous Ti implants were evaluated by scanning electron microscope(SEM). Porosity and average pore size were evaluated by mercury porosimeter. Young's modulus and tensile strength were evaluated by universal testing machine(UTM). Results: Porosity of Implant was increased according to larger particle size of the powder. Boundary portions of particles are sintered fully and others portions were formed pore. Young's modulus was decreased by formed porous structure. Tensile strength was decreased according to larger the particle size of the powder, but higher than human bone. Conclusion: If prepared by adjust the porosity of the porous Ti implant will be able to resolve the stress shielding phenomenon.

• 터널과지하공간
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• 제6권2호
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• pp.101-121
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• 1996

The thermomechanical characteristics of rocks such as temperature dependency of strength and deformation were experimentally investigated using Iksan granite, Cheonan tonalite and Chung-ju dolomite for proper design and stability analysis of underground structures subjected to temperature changes. For the temperature below critical threshold temperature $T_c$, the variation of uniaxial compressive strength, Young's modulus, Brazilian tensile strength and cohesion with temperature were slightly different for each rock type, but these mechanical properties decreased at the temperatures above $T_c$ by the effect of thermal cracking. Tensile strength was most affected by $T_c$, and uniaxial compressive strength was least affected by $T_c$. To the temperature of 20$0^{\circ}C$ with the confining prressure to 150 kg/$\textrm{cm}^2$, failure limit on principal stress plane and failure envelope on $\sigma$-$\tau$ plane of Iksan granite were continuously lowered with increasing temperature but those of Cheonan tonalite and Chung-ju dolomite showed different characteristics depending on minor principal stress on principal stress plane and normal stress on $\sigma$-$\tau$ plane. The reason for this appeared to be the effect of rock characteristics and confining pressure. Young's modulus was also temperature and pressure dependent, but the variation of Young's modulus was about 10%, which was small compared to the variation of compressive strength. In general, Young's modulus increased with increasing confining pressure and increased or decreased with increasing temperature to 20$0^{\circ}C$ depending on the rock type.

• 지질공학
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• 제26권4호
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• pp.593-600
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• 2016

본 연구에서는 국내의 107개 터널 설계 과정에서 수행한 현장 및 실내시험 자료 4,280개를 이용하여 암반 및 무결암의 역학적 특성을 암종 및 강도별로 분석하였다. 분석된 물리 및 역학적 특성은 단위중량, 점착력, 내부마찰각, 변형계수, 탄성계수, 포아송비, 일축압축강도, 인장강도, 투수계수, 비중이다. 평균값의 분석 결과에 의하면 편마암은 비중, 화강암은 투수계수, 퇴적암은 단위중량과 점착력, 내부마찰각, 화산암은 변형계수와 탄성계수, 일축압축강도, 인장강도, 변성암은 포아송비에서 가장 높은 값을 보인다. 역학적 특성의 분포 범위는 암종 및 강도를 고려한 분석에도 불구하고 넓게 분포하며, 이는 암반의 불균질성과 이방성에 기인하는 것으로 판단된다.

• 대한기계학회논문집A
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• 제34권1호
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• pp.73-78
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• 2010

재료의 인장 물성 측정 불확도 평가가 수행되었다. 인장 물성 측정에 영향을 주는 불확도의 요인이 구분되어 분석되었고 인장 시험으로부터 측정되는 측정량, 즉 탄성계수, 항복 강도 그리고 인장 강도의 불확도 평가 모델이 본 연구에서 제시되었고 각 측정량에 대한 대응하는 수학적 모델과 측정치로부터 각 측정치의 감도계수를 계산함으로서 유도 되었다. 각 모델에 근거하여 ISO 6892에 따라 결정되는 SUS316LN의 실험적 데이터로부터 인장 물성의 불확도가 평가되었다.

• Elastomers and Composites
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• 제30권1호
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• pp.20-31
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• 1995

The purpose of this study is to investigate the reinforcement of inorganic filler silica, treated by MDI about SBR vulcanizate. The characteristics of vulcanization, physical properties, surface properties and dynamic properties were investigated after mixing those silica with SBR and unmodified silica with SBR. In this experiment only the quantity of silica was variable. In the vulcanization characteristics tested by rheometer, S-series showed the fastest scorch $time(t_{10})$ and optimum cure $time(t_{90})$. And in test or tensile characteristics hardness, tensile strength, 100%, 300% modulus and elongation were all appeared in the order of M>S-series. The characteristic bonding of urea between unmodified silica and MDI could be confirmed in IR spectrum. The shapes of silicas treated chemically were observed by SEM. And the dispersion of the filler in the SBR composite was uniform. In the dynamic characteristics by the RDS, the order of elastic modulus G' values was as follows : M>S-series, and also the order of damping values was as follows : M>S-series.

• Advances in Computational Design
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• 제8권1호
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• pp.77-96
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• 2023

Calculating size-dependent mechanical properties of the nano-scale materials usually involves cumbersome numerical and theoretical works. In this paper, we aim to present a closed-form relation to calculate the length-dependent Young's modulus of carbon nanotubes (CNTs) based on nonlocal elasticity theory. In this regard, a single wall carbon nanotube (SWCNT) is considered as a rod structure and the governing nonlocal equations are developed under uniaxial tensile load. The equations are solved using analytical methods and strain distribution, total displacement and the size-dependent equivalent Young's modulus are obtained. Further, the results are compared with the molecular dynamics results from the literature. The outcome indicates that the calculated relations are coincident with the molecular dynamics results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.751-754
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• 2000

Stress relaxation experiments were performed to obtain the material properties to be used in the linear viscoelastic study. Master curve of the modulus of polystyrene were obtained by using the time-temperature superposition principle. Because Shyu and Tobolsky's tensile relaxation modulus master curve or Polystyrene material showed very large difference, in-house data were required to calculate the residual stresses in injection-molded products more accurately. Our own experimental data showed that the master curve Shyu's data should be shifted about two orders in material time coordinate.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.204-207
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• 2004

In this paper, mechanical properties of the high strength lightweight self-compacting concrete with simple mixed design method was investigated. Experimental tests were performed as such compressive strength, splitting tensile strength, modulus of elasticity and density of high strength lightweight self-compacting concrete. The 28 days compressive strength of high strength lightweight self-compacting concrete with the LC replacement ratio of $100\%$ reduces about $31\%$ but LF replacement ratio of $100\%$ increase about $20\%$ compared that of the control concrete. The structural efficiency of high strength lightweight self-compacting concrete increase with proportional to the replacement into of LF. The relationship between the splitting tensile strength and 28 days compressive strength can be represented by the equation $f_s=0.076f_{ck}+0.5582$. The modulus of elasticity was found to be lower than that of normal weight concrete, ranging form 24 to 33 GPa.