• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 가을 학술발표회 논문집
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• pp.473-479
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• 1996

Until now, we assumed in the time-dependent analysis of concrete structure that tensile creep has same characteristics as compressive creep has. But, in according to results of researches, it appears that tensile creep is different from compressive creep in quantity and in mechanics because tensile creep is affected significantly by micro cracking. The test results indicate that the creep behavior of concrete in compression and tension is rather different. The test data shows that the amount of creep under tensile loading is larger than that under compressive loading. In this paper, a realistic tensile creep model is suggested and incorporated in the formulation. In order to get more accurate results of time-dependent analysis. The present study indicates that the long-term deflection of concrete structures under realistic tensile creep model is somewhat larger than that under ordinary compressive creep model.

• 대한치과교정학회지
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• 제47권4호
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• pp.229-237
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• 2017

Objective: The aim of this study was to compare the initial stability as insertion and removal torque and the clinical applicability of novel orthodontic zirconia micro-implants made using a powder injection molding (PIM) technique with those parameters in conventional titanium micro-implants. Methods: Sixty zirconia and 60 titanium micro-implants of similar design (diameter, 1.6 mm; length, 8.0 mm) were inserted perpendicularly in solid polyurethane foam with varying densities of 20 pounds per cubic foot (pcf), 30 pcf, and 40 pcf. Primary stability was measured as maximum insertion torque (MIT) and maximum removal torque (MRT). To investigate clinical applicability, compressive and tensile forces were recorded at 0.01, 0.02, and 0.03 mm displacement of the implants at angles of $0^{\circ}$, $10^{\circ}$, $20^{\circ}$, $30^{\circ}$, and $40^{\circ}$. The biocompatibility of zirconia micro-implants was assessed via an experimental animal study. Results: There were no statistically significant differences between zirconia micro-implants and titanium alloy implants with regard to MIT, MRT, or the amount of movement in the angulated lateral displacement test. As angulation increased, the mean compressive and tensile forces required to displace both types of micro-implants increased substantially at all distances. The average bone-to-implant contact ratio of prototype zirconia micro-implants was $56.88{\pm}6.72%$. Conclusions: Zirconia micro-implants showed initial stability and clinical applicability for diverse orthodontic treatments comparable to that of titanium micro-implants under compressive and tensile forces.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2007년도 춘계학술대회 논문집
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• pp.641-642
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• 2007

• 한국재료학회지
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• 제27권4호
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• pp.184-191
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• 2017

This present study deals with the effect of micro-alloying elements and transformation temperature on the correlation of microstructure and tensile properties of low-carbon steels with ferrite-pearlite microstructure. Six kinds of low-carbon steel specimens were fabricated by adding micro-alloying elements of Nb, Ti and V, and by varying isothermal transformation temperature. Ferrite grain size of the specimens containing mirco-alloying elements was smaller than that of the Base specimens because of pinning effect by the precipitates of carbonitrides at austenite grain boundaries. The pearlite interlamellar spacing and cementite thickness decreased with decreasing transformation temperature, while the pearlite volume fraction was hardly affected by micro-alloying elements and transformation temperature. The room-temperature tensile test results showed that the yield strength increased mostly with decreasing ferrite grain size and elongation was slightly improved as the ferrite grain size and pearlite interlamellar spacing decreased. All the specimens exhibited a discontinuous yielding behavior and the yield point elongation of the Nb4 and TiNbV specimens containing micro-alloying elements was larger than that of the Base specimens, presumably due to repetitive pinning and release of dislocation by the fine precipitates of carbonitrides.

• 한국구조물진단유지관리공학회 논문집
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• 제19권4호
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• pp.49-56
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• 2015

초고성능 콘크리트는 높은 강도와 유동성을 갖는 우수한 재료 특성을 나타내는 콘크리트이다. 그러나 고연성 시멘트 복합체에 비하여 낮은 연성을 나타낸다. 이 연구에서는 강섬유와 마이크로섬유의 조합이 초고성능 콘크리트의 인장거동에 미치는 영향을 조사하였다. 이를 위하여 강섬유와 폴리에틸렌, 폴리비닐알코올, 현무암섬유 조합에 따라 4가지 초고성능 콘크리트 배합을 결정하였고, 인장거동을 평가하기 위하여 직접인장 실험을 수행하였다. 또한 마이크로섬유가 제조과정에서 의도하지 않은 과도한 기포를 생성하는지를 확인하기 위하여 밀도실험을 수행하였다. 실험결과 인장강도가 높은 폴리에틸렌섬유는 초고성능 콘크리트의 인장거동을 향상시키는데 효과적임을 확인하였고, 현무암섬유는 초고성능 콘크리트의 균열강도 및 인장강도를 증가시키는데 효과적임을 확인하였다. 또한 마이크로섬유가 의도하지 않은 기포를 생성하지 않는다는 것도 확인하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.254-257
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• 2007

In this paper, anisotropic tensile properties of the AZ31B Mg-alloy sheet are obtained with the tensile test at elevated temperatures. Change of microscopic structures and the hardness is inspected after the solution heat treatment process in order to confirm the micro-structural stability of the used sheet metal. Results obtained from tensile tests show that it is very difficult to apply the conventional modeling scheme with the assumption of strain hardening to the forming analysis of the magnesium alloy sheet which shows the strain-softening behavior at the elevated temperature.

• Advances in concrete construction
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• 제13권3호
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• pp.265-279
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• 2022

The roughness of substrate concrete interfaces before new concrete placement has a major effect on the interface bond behaviour. However, there are challenges associated with the consistency of the final roughness interface prepared using conventional roughness preparation methods which influences the interface bond performance. In this study, five quantitative interface roughness textures with different roughness tooth angles, depths, and tooth distribution were created to ensure consistency of interface roughness and to evaluate the bond behaviour at a precast and new concrete interface using the splitting tensile test, slant shear test, and double-shear test. In addition, smooth interface specimens and two separate the pitting interface roughness were also utilized. Obtained results indicate that the quantitative roughness has a very limited effect on the interface tensile bond strength if no extra micro-roughness or bonding agent is added at the interface. The roughness method however causes enhanced shear bond strength at the interface. Increased tooth depth improved both the tensile and shear bond strength of the interfaces, while the tooth distribution mainly influenced the shear bond strength. Major failure modes of the test specimens include interface failure, splitting cracks, and sliding failure, and are influenced by the tooth depth and tooth distribution. Furthermore, the interface properties were obtained and presented while a comparison between the different testing methods, in terms of bond strength, was performed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1104-1110
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• 2003

There are many applications of nanostructures, have been suggested by lots of researchers. It is highly required to measure the properties of nano-sized materials for design and fabrication of the nanostructures. In this paper, several techniques for measuring the mechanical properties of nano-structures are presented laying emphasis on the activity of Nano Property Measurement Team in KIMM. Some advanced applications of nano-indenter are described for measuring elastic, visco-elastic, frictional and adhesive properties as well as the standard methods of it. Micro-tensile test technique with accurate in-plane strain measurement method is also presented and its role in the property measurement of nanostructures is discussed.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 추계학술대회 논문집
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• pp.273-278
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• 1998

In this paper, basic micro-mechanical properties of unidirectional CFRP composite shell such as bonding strength, fiber volume fraction and void fraction are measured and tensile strength test is performed with a fixture. And then fracture surfaces are observed by SEM. In case of basic micro-mechanical properties, bonding strength is reduce with decreasing of radius of each ply in a shell for the effect of residual stress, fiber volume fraction is smaller than plate, and void fraction is vise versa. For these reason, tensile strength of shell is smaller than plate fabricated with same prepreg. For failure mode shell has many splitted part along its length, and it is assumed that this phenomenon is caused by the difference of bonding strength for residual stress.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1696-1701
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• 2007

This paper presents a micro-mechanical model of ductile fracture for the API X65 steel using the Gurson-Tvergaard-Needleman (GTN) model. Experimental tests and FE damage simulations using the GTN model are performed for smooth and notched tensile bars, from which the parameters in the GTN model are calibrated. As application, the developed GTN model is applied to simulate small-sized, single-edge-cracked tensile and bend bars, via three-dimensional FE damage analyses. Comparison of FE damage analysis results with experimental test data shows overall good agreements.