• 소성∙가공
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• 제23권4호
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• pp.231-237
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• 2014

In the current study, a rate-dependent crystal plasticity finite element method (CPFEM) was used to simulate flow stress behavior and texture evolution of a body-centered cubic (BCC) crystalline material during plastic deformation at room temperature. To account for crystallographic slip and rotation, a rate-dependent crystal constitutive law with a hardening model was incorporated into an in-house finite element program, CAMPform3D. Microstructural heterogeneity and anisotropy were handled by assigning a crystallographic orientation to each integration point of the element and determining the stiffness matrix of the individual crystal. Uniaxial tensile tests of single crystals with different crystallographic orientations were simulated to determine the material parameters in the hardening model. The texture evolution during four different deformation modes - uniaxial tension, uniaxial compression, channel die compression, and simple shear deformation - was investigated based on the comparison with experimental data available in the literature.

• 대한가정학회지
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• 제35권3호
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• pp.115-124
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• 1997

In this study, Water Repellent Finish was carried out before dyeing on cotton fabrics. It was aimed to improve on dyeing properties of cotton fabrics with direct dye. The results obtained were summerized as follows: 1. The K/S value of water repellent finished cotton fabrics increased. This phenomena in water repellent finished cotton fabrics were much more noticiable than unfinished cotton fabrics. 2. The color fastness(light, washing, and rubbing) of water repellent finished cotton-dyed were worse than those of unfinished cotton-dyed with direct dye. △E of water repellent finished cotton fabrics wasn't showed significant difference as compared with that of unfinished cotton fabrics. 3. The water repellency of finished cotton after dyeing got down from 100 to 70. That of finished-cotton before dyeing was 100. 4. Moisture regain, stiffness and weight of finished cotton fabrics were not almost differenciated with unfinished cotton fabrics. Moreover, the tensile strength of finished cotton fabrics was increased compared to that of unfinished cotton fabrics. As conclusion, according to the above results when the cotton fabrics were dyed with direct dye, it was much more effective that water repellent finished cotton fabrics were dyed rather than trational process, that is pre-dyeing after-finishing even if, by low liquor ratio. The physical properties of fabrics were maintained or increased.

• Earthquakes and Structures
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• 제11권5호
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• pp.887-904
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• 2016

An efficient, economical and practical strengthening method for hollow brick infill walls was proposed and investigated in the present study, experimentally and numerically. This method aims at increasing the overall lateral strength and stiffness of the structure by increasing the contribution of the infill walls and providing the non-bearing components of the structure with the capability of absorbing earthquake-induced energy to minimize structural damage during seismic excitations. A total of eleven full-scale infill walls strengthened with expanded mild steel plates were tested under diagonal monotonic loading to simulate the loading condition of the non-bearing walls during an earthquake. The contact surface between the plates and the wall was increased with the help of plaster. Thickness of the plates bonded to both faces of the wall and the spacing of the bolts were adopted as test parameters. The experiments indicated that the plates were able to carry a major portion of the tensile stresses induced by the diagonal loads and provided the walls walls with a considerable confining effect. The composite action attained by the plates and the wall until yielding of the bolts increased the load capacities, rigidities, ductilities and energy-absorption capacities of the walls, considerably.

• Coupled systems mechanics
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• 제5권4호
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• pp.355-369
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• 2016

Changes in chemical structure have profound effects on the physical properties of epoxy-based materials, and eventually affect the durability of the entire system. Microscopic structural voids generally existing in the epoxy cross-linked networks have a detrimental influence on the epoxy mechanical properties, but the relation remains elusive, which is hindered by the complex structure of epoxy-based materials. In this paper, we investigate the effect of structural voids on the epoxy-based materials by using our developed mesoscale model equipped with the concept of multiscale modeling, and SU-8 photoresist is used as a representative of epoxy-based materials. Developed from the results of full atomistic simulations, the mesoscopic model is validated against experimental measurements, which is suitable to describe the elastic deformation of epoxy-based materials over several orders of magnitude in time- and length scales. After that, a certain quantity of the structure voids is incorporated in the mesoscale model. It is found that the existence of structural voids reduces the tensile stiffness of the mesoscale epoxy network, when compared with the case without any voids in the model. In addition, it is noticed that a certain number of the structural voids have an insignificant effect on the epoxy elastic properties, and the mesoscale model containing structural voids is close to those found in real systems.

• Composites Research
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• 제13권5호
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• pp.18-30
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• 2000

일축방향 섬유강화 복합재료 C링의 최적설계를 위하여, 이의 점 하중 하에서의 점탄성적 하중완화거동을 해석하였다. 이를 위하여 곡선보의 굽힘 이론을 이용하여 탄성학적 처짐과 굽힘 강성의 해석을 수행한 후 상당원리(correspondence theorem)를 이용하여 점탄성학적 하중완화 거동을 해석하였다. 일축방향 섬유강화 복합재료의 직교이방성 뿐만 아니라 복합재료의 인장강성과 압축강성의 차이에서 기인하는 비대칭물성도 함께 고려하였다. 그 결과 C링의 단면의 두께가 반지름에 비해 충분히 작은 보라면 보이론만으로도 정확하게 곡선보를 해석할 수 있고 하중완화 이론값 또한 실험값과 잘 일치하고 있음을 알 수 있었다.

• Composites Research
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• 제27권3호
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• pp.115-121
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• 2014

The effect of addition of gypsum on the rheology, physico-mechanical properties, thermal properties and morphology development of polymer composites based on polyvinyl chloride (PVC) and waste-gypsum with and without methylene-butadiene-styrene (MBS) has been studied. It was shown that the replacement of gypsum for methylene-butadiene-styrene (MBS) component in PVC/gypsum polymer composites enhanced the tensile strength and stiffness of composites, but gradually decreased its impact strength. The observation of morphology, the results of the physico-mechanical properties and thermal properties proved simultaneously that PVC/gypsum composite with the waste-gypsum content of 22.56 wt% reached the optimum results among five kinds of PVC/gypsum polymer composite materials investigated.

• Computers and Concrete
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• 제22권5호
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• pp.461-468
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• 2018

In this paper, to access the suitability of recycled aggregate for structural applications, concrete strength i.e., compressive, tensile and flexural strength were evaluated and compared with those specimens made of natural aggregates. Test results indicated that 30 to 42% of the mentioned strength decreases. To study the performance of frame structures made of recycled aggregate concrete (RAC) two reinforced RAC frames were prepared and tested under monotonic loading. The joint regions of one of the RAC frame were casted with micro-concrete. A reference specimen was also prepared using natural aggregate concrete (NAC) and subjected to a similar loading condition. The RAC frame resulted in a brittle mode of failure as compared to NAC frame. However, the presence of a micro-concrete at the joint region of an RAC frame improved the damage tolerance and load resisting capacity. Seismic parameter such as energy dissipation, ductility and stiffness also improves. Conclusively, strengthening of joint region using micro-concrete is found to have a significant contribution in improving the seismic performance of an RAC frame.

• Steel and Composite Structures
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• 제35권3호
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• pp.371-384
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• 2020

The steel-concrete double composite girder in the negative flexural region combines an additional concrete slab to the steel bottom flange to prevent the local steel buckling, however, the additional concrete slab may lower down the neutral axis of the composite section, which is a sensitive factor to the tensile stress restraint on the concrete deck. This is actually of great importance to the structural rationality and durability, but has not been investigated in detail yet. In this case, a series of 5.5 m-long composite girder specimens were tested by negative bending, among which the bottom slab configuration and the longitudinal reinforcement ratio in the concrete deck were the parameters. Furthermore, an analytical study concerning about the influence of bottom concrete slab thickness on the cracking and sectional bending-carrying capacity were carried out. The test results showed that the additional concrete at the bottom improved the composite sectional bending stiffness and bending-carrying capacity, whereas its effect on the concrete crack distribution was not obvious. According to the analytical study, the additional concrete slab at the bottom with an equivalent thickness to the concrete deck slab may provide the best contributions to the improvements of crack initiation bending moment and the sectional bending-carrying capacity. This can be applied for the design practice.

• 한국해안해양공학회지
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• 제7권3호
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• pp.219-226
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• 1995

본 연구에서는 PVC나 PU와 같은 유연성이 있는 유연막 방파제와 임의의 입사각을 갖는 파의 상호작용문제를 다루었다. 유연막 방파제에 작용하는 파랑하증을 구하기 위하여 고유함수전개법(eigen-function expansion method)을 사용하였다. 이때 유연막의 변형이 유체장에 미치는 영향은 경계조건식으로부터 표현된다. 경계조건식에서 유연막의 변형은 막 방정식을 풀어 구한다. 계산 예로 유연막에 작용하는 장력과 계류삭의 강성계수 그리고 유연막의 높이를 변화시키면서 투과율과 반사율의 차이를 비교하였고, 입사각도의 변화에 따른 방파 효과의 차이를 살펴보았다. 결론적으로 유연막 구조물을 적절히 설계한다면 미래의 훌륭한 방파제로 활용이 가능하다고 여겨진다.

• 한국염색가공학회지
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• 제11권1호
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• pp.34-41
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• 1999

To examine the increase of paper strength by solvent-bonding using N-methylmorpholine N-oxide (NMMO), a paper was treated with aqueous solutions of NMMO, concentrated at $90^\circ{C}$ for selected periods of time, and pressed for 5 seconds followed by washing and drying. The effect of the increasing NMMO concentration on bonding state and some important properties of samples were mainly investigated. With increasing concentration of NMMO, the degree of bonding between fibers was increased, the fiber cross-sectional shape was changed from 'thin ribbonlike' to 'round rodlike' by swelling with solvent, and the longitudinal waves (crimp) were introduced to fibers, hence the shrinkage, weight per unit area, and thickness of paper were increased. Consequently, the tensile strength and elongation, under standard and wet conditions, and the stiffness were increased, and the water absorption was decreased generally with increasing concentration of NMMO. The moisture regain of treated samples was lower than that of the untreated sample, because of the reduction of space between fibers. But the moisture regain was increased a little with increasing concentration of NMMO due to the fiber swelling with NMMO followed by structural relaxation.