• Computers and Concrete
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• 제30권4호
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• pp.289-299
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• 2022

Based on the random cracking theory, the cylinder RVE model of reinforced concrete is established and the damage process is divided into three stages as the evolution of the cracks. The stress distribution along longitude direction of the concrete and the steel bar in the cylinder model are derived. The equivalent elastic modulus of the RVE are derived and the user-defined field variable subroutine (USDFLD) for the equivalent elastic modulus is well integrated into the ABAQUS. Regarding the tensile rebars and the concrete surrounding the rebars as the equivalent homogeneous transversely isotropic material, and the FEM analysis for the reinforced concrete beams is conducted with the USDFLD subroutine. Considering the concrete cracking and interfacial debonding, the macroscopic damage process of the reinforced concrete beam under four-point bending loading in the simulation. The volume fraction of rebar and the cracking degree are mainly discussed to reveal their influence on the macro-performance and they are calibrated with experimental results. Comparing with the bending experiment performed with 8 reinforced concrete beams, the bending stiffness of the second stage and the ultimate load simulated are in good agreement with the experimental values, which verifies the effectiveness and the accuracy of the improved finite element method for reinforced concrete beam.

• Structural Engineering and Mechanics
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• 제90권2호
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• pp.107-116
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• 2024

This study examined the changes in the mechanical properties of coral concrete under different coconut fiber admixtures. To accomplish this goal, the compressive strength, splitting tensile strength, flexural strength and elastic modulus properties of coral concrete blocks reinforced with coconut fibers were measured. The results showed that the addition of coconut fiber had little effect on the cube and axial compressive strengths. With increasing coconut fiber content, the flexural strength and splitting tensile strength of the concrete changed substantially, first by increasing and then by decreasing, with maximum increases of 36.0% and 12.8%, respectively; additionally, the addition of coconut fibers resulted in a failure type with some ductility. When the coconut fiber-reinforced coral concrete was 7 days old, it reached approximately 74% of its maximum strength. The addition of coconut fiber did not affect the early strength of the coral concrete mixed with seawater. When the amount of coconut fiber was no more than 3 kg/m3, the resulting concrete elastic modulus decreased only slightly from that of a similar concrete without coconut fiber, and the maximum decrease was 5.4%. The optimal dose of coconut fiber was 3 kg/m3 in this study.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 가을학술발표대회논문집
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• pp.47-48
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• 2023

Reinforced concrete structures are an integrated structure in which reinforcing bars are placed on the tensile side of the beam to compensate for concrete that is strong in compression but weak in tension, so that the concrete receives compressive force and the reinforcing bars receive tensile force. It is durable, fire-resistant, economical, and adapts to the shape and dimensions of the structure. It has been widely used for a long time because it can be made freely without restrictions. However, reinforced concrete structures have the disadvantage that cracks occur easily, so they are repaired using a cross-sectional construction method. During this process, problems such as the repair part falling off occurred, so in order to solve the problem, stress changes due to changes in the size of the repair part were examined. As a result, based on the elastic modulus ratio of 1.0, the stress tended to increase as the size of the repair part decreased when it was less than 1.0, and the opposite tendency was seen when it was more than 1.0. This is believed to be due to an increase in the area of the part with a large elastic modulus.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 가을 학술발표회 논문집
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• pp.159-163
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• 1995

The purpose of this experimental research is to not only devlop the high-strength concrete using sea and river sand, but also investigatc mechanical properites of the high-strength concrete, such as the elastic modulus, the compressive strength of concrete cyllinder, and etc. Also, rational analytical formula for elastic modulus has been proposed together with those for the splitting tensile strength and the flexural strength to be predicted from compressive strength of conccrete cyllinder.

• Elastomers and Composites
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• 제58권3호
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• pp.128-135
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• 2023

To improve the adhesive strength of natural rubber (NR) for a seismic isolation damper, citraconic acid-g-NR (CCA-g-NR) was synthesized via the melt grafting of citraconic acid (CCA) onto NR using an azobisisnomerobutyronitrile (AIBN) initiator. Subsequently, the influence of CCA and AIBN concentrations on the graft ratio G/R (%) and graft efficiency G/E (%) of the CCA-g-NR was investigated. The optimum CCA and AIBN concentrations required to achieve the desired G/R (3.49%) and G/E (49.8%) were found to be 7 phr and 0.13 phr, respectively. Additionally, we studied the influence of CCA-g-NR concentration on the mechanical properties (tensile strength, elongation at break, and modulus at 300%), adhesive strength, and cure characteristics of the rubber compound in the seismic isolation damper. As the concentration of CCA-g-NR increased, the elongation at break and adhesive strength of the compound increased, whereas its tensile strength and modulus at 300% decreased. Moreover, as the concentration increased, the maximum torque decreased and the scorch time was delayed to obtain an optimal vulcanization time.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1115-1119
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• 2005

The paper proposes the elastic modulus evaluation technique of a cantilever beam by vibration analysis based on time-average electronic speckle pattern interferometry (TA-ESPI) with non-contact and nondestructive and Euler-Bernoulli equation. General approaches for the measurement of elastic modulus of thin film are Nano indentation test, Bulge test and Micro-tensile test and so on. They each have strength and weakness in the preparation of test specimen and the analysis of experimental result. ESPI has been developed as a common measurement method for vibration mode visualization and surface displacement. Whole-field vibration mode shape (surface displacement distribution) at a resonance frequency can be visualized by ESPI. And the maximum surface displacement distribution from ESPI is a clue to find the resonance frequency at each vibration mode shape. And the elastic modules of test material can be easily estimated from the measured resonance frequency and Euler-Bernoulli equation. The TA-ESPI vibration analysis technique is able to give the elastic modulus of materials through the simple processing of preparation and analysis.

• 한국생산제조학회지
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• 제21권4호
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• pp.619-624
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• 2012

In this study, MMT/fiber/polymer composites were fabricated by impregnating chopped strand glass mat into a vinylester resin mixed with clay. Tensile tests has been performed by using a universal testing machine to determine the effect of MMT addition on the tensile properties of MMT/chopped strand glass fiber/vinylester composites. And some pictures which are magnified cross section of breaking parts are has been taken by using a FE-SEM to confirm the behavior at breaking. The contents ratio of MMT applied in the composites were 0.5, 1.0, 1.5, and 2.0 wt% respectively. It has been found that the tensile strength and elastic modulus of MMT/chopped strand glass fiber/vinylester composites were improved at a proper content of MMT. Tensile strength and elastic modulus were maximized at a content of 1.0 wt% due to most effective dispersion of MMT. On the contrary, the failure strain was increased as MMT content was increased.

• Composites Research
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• 제16권3호
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• pp.49-57
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• 2003

본 연구에서는 항공기 구조재로 활용되고 있는 카본/에폭시 복합재료와 기체 외부 열차단용 소재로 추천되고 있는 실리카/페놀 및 카본/페놀 복합재료 2종에 대하여 고온 환경하에서 인장시험을 행하였다. 고온용 스트레인게이지를 응용하여 각각의 복합재료에 대한 온도변화에 따른 인장강도, 탄성계수, 프와송비 같은 기계적 물성치를 도출하였으며, 복합재료 방향성에 따른 기계적 물성 및 인장 거동을 강화재 종류별로 비교 고찰하였다. 본 연구결과를 통하여 획득된 기초자료들은 항공기 구조재 및 열차단용 내열재료를 이용한 복합 구조재의 설계 및 해석에 응용되었다.

• 대한기계학회논문집A
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• 제36권9호
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• pp.1053-1057
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• 2012

본 연구에서는 풍력 발전 블레이드용 재료인 GFRP(Glass fiber-Reinforced Plastic) 복합재의 인장특성의 온도에 따른 의존성을 고찰하였다. 섬유 방향이 $0^{\circ}$와 $0/{\pm}45^{\circ}$로 적층된 두 종류의 복합재로 제작된 인장 시험편으로부터 인장 강도와 탄성계수 그리고 푸아송비에 대한 특성을 상온, $-30^{\circ}C$, $-50^{\circ}C$ 그리고 $60^{\circ}C$에서 측정하였다. 인장 시험으로부터 섬유방향이 축방향으로 적층된 복합재의 인장강도와 탄성 계수는 섬유 적층 방향의 의존성을 보였고 단축으로 적층된 복합재의 강도 및 탄성 계수가 상대적으로 우수함을 보았다. 그리고 시험온도의 의존성도 확인할 수 있었으며, 푸아송비는 온도의 영향이 크지 않음을 확인할 수 있었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표대회 논문집(III)
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• pp.803-808
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• 1998

As carbon fiber is a light-weight materials, high tensile strength and durability compared with rebar, the retrofitting method for RC structures using carbon fiber sheet (CFS) must be use widely. In this paper, the tensile strength test for carbon fiber sheet variable of CF's weight and elastic modulus to evaluate the design tensile strength of carbon fiber sheet which is needed for the strengthening design of CFS and the calculation of strengthening effect. As a result, the design tensile strength of CFS can be calculate using the effect coefficient of strengthening(α) of CFS, the average tensile strength of CFS and the standard deviation of CFS(equation 5)