• Computers and Concrete
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• 제7권2호
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• pp.169-190
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• 2010

The focus of this research effort was characterization of the flexural and tensile properties of a specific ultra-high-strength, fiber-reinforced concrete material. The material exhibited a mean unconfined compressive strength of approximately 140 MPa and was reinforced with short, randomly distributed alkali resistant glass fibers. As a part of the study, coupled experimental, analytical and numerical investigations were performed. Flexural and direct tension tests were first conducted to experimentally characterize material behavior. Following experimentation, a micromechanically-based analytical model was utilized to calculate the material's tensile failure response, which was compared to the experimental results. Lastly, to investigate the relationship between the tensile failure and flexural response, a numerical analysis of the flexural experiments was performed utilizing the experimentally developed tensile failure function. Results of the experimental, analytical and numerical investigations are presented herein.

• 터널과지하공간
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• 제18권3호
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• pp.194-201
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• 2008

횡등방성 암석의 인장강도 특성 해석을 위하여 새로운 이방성 인장파괴함수를 제안하였다. 제안된 함수에서 인장강도는 연약면과 수직한 방향에서 최소가 되며 연약면과 평행한 방향쪽으로 지수함수적으로 증가하면서 최대값에 수렴된다. 제안된 이방성 인장파괴함수는 실험적으로 측정이 가능한 3개의 강도정수로 정의된다. 제안된 함수를 임계면법에 적용하여 연약면의 방향성에 따른 횡등방성 암석의 인장강도 및 파괴면의 방향을 탐색할 수 있는 수치해석적 기법을 제시하였다. 문헌에 보고된 횡등방성 암석의 직접인장시험 결과를 모사함으로써 제안된 방법의 적합성을 검토하였다. 수치해석결과와 직접인장시험 결과는 전반적으로 유사한 결과를 보여주었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.310-315
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• 2003

This paper presents the effect of boundary condition of failure pressure model for buried pipelines on failure prediction by using a failure probability model. The first order Taylor series expansion of the limit state function is used in order to estimate the probability of failure associated with various corrosion defects for long exposure periods in years. A failure pressure model based on a failure function composed of failure pressure and operation pressure is adopted for the assessment of pipeline failure. The effects of random variables such as defect depth, pipe diameter, defect length, fluid pressure, corrosion rate, material yield stress, material ultimate tensile strength and pipe thickness on the failure probability of the buried pipelines are systematically studied by using a failure probability model for the corrosion pipeline.

• 펄프종이기술
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• 제31권5호
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• pp.57-72
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• 1999

Traditional theories of the tensile failure of paper have assumed that uniform strain progresses throughout the sheet until an imperfection within the structure causes a catastrophic break. The resistance to tensile elongation is assumed to be elastic , at first, throughout the structure, followed by an overall plastic yield. However, linear image strain analysis (LISA) has demonstrated that the yield in tensile loading of paper is quite non-uniform throughout the structure, Traditional theories have failed to define the flaws that trigger catastrophic failure. It was assumed that a shive or perhaps a low basis weight area filled that role. Studies of the fracture mechanics of paper have typically utilized a well-defined flaw around which yield and failure could be examined . The flaw was a simple razor cut normal to the direction of tensile loading. Such testing is labeled mode I analysis. The included fla in the paper was always normal to the tensile loading direction, never at another orientation . However, shives or low basis weight zones are likely to be at random angular orientations in the sheet. The effects of angular flaws within the tensile test were examined. The strain energy density theory and experimental work demonstrate the change in crack propagation from mode I to mode IIas the initial flaw angle of crack propagation as a function of the initial flaw angle is predicted and experimentally demonstrated.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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• pp.603-610
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• 2003

The influence of Poisson's ratio on the tensile strength of brittle materials is neglected in many studies. When brittle materials are loaded in compression or impact, substantial tensile stresses are induced within the materials. These tensile stresses are responsible for splitting failure of the materials. In this paper, the state of stress in a spherical particle due to two diametrically opposed forces is analyzed theoretically. A simple equation for the state of stress at the center of the particle is obtained. An analysis of the distribution of stresses along the z-axis due to distributed pressures and concentrated forces, and on diametrically horizontal plane due to concentrated forces, shows that it is reasonable to propose the tensile stress at the center of the particle at the point of failure as a tensile strength of the particle. Moreover, the tensile strength is a function of the Poisson's ratio of the material. As the state of stress along the z-axis in an irregular specimen tends to be similar to that in a spherical particle compressed diametrically with the same force, this tensile strength has some validity for irregular particles as well. Therefore, it can be proposed as the tensile strength for brittle materials generally. The effect of Poisson's ratio on the tensile strength is discussed.

• 구강회복응용과학지
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• 제16권1호
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• pp.27-36
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• 2000

One of the methods to improve the softness and comfortness of denture base is the use of soft denture liners. In this study, specimens were made by 2 kinds of acrylic based soft lining materials and 2 kinds of silicone based soft lining materials, and bonded to acrylic resin(Lucitone $199^{(R)}$). Then they were tested the differences of tensile bond strengths according to the materials, thickness, surface treatment and failure mode. 1. Tensile bond strength according to soft lining materials was increased in order of Coe-$soft^{(R)}$, $Mollosil^{(R)}$, $Trusoft^{(R)}$, Ufi-Gel $C^{(R)}$. The differences between groups were statistically significant at level of 0.05. 2. Tensile bond strength according to thickness of soft lining materials was increased in order of 3mm, 2mm, 1mm. The differences between groups were not statistically significant. 3. Tensile bond strength of treated surface showed higher bond strength than nontreated surface. The difference between groups was not statistically significant. 4. The failure mode of Coe-$soft^{(R)}$, $Trusoft^{(R)}$, $Mollosil^{(R)}$ were mainly cohesive failure, and that of Ufi-Gel $C^{(R)}$ were mainly adhesive failure.

• 한국공작기계학회논문집
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• 제14권1호
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• pp.30-36
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• 2005

This study is to investigate a damage estimation of single edge notched tensile specimens as a function of acoustic emission(AE) according to the uni-directionally oriented carbon fiber/epoxy composites, CFRP In fiber reinforced composite materials, AE signals due to several types of failure mechanisms are typically observed. These are due to fiber breakage, fiber pull-out matrix cracking, delamination, and splitting or fiber bundle breaking. And these are usually discriminated on the basis of amplitude distribution, event counts, and energy related parameters. In this case, AE signals were analyzed and classified 3 regions by AE event counts, energy and amplitude for corresponding applied load. Bath-tub curve shows 3 distinct periods during the lifetime of a single-edge-notch(SEN) specimen. The characterization of AE generated from CFRP during SEN tensile test is becoming an useful tool f3r the prediction of damage failure or/and failure mode analysis.

• Structural Engineering and Mechanics
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• 제36권4호
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• pp.447-461
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• 2010

Fiber reinforced polymer (FRP) bars have been widely used as reinforcement for concrete structures. However, under elevated temperatures, the difference between the transverse coefficients of thermal expansion of FRP rebars and concrete may cause the splitting cracks of the concrete cover. As a result, the bonding of FRP-reinforced concrete may not sustain its function to transfer load between the FRP rebar and the surrounding concrete. The current study investigates the cracking resistance of FRP reinforced concrete against the thermal expansion based on a mechanical model that accounts for the tensile softening behavior of concrete. To evaluate the efficacy of the proposed model, the critical temperature increments at which the splitting failure of the concrete cover occurs and the internal crack radii estimated are compared with the results obtained from the previous studies. Simplified equations for estimating the critical temperature increments and the minimum concrete cover required to prevent concrete splitting failure for a designated temperature increment are also derived for design purpose.

• International Journal of Precision Engineering and Manufacturing
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• 제4권6호
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• pp.12-19
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• 2003

This paper presents the effect of boundary conditions in various failure pressure models published for the estimation of failure pressure. Furthermore, this approach is extended to the failure prediction with the aid of a failure probability model. The first order Taylor series expansion of the limit state function is used in order to estimate the probability of failure associated with each corrosion defect in buried pipelines for long exposure period with unit of years. A failure probability model based on the von-Mises failure criterion is adapted. The log-normal and standard normal probability functions for varying random variables are adapted. The effects of random variables such as defect depth, pipe diameter, defect length, fluid pressure, corrosion rate, material yield stress, material ultimate tensile strength and pipe thickness on the failure probability of the buried pipelines are systematically investigated for the corrosion pipeline by using an adapted failure probability model and varying failure pressure model.

• 한국해안해양공학회지
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• 제16권3호
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• pp.142-151
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• 2004

수리학적 안정성과 구조적 안정성을 동시에 만족시키면서 피복재의 중량을 산정할 수 있는 방법이 수립되었다. 수리학적 안정성은 Hudson의 경험식을 이용하여, 구조적 안정성은 충격하중 작용시 피복재 내부에 발생되는 최대인장응력을 산정, 피복재의 인장 저항력과 비교하는 개념으로 해석되었다. 이와 같이 산정된 수리학적 안정성과 구조적 안정성에 대한 적용한계를 재현기간별 설계 유의파고, 피복재의 중량, 그리고 인장 저항력의 함수로 제시하여 실무자들이 쉽게 사용할 수 있도록 하였다. 또한 결정론적 산정법의 불확실성을 고려하기 위하여 수리학적 안정성과 구조적 안정성에 대한 신뢰성 해석이 추가로 수행되었다. 두 파괴모드를 하나의 직렬계로 구성하여, 신뢰성설계법에서 이용되는 목표파괴확률을 가지고 단면파괴율의 함수로 피복재의 최적중량을 산정할 수 있었다.