• Composites Research
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• v.19 no.4
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• pp.15-22
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• 2006

One of the primary factors limiting the application of composite-metal adhesively bonded joints in structural design is the lack of a good evaluation tool for the interfacial strength to predict the load bearing capacity of boned joints. In this paper composite-steel adhesion strength is evaluated in terms of stress intensity factor and fracture toughness of the interface corner. The load bearing capacity of double lap joints, fabricated by co-cured bonding of composite-steel adherends has been determined using fracture mechanical analysis. Bi-material interface comer stress singularity and its order are presented. Finally stress intensities and fracture toughness of the wedge shape bi-material interface corner are determined. Double lap joint failure locus and its mixed mode crack propagation criterion on $K_1-K_{11}$ plane have been developed by tension tests with different bond lengths.

• Journal of the KSME
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• v.31 no.3
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• pp.293-299
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• 1991

단섬유보강 금속복합재료의 2차가공은 금속복합재료의 넓은 범위 응용을 위해 필히 요구된다. 여러 가공방법 중 하나인 열간압출시 보강섬유파괴 및 계면에서의 접합분리 및 균열발생이 없는 제조공정의 최적화를 위해서 가공시 내부조직의 소성변형 기구 규명보다 압출력에 의한 응력분 포와 기지재료와 보강섬유 사이 계면 변화 및 기계적 특성 관계규명이 정량적으로 요구된다. 본 글에서는 유한요소법을 이용하여 계면에서의 접합상태를 임의로 가정하여 압출조건에 따른 압 출후의 보강섬유 방향 및 계면균열 및 접합분리를 거시적으로 예측하고, advanced shear-lag을 이용하여 균열 전, 후의 응력. 변형관계를 미시적으로 규명할 수 있음을 제시하였다. 그러나 향후 현상적 모델인 shear-lag 모델을 수학적 모델인 균질화법에 도입하면 미시적. 거시적 거 동해석이 함께 요구되는 금속복합재료의 열간압출거동 해석을 일체적으로 행할 수 있어 효율적 이고 정확한 예측이 가능하리라고 사료된다.

• The Korean Journal of Rheology
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• v.9 no.2
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• pp.81-87
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• 1997

비상용성 고분자는 그 계면의 특성에 의해서 복잡한 유변학적 거동을 갖는데 그러 한 거동을 해석하기 위해서 최근에 제안된 구성방정식을 토대로 소폭 진동 전단 흐름장에서 의 유변학적 물성과 몰폴로지 전개를 예측한 바 있다. Takahashi[2]등은 이런 흐름하에서의 계면은 거의 변하지 않음을 보여주었고 따라서 이경우는 상대적으로 쉬운편이었다. 본연구 에서는 정상전단흐름장하에서의 몰폴로지 전개에 대한 구성방정식을 간단한 형태로 표현함 으로써 실제 산업계에서 이용될수 있도록 하였다. 그러한 해석을 통하여 원래의 모델에서 제시되었던 3개의 실험변수를 2개로 줄일수 있었으며 계면의 특성을 잘 나타내 주는 새로운 변수($textsc{k}$)를 도입하였다. 계면의 특성을 잘 나타내 주는 이새로운 변수를 통하여 그 계면의 영향을 예측할수 있었다. 한편 분산상의 파괴, 변형, 합체 메카니즘을 모델에 제시되었던 변 수값들을 통하여 해석하였고 이를 실험적인 데이터와 비교해 보았다.

• Journal of the Korean Ceramic Society
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• v.38 no.6
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• pp.575-581
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• 2001

세라믹/금속기지 복합재료에서 횡방향의 단축인장하중을 받는 경우, 복합재료의 특성에 관한 시뮬레이션 결과이다. 세라믹과 금속기지간 계면에 강한 결합이 존재하는 복합재와, 계면에서의 결합이 약한 복합재의 두 경우에 대하여 횡방향 평균응력과 평균변형율에 대한 관계를 계산하였다. 복합재료의 미시역학적개념과 유한요소해석법을 적용하여 세라믹체적분율의 변화에 따라 각기 해석되었다. 본 연구에서 계산된 횡방향 탄성계수는 문헌에 알려져 있는 미시역학개념으로 유도된 식에 의한 횡방향탄성계수값과 잘 일치되었다. 계면에서 강한 결합이 있는 복합재와는 달리, 약한 결합의 복합재는 인장하중에 의하여 세라믹/금속계면에서 금속재료와 세라믹간의 분리가 발생된다. 이 분리는 전체복합재의 강성을 감소시키며, 금속의 부피분율이 감소될수록 (즉, 세라믹의 부피분율이 증가할수록) 횡방향 평균응력의 평균변형율에 대한 감소로 나타났다. 미시역학의 개념을 적용한 유한요소해석기법을 통하여, 이미 알고 있는 복합재 각 성분의 특성으로부터 복합재료의 계면특성과 횡방향특성을 예측할 수 있다.

• Korean Journal of Materials Research
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• v.9 no.10
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• pp.970-977
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• 1999

Effect of Mo interlayer on the relaxation of residual stress in AlN/Cu pint bonded by active-metal brazing method was investigated. The stress analyses by finite-element-method, the measurement of pint strength and the observation of fracture surface were carried out and their results were compared with each other. From the results of stress analysis it is confirmed that a Mo interlayer led to a shift of maximum stress concentration site from AlN/insert-metal interface$\rightarro$ insert-metal/Mo$\rightarro$Mo interlayer. Additionally, with increase of the Mo interlayer thickness the stress concentration with tensile component was separately built both at the interface of Cu/Mo and AlN/Mo. whereby the residual stress in the free surface of AlN close to the bonded interface was drastically reduced. The AlN/Mo/Cu pints with Mo interlayer thickness of above 400$\mu\textrm{m}$ showed the strengths higher than 200 MPa. upto max. 275 MPa, while the AlN/Cu pint only max. 52 MPa.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.773-780
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• 2009

Experiments on steel-concrete interface are performed to investigate and determine the mechanical roles and properties of interface parameters. The intrinsic different nature of bonded and unbonded interfaces are addressed based on the experimental observations that were obtained from two types of tests considering bonded and unbonded interfaces. The unbonded tests are performed for the specimens that are in unbonded when the initially bonded specimens are tested first. Four cases of lateral confinements including pure slip, and low and medium levels of lateral pressure are taken into account to investigate the effects of lateral confinements on interface behavior. It is shown that the maximum shear strengths, the levels of residual strengths and the Mode II fracture energy release rates are linearly related to the confinement levels. Based on the experimental evidences obtained from this study, the values of interface parameters required in a steel-concrete interface constitutive model will be presented in the companion paper.

• Journal of Adhesion and Interface
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• v.9 no.3
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• pp.20-26
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• 2008

It is well know that the structure of shape memory alloy (SMA) can change from martensite austenite by either temperature or stress. Due to their inherent shape recovery properties, SMA fiber can be used such as for stress or cure-monitoring sensor or actuator, during applied stress or temperature. Incomplete superelasticity was observed as the stress hysteresis at stress-strain curve under cyclic loading test and temperature change. Superelasticity behavior was observed for the single-SMA fiber/epoxy composites under cyclic mechanical loading at stress-strain curve. SMA fiber or epoxy embedded SMA fiber composite exhibited the decreased interfacial properties due to the cyclic loading and thus reduced shape memory performance. Rigid epoxy and the changed interfacial adhesion between SMA fiber and epoxy by the surface treatment on SMA fiber exhibited similar incomplete superelastic trend. Epoxy embedded single SMA fiber exhibited the incomplete recovery during cure process by remaining residual heat and thus occurring residual stress in single SMA fiber/epoxy composite.

• Polymer(Korea)
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• v.27 no.3
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• pp.189-194
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• 2003

Interfacial evaluation, damage sensing and cure monitoring of single carbon fiber/thermo setting composite with different curing processes were investigated using electro-micromechanical test. After curing, the residual stress was monitored by measurement of electrical resistance and then compared to various curing processes. In thermal curing case, matrix tensile strength, modulus and interfacial shear strength were higher than those of ultraviolet curing case. The shrinkage measured during thermal curing occurred significantly by matrix shrinkage and residual stress due to the difference in thermal expansion coefficient. The apparent modulus measured in the thermal curing indicated that mechanical and interfacial properties were highly improved. The reaching time to the same stress of thermal curing was faster than that of UV curing case.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.277-284
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• 1993

Interfacial surface crack perpendicular to the surface, which is imbedded into bonded quarter planes under single anti-plane shear load is analyzed. The problem is formulated using Mellin transform, form which single Wiener-Hopf equation is derived. By solving the equation stress intensity factor is obtained in closed form. This solution can be used as a Green's function to generate the solutions of other problems with the same geometry but of different loading conditions.

• Composites Research
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• v.13 no.4
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• pp.67-74
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• 2000

The general solution of the anti-plane shear problem for the curved interfacial crack between viscoelastic foam and composites was investigated with the complex variable displacement function. Kelvin-Maxwell three parameter model is used to present viscoelasticity and the Laplace transform was applied to treat the viscoelastic characteristics of foam in the analysis. The stress intensity factor near the interfacial crack tip was predicted by considering both anisotropic and viscoelastic properties of two different materials. The results showed that the stress intensity factor increased with increasing the curvature of the curved interfacial crack and it also increased and eventually converged to a specific value with increasing time. The stress intensity factor increased with increasing the ratio of stiffness coefficients between foam and composites and the effect of fiber orientation on the stress intensity factor decreased with increasing the ratio of stiffness coefficients between foam and composites.