• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.887-902
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• 1994

Within the framework of anisotropic thermoelasticity, the problem of an interlaminar crack in a laminated fiber-reinforced composite subjected to a uniform heat flow is investigated. Under a state of generalized plane deformation, dissimilar anisotropic half-spaces with different fiber orientations are considered to be bound together by a matrix interlayer containing the crack. The interlayer models the matrix-rich interlaminar region of the fibrous composite laminate. Based on the flexibility/stiffness matrix approach, formulation of the current crack problem results in having to solve two sets of singular integral equations for temperature and thermal stress analyses. Numerical results are obtained, illustrating the parametric effects of laminate stacking sequence, relative crack size, crack location, crack surface partial insulation, and fiber volume fraction on the values of mixed mode thermal stress intensity factors.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.5
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• pp.409-414
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• 2017

In the thin strip coiling process, it is necessary to use a sleeve with a mandrel to prevent excessive deformation of the strip. The stress distribution in the sleeve and strip is an important factor to determine the size of the sleeve. However, an experimental approach is almost impossible because of the accumulation of high pressure. A finite element (FE) model of the strip coiling process was developed in this study. Then, the radial and hoop stresses on the sleeve and strip were investigated using FE analyses. The theoretical values and analysis results under idealized conditions were compared to verify the FE model. The effect of the strip thickness on the stress distribution was also investigated. The radial stress increased by 6.3 times for a 1-mm-thick strip at the coil starting point. The radial stress at the sleeve increased by 14.8 % with a stacked thickness of 90 mm because of the reaction force applied by the mandrel.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.61-68
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• 1999

To analyze several defects and residual stress in sintering of layer structure materials, multiayer materials with TZP/SUS and ZT/SUS, and bilayer materials with porcelain/alumina and porcelain/Y-TZP were fabricated by sintering method. Multilayer materials prepared by pressureless sintering show the sintering defect such as warping, splitting, cracking originated from the difference of sintering shrinkage between each layer, which could be controlled by the adjustment of number and thickness in interlayer. In tape casting, a certain pressure given during sintering relaxed the sintering defects, specially warping. The residual stress in bilayer was examined with Vickers indentation method. A small tensile stress in porcelain/alumina and a large compressive stress in porcelain/Y-TZP were generated on the porcelain interface due to the thermal expansion mismatch, which affected the strength of bilayer materials. As a consequence, the sintering defects of multilayer materials and the residual stresses of bilayer materials were dominantly influenced on material design and starting material constants.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.37-37
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• 2003

탄소-탄소 복합체는 가벼우면서 고온에서도 강도의 저하가 적은 특성을 가지고 있어 터빈 블레이드 소재, 우주왕복선의 내열타일 등 광범위 한 고온재료로 응용이 이루어지고 있거나 기대되는 소재이다. 그러나 고온 산화분위기에서 쉽게 산화되는 단점이 있어 이러 한 산화특성을 향상시키는 방법으로 SiC, Si$_3$N$_4$ 등 내산화 저항성이 우수한 재료를 탄소-탄소 복합체 위에 코팅하는 연구가 행해지고 있다. 하지만 이들 코팅층과 탄소-탄소 복합체간의 열팽창계수 차이에 의한 열응력 발생으로 코팅층에 균열이 발생한다. 따라서 탄소-탄소 복합체와 코팅층간의 열응력을 최소화하여 균열 발생을 억제하기 위해 기능경사재료 (Functionally Graded Material, FGM)를 중간층으로 도입하는 방법이 최근 활발히 연구되고 있다. FGM 중간충의 형성방법 중 화학기상증착법 (CVD)은 증착물의 조성이나 미세구조 조절이 용이한 방법으로 알려져 있어 최근 CVD법에 의한 FGM층의 형성에 많은 연구가 진행되고 있지만, 지금까지 CVD법을 이용한C/SiC FGM 중간충의 형성 연구결과에서는 모든 조성비의 C/SiC층의 증착과 치밀한 구조를 지닌 증착층을 얻기가 어려워 체계적인 연구의 진행이 어려웠다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1349-1353
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• 2003

Previous researches for fiber reinforced composite material(FRCM) have been evaluated the fatigue delamination behavior using the traditional fracture mechanics parameters. Therefore. previous researches for FRCM have not generally been firmed yet. Because delamination growth behavior in FRCM should be consider relationship between delamination area, A$\sub$D/ and crack length, a instead of traditional fracture mechanics parameters. Especially, in case of delamination behavior for FRCM without crack should be considering equivalent crack, i.e., pseudo crack, a$\sub$p/, using the fracture behavior of FRCM with crack. The major purpose of this study was to evaluate the delamination for FRCM without crack. The details of the studies are as follow : 1) Relationship between crack growth rate, da/dN and stress intensity factor, ΔK in FRCM containing a saw-cut and circular hole with crack. 2) Propose of PSEUDO CRACK MODEL for the delamination in FRCM without crack. 3) Analysis of crack propagation energy, E$\sub$crack/ using a total energy, E$\sub$total/ and delamination growth energy, E$\sub$del/.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.1
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• pp.41-51
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• 2006

This paper concerns the effect of lining interface adherence on the lining's load carrying capacity. A series of reduced scale laboratory tests and finite element anlayses were carried out with the aim of gaining insight into the effect of shotcrete lining adherence on the load carrying capacity of double shell lining. The results indicated among other things that the load carrying capacity of a double shell tunnel is significantly affected by the adherence between layers. Also revealed was that for cases with low lining layer adherence stress concentration may occur due to relative movement between the lining layers with this trend being more pronounced with increasing tunnel cover depth. Practical implications from the results of this study are discussed in great detail.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.231-237
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• 2000

A15052/AFRP laminates were developed principally to obtain a material with good fatigue strength, in which possible cracks would grow very slowly. Weight savings of more than 30% should be attainable in practice. Also, the crack bridging fibers could still was carry a significant part of the load over the crack, thus the COD and stress intensity factor was reduced at the crack tip. A15052/ AFRP laminates consists of three thin sheets of 5052-H34 aluminum alloy and two layers of [0] unidirectional aramid fiber prepreg. The cyclic-bending moment test was investigated based on applying the five kinds of bending moments. The size of the delamination zone produced between 5052-H34 aluminum alloy sheets and fiber-adhesive layers was measured from ultrasonic C-scan pictures taken around the fatigue crack. In addition, the relationship between the cyclic-bending moment and the delamination zone size was studied and the effect of fiber bridging mechanism was also considered.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.58-65
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• 2003

The aramid fiber reinforced metal laminates(AFRMLs) used for the wing part fair flight suffer the cyclic bending moment of variable amplitude during service. The fatigue crack propagation and delamination behavior in AFRMLs containing a saw-cut and circular hole was investigated using the average stress criterion(ASC) model. Mechanical tests were carried out using the cyclic bending moment of 4.9 N . m and delamination was observed by ultrasonic C-scan images. In case of AFRMLs containing a saw-cut fatigue crack propagated in aluminum matrix, inducing delamination. However, in case of AFRMLs containing a circular hole, delamination formed with two types under cyclic bending moment of 4.9 N . m. First, delamination formed along the fatigue crack in aluminum matrix. Second, delamination formed without any fatigue crack around the circular hole. Therefore, delamination was formed depending on the stress distribution near the circular hole.

• Composites Research
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• v.18 no.1
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• pp.30-37
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• 2005

The bending strength characteristics and local deformation behaviors of honeycomb sandwich composites were investigated using three-point bending experiment and finite element simulation with a real model of honeycomb core. Two kinds of cell sizes of honeycomb core, two kinds of skin layer thicknesses, perfect bonding specimen as well as initial delamination specimen were used for analysis of stress and deformation behaviors of honeycomb sandwich beams. Various failure modes such as skin layer yielding, interfacial delamination, core shear deformation and local buckling were considered. Its simulation results were very comparable to the experimental ones. Consequently, cell size of honeycomb core and skin layer thickness had dominant effects on the bending strength and deformation behaviors of honeycomb sandwich composites. Specimens of large core cell size and thin skin layer showed that bending strength decreased by $30\~68\%$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.3
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• pp.281-288
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• 2004

The hybrid composite material (Al/GFRP laminates) are applied to the fuselage and wing in a aircraft. Therefore, Al/GFRP laminates suffer from the cyclic bending moments. This study was to evaluate the effect of fiber stacking angle on the fatigue crack propagation and delamination behavior using the relationship between crack growth rate (da/dN) and stress intensity factor range (ΔK) in Al/GFRP laminates under cyclic bending moment. The variable delamination growth behavior in case of three different type of fiber orientations, i.e., [Al/O$_2$/Al], [Al/+45$_2$/Al] and [Al/90$_2$/Al] at the interface of Al layer and glass fiber layer was measured by ultrasonic C-scan images. As results of this study, It represent that the delamination shape should turns out to have more effective characteristics on the fiber stacking angle. The extension of the delamination zone in case of [Al/+45$_2$/Al] and [Al/90$_2$/Al] were not formed along the fatigue crack profile. The shape of delamination zone depend on fiber stacking angle and the variable type with the delamination contour decreased non-linearly toward the crack tip at the Al layer.