• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.4
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• pp.929-940
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• 1995

The fatigue strength and fracture topography in the friction welded interface of high speed steel (HSS-Co) to SM55C carbon steel have been investigated through the fatigue test, SEM fractograph and EDS (energy dispersive spectrometer) analysis. Three kinds of specimens used in this research are the friction welded joints, HSS-Co and SM55C carbon steel with circumferential notch, saw notch and smooth, respectively. The notch sensitivity factor, .eta. of the friction welded joints is lower than that of the base materials, and that represents a superiority of the joint performance of FRW. Fracture topography of the FRW specimens with a notch showed a cleavage or brittle appearance, while that of the FRW smooth specimen appeared to be ductile. Furthermore, although fatigue crack likely initiated near the weld interface of the FRW smooth specimen, crack propagation continued into the HAZ of SM55C steel. Finally, fatigue fractures of the base materials were associated primarily with the inclusions located at the outer periphery of the specimen.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.6
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• pp.627-634
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• 2007

A bonded plate or a coated part can be debonded by external impact or thermal expansion. To analyse adhesive strength, the blister test is generally adopted. In this paper, a blister test is modelled theoretically and then the stability and bifurcation of the blister are studied under several different cases. The blister is simplified to consist of a pure bending plate attached elastically to the rigid substrate. Expression of the energy release rate is obtained as a form of an explicit function for a circular-type blister or tunnel-type blister grown by controlling the internal pressure or internal volume. Stability and bifurcation are also studied in the frame of the quasi-static evolution. The study shows that the circular- type blister propagates with the first mode of bifurcation and that the tunnel-type blister propagates with a regular wave. It is proved that the waves have the same form on two side lines of the tunnel and that the wave length can be obtained. When the internal pressure is controlled, the blister is unstable, but when the internal volume is controlled, it is stable.

• Korean Journal of Materials Research
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• v.11 no.12
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• pp.1009-1013
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• 2001

The effects of coupling agent on the interface characteristics between epoxy resin and natural zeolite were studied by SEM, optical microscope and universal testing machine (UTM). Epoxy resin as a matrix was diglycidyl ether of bisphenol A (DGEBA)/4,4'-methylene dianiline (MDA)/malononitrile (MN) system and natural zeolite as an inorganic fillet was produced in Korea. With the increment of zeolite content, tensile strength decreased and it was due to the different elastic moduli of two materials. When external stress was loaded on the composites, the stress concentrated on the weakly bonded interface and crack grew easily. To improve the interface characteristics, the surface of the natural zeolite was treated with the silane coupling agent and it was found that the tensile strength was increased. The morphology of the interface showed that the bonding characteristics were modified by coupling agent.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.8
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• pp.1322-1331
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• 1997

A method of strength evaluation applying fracture mechanics in the adhesively bonded joints of Al/Steel dissimilar materials was investigated in this paper. Various shapes of adhesively bonded Al/Steel scarf joints focussing on fracture criterion of mixed mode crack were prepared for the static tests. Also, stress intensity factors of the interface cracks in adhesively bonded joints of Al/Steel dissimilar materials were analyzed with 2-dimensional elastic program of boundary element method(BEM), and the experiment of fracture toughness were carried out under various mixed mode conditions. From the results, the fracture criterion and method of strength evaluation by the fracture toughness in adhesively bonded joints of Al/Steel dissimilar materials were proposed.

• Journal of Mechanical Science and Technology
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• v.20 no.12
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• pp.2168-2177
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• 2006

The purpose of this investigation was to determine the specific fracture mechanics response of cracks that initiate at the stem-cement interface and propagate into the cement mantle. Two-dimensional finite element models of idealized stem-cement-bone cross-sections from the proximal femur were developed for this study. Two general stem types were considered; Rectangular shape and Charnley type stem designs. The FE results showed that the highest principal stress in the cement mantle for each case occurred in the upper left and lower right regions adjacent to the stem-cement interface. There was also a general decrease in maximum tensile stress with increasing cement mantle thickness for both Rectangular and Charnley-type stem designs. The cement thickness is found to be one of the important fatigue failure parameters which affect the longevity of cemented femoral components, in which the thinner cement was significantly associated with early mechanical failure for shot-time period.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.6
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• pp.884-894
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• 1987

Stress intensity factors for the bimaterial interface cracks are determined by the boundary element method employing the multiregion technique along with the double-point concept. For this purpose, the formulas relating the stress intensity factors to the crack surface displacements, which are applicable to both the homogeneous and the bimaterial systems, are derived and the accuracy of the results is discussed using the preexisting analytic solutions. Besides, the stress intensity factors for the edge-cracked bimaterial plates are computed with various crack lengths and shear modulus ratios under the biaxial and the uniaxial loadings, respectively, to demonstrate the dependence of stress intensity factors on the loading conditions and the material properties.

• Journal of Mechanical Science and Technology
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• v.17 no.11
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• pp.1638-1649
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• 2003

A study is made on the characterization of damage tolerance by spherical indentation in hardly coated layer structure with modest elastic modulus mismatch. A hard silicon nitride is prepared for the coating material and silicon nitride with 5wt% of boron nitride composites for underlayer. Hot pressing to eliminate the effect of interface delamination during the fracture makes strong interfacial bonding. The elastic modulus mismatch between the layers is not only large enough to suppress the surface crack initiation from the coating layer but sufficiently small to prevent the initiation of radial crack from the interface. The strength degradation of the layer structure after sphere contact indentation does not significantly occur, while the degradation of silicon nitride-boron nitride composite is critical at a high load and high number of contacts.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.6
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• pp.898-904
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• 2003

Using the modified Irwin model and the modified Dugdale model, the plastic zone size near the interface crack tip in a ductile layer bonding two dissimilar elastic substrates is predicted. Validity of the models is examined by finite element method. The effects of several factors such as the mode mixity, T-stress and material properties are explored. The plastic zone size significantly decreases with the Poisson's ratio of the ductile layer.

• Journal of Mechanical Science and Technology
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• v.15 no.8
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• pp.1079-1089
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• 2001

This paper proposes J and CTOD estimation schemes applied to fracture toughness testing, covering typical homogeneous and bi-material specimens. Recommendations are based on the plastic limit analysis (either slip line field or finite element limit analyses), assuming the rigid plastic material behavior. The main outcome of the present study is that the J and CTOD estimation schemes (both codified and non-codified), recommended for homogeneous specimens, can be equally used for bi-material specimens with interface cracks. The effect of yield strength mismatch in bi-material specimens on the J-integral CTOD is discussed.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.03a
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• pp.233-238
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• 1998

Recently, the uses of ceramic/metal bonded joints for structural materials have increased in various engineering fields such as automobiles, heat engines, and so on. A method of strength evaluation focussing on fracture criterion of mixed was investigated in Si3N4/metal bonded joint. Also, Fracture toughness tests of Si3N4/metal bonded joints with an interface crack were carried out and the stress intensity factors of these joints were analyzed by boundary element method. From the results, the fracture criterion and method of strength evaluation by the fracture toughness were proposed in Si3N4/metal bonded joints