• Structural Engineering and Mechanics
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• v.64 no.1
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• pp.71-79
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• 2017

In this study, interaction of several interface cracks located between a functionally graded material (FGM) layer and an elastic layer under anti-plane deformation based on the distributed dislocation technique (DDT) is analyzed. The variation of the shear modulus of the functionally graded coating is modeled by an exponential and linear function along the thickness of the layer. The complex Fourier transform is applied to governing equation to derive a system of singular integral equations with Cauchy type kernel. These equations are solved by a numerical method to obtain the stress intensity factors (SIFs) at the crack tips. The effects of non-homogeneity parameters for exponentially and linearly form of shear modulus, the thickness of the layers and the length of crack on the SIFs for several interface cracks are investigated. The results reveal that the magnitude of SIFs decrease with increasing of FG parameter and thickness of FGM layer. The values of SIFs for FGM layer with exponential form is less than the linear form.

• International Journal of Automotive Technology
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• v.6 no.3
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• pp.293-303
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• 2005

Bonded dissimilar materials are being increasingly used in automobiles, aircraft, rolling stocks, electronic devices and engineering structures. Bonded dissimilar materials have several material advantages over homogeneous materials such as high strength, high reliability, light weight and vibration reduction. Due to their increased use it is necessary to understand how these materials behave under stress conditions. One important area is the analysis of the stress intensity factors for interface cracks emanating from circular holes in bonded dissimilar materials. In this study, the bonded scarf joint is selected for analysis using a model which has comprehensive mixed-mode components. The stress intensity factors were determined by using the boundary element method (BEM) on the interface cracks. Variations of scarf angles and crack lengths emanating from a centered circular hole and an edged semicircular hole in the Al/Epoxy bonded scarf joints of dissimilar materials are computed. From these results, the stress intensity factor calculations are verified. In addition, the relationship between scarf angle variation and the effect by crack length and holes are discussed.

• Structural Engineering and Mechanics
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• v.67 no.3
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• pp.277-281
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• 2018

The analytical solution of two functionally graded layers with Volterra type screw dislocation is investigated under anti-plane shear impact loading. The energy dissipation of FGM layers is modeled by viscous damping and the properties of the materials are assumed to change exponentially along the thickness of the layers. In this study, the rate of gradual change ofshear moduli, mass density and damping constant are assumed to be same. At first, the stress fields in the interface of the FGM layers are derived by using a single dislocation. Then, by determining a distributed dislocation density on the crack surface and by using the Fourier and Laplace integral transforms, the problem are reduce to a system ofsingular integral equations with simple Cauchy kernel. The dynamic stress intensity factors are determined by numerical Laplace inversion and the distributed dislocation technique. Finally, various examples are provided to investigate the effects of the geometrical parameters, material properties, viscous damping and cracks configuration on the dynamic fracture behavior of the interacting cracks.

• Archives of Metallurgy and Materials
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• v.66 no.4
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• pp.1049-1054
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• 2021

In this study, stainless steel 316L and Inconel 625 alloy powders were additively manufactured by using directed energy deposition process. And heat treatment effect on hardness and microstructures of the bonded stainless steel 316L/Inconel 625 sample was investigated. The microstructures shows there are no secondary phases and big inclusions near interfacial region between stainless steel 316L and Inconel 625 except several small cracks. The results of TEM and Vickers Hardness show the interfacial area have a few tens of micrometers in thickness. Interestingly, as the heat treatment temperature increases, the cracks in the stainless steel region does not change in morphology while both hardness values of stainless steel 316L and Inconel 625 decrease. These results can be used for designing pipes and valves with surface treatment of Inconel material based on stainless steel 316L material using the directed energy deposition.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1158-1168
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• 1994

For BEM analyses of the impact problems of dissimilar materials, the connected multi-region method using perfect bonded conditions on the interface boundaries was added to two-dimensional Laplace transformed-domain BEM program for a single region analysis. It was confirmed that the BEM results of impact problems of a single-region and multi-regions for a homogeneous isotropic material are agreed well. The two-dimensional Laplace transformed-domain BEM program combined with connected multi-region method was applied to analyse several impact problems of dissimilar materials. Also the feasibility of BEM impact analyses was investigated for dissimilar materials by the analysis of the BEM results for impact problems of dissimilar materials in terms of physical aspects. As for an application, the two-dimensional Laplace transformed BEM concerning impact problems of cracks at the interface of dissimilar materials and the determinating process of the dynamic stress intensity factors by extrapolation method are presented in this paper.

• Journal of Powder Materials
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• v.27 no.3
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• pp.219-225
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• 2020

The directed energy deposition (DED) process of metal 3D printing technologies has been treated as an effective method for welding, repairing, and even 3-dimensional building of machinery parts. In this study, stainless steel 316L (STS316L) and Inconel 625 (IN625) alloy powders are additively manufactured using the DED process, and the microstructure of the fabricated STS316L/IN625 sample is investigated. In particular, there are no secondary phases in the interface between STS316L and the IN625 alloy. The EDS and Vickers hardness results clearly show compositionally and mechanically transient layers a few tens of micrometers in thickness. Interestingly, several cracks are only observed in the STS 316L rather than in the IN625 alloy near the interface. In addition, small-sized voids 200-400 nm in diameter that look like trapped pores are present in both materials. The cracks present near the interface are formed by tensile stress in STS316L caused by the difference in the CTE (coefficient of thermal expansion) between the two materials during the DED process. These results can provide fundamental information for the fabrication of machinery parts that require joining of two materials, such as valves.

• Smart Structures and Systems
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• v.23 no.1
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• pp.81-90
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• 2019

The shear behavior of soil-concrete interface is mainly affected by the surface roughness of the two contact surfaces. The present research emphasizes on investigating the effect of roughness of soil-concrete interface on the interface shear behavior in two-layered laboratory testing samples. In these specially prepared samples, clay silt layer with density of $2027kg/m^3$ was selected to be in contact a concrete layer for simplifying the laboratory testing. The particle size testing and direct shear tests are performed to determine the appropriate particles sizes and their shear strength properties such as cohesion and friction angle. Then, the surface undulations in form of teeth are provided on the surfaces of both concrete and soil layers in different testing carried out on these mixed specimens. The soil-concrete samples are prepared in form of cubes of 10*10*30 cm. in dimension. The undulations (inter-surface roughness) are provided in form of one tooth or two teeth having angles $15^{\circ}$ and $30^{\circ}$, respectively. Several direct shear tests were carried out under four different normal loads of 80, 150, 300 and 500 KPa with a constant displacement rate of 0.02 mm/min. These testing results show that the shear failure mechanism is affected by the tooth number, the roughness angle and the applied normal stress on the sample. The teeth are sheared from the base under low normal load while the oblique cracks may lead to a failure under a higher normal load. As the number of teeth increase the shear strength of the sample also increases. When the tooth roughness angle increases a wider portion of the tooth base will be failed which means the shear strength of the sample is increased.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.389-398
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• 2002

The mixed mode problem (I and II) of a peny-shaped interface cracks in remote tension loading on a bi-material cylinder is studied using finite element method. The energy release rates for the tip of the crack in the interface were calibrated for several different moduli combinations and crack ratios using the modified crack closure integral technique and J-integral method, with numerical results obtained from a commercial finite element program. Numerical results show that non-dimensional value of$\sqrt{G_{II}E^*}/\sqrt[p]{\pi a}$ increases as the crack size or moduli ratio increases. Meanwhile, non-dimensional value of$\sqrt{G_{I}E^*}/\sqrt[p]{\pi a}$ decreases as the moduli ratio increases, but above the moduli ratio of 3 its value decreases then increases again as the crack size increases. Reliability of the numerical analysis in this study was acquired with comparison to an analytical solution for the peny-shaped interface crack in an infinite medium.

• Journal of the Korean Society of Safety
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• v.33 no.2
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• pp.8-13
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• 2018

The light weight composite materials have been replacing in high performance structures. The object of this study is to examine the effects of the initial crack location about a delamination in a PVC foam cored sandwich composite that is used for the strength improvement of structures. The initial crack location and fiber laminates thickness were changed with several types. The MMB specimen was used for evaluating the fracture toughness and crack behaviors. The material used in the experiment is a commercial twill carbon prepreg in CFRP material and Airex in PVC foam core. Sandwich laminate composites are composed by PVC foam core layer between CFRP face sheets. The face sheets were fabricated as 2 types of 5 and 8 plies. The initial cracks were located in a PVC form core and the interface of upper CFRP sheet. From the results, the crack initiation was affected with the location of the initial crack inserted in the PVC foam core. Among them, the initial crack at 1/3 of the upper part of the PVC foam core was the most rapid progression. And the critical energy release rate was $0.40kJ/m^2$, which is the lowest value when the initial crack was inserted into the interface between a PVC foam core and CFRP laminated with 5 plies. Meanwhile, the highest value of $1.27kJ/m^2$ was obtained when the initial crack was located at the center line in case of the 8 plies.

• Composites Research
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• v.32 no.6
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• pp.327-334
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• 2019

The delamination is a special mode of failure occurring in composite laminates. Several numerical studies with finite element analysis have been carried out on the delamination behavior of unidirectional composite laminates. On the other hand, the fracture for the multi-directional composite laminates may occur not only along the resin-fiber interface between plies known as interply or interlaminar fracture but also within a ply known as interyarn or intralaminar fracture accompanied by matrix cracking and fiber bridging. In addition, interlaminar and intralaminar cracks appear at irregular proportions and intralaminar cracks proceeded at arbitrary angle. The probabilistic analysis method for the prediction of crack growth behavior within a layer is more advantageous than the deterministic analysis method. In this paper, we analyze the crack path when the mode I load is applied to the cross-ply carbon/epoxy composite laminates and collect and analyze the probability data to be used as the basis of the probabilistic analysis in the future. Two criteria for the theoretical analysis of the crack growth direction were proposed by analyzing the stress field at the crack tip of orthotropic materials. Using the proposed method, the crack growth directions of the cross-ply carbon/epoxy laminates were analyzed qualitatively and quantitatively and compared with experimental results.