• 대한기계학회논문집A
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• 제24권6호
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• pp.1565-1574
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• 2000

Surface edge crack subjected to contact stresses is analysed. A punch with corner radii is considered to press the semi-infinite plane. Partial slip problem is solved when a shear force is applied to the punch. Dislocation density function method is used to solve the present mixed mode crack problem. The crack length of positive K1 is examined, which is affected by the ratio of the flat portion to the total width of the punch. Surface traction during one cycle of the shear force is evaluated to simulate the fretting condition. The compliance change of the contact surface is also investigated during the shear cycle. It is found that the crack grows during only a part of the cycle, which may be termed as effective period of crack growing. A design method for restraining the fretting failure is discussed, from which recommendable geometry of the punch is suggested.

• 한국공작기계학회논문집
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• 제14권3호
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• pp.74-80
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• 2005

Steel plates used for common structures are manufactured by rolling processes in general. The rolling direction traces generated during the processes have significant influences on mechanical properties and fatigue behavior of the plates. The objective of present study is to investigate those directional characteristics for the enhancement of steel structure safety. SS400 steel plates of 3 mm thickness are tested in this study, When the angles between the tensile loading direction and the rolling direction of the plates are increased, their yield strengths are increased and elongations are rather decreased. It is also shown that fatigue crack growth rates in the plates can be increased according to the changes of those mechanical characteristics. For the safety of the structures, therefore, it is critical to decrease the angles between the rolling direction and the tensile loading direction.

• 한국정밀공학회지
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• 제21권4호
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• pp.161-169
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• 2004

In this study, we investigated fatigue crack growth behavior of laser welded sheet metal due to a single overload. Fatigue specimens were made using butt joint of cold rolled sheet metal that was welded by $CO_2$ laser. The fatigue crack propagation tests were performed in such a way that fatigue loading was parallel to the weld line while crack propagation was perpendicular to the weld line. Single overload was applied when fatigue crack tip was arrived near the weld line. The distances between the crack tip and the weld line at which a single overload was applied were 6, 4 and 2mm. The effect of specimen thickness and overload ratio on the fatigue behavior was determined. The plastic zone size of crack tip due to the single overload was determined from the finite element analysis. For investigating fatigue crack growth behavior, we used different thickness specimen 0.9mm and 2.0mm, and variable overload ratio applied fatigue crack propagation test. Also we used finite element analysis for investigating the plastic zone size of crack tip when single overload applied

• Advances in materials Research
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• 제8권4호
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• pp.295-311
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• 2019

In this study, a three-dimensional Finite Element Model has been developed to estimate the size of the weakened zone in a bi-material a ceramic bonded to metal. The calculations results were compared to those obtained using Scanning Electron Microscope (SEM). In the case of elastic-plastic behaviour of the structure, it has been shown that the simulation results are coherent with the experimental findings. This indicates that Finite Element modeling allows an accurate prediction and estimation of the weakening effect of residual stresses on the bonding interface of Alumina. The obtained results show us that the three-dimensional numerical simulation used by the Finite Element Method, allows a good prediction of the weakened zone extent of a ceramic, which is bonded with a metal.

• Computers and Concrete
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• 제4권3호
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• pp.221-241
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• 2007

Based on the experiment results, the damage and fracture behavior of concrete at the ages of 1d, 2d, 7d and 28d, in three-point bending and uniaxial tensile tests, were simulated with a finite element program, ABAQUS. The critical stress intensity factor $K_{IC}^s$ and the critical crack tip opening displacement ($CTOD_C$) of concrete were calculated with effective-elastic crack approach for the three-point bending test of grade C30 concrete. Based on the crack band model, a bilinear strain-softening curve was derived to simulate the LOAD-CMOD curves and LOAD-Displacement curves. In numerical analysis of the uniaxial tension test of concrete of grade C40, the damage and fracture mechanics were combined. The smeared cracking model coupling with damaged variable was adopted to evaluate the onset and development of microcracking of uniaxial tensile specimen. The uniaxial tension test was simulated by invoking the damage plastic model which took both damage and plasticity as inner variables with user subroutines. All the numerical simulated results show good agreement with the experimental results.

• Carbon letters
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• 제20권
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• pp.39-46
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• 2016

In this work, the effects of maleic anhydride (MA) content on mechanical properties of chopped carbon fibers (CFs)-reinforced MA-grafted-polypropylene (MAPP) matrix composites. A direct oxyfluorination on CF surfaces was applied to increase the interfacial strength between the CFs and MAPP matrix. The mechanical properties of the CFs/MAPP composites are likely to be different in terms of MA content. Surface characteristics were observed by scanning electron microscope, Fourier transform infrared spectroscopy, and single fiber contact angle method. The mechanical properties of the composites were also measured by a critical stress intensity factor (K_IC). From the K_IC test results, the K_IC values were increased to a maximum value of 3.4 MPa with the 0.1 % of MA in the PP, and then decreased with higher MA content.

• International Journal of Concrete Structures and Materials
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• 제6권1호
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• pp.19-29
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• 2012

In this study, three isolated interior flat slab-column connections that include three types of shear reinforcement details; stirrup, shear stud and shear band were tested under reversed cyclic lateral loading to observe the capacity of slab-column connections. These reinforced joints are 2/3 scale miniatures designed to have identical punching capacities. These experiments showed that the flexural failure mode appears in most specimens while the maximum unbalanced moment and energy absorbing capacity increases effectively, with the exception of an unreinforced standard specimen. Finally, the results of the experiments, as wel l as those of experiments previously carried out by researchers, are applied to the eccentricity shear stress model presented in ACI 318-08. The failure mode is therefore defined in this study by considering the upper limits for punching shear and unbalanced moment. In addition, an intensity factor is proposed for effective widths of slabs that carry an unbalanced moment delivered by bending.

• 한국해양공학회지
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• 제23권5호
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• pp.79-84
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• 2009

Super duplex stainless steel has long life in severe environments by showing the enough strength and corrosion resistance. Therefore, the fracture mechanics approach needs to support the structural strength integrity for the used material. In this study, fatigue crack propagation behavior was investigated to super duplex stainless steel with 0.2% nitrogen. The various volume fraction and distribution of austenite structure for applied specimen in test were obtained by changing the heat treatment temperature and cycle. From test results, fatigue crack propagation rate showed two kinds of tendency between da/dN and ${\Delta}K$ according to distribution of austenite structure and structure anisotropy.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.100-103
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• 2004

In this work, the effects of oxy-fluorination on surface characteristics of carbon fibers were investigated in mechanical interfacial properties of carbon fibers-reinforced composites. The surface properties of the carbon fibers were determined by X-ray photoelectron spectroscopy (XPS), FT-IR. and contact angle measurements. And their mechanical interfacial properties of the composites were studied in interlaminar shear strength (ILSS) and critical stress intensity factor $(K_{IC})$. As experimental results, the $F_{1S}/C_{1S}$ ratio of carbon fiber surfaces was increased by oxy-fluorination, due to the development of the oxygen containing functional groups. The mechanical interfacial properties of the composites, including ILSS and $K_{IC}$, had been improved in the oxy-fluorination on fibers. These results could be explained that the oxy-fluorination was resulted in the increase of the adhesion between fibers and matrix in a composite system.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.265-268
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• 2002

In this work, the blend system of epoxy and PMR-15 polyimide is investigated in terms of the cure behaviors and thermal stabilities. The cure behaviors are studied in DSC measurements and thermal stabilities are also carried out by TGA analysis. DDM (4, 4'-diamino diphenyl methane) is used as curing agent for EP and the content of PMR-15 is varied within 0, 5, 10, 35, and 20 phr to neat EP. As a result, the cure activation energy ($E_a$) is increased at 10 phr of PMR-15, compared with that of neat EP. From the TGA results of EP/PMR-15 blend system, the thermal stabilities based in the initial decomposed temperature (IDT) and integral procedural decomposition temperature (IPDT) are increased with increasing the PMR-15 content. The fracture toughness, measured in the context of critical stress intensity factor ($K_{IC}$) and critical strain energy release rate ($G_{IC}$), shows a similar behavior with $E_a$. This result is probably due to the crosslinking developed by the interactions between intermolecules in the polymer chains.