• Journal of Advanced Marine Engineering and Technology
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• v.23 no.4
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• pp.488-503
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• 1999

The present paper considers the constraint effect on J-R curves under the two-parameter $J-A_2$ controlled crack growth within a certain amount of crack extension. Since the parameter $A_2$ in $J-A_2$ three-term solution is independent of applied loading under fully plasticity or large-scale defor-mation $A_2$ is a proper constraint parameter uring crack extension. Both J and $A_2$ are used to char-acterize the resistance curves of ductile crack growth using J as the loading level and $A_2$ are used to char-acterize the resistance curves of ductile crack growth using J as the loading level and A2 as a con-straint parameter. Approach of the constraint-corrected J-R curve is proposed and a procedure of transferring the J-R curves determined from standard ASTM procedure to non-standard speci-mens or real cracked structures is outlined. The test data(e.g. initiation toughness JIC and tearing modulus $T_R$) of Joyce and Link(Engineer-ing Fracture Mechanics 1997, 57(4) : 431-446) for single-edge notched bend[SENB] specimen with from shallow to deep cracks is employed to demonstrate the efficiency of the present approach. The variation of $J_{IC}$ and $T_R$ with the constraint parameter $A_2$ is obtained and a con-straint-corrected J-R curves is constructed for the test material of HY80 steel. Comparisons show that the predicted J-R curves can very well match with the experimental data for both deep and shallow cracked specimens over a reasonably large amount of crack extension. Finally the present constraint-corrected J-R curve is used to predict the crack growth resistance curves for different fracture specimens. over a reasonably large amount of crack extension. Finally the present constraint-corrected J-R curve is used to predict the crack growth resistance curves for different fracture specimens. The constraint effects of specimen types and specimen sizes on the J-R curves can be easily obtained from the constrain-corrected J-R curves.

• Journal of the Korean Ceramic Society
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• v.29 no.12
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• pp.949-955
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• 1992

R-curves, fracture resistance (KR) as a function of crack extension (Δa), of a gas-pressure sintered monolithic Si3N4 were determined by controlled flaw/strength technique. Rising R-curve behavior was observed, confirming the operation of microstructural toughening process during crack growth. The R-curve parameters, k and m in the equation, KR=k(Δa)m, were determined to 30.301 and 0.1146, respectively. Microstructural observation of growing crack revealed that the bridging in the crack wake by unbroken ligament of large elongated ${\beta}$-grains was the mechanism primarily for the rising R-curve behavior.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.3
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• pp.311-320
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• 2014

High strength concrete is not only vulnerable to the occurrence of spalling which generates the loss of cross-section in concrete structures but produces faster degradation in its mechanical properties than normal strength concrete in the event of fire. This study aims to evaluate fire resistance of high strength segment concrete with PET fibers mixed to prevent spalling under ISO834 (2hr) and RABT fire curve. As results, the samples without PET fibers show the concrete loss up to the depth of about 8 cm and 9.5 cm from the surface exposed to fire under ISO834 and RABT fire curve respectively. The samples mixed with PET fiber of 0.1% show no spalling under ISO834 fire curve and the spalled thickness of 6.5 cm under RABT fire curve after the fire tests. Finally, the sample mixed with PET fiber of 0.2% shows no spalling under RABT fire curve. The results indicate that the suitable amounts of PET fiber for securing fire resistance performance of this high strength segment concrete are 0.1% under ISO834 fire curve and 0.2% under RABT fire curve. However, even though spalling does not occur, it is necessary to repair the deterioration of concrete up to 4 cm from the surface exposed to fire after fire.

• Geomechanics and Engineering
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• v.12 no.3
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• pp.399-415
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• 2017

A series of direct shear tests were conducted to investigate the frictional properties of the interface between structures and the filling soil of Chongqing airport fourth stage expansion project. Two types of structures are investigated, one is low carbon steel and the other is the bedrock sampled from the site. The influence of soil water content, surface roughness and material types of structure were analyzed. The tests show that the interface friction and shear displacement curve has no softening stage and the curve shape is close to the Clough-Duncan hyperbola, while the soil is mainly shear contraction during testing. The interface frictional resistance and normal stress curve meets the Mohr-Coulomb criterion and the derived friction angle and frictional resistance of interface increase as surface roughness increases but is always lower than the internal friction angle and shear strength of soil respectively. When surface roughness is much larger than soil grain size, soil-structure interface is nearly shear surface in soil. In addition to the geometry of structural surface, the material types of structure also affects the performance of soil-structure interface. The wet interface frictional resistance will become lower than the natural one under specific conditions.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1993.10a
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• pp.1095-1101
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• 1993

This paper discussed the action on soil of two-sided wedge in high speed curve movement, with the emphasis on the deformation of soil and its cutting resistance.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.14 no.1
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• pp.1-7
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• 2018

Materials in nuclear power plants can be embrittled by neutron irradiation. According to existing studies, the effect of the material property by irradiation embrittlement can be approximately simulated by cold working (pre-strain). In this study, finite element damage analysis method using the stress-modified fracture strain model is proposed to predict J-Resistance curves of irradiated SUS316 stainless steel. Experimental data of pre-strained SUS316 stainless steel material are obtained from literature and the damage model is determined by simulating the tensile and fracture toughness tests. In order to consider damage caused by the pre-strain, a pre-strain constant is newly introduced. Experimental J-Resistance curves for various degrees of pre-strain are well predicted.

• Journal of Welding and Joining
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• v.27 no.1
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• pp.102-107
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• 2009

Weldability of Mg alloy was investigated using servo-actuated DC resistance spot welder. Due to its uncommon electrical and mechanical properties, lots of voids and cracks were observed inside nugget with conventional weld schedule. Lobe curve was proposed to clarify proper electrode force and weld current, which guarantee reasonable weld strength and fatigue life. Macro structure of sectioned specimen was examined to count total number of void and crack. Post weld schedule is also proposed to reduce micro victors hardness value of weld zone.

• Electrical & Electronic Materials
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• v.9 no.10
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• pp.1013-1018
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• 1996

The annealing effects of Au/Te/Au/n-GaAs structure was investigated by using x-ray diffraction, scanning electron microscope, the specific contact resistance and I-V measurement. Increasing the annealing temperature, the intensity of Au-Ga peak by X-ray diffraction was increased. The Ga$\_$2/Te$\_$3/peak got evident for the samples annealed at 400.deg. C and GaAs peak by recrystallization appeared for the samples annealed at 500.deg. C. The variation from the schottky to low resistance contact was confirmed by I-V curve. The lowest value of the specific contact resistance of the samples annealed at 500.deg. C was 3.8*10$\^$-5/.ohm.-cm$\^$2/ but the value increased above 600.deg. C.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.5
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• pp.519-525
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• 2005

An electrochemical evaluation on the corrosion resistance for heavy anticorrosive paint(DFT:25um) was carried out for 5 kinds of heavy anticorrosive paints such as high solid epoxy(HE), solvent free epoxy(SE). tar epoxy(TE), phenol epoxy(PE). and ceramic epoxy(CE). Corrosion current densities obtained by Tafel extrapolation method from anodic and cathodic polarization curves didn't correspond with the values obtained by AC impedance measurement, however, the values of polarization resistance obtained from the cyclic voltammogram showed a good tendency corresponding well with the values of AC impedance measurement. Futhermore there was a good correlation against the corrosion resistance evaluation between passivity current density of the anodic polarization curve and diffusion limiting current density of the cathodic polarization curve. And corrosion resistance increased with corrosion potential shifting to noble direction. From the results discussed above. HE and CE had a relatively good corrosion resistance than other heavy anticorrosive paints.

• Proceedings of the Korean Geotechical Society Conference
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• 1997.10a
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• pp.383-390
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• 1997