• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.3
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• pp.381-389
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• 2001

The objective of this paper is to evaluate the fracture resistance characteristics of SA508 Cl.1a to SA508 Cl.3 welds manufactured for the reactor coolant loop piping system of nuclear power plants. The effect of the crack plane orientation to the welding process orientation and the preheat temperature on the fracture resistance characteristics were discussed. Results of the fracture resistance test showed that the effect of the crack plane orientation to the welding process orientation of the fracture toughness is significant, while that of preheat temperature on the fracture toughness is negligible. The micro Vickers hardness test, the metallographic observation and the fractography analysis were conducted to analyse the crack jump phenomenon on the L-R crack plane orientation in the multi-pass welding zone. As these results, it is shown that the crack jump phenomenon was produced because of the inhomogeneity between welding beads and the crack plane orientation must be considered for the safety of the welding zone in the piping system.

• Journal of Ocean Engineering and Technology
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• v.8 no.2
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• pp.157-165
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• 1994

Effect of an accelerated iso-thermal aging (375 degree C x 66days, 375 degree C x 200days) on elastic-plastic fracture resistance curve were examined in SA533B low alloy steel. Fracture toughness test are conducted by unloading compliance method at room temperature. But the apparent negative crack growth phenomenon, usually arise in partial unloading compliance test. The phenomenon of negative crack growth may be eliminated by the offset technique. There is no effect of aging on J sub(IC) and dJ/da in iso-thermal aged (375 degree C x 66 days) specimen, but there is very little effect in iso-thermal aged (375 degree C x 200 days) specimen.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1460-1468
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• 1995

The objective of this paper is to evaluate the material properties of SA106 Gr. C carbon steel and its associated weld manufactured for main steam system of Yonggwang 3,4 nuclear generating stations. A total of 43 tensile and 35 fracture toughness tests were performed and the effects of various parameters such as pipe size, crack plane orientation, test temperature, welding on material properties were discussed. Test results show that the effects of crack plane orientation, test temperature, and welding on fracture toughness were significant while the effects of pipe size, specimen orientation and test temperature on tensile properties were negligible. Especially the dependence of J-R curves on the crack plane orientation appears to be the characteristics of carbon steel.

• Journal of Welding and Joining
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• v.7 no.1
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• pp.42-50
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• 1989

The application of fracture mechanics is being increased gradually to assess the safety of welded structures containing crack. Fatigue crack propagation behavior and elastic-plastic fracture toughness J$_{IC}$ of home made flux cored wire(1.22mm) CO$_{2}$ weldments was discussed. Especially fatigue crack propagation test was carried out by .DELTA.K control instead of load control and elastic-plastic fracture toughness J$_{IC}$ was obtained by ASTM-R curve method on C.T.specimen in transverse direction of weldments. The results obtained are as follows; (1) Weld metal presented an almost complete similarity to base metal on fatigue crack propagation rate in transverse direction. (2) Weld metal was more than base metal on J$_{IC}$ value in transverse direction. (3) F.C.W. CO$_{2}$ weldments had an excellent characteristic of fatigue crack propagation rate and J$_{IC}$ in less than 50kg/mm$^{2}$ steel grade, this would result from that weld metal had good static strength.trength.

• 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 Society for Precision Engineering
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• v.31 no.6
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• pp.551-557
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• 2014

Ideally, it is preferable to obtain the fracture characteristics of a piping from the fracture toughness of real pipes. However, a fracture toughness test on real pipes not only incurs much expense, but is very difficult to perform. Therefore fracture toughness tests have been carried out with standard specimens instead of real pipes. But, the estimates of fracture toughness obtained from standard specimens are more conservative than those of real pipes owing to the difference in the constraint effect between real pipes and standard specimens. Therefore, we have been studied with equivalent stress gradient specimen (ESG) which is designed to behave equally compared to real pipe about stress gradient on crack tip. In this study, we will evaluate fracture characteristics of equivalent stress gradient specimen by using analytical methods and compare with those of real pipe. And finally investigate suitability of equivalent stress gradient specimen.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.539-546
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• 2016

In this paper, the effect of J-R curve changes on the determination of parameters in a failure model owing to the presence or absence of a side groove in a C(T) specimen is investigated. A stress-modified fracture strain model is implemented for FE damage simulations. C(T) specimens were taken from SA508 grade 1a low-alloy steel piping material, and some of them were processed with a side groove. Fracture toughness tests were performed at room temperature and at $316^{\circ}C$. The parameters of the failure model were determined by damage simulations using the J-R curves obtained from the tests. Finally, the results show that the determination of failure model parameters is not affected by variations in J-R curves owing to the presence or absence of a side groove.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.2
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• pp.529-539
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• 1996

Fracture resistance(J-R) curves, which are used for elastic-plastic fracture mechanics analyses, are known to be dependent on the specimen geometry. The objective of this paper is to investigate the effect of crack tip constraint an the J-R curves in CT specimens. Fracture toughness tests on CT specimens with varying planform size were performed and test results showed that the J-R curves were increased with an increase in the planform size. Finite element analysis were also performed and the numerical results showed that this experimental phenomenon was probably due to the relaxation of crack tip constraint resulting from the stress triaxiality.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.12
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• pp.2963-2971
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• 2000

In order to obtain more realistic fracture resistance curve, research is currently underway to introduce new parameter and to quantify the constraint effect. The objective of this study is to investigate the relationship between the constraint effect of a size(plane size and thickness) and the fracture resistance curve. In this paper fracture toughness tests were performed with various plane size and various thickness of specimens in two materials. The test results showed that the effects of plane size in th4 J-R curve were significant and the curve was risen with an increase in plane size. However, relatively weak influence was observed form the change of the specimen thickness and size. The stress fields near the crack tip of th specimen is close to the HRR field according to increasing the plane size and Q stress appears different value according to material properties and the plane size.

• Journal of Welding and Joining
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• v.12 no.2
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• pp.108-118
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• 1994

In the present study, the dynamic crack initiation toughness and total absorbed energy behavior of Heat Affected Zone(HAZ) was experimentally evaluated for SS41 steel welding. The materials were submerged arc-welded SS41 steel plate with thickness 19mm. The test temperature range was from $20^{\circ}C$(room temperature) to $-70^{\circ}C$ The HAZ of welding were divided into three sub-zones for analysis; H1, H2, H3, according to the distance from the fushion line. From the experimental studies, the reference value of dynamic crack initiation toughness $(J_{Id(R)})$ can be use to estimate dynamic fracture toughness characteristics of steel welding.