• Nuclear Engineering and Technology
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• v.39 no.1
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• pp.75-84
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• 2007

This paper presents a closed-form model for evaluating the restraint effect of pressure induced bending on the opening of a circumferential through-wall crack, which is considered plastic deformation behavior. Three-dimensional finite element analyses with different crack lengths, restraint conditions, pipe geometries, magnitudes of internal pressure, and tensile properties were used to investigate the influence of each parameter on the pressure-induced bending restraint on the crack opening displacement. From these investigations, an analytical model based on elastic-perfectly plastic material was developed in terms of the crack length, symmetric restraint length, mean radius to thickness ratio, axial stress corresponding to the internal pressure, and normalized crack opening displacement evaluated from a linear-elastic crack opening condition. Finite element analyses results demonstrate that the proposed analytical model reliably estimated the restraint effect of pressure-induced bending on the plastic crack opening of a circumferential through-wall crack and properly reflected the dependence on each parameter within the range over which the analytical expression was derived.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.1
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• pp.49-60
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• 2002

Welding is essential in ship production since welding is very popular method for joining two or more metals. However, welding causes residual stress and distortion and these give a bad influence to the structure strength and assembly of ship blocks. Therefore, prediction and treatment of residual stress and distortion is a key to accuracy control in shipyard. In this paper, a computational procedure, based on thermal-elastic-plastic 3-dimensional FEA, has been suggested to simulate butt and fillet welding process. In the simulation process, temperature distribution at each time step is obtained by heat transfer analysis and then thermal deformation analysis is done with obtained temperature distributions to find the residual stress and distortion. In heat transfer analysis, enthalpy method is used to realize phase change at melting temperature. Also element birth and death method is used to simulate adding of weld metal in both heat transfer analysis and thermal elastic plastic analysis. The proposed procedure is verified by related researches and the results show good agreement with those of related researches.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1836-1841
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• 2007

Based on three-dimensional (3-D) FE limit analyses, this paper provides plastic limit and TES(Twice-Elastic-Slope) loads for pipe bends under combined pressure and out-of-plane bending. The plastic limit loads are determined from FE limit analyses based on elastic-perfectly-plastic materials using the small geometry change option, and the FE limit analyses using the large geometry change option provide TES plastic loads. A wide range of parameters related to the bend geometry is considered. Based on the FE results, closed-form approximations of plastic limit and TES plastic load solutions for pipe bends under out-of-plane bending are proposed.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.1
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• pp.43-50
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• 1998

The purpose of the paper is to protect the damage of plastic IC package with searching the cause of the fracture due to the delamination and crack when the encapsulant of plastic IC package is on viscoelastic behavior with the effect of creep on high temperature, The model for analysis is the plastic SOJ package with dimpled diepad in the IR soldering process of surface mounting technology. The risk of delamination with calculating the distribution of viscoelastic thermal stress in the package without the crack in the surface mounting process is checked. The package model with the perfect delamination between chip and diepad is chosen to estimate the resistance against fracture in thermal loading with calculating C (t)-integrals according to the change of the design. The optimum design to depress the delamination and crack is presented.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.10
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• pp.1009-1016
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• 2007

Finite element alternating method has been suggested and used effectively to obtain the fracture parameters in assessing the integrity of cracked structures. The method obtains the solution from alternating independently between the FEM solution for an uncracked body and the crack solution in an infinite body. In the paper, the finite element alternating method is extended in order to obtain the elastic-plastic stress fields of a three dimensional inner crack. The three dimensional crack solutions for an infinite body were obtained using symmetric Galerkin boundary element method. As an example of a three dimensional inner crack, a penny-shaped crack in a finite body was analyzed and the obtained elastc-plastic stress fields were compared with the solution obtained from the finite element analysis with fine mesh. It is noted that in the region ahead of the crack front the stress values from FEAM are close to the values from FEM. But large discrepancy between two values is observed near the crack surfaces.

• Journal of Welding and Joining
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• v.6 no.2
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• pp.19-29
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• 1988

This paper reports on the elatic-plastic analysis and fracture behavior of cylinder with outer surface crack which is under external or internal pressure. For the studuty of crack length effects in cylinder, ratios of crack lengths to finite thickness (a/t) are dertermined 0.3, 0.4, 0.5. For the study of curvature effects in cylinders, ratios of mean diameter to finite thicknees (Rm/t) are determined 10.0, 15.0, 20.0. Analysis is conduceted using the theory of fracture mechanics and two dimensional finite element solution assuming the axi-symmetrical plane strain conditon. Main results of this study are as follows. 1) It is known from this paper that elastic-plastic strain is initiated near crack tip and enlarged between crack tip and inner side of cylinder. 2) $K_{1}$ of cylinder under external or internal pressure is evaluated memebrane stress .root..pi.* crack length. The results of this study are inclined to Lomacky's results and Kobayshi's result. 3) Distribution of stress near crack tip is looked higher than of other zone, as crack length of equal model is longer, and as diameter of cylinder is longer. 4) When other conditions are equal, displacemenet near crack tip is looked duller, as length is longer.

• Structural Engineering and Mechanics
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• v.47 no.1
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• pp.131-147
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• 2013

In this paper, constraint-based fracture mechanics analyses of hollow cylinders with internal circumferential crack under tensile loading are conducted. Finite element analyses of the cracked cylinders are carried out to determine the fracture parameters including elastic T-stresses, and fully-plastic J-integrals. Linear elastic finite element analysis is conducted to obtain the T-stresses, and elastic-plastic analysis is conducted to obtain the fully plastic J-integrals. A wide range of cylinder geometries are studied, with cylinder radius ratios of $r_i/r_o$ = 0.2 to 0.8 and crack depth ratio a/t = 0.2 to 0.8. Fully plastic J-integrals are obtained for Ramberg-Osgood power law hardening material of n = 3, 5 and 10. These fracture parameters are then used to construct conventional and constraint-based failure assessment diagrams (FADs) to determine the maximum load carrying capacity of cracked cylinders. It is demonstrated that these tensile loaded cylinders with circumferential cracks are under low constraint conditions, and the load carrying capacity are higher when the low constraint effects are properly accounted for, using constraint-based FADs, comparing to the predictions from the conventional FADs.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.20 no.1
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• pp.30-36
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• 1984

It is well known that the application of linear elastic fracture mechanics is inadequate to solve the large deformation fracture failures which occurr in ductile manner because of the large scale yielding due to the severe stress concentration in the region adjacent to the crack tip. The authors have been evolved a fracture model, the crack plane equilibrium model, for this kinds of elastic-plastic fracture problems in the previous report. In this report, the crack plane equilibrium model was compared with the Irwin's plastic zone corrected linear elastic fracture mechanics through theoretical comparisons and experimental results to examine the validity of the crack plane equilibrium model as an available tool for nonlinear fracture analysis. Through this study, the main results were reached as follows; Irwin's plastic zone corrected linear elastic fracture mechanics could be applicable only for small scale yielding problems as expected while the crack plane equilibrium model valid as a fracture model for large deformation fracture failure. However, the followings should be considered for the more precise evaluations of CPE model; 1) It is necessary to test more specimens which contain small cracks in the range of 2a/W<0.1. 2) It is important to detect the crack initiation point during the fracture test for determining an accurate fracture load. 3) Effects of specimen thickness in the fracture process zone should be examined.

• Journal of Welding and Joining
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• v.17 no.5
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• pp.77-82
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• 1999

Resistance spot welding process is completed in very short time and there are many factors affecting on the generation of heat. It is difficult to control these experimental factors and monitor distribution of the temperature and stresses in the experimental analysis case. and too much time and expense are required for the experimental trials to fine proper welding condition. So numerical analyses have been attempted steadily, but most numerical analyses on the resistance spot welding are mainly focused on thermal behavior. Therefore, in this paper, the numerical analysis of mechanical behavior as well as heat conduction is carried out for the spot welding process. For this numerical analysis, axial symmetric computer program for the spot welding analysis by F.E.M. has been developed considering heat conduction and thermal elastic-plastic theory. Material properties depending on temperature such as density, heat conductivity, heat expansion coefficient, specific heat, yield stress, elastic modulus, and specific resistance are considered. Using the results of temperature distribution obtained from heat conduction analysis, the thermal elastic-plastic analysis is carried out to clarify mechanical behavior of spot welded specimen. In order to evaluate the effect of residual stresses, numerical analyses are carried out under tension-shear load in two cases respectively; one with residual stress, the other without residual stresses.

• Nuclear Engineering and Technology
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• v.51 no.5
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• pp.1451-1469
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• 2019

This paper proposes a residual stress mitigation of a nuclear safety-related austenitic stainless steel TP304 pipe bended by local induction heating process via performing elastic-plastic finite element analysis. Residual stress distributions of the pipe bend were calculated by performing finite element analysis. Validity of the finite element analysis procedure was verified via comparing with temperature histories measured by using thermocouples, ultrasonic thickness measurement results, and residual stress measurement results by a hole-drilling method. Parametric finite element stress analysis was performed to investigate effects of the process and geometric shape variables on the residual stresses on inner surfaces of the pipe by applying the verified procedure. As a result of the parametric analysis, it was found that it is difficult to considerably reduce the inner surface residual stresses by changing the existing process and geometric shape variables. So, in order to mitigate the residual stresses, effect of an additional process such as cooling after the bending on the residual stresses was investigated. Finally, it was identified that the additional heating after the bending can significantly reduce the residual stresses while other variables have insignificant effect.