• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.461-464
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• 2000

A branched crack in a semi-infinite plate under tension and bending moment is considered. Intensity factors of the stress and moment for the branched crack are evaluated. The stress intensity factors are obtained by using the finite element method and the J-based mutual integral. The moment intensity factors are calculated by extrapolating the values of the moment near the crack tip. Approximate expressions are also obtained as functions of the branched crack length and branching angle.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.4
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• pp.73-81
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• 1994

The source and source/dipole distribution methods using 3-dimensional panel method have been widely used for ship motion analysis. When these methods are used, large errors in the predicted hydrodynamic coefficients are introduced around the irregular frequencies caused by the resonance of imaginary internal flow. Therefore, the irregular frequencies need to be removed for an accurate prediction of ship motion. This paper adopts 3-dimensional translating and oscillating Green function derived by Wu. The adaptive integration method, stretching transform and stationary phase method are used for the calculation of the calculation of Green function and the integral equation is derived by distributing the Green function n ship surface and inner free-surface. The condition of zero normal velocity, that is, wall condition on inner free-surface has been successfully used for the removal of irregular frequencies in oscillating problems. The calculations are carried out for series 60($C_B=0.7$) vessel and the results are compared with those of other theoretical analyses and experiment.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.5
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• pp.393-399
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• 2013

In this paper, a novel approach to estimate cohesive laws for the mode I fracture of the graphene is presented by combining molecular dynamic simulations and an inverse algorithm based on field projection method and finite element method. The determination of crack-tip cohesive laws of the graphene based on continuum mechanics is a non-trivial inverse problem of finding unknown tractions and separations from atomic simulations. The displacements of molecular dynamic simulations in a region far away from the crack tip are transferred to finite element nodes by using moving least square approximation. Inverse analyses for extracting unknown cohesive tractions and separation behind the crack tip can be carried out by using conservation nature of the interaction J- and M-integrals with numerical auxiliary fields which are generated by systematically imposing uniform surface tractions element-by-element along the crack surfaces in finite element models. The preset method can be a very successful approach to extract crack-tip cohesive laws from molecular dynamic simulations as a scale bridging method.

• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.75-80
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• 2001

The elastic plastic fracture toughness of this material is evaluated by the an unloading compliance method according to the ASTM E813-97 and E1152-97 method on the smooth and side groove 1CT specimens. The effect of smooth and side groove is studied on the material tearing modulus and characterizes the crack tip field under the plane stress and strain. SG-365 steel is observed that J-R curve and Tmat value decrease as 0%, 20%, 30%, and 40%. The 40% side grooved specimen is very useful in estimation of the $J_IC$. Because it is much easier than the smooth specimen to the onset of the ductile tearing by the R curve method. Besides. it improves the accuracy of toughness values, decreases the scattering the them and tunneling and shear lip by the side groove. Applicability of tearing modulus($T_J$ proposed by paris et al as instability panameter for this material is investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.6
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• pp.1127-1134
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• 2002

The present paper provides an engineering J estimation equation for surface cracked plates under combined bending and tension. The proposed equation is based on the reference stress approach, and the most relevant normalising loads to define the reference stress for accurate J estimations are given for surface cracked plates under combined bending and tension. Comparisons with J results from extensive 3-D FE analyses, covering a wide range of crack geometry, plate geometry and loading combination, show overall good agreement not only at the deepest point but also at arbitrary points along the crack front. for pure tension, agreement between the estimated J and the FE results is excellent, even at the surface point. On the other hand, for pure bending and combined bending and tension, the estimated J values become less accurate for locations close to the surface point. Thus the results in this paper will be useful to assess short-term fracture or low cycle fatigue of surface defects in plates under combined bending and tension.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.170-177
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• 2003

This paper proposes a robust method for the Ramberg-Osgood (R-O) fit to accurately estimate elastic-plastic J from engineering fracture mechanics analysis based on deformation plasticity. The proposal is based on engineering stress-strain data to determine the R-O parameters, instead of true stress-strain data. Moreover, for practical applications, the method is given not only for the case when full stress-strain data are available but also for the case when only yield and tensile strengths are available. Reliability of the proposed method for the R-O fit is validated against detailed 3-D Finite Element (FE) analyses for circumferential through-wall cracked pipes under global bending using five different materials, three stainless steels and two ferritic steels. Taking the FE J results based on incremental plasticity using actual stress-strain data as reference, the FE J results based on deformation plasticity using various R-O fits are compared with reference J values. Comparisons show that the proposed R-O fit provides more accurate J values for all cases, compared to existing methods for the R-O fit. Advantages of the proposed R-O fit in practical applications are discussed, together with its accuracy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1571-1578
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• 2003

This paper proposes a robust method for the Ramberg-Osgood(R-O)fit to accurately estimate elastic-plastic J from engineering fracture mechanics analysis based on deformation plasticity. The proposal is based on engineering stress-strain data to determine the R-O parameters, instead of true stress-strain data. Moreover, for practical applications, the method is given not only for the case when full stress-strain data are available but also for the case when only yield and tensile strengths are available. Reliability of the proposed method for the R-O fit is validated against detailed 3-D Finite Element (FE) analyses for circumferential through-wall cracked pipes under global bending using five different materials, three stainless steels and two ferritic steels. Taking the FE J results based on incremental plasticity using actual stress-strain data as reference, the FE J results based on deformation plasticity using various R-O fits are compared with reference J values. Comparisons show that the proposed R-O fit provides more accurate J values for all cases, compared to existing methods for the R-O fit. Advantages of the proposed R-O fit in practical applications are discussed, together with its accuracy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1531-1538
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• 2003

This paper compiles solutions of plastic $\eta$ factors and crack tip stress triaxialites for standard and nonstandard fracture toughness testing specimens, via detailed three-dimensional (3-D) finite element (FE) analyses. Fracture toughness testing specimens include a middle cracked tension (M(T)) specimen, SE(B), single-edge cracked bar in tension (SE(T)) and C(T) specimen. The ligament-to-thickness ratio of the specimen is systematically varied. It is found that the use of the CMOD overall provides more robust experimental J estimation than that of the LLD, for all cases considered in the present work. Moreover, the J estimation based on the load-CMOD record is shown to be insensitive to the specimen thickness, and thus can be used for testing specimen with any thickness. The effects of in-plane and out-of-plane constraint on the crack tip stress triaxiality are also quantified, so that when experimental J value is estimated according to the procedure recommended in this paper, the corresponding crack tip stress triaxiality can be estimated. Moreover, it is found that the out-of-plane constraint effect is related to the in-plane constraint effect.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.6
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• pp.1099-1106
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• 2002

This paper provides engineering J-integral and crack opening displacement (COD) estimation equations for circumferential through-wall cracked pipes under internal pressure and under combined internal pressure and bending. Based on selected 3-D finite element calculations for the circumferential through-wall cracked pipes under internal pressure using the idealized power law materials, the elastic and plastic influence functions for fully plastic J-integral and COD solutions are found as a function of the normalized crack length and the mean radius-to-thickness ratio. These developed GE/EPRI-type solutions are then re-formulated based on the enhanced reference stress method. Such re-formulation not only provides simpler equations for J-integral and COD estimations, but also can be easily extended to combined internal pressure and bending. The proposed equations are compared with elastic-plastic finite element results using actual stress-strain data, which shows overall excellent agreement.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.5
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• pp.47-57
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• 2000

In this study, a fundamental approach to make clear the mechanism of the mutual interference and coalescence of stress fields in the vicinity of two crack tips on the process of their slow growth, using boundary element method. Automatic generation of quadratic discontinuous elements along both of the crack boundaries which can be defined by an arbitrary piece-wise straight geometry. The direction of the crack-extension increment is predicted by the maximum principal stress criterion, corrected to account for the discreteness of the crack extension. Along the computed direction, the crack is extended one increment. Automatic incremental crack-extension analysis with no remeshing, computation of the stress intensity factors by J-integral. Numerical stress intensity factors for two growing cracks in plane-homogeneous regions were determined.