• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.10
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• pp.2172-2179
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• 2002

In this paper, we examine the dynamic electromechanical behavior of an edge crack in a piezoelectric ceramic layer bonded between two elastic layers under the combined anti-plane mechanical shear and in-plane electric transient loadings. We adopted both the permeable and impermeable crack boundary conditions. Fourier transforms are used to reduce the problem to the solution of two pairs of dual integral equations, which are then expressed to a Fredholm integral equation of the second kind. Numerical values on the dynamic energy release rate are presented to show the dependences upon the geometry, material combination, electromechanical coupling coefficient and electric field.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.11
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• pp.158-165
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• 1999

It has been established that a crack has an important effect on the dynamic behavior of a structure. This effect depends mainly on the location and depth of the crack. To identify the location and depth of a crack in a structure, a method is presented in this paper which uses hybrid neuro-genetic technique. Feed-forward multilayer neural networks trained by back-propagation are used to learn the input)the location and dept of a crack)-output(the structural eigenfrequencies) relation of the structural system. With this neural network and genetic algorithm, it is possible to formulate the inverse problem. Neural network training algorithm is the back propagation algorithm with the momentum method to attain stable convergence in the training process and with the adaptive learning rate method to speed up convergence. Finally, genetic algorithm is used to fine the minimum square error.

• Journal of Mechanical Science and Technology
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• v.17 no.8
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• pp.1120-1132
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• 2003

A problem of a circular elastic inhomogeneity interacting with a crack under uniform loadings (mechanical tension and heat flux at infinity) is solved. The singular. integral equations for edge and temperature dislocation distribution functions are constructed and solved numeric-ally, to obtain the stress intensity factors. The effects of the material property ratio on the stress intensity factor (SIF) are investigated. The computed SIFs are used to predict the kink angle of the crack when the crack grows.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.1
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• pp.22-31
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• 2001

Some techniques developed recently for sizing smalt fatigue cracks are described. One is an ultrasonic technique which deals with a small closed crack, where both the stress closing the crack and the crack size are determined by analyzing inverse problem. Here, difficulties encountered in NDE of closed cracks by usual ultrasonic techniques are summarized in advance. Secondly, the closely coupled probes potential drop (CCPPD) technique, which is based on d-c potential drop measurement, is explained fur sizing small cracks. The CCPPD technique is not affected by crack closure. Finally, a discussion is given on NDE of materials degradation in conjunction with sensitive NDE of small cracks.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.4
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• pp.423-431
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• 2004

For the fracture mechanics analysis of cracks in welds of dissimilar steels, residual stress analysis and fracture analysis must be performed simultaneously. The standard definition of the J -integral leads to a path dependent value in the presence of a residual stress field. And unlike cracks in homogeneous materials, a bimaterial interface crack always induces both opening and shearing modes of stress in the vicinity of the crack tip. Therefore, it is necessary to develope a path independent J-integral definition for a crack in a residual stress field generated by welding of dissimilar steels. This paper addresses the modification of the Rice-J-integral to produce a path independent J -integral when residual stresses due to welding of dissimilar steels and external forces are present. The residual stress problem is treated as an initial strain problem and the J-integral proposed for this class of problems is used. And a program which can evaluate the J -integral for a crack in a weld of dissimialr steels is developed using proposed J integral definition.

• Journal of Welding and Joining
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• v.34 no.6
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• pp.42-46
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• 2016

Hydrogen assisted cracking (HAC) is one of the most complicated problem in welding. Huge amount of studies have been done for decades. Based on them, various standards have been established to avoid HAC. But it is still a chronic problem in industrial field. It is well known that the main causes of the hydrogen crack are residual stress, crack susceptible micro structures and a certain critical level of hydrogen concentration. Even though the exact generating mechanism is unclear till today, it has been reported that the hydrogen level in the weld metal should be managed less than a certain amount to prevent it. Matsuda studied that the residual hydrogen level in the weld metal can be varied even if the initial hydrogen content is same. It is also insisted in this report that the residual hydrogen concentration is in stronger correlation with hydrogen crack than the initial hydrogen content. But, in practical point of view, the residual hydrogen is still hard to consider because measuring hydrogen level is time and cost consuming process. In this regard, numerical analysis is the only solution for considering the residual hydrogen content. Meanwhile, Takahashi showed the possibility of predicting the residual hydrogen by a rigorous FE analysis. But, few commercial software suitable for solving the weld metal hydrogen has been reported yet. In this study, two dimensional thermal - hydrogen coupled analysis was developed by using the commercial FE software MARC. Since the governing equation of the hydrogen diffusion is similar to the heat transfer, it is shown that the heat transfer FE analysis in association with hydrogen diffusion property can be used for hydrogen diffusion analysis. A series of simulation was performed to verify the accuracy of the model. For BOP (Bead-On-Plate) and the multi-pass butt welding simulations, remaining hydrogen contents in the weld metal is well matched with measurements which are referred from Kim and Masamitsu.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.10a
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• pp.270-277
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• 2004

In this paper, path-independent values of the J-integral in the fininte element context for arbitrary two-dimensional and three-dimensional crack configurations in welds are presented. For the fracture mechanics analysis of cracks in welds, residual stress analysis and fracture analysis must be performed simultaneously. In the analysis of cracked bodies containing residual stress, the usual domain integral formulation results in path-dependent values of the J-integral. This paper discusses modifications of the conventional J-integral that yield path independence in the presence of residual stress generated by welding. The residual stress problem is treated as an initial strain problem and the J-integral modified for this class of problem is used. And a finite element program which can evaluate the J-integral for cracks in two-dimensional and three-dimensional residual stress bearing bodies is developed using the modified J-integral definition. The situation when residual stress only is present is examed as is the case when mechanical stresses are applied in conjunction with a residual stress field.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.05a
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• pp.185-186
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• 2011

The latest domestic construction sector is receiving economic damage because of defect litigation. The Concrete Crack among them has the largest component in expense of apartment house defect. Also, contradictory suggestion of appraiser is problem. To improve these problem, need objective plan that people concerned can recognize about decision sequence. Therefore, in this study, compared general defect investigation and defect decision of appraiser taking advantage of Data Dictionary analysis method. Also, deduced current problem and amelioration plan.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.1
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• pp.121-126
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• 1994

A mutual integral, which has the conservation property, is applied to the problem of a crack in an isotropic elastic material. The stress intensity factors $K_{I}, K_{II}, K_{III}$ and T-stress for the problem in an infinite medium are easily obtained by using the mutual integral without solving the boundary value problem. The auxiliary solutions necessary in the proposed method are taken from the known asymptotic solutions. This method is amenable to numerical evaluation of the stress intensity factors and T-stress if the crack in a finite medium is considered.

• Journal of Ocean Engineering and Technology
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• v.13 no.3 s.33
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• pp.57-67
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• 1999

Welding is widely applicable and reliable process and is mainly adopted for fabricating heavy structures. Recently, weld metal transverse cracks in butt and fillet weld joint is a serious problem, and they must be eliminated for improving weld joint reliability. The weld metal transverse crack susceptibility of butt and fillet joint was carried out by cantilever type tensile crack testing jig and CTS test. In this view of point, this study investigated the potential factors for weld metal transverse crack. The main results obtained were as follows: 1. The content o fdiffusible hydrogen in weld metal played an important role for weld metal transverse cracks. 2. From cantilever type tensile crack tests, it was pointed out that the higher the diffusible hydrogen content and tensile restraint, the more susceptible to weld metal transverse craking. 3. The TSN(thermal severity number) and diffusible hydrogen were important factors for determining weld metal transverse cracks in fillet weld joints.