• Journal of Aerospace System Engineering
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• v.18 no.3
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• pp.17-26
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• 2024

Aircraft engines are exposed to high temperatures, high pressures, and stress caused by the rotation of the turbine shaft during flight. These loads can result in microcracks both on the inside and outside surfaces of the structure. Consequently, this can lead to structural defects and negatively impact the lifespan of the parts. To proactively prevent these defects, a finite element analysis is carried out to identify cracks. However, this process is time-consuming and requires significant effort due to the repetitive nature of crack modeling. This study aims to develop a crack modeling method based on the finite element model. To achieve this, the Constrained Delaunay Triangulation (CDT) technique is employed to triangulate the space while considering limitations on point connections. The effectiveness of this method is validated by comparing stress intensity factors for semi-elliptical cracks in plates and cylindrical vessels. This approach proves to be a valuable tool for crack analysis studies.

• Journal of the Korean Society of Safety
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• v.15 no.4
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• pp.15-19
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• 2000

The exact estimation of the ductile crack growth in a thin sheet would be needed in part of the commercial transport aircraft industry fields. A 2-dimensional elastic plastic finite element analysis was carried out to simulate a stable crack extension in a thin sheet 2024 aluminium alloy. Two kinds of crack modeling were used to evaluate curves of the stable crack extension. And then CTOA(crack tip opening angle) and CTED(crack tip energy density) were calculated in order to determine whether they can be used as useful crack extension criterions in a thin sheet. Results indicate that stable crack extension behaviors were simulated well and CTED is more admirable even though CTOA also is reasonable as a criterion for a stable crack extension in a thin 2024 aluminium alloy sheet.

• Journal of Mechanical Science and Technology
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• v.19 no.7
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• pp.1393-1404
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• 2005

Fatigue crack growth and life have been estimated based on established empirical equations. In this paper, an alternative method using artificial neural network (ANN) -based model developed to predict fatigue damages simultaneously. To learn and generalize the ANN, fatigue crack growth rate and life data were built up using in-plane bending fatigue test results. Single fracture mechanical parameter or nondestructive parameter can't predict fatigue damage accurately but multiple fracture mechanical parameters or nondestructive parameters can. Existing fatigue damage modeling used this merit but limited real-time damage monitoring. Therefore, this study shows fatigue damage model using backpropagation neural networks on the basis of X -ray half breadth ratio B / $B_o$, fractal dimension $D_f$ and fracture mechanical parameters can estimate fatigue crack growth rate da/ dN and cycle ratio N / $N_f$ at the same time within engineering limit error ($5\%$).

• Smart Structures and Systems
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• v.19 no.4
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• pp.361-369
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• 2017

Electromechanical impedance method as an efficient tool in Structural Health Monitoring (SHM) utilizes the electromechanical impedance of piezoelectric materials which is directly related to the mechanical impedance of the host structure and will be affected by damages. In this paper, electromechanical impedance of piezoelectric patches attached to simply support rectangular plate is determined theoretically and experimentally in order to detect damage. A pairs of piezoelectric wafer active sensor (PWAS) patches are used on top and bottom of an aluminum plate to generate pure bending. The analytical model and experiments are carried out both for undamaged and damaged plates. To validate theoretical models, the electromechanical impedances of PWAS for undamaged and damaged plate using theoretical models are compared with those obtained experimentally. Both theoretical and experimental results demonstrate that by crack generation and intensifying this crack, natural frequency of structure decreases. Finally, in order to evaluate damage severity, damage metrics such as Root Mean Square Deviation (RMSD), Mean Absolute Percentage Deviation (MAPD), and Correlation Coefficient Deviation (CCD) are used based on experimental results. The results show that generation of crack and crack depth increasing can be detectable by CCD.

• Nuclear Engineering and Technology
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• v.53 no.1
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• pp.304-313
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• 2021

Nickel base Alloy X-750, which is used as fastener parts in light-water reactor (LWR), has experienced many failures by environmentally assisted cracking (EAC). In order to improve the reliability of passive components for nuclear power plants (NPP's), it is necessary to study the failure mechanism and to predict crack growth behavior by developing a probabilistic failure model. In this study, The Bayesian inference was employed to reduce the uncertainties contained in EAC modeling parameters that have been established from experiments with Alloy X-750. Corrosion fatigue crack growth rate model (FCGR) was developed by fitting into Paris' Law of measured data from the several fatigue tests conducted either in constant load or constant ΔK mode. These parameters characterizing the corrosion fatigue crack growth behavior of X-750 were successfully updated to reduce the uncertainty in the model by using the Bayesian inference method. It is demonstrated that probabilistic failure models for passive components can be developed by updating a laboratory model with field-inspection data, when crack growth rates (CGRs) are low and multiple inspections can be made prior to the component failure.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.4
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• pp.290-299
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• 2003

This paper presents an efficient modeling and dynamic analysis method for open cracked rotor bearing systems. An equivalent bending spring model is introduced to represent the structural weakening effect in the presence of cracks. The proposed modeling method is validated through a series of simulations and experiments. First, the proposed method Is rigorously compared with a commercial finite element code. Then, an experiment is performed to validate the proposed modeling method. Finally, a numerical example is introduced to demonstrate the possible application of the proposed method in the crack diagnosis for rotor systems.

• Journal of Ocean Engineering and Technology
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• v.8 no.2
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• pp.115-123
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• 1994

Under variable amplitude loading conditions, retardation or accelerated condition of fatigue crack growth occurs with every cycle, Because fatigue crack growth behavior varied depend on load time history. The modeling of stress amplitude with storm loading acted to ships and offshore structures applied this paper. The crack closure behavior examine by recording the variation in load-strain relationship. By taking process mentioned above, fatigue crack growth rate, crack length, stress intensity factor, and crack closure stress intensity factor were obtained from the stress cycles of each type of storm ; A(6m), B(7m), C(8m), D(9m), E(11m) and F(15m) which was wave height. It showed that the good agreement with between the experiment results and simulation of storm loads. So this estimated method of crack propagtion rate gives a good criterion for the safe design of vessels and marine structure.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.372.2-372
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• 2002

This paper presents an efficient modeling method fur open cracked beam structures. An equivalent bending spring model is introduced to represent the structural weakening effect in the presence of open cracks. The proposed method adopts the exact dynamic element method (EDEM) to avoid the difficulty and numerical errors in association with re-meshing the structure. The proposed method is rigorously compared with a commercial finite element code. (omitted)

• Computers and Concrete
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• v.12 no.4
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• pp.443-498
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• 2013

A detailed finite element modeling is presented for the simulation of the nonlinear behavior of reinforced concrete structures which manages to predict the nonlinear behavior of four different experimental setups with computational efficiency, robustness and accuracy. The proposed modeling method uses 8-node hexahedral isoparametric elements for the discretization of concrete. Steel rebars may have any orientation inside the solid concrete elements allowing the simulation of longitudinal as well as transverse reinforcement. Concrete cracking is treated with the smeared crack approach, while steel reinforcement is modeled with the natural beam-column flexibility-based element that takes into consideration shear and bending stiffness. The performance of the proposed modeling is demonstrated by comparing the numerical predictions with existing experimental and numerical results in the literature as well as with those of a commercial code. The results show that the proposed refined simulation predicts accurately the nonlinear inelastic behavior of reinforced concrete structures achieving numerical robustness and computational efficiency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.88-93
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• 2003

This paper presents an efficient dynamic modeling method for open cracked rotor-bearing systems. An equivalent bending spring model is introduced to represent the structural weakening effect in the presence of cracks. The proposed modeling method is validated through a series of simulations and experiments. First, the proposed method is rigorously compared with a commercial finite element code. Then, an experiment is performed to validate the proposed modeling method. Finally, a numerical example is introduced to demonstrate the possible application of the proposed method in the crack diagnosis fur rotor systems.