• Journal of the Korean Society of Safety
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• v.19 no.2
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• pp.16-20
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• 2004

This paper aims to analyze fatigue fracture mechnisms with high strength aluminum alloys, which are widely used in vehicles or airplanes to prevent accidents. Usefulness of the crack opening point was proposed by using an effective stress intensity facor when evaluating the fatigue crack propagaion rate. Therefore an exact crack opening ratio can be measured for a more exact fatigue crack propagation rate. It is found that the fatigue crack propagation rate was valid within the range of experimentation as an effective stress intensity factor. Summarizing the results are as follows in this paper ; (1) It is found that the value of the crack opening ratio is constant at the rear of the specimen, U'=0.25 at the crack mouth and U'=0.45 at the crack tip, respectively regardless of the stress ratio. (2) The crack opening ratio is different according to measurement locations. The crack opening ratio value was measured at the crack mouth by a clip gage or measured behind the specimen by a strain gage. It is found that the crack opening ratio value is more accurate that any other measuring test for evaluating the crack propagation ratio test by effective stress intensity factor.

• Structural Engineering and Mechanics
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• v.46 no.3
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• pp.417-431
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• 2013

This paper presents responses of the free end of a cantilever micro beam under the effect of an impact force based on the modified couple stress theory. The beam is excited by a transverse triangular force impulse modulated by a harmonic motion. The Kelvin-Voigt model for the material of the beam is used. The considered problem is investigated within the Bernoulli-Euler beam theory by using energy based finite element method. The system of equations of motion is derived by using Lagrange's equations. The obtained system of linear differential equations is reduced to a linear algebraic equation system and solved in the time domain by using Newmark average acceleration method. In the study, the difference of the modified couple stress theory and the classical beam theory is investigated for the wave propagation. A few of the obtained results are compared with the previously published results. The influences of the material length scale parameter on the wave propagation are investigated in detail. It is clearly seen from the results that the classical beam theory based on the modified couple stress theory must be used instead of the classical theory for small values of beam height.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.10a
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• pp.147-153
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• 2000

The fatigue crack propagation behavior of the SA516/70 steel which is used for pressure vessels was examined experimentally at room temperature, $150^{\circ}C$, $250^{\circ}C$ and $370^{\circ}C$ with stress ratio of R=0.1 and 0.3. The fatigue crack propagation rate da/dN related with the stress intensity factor range $\Omega\textrm{K}$ was influenced by the stress ratio within the stable growth of fatigue crack(Region II) with an increase in $\Omega\textrm{K}$. The resistance to the fatigue crack growth at high temperature is higher in comparison with that at room temperature, and the resistance attributed to the extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations reveal that the differences of the fatigue crack growth characteristics between room and high temperatures are mainly explained by the crack closure and oxide-induced by high temperature.

• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.105-110
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• 2001

The fatigue crack propagation behavior of the SA516/70 steel which is used for pressure vessels was examined experimentally at room temperature, 150$^{\circ}C $, 250$^{\circ}C $ and 370$^{\circ}C $ with stress ratio of R=0.1 and 0.3. The fatigue crack propagation rate da/dN related with the stress intensity factor range $\Delta K$ was influenced by the stress ratio within the stable growth of fatigue crack(Region II) with an increase in $\Delta K$. The resistance to the fatigue crack growth at high temperature is higher in comparison with that at room temperature, and the resistance attributed to the extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations reveal that the differences of the fatigue crack growth characteristics between room and high temperature are mainly explained by the crack closure and oxide-induced by high temperature.

• Structural Engineering and Mechanics
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• v.35 no.3
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• pp.283-299
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• 2010

This paper addresses the numerical simulation of fatigue crack growth in arbitrary 2D geometries under constant amplitude loading by the using a new finite element software. The purpose of this software is on the determination of 2D crack paths and surfaces as well as on the evaluation of components Lifetimes as a part of the damage tolerant assessment. Throughout the simulation of fatigue crack propagation an automatic adaptive mesh is carried out in the vicinity of the crack front nodes and in the elements which represent the higher stresses distribution. The fatigue crack direction and the corresponding stress-intensity factors are estimated at each small crack increment by employing the displacement extrapolation technique under facilitation of singular crack tip elements. The propagation is modeled by successive linear extensions, which are determined by the stress intensity factors under linear elastic fracture mechanics (LEFM) assumption. The stress intensity factors range history must be recorded along the small crack increments. Upon completion of the stress intensity factors range history recording, fatigue crack propagation life of the examined specimen is predicted. A consistent transfer algorithm and a crack relaxation method are proposed and implemented for this purpose. Verification of the predicted fatigue life is validated with relevant experimental data and numerical results obtained by other researchers. The comparisons show that the program is capable of demonstrating the fatigue life prediction results as well as the fatigue crack path satisfactorily.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.8 s.227
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• pp.1229-1236
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• 2004

The specimen materials used in this research are isotropic epoxy resins. The static photoelastic experiment was applied to them. And then the specimens used in photoelastic experiment were fractured under static load. The static photoelastic experimental hybrid method was introduced and its validity had been assured. Crack propagation criterion used the stress components, which are considered the higher order terms, obtained from the static photoelastic experimental hybrid method was introduced and it was applied to the minimum strain energy density criterion, the maximum tangential stress criterion and mode mixity. Comparing the actual initial angle of crack propagation with the theoretical initial angle of crack propagation obtained from the above failure criterions, the validities of the above two criterions are assured and the optimal distance (r) from the crack-tip is 0.01mm in order to get the initial angle of crack propagation of isotropic epoxy resin.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.11
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• pp.1799-1806
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• 2004

The static photoelastic experiment was applied to orthotropic materials. And then the specimens used in photoelastic experiment were fractured under static load. The static photoelastic experimental hybrid method for orthotropic material was introduced and its validity had been assured. Crack propagation criterion used the stress components, which are considered the higher order terms, obtained from the static photoelastic experimental hybrid method was introduced and it was applied to the minimum strain energy density criterion, the maximum tangential stress criterion and mode mixity. Comparing the actual initial angle of crack propagation with the theoretical initial angle of crack propagation obtained from the above failure criterions, the validities of the above two criterions are assured and the optimal distance (${\gamma}$) from the crack-tip is 0.01mm in order to get the initial angle of crack propagation of orthotropic material(C.F.E.C.).

• Journal of Ocean Engineering and Technology
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• v.16 no.5
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• pp.73-79
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• 2002

In this paper, the effect of the compressive residual stresses was obtained at the test conditions of the higher temperature than the ambient temperature. The examination was performed with the CT specimen result of the material(JISG SUP9) which is being commonly used for the marine engine parts and the ocean structures. As a result, the test conditions at the higher temperature were acquired considering the peak values of the compressive residual stresses of the specimens and the effect on the fatigue crack propagation speed da／dN in stage II and the threshold stress intensity factor range Δth in stage I. Also the material constant C and the fatigue crack propagation index m in the formula of Paris Law da／dN＝C (ΔK)$^{m}$ were suggested to estimate the dependence on the test temperature.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.481-484
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• 2000

Practical structures are subject not only to tension but also to shear and torsional loading. Even under uniaxial loading, when the load is not perpendicular to the crack plane, mixed mode crack can occur. Hence, it is necessary to evaluate the fatigue behavior under mixed mode loading. In this study, the propagation behavior of the fatigue crack of the STS304 steels under mixed mode loading condition was investigated. The mode I and II stress intensity factors of CTS specimen were calculated using elastic finite element method with experimental results. The fatigue crack propagation under mixed mode was evaluated by the effective stress intensity factor proposed by Tanaka.

• Journal of Welding and Joining
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• v.28 no.1
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• pp.100-106
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• 2010

In this paper crack propagation analyses in the dissimilar metal weldment of a nozzle were performed using a finite element alternating method (FEAM). A two-dimensional axisymmetric finite element nozzle model was prepared and welding simulation including the thermal heat transfer analysis and the thermal stress analysis was performed. Initial cracks were inserted at weld and heat affected zone in the finite element model which has welding residual stress distribution obtained from the welding simulation. To calculate crack propagation trajectories of these cracks, a new fatigue crack evaluation module was developed in addition to the previous FEAM program. With the new FEAM fatigue crack evaluation module, crack propagation trajectory and crack growth time were calculated automatically and effectively.