• Journal of Mechanical Science and Technology
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• v.18 no.11
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• pp.1989-1995
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• 2004

Finite element analysis(FEA) is the most popular numerical method to simulate plasticity-induced fatigue crack closure and can predict fatigue crack closure behavior. Finite element analysis under plane stress state using 4-node isoparametric elements is performed to investigate the detailed closure behavior of fatigue cracks and the numerical results are compared with experimental results. The mesh of constant size elements on the crack surface can not correctly predict the opening level for fatigue crack as shown in the previous works. The crack opening behavior for the size mesh with a linear change shows almost flat stress level after a crack tip has passed by the monotonic plastic zone. The prediction of crack opening level presents a good agreement with published experimental data regardless of stress ratios, which are using the mesh of the elements that are in proportion to the reversed plastic zone size considering the opening stress intensity factors. Numerical interpolation results of finite element analysis can precisely predict the crack opening level. This method shows a good agreement with the experimental data regardless of the stress ratios and kinds of materials.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.10
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• pp.113-119
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• 1998

Ship structures and aircraft structures are consisted of thin sheet alloy, so it is very important to understand the characteristics of fatigue crack propagation of that material and to establish the data base. The data for fatigue crack propagation behavior scatter very much even under identical experimental conditions with constant loading. The behavior of fatigue crack propagation under regular and irregular cyclic loadings is known to be highly affected by complicated factors such as plastic zone developed at the vicinity of crack tip and reduction of cross sectional area. In this paper, the controlled stress amplitude and overload fatigue crack propagation tests have been conducted to investigate the effect of varying factors such as plastic zone size near the crack tip and area reduction factor (AF) on the fatigue crack propagation behavior A better simulation of fatigue crack propagation behavior is found to be obtainable by using Wheeler and Willenborg models with AF effect.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1349-1353
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• 2003

Previous researches for fiber reinforced composite material(FRCM) have been evaluated the fatigue delamination behavior using the traditional fracture mechanics parameters. Therefore. previous researches for FRCM have not generally been firmed yet. Because delamination growth behavior in FRCM should be consider relationship between delamination area, A$\sub$D/ and crack length, a instead of traditional fracture mechanics parameters. Especially, in case of delamination behavior for FRCM without crack should be considering equivalent crack, i.e., pseudo crack, a$\sub$p/, using the fracture behavior of FRCM with crack. The major purpose of this study was to evaluate the delamination for FRCM without crack. The details of the studies are as follow : 1) Relationship between crack growth rate, da/dN and stress intensity factor, ΔK in FRCM containing a saw-cut and circular hole with crack. 2) Propose of PSEUDO CRACK MODEL for the delamination in FRCM without crack. 3) Analysis of crack propagation energy, E$\sub$crack/ using a total energy, E$\sub$total/ and delamination growth energy, E$\sub$del/.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.1
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• pp.143-151
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• 2005

This paper study the effect of open cracks on the dynamic behavior of simply supported Timoshenko beam with a moving mass. The influences of the depth and the position of the crack in the beam have been studied on the dynamic behavior of the simply supported beam system by numerical method. Using Lagrange's equation derives the equation of motion. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments i.e. the crack is modeled as a rotational spring. This flexibility matrix defines the relationship between the displacements and forces on the crack section and is derived by the applying fundamental fracture mechanics theory. As the depth of the crack is increased the mid-span deflection of the Timoshenko beam with the moving mass is increased. And the effects of depth and position of crack on dynamic behavior of simply supported beam with moving mass are discussed.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.28 no.2
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• pp.197-207
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• 1992

Fatigue life and penetration behavior were examined analytically by variety of initial front face crack length and initial crack depth. The fatigue crack shape before penetration is almost semielliptical, and the aspect ratio by calculation using the Newman-Raju's formula is smaller than the value obtained by the experiment. It is found that the crack growth behavior on the back surface after penetration is unique and can be divided into three stage a, b and c. By using the K value proposed by the authors, particular crack growth behavior and the change in crack shape can be evaluated quantitatively. It is found that fatigue life and penetration behavior were more dependent on initial front face crack length than initial crack depth.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.67-72
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• 2001

The LBB behavior and the crack opening displacement after a crack penetrated wall thickness of statically indeterminate piping system were investigated in this study, compared with statically determinate piping system. The reduction of ultimate strength caused by a crack was relatively small in the statically indeterminate piping system. The statically indeterminate piping system has more safety margin for LBB behavior than the statically determinate piping system. The crack opening displacement could be evaluated by using the plastic rotation angle proposed to evaluate the crack opening displacement after crack penetration in pipe with a non-penetrating crack.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.6
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• pp.834-840
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• 2008

We carried out fatigue testing with materials of aluminum alloyC7075-T6, 2024-T4) by rotary bending fatigue tester. We investigated fatigue limit, fatigue crack initiation, fatigue crack propagation behavior and possibility of fatigue life prediction to the different small circular hole defect. The summarized result are as follows; Fatigue limit of the smooth specimens were related tensile strength and yield strength. In case of more large applied stress and small circular hole crack defect, the fatigue crack was grown rapidly. The fatigue crack propagation behavior proceed at according to inclusion. Fatigue crack propagation ratio appeared instability and retardation phenomenon in the first half of fatigue life but appeared stability and replied in the latter half. On other hand, this experimental data of the materials are appeared fatigue life predictability.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.928-932
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• 1996

Single overload fatigue tests with overload sizes ranging from 50% and 100% have been performed to investing ate the fatigue crack growth retardation behavior. A modified and experimental method of Willenborg's model for prediction of crack growth retardation behavior has been developed, based on evaluations of equivalent plastic zone size (EPZS) changing its size along the overload plastic zone boundary. The minimum crack growth rates of each overload size are linearly decreased with overload size increasing, but fatigue lives extended by single overload are increasing much more unlike the crack growth rates. Comparisons of crack growth behavior predicted by EPZS model and Willenborg model have shown that the EPZS model accounts for overload effects better than Willenborg model. These effects include delayed retardation, large retardation region, minimum crack growth rate, and the increase rate of crack growth rate in the region crack growth rate recovered.

• Journal of Ocean Engineering and Technology
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• v.11 no.3
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• pp.29-38
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• 1997

Crack penetration behavior by fatigue crack propagation and measurements of AE before-and-after crack penetration were examined using SS41 steel plate. Experimental crack shape of SU type was in good agreement with calculated shape rather than S type. Crack propagation behavior on the front surface appears not to change markedly after penetration. However, crack growth on the back surface appears to accelerate as reported by author. As a crack propagates, AE occurred heavily just before penetration. Then, it decreases and crack is penetrating. A transition from plane strain to plane stress was observed by fractographic study. At this time, separation of fracture surface was shown which affects AE occurrence.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1990-2001
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• 1991

The fatigue life and crack penetration behavior of high strength steel have been studied in detail both experimentally and analytically. The fatigue crack shape of a smooth specimen is almost semicircular, while a specimen with stress concentration becomes semielliptical according to stress concentration shape. The aspect ratio of smooth specimens calculated using the Newman-Raju's formular is smaller than the value obtained from the experiment. On the other hand, the aspect ratio of the stress concentration specimen shows a good agreement with experimental results. It is found that the crack growth behavior on the back surface after the penetration is unique and can be divided into three stages ; rapid growth region, constant growth region and acceleration growth region. By using the K value suggested in this study, the particular crack growth behavior and crack shape can be estimated quantitatively.