• Structural Engineering and Mechanics
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• 제73권2호
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• pp.109-121
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• 2020

This study aims to estimate crack location and crack length in damaged beam structures using transfer matrix formulations, which are based on analytical solutions of governing equations of motion. A single variable shear deformation theory (SVSDT) that considers parabolic shear stress distribution along beam cross-section is used, as well as, Timoshenko beam theory (TBT). The cracks are modelled using massless rotational springs that divide beams into segments. In the forward problem, natural frequencies of intact and cracked beam models are calculated for different crack length and location combinations. In the inverse approach, which is the main concern of this paper, the natural frequency values obtained from experimental studies, finite element simulations and analytical solutions are used for crack identification via plots of rotational spring flexibilities against crack location. The estimated crack length and crack location values are tabulated with actual data. Three different beam models that have free-free, fixed-free and simple-simple boundary conditions are considered in the numerical analyses.

• 한국생산제조학회지
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• 제9권5호
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• pp.73-79
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• 2000

The applications of fracture mechanics have traditionally concentrated on cracks loaded by tensile stresses, and growing under an opening or mode I mechanism. However, many cases of failures occur from growth of cracks subjected to mixed mode loading. Several criteria have been proposed regarding the crack growth direction under mixed mode loadings. This paper is aimed at investigation of fatigue crack growth behaviour under mixed mode(I＋II) with variation of angle and pre-crack length in two dimensional branched type precrack. Especially the direction of fatigue crack propagation was predicted and effective stress intensity factor was calculated by finite element analysis(FEA. In this paper, the maximum tangential stress(MTS) criterion was used to predict crack growth direction. Not only experiment but also finite element analysis was carried out and the theoretical predictions were compared with experimental results.

• 대한조선학회지
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• 제25권4호
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• pp.39-46
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• 1988

The purpose of this paper is to apply the boundary element method to predict the crack growth path. The quarter point element with traction singularity at the crack tip is applied to compact tension type specimens and two inclined slit problems under compression load. The maximum stress criterion which was originally derived for the crack initiation is extended to the analysis of the crack propagation. The predicted crack paths with 1/4 crack growth increment of initial crack length agree quite well with experimental results. It is found that the computed crack path of the boundary element analysis is not mainly affected by the crack increment length.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 춘계학술대회 논문집
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• pp.32-38
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• 1999

Fatigue crack propagation behavior for block load in high strength aluminum alloys was investigated in this study. The materials used in this study are aluminum alloy 5052-H32. Initial crack was made by applying cyclic load to a through crack with chevron notch. Crack length was measured from calibration curve, which was plotted by known crack length and resistance of standard specimens. Load was obtained from linear regression formula. Unloading elastic compliance method was applied to check the crack closure and cracked area. The present study results can be usefully applied to predicting the change of crack propagation rate, the crack closure, and the delay of crack propagation.

• 한국해양공학회지
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• 제7권2호
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• pp.57-67
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• 1993

The fracture behavior of plain woven glass/epoxy composite plates with a crack is investigated under static tensile loading. It is shown in this paper that the characteristic length associated with the point stress criterion depends on the crack length. To predict the not ched tensile strength, the point stress criterion proposed by Whitney and Nuismer are modified. An excellent agreement is found between the experimental results and the analytical prediction of the modified point stress criterion. The condition of unstable crack growth in the presence of a per-existing flaw(machined notch) is examined by means of the maximum stress intensity factor $K_max$ using maximumload P$_max$. The values of $K_max$ evaluated from energy release rate G$_max$(the compliance me thod) indicate a wide difference. Therefore in regard to anisotropy and heterogeneity of the composite materials studied, the modified shape correction factor f(a/W) is obtained. $K_max$evaluated by the compliance method a little or insignificantly depends on the initial crack length a, the specimen thickness B, the crack angle .theta. and the specimen geometry.

• 한국생산제조학회지
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• 제25권5호
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• pp.386-392
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• 2016

The sizes of last stage blades (LSB) in a low-pressure steam turbine have been getting larger for the development of high-capacity power plants. They are also larger than other blades in the same system. As a result, crack propagation in an LSB is caused by the large centrifugal force, low natural frequency, and repeated turbine startups. In this study, the critical crack length for a fracture and vibration characteristics, in accordance with crack propagation, were analyzed using a finite element method to calculate the stress intensity factor (SIF) and the natural frequency that was affected by the stress-stiffening effect. It was calculated that the frequency of the third and fifth modes passed the excited harmonic resonance (5X and 10X) and the observed calculated critical crack length matched that of the real fractured surface.

• 동력기계공학회지
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• 제1권1호
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• pp.80-90
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• 1997

The purpose of this study is to evaluate the validity examination of the J-R curve characteristics for the nuclear reactor pressure vessel steels and Al alloys by the load ratio analysis. The results of the load ratio analysis are compared with those of the J-R curve which are obtained by the ASTM unloading compliance method. The crack length calculated by the load ratio analysis is agree well with the measured final crack length. The slope of the exponential J-R curve estimated by the load ratio analysis is slightly smaller than that by the ASTM unloading compliance method. The J-R curve obtained by the ASTM unloading compliance method is over-predicted and should be offsetted due to the initial negative crack. On the other hand, the load ratio analysis method can evaluate the J-R curve by only load-displacement curve without particular crack measurement equipment.

• 대한기계학회논문집A
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• 제21권7호
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• pp.1149-1155
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• 1997

J-integral for a subsurface horizontal crack in a circular plate with an inner hole under rolling line contact is evaluated according to loading positions with various load conditions, crack length and crack location. Two-dimensional crack is modeled, and the relation between Tresca stress for uncracked model and J-integral is discussed. The loading location which gives the maximum J-integral depends on load condition and crack location, and the presence of friction force increases Tresca stress and J-integral near the surface. Regardless of friction force, crack location that gives maximum J-integral is the same as that of maximum Tresca stress in an uncracked model, and the value of J-integral is propotional to crack length. It is also showed that the variation of an inner radius of a disk does not effect J-integral value.

• Journal of Mechanical Science and Technology
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• 제16권1호
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• pp.24-31
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• 2002

The leak-before-break (LBB) behaviors of a structural component under high and low fatigue loads are an important problem in nuclear power plants, liquid nitrogen gas tankers and chemical plants. This paper is an experimental study to evaluate the crack opening behavior after penetration for plate and pipe specimens. Crack opening displacement after penetration under low fatigue load could be satisfactorily determined at the center of the plate thickness regardless of the specimen size. In the case of high fatigue load, it is shown that the crack opening displacement at the center of a penetrated crack carl be derived using the gross stress, $\sigma$/sug G/, and the front surface crack length, a$\_$s/, together with the back surface crack length, a$\_$b/.

• 대한기계학회논문집A
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• 제30권9호
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• pp.1134-1141
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• 2006

This paper presents the model for evaluating restraint effect of pressure induced bending (PIB) on the circumferential through-wall crack opening displacement (COD), which considers plastic behavior of crack. This study performed three-dimensional elastic-plastic finite element (FE) analyses for different crack angle, restraint length, pipe geometry, stress level, and material conditions, and evaluated the influence of each parameter on the PIB restraint effect on COD. Based on these evaluations and additional perfectly-plastic FE analyses, a closed-form model to evaluate the restraint effect of PIB on the plastic crack opening of circumferential through-wall crack, was proposed as functions of crack angle, restraint length, radius to thickness ratio, axial stress corresponding to an internal pressure, and normalized COD evaluated from linear-elastic crack opening condition.