• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.53-58
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• 2002

This paper aims to synthesize the research on fatigue mechanisms of high strength aluminum alloys which are widely used in motorcars or airplanes to prevent accidents. To measure the data of crack opening ratio, the same materials and methods are used for evaluating the fatigue crack propagation rate as an effective stress intensity factor. But, many researchers have brought different results. An exact crack opening ratio was, therefore, proposed for getting a more accurate fatigue crack propagation rate.

• Journal of Mechanical Science and Technology
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• v.17 no.6
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• pp.796-804
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• 2003

The use of fracture mechanics has traditionally concentrated on crack growth under an opening mechanism. However, many service failures occur from cracks subjected to mixed-mode loading. Hence, it is necessary to evaluate the fatigue behavior under mixed-mode loading. Under mixed-mode loading, not only the fatigue crack propagation rate is of importance, but also the crack propagation direction. In modified range 0.3$\leq$a/W$\leq$0.5, the stress intensity factors (SIFs) of mode I and mode II for the compact tension shear (CTS) specimen were calculated by using elastic finite element analysis. The propagation behavior of the fatigue cracks of cold rolled stainless steels (STS304) under mixed-mode conditions was evaluated by using K$\_$I/ and $_{4}$ (SIFs of mode I and mode II). The maximum tangential stress (MTS) criterion and stress intensity factor were applied to predict the crack propagation direction and the propagation behavior of fatigue cracks.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.7
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• pp.214-220
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• 1999

In order to use effectively a machinery part with fillet, it is necessary to determine a proper fillet shape in design step, Study of such problem by fracture mechanical criterion is rare. So, this paper focuses on the design of fillet radius in fracture mechanical aspect. Finite element method was used to obtain crack tip stress intensity factor. Stress intensity factor was calculated by COD(crack opening displacement0method proposed by Ingraffea and Manu. The parameter used in this study are thickness ration, filet radium and crack length . If fillet radius increase , crack propagation may be accelerated. Critical crack length is inversely proportional to fillet radius.

• Geomechanics and Engineering
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• v.33 no.4
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• pp.393-400
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• 2023

Displacements near crack and stress intensity factor (SIF) are key parameters to solve rock failure issue when using fracture mechanics. In order to study the horizontal displacement and stress intensity factor of the mode I fracture, a series of three-point bending tests of granite specimens with central notch were carried out. The evolution of horizontal displacements of precast notch and crack tip opening displacements (CTOD) were analyzed based on the digital image correlation (DIC) method. Stress intensity factors for three-point bending beams with arbitrary span-to-width ratios(S/W) were calculated by using the WU-Carlsson analytical weight function for edge-crack finite width plate and the analytical solution of un-cracked stress by Filon. The present study provides a high efficient and accurate method for fracture mechanics analysis of the three-point bending granite beams.

• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.961-971
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• 2004

Methods for determination of the crack opening stress intensity factor ($K_{op}$) and for estimation of the effective stress intensity factor range ($\Delta{K}_{eff}$) are evaluated for crack growth test data of aluminum alloys. Three methods of determining $K_{op}$, visual measurement, ASTM offset compliance method, and the neural network method proposed by Kang and Song, and three methods of estimating $\Delta{K}_{eff}$, conventional, the 2/PIO and 2/PI methods proposed by Donald and Paris, are compared in a quantitative manner by using evaluation criteria. For all $K_{op}$ determination methods discussed, the 2/PI method of estimating $\Delta{K}_{eff}$ provides good results. The neural network method of determining $K_{op}$ provides good correlation of crack growth data. It is recommended to use 2/PI estimation with the neural $K_{op}$ determination method. The ASTM offset method used in conjunction with 2/PI estimation shows a possibility of successful application. It is desired to improve the ASTM method.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.3
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• pp.924-930
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• 1991

본 연구에서는 크립게이지와 스트레인게이지를 사용하여 정확한 크랙 열림점 의 값을 제시하고져 한다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1493-1502
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• 1992

The purpose of this study is to identify the effects of loading variables on fatigue crack opening behavior, using structural steel SS41. To use various stress ratios, three kinds of the methods varying stress ratio were used; .DELTA.P const., P$_{max}$ const., and P$_{min}$ const.. To measure the opening load, the direct measuring method which measures the distance between two micro indentations 20 .mu.m behind crack tip and the elastic compliance method were used. As the results of present study, the following conclusions are obtained. First, using the direct measuring method, it was possible to measure the COD at any location behind crack tip. Second, as measuring point becomes farther from crack tip, opening load becomes smaller. Third, the acceleration of da/dN near notch is due to crack opening behavior. Finally, opening ratio is a function of not only R, but .DELTA.K.K.K.

• Journal of the Korean Wood Science and Technology
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• v.27 no.4
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• pp.51-56
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• 1999

Finite element method was utilized to analyze crack tip stress and displacement field under drying stress case as stepwise loading. Opening mode of single-edge-notched model was employed and analyzed by linear elastic fracture mechanics of plane stress case. The drying stresses were applied as stepwise loads at the boundary elements of the model with 10 steps of time serial. The stress intensity factor($K_I$) for opening mode reached to its maximum just prior to the stress reversal. The $K_I$ from the displacement fields revealed 1.7 times higher than those from stress fields. By comparing the two sets of $K_I$ from displacement and stress fields, single parameter $K_I$ showed its validity to characterize displacement fields around the crack tip front while stress field could not be characterized due to large variations between two sets of data.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.138-144
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• 2003

Rencentely, the request for the light weight is more incresed in the area of industrial environment and machinery and consistent effort is needed to accomplish high strength of material for the direction of light weight. we got the following characteristic from crack growth test carried out in the range of stress ration of 0.1, 0.3 and 0.6 by means of opening mode displacement. At the content stress ratio, the threshold stress intensity factor crack range ${\Delta}K_{th}$in the early stage of fatigue crack growth (Region I) and dtress intensity factor range ${\Delta}K$ in the stable of fatigue crack growth (Region II) with an increase in ${\Delta}K$. Fatigue life shows more improvement in the Shot-peened material than in the Un-peening material. And compressive residual stress of surface on the Shot peening processed operate resistance force of fatigue. So we can obtain fallowings. (1) The fatigue crack growth rate on stage II is conspicuous with the size of compressive residual stress and is depend on Paris equation. (2) Although the maxium compressive residual stress is deeply and widely formed from surface, fatigue life does not improve than when maxium compressive residual stress is formed in surface. (3) The threshold stress intensity factor range is increased with increasing compressive residual stress.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.5
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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.