• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1193-1199
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• 1990

Effects of strain hardening exponents on the behavior of fatigue crack propagation are experimentally investigated. The retardation effect of fatigue crack propagation after single overloading is investigated in relation to strain hardening exponent and crack closure. A relationship between crack opening ratio and strain hardening exponents is inspected through an examination of the crack closure behavior. An empirical equation relating retardation effect of fatigue crack propagation after single overloading, percent peak load and strain hardening exponent of materials is proposed.

• Smart Structures and Systems
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• v.9 no.4
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• pp.355-371
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• 2012

A composite element method (CEM) is presented to analyze the free and forced vibrations of a cracked Euler-Bernoulli beam with axial force. The cracks are introduced by using Christides and Barr crack model with an adjustment on one crack parameter. The effects of the cracks and axial force on the reduction of natural frequencies and the dynamic responses of the beam are investigated. The time response sensitivities with respect to the crack parameters (i.e., crack location, crack depth) and the axial force are calculated. The natural frequencies obtained from the proposed method are compared with the analytical results in the literature, and good agreement is found. This study shows that the cracks in the beam may have significant effects on the dynamic responses of the beam. In the inverse problem, a response sensitivity-based model updating method is proposed to identify both a single crack and multiple cracks from measured dynamic responses. The cracks can be identified successfully even using simulated noisy acceleration responses.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.264-271
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• 2005

This study investigates the behavior of fatigue crack propagating between holes or holes filled with another materials. When holes or the holes bonded with another materials exist near center crack symmetrically, crack propagation rate is influenced by the bonding force of brazing part and the elastic modulus ratio of another material to matrix. It is experimentally and analytically confirmed that the center crack stops when its tip reaches near the center line of the holes and a small crack is initiated from the boundaries of holes or the holes filled with another materials and it propagates to final fracture. The mechanical behaviors of center crack near another materials are also investigated.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.6
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• pp.74-82
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• 2005

This study investigates the behavior of fatigue crack propagating between holes or holes filled with another materials. When holes or the holes bonded with another materials exist near center crack symmetrically, crack propagation rate is influenced by the bonding force of brazing part and the elastic modulus ratio of another material to matrix. It is experimentally and analytically confirmed that the center crack stops when its tip reaches near the center line of the holes and a small crack is initiated from the boundaries of holes or the holes filled with another materials and it propagates to final fracture. The mechanical behaviors of center crack near another materials are also investigated.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.289-292
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• 2004

This study was performed to know effective control of crack occurred by hydration heat, restraint of multiplication of hydration heat, through mechanical test, strength test and crack control test using fluosilicate salt based anti-crack agent made from by-product during phosphoric acid manufacturing process. Mix proportions for experiment were modulated at 0.495 of water to cement ratio and addition amount of fluosilicate salt based anti-crack agent to $1.0\%$. Condensation time was late and compressive strength of hardened concrete cured at several days was executed to evaluate characteristics of crack control for concrete. It is ascertained that characteristics of crack control for concrete could be improved by an adequate addition of fluosilicate salt based anti-crack agent.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.9 s.252
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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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1536-1544
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• 1992

A relatively simple prediction method is proposed for initially semicircular surface crack growth under axial loading. The method takes into account the difference in surface crack closure behavior at the depth point and at the surface intersection point, and also the relationship of crack closure for surface crack and through-thickness crack. The prediction method provides conservative estimation for fatigue life within factor of two, and the predicted crack geometry variations agree well with the observed results. As a result, the prediction method proposed here is considered to be useful for engineering application.

• Journal of the Korean Society of Safety
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• v.17 no.4
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• pp.38-44
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• 2002

The application of fractal concept provides an useful method in the study for the quantitative analysis of irregular variations like the fracture surfaces and crack profiles. Fractal curves have characteristics that represents a self-similarity based on the fractal dimension. The fractal dimensions were obtained by the box counting method. In this report, we obtained the nearly stable fractal dimensions of fracture crack profiles for STS316 with CT specimen as the crack advances and the relationships between crack length and fractal dimension. Moreover fractal fracture parameter that corresponds to J-R curve is shown by the relationships between fractal dimension and crack extension. From the results, we concluded that crack extension of high toughness material also shows the fractal characteristics, which can be used in order to evaluate the crack life precisely.

• Journal of the Korean Society of Safety
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• v.12 no.2
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• pp.57-64
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• 1997

Fatigue crack propagation behaviors and life prediction for SUS 321 plate and its electron beam weld metal were investigated using compact tension specimens. The larger the stress ratio is, the faster the crack propagates, but the variation of crack propagation rate decreases. The effect of stress ratio is greater in the slow crack propagation area than in the faster one. The crack propagation rate of electron beam weld metal is faster than that of base metal because of hardening, weld defect and residual stress in welding area. The crack propagation rate of transverse weld metal has a lower than that of base metal due to the effect of residual stress, but in the time of passing through welding area, has a higher rate. The crack propagation rate using $\Delta$K$_{eff}$ can be well plotted regardless of stress ratio. The fatigue life prediction method of considering crack closure more exactly predicts fatigue life than conventional one. conventional one.e.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.4
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• pp.181-188
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• 2002

The objective of this study is to determine crack depth located under steel reinforcement in concrete specimens using ultrasonic method. Experimental studies were performed on concrete specimens containing vertical and inclined surface-opening cracks with known depths. The other studies were carried out on specimens with flexural crack. Experimental results have shown that the crack depth is effectually measured when the distance between the probes is less than the crack depth. The effect of steel on crack depth estimation is studied through a model by considering P-waves diffaction at the tip of crack and steel. In addition, experimental results show that the ultrasonic method is one of useful methods to evaluate the crack depth in reinforced concrete.