• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.402-407
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• 1995

The effects of room temperature and strain aging treatment are discussed on the critical condition for the onset of growth of non-propagating cracks on 0.15% C low carbon steel, with special emphasis on the length of the critical non-propagating crack and on the crack opening displacement(COD) at the crack tip. It is found from the experimental analysis that room temperature and strain aging of a fatigue pre-cracked specimen introduced the closure of a crack tip of the pre-crack and the reduction of crack opening displacement at the wake of crack, together with an improvement in crack growth resistance of the microstructure. This may cause an increase in the endurance limit of the specimen, through the enhancement of effective stress for the onset of growth of the critical non-propagating crack.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.2
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• pp.179-188
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• 2011

Steel structures have been allowed to have fatigue damage tolerance in fact. If it would be assessed whether fatigue crack is growing or not and How fast fatigue crack is propagating, we should make a rational decision on methods and a period of reinforcement in the maintenance. In this study, fatigue crack growth tests on two kinds of through-thickness cracked steel plates and a out-of-plane gusset welded joint were conducted to evaluate fatigue crack growth rate using the COD(Crack Opening Displacement), and COD measurement using strain gauges was examined to offer a practical method. As a result, we proposed a reasonable assessing method for fatigue crack growth rate using the COD and it was experimentally proved practical to estimate the COD through measuring strains.

• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.589-597
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• 2010

Steel structures have a higher probability of being damaged by fatigue than by other causes of deterioration. As such, their maintenance to prevent fatigue damage is essential to sustain their safety and performance during their service period. In their maintenance, the current state of their fatigue cracks must be assessed to determine appropriate reinforcement methods and the suitable time intervals of periodic inspections when fatigue cracks are detected. Determining the crack growth rate is a successful method of predicting fractures, but it requires technical knowledge on fracture mechanics and experience in numerical methods and software for finite element analysis. In this study, a fatigue crack growth test on through-thickness cracked steel plates was conducted to assess the crack growth rate without superior technical knowledge and experience. The relationship between the Crack Opening Displacement (COD) and the crack growth rate was found in relatively long fatigue cracks.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.725-730
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• 2010

The leak-before-break behavior and the crack opening displacement were investigated of statically indeterminate piping system and statically determinate piping system after a crack penetration. The reduction in the ultimate strength caused by a crack was relatively small in the statically indeterminate piping system. The leak-before-break in the statically indeterminate piping system had a larger safety margin than that in the statically determinate piping system. The crack opening displacement after crack penetration in a pipe with a nonpenetrating crack was evaluated by using a plastic rotation angle.

• International Journal of Automotive Technology
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• v.7 no.3
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• pp.337-343
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• 2006

Numerical calculations are made in order to find a possible correlation between the J-integral and the crack mouth opening displacement(CMOD) in dynamic nonlinear fracture experiments of 3-point bend(3PB) specimens. Both elastic-plastic and elastic-viscoplastic materials are considered at different impact velocities. The J-integral may be estimated from the crack mouth opening displacement which can be measured directly from photographs taken during dynamic experiments.

• Steel and Composite Structures
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• v.20 no.4
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• pp.951-962
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• 2016

The determination of the stress intensity factor at the crack tip is one of the most widely used methods to predict the fatigue life of aircraft structures. This prediction is more complicated for repaired cracks with bonded composite patch. This study is used to compute the stress intensity factor (SIF) and crack opening displacement (COD) for cracks repaired with single and double-sided composite patches. The effect of the presence of disbond region in adhesive at the crack was taken into consideration. The results show that there is a considerable reduction in the asymptotic value of the stress-intensity factors and the crack opening displacement at the crack tip. The use of a double-sided patch suppresses the bending effect due to the eccentricity of the patch on one side only.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.11
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• pp.1873-1880
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• 2001

The effects of restraint of pressure induced bending(PIB) on crack opening for circumferential through-wall crack in a pipe were investigated. In this study, the elastic and elastic-plastic finite element analyses were performed to evaluate crack opening displacement(COD) for various restraint conditions and crack size. The results showed the restraint of PIB decreased crack opening for a given crack size and tensile stress, and the decrease in crack opening was considerable for large crack and short restraint length. A1so, the effect was more significant in tole results of elastic-plastic analysis compared with in the elastic analysis results. In the elastic-plastic analysis results, tole restraint effect was increased with increasing applied tensile stress corresponding to internal pressure. Additionally, the restraint effect on COD was independent on the variation in pipe diameter and decreased with increasing pipe thickness, and It depended on not total restraint length but shorter restraint length for non-symmetrically restrained.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.849-855
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• 2000

This study evaluated the effect of restraint of pressure induced bending(PIB) on crack mouth opening displacement(CMOD) for circumferential through-wall crack in pipe by using both elastic and elastic-plastic finite element analyses. The analyses results showed the restraint of PIB was decreased crack opening for a given crack length and tensile stress, and the effect was considerable for large crack and short restraint length. Also, the restraint effect on CMOD was independent on the variation in pipe diameter and decreased with increasing pipe thickness, and it depended on not total restraint length but short restraint length for non-symmetrically restrained. Additionally, the effect of restraint of PIB was more significant in the elastic-plastic analysis results compared with in the elastic analysis results.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.3
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• pp.178-185
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• 2005

Crack tip displacement is originated by tensile stress component, s and shear stress component, t on pure Mode I and pure Mode II. The crack tip displacement(CTD) depends on combined types of different two stress components under mixed-mode loading conditions (MMLC). Thus, the analysis of crack tip displacement must be CTD vector, dv which is composition of ds and dt under MMLC. In this paper, various effects of MMLC on the crack closure are studied experimentally. The crack closure magnitude is calculated from the information of crack tip displacement under MMLC. This information has been obtained from the high resolution optical microscope in direct observations of crack displacement behavior at the crack tip. Observed crack tip displacement is analyzed by using CTD vector to determine crack opening load. The various effects of MMLC on the crack closure are explained using crack opening ratio with crack length and mode mixture. The effective stress intensity factor considering crack closure is also discussed.

• Journal of Ocean Engineering and Technology
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• v.12 no.1
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• pp.50-57
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• 1998

The leak before break(LBB) concept is generalized on the design of LNG tanks, pressure vessels and nuclear reactor in that any leakage of containment, in whatever amount, will not result in catastropic failure. For this purpose it is necessary to determine the surface crack shape, the opening displacement and the risk of catastropic brittle fracture when it becomes a through crack. In this study the crack propagation behavior of surface flaws and the crack opening displacement of through cracks under combined membrane and bending stresses were investigated with fatigue tests and fracture toughness test of aluminium alloy A5083-O. And fracture mechanics analysis of the crack opening displacement of through cracks were made in order to develop a new model expressing the behaviors of COD under combined membrane and bending stresses.