• 한국안전학회지
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• 제8권2호
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• pp.51-57
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• 1993

This study was done by ultrasonic testing. The proves used in this study were 5Z10$\times$10A70. The useful fatigue life of structural components is determined by the sum of the elapsed load cycles required to initiate a fatigue crack and to propagate the crack from subcritical size to critical dimensions. Thus, to predict the service life of many steel structures and to establish safe inspection intervals, an understanding of the Fatigue Crack Initiation and Fatigue Crack Propagation behavior in the steel is required. In the present study, the Fatigue Crack Initiation Life in SPS 5A steel was investigated by testing specimens having widely varying notch acuities. The variation in the notch acuity covered the range from notch root raidus 0.5mm to 2.5mm, and Fatigue Crack Initiation Life data were obtained in that range.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.600-603
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• 2005

In this paper we studied about the effect of the double cracks on the dynamic behavior of a simply supported beam. The equation of motion is derived by using Lagrange's equation and analyzed by numerical method. The simply supported beam is modeled by the Euler-Bernoulli beam theory. The crack section is represented by a local flexibility matrix connecting three undamaged beam segments. The influences of the crack depth and position of each crack on the vibration mode and the natural frequencies of a simply supported beam are analytically clarified. The theoretical results are also validated by a comparison with experimental measurements.

• 대한기계학회논문집A
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• 제27권6호
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• pp.981-986
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• 2003

In order to investigate the possibility of processing of brittle material by ball impact, the effects of boundary conditions about impact damage of soda-lime glass by small spheres were evaluated experimentally. It was investigated that crack appearance developed in soda-lime glass with boundary conditions of without sealing, single-sealing and double-sealing by impact velocity. The double-sealing was most effective in the development of perfect cone than other boundary condition. In case of double-sealing condition, PVC and Polyurethane sealing were more effective in producing a perfect cone formation than other sealing materials. The impact velocity range over which perfect cones were formed was influenced by both the contact area and diameter of impact particle.

• International Journal of Precision Engineering and Manufacturing
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• 제9권3호
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• pp.33-39
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• 2008

The effects of a double crack and tip masses on the dynamic behavior of cantilever beams with a moving mass are studied using numerical methods. The cantilever beams are modeled by applying Euler-Bernoulli beam theory. The cracked sections are represented by a local flexibility matrix connecting three undamaged beam segments. The influences of the crack, moving mass, and tip mass, and the coupling of these factors on the vibration mode and the frequencies of the double-cracked cantilever beams are determined analytically. The methodology provides a basis for analyzing the dynamic behavior of a beam with an arbitrary number of cracks and a moving mass.

• 한국소음진동공학회논문집
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• 제15권4호
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• pp.483-491
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• 2005

In this paper a dynamic behavior of a double-cracked cantilever pipe with the tip mass and a moving mass is presented. Based on the Euler-Bernoulli beam theory, the equation of motion is derived by using Lagrange's equation. The influences of the moving mass, the tip mass and double cracks have been studied on the dynamic behavior of a cantilever pipe system by numerical method. The cracks section are represented by the local flexibility matrix connecting two undamaged beam segments. Therefore, the cracks are modelled as a rotational spring. This matrix defines the relationship between the displacements and forces across the crack section and is derived by applying fundamental fracture mechanics theory. We investigated about the effect of the two cracks and a tip mass on the dynamic behavior of a cantilever pipe with a moving mass.

• 대한기계학회논문집A
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• 제22권2호
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• pp.321-329
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• 1998

To ensure the structural integrity of the autofrettaged thick-walled cylinder subjected to cyclic internal pressure loading, the fatigue crack propagation life of the cylinder was evaluated. Stress intensity factors of the external cracked cylinder due to internal pressure and autofrettage loadings were calculated using the finite element method. The fatigue crack propagation lives of the cylinder based on the fracture mechanics concepts were predicted and compared to the experimental fatigue lives evaluated from the C-shaped simulation specimens. There were good correlations between the predicted and experimental fatigue lives within a factor of 3 for the single and double grooved C-shaped simulation specimens. Predicted fatigue crack propagation lives of the double grooved cylinders were about 1.5-5 times longer than those of the single grooved cylinders depending on the levels of autofrettage.

• International Journal of Automotive Technology
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• 제5권4호
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• pp.303-309
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• 2004

In this paper, an interfacial crack length has been detected by using the ultrasonic attenuation coefficient on the adhesively bonded double-cantilever beam (DCB) joints. The correlations between energy release rates which were investigated by experimental measurement, the boundary element method (BEM) and Ripling's equation are compared with each other. The experimental results show that the interfacial crack length for the ultrasonic attenuation coefficient and energy release rate increases proportionally. From the experimental results, we propose a method to detect the interfacial crack length by using the ultrasonic attenuation coefficient and discuss it.

• Tribology and Lubricants
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• 제18권3호
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• pp.219-227
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• 2002

A linear elastic fracture mechanics analysis of double subsurface cracks propagation in a half-space subjected to moving thermomechanical surface traction was performed using the finite element method. The effect of frictional heat at the sliding surface on the crack growth behavior is analyzed in terms of the thermal load and peclet number. The crack propagation direction is predicted in light of the magnitudes of the maximum shear and tensile stress intensity factor ranges. When moving thermomechanical surface traction exists, subsurface horizontal cracks are propagation in-plane crack growth rate at the beginning but they are propagation out-of-plane crack growth rate by the frictional heat which is occurrence by the repeated sliding contact.

• Steel and Composite Structures
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• 제20권4호
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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.

• 연구논문집
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• 통권31호
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• pp.127-133
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• 2001

In chromium electrodeposition, crack is inevitably accompanied by chromium layer. Behavior of crack formation and crack density were different from the plating conditions such as current density, temperature, waveform of applied current and so on. And cracks have an influence on the corrosion resistance of chromium deposit, because corrosion occurs through the network of cracks between deposit and substrate. Therefore, many researches have been achieved in order to remove the cracks in chromium deposit. Formation of double layers, Cr/Cr and Ni/Cr were investigated to increase corrosion resistance of chromium deposit in this study. As pretreatment prior to outer chromium coating, acid pickling and current control method were examined. Cracks in cross-section of each sample were observed with SEM and CASS(Copper modified acetic acid salt spray) test was performed to evaluate corrosion resistance. It was found that corrosion resistance of Cr/Cr and Ni/Cr double layers were superior to Cr or Ni single layer from the results of CASS test.