• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.7
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• pp.1373-1380
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• 1992

The local cyclic strain distribution near the crack tip has been investigated by the fine Dot Grid Strain Measurement Method, which had been suggested strain measurement method to resolve experimental difficulties by authors. It has been found that the magnitude of the local cyclic strain distribution(.DELTA..epsilon.$_{eq}$ )near a crack tip has been varied by the applied cyclic load level and material, but the shape of the local cyclic strain distribution near the crack tip has been experimentally scrarcely altered : that is .DELTA..epsilon.$_{eq}$ = .DELTA.A.f(.theta.). $r^{-1}$ . Consequently, the local cyclic strain field near the crack tip could be favorably characterized by a single parameter fatigue strain intensity factor .DELTA.A. In addition, with the viewpoint that .DELTA.A depends on material and load level, .DELTA.A has been applied to evaluate the fatigue crack propagation rate and usefulness of the result has been considered. As a result, it has been ascertained that .DELTA.A has been a useful parameter to evaluate the fatigue crack propagation rate.

• Elastomers and Composites
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• v.34 no.4
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• pp.341-349
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• 1999

In this study, heat and crack resistance of natural rubber (NR) compounds was evaluated. To prevent the effects of the crosslinking system, a conventional vulcanization system was selected, where the accelerator/sulfur ratio was fixed to 0.25. Vulcanizates containing phenylenediamine showed high tensile strength and tear strength compared to other vulcanizates because phenylenediamine can cause additional crosslinking and high dispersion In the vulcanizates. In the pure shear test, vulcanizates containing phenylenediamine showed an excellent tearing energy which was due to the irregular crack path, and showed excellent heat and crack resistance which was also due to the good dispersity of antioxidant and additional crosslinks in the rubbber vulcanizates.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.46-50
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• 1993

The sensitivity study to evaluate the effects of parameters on the fatigue crack propagation life under the constant loadings is executed in the previous study of the authors. It is shown that the effect of the crack opening ratio is large comparatively. The purpose of this paper is to evaluate the effects of parameters on the fatigue crack propagation life under the random loadings. A new method of evaluation of the effective stress under the random loadings is developed. The sensitivity study of parameters on the fatigue crack propagation life under the random loadings is executed by using it.

• Proceedings of the Korean Nuclear Society Conference
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• 2002.10a
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• pp.300.1-300
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• 2002

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.8
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• pp.1015-1021
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• 2010

In this study, the effect of the C/SiC composition ratio on the impact damage of a reaction sintered SiC (RS-SiC) plates was evaluated. An impact test was conducted by using an air gun. The impacter used was a steel ball with a diameter of 2 mm, and the impact velocities were 113, 122, and 180 m/s. The RS-SiC plates were $20\times20\times3$ mm with different C/SiC composition ratios. The ring crack diameters damaged by a steel ball were determined using SEM images. It was observed that the maximum diameter increased with increasing impact velocity, and it rapidly changed with increasing C/SiC composition ratio because of the effect of residual Si and the variation flexural strength. Cone cracks were formed in the case of C/SiC composition ratios of 0.4~0.5, this indicated that the impact damage changed from a ring crack to a cone crack in this critical range of C/SiC composition ratios. The C/SiC composition ratio of 0.3 was determined to be the optimal ratio for the RS-SiC manufacturing process.

• Journal of the korean Society of Automotive Engineers
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• v.15 no.1
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• pp.100-106
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• 1993

This paper aims to synthesize the research on fatigue fracture 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 method 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. The main conclusions obtained are as follows. (1) As a result of the fatigue test, the value of the crack opening ratio is the same regardless of the stress ratio. (2) The value of crack opening ratio is different according to the measuring point. After measuring the crack propagation rate by using an effective stress intensity factor, the crack opening ratio value measured at the crack mouth by a clip gage, or measured rear of the specimen by a strain gage is more accurate than that by any other measuring test.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.598-606
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• 2001

Recently, semiconductor packages trend to be thinner, which makes difficult to detect defects therein. A preconditioning test is generally performed to evaluate the reliability of semiconductor packages. The test procedure includes two scanning acoustic microscope (SAM) tests at the beginning and end of the entire test, in order to help detect physical defects such as delaminations and package cracks. In particular, of primary concern are package cracks and delaminations caused by moisture absorbed under ambient conditions. This paper discusses the failure mechanism associated with the moisture absorbed and encapsulated in semiconductors, and the use SAM to detect failures such as tracks and delaminations grown during the preconditioning test.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.3
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• pp.313-318
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• 2001

To establish nondestructive test method for aerospace composite materials, various composite specimens were tested and analyzed using acoutic emission. The hit rate of acoustic emission closely was rotated with crack initiation and propagation. This report also presents defection capability of crack initiation pressure, initial crack active location, and crack propagation using acoustic emission.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.5 no.1
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• pp.65-68
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• 2004

When a monolithic component of piston and rebound is produced by sintering process, some technical problems such as clogging of holes during post-machining, dimensional change around the holes, and cracking of the component edges due to concentration of mechanical stress during machining are frequently encountered. To solve these problems, we systematically evaluated and investigated the density of green compacts and sintered parts, the microstructural change around the holes, and the attenuation and durability of the sintered parts in this study. By doing so, it was able to solve above problems.

• The Journal of Engineering Geology
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• v.4 no.2
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• pp.139-151
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• 1994

Rocks are composed of the discrete elements of microstructures such as different grains and microcracks. The studies of these microstructures are of increasing interest in engineering geology and civil engineering related to construction of a deep under-ground space. Accordingly, instead of a simplified continuum approach, discrete structural elements and mechanical properties of various grains must be accounted. But it is difficult to analyse crack and discontinuity surfaces in Euclidean geometry. So, Mandelbrot( 1983) developed fractal theory to manage irregular body in nature. In this study, geometrical properties of microstructures to estimate a relation between crack propagation and stress were calculated. Then it is shown that fractal theory can be applied to research real mechanical behavior of rocks.