• Geomechanics and Engineering
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• 제14권1호
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• pp.29-42
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• 2018

This paper presents the results of an empirical study in which square rock-like blocks containing two parallel pre-existing rough non-persistent joints were subjected to uniaxial compression load. The main purpose of this study was to investigate uniaxial compressive strength and deformation modulus of jointed specimens. Response Surface Method (RSM) was utilized to design experiments and investigate the effect of four joint parameters, namely joint roughness coefficient (JRC), bridge length (L), bridge angle (${\gamma}$), and joint inclination (${\theta}$). The interaction of these parameters on the uniaxial compressive strength (UCS) and deformation modulus of the blocks was investigated as well. The results indicated that an increase in joint roughness coefficient, bridge length and bridge angle increased compressive strength and deformation modulus. Moreover, increasing joint inclination decreased the two mechanical properties. The concept of 'interlocking cracks' which are mixed mode (shear-tensile cracks) was introduced. This type of cracks can happen in higher level of JRC. Initiation and propagation of this type of cracks reduces mechanical properties of sample before reaching its peak strength. The results of the Response Surface Methodology showed that the mutual interaction of the joint parameters had a significant influence on the compressive strength and deformation modulus.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.383-388
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• 2001

Effects of particle property variation of cone crack shape according to impact velocity in silicon carbide materials were investigated. The damage induced by spherical impact having different material and size was different according to materials. The size of ring cracks induced on the surface of specimen increased with increase of impact velocity within elastic contact conditions. The impact of steel particle produced larger ring cracks than that of SiC particle. In case of high impact velocity, the impact of SiC particle produced radial cracks by the elastic-plastic deformation at impact regions. Also percussion cone was formed from the back surface of specimen when particle size become large and its impact velocity exceeded a critical value. Increasing impact velocity, zenithal angle of cone cracks in SiC material was linearly decreasing not effect of impact particle size. An empirical equation, $\theta=\theta_{st}-\upsilon_p(180-\theta_{st})(\rho_p/\rho_s)^{1/2}/415$, was obtained from the test data as a function of quasi-static zenithal angle of cone crack($\theta_{st}$), the density of impact particle(${\rho}_p$) and specimen(${\rho}_s$). Applying this equation to the another materials, the variation of zenithal angle of cone crack could be predicted from the particle impact velocity.

• 한국정보통신학회논문지
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• 제9권7호
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• pp.1575-1581
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• 2005

최근에 콘크리트 구조물에 발생한 균열의 영향에 대한 관심이 커져 과거와 다르게 발생한 균열을 방치하기보다 보수를 통해 그 영향을 최소화시키고자 노력하고 있다. 본 논문에서는 콘크리트 표면 균열의 효율적인 측정을 위하여 점검자의 육안조사를 통한 수작업 대신 컴퓨터가 균열의 길이, 방향, 폭등의 특징을 자동으로 처리하는 화상처리 기법을 제안한다. 정확한 균열의 특징 추출을 위하여 빛의 영향을 보정할 수 있는 모폴로지 기법인 채움(Closing)연산을 적용하여 영상의 빛의 영향을 보정하고 Sobel 마스크를 적용하여 균열영상의 에지를 추출한 후, 반복 이진화를 적용하여 균열 영상을 이진화한다 그리고 이진화된 영상에서 잡음을 제거하기 위해 3${\times}$3 마스크를 이용하여 인접화소의 평균을 이용한 잡음 제거와 Glassfire Labeling 알고리즘을 이용한 잡음 제거를 각각 수행하여 균열의 에지를 추출하게 된다. 그리고 본 논문에서는 추출된 균열의 에지를 이용하여 균열의 특정부분의 길이, 방향, 폭을 자동으로 측정하는 표면 균열의 자동 처리 기법을 제안한다. 실험 결과에서는 제시된 방법이 균열의 검출에 효율적임을 나타내었고 검시자의 주관이 개입될 수 있는 가능성을 제거할 수 있는 가능성을 나타내었다.

• 열처리공학회지
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• 제16권6호
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• pp.335-340
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• 2003

To improve properties of wear resistance and anti-corrosion of the trivalent chromium platings, oxinitrocarbunsing and steam oxidation were conducted. Armophous trivalent Cr platings could be transformed to chromium carbides of high hardness, that showed low friction and wear rate. Even though micro-cracks were within as platings, superior anti-corrosion property was obtained by these treatments due to healing of cracks at the interface between the trivalent chromium platings and substrate.

• Journal of Welding and Joining
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• 제10권1호
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• pp.20-34
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• 1992

Characteristics of two correcting methods, a new Autogeneous GTAW heating (TIG) method and the conventional GMAW bead-on plate welding(MIG) method, for distorted aluminum fabrication structures were studied. As a result of microscopic study of Autogeneous GTAW heating and GMAW bead-on plate welding areas, porosities in weld metal and surface cracks in local heating zone were found. Through the mechanical tests, it was verified that porosities decrease tensile strength and surface of distortion, angular displacement and transeverse shrinkage were measures and compared. In order to investigate changes of material properties in heating area and cause of defects such thermal stresses were calculated by ADINA. Through the computations of transient thermal stresses and microscopic observation of fracture surface, thermal stress was found to be the cause of crack during Autogeneous GTAW heating.

• 한국정밀공학회지
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• 제12권11호
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• pp.36-44
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• 1995

When sliding a hard cylinder along the surface of glass, periodic surface cracks appear on the flat surface due to tensile stresses induced by the slider. These cracks propagate into the substrate and will affect the fracture properties of a body. Crack spacings and the directions of crack propagation into glass were calculated numerically by applying the finite element method and linear elastic fracture mechanics. The calculated crack spacings were in the range of the experimental results. Stress intensity factors and crack extension angles depended on the radius of slider and the load, and from these two factors the possible directions of crack propagation were calculated. The calculated propagation directions were in good agreement with real crack propagation.

• 한국정밀공학회지
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• 제8권4호
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• pp.118-125
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• 1991

Acoustic microscopy has attracted much interest recently as potential nondestructive evaluation technique for detecting and sizing defects of surface and sub-surface. Also acoustic emission testing method has been developed for detecting microcracks which is more than 30${\mu}m$ in length quantitatively on ceramics. In the present paper, acoustic emission during the four point bending test in hot-pressed sintered $Si_3N_4$ specimen which was stressed by thermal shock, has been measured by high sensitive sensing system. The surface and sub-surface cracks were detected by scanning acoustic micrscope of 800 MHz and conventional ultrasonic testing in C-scope image. The purpose was to investigate the location and size of cracks by SAM and AE technique, whose experimental data demonstrate good for detecting microcracks.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.165-170
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• 2000

The weight function method is an efficient technique to calculate the stress intensity factors for various loading conditions in that only the stress analysis of an uncracked model is required. This paper analyzes the mixed-mode stress intensity factors of surface and deepest points for quarter elliptical surface cracks in mechanical joints by weight function method and the coefficients included in weight function are determined by finite element analyses for reference loadings. Results for the different number of terms in weight function are presented.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1991년도 춘계학술대회 논문집
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• pp.127-133
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• 1991

Acoustic microscopy has attracted much intrest recently as potential mondestructive evalution technique for detecting and sizing defects of surface and sub-surface. Also acoustic emission testing method has been developed for detecting microcracks which is more than 30 umm in length quintitatively on ceramics material. In the present paper, acoustic emission during the four point bending test in hot-pressed sintered Si$\_$3/N$\_$4/ specimen which was stressed bythermal shock has been measured by high sensitive sensing system. The surface and sub-surface cracks were detected by scanning acoustic microscope of 800 MHz and conventional ultrasonic testing in C-scope image. The purpose was to investigate the location and size of cracks by SAM and AE technique, whose experimental datas demontrates good agreement for detecting microcracks.

• 대한기계학회논문집A
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• 제29권10호
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• pp.1336-1343
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• 2005

The detection mechanism of the flaw for the nondestructive testing using eddy current is related to the interaction of the induced eddy currents in the test specimen with flaws and the coupling of these interaction effects with the moving test probe. In this study, the two-dimensional electromagnetic finite element analysis(FEM) fur the eddy current signals of the aluminum plate with different depth of surface cracks is described and the comparison is also made between experimental and predicted signals analyzed by FEM. In addition, the characteristics of attenuation of the eddy current density due to the variation of the depth of a conductor are evaluated. The effective parameters for the application of eddy current technique to evaluate surface cracks are discussed by analyzing the characteristics of the eddy current signals due to the variation of crack depths.