• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.11a
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• pp.177-179
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• 2002

A1$_2$ $O_3$기판재료의 $K_{IC}$ 증가를 위한 재료설계를 시도하였다. 먼저 A1$_2$ $O_3$기판을 구성하는 A1$_2$ $O_3$다층구조물에 적절한 다공성 중간층을 삽입하는 샌드위치 구조물을 제조하였다. 제조된 A1$_2$ $O_3$구조물의 미세구조를 관찰하였고, Vickers 경도와 three-point bending test를 통해서 단일조성 구조물과 샌드위치 구조물의 경도와 인성 측정치를 비교하였다. 다공층을 삽입한 A1$_2$ $O_3$샌드위치 구조물의 Single-Edge Notched Beam이 단일 조성의 구조물에 비해 파괴강도와 인성이 향상되는 결과를 얻었다.

• Journal of the Korean Society for Precision Engineering
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• v.7 no.2
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• pp.65-73
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• 1990

Speckle photography is a simple non-contacting method for analysing surface displacement. In its basic form, the object to be studied is illuminated with a beam of laser light from any convenient direction, and a double exposure photography of the surface recorded on the fine-grain film, the object is undergone the displacement to be measured between exposures. Like this, it allows the strain field to be evaluated in two dimensions. A direct experimental comparison of speckle photography with theoretical value on a notched tensile test specimen showed that serious errors could, however, occur due to local surface tilting and due to aberra- tions of the imaging lens. Methods of minimising these effects and those of the speckle de-correlation which occurs by the various conditions are discussed.

• Advances in materials Research
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• v.11 no.4
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• pp.351-374
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• 2022

Softening function is the primary input for modeling the fracture of concrete when the cohesive crack approach is used. In this paper, based on the laboratory data on notched beams, an inverse algorithm is proposed that can accurately find the softening curve of the concrete. This algorithm uses non-linear finite element analysis and the damage-plasticity model. It is based on the kinematics of the beam at the late stages of loading. The softening curve, obtained from the corresponding algorithm, has been compared to other softening curves in the literature. It was observed that in determining the behavior of concrete, the usage of the presented curve made accurate results in predicting the peak loads and the load-deflection curves of the beams with different concrete mixtures. In fact, the proposed algorithm leads to softening curves that can be used for modeling the tensile cracking of concrete precisely. Moreover, the advantage of this algorithm is the low number of iterations for converging to an appropriate answer.

• Structural Engineering and Mechanics
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• v.91 no.3
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• pp.239-250
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• 2024

With the aim to provide better predication about fracture behavior, a numerical simulating strategy based on the rigid spring model is proposed for reinforced concrete (RC) structures in this study. According to the proposed strategy, concrete is partitioned into a series of irregular rigid blocks based on the Voronoi diagram, which are connected by interface springs. Steel bars are simulated by bar elements, and the bond slip element is defined at bar element nodes to describe the interaction between reinforcement and concrete. A concrete damage evolution model based on the separation criterion is adopted to describe the weakening process of interface spring between adjacent blocks, while a nonlinear bond slip model is introduced to simulate the synergy behaviour of reinforced steel bars and concrete. In the damage evolution model of concrete, the influence of compressive stress perpendicular to the interface on the shear strength is considered. To check the effectiveness and applicability of the proposed modelling, experimental and numerical studies about a simply-supported RC beam and the two-notched concrete plates in Nooru-Mohamed's experiment are conducted, and the grid sensitivity are investigated.

• Journal of the Korean Ceramic Society
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• v.43 no.1 s.284
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• pp.4-9
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• 2006

To test the fracture toughness of alumina; a Surface-Crack-in-Flexure (SCF) method, a Single-Edge-Precracked-Beam (SEPB) method and a Single-Edge-V-Notched-Beam (SEVNB) method were used at crosshead rates ranging from 0.005 mm/min to 2 mm/ min and relative humidity ranging from $15\%\;to\;80\%$. The results show that the fracture toughness tested by the SCF method increases with either an increasing loading rate or decreasing relative humidity; in contrast, the toughness by the SEPB method and the SEVNB method does not depend on the loading rate or the relative humidity. Theoretical analysis of the way slow crack growth affects the apparent fracture toughness indicates that the three testing methods have different effects with respect to the loading rate and the relative humidity; moreover, these differences are attributable to differences in the size of the cracks or notches.

• Journal of the Korean Ceramic Society
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• v.44 no.7
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• pp.343-348
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• 2007

Alumina/silver nanocomposites were fabricated using a soaking method through a sol-gel route to construct an intra-type nanostructure. The pulse electric-current sintering (PECS) technique was used to sinter the nanocomposites. Several specimens were annealed after sintering. The microstructure, mechanical properties, critical frontal process zone (FPZ) size, and thermo-mechanical properties of the nanocomposites were estimated. The relative densities of the specimens sintered at 1350 and $1450^{\circ}C$ were 95% and 99%, respectively. The maximum value of the three-point bending strength was found to be 780 MPa for the $2{\times}2{\times}10 mm$ specimen sintered at $1350^{\circ}C$. The fracture toughness of the specimen sintered at $1350^{\circ}C$ was measured to be $3.60 MPa{\cdot}m^{1/2}$ using the single-edge V-notched beam (SEVNB) technique. The fracture mode of the nanocomposites was transgranular, in contrast to the intergranular mode of monolithic alumina. The fracture morphology suggested that dislocations were generated around the silver nanoparticles dispersed within the alumina matrix. The specimens sintered at $1350^{\circ}C$ were annealed at $800^{\circ}C$ for 5 min, following which the maximum fracture strength became 810 MPa and the fracture toughness improved to $4.21 MPam^{1/2}$. The critical FPZ size was the largest for the specimen annealed at $800^{\circ}C$ for 5 min. Thermal conductivity of the alumina/silver nanocomposites sintered at $1350^{\circ}C$ was 38 W/mK at room temperature, which was higher than the value obtained with the law of mixture.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3A
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• pp.309-316
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• 2010

This paper proposed a nonlocal anisotropic damage model to simulate the behavior of plain and reinforced concrete structures that are predominantly tensile and compressive load. This model based on continuum damage mechanics, used a symmetric second-order tensor as the damage variable. For quasi-brittle materials, such as concrete, the damage patterns were different in tension and in compression. These two damage states were modeled by damage evolution laws ensuring a damage tensor rate proportional to the total strain tensor in terms of principal components. To investigate the effectiveness of proposed model, the double edge notched specimen experimented by nooru-mohamed and reinforced concrete bending beam were analyzed using the implementation of the proposed model. As the results for the simulation, the nonlocal anisotropic damage model with an adequate control of rupture correctly represented the crack propagation for mixed mode fracture. In the structural failure of reinforced concrete bending beam, the proposed model can be showed up to a very high damage level and yielding of the reinforcements.

• Korean Journal of Materials Research
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• v.28 no.3
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• pp.142-147
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• 2018

${\beta}-Tricalcium$ phosphate (TCP) was added to $Al_2O_3$ to make a biomaterial with good mechanical properties. Using a TCP powder synthesized by a polymer complexation method, $Al_2O_3$ composites containing 30 wt% TCP were fabricated and characterized for densification, phase, microstructure, strength, and fracture toughness. With optimizing the powder preparation conditions, a high densification of 97 % was obtained by sintering at $1350^{\circ}C$ for 2 h. No reaction between the two components occurred and there was no transition to ${\alpha}-TCP$. TCP grains with a size of $2-4{\mu}m$ were well surrounded by $Al_2O_3$ grains with a size of $1{\mu}m$ or less. Strength 61(Brazilian) or 187(3-p MOR) MPa, and fracture toughness 1.7 (notched beam) or 2.5 (indentation) $MPa{\cdot}m^{1/2}$ were obtained, which are large improvements over the strength of $TCP/Al_2O_3$ composites and toughness of TCP and hydroxyapatite in previous studies.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.6
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• pp.437-443
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• 2014

Vibration testing is conducted for evaluate the fatigue resistance of responsible system over excitation situations and two kinds of vibration profiles, harmonic or random, are widely used in engineering fields. Harmonic excitation profile is adequate for the rotating machinery that is primarily exposed to the orderly excited force subjected for a rotating speed; Random profile is suitable for the non-stationary vibration input, that is a ground excitation for example. Recently, the sine on random(SOR) testing method was sometimes considered to represent the real excitation conditions since the measured response signals of a target system, expecially for moving mobility, shows usually a mixture of them. So, it is important to understand the accumulated fatigue damage over different excitation patterns, harmonic and/or random, to determine the efficient vibration profile of a target system. A uniaxial vibration testing with a notched simple beam was introduced to evaluate the fatigue damage for different excitation profiles and the best choice of vibration profile was concluded from those comparison of calculated fatigue damages.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.340-345
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• 2014

Vibration testing is conducted for evaluate the fatigue resistance of responsible system over excitation situations and two kinds of vibration profiles, harmonic or random, are widely used in engineering fields. Harmonic excitation profile is adequate for the rotating machinery that is primarily exposed to the orderly excited force subjected for a rotating speed; Random profile is suitable for the non-stationary vibration input, that is a ground excitation for example. Recently, the sine on random (SOR) testing method was sometimes considered to represent the real excitation conditions since the measured response signals of a target system, expecially for moving mobility, shows usually a mixture of them. So, it is important to understand the accumulated fatigue damage over different excitation patterns, harmonic and/or random, to determine the efficient vibration profile of a target system. A uniaxial vibration testing with a notched simple beam was introduced to evaluate the fatigue damage for different excitation profiles and the best choice of vibration profile was concluded from those comparison of calculated fatigue damages.