• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.890-893
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• 2002

This study is focused to predict the behavior of Al foam with closed-cell structure during the 3 point bending test and the upsetting test according to aspect ratio. We calculated characters of aluminum foams with closed-cell structure and took the simulation. The effects on the aspect ratio of the cell was investigated parametrically. The analysis was carried out on two models, First, the bending test in elasticity of the rectangular beam, and Second, the upsetting test in plasticity of the circular cylinder. In the analysis, the deformation of the beam and the cylinder was influenced by the aspect ratio of the cell. Further, We assumed that the geometry of feared aluminum cell change the stress and strain in the test.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.381-382
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• 2006

The mechanical behaviors of multi-layered foam core sandwich composite were investigated through a 3-point bending test. The sandwich specimens were obtained from sandwich panel consisting of aluminum faces and urethane foam core. Three types of sandwich specimens such as a single structure, a double structure and a triple structure were considered. The span of sandwich specimens were varied from 170mm to 350mm. According to the results, the flexural and shear properties of multi-layered sandwich composite were found to be higher than those of single-layered sandwich composite.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.3
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• pp.63-67
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• 2016

In this paper, we present an indirect method of elastic modulus measurement for various lamination layers formed on polymer-based compliant substrates. Although the elastic modulus of every component is crucial for mechanically reliable microelectronic devices, it is difficult to accurately measure the film properties because the lamination layers are hardly detached from the substrate. In order to resolve the problem, 3-point bending test is conducted with a film-substrate specimen and area transformation rule is applied to the cross-sectional area of the film region. With known substrate modulus, a modulus ratio between the film and the substrate is calculated using bending stiffness of the multilayered specimen obtained from the 3-point bending test. This method is verified using electroplated copper specimens with two types of film-substrate structure; double-sided film and single sided film. Also, common dielectric layers, prepreg (PPG) and dry film solder resist (DF SR), are measured with the double-sided specimen type. The results of copper (110.3 GPa), PPG (22.3 GPa), DF SR (5.0 GPa) were measured with high precision.

• Composites Research
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• v.34 no.4
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• pp.226-232
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• 2021

In this paper, development of tape-springs made of composite materials was conducted for the deployment structures along with design, analysis, fabrication, and numerical and experimental investigation of mechanical behavior of the tape-springs. To this end, the tape-springs were manufactured according to three stacking patterns, and numerical and experimental investigation were conducted to determine whether or not they were damaged during bending with various selected composite materials. Finally, optimal stacking patterns that do not cause damage were selected during bending. With this information, the four-point bending test was conducted to obtain the moment-rotation curves. From results, it was confirmed that the nonlinear hysteresis phenomenon of the tape-springs was properly realized according to folding and unfolding. Therefore, it was confirmed that the composite material tape spring was properly developed.

• Composites Research
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• v.36 no.3
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• pp.180-185
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• 2023

This paper investigates the impact of fiber dispersion on the internal structure and mechanical strength of SiC_f/SiC composites manufactured using spread SiC fibers. The fiber volume ratio of the specimen to which spread SiC fiber was applied decreased by 9%p compared to the non-spread specimen, and the resin slurry impregnated between the fibers more smoothly, resulting in minimal matrix porosity. In order to compare the fiber dispersion of each specimen, a method was proposed to quantify and evaluate the separation distance between fibers in composite materials. The results showed that the distance between fibers in the spread specimen increased by 2.23 ㎛ compared to the non-spread specimen, with a significant 42.6% increase in the distance between fiber surfaces. Furthermore, the 3pt bending test demonstrated a 49.3% higher flexural strength in the spread specimen, accompanied by a more uniform deviation in test data. These findings highlight the significant influence of SiC fiber dispersion on achieving uniform densification of the SiC_f/SiC matrix and increasing mechanical strength.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.13-13
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• 2009

현재 열간단조 금형을 제작함에 있어 육성용접을 실시하는 방법이 금형강 STD61, STD11 등으로 제작하는 방법에 비해 보수나 비용적인 측면에서 이점을 가지고 있기 때문에 점차적으로 증가하고 있는 추세이다. 열간단조 공정에서 금형은 $1000^{\circ}C$이상의 고온재료와 반복접촉하게 된다. 이때 이형제의 사용은 급속냉각 및 급속가열의 열피로를 가속시킨다. 또한, 금형은 반복충격에 의한 기계적 피로를 받게 된다. 이러한 금형의 사용환경을 고려한 FCW는 종래 고가의 $2.8{\sim}3.2{\Phi}$인 외국산 FCW를 사용하였으나 이를 대체한 $3.2{\Phi}$ 태경 FCW가 국내에서 개발되었다. 하지만 개발된 FCW를 사용하여 제작된 금형의 수명이 부족한 현상이 발생하였다. 이에 금형의 수명을 연장시킬 수 있는 내균열성 및 내열충격성을 확보한 태경 FCW의 개발과 개발된 FCW의 성능평가가 요구되었다. 특히 열간단조 금형에 있어서 중요한 내열충격성의 경우 가열과 냉각의 반복 Cycle에 의한 Thermal shock의 평가가 대부분이며 높은 Cycle로 인해 많은 시간이 걸리며, 또한 가열과 냉각을 오갈 수 있는 고가의 시험장치가 요구된다. 그러므로 개발된 FCW 육성용접부의 내균열성 및 내열충격성을 평가할 수 있는 방법에 대한 연구와 특히 내열충격성을 시간이 적게 걸리면서도 경제적으로 평가할 수 있는 방법에 대한 연구가 필요하다. 본 연구의 목적은 열간단조 금형 육성용접부의 내균열성 및 열충격특성을 평가할 수 있는 방법에 대한 검토와 특히 내열충격성에 대해 J.W.Kim등의 시험방법을 참고하여 시간이 적게 걸리면서 저 비용으로 열 충격특성을 평가할 수 있는 시험법을 고안하는 것이다. 이를 위한 방법으로 육성용접부의 내균열성을 평가하기 위한 상온 Bending을 실시하였고, 내열충격성을 평가하기 위한 염욕로를 이용하는 고온 Bending을 고안하여 실시하였다. 상온 Bending, 고온 Bending 모두 3점 굽힘시험을 적용하였다. 고온 Bending의 가열방법으로는 염욕로를 사용하여 시편이 대기중에서 약 $850^{\circ}C$의 온도가 될 수 있도록 하였다. 시편은 각각 열처리를 하여 요구 경도를 확보하였고, 이를 염욕로에서 5분간 가열 및 유지하여 취출 후 굽힘하중을 가하여 변위의 정도로 열충격을 평가하는 방법을 사용하였다. 상온 Bending은 극한변형량과 파단부 극한응력으로, 고온 Bending은 고온 극한변형량으로 평가를 하였고, 외국산 FCW를 사용한 육성용접부를 비교대상으로 하였다. 평가 결과 개발된 국산 $3.2{\Phi}$ 태경 FCW의 성능은 외국산 FCW와 유사하거나 우수한 것으로 평가되었고, 실제 금형을 제작하여 현장에 적용한 결과 금형의 수명이 연장된 것이 나타났다.

• Journal of Dental Rehabilitation and Applied Science
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• v.32 no.3
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• pp.169-175
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• 2016

Purpose: Direct splinting material should have high flexural strength to withstand force during mastication and low modulus of elasticity to provide some movement while force applied for relief of stress. The purpose of this study was to compare flexural strength and modulus of elasticity of several resinous splinting materials. Materials and Methods: Four materials; Super-Bond C&B, G-FIX, G-aenial Universal Flo, FiltekTM Z350 XT; were used in this study. Fifteen rectangular bar specimens of each material were prepared. Three-point bending test were performed to determine physical properties. Maximum load at fracture was recorded and flexural strength and modulus of elasticity were calculated. One-way analysis of variance (ANOVA) and Scheffe's tests at a 0.05 level of significance were conducted on all test results. Results: Statistical analysis reveals that Super-Bond C&B had significant low mean value for flexible strength and the other three materials showed no significant difference. For modulus of elasticity, Super-Bond C&B exhibited statistically lower modulus of elasticity. G-FIX presented intermediate result, showing statistically higher modulus of elasticity than Super-Bond C&B but lower than G-aenial Universal Flo and FiltekTM Z350 XT. There was no significant difference on modulus of elasticity between G-aenial Universal Flo and FiltekTM Z350 XT. Conclusion: Using a G-FIX, the newly commercially available splinting material, which shows higher fracture resistance properties comparable to flowable and restorative composite resin and a relatively flexible nature might be a beneficial for stabilizing teeth mobility.

• Computational Structural Engineering
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• v.8 no.4
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• pp.87-97
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• 1995

For the same configuration of two-dimensional finite element models, 6-node element exhibits stiffer bending stiffness than 8-node element. This is true in the relation between 16-node element and 20-node element for three-dimensional model. This stiffening phenomenon comes from the elimination of several mid nodes from full-node elements. Therefore, this may be called 'relative stiffness stiffening phenomenon'. It seems that there are a couple of ways to correct the stiffening effect, however, we could find only one effective method-the method of modification of Gauss sampling points-which passes the patch test and does not alter other kinds of stiffness, such as extensional stiffness. The quantity of modification is a function of Poisson's ratios of the constituent materials. We could obtain two modification equations, one for plane stress case and the other for plane strain case. This method can be extended to 3-dimensional solid elements. Except the exact plane strain cases, most 3-dimensional plates could be modeled successfully with 16-node element modified by the equation for the plane stress case. The effectiveness of the modification method is checked by applying it to several examples with excellent improvements. In numerical examples, beams with various boundary conditions are subjected to static and time-dependent loads. Free and forced motion analyses of beams and plates are also tested. The beam and plate may be composed of isotropic multilayers as well as a single layer.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.2
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• pp.114-119
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• 2008

The modern automotive industry develops innovative vehicle designs to meet increasing stability of car and performance demands of their customers. The improvement of frame rigidity by the structural foam is thought to be an effective means to improve the performance because of high applicability and minimum weight. The object of this paper is to examine the use of structural foam in a hat section as an optimum reinforcing means, to compare the reinforcing performance of structural foam versus a plastic reinforcement. The result of this paper indicated that reinforcing efficiencies are achieved by structural foam and plastic reinforcement shape.

• Journal of Ocean Engineering and Technology
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• v.13 no.2 s.32
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• pp.35-40
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• 1999

Effects of CuO addition on the sintering ability and the phase stability of Y-TZP. (Yttria doped Tetragonal Zirconia Polycrystals) were studied. The CuO dopants were found to be quite effective in reducing the sintering temperature to obtain full density and refining the grain size. The maximum allowable concentration of the dopants was limited to 0.3%mol% for CuO to maintain fully tetragonal phase. With the addition of these dopants, the flexual strength decreased by 20% in comparison with the undoped specimen but the fracture toughness increased by 15%.