• 한국산학기술학회논문지
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• 제21권12호
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• pp.434-439
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• 2020

최근, 치과 산업에서 레이저를 열원으로 합금을 제조하는 선택적 레이저 용융법(Selective laser melting, SLM)이 소개되고 있다. 하지만 SLM으로 제작된 금속-세라믹 수복물에 대한 연구가 부족한 실정이다. 따라서 본 연구의 목적은 SLM 그리고 CAST(casting)에 의해 제조된 Co-Cr 합금의 금속-세라믹(metal-ceramic) 결합 강도(bond strength)를 평가하는 것이다. SLM 그리고 CAST 방법을 사용하여 Co-Cr 시편을 제조하고 세라믹을 소결하여 시료를 제작하였다. 연구의 실험은 표본 준비 및 분석을 통해 2020년 1월부터 6월까지 수행되었다. 금속-세라믹 결합 강도는 만능 시험기에 의해 측정되었다. 부착 세라믹의 면적분(The area fraction of adherence ceramic, AFAC)은 SEM/EDS로 시편의 Si 함량을 측정하였다. 금속-세라믹 결합 강도 및 AFAC 결과는 t-test를 사용하여 분석하였다(α = .05). SLM 그리고 CAST Co-Cr 합금 사이의 결합 강도에 대해서는 유의한 차이가 발견되지 않았다(P>.05). SLM은 CAST 그룹보다 많은 세라믹 부착성(ceramic adherence)을 나타냈다(P<.001). 세라믹과 합금의 결합 강도는 제조 방법엥 영향을 받지 않았다. 그러나 SLM은 더 우수한 세라믹 부착성을 보였다. 이는 향후 임플란트 상부 보철물 제작에도 SLM으로 제작한 합금이 사용 가능한 것을 시사한다. CAST 방식의 단점을 극복하고 시간과 비용을 절약할 수 있을 것으로 기대된다.

• 대한치과보철학회지
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• 제36권6호
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• pp.858-866
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• 1998

Soldering is the usual method used to correct an unstable fixed partial denture framework at patient's try-in; However, presoldering base metal alloys is technique-sensitve and results are unstable because it is difficult to maintain uniform heat distribution and to prevent oxidation of an alloy. A cast-joining technique has been developed by Weiss and Munyon for repair, correction and addition to base metal framework. This joining technique eliminates the problem with presoldering of non-precious frameworks. The object of this study was to 1) compare the relative flexure strength and the joining effectiveness of Ni-Cr-Be cast in two pieces and 'pre-soldered' versus in two pieces and 'cast-joined'. 2) determine the effect of increasing the number of retentive grooves on the face of the cast and 3) determine the effect of the relative matched position of groove patterns on flexure strength. The joining effectiveness can be expressed by the ratio of the mean flexure stress of soldered or cast-joined specimens to that of one-piece cast. Resin rods 3mm in diameter were used as pattern of specimens for one-piece casted, presoldered, and cast-joined groups. Cast-joined specimens had two different patterns of retentive grooves on the joined faces. Type A had cross-shaped grooves 1mm in depth. 0.6mm in width. Type B was the same except for the addition of one more retentive groove. In the experiment connecting cast-joined specimens, half of specimens with type A pattern had their patterns on the faces of paired casts matched with each other as mirror image. With the rest pairs, it was proceeded that one of paired casts turned 45 degrees so that the patterns crossed. Half of specimens with type B pattern also had the patterns matched as mirror image; However, here, one of paired casts turned 90 degrees with the other pairs. Retentive groove in this study lacked the intentional undercuts, in contrast with the suggestion of Weiss and Munyon. The specimens were subjected to four-point flexural loading in an Instron testing machine. The midspan flexural stress was calculated at the point of initial plastic strain as determined from a strip-chart recorder or at the point of failure if this occured at a lower stress level. Within the scope of this study, the following results were obtained. 1. The presoldered group showed flexural strength at least 2 times higher than the cast-joined groups. Its joining effectiveness was 82%. 2. In cast-joined groups, the flexural strength of joints with type B patterns exhibited 1.5 times that of joints with type A patterns. Joining effectivenesses were 38% for type B patterns, 25-26% for type A patterns. 3. The relative matched position of groove patterns did not have any significant effect on flexural strength of the cast-joined specimens with either type A patterns or type B patterns(p>.05).

• 한국산학기술학회논문지
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• 제10권12호
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• pp.3559-3566
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• 2009

종래에는 신발 부품 등을 제작하는데 주조금형을 가열, 냉각하는 별도의 가열판과 냉각판을 사용해 왔다. 그러나 이것은 금형을 가열 및 냉각하는데 시간이 너무 오래 걸리는 단점이 있었다. 따라서 본 연구에서는 기존의 가열판과 냉각판을 사용하던 방법을 대체하여 파이프 인서트 주조 금형을 사용한 신발창의 프레스 성형에 대한 적용 가능성을 제안하였다. 유한요소법을 사용한 수치해석이 금형의 온도분포 해석에 적용되었으며, 또한 LabView에 의해 그 온도를 실제로 측정하였다. 프레스 성형용 파이프 인서트 주조금형에 의해 부품을 제작하는 공정은 특히 생산성면에서 아주 효과적이라고 검증되었다.

• 한국주조공학회지
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• 제19권1호
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• pp.47-53
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• 1999

Squeeze casting process has been used in the field of a commercial manufacturing method, in which metal is enforcedly solidified under pressure enough to prevent the cast defects such as either gas porosity or shrinkage defect. In this paper, to clarify the relationship between applied pressures and macro ${\cdot}$ microstructural behaviors in gravity and direct squeeze casts, specimens were cast by various squeezing pressures during solidification of 7000 series Al wrought alloy in the metal die designed specially. The applied pressures used in this study were 0, 25, 50, and 75 MPa. The microstructural morphologies of squeeze cast were more fine and dense with increasing the applied pressures, because of the greater solidification rate of billet resulting from the applied pressure. A normal segregation phenomenon of an increasing in amount of eutectics towards the center of the billet was observed for squeeze casts, whereas gravity cast showed an inverse segregation phenomenon of an increasing in amount of eutectics towards the edge in the billet. This change in segregation pattern which is normal or inverse is due to a higher radial temperature gradient and reduced time in the semi solid state for squeeze casting.

• Structural Engineering and Mechanics
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• 제19권2호
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• pp.173-184
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• 2005

For reducing construction cost, two-plate-girder bridges are getting popular in Japan. This type of bridge employs a PC slab, which is often cast-in-place. In such a case, concrete is not usually cast over the whole slab at one time: some portions are constructed earlier than the rest. Therefore, a construction joint is inevitably created. Due to the drying shrinkage of concrete, tension stress may occur in concrete slab. High tensile stress can be expected near the construction joint where concretes with different ages meet. Moreover, prestressing is not applied over the whole length of slab at one time. This may also serve as a source of tensile stress in the slab. Thus there is a chance that cast-in-place PC slab, especially near the construction joint, may be subjected to tensile cracking. In the present study, stress states near the construction joint in the cast-in-place PC slab of a two-plate-girder bridge are investigated numerically. The finite element method is employed and the three-dimensional analysis is conducted to see the influence of dry shrinkage and prestressing. The stress states in the PC slab thus obtained are discussed. The simplified model of a plate girder for this class of analysis is also proposed.

• Geomechanics and Engineering
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• 제19권2호
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• pp.115-126
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• 2019

The long-term settlement characteristics for the cast-in-place bored pile in the deep-thick soft soil are investigated by post-grouting field tests. Six cast-in-place bored engineering piles and three cast-in-place bored test piles are installed to study the long-term settlement characteristics. Three post-grouting methods (i.e., post-tip-grouting, post-side-grouting, and tip and side post-grouting) are designed and carried out by field tests. Results of the local test show that decreased settlements for the post-side-grouted pile, the post-tip-grouted pile and the tip and side post-grouted pile are 22.2%~25.8%, 30.10%~35.98% and 32.40%~35.50%, respectively, compared with non-grouted piles. The side friction resistance for non-grouted piles, post-side-grouted pile, post-tip-grouted pile and the tip and side post-grouted pile undertakes 89.6~91.3%, 94.6%, 92.4%~93.0%, 95.7% of the total loading, respectively. At last, the parameters back analysis method and numerical calculation are adopted to predict the long-term settlement characteristics of the cast-in-place bored pile in the deep-thick soft soil. Determined Bulk modulus (K) and a creep parameter (Ks) are used for the back analysis of the long-term settlement of the post-grouted pile. The settlement difference between the back analysis and the measurement data is about 1.11%-7.41%. Long-term settlement of the post-grouted piles are predicted by the back analysis method, and the predicted results show that the settlement of the post-grouted pile are less than 6 mm and will be stable in 30 days.

• 소성∙가공
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• 제19권6호
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• pp.378-386
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• 2010

Nowadays there has been great interest in using heat treated cast material for press dies due to several advantages like reduction in die production costs. However, in hot press forming processes H13 forged tool steel is mostly used. Cooling performance of dies in hot press forming processes is considered as an important factor of study and also the IHTC parameter between cast material die and sheet metal should be considered as an essential. In the present study, the IHTC was calculated for the sheet metal in the hot press forming process with cast and forged material dies. The temperature measurements were performed for the sheet metal, casting and forged material dies by applying various contact pressure in hot press forming. IHTC was calculated and studied by adopting the inverse heat convection method in DEFORM-2D. Each IHTC was considered as a function of contact time and contact pressure. The experimental data were compared with calculated data obtained from the proposed equation and references.

• 한국기계가공학회지
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• 제18권7호
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• pp.90-96
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• 2019

Recently, friction stir welding of dissimilar materials are one of the biggest issues in terms of light-weight and eco-friendly technology of the automotive, aircraft and ship industry. In this study, friction stir welding of dissimilar materials is introduced with different tool rotational speed. Materials used in experimentation consist of A357 gravity cast aluminum alloy and FB590 high-strength steel plates. Dissimilar materials of plate type are fabricated with width of 150mm, length of 300mm and thickness of 3mm and welding is carried out by the lap joint method. The correlation between probe length and mechanical properties were investigated according to rotational speed and welding speed at tool tilt angle 0 degree. Consequently, feasibility of FSWed dissimilar materials were successfully presented in case of cast aluminum and high-strength steel at lap joint method.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.113-120
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• 2005

Soil nailing system can be mentioned to a method of supporting as the shear strength of in-situ soils is increased by passive inclusions. In the general soil nailing system, facing walls are used in two kind of a lattice concrete block or a cast in placed concrete wall. A case of lattice concrete blocks is used in slow slopes greater than 1:0.7. Also, a case of a cast in placed concrete wall is used in steep slopes less than 1:0.5. The cast in placed concrete walls are constructed to 30cm thick together with a shotcrete facing. In this study, the assembling soil nailing method as a new soil nailing system is proposed. This method is constructed assembly using precast concrete panels. Therefore ability of the construction and quality of the facings can be modified than a usual soil nailing system. Also, this method can be obtained the effects that a global slope stability increase, as precast concrete panels is put on cutting face after excavating a slope.

• 비파괴검사학회지
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• 제6권2호
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• pp.17-36
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• 1987

In this experimental research, fracture mechanisms of spheroidal graphite cast iron (As Cast, annealed and normalized) were investigated by using Acoustic Emission (AE) technique. In this study, the data (AE signal) are digitized and processed with the 8 bits micro-computer (APPLE II) connected to the AE measuring device without data processing unit. The source of AE signal was estimated by fractography analysis. The results obtained in this experimental study are summarized as follows : For the heterogeneous materials (spheroidal graphite cast iron) with inclusions which may considered as cracks, it is found that low and high AE amplitude appear simultaneously and the load is found to be fluctuated in the final stage of deformation. But the lad is not fluctuated in tension test with low AE amplitude only. AE is measured within elastic region and it is confirmed that 0.2% offset yield load agrees approximately with the load point where AE counts decrease steeply after the point of maximum AE counts.