• Design & Manufacturing
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• 제17권2호
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• pp.42-46
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• 2023

Currently, fossil resources are depleting rapidly. We are looking for energy to replace fossil fuels. They are trying to use electricity to replace internal combustion locomotives. Secondary battery raw materials and chemical additives are pulverized by the high-speed rotation of the grinding disc of the Classifier Separator Mill. Grinding Disc Assembly requires characteristics to withstand abrasion, corrosion, high-speed rotational force and impact. Domestic and foreign grinding discs were analyzed through abrasion resistance, hardness, bending strength, and tensile adhesion strength tests.

• 한국자동차공학회논문집
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• 제18권1호
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• pp.127-130
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• 2010

This paper deals with the formability of DP590 steel considering the strain rate. The strain hardening coefficient, elongation and r-value were obtained from the static and dynamic tensile test. As strain rate increases from static to 100/s, the strain hardening coefficient and the uniform elongation decrease and the elongation at fracture and r-value decrease to 0.1/s and increase again to 100/s. The high speed forming limit tests with hemi-spherical punch were carried out using the high speed crash testing machine and high speed forming jig. The high speed forming limit of DP590(order of $10^2$/s) decreases compared to the static forming limit(order of $10^{-3}$/s) and the forming limit band in high speed forming test is narrower than that in the static forming test. This tendency may be due to the development of brittleness with increase of stain rate.

• 대한치과보철학회지
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• 제40권4호
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• pp.344-351
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• 2002

The purpose of this study is to compare tensile bond strength between Cr-Co alloy and three denture base resins after surface treatment. Following the manufacturer's instructions, 180 bonded specimens were made from three denture base resins (Lucitone 199. Paladent 20. POSS resin) and three surface treatment methods (sandblasting. metal primer. silicoating) 20 samples were made in each group and a half was ther-mocycled 1000 times between $5^{\circ}C$ and $55^{\circ}C$. The tensile bond strength was measured using an Instron with 5mm/min crosshead speed. Data was analyzed with one-way ANOVA, T-test and Duncan test. The results were as follows : 1. Samples with metal primer coating had significantly high tensile bond strength than the other surface treated groups (p<.05). Significantly low tensile bond strength was shown in sand blasted groups (p<.05). 2. No significant difference was observed in metal primer coating groups before and after ther-mocycling (p>.05) 3. Tensile bond strength was decreased in silicoated samples after thermocycling (p<.05). 4. Of the surface treated groups with metal primer, Lucitone 199 had the greatest bond strength and POSS resin and Paladent 20 were followed (p<.05). 5. Of the surface treated groups with silicoating, POSS resin and Lucitone 199 had greater bond strength than Paladent 20 (p<.05).

• 한국자동차공학회논문집
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• 제20권5호
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• pp.8-12
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• 2012

Application for laser welding have increased steadily in recent years due to its benefits such as high speed, high productivity and high density energy heat source. In this study, the influence of welding parameters was investigated on penetration characteristics, mechanical properties including formability test in disk laser welded 1000MPa class steels. A shielding gas was used and bead-on-plate test was performed with various welding speeds. The main welding test was performed by butt welding with various welding speeds at 2.5 kW laser power.

• 한국레이저가공학회지
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• 제7권2호
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• pp.1-10
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• 2004

This work was attempted to join SCP sheet and STS304 sheet by using Nd:YAC laser beam. SCP sheet has good formability and low cost, while STS304 has excellent corrosion resistance and mechanical properties in high temp. In this experiment, butt joint type was used to develop the tailored blank welding for dissimilar steel. Sheets which have different thermal properties. Computer simulation was conducted to obtain the off-set position for efficient welding by considering laser power, scanning speed, focal length and basic properties. The result showed that the optimum thermal distribution was obtained when the laser beam was irradiated at $0.05{\sim}0.1$ mm off-set toward the SCP sheet side. The experiment was conducted based on the result of computer simulation to show the same optimum conditions. Optimum conditions were 3KW in laser beam power, 6m/min in scanning speed, -0.5mm in focal position, 0.1mm off-set toward SCP. Microhardness test, tensile test, bulge test, optical microscopy, EDS, and XRD were performed to observe the microstructure around fusion zone and to evaluate the mechanical properties of optimum conditions, The weld zone had high microhardness values by the formation of the martensitic structure. Tensile test measured the strength of welded region by vertical to strain direction and the elongation of welded region by parallel to strain direction. Bulge test showed $52\%$ formability of the original materials. Bead shape, grain size, and martensitic structure were observed by the optical microscopy in the weld zone. Detailed results of EDS, XRD confirmed that the welded region was connected of martensitic structure.

• 대한기계학회논문집A
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• 제40권3호
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• pp.281-288
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• 2016

복합재는 재료 불균질성에 의해 고속 충돌 시 방호성능 자료가 산포한다. 본 연구에서는 다수의 충돌시험으로 복합판재 잔류속도 산포를 확보하고 수치해석으로 예측하는 방법을 정립하였다. 먼저 10개의 동일 시편으로 인장시험을 수행하여 파단변형률 산포를 얻었다. 같은 재료로 제작된 4ply([0/90]s)와 8ply([0/90/0/90]s) GFRP(Glass Fiber Reinforced Plastic) 복합판재에 FSP(Fragment Simulating Projectile) 고속 충돌시험을 동일 조건에서 다수 수행하여 잔류속도 산포를 얻었다. 인장시험에서 얻어진 파단 변형률 분포를 이용하여 수치해석을 수행하였다. 충돌속도는 4ply와 8ply 각각 411.7m/s와 592.5m/s이다. 시험 결과와 비교하여 적절한 잔류속도의 산포를 예측할 수 있었다. 추가적으로 복합판재의 경우 Solid요소 대비 Layered Solid요소로 모델링하면 계산시간이 감소되었다.

• 대한조선학회논문집
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• 제58권5호
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• pp.322-329
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• 2021

Naval ships are designed to have a variety of active and passive systems to defend against enemy threats. One of the passive defense systems is to protect crew members and core equipment against the threat by using the outer plate of the equipment. This study was intended to deal with design methods against small arms ammunition and fragments. The Korea Institute of Machinery and Materials has measured the ballistic limit velocity of two types of high-tensile plate materials (AH36 and EH36) widely used in ships and offshore structures through tests in cooperation with various related organizations, and the result data is continuously accumulated. Based on the accumulated test results and data, such as mil test certificates of plate materials, it is intended to estimate the protection limit speed of high-tensile plates and to develop a simple calculating formula that can be used in the early design stage.

• 소성∙가공
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• 제20권4호
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• pp.309-315
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• 2011

The behavior of metallic materials at high strain rates shows different characteristics from those in quasi-static deformation. Therefore, the strain rate should be considered when simulating crash events. The objective of this paper is to evaluate the dynamic tensile characteristics of SPRC440 as a function of the volume fraction of phases. As-received SPRC440 is composed of ferrite and pearlite phases. However, ferrite and martensite phases were observed after heat treatment at $730^{\circ}C$ and $780^{\circ}C$ for 5 minutes, as expected by calculations based on the curves from dilatometry tests. High cross-head speed tensile tests were performed to acquire strain-stress curves at various strain rates ranging from 0.001 to $300\;s^{-1}$, which are typical in real vehicle crashes. It was observed that the flow stress increases with the strain rate and this trend was more pronounced in the as-received specimens consisting of ferrite and pearlite phases. It is speculated that the dislocation density in each phase has an influence on the strain rate sensitivity.

• 한국해양공학회지
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• 제15권4호
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• pp.60-65
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• 2001

Thermal spray coating is formed by a process in which melted particles flying with high speed towards substrate, then crash and spread on the substrate surface cooled and solidified in a very short time, Stacking of the particles makes coating. In this study, the exfoliation of $Al_2$O$_3$ and Ni-4.5wt.%Al thermally sprayed coating which were deposited by an atmospheric plasma spray apparatus are investigated using an AE method. A tensile test is conducted on notch specimens in a stress range below the elastic limit of substrate. The wave forms of AE generated from the three coating specimens can be classified by FFT analysis into two types which low frequency(type I waveform is considered to corresponds exfoliation of coating layers and type II waveform corresponds the plastic deformation of notch tip or the resultant fracture of coating. The fracture of the coating layers can estimate by AE event and amplitude, because AE features increase when the deformation generates.

• 소성∙가공
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• 제14권6호
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• pp.559-564
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• 2005

INCONEL 718, nickel based superalloy, has good formability, high strength, excellent corrosion resistance and mechanical properties at high temperature. Owing to theses attractive properties, it is utilized in applications such as combustion system, turbine engines and nuclear reactors. In such applications, components are typically required to be tolerant of high stress impact loading. This may cause material degradation and lead to catastrophic failure during service operation. Accurate understanding of material's mechanical properties with various strain rates is required in order to guarantee the reliability of structural parts made of INCONEL 718. This paper is concerned with the dynamic material properties of the INCONEL 718 at various strain rates. The dynamic response of the INCONEL 718 at the intermediate strain rate is obtained from the high speed tensile test and at the high strain rate is from the split Hopkinson pressure bar test. The effect of the strain rate on dynamic flow stress, work hardening characteristics, strain rate sensitivity and elongation to the failure is evaluated with the experimental results. Experimental results from both the quasi-static and the high strain rate up to 5000/sec are interpolated in order to construct the Johnson-Cook model as the constitutive relation that should be applied to simulate and design the structural parts made of rNCONEL 718.