• 한국산업융합학회 논문집
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• 제27권1호
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• pp.1-7
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• 2024

This study was investigated the effect of heat treatment on the microstructure and hardness of internally hardened ductile cast iron roll. The following conclusions were obtained. Some of the graphite was decreased and a bainite was produced by heat treatment. It decreased due to the decomposition of some of the cementite precipitated in the as-cast by heat treatment, but there was no significant change when it reached a certain depth. Hardness increased due to formation of bainite by heat treatment. On the surface, the hardness decreased due to the decrease in the amount of transformation of cementite into bainite, but there was no change beyond a certain depth.

• 한방재활의학과학회지
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• 제19권1호
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• pp.187-199
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• 2009

Objectives : The electroacupuncture was generally has been used in oriental medicine doctors. In recent years, there have been a few studies about safety and stability of acupuncture needle in itself, but then again research of acupuncture needle safety and stability on applying electroacupuncture have been insignificant. Therefore we investigated the safety and change in mechanical characteristic of acupuncture needle in electroacupuncture therapy. Methods : We observed mechanical characteristic change by SEM(Scanning Electron Microscope) and EDX(Energy Dispersive X-ray Spectroscopy), evaluated the hardness by vickers hardness tester. We used MTT assay and cell stain to study about biocompatibility of electroacupuncture. Results : In this study, any corrosion of material, alternation of elements, and change of hardness were not observed in surface analysis using SEM and EDX. In cytotoxity evaluation using MTT assay and cell stain, cell survival rate was low when practicing the electroacupuncture for more than 3 hours. Conclusions : Change of mechanical property was not observed based on the test results using surface analysis and hardness estimation by the electroacupuncture. And considering the biocompatibility, electroacupuncture was thought to be safe in an hour based on cytotoxity evaluation using MTT assay and cell stain.

• 대한치과기공학회지
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• 제45권3호
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• pp.55-60
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• 2023

Purpose: This study aimed to evaluate the effects of a special heat treatment on Pd-Au-Ag metal-ceramic alloy after degassing treatment and on changes in the hardness of the alloy during the firing process. Methods: Specimen alloys were cast and subjected to degassing at 900℃ for 10 minutes. These specimens were then subjected to a special heat treatment at 600℃ for 15 minutes in a dental porcelain furnace. Further, the specimens were subjected to simulated firing in the porcelain furnace. The resulting specimens were then tested for hardness, and changes in the microstructure were observed. Results: There was a decrease in the hardness of the alloy during the simulated firing of the cast alloy due to the coarsening of the particles. Meanwhile, additional heat treatment after degassing was found to play a crucial role in preventing a decrease in hardness. This treatment effectively suppressed the coarsening of the precipitates during repeated firing at high temperatures. Conclusion: Specific heat treatment of the Pd-Au-Ag metal-ceramic alloy prevented a decrease in its hardness and extended the lifespan of the metal-ceramic prosthesis.

• 열처리공학회지
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• 제8권4호
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• pp.318-325
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• 1995

Information of change of hardness values during applying load is needed often to control the quality of metal products efficiently, but the relation between applied stress and hardness has not been established. In this paper the theoretical relation between the rebound hardness and stress was examined briefly and the experiment was performed with some materials. Materials used in test were mild steel(SB41), 7-3 brass and copper, which were widely used in the commercial plants. Hardness was measured during stress applied using the Equo-Tip hardness tester as a kind of rebound hardness tester. Hardness values decreased as tensile stress increased, the decreasing rate was effected by the Young's modulus of each material, and the rebound hardness values showed linear relationship with the applied stress in elastic region.

• 열처리공학회지
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• 제4권1호
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• pp.19-29
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• 1991

This study was to investigate the influence of the substrate hardness on the hardness and adhesion of TiN thin film deposited by R.F. PACVD. Although the substrate hardness changed, chemical composition, stoichiometry and structure of TiN thin film did not change. ISE index was 1.96-1.99 for the substrate and was 1.57-1.79 for TiN thin film. And ISE index of TiN thin film was inverse proportion to the substrate hardness. When the substrate hardness was low, TiN thin film had many cracks around the indentation. But as the substrate hardness increased, TiN thin film had a few cracks and the deformation was limited within indentation. In having measured the adhesion of TiN thin film by SAT, the critical load (Lc) generally increased as the substrate hardness decreased.

• 한국전기전자재료학회논문지
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• 제25권11호
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• pp.916-921
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• 2012

This research measured the dielectric properties of silicone rubber with various hardness in 100 Hz~3 MHz, $30{\sim}170^{\circ}C$ conditions. When the hardness increases from 65 degree to 75 degree, the dielectric loss increased within frequency range of 100 kHz~3 MHz and was a little change in dielectric loss within temperature range of $90^{\circ}C{\sim}170^{\circ}C$. Thermogravimetric Analysis (TGA) showed the weight change rate increased a little while heated until $800^{\circ}C$. Scanning Electron Microscope (SEM) measurement showed that Aluminium Trihydroxide($AlOH_3$) which acts as a reinforcement agent reduced the size of the particles as the hardness increased.

• 한국공작기계학회논문집
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• 제16권3호
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• pp.109-116
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• 2007

The present study examined mechanical properties according to the change of outer circumference in the friction welding of A2024-T4 stock, which is used much as aircraft structure, truck wheel, stainless materials and A2024-T4 stock with 10 hollow at the center. Welding conditions were fixed at RPM 2,000rpm, friction pressure of 50MPa, friction time of 1.5sec, upset pressure of 120MPa and upset time of 2.0 seconds. From the result of this study were drawn conclusions as follows : According to the result of a tensile strength test, the solid shaft showed linear increase of tensile strength with the change of outer circumference, the hollow shaft showed maximum tensile stength when the length (L) was 2mm and decrease of tensile strength with the change of outer circumference, hardness appeared to increase and then decrease for welding interface, and it showed maximum hardness 155Hv at L=5mm of the solid shaft. Bending strength increased linearly far change of the distance (L) of outer circumference in the solid shaft and then decreased linearly in the hollow shaft. the result of examining tissue, the tissue grew finer around the welding interface and divided the basic material and the welding surface.

• 한국정밀공학회지
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• 제4권1호
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• pp.65-73
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• 1987

In recent days, the application of ultrasonics has been increased in the field of engineering and medicine. The ultrasonic hardness tester to apply the principle of contact compliance method is entirely different from hardness tester in the past and in the practical use, the more pre- cisive measurement is required because it has a slight change of hardness value due to the difference of resonance frequency. Therefore, in this study, as one type of applicative transducers which can detect the optimum pressure load, ring type load cell was used in the measurement of ultrasonic hardness. From experimental results, it was compared ultrasonic hardness testing method with the other hardness testing methods. Also, the measurement error of ultrasonic hardness tester could be measured within .+-. 0.5 HRC F.S. in the case of 3.0Kg pressure load.

• Elastomers and Composites
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• 제42권3호
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• pp.143-150
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• 2007

본 연구에서는 고무제품의 수치 안정성과 성능유지에 직접적으로 영향을 미치는 중요한 특성 중 하나인 온도변화에 따른 고무재료의 경도변화를 고찰하였다. 새롭게 제작된 Inter-national Rubber Hardness Degree(IRHD, Normal type) 경도측정 시험기를 사용하여 미충전된 NR과 SBR 시편의 여러 온도에서 경도변화를 측정하였으며 Young's modulus 값과 비교하였다. NR과 SBR 모두 유리전이온도 근처에서 경도와 Young's modulus의 급격한 변화를 보였다. 온도가 증가함에 따라 경도와 Young's modulus 값이 증가하는 경향을 보였으며 이는 분자의 운동성과 엔트로피 영향으로 해석할 수 있다. 카본블랙과 실리카가 충전된 NR과 SBR의 경우 충전제의 함량이 증가함에 따라 경도에 미치는 온도의 영향이 감소함을 관찰하였다.

• Journal of Welding and Joining
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• 제30권2호
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• pp.76-80
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• 2012

In this study, the effect of the welding current on the hardness characteristics and microstructure in the resistance spot welding of 1GPa grade cold-rolled DP steel was investigated, Also, correlation between the hardness and microstructure was discussed. In spite of the change in the welding current, the hardness distributions near weld was similar. the hardness in the HAZ and the fusion zone was higher than that of the base metal and the hardness in the fusion zone was variated with the location. Especially, the hardness of HAZ adjacent to the base metal showed maximum value, and softening zone in the base metal adjacent to HAZ was found. With the increasing of welding current, there were no difference in maximum hardness and average hardness in the fusion zone were, but the hardness of the softening zone reduced. The difference in the hardness in each location of weld due to grain size of prior austenite. The softening of the base metal occurred by tempering of the martensite.