• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2009년도 춘계학술대회 논문집
• /
• pp.107-113
• /
• 2009

In this study, the importance of failure analysis on large ring forged products was assessed and the process and methodology were introduced. Failure analysis case study of the large ring forged steel product with approximately 10 mm long internal crack found by non-destructive test (NDT) was presented. The micrographic and fractographic observations and the verifying tests were conducted on the cracked specimen to identify the possible metallurgical reason for the defects, and the metallurgical aspects of internal crack formation were discussed.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
• /
• pp.525-526
• /
• 2006

Calcium-hexaluminate phase $(CA_6)$ is known to be effective for the crack shielding due to the spinel block crystal structure. In this study, we focused to the control of $CA_6$ morphology for good damage tolerance behavior in alumina and zirconia/calcium-hexaluminate $(CA_6)$ composites. Calcium-hexaluminate $(CA_6)$ composites were prepared from zirconia, alumina and calcium carbornate powders. Calcium-hexaluminate $(CA_6)$ phase was obtained by the solid reaction through the formation of intermediate phase $(CA_2)$. $CA_6$ phase showed the column type abnormal grain grown behavior composed of small blocks. Due to the typical microstructure of $CA_6$, alumina and zirconia/calcium-hexaluminate composites provide a well controlled crack propagation behavior.

• 마이크로전자및패키징학회지
• /
• 제26권2호
• /
• pp.51-54
• /
• 2019

실리콘 기판상에 여러 조건의 전류밀도에서 로듐 도금을 실시하였다. 직류전원의 경우 전류밀도가 증가하면 로듐 표면에 균열이 발생하였다. 잔류응력을 낮추기 위하여 펄스전류를 인가하였다. 펄스전류의 off 시간이 도금층의 잔류응력을 낮추는데 영향을 주었다. 펄스전류의 인가 주기를 5:5로 하였을 경우 균열 없는 로듐 도금층을 얻었다.

• Journal of Animal Science and Technology
• /
• 제59권2호
• /
• pp.4.1-4.5
• /
• 2017

Background: Biofilms were the third-dimensional structure in the solid surface of bacteria. Bacterial biofilms were difficult to control by host defenses and antibiotic therapies. Escherichia coli (E. coli) and Salmonella were popular pathogenic bacteria that live in human and animal intestines. Essential oils are aromatic oily liquids from plant materials and well known for their antibacterial activities. Method: This study was conducted to determine effect of essential oil on anti-biological biofilm formation of E. coli and Salmonella strains in in vitro experiment. Two kinds of bacterial strains were separated from 0.2 g pig feces. Bacterial strains were distributed in 24 plates per treatment and each plates as a replication. The sample was coated with a Bacterial biofilm formation was. Result: Photographic result, Escherichia coli (E. coli) and Salmonella bacteria colony surface were thick smooth surface in control. However, colony surface in blended and single essential oil treatment has shown crack surface layer compared with colony surfaces in control. Conclusion: In conclusion, this study could confirm that essential oils have some interesting effect on anti-biofilm formation of E. coli and Salmonella strains from pig feces.

• 대한치과보철학회지
• /
• 제46권3호
• /
• pp.298-306
• /
• 2008

STATEMENT OF PROBLEM: Effect of surface treatment of ceramic under loading does not appear to have been investigated. PURPOSE: The aim of this study was to investigate the effect of surface treatment of esthetic ceramic, which is performed to increase the bonding strength, on the fracture stress under controlled cyclic loading condition. MATERIAL AND METHODS: Sixty 1.0 mm-thick specimens were made from Mark II Vitablocs (Vita Zahnfabrik, Germany) and divided into 3 groups: polished (control), sandblasted, and etched. Specimens of each group were bonded to a dentin analog material base including micro-channels to facilitate the flow of water to the bonding interface. Bonded ceramics were cyclically loaded with a flat-end piston in the water (500,000 cycles, 15Hz). Following completion of cyclic loading, specimens were examined for subsurface crack formation and subsequent stress was determined and loaded to next specimen by the staircase method according to the crack existence. RESULTS: There were significant differences of mean fatigue limit in the sandblasted (222.86 ${\pm}$ 23.42 N) and etched group (222.86 ${\pm}$ 14.16 N) when compared to polished group (251.43 ${\pm}$ 10.6 N) (P<.05; Wald-type pair-wise comparison and post hoc Bonferroni test). Of cracked specimens, surface treated group showed longer crack propagation after 24 hours. All failures originated from the radial cracking without cone crack. Fracture resistance of this study was very low and comparable to failure load in the oral cavity. CONCLUSION: Well controlled cyclic loading could induce clinically relevant cracks and fracture resistance of Mark II ceramic was relatively low applicable only to anterior restorations. Surface treatment of inner surface of feldspathic porcelain in the matsicatory area could influence lifetime of restorations.

• 대한기계학회논문집
• /
• 제18권6호
• /
• pp.1388-1398
• /
• 1994

The fracture toughness and micro-fracture mechanisms of the porous glass and stainless fiber reinforced glass composite were evaluated by using the acoustice mission(AE) technique, fracture toughness $test(K_{IC})$ and the macroscopic observation of the specimen surface which was being under the loading. At initial portion of the loading, the AE signals with low energy, of which origins were considered as the micro-cracks formated at the crack tip, were emitted. With increasing the applied load, AE signals having higher energies were generated due to the coalesence of micro-cracks and fast fracture. Based on the such relationship between AE emission and loading condition, fracture toughness $K_{IAE}$ could be defined successfully be using the $K_I$ value corresponding to an abrupt change of the accumulated AE signal energies emitted during the fracture toughness test. In spite of its brittleness of glass material, nonlinear deformation behavior before maximum load was observed due to the formation of micro-cracks. Further, the stainless fiber may have attributed to the improvement of fracture toughness and the resistance to crack propagation comparing to noncomposited materials Finally, models of the micro-fracture process combined with the AE sources for the porous glass material and its composite were proposed paying attention to the micro-crack nucleation and its coalescence at the crack tip. Fiber fracture and its Pullout, deformation of fiber itself were also delinated from the model.

• 한국정밀공학회지
• /
• 제28권5호
• /
• pp.537-542
• /
• 2011

The thermo-mechanical interaction between brake block and wheel tread during braking has been found to cause thermal crack on the wheel tread. Due to thermal expansion of the rim material, the thermal cracks will protrude from the wheel tread and be more exposed to wear during the wheel/block contact than the rest of the tread surface. The wheel rim is in residual compression stress when is new. After service running, the region in the tread has reversed to tension. This condition can lead to the formation and growth of thermal cracks in the rim which can ultimately lead to premature failure of wheel. In the present paper, the thermal cracks of railway wheel, one of severe damages on the wheel tread, were evaluated to understand the safety of railway wheel in running condition. The residual stresses for damaged wheel which are applied to tread brake are investigated. Mainly X-ray diffusion method is used. Under the condition of concurrent loading of continuous rolling contact with rails and cyclic frictional heat from brake blocks, the reduction of residual stress is found to correlate well with the thermal crack initiation.

• Earthquakes and Structures
• /
• 제20권4호
• /
• pp.365-375
• /
• 2021

Rammed earth (RE) buildings have existed all over the world for thousands of years, and have gained increasing attention because of its sustainable advantages, however, the shrinkage cracks reduce its bearing capacity and seriously affect its durability and applicability. In this study, the shrinkage cracks test was carried out to investigate the effects of initial water content, proportion of sand and gravel, compaction degree, thickness and the additives (polypropylene fiber, cement and sodium silicate) of shrinkage cracks in RE buildings, ten groups of RE samples were prepared and dried outdoors to crack. Four quantitative parameters of geometrical structure of crack patterns were used to evaluate the development of cracks. The results show that the specimens cracking behavior and the geometrical structure of crack patterns are significantly influenced by these considered factors. The formation of crack can be accelerated with the increase of initial water content and thickness of specimen, while restricted with the increase of the compaction degree and the proportion of sand and gravel. Moreover, the addition of 1% polypropylene fiber, 10% cement and 0.5 volume ratio sodium silicate can significantly restrain the form and development of cracks. In RE construction, these factors should be considered comprehensively to prevent the harm caused by shrinkage cracks. Further works should be carried out to obtain the optimum dosage of the additives, which can benefit the construction of RE buildings in future.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1994년도 봄 학술발표회 논문집
• /
• pp.155-162
• /
• 1994

The drying shrinkage of concrete has a close relation to the water movement, Since the diffusion process of water in concrete is strongly dependent on the temperature and pore humidity, the process is highly nonlinear phenomena. It is shown that the analytical results of this study are in good agreement with experimental data in the literatures, and results calculated by BP-KX model. The internal stress caused by moisture distribution which was resulted from the diffusion process, was calculated quantitatively. The tensile stress which occurred in the drying outer zone mostly exceeded the tensile strength of concrete, and necessarily would result in crack formation.

• 대한기계학회논문집
• /
• 제7권4호
• /
• pp.398-403
• /
• 1983

In this investigation, the effect of microstructural factors on the impact energy was studied, using dual phase steels with soft phase of ferrite encapsulated by hard phase of martensite. It was found that the effect of the ferrite grain size on the impact energy decreases as the strength ratio increases, these results are due to the micro-brittlefracture facet by the difficulty of cleavage crack formation in the ferrite grain.