• 한국산업융합학회 논문집
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• 제25권6_2호
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• pp.1047-1053
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• 2022

The leaf spring for a truck absorbs shocks or vibrations from the road surface while driving with the elastic force of the material and prevents the shock from being transmitted to the vehicle body. It is subjected to cyclic stress, and fatigue fracture occurs frequently. This study analyzes fractured leaf spring from a 25 ton truck that has been operating for about a year. In the fractured portion, which is the origin of crack, inclusions were observed, and fatigue failure was caused by cyclic stress. In the stress calculation and FE analysis, the stress at the center of the leaf spring was obtained to be 54~65% of the yield strength of the base material and damaged material. It is most important to prevent the mixing of impurities in the steel manufacturing for leaf springs. The large stress portion of the leaf spring needs to introduce compressive residual stress by peening etc.

• Restorative Dentistry and Endodontics
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• 제15권2호
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• pp.17-33
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• 1990

The purpose of this study was to evaluate the fracture toughness of dental composite resins and to investigate the filler factor affecting the fracture behaviour on which the degree of fracture toughness depends. Six kinds of commercially available composite resin;, including two of each macrofilled, microfilled, and hybrid type were used for this study, The plane strain fracture toughness ($K_{10}$) was determined by three-point bending test using the single edge notch specimen according to the ASTM-E399. The specimens were fabricated with visible light curing or self curing of each composite resin previously inserted into a metal mold, and three-point bending test was conducted with cross-head speed of 0.1mm/min following a day's storage of the specimens in $37^{\circ}C$ distilled water. The filler volume fractions were determined by the standard ashing test according to the ISO-4049. Acoustic Emission(AE), a nondestructive testing method detecting the elastic wave released from the localized sources In material under a certain stress, was detected during three-point bending test and its analyzed data was compared with, canning electron fractographs of each specimen. The results were as follows : 1. The filler content of composite resin material was found to be highest in the hybrid type followed by the macrofilled type, and the microfilled type. 2. It was found that the value of plane strain fracture toughness of composite resin material was in the range from 0.69 MPa$\sqrt{m}$ to 1 46 MPa$\sqrt{m}$ and highest In the macrofilled type followed by the hybrid type, and the microfilled type. 3. The consequence of Acoustic Emission analysis revealed that the plane strain fracture toughness increased according as the count of Acoustic Emission events increased. 4. The higher the plane strain fracture toughness became, the higher degree of surface roughness and irregularity the fractographs demonstrated.

• Elastomers and Composites
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• 제34권4호
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• pp.321-331
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• 1999

타이어 가황공정(curing process)은 타이어 제조를 위한 최종공정으로 여러 개의 고무배합물 층으로부터 성형된 그린타이어(green tire)를 가황기(mold)내에서 고압/고온 조건하에 유지시킴으로써 원하는 형상을 얻게 하고, 아울러 각 고무배합물이 고탄성을 갖도록 물성을 변화시키는 공정이다. 본 연구에서는 타이어 품질의 향상을 위해 가황공정을 수치적으로 최적화하는 기법을 개발하였다. 먼저, 가황공정 중 가황매체(cure media)의 최적공급 조건을 경정하기 위해 제약조건을 갖는 동적최적화문제(dynamic constrained optimization problem)로 정형화하였다. 즉, 가황기 내의 전열 및 가황 반응 현상을 묘사하는 공정모델로 표현되는 등위제약조건(equality constraint)과 가황매체가 갖는 온도의 한계를 표현하는 부등위제약조건(Inequality constraint) 아래 목적함수를 최적화 시켰다. 다음, 공급되는 가황매체의 최적조건을 결정하기 위해 구성된 최적화문제를 유한요소법(FEM)과 complex 알고리즘을 적용하여 풀었다.

• Design & Manufacturing
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• 제18권2호
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• pp.17-22
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• 2024

Lightweight of plastic containers is becoming an important issue due to increasing environmental legislation and consumer awareness. In this study, the CAE analysis was conducted to optimize the shape of a 500 ml lightweight square polyethylene terephthalate(PET) bottle. First, the linear buckling alaysis using the finite element method was performed to analyze the correlation between the primary geometric parameters of the bottle and the buckling critical load. Then, the optimal geometry parameters were derived, and the actual buckling load was predicted by non-linear buckling simulation. The validity of the simulation results was verified by top-loading tests of PET bottles molded with the optimized geometry. The elastic modulus and tensile yield strength of PET through tensile tests were measured to improve the accuracy of the simulation. As a result of the tensile tests, the modulus of elasticity of PET increased from 2,900 MPa to 4,275 MPa, and the tensile yield strength increased from 52.4 MPa to 88.1 MPa. Finally the buckling load of the optimized PET bottle was found to be approximately 236 N, which is very similar to the simulation precition of 238 N. This study shows the feasibility and accuracy of the CAE analysis approach for the lightweight design of PET bottles, and will provide useful guidelines for the design of PET bottles.

• Restorative Dentistry and Endodontics
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• 제22권2호
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• pp.751-760
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• 1997

Resin-modified glass ionomers were introduced in 1988 to overcome the problems of moisture sensitivity and low early mechanical strengths of the conventional glass ionomers, and to maintain their dinical advantages. The purpose of this study was to evaluate the bi-axial fracture strength of four resinmodified glass-ionomers(Fuji II LC, Vitremer, Dyract, VariGlass), one resin composite material(Z-100), and one conventional glass-ionomer(Fuji II). Three specimens of each material and shade combination were made according to the manufacturers' instructions. Materials were condensed into metal mold with a diameter of 10mm and a thickness of 2.0mm and pressed between two glass plates. Resin-modified glass ionomers were polymerized using a Visilux II light curing unit by irradiating for 60 seconds from both sides, and conventional glass ionomer was cured chemically. After specimens were removed from the molds, surfaces were polished sequentially on wet sandpapers up to No. 600 silicone carbide paper. The specimens were thermocycled for 2,000 cycles between $5^{\circ}C$ and $55^{\circ}C$ distilled water. After thermocycling, bi-axial fracture strengths were measured using a compressive-tensile tester(Zwick 1456 Z020, Germany) with the cross head speed of 0.5mm/minute. The results were as follows: 1. Two factors of the kind and color of materials had a main effect on bi-axial fracture strength (p<0.01), and bi-axial fracture strength was influenced significantly by the kinds of materials (p<0.01). But there was no significant interaction between two variables of the kind and color of materials (p>0.05). 2. Comparing the mechanical properties of the materials, the elastic modulus of Z100 was higher than any other material, and there was no difference in the displacement at fracture among materials. The bi-axial fracture strength of Z100 was significantly higher than any other material, and that of resin-modified glass ionomers was significantly higher than that of conventional glass ionomer (p<0.05). 3. In the same material group, the color of material had little influence on the mechanical properties.

• 한국환경복원기술학회지
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• 제5권4호
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• pp.1-9
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• 2002

This study is carried out to make the environmentally affinitive porous planting block for revegetation and to make a effective program for greening plans. The summary is shown below. 1. In order to get stronger intensity and distribute proper porosity in the block for planting, the cements mixed with fine soil were used and the finer in soil grains gives the stronger in intensity of the cements. Use of the furnace slag cements instead of the portland cements showed relatively stronger in intensity of the block. The intensity of the block became stronger when the mixed ratio of the cements to soil is 5 : 1, but the pore space ratio was lower. The percolate pH of the portland cements after one month of treatment was 13.1 but the percolate pH of the furnace slag cements was shown lower. To mold proper porous planting blocks, the proper combination of additives such as the dehydrating agent, elastic agent and adhesives into the mixture of cements and soil gives better effectives. 2. After molding the porous planting blocks, it gave a better result when the grains of the filler made of peat moss, upland soil and compound fertilizer were smaller than 2 mm in size. Shaking of the filling materials also gave the better result, but it took more time and cost much more. Therefore, it was better when the filling materials were mixed with water first then flew down for stuffing. 3. It was necessary to cover with soil after seeding or planting on the porous planting blocks. The proper thickness of the soil to help root development and keep moisture is about 3~5 cm. 4. The plants for planting on the porous planting block were required stronger in the growth condition of their roots and their environmental adaptability. The average germination percentage and rate of Platycodon grandiflorum on the porous planting block were 88.8% and 85% accordingly and their rate is very uniform. The germination rates of Dianthus superbus var. longicalycinus and Taraxacum officinale were more than 50%. These grass species, Chelidonium majus var. asiaticum, Lysimachia mauritiana and Scabiosa mansenensis were the suggested biennial grasses in the planting area where exchanging of the seedling or nursery plants was not necessary because their germination rates were 59.3, 45.6 and 40.3% accordingly. Viola kapsanensis, Chrysanthemum sp., Taraxacum sp. and Iris ensata var. spontanea are the grass species that could be used by seeding for greening. However, the germination rate of Solidago virga-aurea var. asiatica, Aster scaber and Lythrum anceps were lower than 10%. The coverage ratio of Ixeris stolonifera is more than 80% after 60 days seeding and the root length of most of species are more than 10 cm except Iris ensata var. spontanea and Platycodon grandiflorum because their root developed thicker than other species.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2009년도 춘계학술대회 논문집
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• pp.111-112
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• 2009

Diamond-like carbon (DLC) is a convenient term to indicate the compositions of the various forms of amorphous carbon (a-C), tetrahedral amorphous carbon (ta-C), hydrogenated amorphous carbon and tetrahedral amorphous carbon (a-C:H and ta-C:H). The a-C film with disordered graphitic ordering, such as soot, chars, glassy carbon, and evaporated a-C, is shown in the lower left hand corner. If the fraction of sp3 bonding reaches a high degree, such an a-C is denoted as tetrahedral amorphous carbon (ta-C), in order to distinguish it from sp2 a-C [2]. Two hydrocarbon polymers, that is, polyethylene (CH2)n and polyacetylene (CH)n, define the limits of the triangle in the right hand corner beyond which interconnecting C-C networks do not form, and only strait-chain molecules are formed. The DLC films, i.e. a-C, ta-C, a-C:H and ta-C:H, have some extreme properties similar to diamond, such as hardness, elastic modulus and chemical inertness. These films are great advantages for many applications. One of the most important applications of the carbon-based films is the coating for magnetic hard disk recording. The second successful application is wear protective and antireflective films for IR windows. The third application is wear protection of bearings and sliding friction parts. The fourth is precision gages for the automotive industry. Recently, exciting ongoing study [1] tries to deposit a carbon-based protective film on engine parts (e.g. engine cylinders and pistons) taking into account not only low friction and wear, but also self lubricating properties. Reduction of the oil consumption is expected. Currently, for an additional application field, the carbon-based films are extensively studied as excellent candidates for biocompatible films on biomedical implants. The carbon-based films consist of carbon, hydrogen and nitrogen, which are biologically harmless as well as the main elements of human body. Some in vitro and limited in vivo studies on the biological effects of carbon-based films have been studied [$2{\sim}5$].The carbon-based films have great potentials in many fields. However, a few technological issues for carbon-based film are still needed to be studied to improve the applicability. Aisenberg and Chabot [3] firstly prepared an amorphous carbon film on substrates remained at room temperature using a beam of carbon ions produced using argon plasma. Spencer et al. [4] had subsequently developed this field. Many deposition techniques for DLC films have been developed to increase the fraction of sp3 bonding in the films. The a-C films have been prepared by a variety of deposition methods such as ion plating, DC or RF sputtering, RF or DC plasma enhanced chemical vapor deposition (PECVD), electron cyclotron resonance chemical vapor deposition (ECR-CVD), ion implantation, ablation, pulsed laser deposition and cathodic arc deposition, from a variety of carbon target or gaseous sources materials [5]. Sputtering is the most common deposition method for a-C film. Deposited films by these plasma methods, such as plasma enhanced chemical vapor deposition (PECVD) [6], are ranged into the interior of the triangle. Application fields of DLC films investigated from papers. Many papers purposed to apply for tribology due to the carbon-based films of low friction and wear resistance. Figure 1 shows the percentage of DLC research interest for application field. The biggest portion is tribology field. It is occupied 57%. Second, biomedical field hold 14%. Nowadays, biomedical field is took notice in many countries and significantly increased the research papers. DLC films actually applied to many industries in 2005 as shown figure 2. The most applied fields are mold and machinery industries. It took over 50%. The automobile industry is more and more increase application parts. In the near future, automobile industry is expected a big market for DLC coating. Figure 1 Research interests of carbon-based filmsFigure 2 Demand ratio of DLC coating for industry in 2005. In this presentation, I will introduce a trend of carbon-based coating research and applications.