• Applied Chemistry for Engineering
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• v.29 no.2
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• pp.168-175
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• 2018

In order to investigate the effect of the chemical treatment of bamboo fiber on physical properties of polypropylene (PP)/bamboo fiber (BF) composites, silane coupling agents such as ${\gamma}$-aminopropyltriethoxysilane (APS), ${\gamma}$-glycidoxypropyl-trimethoxysilane (GPS) and ${\gamma}$-mercaptopropyltrimethoxysilane (MRPS) were applied to BF and alkaline treated BF. Morphological properties of the chemically treated BF were confirmed by optical microscope and SEM measurements, and chemical structure changes were confirmed by FT-IR and EDS. TGA results showed that the thermal stability of silane treated BF increased. Based on the analysis of a universal testing machine and an Izod impact test, the flexural and impact properties of PP/silane treated BF composites showed higher values than those of PP/BF composites. The enhancement of interfacial adhesion properties of the PP/BF composite was checked from SEM images of the fracture of specimens after the tensile test.

• Composites Research
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• v.30 no.6
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• pp.399-405
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• 2017

We manufactured the long fiber-reinforced thermoplastic prototype of under cover using in-line compounding technology, and investigated the formability, mechanical properties and durability of the prototype of under cover. We manufactured the injection mold for the prototype through injection molding analysis and consideration of weight reduction. We investigated the formability of the prototype by evaluating the residual length and dispersion of fiber, and also tested the mechanical properties such as flexural strength, stiffness and impact strength. We investigated the durability of the prototype by the Key-Life Test(KLT) method which is generally used for the automotive interior parts.

• Journal of Adhesion and Interface
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• v.16 no.3
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• pp.101-107
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• 2015

Epoxy resin toughening agents such as core/shell nanoparticles, CTBN epoxy, polyester polyols, and polyurethane have been widely used in order to compensate for the brittleness and improve the impact resistance of the epoxy resin. In this work, a few tougheners mentioned above were individually added into adhesive compositions to observe the effects of physical and mechanical properties. Both flexural strength and flexural modulus were measured with UTM while impact strength was analyzed with Izod impact tester. The obtained results showed that the addition of toughening agents afforded positive performance in terms of flexibility and impact resistance of the cured epoxy resin. Furthermore, DMA experiments suggested that the trends of storage modulus data of each epoxy resin composition coincided with the trends of flexural modulus data. FE-SEM images showed that toughening agents formed circled-shape particles when it was cured in epoxy resin composition at high temperature by phase separation. The existence of particles in the cured samples explains why epoxy resin with toughener has higher impact resistance.

• Applied Chemistry for Engineering
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• v.21 no.2
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• pp.217-223
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• 2010

In general, fiber-reinforced plastics (FRP) wastes are simply buried or burned. Landfill brings about a permanent contamination of soil due to the inability of FRP to decompose and incineration causes an issue of generating toxic gases and dusts. There have been several ways to treat the FRP wastes such as landfill, incineration, chemical recycling, material recycling and the utilization of energy from combustion. Most methods excluding material recycling are known to have critical limitations in economic, technical and environmental manners. However it is known that material recycling is most desirable among the methods handling FRP wastes. In this study, to investigate the purpose of feasibility of material recycling, various bulk molding compound (BMC) specimens were prepared with the various contents of unsaturated polyester resin binder (25, 30, 35 wt%) and the various replacement ratios of FRP wastes powder (0, 25, 50, 75, 100 wt%) substituted for filler. To evaluate the physical properties BMC specimens, various tests such as tensile strength, flexural strength, impact strength, hot water resistance and SEM imaging were conducted. As a results, mechanical strengths decreased with an increase of replacement ratio of FRP waste powder and physical properties of BMC specimens were deteriorated in the hot water resistance. The fluidity of BMC with more than 50 wt% of the replacement ratio of FRP wastes powder decreased remarkably, causing a problem in the BMC composite.

• Horticultural Science & Technology
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• v.29 no.4
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• pp.298-305
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• 2011

This study was conducted to enhance the stem firmness of standard chrysanthemum 'Baekma' bred in Korea for commercial quality improvement and inhibition of stem breaking during transportation through foliar spray with calcium agents. Calcium agent screening 'Baekma' was examined using $CaCl_2{\cdot}2H_2O$, $Ca(NO_3)_2{\cdot}4H_2O$, and OS-Ca (natural liquid calcium compounds extracted from oyster shell) depending on each concentration (0, 0.001, 0.01, 0.1, and 1.0%, respectively). All calcium agents sprayed with 1.0% caused chemical injury such as stem bending or leaf burn. OS-Ca also showed more sensitive response to chemical injury than the other calcium agents because OS-Ca was absorbed very well by 'Baekma' leaves. Maximum stem firmness measured during the final harvest was greater in OS-Ca than in the other calcium agents. Especially, maximum stem firmness was greatest in 0.01% OS-Ca. However, elastic strength and maximum bending stress were greater in 0.001% OS-Ca than in the others. Thus, OS-Ca ranged from 0.005 to 0.05%, which did not show any chemical injury, was finally selected as the first candidate for hardening the stem of 'Baekma'. The next experiment using OS-Ca was conducted with the concentrations of 0, 0.005, 0.01, and 0.05%, respectively. From the results, 0.05% OS-Ca showed better plant growth and parameters such as plant height, stem diameter (upper and middle part), the number of leaves, and dry weights of each part than the other concentrations of OS-Ca and control. As for stem firmness depending on OS-Ca concentration, the Ca content within stem, maximum firmness, elastic strength, and maximum bending stress of stem in 'Baekma' sprayed with 0.05% OS-Ca showed the highest values among all the treatments and it turned out to be very high level of significance between control and OS-Ca treatments. However, the area and percentage of the inside cavity within horizontal stem section in 'Baekma' did not show any significance between any treatments including control. Thus, stem firmness of 'Baekma' did not show any correlation with the inside cavity area of stem. In conclusion, we recommend foliar sprays with 0.05% OS-Ca at vegetative growth stage to enhance stem firmness of 'Baekma' during transportation.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1994.10b
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• pp.15-15
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• 1994

M MA ODS 합금의 보다 폭넓용 실용확훌 위해 크게 요구되고 있는 적정 접합기술 개발의 한 방안￡로, 마찰압접(Friction Welding) 방법의 가능성옳 조사하기 위하여 마찰압력과 시간, 마 찰 후 접촉압력(Upset Pressure) 풍을 다양하게 변화시켜 접합체톨 제조한 후, 접합체 강도에 대한 인장시험과 접합계연의 결합 및 미세구조에 대한 현미경 관찰, EDS에 의한 원소분석, 접 합이옴부의 경도분포와 파단면 분석 풍율 행하였다. 실험에 사용된 모재는 기계적 합금법으로 제조된 Inca사의 Ni기 MA 754 합금이었으며, 직경 l 10 mm, 길이 50 mm로 가공한 후, 아세통￡로 초음파 세척하여 접합에 사용하였다. 접합온 브 레이크식 마찰압접기틀 사용하여 행하였으며, 회전시험편의 회전수는 2400 rpm이었A며, 다른 한쪽의 고정시험편과의 마찰압력 및 마찰시간온 각각 50 - 500 MPa과 1-5초로, 또한 업셋압 력도 50 - 600 MPa로 변화시켰다. 이때 업셋압력은 모든 시편에 대해 일정하게 6초동안 가하 였다. 얻어진 접합체는 각 압접조건 당 2개 이상의 접합시험편에 대해 상온 인장강도톨 측정하 였으며, 파단이 일어난 위치를 확인한 후 파면에 대한 분석율 주사전자현미경(SEM)과 에너지 분산형 분광분석기mDS)릎 사용하여 행하였다. 컵합이옴부의 첩합성올 확인하기 위하여, 접합 체를 접합변에 수직으로 절단, 연마한 후 광학현미경과 SEM, EDS 퉁으로 관찰, 분석하여 접 합부의 형상과 결합형성 여부, 접합계면의 미세조직 퉁옳 조사하였다. 또한 마찰압접에 따론 모재와 접합계연부의 경도분포훌 접합이옴부로부터 모재쪽으로 일정 간격율 두어 마이크로 비 커스 경도기로 측정, 조사하였다. 이상의 설험 결과, 다옴과 같온 결론옳 얻었다. ( (1) 접합체 강도가 모채 강도의 95% 이상이 되는 양호한 렵합체흩 얻기 위한 마찰압력 조건 온, 2400 rpm의 회전속도와 6초의 업셋압력 유지시간에서 마찰압력과 업셋압력, 그리고 마찰시 간이 각각 400 MPa 이상과 500 MPa 이상,2초입율 확인하였다. ( (2) 컵합이옴부의 관찰 결과, 모든 마찰압접 조건에서 컵합이옴부는, 기폰 모재의 texture 조직 을 유지하고 있는 모재부 영역(영역 ill)과 첩합계면부에 인접하여 업셋압력이 주어질 때 단조 효과에 의해 계연 외부로 metal flow가 일어나면서 형성된 영역 II, 매우 미세한 결정립으로 구성된 중앙부의 영역 1 로 이투어져 있옴융 확인하였다. ( (3) 최적접합조건이 충족되지 않온 경우, 접합부의 영역 I 에서 관찰된 void와 균열, 불균일한 접합계면 통의 접합결함에 Al과 Y. Ti 퉁￡로 구성된 산화물률이 용집되어 있옴을 확인하였 다-( (4) 접합체의 파단 양상온 크게 접합부 파단과 모재부 파단, 이률의 혼합형 파단i로 나눌수 있었다. 모재부 파단의 경우, 파단면이 매끄럽고 파변상의 결정립도 매우 미세하였으며, 산확물 의 용집도 찾아보기 어려웠 나, 접합부 파단의 경우에는 파변의 굴곡이 비교척 심하고 연성 입계파괴의 형태를 보였￡며, 결정립도 모채부 파단의 경우에 비해 조대하였다. 조대하였다.

• Journal of Dental Rehabilitation and Applied Science
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• v.36 no.3
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• pp.168-175
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• 2020

Purpose: The purpose is to test and evaluate the physical properties of commonly used temporary restoration materials and newly emerged materials. Materials and Methods: Four groups of polymer materials were evaluated: Polymethyl methacrylate (PMMA) 2 groups, Polyetheretherketone (PEEK), Polycarbonate. Four physical properties were tested: surface hardness, bending strength, abrasion resistance during wear, wear behavior. The 3-axis bending strength and Vickers hardness test were measured using a universal testing machines respectively. The microstructure was observed with a scanning electron microscope and weight comparison was evaluated after 100,000 chewing tests using a chewing simulator. Kruskal wallis test was performed to evaluate statistical significance. Results: The four groups showed the highest flexural strength and Vickers hardness of PEEK, followed by PC, PMMA-H, PMMA-T. Microstructure observation also showed the least surface roughness in the PEEK group, followed by PC, PMMA-H, PMMA-T. Conclusion: PC is considered to have sufficient mechanical properties that can be applied to the manufacture of temporary teeth. However, further studies, such as biocompatibility, are considered to be necessary for practical clinical applications.

• Restorative Dentistry and Endodontics
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• v.34 no.3
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• pp.184-191
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• 2009

The purpose of this study was to evaluate the physical properties of different self-adhesive resin cements and their shear bond strength on dentin and lithium disilicate ceramic and compare these result with that of conventional resin cement. For this study, four self-adhesive resin cements (Rely-X Unicem, Embrace Wetbond, Mexcem, BisCem), one conventional resin cement (Rely-X ARC) and one restorative resin composite (Z-350) were used. In order to evaluate the physical properties, compressive strength, diametral tensile strength and flexural strength were measured. To evaluate the shear bond strength on dentin, each cement was adhered to buccal dentinal surface of extracted human lower molars. Dentin bonding agent was applied after acid etching for groups of Rely-X ARC and Z-350. In order to evaluate the shear bond strength on ceramic, lithium disilicate glass ceramic (IPS Empress 2) disks were prepared. Only Rely-X ARC and Z-350 groups were pretreated with hydrofluoric acid and silane. And then each resin cement was adhered to ceramic surface in 2 mm diameter. Physical properties and shear bond strengths were measured using a universal testing machine. Results were as follows 1. BisCem showed the lowest compressive strength, diametral tensile strength and flexural strength. (P<0.05) 2. Self-adhesive resin cements showed significantly lower shear bond strength on the dentin and lithium disilicate ceramic than Rely-X ARC and Z-350 (P<0.05) In conclusion, self-adhesive resin cements represent the lower physical properties and shear bond strength than a conventional resin cement.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.7
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• pp.4357-4363
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• 2015

This study is to compare the differences of bonding strength based on the Degassing temperatures and various opaque materials for Ni-Cr alloy specimen which does not contain beryllium(Be). Numerous comparison tests have been performed to measure the bonding strength by experimenting 3-point flexural rigidity tests in order to find out ways of stabilization and enhancement of bonding strength between metal and porcelain. AVOVA, surface component observation experiment by SAM/EDS, and Tukey's HSAD posteriori tests results are as follows: First, The bonding strength in all groups has exceeded the minimum (25MPa) of ISO9693 bonding strength regulation for dental mental-porcelain specimen. Second, The bonding strength of Group V1 was $32.37{\pm}1.91MPa$, $38.25{\pm}1.38MPa$ in Group V2, $46.43{\pm}2.14MPa$ in Group V3 and $47.21{\pm}1.72MPa$ Group V4. The difference has been statistically meaningful. Tukey's HSAD posteriori tests results have shown that the bonding strength in Group V4 was higher than that of Group V1. Third, the bonding strength between metal and porcelain without degassing process was higher than that of with degassing process, and the bonding strength of powder opaque was higher than that of paste opaque. Fourth, Group V4 has ranked the highest on the comparison table of metal and porcelain bonding strength.

• Composites Research
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• v.15 no.4
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• pp.23-31
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• 2002

The two dimensional size effect of specimen gauge section ($length{\;}{\times}{\;}width$) was investigated on the compressive behavior of a T300/924 $\textrm{[}45/-45/0/90\textrm{]}_{3s}$, carbon fiber-epoxy laminate. A modified ICSTM compression test fixture was used together with an anti-buckling device to test 3mm thick specimens with a $30mm{\;}{\times}{\;}30mm,{\;}50mm{\;}{\times}{\;}50mm,{\;}70mm{\;}{\times}{\;}70mm{\;}and{\;}90mm{\;}{\times}{\;}90mm$ gauge length by width section. In all cases failure was sudden and occurred mainly within the gauge length. Post failure examination suggests that $0^{\circ}$ fiber microbuckling is the critical damage mechanism that causes final failure. This is the matrix dominated failure mode and its triggering depends very much on initial fiber waviness. It is suggested that manufacturing process and quality may play a significant role in determining the compressive strength. When the anti-buckling device was used on specimens, it was showed that the compressive strength with the device was slightly greater than that without the device due to surface friction between the specimen and the device by pretoque in bolts of the device. In the analysis result on influence of the anti-buckling device using the finite element method, it was found that the compressive strength with the anti-buckling device by loaded bolts was about 7% higher than actual compressive strength. Additionally, compressive tests on specimen with an open hole were performed. The local stress concentration arising from the hole dominates the strength of the laminate rather than the stresses in the bulk of the material. It is observed that the remote failure stress decreases with increasing hole size and specimen width but is generally well above the value one might predict from the elastic stress concentration factor. This suggests that the material is not ideally brittle and some stress relief occurs around the hole. X-ray radiography reveals that damage in the form of fiber microbuckling and delamination initiates at the edge of the hole at approximately 80% of the failure load and extends stably under increasing load before becoming unstable at a critical length of 2-3mm (depends on specimen geometry). This damage growth and failure are analysed by a linear cohesive zone model. Using the independently measured laminate parameters of unnotched compressive strength and in-plane fracture toughness the model predicts successfully the notched strength as a function of hole size and width.