• KCI Concrete Journal
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• 제14권2호
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• pp.81-85
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• 2002

The strength development of concrete is influenced by temperature and cement type which greatly affect hydration degree of cement. There is not pertinent concrete strength management method in korea. There are several methods for estimating the in-place strength of concrete. One such method is the maturity concept. The maturity concept is based on the fact that concrete gains strength gradually as a result of chemical reactions between cement and water; and for a specific concrete mixture, strength at any age and at normal conditions is related to the degree of hydration. The rate of hydration and, therefore, strength development of a given concrete will be a function of its temperature. Thus, strength of concrete depends on its time-temperature history. The goals of the present study are to investigate a relationship between strength of high-strength concrete and maturity that is expressed as a function of an integral of the curing period and temperature and predict strength of concrete.

• Composites Research
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• 제30권3호
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• pp.202-208
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• 2017

RTM은 작은 크기에서 큰 크기의 복합재료를 생산할 수 있는 대량 생산 공정이다. 최근 경화 시간이 약 10분 이내인 속경화 수지가 자동차 및 항공우주 산업에 사용되고 있다. 수지의 점도는 경화 정도와 관련이 있으며, 금형 내부로 충진되는 과정에서 급격히 점도가 변할 수 있다. 따라서 속경화 수지의 유동 특성과 경화도를 해석적으로 예측하는 데 많은 노력이 필요하므로 실험적으로 측정하고 평가하는 것이 유리하다. 복합재료의 경화도를 측정하는 방법은 대표적으로 DMA, 유전기법 등이 있다. 본 논문에서는 다채널 경화 모니터링 시스템을 이용하여 속경화 수지의 유동과 경화도를 측정하였다. 총 8채널의 유전센서가 사용되었으며, 다양한 압력 조건에 따른 금형 내부의 유동과 경화도를 측정하고 상호 비교하였다.

• 한국도로학회논문집
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• 제19권2호
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• pp.67-74
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• 2017

PURPOSES : The objective of this study is to ascertain the curing period of cementless cold central plant recycled asphalt base-layer, using mechanical analyses and specimen quality tests on the field. METHODS : Cold central plant recycled asphalt base-layer mixture was produced in the plant from reclaimed asphalt, natural aggregate, filler for the cold mix, and the modified emulsion AP using asphalt mix design and plant mix design. In order to examine the applicability of the curing period during the field test, the international standards for the possibility of core extraction and the degree of compaction and LFWD deflection were analyzed. Moreover, Marshall stability test, porosity test, and indirect tensile strength test were performed on the specimens of asphalt mix and plant mix design. RESULTS : The plant production process and compaction method of cementless cold central plant recycled asphalt base-layer were established, and the applicability of the optical moisture content for producing the mixture was verified through the field test. In addition, it was determined that the core extraction method of the conventional international curing standard was insufficient to ensure performance, and the LFWD test demonstrated that the deflection converges after a two-day curing. However, the back-calculation analysis reveals that a three-day curing is satisfactory, resulting in a general level of performance of dense asphalt base-layer. Moreover, from the result of the specimen quality test of the asphalt mix design and plant mix design according to the curing period, it was determined that the qualities satisfied both domestic and international standards, after a two-day curing. However, it was determined that the strength and stiffness after three-day curing are higher than those after a two-day curing by approximately 3.5 % and 20 %, respectively. CONCLUSIONS:A three-day curing period is proposed for the cementless cold central plant recycled asphalt base-layer; this curing period can be demonstrated to retain the modulus of asphalt-base layer in the field and ensure stable quality characteristics.

• Journal of Welding and Joining
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• 제33권5호
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• pp.41-46
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• 2015

The snap cure NCP(non-conducive paste) adhesive material is essentially required for the high productivity flip chip bonding process. In this study, the accessibility of DEA(dielectric analysis) method for the evaluation of snap cure behavior was investigated with comparison to the isothermal DSC(differential scanning calorimetry) method. NCP adhesive was mainly formulated with epoxy resin and imidazole curing agent. Even though there were some noise in the dielectric loss factor curve measured by DEA, the cure start and completion points could be specified clearly through the data processing of cumulation and deviation method. Degree of cure by DEA method which was measured from the variation of the dielectric loss factor of adhesive material was corresponded to about 80% of the degree of cure by DSC method which was measured from the heat of curing reaction. Because the adhesive joint cured to the degree of 80% in the view point of chemical reaction reveals the sufficient mechanical strength, DEA method is expected to be used effectively in the estimation of the high speed curing behavior of snap cure type NCP adhesive material for flip chip bonding.

• The Journal of Advanced Prosthodontics
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• 제7권4호
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• pp.317-322
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• 2015

PURPOSE. The aim was to evaluate the effect of curing mode and different dentin surface pretreatment on microtensile bond strength (${\mu}TBS$) of self-adhesive resin cements. MATERIALS AND METHODS. Thirty-six extracted human permanent molars were sectioned horizontally exposing flat dentin surface. The teeth were divided into 12 groups (3 teeth/group) according to the dentin surface pretreatment methods (control, 18% EDTA, 10% Polyacrylic acid) and curing mode (self-curing vs. light-curing) of cement. After pretreatment, composite resin blocks were cemented with the following: (a) G-CEM LinkAce; (b) RelyX U200, followed by either self-curing or light-curing. After storage, the teeth were sectioned and ${\mu}TBS$ test was performed using a microtensile testing machine. The data was statistically analyzed using one-way ANOVA, Student T-test and Scheffe's post-hoc test at P<.05 level. RESULTS. For G-CEM LinkAce cement groups, polyacrylic acid pretreatment showed the highest ${\mu}TBS$ in the self-cured group. In the light-cured group, no significant improvements were observed according to the dentin surface pretreatment. There were no significant differences between curing modes. Both dentin surface pretreatment methods helped to increase the ${\mu}TBS$ of RelyX U200 resin cement significantly and degree of pretreatment effect was similar. No significant differences were found regarding curing modes except control groups. In the comparisons of two self-adhesive resin cements, all groups within the same pretreatment and curing mode were significantly different excluding self-cured control groups. CONCLUSION. Selecting RelyX U200 used in this study and application of dentin surface pretreatment with EDTA and polyacrylic acid might be recommended to enhance the bond strength of cement to dentin.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.504-507
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• 2017

추진제의 주 바인더로 사용하고 있는 폴리부타디엔 계열인 HTPB(Hydroxyl Terminated Polybutadiene)는 합성 뱃취에 따라 바인더 및 추진제의 경화 속도에 영향을 미치는 현상을 보였다. 이에 각기 다른 뱃취에서 합성된 HTPB의 바인더 특성 분석을 통해 추진제에 적용하여 경화반응 속도 및 기계적 특성을 확인하였다. 최종적으로 이러한 추진제의 경화 반응속도가 추진제 물성에 영향을 미치며, 우수한 물성의 추진제를 제조하기 위해서는 적절한 수준의 바인더의 경화 반응이 필요한 것으로 분석되었다.

• 대한소아치과학회지
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• 제33권4호
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• pp.624-632
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• 2006

기존에 사용하고 있는 할로겐 광중합기는 여러 가지 장점에도 불구하고 중합시간이 오래 걸린다는 문제 때문에 시술시간이 길어지는 단점이 있는데, 최근에 개발된 플라즈마 광중합기는 매우 짧은 시간에 중합시킬 수 있다고 제조회사는 주장하고 있다. 본 연구에서는 임상에서 흔히 상용하고 있는 복합 레진을 광중합 할 때, 할로겐 광중합으로 얻을 수 있는 플라즈마 광중합기의 적절한 중합시간을 알아보고자 한다. 2mm 두께의 레진 샘플을 만들어 광중합 하고 24 시간 후 상, 하면의 미세경도를 측정하였다. point $4^{(R)}$에서는 플라즈마 광중합기로 6초간 중합했을 때 할로겐과 유사한 경도를 얻었지만, $Z250^{(R)}$에서는 $Flipo^{(R)}$만 9초간 중합시 할로겐과 유사한 광중합을 나타냈다. 이번 연구에서 사용한 플라즈마 광중합기는 적어도 6초 혹은 9초정도 광중합 했을 때 할로겐과 유사한 중합을 얻을 수 있다는 것을 알 수 있었다.

• Composites Research
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• 제13권4호
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• pp.42-53
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• 2000

차세대 항공기소재로 관심을 가지고 있는 Al 7075/CFRP 적층 복합재인 CARALL(CARbon ALuminum Laminates)하이브리드 복합소재 제조를 위한 중요조건중의 하나인 Al 표면처리조건과 경화방법에 대해 조사하였다. 항공기용 Al 전처리 중 대표적인 것으로 증기탈지, 크롬산 양극산화 피막처리, 황산-중크롬산 나트륨 에칭처리 및 인산 양극산화 피막처리공정이 있다. 본 실험에서는 상기 전처리 공정을 모두 항공 규격에 준해서 실시하여 Lap shear 및 Bell peel strength를 비교함으로써 효과적인 접착강도를 나타내는 표면처리 공정을 찾아내고, 시편의 자연표면상태를 그대로 관찰할 수 있는 AFM(Atomic Force Microscope)장비를 이용하여 각 전처리 시편의 표면형상을 측정함으로써 표면형상과 접착강도와의 상관관계를 고찰 하였다. 그리고 Al 표면처리와 별도로 Al과 접착제 및 탄소섬유 프리프레그를 동시에 경화시키는 방법과 탄소섬유 프리프레그를 미리 경화시킨후 다시 Al과 탄소섬유 라미네이트를 접착필름을 이용하여 재 접착시키는 이차 경화법을 적용하여 상호 접착강도 및 물성을 비교하였다. 또한 이차경화법에서의 오토클레이브 압력 변화와 DMA(Dynamic Mechanical Analysis) 장비를 이용한 접착필름의 유리전이온도($T_g$) 측정을 통해 효과적인 공정압력 및 접착내구성 유지에 필요한 최소 경화시간을 파악하였다. 상기 결과로부터 정밀 치수관리가 필요하며 고접착강도, 내구성 항공기 부품을 제작하기 위한 알루미늄 표면처리 공정과 복합재 경화공정 조건을 제시하고자 하였다.

• Restorative Dentistry and Endodontics
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• 제27권1호
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• pp.16-23
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• 2002

Physical properties of composite resins such as strength, resistance to wear, discoloration, etc depend on the degree of conversion of the resin components. The purpose of this study was to evaluate the degree of conversion of the composite resins according to the thickness of tooth structure penetrated by light and applied light curing time. The coronal portions of extracted human teeth (one anterior tooth, three posterior tooth) was embedded by pink denture material. the mounted teeth were cut into three illumination sections (1mm thickness enamel section, 1mm thickness dentin section, 2mm thicknes dentin section) and one backing section with cutting wheel. Thin resin films were made by using 6kg pressure between slide glass during 5 minutes Thin resin film was light cured on coupled illumination section during 40sec, 80sec and 120sec. each illumination section was coupled as follows; no tooth structure(X), ename section(E), enamel section + 1mm dentin section(ED1), enamel section + 2mm dentin section(ED2), enamel section + 1mm dentin section + 2mm dentin section(EDD). To simulate the clinical situation more closely, thin resin films was cured against a backing section of tooth structure. The degree of conversion of carbon double bonds to single bonds in the resin films were examined by means of Fourier Transform Infrared Spectrometer. The results were obtained as follows ; 1 As curing time was increased, conversion rate was increased and as tooth thickness which was penetrated by curing light was increased, conversion rate was decreased. 2. At all tooth thickness groups, conversion rate between 80sec and 120sec was not significantly increased(P＞0.05). 3. At 40sec group and 80sec, conversion rate between no tooth structure(X) group and 1mm enamel section(E) group was not significantly decreased(P＞0.05). 4. At 80sec group and 120sec, conversion rate between 1mm enamel section(E) group and 1mm enamel section + 1mm dentin section(ED1) group was not significantly decreased(P＞0.05).

• 대한치과보철학회지
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• 제34권3호
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• pp.464-474
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• 1996

A principal advantage of a plastic tooth over a porcelain tooth should be its ability to bond to the denture base material. But plastic teeth could craze and wear easily, so more abrasion resistant plastic denture teeth have been developed. To resist abrasion, the degree of cross-linking was increased, but bonding to denture base meterial became more difficult. The purpose of this study was to evaluate the bond strength of plastic teeth and abrasion resistant teeth bonded to heat-curing, self-curing and light-curing denture base material. Denture tooth molds were chosen that had a>8mm diameter. The denture teeth was bonded to three denture base materials and then machined to the same dimensions. Three denture base materials were used as control groups. Prior to tensile testing, the specimens were thermocycled between $5^{\circ}C\;and\;55^{\circ}C$ for 1000cycles. Tensile testing was performed on an Instron Universal testing mechine. Experimental group ; plastic teeth(Justi Imperial)+heat-curing resin(Lucitone 199) plastic teeth(Justi Imperial)+light-curing resin(Triad) plastic teeth(Justi Imperial)+self-curing resin(Vertex SC) abrasion resistant teeth(IPN)+heat-curing resin(Lucitone 199) abrasion resistant teeth(IPN)+light-curing resin(Triad) abrasion resistant teeth(IPN)+self-curing resin(Vertex SC) Control group ; heat-curing resin(Lucitone 199) light-curing resin (Triad) self-curing resin(Vertex SC). The results were as follows : 1. The denture teeth bonded to heat-curing resin showed the cohesive failure and those bonded to the other resins showed adhesive failure. 2. Tensile bond strength of the plastic teeth bonded to self-curing resin was not significantly greater than bonded to light-curing resin(p>0.05). 3. Tensile bond strength of the abrasion resistant teeth bonded to self-curing resin was not significantly greater than bonded to light-curing resin(p>0.05). 4. Tensile bond strength of the plastic teeth to self-curing resin was not significantly different from that of the abrasion-resistant teeth(p>0.05). 5. Tensile bond strength of the plastic teeth to light-curing resin was significantly greater than that of the abrasion resistant teeth(p<0.01).