• Journal of Forest and Environmental Science
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• 제36권3호
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• pp.219-224
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• 2020

Urea formaldehyde resins are widely used in the manufacturing of wood composite and their usage is always combined with release of formaldehyde characterized to be hazardous to health during and after the manufacturing of the products. This study investigates the effectiveness of wood-based adhesive from oil of pyrolysed Triplochiton scleroxylon sawdust for the production of composite board. The wood-derived Pyrolytic Oil (PyO) was blended with Urea Formaldehyde (UF) resin to formed Pyrolytic Oil-Urea Formaldehyde (PyOUF). The obtained PyOUF called Wood-Based Adhesives at four blends and control (UF) viz; 1:1, 1:2, 1:3, 2:1, 1:3 were further employed to prepare the composite board and test for their bonding strength by physical (water absorption-WA and thickness swelling-Th.S) and mechanical properties (modulus of elasticity-MOE, modulus of rupture-MOR, and impact bending-IB). Data obtained was analysed using analysis of variance at α 0.05. The result of analysis of variance conducted on physical properties show significant difference (p≤0.05) between the WA values obtained when testing the different blending proportion of PyOUF and likewise between 2 and 24 h of immersion. PyOUF had significant effect (p≤0.05) on Th. S for 24 h but no significant different (p>0.05) for the 2 h period of soaking. The analysis of variance on mechanical properties of the composite board (MOE, MOR, and IB) show significance differences (p≤0.05) between the strength values obtained when testing the different ratios of PyO with UF. PyO content influenced the properties of the boards and it is evident that PyO can be used in the manufacture of composite board.

• 한국세라믹학회지
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• 제35권2호
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• pp.172-179
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• 1998

Valve lifter namely tappet is supported by lifter hole which is located upper side of camshaft in cylinder block transforms rotatic mvement of camshaft into linear movement and helps to open and shut the en-gine valve as an engine parts. The face of valve lifter which is continuously contacting with camshaft brings about abnormal wears such as unfair wear and early wear because it is severely loaded in the valve train system. These wears act as a defect like over-clearance and cause imperfect combustion of fuel during the valve lifting in the combustion chamber. Consequently this imperfect combustion makes the engine out-put decrease and has cause on air pollution. To prevent these wears therefore The valve lifter cast in me-tal developed into SiC ceramics valve lifter which has an excellence in wear and impact resistance As a results the optimum process conditions like injection condition mixture ratio and debonding process could be established. After sintering fine-sinered dual microstructure in which prior ${\alpha}$-SiC matches well with new SiC(${\beta}$-SiC) produced by reaction among the ${\alpha}$-SiC carbon and silicon was obtained. Based on the study it is verified that mechanical properties of SiC valve lifter are excellent in Vickers hardness 1100-1200 bending strength (300-350 Pa) fracture toughness(1.5-1.7 Mpa$.$m1/2) Through engine dynamo test-ing SiC valve lifter and metal valve lifter are examined and compared into abnormal phenomena such as early fracture unfair and early wear. It is hoped that this research will serve as an important springboard for the future study of heavy duty diesel engine parts developed by ceramics which has a good wear resis-tance relaibility and lightability.

• Steel and Composite Structures
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• 제7권6호
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• pp.457-468
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• 2007

Analytical and experimental investigation on dynamic properties of extra lightweight concrete sandwich beams reinforced with various lay ups of carbon reinforced epoxy polymer composites (CFRP) are discussed. The lightweight concrete used in the core of the sandwich beams was made up of extra lightweight aggregate, Lica. The density of concrete was half of that of the ordinary concrete and its compressive strength was about $100Kg/cm^2$. Two extra lightweight unreinforced (control) beams and six extra lightweight sandwich beams with various lay ups of CFRP were clamped in one end and tested under an impact load. The dimension of the beams without considering any reinforcement was 20 cm ${\times}$ 10 cm ${\times}$ 1.4 m. These were selected to ensure that the effect of shear during the bending test would be minimized. Three other beams, made up of ordinary concrete reinforced with steel bars, were tested in the same conditions. For measuring the damping capacity of sandwich beams three methods, Logarithmic Decrement Analysis (LDA), Hilbert Transform Analysis (HTA) and Moving Block Analysis (MBA) were applied. The first two methods are in time domain and the last one is in frequency domain. A comparison between the damping capacity of the beams obtained from all three methods, shows that the damping capacity of the extra lightweight concrete decreases by adding the composite reinforced layers to the upper and lower sides of the beams, and becomes most similar to the damping of the ordinary beams. Also the results show that the stiffness of the extra lightweight concrete beams increases by adding the composite reinforced layer to their both sides and become similar to the ordinary beams.

• Earthquakes and Structures
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• 제19권4호
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• pp.273-286
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• 2020

The pile group foundation is widely used for gravity pier of high-speed railway bridges in China. If a moderate or strong earthquake occurs, the pile-surrounding soil will exhibit obvious nonlinearity and significant pile group effect. In this study, an improved pushover analysis model for the pile group foundation with consideration of pile group effect is presented and validated by the quasi-static test. The improved model uses simplified springs to simulate the soil lateral resistance, side friction and tip resistance. PM (axial load-bending moment) plastic hinge model is introduced to simulate the impact of the axial force changing of pile group on their elastic-plastic characteristics. The pile group effect is considered in stress-stain relations of the lateral soil resistance with a reduction factor. The influence factors on nonlinear characteristics and plastic hinge distribution of the pile group foundation are discussed, including the pier height, longitudinal reinforcement ratio and stirrup ratio of the pile, and soil mechanical parameters. Furthermore, the displacement ductility factor, resistance increase factor and yielding stiffness ratio are provided to evaluate the seismic performance of soil-pile system. A case study for the pile group foundation of a railway simply supported beam bridge with a 32 m-span is conducted by numerical analysis. It is shown that the ultimate lateral force of pile group is not determined by the yielding force of the single one in these piles. Therefore, the pile group effect is essential for the seismic performance evaluation of the railway bridge with pile group foundation.

• 한국전산구조공학회논문집
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• 제37권1호
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• pp.67-76
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• 2024

본 논문에서는 역학적 변수들을 측정하는 방안으로 디지털 이미지 프로세싱과 강형식 기반의 MLS 차분법을 융합한 DIP-MLS 시험법을 소개하고 추적점의 위치와 이미지 해상도에 대한 영향을 분석하였다. 이 방법은 디지털 이미지 프로세싱을 통해 시료에 부착된 표적의 변위 값을 측정하고 이를 절점만 사용하는 MLS 차분법 모델의 절점 변위로 분배하여 대상 물체의 응력, 변형률과 같은 역학적 변수를 계산한다. 디지털 이미지 프로세싱을 통해서 표적의 무게중심 점의 변위를 측정하기 위한 효과적인 방안을 제시하였다. 이미지 기반의 표적 변위를 이용한 MLS 차분법의 역학적 변수의 계산은 정확한 시험체의 변위 이력을 취득하고 정형성이 부족한 추적 점들의 변위를 이용해 mesh나 grid의 제약 없이 임의의 위치에서 역학적 변수를 쉽게 계산할 수 있다. 개발된 시험법은 고무 보의 3점 휨 실험을 대상으로 센서의 계측 결과와 DIP-MLS 시험법의 결과를 비교하고, 추가적으로 MLS 차분법만으로 시뮬레이션한 수치해석 결과와도 비교하여 검증하였다. 이를 통해 개발된 기법이 대변형 이전까지의 단계에서 실제 시험을 정확히 모사하고 수치해석 결과와도 잘 일치하는 것을 확인하였다. 또한, 모서리 점을 추가한 46개의 추적점을 DIP-MLS 시험법에 적용하고 표적의 내부 점만을 이용한 경우와 비교하여 경계 점의 영향을 분석하였고 이 시험법을 위한 최적의 이미지 해상도를 제시하였다. 이를 통해 직접 실험이나 기존의 요소망 기반 시뮬레이션의 부족한 점을 효율적으로 보완하는 한편, 실험-시뮬레이션 과정의 디지털화가 상당한 수준까지 가능하다는 것을 보여주었다.

• 한국구조물진단유지관리공학회 논문집
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• 제21권2호
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• pp.130-137
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• 2017

최근 경제 성장과 건설 기술의 발달로 인해 구조물이 대형화, 고층화됨에 따라 상부구조물을 지지할 수 있는 기초의 역할이 중요시 되고 있다. 이 연구에서는 철근콘크리트 말뚝 성능향상을 목적으로 프리캐스트공법과 철근 및 속채움 콘크리트로 말뚝머리부를 보강한 철근 콘크리트 말뚝(HPC)을 개발하고 한계상태설계법을 바탕으로 말뚝성능을 예측하였고 설계와 실제강도와 비교를 통해 말뚝 내력의 안전성을 평가하였다. HPC말뚝 본체의 단면형상은 최대폭 500 mm, 최소폭 475 mm의 10각 단면으로 말뚝머리부 본체 두께는 70 mm이다. 중공부 본체 내측은 도로교설계기준에서 제시하는 수평전단강도를 확보하기 위해 요철형상으로 제작하였다. 전단강도 실험 결과 사인장균열이 발생하였지만 최종 파괴단계까지 급격한 파괴 없이 안정적인 전단내력을 확보하였고 한계상태설계법으로 예측한 전단강도를 135%, 119% 상회하였다. 말뚝머리 본체부 두께에 가외철근 보강 유무에 따라 제작된 실험체의 항타실험 결과 모든 말뚝 실험체에 균열이 발생하지 않아 충격에 대한 저항이 우수한 것으로 나타났다. 기성 PHC말뚝과 HPC말뚝 연결부 휨실험을 통해 측정된 휨하중을 평가한 결과 기성 PHC말뚝 설계 휨균열 하중에 비해 1.51배 및 1.48배 높은 값을 나타내어 충분한 연결부 휨내력을 확보하는 것으로 나타났다.

• Composites Research
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• 제36권3호
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• pp.180-185
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• 2023

본 논문에서는 스프레딩된 SiC 섬유를 적용해 SiC_f/SiC를 제조하였을 경우, 섬유의 분산도가 복합소재의 내부구조 및 기계적 강도에 어떠한 영향을 주는지를 연구하였다. Spread SiC 섬유를 적용한 시편의 섬유 체적비는 non-spread 시편 대비 9%p 감소하였으며, 수지 슬러리가 섬유 사이로 더 원활히 함침되어 기지내 기공도 거의 발견되지 않았다. 각 시편의 섬유 분산도를 비교하기 위해, 복합소재 내 섬유간 이격거리를 수치화하고 평가하는 방법을 제안하였다. 그 결과 spread 시편의 섬유간 중심거리는 non-spread 시편 대비 2.23 ㎛ 증가하였으며, 섬유 표면 사이 거리는 42.6%로 대폭 증가하였다. 3점 굽힘시험을 통해 spread 시편의 굽힘강도가 non-spread 시편 대비 49.3% 가량 높으며, 시험 데이터의 편차도 더 균일함을 확인하였다. 따라서 복합소재 기지내 SiC 섬유의 분산도 향상이 SiC_f/SiC의 균일한 기지상 치밀화와 기계적 강도 증가에 매우 큰 영향을 미친다는 점을 알 수 있다.

• Journal of the Korean Wood Science and Technology
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• 제17권1호
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• pp.3-11
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• 1989

리기다소나무 단판적층재(單板積層材)(LVL)의 가구용재(家具用材)로서의 적합성(適合成) 여부(與否)를 판단(判斷)하기 위한 기초자료(基礎資料)를 제공(提供)하고자 요소 멜라민수지(樹脂)와 페놀수지접착제(樹脂接着劑)를 사용(使用)하여 단판적층재(單板積層材)를 제조(製造), 그 물리적(物理的), 기계적(機械的) 성질(性質), 접착내구성(接着耐久性) 및 제조성능(製造性能)을 검토(檢討)한 결과(結果)는 다음과 같다. 1. 리기다소나무 LVL 제조(製造)를 위한 적정압체시간(適正壓締時間)은 단판(單板)두께 1mm당(當) 45초(秒) 이상이 요구(要求)되었다. 2. 휨강도(强度)는 소재(素材)에 비(比)해 낮았으나 압축강도(壓縮强度)는 비슷하였고 단판(單板)의 두께가 얇을수록 강도(强度)는 증가(增加)하는 경향(傾向)이였다. 3. 충격(衝擊)휨흡수(吸收)에너지는 두께 2.5cm의 경우(境遇) 섬유직각방향(纖維直角方向)(상(上))이 $0.03kg{\cdot}m/cm^2$, 섬유방향(纖維方向)이 $0.24kg{\cdot}m/cm^2$으로 $0.68kg{\cdot}m/cm^2$인 소재(素材)에 비(比)해 매우 낮았다. 4. 열압체시간(熱壓締時間)을 45초(秒)/mm 이상(以上)으로 하면 침지박리(浸漬剝離) 및 한열반복시험시(寒熱反復試驗時), 접착층(接着層)의 박리(剝離), 표면할열(表面割裂), 부풀음, 변색(變色) 등(等)이 발생(發生)하지 않았다. 5. 진공침수시험(眞空侵水試驗)은 결과(結果), 섬유방향(纖維方向)으로서 수축율(收縮率)은 약(約) 1.0%, 섬유직각방향(纖維直角方向)(횡방향(橫方向))은 약(約) 3%였으며, 1~4개(個) 정도(程度)의 표면할제(表面割裂)이 관찰(觀察)되었다. 6. 온냉건고시험(溫冷乾燥試驗)에 의한 리기다소나무 LVL의 도막할열(塗膜割裂)은 전혀 관찰(觀察)되지 않았다. 7. 리기다소나무 LVL을 내장용(內粧用)으로 사용(使用)할 경우(境遇), 부착용화장단판(付着用化粧單板)으로서는 단판자체(單板自體)의 할열(割裂)이 적은 단판(單板)을 사용(使用)하여야 하며 부착용화장단판(付着用化粧單板)과 LVL의 표면(表面)이 서로 직교(直交)되도록 접착(接着)해야 표면할열(表面割裂)의 발생(發生)이 적고 표면부착성(表面付着性)이 향상(向上)되었다. 결론적(結論的)으로 리기다소나무 LVL은 접착성(接着性)은 매우 양호(良好)하였으며 휨강도(强度), 압축강도(壓縮强度) 및 충격(衝擊)휨흡수(吸收)에너지 등(等)은 가구재료(家具材料)로써 적정수준(適正水準)이었으나 단판자체(單板自體)의 옹이 및 할열(割裂)로 인(因)해 가구재료(家具材料)로 사용(使用)할 경우(境遇), 품질(品質)이 좋은 단판(單板) 즉, 화장단판(化粧單板) 등(等)으로 표면(表面)해양 할 것으로 생각되었다.

• The Journal of Advanced Prosthodontics
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• 제13권4호
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• pp.226-236
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• 2021

PURPOSE. This study aimed to evaluate the effect of incorporating zirconium oxide nanoparticles (nano-ZrO₂) in polymethylmethacrylate (PMMA) denture base resin on flexural properties at different material thicknesses. MATERIALS AND METHODS. Heat polymerized acrylic resin specimens (N = 120) were fabricated and divided into 4 groups according to denture base thickness (2.5 mm, 2.0 mm, 1.5 mm, 1.0 mm). Each group was subdivided into 3 subgroups (n = 10) according to nano-ZrO₂ concentration (0%, 2.5%, and 5%). Flexural strength and elastic modulus were evaluated using a three-point bending test. One-way ANOVA, Tukey's post hoc, and two-way ANOVA were used for data analysis (α = .05). Scanning electron microscopy (SEM) was used for fracture surface analysis and nanoparticles distributions. RESULTS. Groups with 0% nano-ZrO₂ showed no significant difference in the flexural strength as thickness decreased (P = .153). The addition of nano-zirconia significantly increased the flexural strength (P < .001). The highest value was with 5% nano-ZrO₂ and 2 mm-thickness (125.4 ± 18.3 MPa), followed by 5% nano-ZrO₂ and 1.5 mm-thickness (110.3 ± 8.5 MPa). Moreover, the effect of various concentration levels on elastic modulus was statistically significant for 2 mm thickness (P = .001), but the combined effect of thickness and concentration on elastic modulus was insignificant (P = .10). CONCLUSION. Reinforcement of denture base material with nano-ZrO₂ significantly increased flexural strength and modulus of elasticity. Reducing material thickness did not decrease flexural strength when nano-ZrO₂ was incorporated. In clinical practice, when low thickness of denture base material is indicated, PMMA/nano-ZrO₂ could be used with minimum acceptable thickness of 1.5 mm.

• The Journal of Advanced Prosthodontics
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• 제15권5호
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• pp.227-237
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• 2023

PURPOSE. This study aimed to assess and compare the color stability, flexural strength (FS), and surface roughness of occlusal splints fabricated from heat-cured acrylic resin, milled polymethyl methacrylate (PMMA)-based resin, and 3D-printed (PMMA) based-resin. MATERIALS AND METHODS. Samples of each type of resin were obtained, and baseline measurements of color and surface roughness were recorded. The specimens were divided into three groups (n = 10) and subjected to distinct aging protocols: thermomechanical cycling (TMC), simulated brushing (SB), and control (without aging). Final assessments of color and surface roughness and three-point bending test (ODM100; Odeme) were conducted, and data were statistically analyzed (2-way ANOVA, Tukey, P <.05). RESULTS. Across all resin types, the most significant increase in surface roughness (Ra) was observed after TMC (P < .05), with the 3D-printed resin exhibiting the lowest Ra (P < .05). After brushing, milled resin displayed the highest Ra (P < .05) and greater color alteration (∆E₀₀) compared to 3D-printed resin. The most substantial ∆E₀₀ was recorded after brushing for all resins, except for heat-cured resin subjected to TMC. Regardless of aging, milled resin exhibited the highest FS (P < .05), except when compared to 3D-printed resin subjected to TMC. Heat-cured resin exposed to TMC demonstrated the lowest FS, different (P < .05) from the control. Under control conditions, milled resin exhibited the highest FS, different (P < .05) from the brushed group. 3D-printed resin subjected to TMC displayed the highest FS (P < .05). CONCLUSION. Among the tested resins, 3D-printed resin demonstrated superior longevity, characterized by minimal surface roughness and color alterations. Aging had a negligible impact on its mechanical properties.