In this study, the strength property is investigated through structural and vibration analysis on the lead screw of height drive module for automotive power seat. The positions of applied loads are lowest, middle and highest on the model of lead screw in cases of 1, 2 and 3. Natural frequencies are examined about three kinds of models and critical frequencies are also checked by harmonic responses. Maximum deformations are shown as 0.033mm, 0.026mm and 0.551mm respectively in models of 1, 2 and 3. In case 3 at highest position, this strength becomes weakest by comparing with cases 2 and 3. By use of this analysis result, it is possible to design the model effectively applied at automotive safe driving.

본 연구는 소나무 1년생 묘목을 대상으로 단근의 정도가 이식 후 지상부 생장 및 뿌리발달에 미치는 영향을 구명하고자 실시하였다. 이를 위해 전체 뿌리길이의 25%, 50%, 75%를 단근하였으며, 단근하지 않는 묘목과 비교하였다. 이식한 후 1년의 경과한 시점에서 생존율, 묘고 및 근원경, 각 부위별 건중량 및 뿌리생장 특성 등을 조사하였다. 생존율은 단근된 묘목(25∼75% 단근)이 단근하지 않는 묘목보다 우수하게 나타났으며, 단근 강도간의 생장 차이는 나타나지 않았다. 이식 후 묘고를 비롯한 줄기 건중량, 근원경 등 지상부 생장량과 뿌리 및 전체 묘목 건중량은 단근하지 않은 묘목과 25%로 단근된 묘목이 가장 우수하게 나타났다. 묘목의 품질을 판단할 수 있는 뿌리 대 지상부 비율과 묘목품질지수는 25%로 단근된 묘목이 우수하게 나타났다. 따라서 본 연구결과를 종합해볼 때, 소나무 1년생 노지묘의 높은 생존율을 위해서는 이식 전 단근작업을 해 주는 것이 좋으며, 이때 단근 강도는 전체 뿌리길이의 25%를 단근하는 것이 적절하다고 판단된다.

In this study, recliner is modelled and compared with 2 types of models as conventional recliner and round recliner by investigating stress and displacement through strength analysis. The maximum deformation of 0.018mm at round recliner is much smaller than that of 0.18mm at conventional recliner. It can be seen that the round recliner has more safety than conventional recliner. Round recliner model has more durability and safety than conventional model by the result of structural and vibration analysis. The model design of automotive recliner can be designed effectively at applying the safe driving of automobile practically by using the result of this study.

CSA, a cement mineral compound that is mainly composed of 3CaO·3Al2O3·CaSO4, generates ettringite as a hydration product after a reaction with glass (lime), gypsum and water to speed up the hardening process and enhance the strength and degree of expansion. When used as a cement admixture, there is increased production of ettringite, which can improve the initial strength in the first three days and ameliorate the reduction in the initial strength caused by the use of fly ash in particular. In this study, a hydrate analysis was performed using XRD and SEM after substitution with fly ash (30%) and CSA (8%) with the goal of observing the effect of CSA on the initial strength of a cement mixture containing fly ash. The results of the analysis showed that an addition of CSA promoted the production of ettringite and improved the initial strength, resulting in the generation of hydrates, which can effectively enhance the long-term strength of these materials.

This study investigated the continuous cooling transformation, microstructure, and mechanical properties of highstrength low-alloy steels containing B and Cu. Continuous cooling transformation diagrams under non-deformed and deformed conditions were constructed by means of dilatometry, metallographic methods, and hardness data. Based on the continuous cooling transformation behaviors, six kinds of steel specimens with different B and Cu contents were fabricated by a thermomechanical control process comprising controlled rolling and accelerated cooling. Then, tensile and Charpy impact tests were conducted to examine the correlation of the microstructure with mechanical properties. Deformation in the austenite region promoted the formation of quasi-polygonal ferrite and granular bainite with a significant increase in transformation start temperatures. The mechanical test results indicate that the B-added steel specimens had higher strength and lower upper-shelf energy than the B-free steel specimens without deterioration in low-temperature toughness because their microstructures were mostly composed of lower bainite and lath martensite with a small amount of degenerate upper bainite. On the other hand, the increase of Cu content from 0.5 wt.% to 1.5 wt.% noticeably increased yield and tensile strengths by 100 MPa without loss of ductility, which may be attributed to the enhanced solid solution hardening and precipitation hardening resulting from veryfine Cu precipitates formed during accelerated cooling.

Ultra high performance concrete which has recently been studied was developed to complement the brittle behaviour and dynamic uppermost limit of high strength concrete. Fiber reinforced concrete which mixed steel fiber is receiving attention as an alternative about this and is being developed to complement the disadvantages of high strength concrete including lower toughness coefficients and crack resistance and spalling in fires. Review about fiber reinforced ultra high strength concrete that this study tries to treat includes reduction of self shrinkage generated by high cement content per unit volume of concrete, evaluation of compression and tension strength to lower internal and external spalling resistance and fragility factors of member of framework, and flow characteristics of concrete which doesn't harden according to steel fiber amounts and used materials. As the result, the more fiber reinforcement increases, the more compression and tensile strength increase and deformation control of cement matrix and improvement of energy absorption ability showed the great effect in shrinkage reduction.

공항 포장의 경우 항공기의 하중과 규모를 비롯하여 여러가지 극한 상황에 놓이기 때문에 공항용 구조 물은 높은 신뢰성이 담보 되어야 한다. 그러므로 공항 콘크리트 포장용 유지보수 재료는 높은 수준의 성능과 내구성이 요구된다. 부분 유지보수가 적용된 부분의 재파손이 빈번하게 발생하는데 접합면이 떨어지는 형태가 주를 이룬다. 부착강도는 부분 유지보수 재료의 성능을 평가 할 수 있는 매우 중요한 특성이라고 할 수 있다. 이 연구에서는 기존 공항 콘크리트 포장과 부분보수 재료와의 전단부착강도와 인장부착강도를 측정하 였다. 부분보수재료는 기존 공항용으로 사용되던 폴리머콘크리트와, 새로 고안된 PMC(Polymer Modified Concrete), 기존 도로용 보수재료로 사용되는 LMC(Latex Modified Concrete)를 대상으로 하였다. 전단부착강도는 Slant shear test, 인장부착강도는 Splitting tensile test를 각각 이용하였다. 또한 열팽창계수와 건조수축의 차이에 따른 포장재료와 부분보수재료의 부적합성의 결과로 부착강도가 시간에 따라 저하된다. 실험을 통해 접합면의 노화에 따라 재료별 부착강도의 변화를 비교하였다.

Recently, steel structures have increasingly been required to have sufficient deformability because they are subjected to progressive or abrupt displacement arising from structure loading itself, earthquake, and ground movement in their service environment. In this study, high-strength low-carbon bainitic steel specimens with enhanced deformability were fabricated by varying thermo-mechanical control process conditions consisting of controlled rolling and accelerated cooling, and then tensile and Charpy V-notch impact tests were conducted to investigate the correlation between microstructure and mechanical properties such as strength, deformability, and low-temperature toughness. Low-temperature transformation phases, i.e. granular bainite (GB), degenerate upper bainite(DUB), lower bainite(LB) and lath martensite(LM), together with fine polygonal ferrite(PF) were well developed, and the microstructural evolution was more critically affected by start and finish cooling temperatures than by finish rolling temperature. The steel specimens start-cooled at higher temperature had the best combination of strength and deformability because of the appropriate mixture of fine PF and low-temperature transformation phases such as GB, DUB, and LB/LM. On the other hand, the steel specimens start-cooled at lower temperature and finish-cooled at higher temperature exhibited a good low-temperature toughness because the interphase boundaries between the low-temperature transformation phases and/or PF act as beneficial barriers to cleavage crack propagation.

PURPOSES: The performance of tack coat, commonly used for layer interface bonding, is affected by application rate and curing time. In this study, bonding strength tests were performed according to the application rate and curing time of asphalt emulsion. Based on finding from this study, optimum application rates and curing times are proposed. METHODS: In order to investigate bonding characteristic of asphalt emulsion, tests were performed on both asphalt concrete pavement and portland concrete pavement. Also, asphalt emulsions were tested at the application rate of 0, 0.2, 0.4, 0.6, and 0.8l/m2 and at the curing time of 0, 0.5, 1, 2, and 24 hours. Pull-off test and shear bonding strength test, which commonly used for bonding strength measurement of asphalt emulsion, were adopted for this study. To assess field performance under different testing condition, asphalt emulsions were applied to in-service pavement. Throughout coefficient of determination analysis between material index properties from asphalt emulsion and mechanical response from bonding strength tests, performance correlativity was analyzed. RESULTS: Test results show that optimum application rate for asphalt overlay on asphalt concrete pavement (AOA) and asphalt overlay on concrete pavement (AOC) was 0.4~0.5l/m2 and 0.3~0.5l/m2, respectively. According to the curing time increment, tensile strength and shear strength of AOC were increased to 22~44% and 20~39%, respectively. AOA case also show strength increment in tensile strength (42%) and shear strength (9%). We tested the applicability of tack coat materials at the field sites, and our findings demonstrated that the bonding (for D and E) and rapid curing (for B, C, and D, E) performances were superior than others. Among material index properties, there was a high correlation between penetration ratio and bonding strength test result. CONCLUSIONS : Result show that interlayer bonding strength was affected by asphalt emulsion type, application rate and curing time. AOC required slightly higher application (0.1l/m2) than AOA. Both AOA and AOC cases show higher strength at longer curing time. Up to 2hours of curing, rapid strength increments were observed, but strength increment ratio was decreased after 2hours of curing. From the observed correlation between penetration ratio and bonding strength, it is expected that penetration ratio can be used as one of important factors affecting bonding strength analysis.

PURPOSES : Bonded concrete overlay is a favorable maintenance method since the material properties are similar to existing concrete pavements. In addition, bonded concrete overlay has advantage of structural performance since the overlay layer and the existing pavement perform as a monolithic layer. It is important to have suitable bond strength criteria to secure the performance of bonded concrete overlay. This study aimed to investigate the factors influencing bond strength characteristics between existing concrete pavement and overlay material. METHODS: Bond strength between overlay and existing pavement are measured and analyzed for various conditions such as the type of overlay materials, compressive and flexure strength of overlay and existing pavement, and deterioration status of existing pavement. RESULTS: The strength of overlay material does not significantly influence the bond strength. The overlay of ultra-rapid hardening cement generally gives low bond strength. However, ultra rapid hardening polymer modified concrete gives robust bond strength. The deterioration of existing concrete significantly decrease the bond strength. CONCLUSIONS: Bond strength of bonded concrete overlay highly depends on condition of existing concrete pavement rather than overlay material.

차량용 시트는 쿠션부와 철제 구조물로 되어 있는데 철제 구조물은 프레임, 레일, 리클라이너로 구성된다. 특히 시트의 안정성과 직결된 리클라이너(Seat recliner)부품의 복합 성형제품은 파인블랭킹 제조기술을 활용하여 제작하는 연구가 진행되고 있다. 본 연구에서는 열처리 된 구조용강이 적용된 리클라이너를 CATIA 프로그램을 사용하여 3D 모델링하였으며, 이를 유한요소 해석 프로그램을 사용하여 라운드 리클라이너와 기준의 리클라이너의 강도 해석의 하중전달 경로, 응력 및 변형률을 연구하였다. 따라서 본 연구에서는 라운드 리클라이너와 기준의 리클라이너의 강도 해석의 응력 및 변형률을 비교/분석하였으며 기계적 특성을 파악했다.

최근 국내에서는 원자력발전소의 모듈화 공법에 적용하기 위하여 SC(steel plate concrete) 구조를 개발하는 연구를 진행하고 있다. 이 연구에서는 전단보강이 없는 비보강 SC 전단벽의 횡방향 내진성능 및 강성특성에 대하여 분석하기 위하여 전단벽 모형시편을 제작하고, 이를 대상으로 정적가력실험을 수행하였다. 실험 결과를 이용하여, 이 논문에서는 비보강 SC 구조의 횡력에 대한 파괴모드의 유형을 분석하고, 단면강도와 부재의 강성 특성을 검토하였다. 그리고 SC 구조용 설계기준에서 제시하는 단면의 강도 계산식과실험결과를 비교하였다. 연구결과, 비보강 SC 전단벽의 파괴 형태의 하나는 콘크리트와 강판의 부착 상실로 인한 휨전단파괴라는 사실을발견하였다. SC 구조 전단벽의 벽체 길이방향 거동은 파괴 시까지 벽체 외측의 강판이 내부 콘크리트를 구속하는 효과를 기대할 수 있으므로 연성능력이 향상되는 것이 확인되었다

This paper has fabricated insulation gang-form adhering general gang-form to the polyisocyanurate board and analyzed type of members, temperature record by locations and strength development after placing the concrete, in order to ensure efficient concrete quality under cold weather. According to our test, we can see that general gang-form member with curing under the same conditions as the actual field has a trend of constantly decreasing concrete temperature regardless to surface or central area due to rapid outdoor air temperature reduction, while in the case of insulation gang-from I and II, temperature increased up to around 25℃ after 12 hours under rapid outdoor air temperature change and temperature distribution did not appear large separation according to hydration reaction measurement locations. In addition, results of measurement for temperature records on weak insulation area by types of gang-forms showed that the temperature record distribution on the form tie surface and horizontal bar surface of angle bar has generally similar trend as the temperature records on the surface of the insulation gang-form, while corner area of the insulation gang-form did not have large insulation effect. It is determined that it requires additional curing measure for the weak corner area of the insulation gang-form in the future.

이 연구에서는 프리스트레싱용 고강도 강연선의 정착장치 중 강연선을 직접 정착하는 앵커헤드(anchor head)에 대해 거 동특성을 분석하고, 앵커헤드의 제원을 결정하는 단계에 있어서 해석적 검토에 요구되는 프로세스에 대해 정립하였다. 앵 커헤드는 쐐기와의 접촉(contact)을 통해 강연선으로부터의 힘이 전달되고 거동변화에 따라 접촉상태 또한 변하게 된다. 이 를 고려한 상세 거동분석을 위해 쐐기와 헤드 사이의 접촉(contact)조건을 설정하였으며, 앵커헤드의 비선형 재료모델을 적 용하여 기하 및 재료 비선형성을 고려한 구조해석을 수행하였다. 해석결과로부터 다음의 결과를 얻을 수 있었다. 앵커헤드 의 거동은 앵커헤드와 쐐기 간의 상호거동에 크게 영향을 받기 때문에 초기 설계단계부터 상대 영향을 고려해야 한다. 쐐 기홀(wedge hole)의 배치는 층배열(layered) 보다는 원형배열(circular)이 보다 응력분배에 효과적이고, 쐐기홀의 간격을 증 가시키고 헤드 하면 구멍의 크기를 줄여 구멍사이 강재의 두께를 다소 늘이는 것이 구조거동에 효과적이다.

When a new bonding agent using coal ash is utilized as a substitute for cement, it has the advantages of offering a reduction in the generation of carbon dioxide and securing the initial mechanical strength such that the agent has attracted strong interest from recycling and eco-friendly construction industries. This study aims to establish the production conditions of new hardening materials using clean bottom ash and an alkali activation process to evaluate the characteristics of newly manufactured hardening materials. The alkali activator for the compression process uses a NaOH solution. This study concentrated on strength development according to the concentration of the NaOH solution, the curing temperature, and the curing time. The highest compressive strength of a compressed body appeared at 61.24MPa after curing at 60˚C for 28 days. This result indicates that a higher curing temperature is required to obtain a higher strength body. Also, the degree of geopolymerization was examined using a scanning electron microscope, revealing a micro-structure consisting of a glass-like matrix and crystalized grains. The microstructures generated from the activation reaction of sodium hydroxide were widely distributed in terms of the factors that exercise an effect on the compressive strength of the geopolymer hardening bodies. The Si/Al ratio of the geopolymer having the maximum strength was about 2.41.

In this paper deals with strength of glass fiber reinforced plastics produced by shouting machine was investigated by universal testing instrument. We can obtain following results by performing the strength evaluation of polymer composite material according as varied environment temperature. The effect of environmental temperature on Strength properties was more sensitive in the weld specimen than parent. When changed environmental temperature, variation of strength in the parent was much bigger than it of weld specimen, that is, matrix in the parent, orientation in the specimen ware more sensitive to environmental strength. Tensile strength of polycarbonate matrix was similar regardless of mold temperature.