In this study, the fatigue properties of press die steel, such as SKD11, and three high-durability die steel for the cold forming of ultra-high-strength steel sheets are evaluated. Specimens for fatigue, tensile, and hardness tests are manufactured through the heat treatment recommended by steelmakers and ultra-high precision processing. The general mechanical properties and fatigue properties are derived from hardness, tensile, and fatigue tests for four die steel. The tensile and fatigue properties of die steel derived through the tests are compared and analyzed. In particular, the correlation between the fatigue limit and the general mechanical properties such as tensile strength and elongation is analyzed, which allows relational expressions to be obtained through regression analysis. Finally, the study confirms that applying high-durability die steel is necessary for improving the die life in the manufacturing of press dies for ultra-high-strength steel sheets.

This paper aims at investigating the adhesive property at damage analysis according to the shape of the DCB test specimen made of Titanium, Dualumin as the high strength nonferrous metals. In this analysis, all three specimens had the lower holes bound by the cylinder support and the top holes were elongated with the rate of 6mm/min. The study results show that the longer the load block of DCB specimens, the more reliable and durable they are. It is utilized as the basic data at investigating the damage properties of adhesives in DCB specimens made of high strength nonferrous metals.

This research presents assessmental FRP plate, one of materials used for reinforcing damage of RC structure caused by deterioration. in order to investigate effective bonding length and bonding strength according to material property of epoxy used for bonding between FRP-Concrete, experimental tests for 3 specimens with each bonding length of 50,100,150,200and 250mm respectively are performed. test results indicate frat material property of epoxy can affect effective bonding length of FRP-Concrete.

TiC-21mol% Mo solid solution (δ-phase) and TiC-99 mol% Mo solid solution (β-phase), and TiC-(80~90)mol%Mo hypo-eutectic composite were deformed by compression in a temperature range from room to 2300 K and in a strain raterange from 4.9×10−5 to 6.9×10−3/s. The deformation behaviors of the composites were analyzed from the strengths of theδ- and β-phases. It was found that the high strength of the eutectic composite is due primarily to solution hardening of TiCby Mo, and that the δ-phase undergoes an appreciable plastic deformation at and above 1420 K even at 0.2% plastic strainof the composite. The yield strength of the three kinds of phase up to 1420 K is quantitatively explained by the rule of mixture,where internal stresses introduced by plastic deformation are taken into account. Above 1420 K, however, the calculated yieldstrength was considerably larger than the measured strength. The yield stress of β-phase was much larger than that of pure TiC.A good linear relationship was held between the yield stress and the plastic strain rate in a double-logarithmic plot. Thedeformation behavior in δ-phase was different among the three temperature ranges tested, i.e., low, intermediate and high. Atan intermediate temperature, no yield drop occurred, and from the beginning the work hardening level was high. At the testedtemperature, a good linear relationship was held in the double logarithmic plot of the yield stress against the plastic strain rate.The strain rate dependence of the yield stress was very weak up to 1273 K in the hypo-eutectic composite, but it becamestronger as the temperature rose.

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.

Nondestructive evaluation (NDE) technique method using a resonance frequency by free vibration mode was carried out for damaged and sound black pine woods( Pinus thunbergii ) by Matstucoccus thunbergianae in order to utilize damaged trees. There were a close relationship of dynamic modulus of elasticity and static bending modulus of elasticity to MOR. It was found that there were a high correlation at 1% level between dynamic modulus of elasticity and MOR, and static modulus of elasticity and MOR in all conditions. However, the result indicated that correlation coefficient is higher in dynamic modulus of elasticity to MOR than that in static modulus of elasticity to MOR. Therefore, the dynamic modulus of elasticity using resonance frequency by free vibration mode is more useful as a nondestructive evaluation method for predicting the MOR of sound and damaged woods by Matstucoccus thunbergianae.

Nondestructive evaluation (NDE) technique method using a resonance frequency by free vibration mode was carried out for heat-treated wood produced under different conditions. The effect of heat treatment on the bending strength and NDE technique using the resonance frequency by free vibration mode of wood for Korean paulownia, Pinus densiflora, Lidiodendron tulipifera and Betula costata were measured. The heat treatment temperature has been investigated at 175℃ and 200℃, respectively. There were a close relationship of dynamic modulus of elasticity and static bending modulus of elasticity to MOR. In all conditions, It was found that there were a high correlation at 1% level between dynamic modulus of elasticity and MOR, and static modulus of elasticity and MOR. However, the result indicated that correlation coefficient is higher in dynamic modulus of elasticity to MOR than that in static modulus of elasticity to MOR. Therefore, the dynamic modulus of elasticity using resonance frequency by free vibration mode is more useful as a nondestructive evaluation method for predicting the MOR of heat-treated wood under different temperature and species conditions.

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.

Alloys of nylon(PA6) and ethylene-propylene-diene polymer, modified with maleic anhydride(MEPDM) were prepared using a melt kneading process. This study focuses on the effects of the content of MEPDM in PA6 blend on the mechanical and thermal properties of such blends where MEPDM is the dispersed phase. Mechanical properties were examined by stress-strain measurements and impact strength test. Both impact strength of PA6/MEPDM at room temperature and at -20℃ were improved up to 400-550% with the amounts of MEPDM. However, PA6/MEPDM containing 3-5 wt% of MEPDM showed the about 700kgf/m2 of the maximum tensile strength but 8.5 % of the lowest elongation. For certain compositions of PA6 with rubbery MEPDM, the interesting reduction of elongation is caused by the reaction of the polyamide amine end groups with maleic anhydride portion in MEPDM, that provided a reinforcement in the PA6 matrix. In addition, the introduction of antistatic agent on the surface of alloys causes significant reduction of their surface electrostatic resistance.

아스팔트 바인더 Stiffness와 혼합물의 변형강도 및 동적크리프 특성과의 상관성 분석을 토대로 혼합물의 소성변형 저항성 (내변형성) 추정을 위한 Kim test의 적용성을 고찰하였다. 본 연구는 골재 2종류, AC 60-80 및 이를 개질한 총 8종류의 바인더로 총 16가지 혼합물을 제조하였다. DSR로 각 바인더의 G*/sineδ를 측정하였으며 Kim test의 변형강도와 동적크리프 시험의 최종변위(FD)와 동적안정도(DS)를 각 혼합물로부터 측정하였다. 바인더의 G*/sineδ와 소성변형 관련 3가지 특성(SD. FD, DS)과의 상관성 분석 결과 G*/sineδ와 SD와 상관성이 가장 높은 것으로 나타났다 (R2=0.88) 이는 혼합물에 내재해 있는 내변형성의 차이를 Kim test가 더 잘 구분해 낼 수 있음을 의미한다. 또한 DS와 SD의 회귀분석 결과, R2이 약 0.84 이상을 보여 변형강도는 동적크리프 시험의 동적안정도와 좋은 상관성을 가짐을 확인하였다. 따라서 본 연구를 통하여 아스팔트 혼합물의 내변형성 평가시 Kim test의 활용 가능성이 매우 높음을 확인하였다.

By analyzing the strength of shotcrete mixture with blast furnace slag and confirmed the suitability as subsea tunnel support. As a result, the shotcrete mixture with slag is excellent evaluated in terms of durability compared with existing shotcrete.

In this study, It was found that replacing a large amount of mineral admixture, we satisfied the target, compressive strength of 30, 50MPa and manufactured lightweight concrete reducing CO2 emissions up to 42.1～52.8% comparing normal concrete

The purpose of this study is to investigate the characteristics of compressive strength and workability according to the NaOH and KOH addition method as powder of mortar which is made of Non-sintered binder for the reuse of resources and the CO2 reduction

In this study, KS F 2405 was used to investigated the compressive strength of property of high performance concrete (HPC) using the fly ash and silica fume. The experiments were carried out silica fume-binder ratio from 5% (SF5) and fly ash 25%+silica fume 5% (FA25SF5). The compressive strength of HPC determined on 7days and 28days.

고로슬래그 미분말을 순환골재 모르타르 및 콘크리트의 제조에 활용할 경우, 순환골재에서 용출된 Ca(OH)2가 고로슬래그에 대한 자극제 역할을 수행하여 수화반응을 개선할 수 있을 것으로 판단되고 고로슬래그를 통해 알칼리 저감 효과를 얻을 것으로 예상되어 본 연구를 진행하게 되었다. 그 결과 고로슬래그 미분말을 혼입․사용한 순환 잔골재 모르타르는 재령 3일에서는 고로슬래그 혼입율에 따라 강도가 감소하는 결과를 나타냈다. 이는 고로슬래그의 수화반응이 일어나지 않았기 때문으로 판단되며 또한, 순환 잔골재 혼입률에 관계없이 고로슬래그 미분말의 혼입률이 증가함에 따라 재령 3일 측정한 수화활성도도 저하되는 것으로 나타났다. 재령 7일에서는 순환 잔골재에서 용출된 수산화칼슘(Ca(OH)2)이 자극제 역할을 수행하여 고로슬래그 미분말을 혼입한 배합의 압축강도 발현이 천연 잔골재를 사용한 모르타르보다 서서히 증가하는 결과를 보이기 시작하였으며 이로 인해 재령 7일 측정한 고로슬래그 미분말을 단계별로 혼입한 배합의 수화활성도가 고로슬래그를 혼입하지 않은 배합보다 높아지는 것으로 나타났다. 재령 28일에서는 고로슬래그 미분말 혼입률 30% 배합에서는 고로슬래그의 수화반응으로 인해 천연 잔골재를 사용한 배합보다 높은 압축강도를 보이기 시작하였으며 이때 측정한 수화활성도는 천연 잔골재를 사용한 배합과 특별한 차이를 보이지 않았으며, 이는 지속적으로 수산화칼슘(Ca(OH)2)이 공급되지 못하였기 때문으로 판단된다.