• Title/Summary/Keyword: Control of Cracking

검색결과 354건 처리시간 0.03초

고압 다이캐스팅용 알루미늄 합금의 열전도성 및 주조성에 미치는 첨가원소의 영향 (Effect of Alloying Elements on the Thermal Conductivity and Casting Characteristics of Aluminum Alloys in High Pressure Die Casting)

  • 김철우;김영찬;김정한;조재익;오민석
    • 대한금속재료학회지
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    • 제56권11호
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    • pp.805-812
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    • 2018
  • High pressure die casting is one of the precision casting methods. It is highly productivity and suitable for manufacturing components with complex shapes and accurate dimensions. Recently, there has been increasing demand for efficient heat dissipation components, to control the heat generated by devices, which directly affects the efficiency and life of the product. Die cast aluminum alloys with high thermal conductivity are especially needed for this application. In this study, the influence of elements added to the die cast aluminum alloy on its thermal conductivity was evaluated. The results showed that Mn remarkably deteriorated the thermal conductivity of the aluminum alloy. When Cu content was increased, the tensile strength of cast aluminum alloy increased, showing 1 wt% of Cu ensured the minimum mechanical properties of the cast aluminum. As Si content increased, the flow length of the alloy proportionally increased. The flow length of aluminum alloy containing 2 wt% Si was about 85% of that of the ALDC12 alloy. A heat dissipation component was successfully fabricated using an optimized composition of Al-1 wt%Cu-0.6 wt%Fe-2 wt%Si die casting alloy without surface cracks, which were turned out as intergranular cracking originated from the solidification contraction of the alloy with Si composition lower than 2 wt%.

토양수분 조건에 따른 블랙쵸크베리 'Nero' 과실의 품질 및 세포 발달 비교 (Comparison of Quality and Cell Enlargement of 'Nero' Black Chokeberry Fruits According to Different Soil Water Conditions)

  • 원정연;신현석;오영재;한현대;김금선;오세원;김대일
    • 한국자원식물학회지
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    • 제30권1호
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    • pp.88-95
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    • 2017
  • 토양수분의 변화가 블랙쵸크베리 'Nero'의 과실 특성에 미치는 영향을 조사하여 고품질 블랙쵸크베리 재배 연구의 기초자료를 제공하고자 수행하였다. 토양수분 감소로 인한 건조스트레스는 수확기 동안 블랙쵸크베리의 과실의 과중, 당도, 안토시아닌 함량 등의 품질을 저하시켰다. 또한 건조기간이 길수록 이후 토양수분 공급시, 과실 표피 세포 크기는 감소하는 반면 아표피, 과육 세포의 크기가 증가하여 열과를 유발할 수 있다. 따라서 관수시설을 통한 일정 주기의 관수가 블랙쵸크베리 과실 생산량 및 품질 향상을 위해 필요할 것으로 생각된다.

Engineering Performance of a Rapid Hardening Hydraulic Binder with Hybrid Fiber

  • Li, Mao;Kim, Jin-Man;Choi, Sun-Mi
    • 한국건축시공학회지
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    • 제16권3호
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    • pp.279-288
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    • 2016
  • The fundamental performance of any construction material should cover at least two phases: safety and serviceability. Safety commonly represents adequate strength, while serviceability encompasses the control of cracking and deflections at service loads. With respect to rapid hydraulic binders as a construction material, the above two phases should also be considered. Recent research on rapid cooling ladle furnace slag (RC-LFS) has drawn much attention, particularly given that it shows remarkable rapid hydraulic ability to pulverize to a fineness of $6,300cm^2/g$. This industrial byproduct could contribute to developing the sustainability of the rapidly hardening cementitious material system. This paper aims to expand upon the applicability of an RC-LFS-based binder that is composed of two parts. It also seeks to illustrate the engineering performance of an RC-LFS-based hybrid fiber-reinforced composite and to increase the strength of the RC-LFS-based composite. Each step of this experiment followed ASTM standards. The engineering performance, in both fresh state and hardening state, was tested and discussed in this paper. According to the experimental results for fresh concrete, the air content increased following the addition of polypropylene fiber. For hardened concrete, the toughness and strength improved following the addition of a hybrid fiber. The hybrid fiber mixture, which contains 0.75% of steel fiber and 0.25% of polypropylene fiber, shows even better engineering performance than other mixtures.

규사 혼입과 플라이애쉬 혼입에 따른 폴리에틸렌 섬유보강 복합재료의 압축 및 인장거동 (Compressive and Tensile Behavior of Polyetylene Fiber Reinforced Composite According to Silica Sand and Fly Ash)

  • 권성준;강수태;최정일;이방연
    • 한국건설순환자원학회논문집
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    • 제4권1호
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    • pp.25-30
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    • 2016
  • 이 연구의 목적은 폴리에틸렌 섬유보강, 규사 혼입, 시멘트를 플라이애쉬로 치환함에 따라 나타나는 복합재료의 압축강도 및 인장거동에 대해 실험적으로 조사하는 것이다. 이를 위하여 총 5가지 배합을 결정하였고, 압축강도 실험과 일축인장 실험을 수행하였다. 실험결과 섬유보강을 통해 강도와 연성 및 균열제어 측면에서 효과적인 것으로 나타났으며, 절대건조상태의 골재를 혼입하면 강도 증진에 효과적이지만 연성과 균열제어 측면에서 성능이 떨어지는 것으로 나타났다. 또한 시멘트를 플라이애쉬로 대체하면 강도는 떨어지지만 연성이 증가하고 균열폭이 줄어드는 것으로 나타났다.

Potential side-NSM strengthening approach to enhance the flexural performance of RC beams: Experimental, numerical and analytical investigations

  • Md. Akter, Hosen; Mohd Zamin, Jumaat;A.B.M. Saiful, Islam;Khalid Ahmed, Al Kaaf;Mahaad Issa, Shammas;Ibrahim Y., Hakeem;Mohammad Momeen, Ul Islam
    • Structural Engineering and Mechanics
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    • 제85권2호
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    • pp.179-195
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    • 2023
  • The performance of reinforced concrete (RC) beam specimens strengthened using a newly proposed Side Near Surface Mounted (S-NSM) technology was investigated experimentally in this work. In addition, analytical and nonlinear finite element (FE) modeling was exploited to forecast the performance of RC members reinforced with S-NSM utilizing steel bars. Five (one control and four strengthened) RC beams were evaluated for flexural performance under static loading conditions employing four-point bending loads. Experimental variables comprise different S-NSM reinforcement ratios. The constitutive models were applied for simulating the non-linear material characteristics of used concrete, major, and strengthening reinforcements. The failure load and mode, yield and ultimate strengths, deflection, strain, cracking behavior as well as ductility of the beams were evaluated and discussed. To cope with the flexural behavior of the tested beams, a 3D non-linear FE model was simulated. In parametric investigations, the influence of S-NSM reinforcement, the efficacy of the S-NSM procedure, and the structural response ductility are examined. The experimental, numerical, and analytical outcomes show good agreement. The results revealed a significant increase in yield and ultimate strengths as well as improved failure modes.

Effect of soil in controlling the seismic response of three-dimensional PBPD high-rise concrete structures

  • Mortezaie, Hamid;Rezaie, Freydoon
    • Structural Engineering and Mechanics
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    • 제66권2호
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    • pp.217-227
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    • 2018
  • In the last decades, valuable results have been reported regarding conventional passive, active, semi-active, and hybrid structural control systems on two-dimensional and a few three-dimensional shear buildings. In this research, using a three-dimensional finite element model of high-rise concrete structures, designed by performance based plastic design method, it was attempted to construct a relatively close to reality model of concrete structures equipped with Tuned Mass Damper (TMD) by considering the effect of soil-structure interaction (SSI), torsion effect, hysteresis behavior and cracking effect of concrete. In contrast to previous studies which have focused mainly on linearly designed structures, in this study, using performance-based plastic design (PBPD) design approach, nonlinear behavior of the structures was considered from the beginning of the design stage. Inelastic time history analysis on a detailed model of twenty-story concrete structure was performed under a far-field ground motion record set. The seismic responses of the structure by considering SSI effect are studied by eight main objective functions that are related to the performance of the structure, containing: lateral displacement, acceleration, inter-story drift, plastic energy dissipation, shear force, number of plastic hinges, local plastic energy and rotation of plastic hinges. The tuning problem of TMD based on tuned mass spectra is set by considering five of the eight previously described functions. Results reveal that the structural damage distribution range is retracted and inter-story drift distribution in height of the structure is more uniform. It is strongly suggested to consider the effect of SSI in structural design and analysis.

변형률분할법에 의한 12Cr 단조강의 열피로 수명예측 (Thermal-mechanical Fatigue Life Prediction of 12Cr Forged Steel Using Strain Range Partitioning method)

  • 하정수;옹장우;고승기
    • 대한기계학회논문집
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    • 제18권5호
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    • pp.1192-1202
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    • 1994
  • Fatigue behavior and life prediction were presented for thermal-mechanical and isothermal low cycle fatigue of 12Cr forged steel used for high temperature applications. In-phase and out-of-phase thermal-mechanical fatigue test at 350 to 600.deg. C and isothermal low cycle fatigue test at 600.deg. C were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. Cyclic softening behavior was observed regardless of thermal-mechanical and isothermal fatigue tests. The phase difference between temperature and strain in thermal-mechanical fatigue resulted in significantly shorter fatigue life for out-of-phase than for in-phase. The difference in fatigue lives was dependent upon the magnitudes of inelastic strain ranges and mean stresses. Increase in inelastic strain range showed a tendency of intergranular cracking and decrease in fatigue life, especially for out-of-phase thermal-mechanical fatigue. Thermal-mechanical fatigue life prediction was made by partitioning the strain ranges of the hysteresis loops and the results of isothermal low cycle fatigue tests which were performed under the combination of slow and fast strain rates. Predicted fatigue lives for out-of-phase using the strain range partitioning method showed an excellent agreement with the actual out-of-phase thermal-mechanical fatigue lives within a factor of 1.5. Conventional strain range partitioning method exhibited a poor accuracy in the prediction of in-phase thermal-mechanical fatigue lives, which was quite improved conservatively by a proposed strain range partitioning method.

스퍼 기어의 FEM 해석 및 IRT 기법을 적용한 건전성 평가 (Integrity Evaluation By IRT Technique And FEM Analysis of Spur Gear)

  • 노치성;정윤수;이경일;김재열
    • Tribology and Lubricants
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    • 제32권4호
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    • pp.113-118
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    • 2016
  • As an economic, high quality, and highly reliable gear with low noise and low vibration is demanded, an overall finite element analysis regarding a gear is required. Also, an infrared thermography test, which is a quantitative testing technique, is demanded for safety and longer lifespan of gear products. In order to manufacture a gear product or to determine safety of a gear being used, it is necessary to precisely determine ingredients of a material constituting a gear and detect any internal defect. This study aims to realize a design that minimizes the spur gear displacement with respect to power during its rotation and ensures the spur gear control capacity by using a 3D model and the midasNFX program. This facilitates the assessment of the possibility of cracking by evaluating the stress intensity and focusing on the integrity of the spur gear. We prepare the specimen of the spur gear based on the possibility of cranking as per the result of the structural interpretation from an infrared ray thermal measuring technique. After cooling the spur gear, we perform experiments using thermography and halogen lamps and analyze the temperature data according to the results of the experiment. In the experiment which we use thermography after cooling, we find a rise in the temperature of the room. As a result, the defective part show temperatures lower than their surroundings while the normal parts have temperatures higher than the defective parts. Therefore, it possible to precisely identify defective part owing to its low temperature.

페인트 도장공사의 색관리에 관한 연구 (A study on the color controlled of painter's work)

  • 심명섭;이현정
    • 한국건축시공학회지
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    • 제3권1호
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    • pp.107-114
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    • 2003
  • This study aims to find methods that prevents aging of buildings paint coating and that limits defects in construction. Defects in painting can occur in four stages: pure paint, during painting, after the paint coating has dried, and after some period of time has passed after coating. Paint may become bad due to precipitation of pigments, formation of membranes, and seeding during manufacturing. Therefore, it is important that the paint is well mixed and kept airtight at a cool, dark place. Indents, paint brush strokes, orange peel, separation of colors, and paint running and spreading during the paint work process can be prevented by using high quality materials and applying a high-level of construction method. After the paint coating has dried, boiling, yellowing, poor drying, poor bonding, and/or glen deficiency may occur. These are influenced by the levels of cleanness of the dried product, drying temperature and hydration. Then, when the coating has been left dried for some period of time, cracking, peeling, scaling, swelling, discoloring, and/or rusting may develop due to the ultraviolet and contaminants in the air. Since these defects occur due to inappropriate construction schedule and/or hot and humid condition, one must use weatherproof materials. Furthermore, poor paint color may be caused by contamination in the sample plate, discoloration, and/or discrepancies in colors which are due to material differences, level of glossiness, degree of dispersion, dual color property of metallic colors, precipitation of pigments, etc. One should achieve reduction in construction cost and effectiveness in paint work by limiting contaminations in the construction site and strictly observing to construction regulations.

Evaluation of the Biodurability of Polyurethane-Covered Stent Using a Flow Phantom

  • Dong Hyun Kim;Sung-Gwon Kang;Jung Ryul Choi;Ju Nam Byun;Young Chul Kim;Young Moo Ahn
    • Korean Journal of Radiology
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    • 제2권2호
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    • pp.75-79
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    • 2001
  • Objective: To evaluate the biodurability of the covering material in retrievable metallic stents covered with polycarbonate polyurethane. Materials and Methods: Using a peristaltic pump at a constant rate of 1ml/min, bile was recirculated from a reservoir through a long tube containing four stents. Each of these was removed from the system every two weeks and a radial tensile strength test and scanning electron microscopy (SEM) were performed. Each stent, removed at 2, 4, 6 and 8 weeks, was compared with a control stent not exposed to bile juice. Results: Gross examination showed that stents were intact at 2 weeks, but at 4, 6 and 8 weeks cracks were observed. The size of these increased gradually in accordance with the duration of exposure, and at 8 weeks several large holes in the polyurethane membrane were evident. With regard to radial tensile strength, extension and peak load at break were 84.47% and 10.030 N/mm, 54.90% and 6.769 N/mm, 16.55% and 2.452 N/mm, 11.21% and 1.373 N/mm at 0, 2, 4 and 6 weeks, respectively. Scanning electron microscopy at 2 weeks revealed intermittent pitting and cracking, and examination at 4, 6 and 8 weeks showed that the size of these defects was gradually increasing. Conclusion: When the polyurethane membrane was exposed to bile, biodegradation was first observed at week two and increased gradually according to the duration of exposure.

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