• Elastomers and Composites
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• v.47 no.2
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• pp.121-128
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• 2012

Waste EPDM(W-EPDM) collected from the automotive weather strip and the gasket of a laundry machine has not been effectively recycled. Using this W-EPDM powder and other ingredients, i.e., binder(polyolefin resin, polyolefin elastomer, etc.), filler and additives, various economic rubber composites were made by extrusion. In advance of main experiments, the effects of ultrasonic treatment of W-EPDM on the property of rubber composites, comparison in the property of the composites of W-EPDM with those of virgin and devulcanized EPDM, and waste tire rubber were investigated. Also, the properties of the rubber composites extruded with a 12-screw extruder were compared with those extruded with twin-screw extruder. Various W-EPDM composites for synthetic turf filler and car mat were extruded and injection molded, and 3 main properties of tensile strength, elongation and hardness were investigated to develop economical and proper recipes of the rubber composites.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.3
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• pp.83-90
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• 2024

This study investigates the 3D printing characteristics of strain hardening cement composites (SHCC) reinforced by PVA fibers. Three SHCC mixtures with diverse fiber volume fractions (1.0% for F1.0 mixture, 1.5% for F1.5 mixture, and 1.8% for F1.8 mixture) were designed. Except for the F1.0 mixture, all mixtures met the necessary conditions for multiple micro-cracking, with higher fiber volume fractions more readily satisfying these conditions. The flow values of three SHCC mixtures were within the 3D printable range of 120~160 mm, exhibiting decreased flow values with increasing the fiber volume fractions. Observation of the printed SHCC surfaces indicated that the F1.0 mixture had a Level-3 (good) rating, while F1.5 and F1.8 were rated as Level-2 (average). Higher fiber volume fractions resulted in poorer surface quality, thus, further research needs to be performed for modulating SHCC mixture suitable for 3D printing. The uniaxial tension behavior showed that the F1.0 mixture failed at lower strain, whereas F1.5 and F1.8 exhibited higher strain performance with multiple micro-cracks occurring.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.8
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• pp.3631-3637
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• 2013

Gangway bellows in this study is the double wrinkled neoprene rubber component to accept various deviations between the carriage end parts of the articulated type high speed railway vehicle(HSRV). The fatigue failure of the bellows has a harmful effect on the riding comfort for the passengers with the increase of noise and ringing in the ears due to air-tightness failure during pass through a long tunnel. In this study, to assure the safety of gangway bellows of the HSRV, non-linear analysis of the gangway bellows considering triaxial angular displacement(rolling /yawing/pitching) between the carriage end parts are performed. The non-linear properties of the rubber are determined by uniaxial tension and equi-biaxial tension test. Moreover, from the results of non-linear analysis, the effects of the angular displacements and frictional coefficients are evaluated.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.35 no.3
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• pp.239-247
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• 1990

In order to investigate the degree of grain shedding of red rices collected in Korea, breaking tensile and breaking bending strengths of 269 varieties; 82 Korean and 100 foreign red rices and 87 Korean cultivars including 26 native varieties, 30 Japonica-Indica hybrids and 31 Japonica type varieties, were measured at harvest time. Also, histological characteristics of abscission region between spikelet and pedicel were observed. The breaking tensile and breaking bending strengths of both Korean and foreign red rices were weaker than those of Japonica-Indica hybrids which were known as easily shedding varieties in Korea. Abscission layers were observed in the majority of Korean red rices except for 5 varieties, and those of all varieties belonging to both long grain types and 'Sare's were cracked completely at harvest time, while those of round grain types were not cracked except one variety. The breaking tensile and breaking bending strengths of the tested varieties having cracked abscission layer were weaker than those of non-cracked ones. Both strengths of breaking tensile and breaking bending were positively correlated with diameter of supporting zone and thickness of sclerenchyma tissue surrounding central vascular tissue of suporting zone at 0.1% significant level, respectively.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.27-35
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• 2004

Most of concrete fatigue tests currently used are flexural tension or compression methods to investigate the tensile or compressive properties, respectively. However, the concrete pavement or concrete slab is actually subjected to a combined stress condition such as biaxial or triaxial. The split tension test may result in similar stress condition to biaxial stress condition. The purposes of this study were to evaluate the split tension fatigue test method for application in concrete. These were done by a finite element analysis and experimental series. The results were as follows: The optimum configuration of split tension fatigue test was a cylinder of 15cm in diameter and 7.5cm in thickness, which had a little different thickness compared to the KS standard cylinder of ${\phi}15{\times}30cm$. The concrete stress ratio of compressive against horizontal from FEA was 3.1, while that from theory was 3.0. The stress distributions of mortar and steel were almost similar at different thicknesses. The measured static split tensile strengths of concrete and mortar were quite similar at 30cm and 7.5cm thickness cylinders. The measured stress-strain relationship showed their consistency at all specimens regardless of thickness, and confirmed the results from FEA. As a results, the concrete split tension specimen, cylinder of 15cm in diameter and 7.5cm in thickness, could be used at fatigue test because of its accuracy, simplicity and convenience.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.2
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• pp.241-251
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• 1988

The purpose of this paper is to evaluate fracture strength of WA-vitrified and resinoid bond grinding wheels by means of acoustic emission. The paper conducts tension test, compression test, splitting tensile test and bending test with AE measuring system. These tests have been carried out in accordance with the grain sizes and grades of grinding wheels. The fracture strength of grinding wheels is evaluated by the clarification of biaxal fracture criterion of Babel and Sines. It clarifies the influence of factors of grinding wheel upon AE characteristics and evaluates the predictability of life of grinding wheels and the perception of fracture.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.597-605
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• 2009

The present study has been proposed a model for the in-plane shear behavior of reinforced(Engineered Cementitious Composite(ECC) panels under biaxial stress states. The model newly considers the high-ductile tensile characteristic of cracked ECC by its multiple micro-cracking mechanism, the compressive strain-softening characteristic of cracked ECC, and the shear transfer mechanism in the cracked interface of ECC element. A series of numerical analyses were performed, and the predicted curves were compared with experimental results. The proposed in-plane shear model, R-ECC-MCFT, was found to be well matched with the experimental results, and it was also demonstrated that reinforced ECC panel showed more improved in-plane shear strength and post peak behavior, in comparing with the conventional reinforced concrete panel.

• Journal of the Korea Concrete Institute
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• v.23 no.4
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• pp.503-509
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• 2011

ECC is a micro-mechanically designed cementitious composite which exhibits tightly controlled crack width and strain hardening behavior in uniaxial tension while using a moderate amount of reinforcing fiber, typically less than 2% fiber volume fraction. Recently, a variety of applications of this material ranging from repair and retrofit of structures, cast-in-place structures, to precast structural elements requiring high ductility are developed. In the present study, a retrofitting method using ECC reinforced with high strength rebar was proposed to enhance load-carrying capacity and crack control performance of deteriorated reinforced concrete (RC) beams. Six beam specimens were designed and tested under a four-point loading setup. The flexural test revealed that load-carrying capacity and crack control performance were significantly enhanced by the use of ECC and high strength rebar. This result will be useful for practical field applications of the proposed retrofitting method.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2012.03a
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• pp.65-65
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• 2012

The air texturing공정은 노즐에서 전달되는 초음속 에어기류에 의해 overfeed를 수반하여 yarn속 fiber가 뒤얽혀 loop와 crimp를 발달시키는데, 고강력 고탄성율 고내열성 내절단성 등의 특성을 가지는 아라미드섬유를 에어 가공사로 가공 할 경우 가공 전 필라멘트 상태일 때 보다 표면에 생기는 loop로 인하여 촉감이 좋아지고 또한 타 소재와 접착 시 접착제 담지 성능이 향상 되어 접착력이 상승되고, 이를 통해 보강재로서의 기능이 강화되는 반면 역학물성이 기존의 아라미드 보다 저하되는 약점을 가지고 있어 최근 ATY 공정조건이 ATY 사의 구조와 물성변화에 미치는 영향에 대한 많은 연구결과가 발표되고 있다. 본 연구에서는 Aiki air jet texturing machine에서 $Heracron^{(R)}$ para-aramid(840, 1000d, 1500d)를 사용하여 ATY nozzle의 직경을 0.6, 0.75, 1, 1.2mm로 변화를 주어 12개의 para-aramid ATY 시료를 제조하여 이들의 섬도, 강신도, 초기탄성률, 열수축률 그리고 형태불안정성(instability)등의 물성변화를 분석하여 다음과 같은 결과를 얻었다. 노즐의 직경이 증가함에 따라 사 내의 filament간의 움직임이 자유로워 교락이 증가하고 루프가 형성되어 단위길이 당 mass가 커지므로 섬도가 미세하게 증가하는 것을 볼 수 있다. 또한 직경이 증가할수록 절단강도와 초기탄성률은 감소하고 절단신도가 증가하는 경향을 볼 수 있는데 이는 축 방향으로의 배열이 적어져 하중을 분담하는 portion이 감소하고 사의 loop형성이 많아짐으로서 상대적으로 인장력에 대응하는 fiber의 수가 적어지기 때문으로 사료된다. 이는 현미경 관찰로 확인할 수 있는데 직경이 증가함에 따라 사의 loop의 엉킴이 증가하고 filament가 조밀한 것을 확인할 수 있다. 직경 변화에 따른 건 습열 수축률은 1% 미만의 매우 낮은 값으로 영향을 받지 않는 것을 확인 할 수 있는데 para-aramid의 열적특성의 안정성에 기인하는 것으로 사료되며 ATY의 불안정성은 노즐 직경 증가에 따른 어떤 경향성을 찾아볼 수 없었지만 840d, 1000d, 1500d로 섬도가 증가함에 따라 사의 불안정성이 증가하였다.

• Nuclear Engineering and Technology
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• v.23 no.1
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• pp.1-11
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• 1991

The objective of this study is to investigate the effect of weld line on the mechanical strengths and the process of weld line elimination in the Zircaloy-4 resistance upset welding for the fabrication of heavy water reactor fuel rods. The weld current and the amount of upset increased linearly with the main heat, in which two relations between them were derived. It was found that the threshold to obtain sound weld was 50% of main heat in terms of weld upset size, mechanical strengths and weld line elimination. The weld microstructure of resistance upset welds of Zircaloy-4 comprsied basketweave, Widmanstatten and martensite respectively by changing the main heats. Dimples on uniaxially fractured surface at weld line in the Zr-4 welds were larger and deeper compared with those on biaxially fractured surface. It was also found that the process of the weld line elimination in the resistance upset weld of Zircaloy-4 could be divided into three stages in terms of the presence of many pores, their shrinkage and elimination, and the shrinkage of the original weld interface with increasing weld currents.