• Advances in concrete construction
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• 제10권3호
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• pp.195-209
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• 2020

This study investigates the behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) with hybrid macro-micro steel and macro steel-polypropylene (PP) fibers. Compression, direct and indirect tension tests were carried out on cubic and cylindrical, dogbone and prismatic specimens, respectively. Three types of macro steel fibers, i.e., round crimped (RC), crimped (C), and hooked (H) were combined with micro steel (MS) and PP fibers in overall ratios of 2% by volume. Additionally, numerical analyses were performed to validate the test results. Parameters studied included, fracture energy, tensile strength, compressive strength, flexural strength, and residual strength. Tests showed that replacing PP fibers with MS significantly improves all parameters particularly flexural strength (17.38 MPa compared to 37.71 MPa). Additionally, the adopted numerical approach successfully captured the flexural load-deflection response of experimental beams. Lastly, the proposed regression model for the flexural load-deflection curve compared very well with experimental results, as evidenced by its coefficient of correlation (R²) of over 0.90.

• Journal of Welding and Joining
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• 제31권5호
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• pp.71-76
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• 2013

The effect of zirconate having - NH functional group on the T-peel and lap shear strength of $CaCO_3$ containing structural epoxy adhesive for car body assembly was investigated. Curing behavior of epoxy adhesive samples were investigated by differential scanning calorimeter (DSC) techniques. The addition of zirconate up to 7.5 phr did not affect the curing mechanism of epoxy adhesive. While the small amount of zirconate addition less than 1.1 phr increased the cross-linking density, the excess addition of zirconate resulted in the increase of uncross-linked impurity. From the increase of T-peel and lap shear strength and the change of fracture mode from the adhesive failure to the mixed one, it was considered that the small addition of zirconate was effective in improving the adhesion strength of epoxy adhesive to the adherend and inorganic filler surfaces. The formation of uncross-linked impurity with the excess addition of zirconate was considered to decrease the joint strength by decreasing the cohesive strength of the cured epoxy.

• 한국안전학회지
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• 제28권6호
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• pp.57-63
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• 2013

This paper discusses 2D models of beams for simulating the fracture of brittle materials. A simulation of an experiment on a concrete beam subjected to bending, in which two overlapping cracks occur, is used to study the effect of individual beam characteristics and different arrangements of the beams in the overall network mesh. It was found that any regular orientation of the beams influences the resulting crack patterns. Methods to implement a wide range of poisson's ratios are also developed, the use of the mesh to study arbitrary micro-structures is outlined. The crack pattern that are obtained with mesh are in good agreement with the experimental results. Also, numerical simulations of the tests were performed by means of a model, and non-integer dimensions were measured on the predicted mesh damage patterns.

• Biomaterials and Biomechanics in Bioengineering
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• 제2권4호
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• pp.197-206
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• 2015

This paper presents three-dimensional finite element method analyses of the distribution of equivalents stress of Von Mises. Induced around a cavity located in the bone cement polymethylmethacrylate (PMMA). The presences and effect of its position in the cement was demonstrated, thus on the stress level and distribution. The porosity interaction depending on their positions, and their orientations on the interdistances their mechanical behaviour of bone cement effects were analysed. The obtained results show that micro-porosity located in the proximal and distal zone of the prosthesis is subject to higher stress field. We show that the breaking strain of the cement is largely taken when the cement, containing the porosities very close adjacent to each other.

• 한국세라믹학회지
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• 제24권4호
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• pp.349-356
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• 1987

${\beta}$-Sialon powder was synthesized by the simultaneous reduction and nitridation of Hadong kaolin at 1350$^{\circ}C$ in N2-H2 atmosphere, using graphite as a reducing agent. The synthesized ${\beta}$-Sialon powder was pressurelessly sintered over 1450-1850$^{\circ}C$ in nitrogen atmosphere. The average particle size of ${\beta}$-Sialon powder was about 4.5$\mu\textrm{m}$. The relative density, M.O.R., fracture toughness and micro-hardness of ${\beta}$-Sialon ceramics sintered at 1800$^{\circ}C$ for 1 hour were 92%, 36 kpsi, 2.8MN/㎥/2 and 13.3 GN/㎡, respectively. The critical temperature difference (ΔT) in water quench thermal shock behavior showed about 375$^{\circ}C$ for the synthesized ${\beta}$-Sialon ceramics.

• Journal of Mechanical Science and Technology
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• 제20권3호
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• pp.310-318
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• 2006

In this study, we investigate the feasibility of in-situ crack propagation by using a double cleavage drilled compression (DCDC) specimen showing a slow crack velocity down to 0.03 mm/s under 0.01 mm/s of displacement control. Finite element analysis predicted that the DCDC specimens would show at least 4.3 fold delayed crack initiation time than conventional tensile fracture specimens under a constant loading speed. Using DCDC specimens, we were able to observe the in-situ crack propagation process in a particle reinforced transparent polymer composite. Our results confirmed that the DCDC specimen would be a good candidate for the in-situ observation of the behavior of particle reinforced composites with slow crack velocity, such as the self-healing process of micro-particle reinforced composites.

• 한국구조물진단유지관리공학회 논문집
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• 제21권6호
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• pp.98-105
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• 2017

본 연구에서는 후크형 강섬유와 PVA 섬유의 혼합비에 따른 하이브리드 섬유보강 시멘트 복합체의 인장거동에 미치는 변형속도의 효과에 대하여 평가하기 위하여, 후크형 강섬유와 PVA 섬유를 각각 1.5+0.5, 1.0+1.0, 0.5+1.0vol.%의 혼합비로 보강한 하이브리드 섬유보강 시멘트 복합체를 제작하였다. 그 결과, 후크형 강섬유보강 시멘트 복합체는 변형속도가 증가함에 따라 섬유와 매트릭스의 부착력이 향상되어 인장강도, 변형능력 및 파괴인성이 크게 향상되었으며, 후크형 강섬유 주변의 매트릭스에 발생하는 마이크로 균열에 의해 직선형으로 인발되는 섬유의 수가 감소하고, 인장강도 점 이후의 응력 저하가 급격하게 발생하였다. 한편, PVA 섬유는 변형속도 $10^{-6}/s$에서는 끊어지는 파괴거동이 나타났으나, 변형속도 $10^1/s$에서는 변형속도가 증가함에 따라 섬유가 인발되는 파괴거동에 의해 다중균열 개수 및 변형능력이 감소하였다. 후크형 강섬유 1.5vol.%, PVA 섬유 0.5vol.%를 혼입한 시험체(HSF1.5PVA0.5)는 PVA가 후크형 강섬유의 주변 매트릭스에 발생하는 마이크로 균열을 억제하여 후크형 강섬유의 인발저항성능을 향상시키기 때문에 가장 높은 인장강도를 나타내었으며, 변형능력 및 파괴인성의 DIF가 크게 향상되었다. 또한, 변형속도 $10^1/s$에서는 후크형 강섬유의 인발저항성능의 증가로 인하여 직선형으로 인발되는 섬유의 수가 증가하기 때문에 인장강도 점 이후의 응력 저하가 감소하여 파괴인성의 시너지는 양의 값을 나타내었다.

• 콘크리트학회논문집
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• 제14권5호
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• pp.689-697
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• 2002

콘크리트 삼점휨 시험편의 변위제어에 의한 동적 파괴실험으로 하중과 하중점-변위가 측정되었다. 변형률 게이지를 사용하여 균열의 성장길이가 측정되었으며, 균열이 성장되는 동안의 평균속도는 0.16 ~ 66 m/sec이었다. 균열성장에 대한 파괴에너지는 측정된 외부일에 대한 하중점-변위에 대한 운동에너지와 영구변형이 고려되지 않은 탄성에너지의 차이로부터 계산되었다. 모든 균열속도에 대해 23mm의 균열성장 동안 미소균열이 성장되며, 51 mm의 최대 탄성0에너지까지 안정 균열성장과 이후의 불안정 균열성장을 보였다. 균열속도가 66msec인 경우를 제외하고 80mm의 균열성장에서 균열성장의 구속이 관측되었다. 균열속도에 대한 파괴에너지와 파괴에너지율의 분석은 13mm/sec보다 느린 경우에 정적 거동을 그리고 1.9m/sec보다 빠른 속도에서 동적 거동을 보였다. 동적 실험에서 측정된 하중과 하중점-변위 관계의 큰 차이에도 불구하고 관성력과 균열성장길이 그리고 탄성에너지의 차이로 불안정 균열성장 이전의 균열속도에 대한 파괴저항은 균열속도에 영향을 받지 않았다. 안정 균열성장 동안의 최대 파괴저항은 최대하중 이후 최대 탄성에너지에서 발생되며, 동적 실험이 정적 실험보다 147% 큰 값이었다.

• Journal of Welding and Joining
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• 제19권1호
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• pp.65-74
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• 2001

A study on the corrosion behavior in case of As-welded and PWHT temperature 55$0^{\circ}C$ of welding part of RE36 steel for marine structure was investigated with parameters such as micro-Vickers hardness, corrosion potential measurement of weld metal(WM), base metal(BM) and heat affected zone(HAZ), both Al anode generating current and Al anode weight loss quantity under sacrificial anode cathodic protection conditions. And also we carried out slow strain rate test(SSRT) in order to research both limiting cathodic polarization potential for hydrogen embrittlement and optimum cathodic protection potential as well as mechanical properties by post-weld heat treatment(PWHT) effect. Hardness of HAZ was the highest among three parts(WM, BM and HAZ) and the highest galvanic corrosion susceptibility was HAZ. And the optimum cathodic polarization potential showing the best mechanical properties by SSRT method was from -770mV to -875mV(SCE). In analysis of SEM fractography, applied cathodic potential from -770mV to -875mV(SCE) it appeared dimple pattern with ductile fracture while it showed transgranular pattern (Q. C : quasicleavage) under -900mV(SCE). However it is suggested that limiting cathodic polarization potential indicating hydrogen embrittlement was under -900mV(SCE).

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(II)
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• pp.321-324
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• 2005

This paper presents a preliminary study on the influence of material ductility on diagonal tension behavior of shear-wall panels. There have been a number of previous studies, which suggest that the use of high ductile material such as ECC (Engineered Cementitious Composite) significantly enhanced shear capacity of structural elements even without shear reinforcements involved. The present study emphasizes increased shear capacity of shear-wall panels by employing a unique strain-hardening ECC reinforced with poly(vinyl alcohol) (PVA) short random fibers. Normal concrete was adopted as the reference material. Experimental investigation was performed to assess the failure mode of shear-wall panels subjected to knife-edge loading. The results from experiments show that ECC panels exhibit a more ductile failure mode and higher shear capacity when compared to ordinary concrete panels. The superior ductility of ECC was clearly reflected by micro-crack development, suppressing the localized drastic fracture typically observed in concrete specimen. This enhanced structural performance indicates that the application of ECC for a in-filled frame panel can be effective in enhancing seismic resistance of an existing frame in service.