면저항 45 ohms/sq.의 ITO/PET Sheets의 변형률 속도에 따른 균열 형성 거동

김진열,홍순익,Kim, Jin-Yeol,Hong, Sun-Ig 한국전기전자재료학회 2009 전기전자재료학회논문지 Vol.22 No.1

The stress-strain behavior and its effects on the crack initiation and growth of ITO film on PET substrate with a sheet resistance of 45 ohms/sq were investigated. Electrical resistance increased gradually at the strain of 0.7% in the elastic to plastic transition region of the stress strain curves. Numerous cracks were observed after 1% strain and the increase of the resistance can be linked to the cracking of ITO thin films. The onset strain for the increase of resistance increased with increasing strain rate, suggesting the crack initiation is dependent on the strain rate. Upon loading, the initial cracks perpendicular to the tensile axis were observed and propagated the whole sample width with increasing strain. The spacing between horizontal cracks is thought to be determined by the fracture strength and the interfacial strength between ITO and PET. The crack density increased with increasing strain. The spacing between horizontal cracks (perpendicular to the stress axis) increased with decreasing strain rate, The increase of crack density with decreasing strain rate can be attributed to the higher fraction of the plastic strain to the total strain at a given total strain. As the strain increased over 5% strain, cracks parallel to the stress axis were developed and increased in number with strain, accompanied by drastic increases of resistance.

Silica/Carbon Black이 충전된 NR가황물의 내Crack 및 내 Cutting 특성

손우정,김원호,조을룡 한국고무학회 2002 엘라스토머 및 콤포지트 Vol.37 No.2

본 연구에서는 실리카/카본블랙 혼합사용과 카본블랙 단독 사용의 경우 상온 또는 고온에서의 인장강도(modulus) 및 인열저항성, 내cutting성, 내crack성을 비교 평가하였다. 실리카와 카본블랙의 함량비 및 단계배합 방법을 통해 NR가황물을 제조하였으며, 충전제의 함량은 60phr로 고정하였고, semi-EV 가황시스템을 적용하여 실험을 실시하였다. 실리카의 분산은 25phr이하일 때 양호하였으며, 실리카/카본블랙의 함량비가 25/35인 경우 인열에너지, 내crack특성, 내 cutting특성이 가장 우수하였다. 충전제로써 카본블랙 단독사용과 실리카/카본블랙(25/35) 혼합사용의 경우를 비교해 보면, 열화에 따른 modulus 및 인장강도, 인열에너지는 실리카/카본블랙(25/35)을 사용한 시편이 더 낮은 감소율을 나타내었다. Cutting특성에서는 카본블랙 단독 사용보다는 실리카/카본블랙(25/35) 혼합사용의 경우가 더 높은 cutting 저항성을 나타내었다. 내crack 특성 또한 실리카/카본블랙(25/35)을 혼합사용한 경우가 온도에 따른 더 높은 변형에너지 완화율(GP )에도 불구하고 더 낮은 크랙성장속도를 나타내었다. The application of silica/carbon black dual phase fillers to natural rubber(NR) compound was investigated. When the amounts of filler content were restricted to 60phr, the optimum ratio of dual phase fillers were 25phr/35phr of silica/carbon black. It was found that these new fillers give better overall performance in comparison with carbon black in tear strength, crack resistance, and cutting resistance. Also the thermal degradation resistance of NR vulcanizates which were filled with dual phase fillers was better than that of the carbon black. Dual phase fillers filled NR vulcanizates showed better viscoelastic properties, like tanδ , for the wet skid resistance and rolling resistance of motor vehicle tires.

Study on Evaluation Method of Crack Resistance of Asphalt Mixtures

Kyu-dong Jeong,Soo-Ahn Kwon,Moon-Sup Lee,Jun-Tan Son 한국도로학회 2018 한국도로학회 학술대회 발표논문 초록집 Vol.2018 No.05

The relationship between asphalt mixture and crack resistance is difficult to predict because it is influenced by aggregate particle size, aggregate and asphalt interface characteristics, rheological properties of asphalt type, asphalt coating thickness, temperature sensitivity and porosity. For this reason, various evaluation methods of crack resistance have been developed. In Korea, indirect tensile strength and toughness are used as criteria for crack resistance test of asphalt mixture. DC (T), SCB, Fenix test, and OT (overlay test) have been developed and used internationally as crack resistance test methods. In this study, we compared the conventional crack resistance evaluation methods, and developed a direct tensile fatigue test method which was modified with OT method and Fenix method. Crack resistances were evaluated using reclaimed asphalt pavements (RAP) and virgin asphalt mixtures. As a result, direct tensile fatigue test method was evaluated as suitable for evaluation of crack resistance.

Crack Resistance and Strength Properties of Red Clay Modified with Lignocellulose and Guar gum

Hong-Yuan Fu,Guang-Tao Yu,Qian-Feng Gao,Ling Zeng,Shuo-Peng Cao 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.10

Desiccation cracking is a common problem of red clay under wet and dry conditions. The presence of cracks could reduce soil strength properties, which is the major reason for shallow failure of red clay slopes. This study aims to propose some additives to improve the crack resistance as well as the strength of red clay. To this end, three natural fibers and three natural gels were primarily selected to modify red clay. Desiccation crack tests were conducted to identify the best fiber and gel in terms of crack resistance. Then, direct shear tests and uniaxial tensile tests were performed on the soil specimens modified by the best fiber and gel to determine the optimal dosages regarding strength improvements. The results demonstrated that natural gels reduced the crack resistance of red clay, while natural fibers could enhance the crack resistance. Lignocellulose was the best additive in improving the crack resistance of red clay, and the modified effect was positively correlated with the fiber dosage. Adding 1.5% lignocellulose into red clay could reduce the crack rate from 2.19% to 0.30%, with a reduction of 0.86 times. The tensile strength, shear strength and its parameters of lignocellulose-modified red clay showed a trend of increasing first and then decreasing with increasing lignocellulose dosage. At the optimal lignocellulose dosage of 0.75%, the shear strength and tensile strength were increased by 44.63% and 18.21%, respectively. The strength of red clay modified by both lignocellulose and guar gum was positively correlated with the dosage of guar gum, and the desirable dosage of guar gum was 1.0%. In engineering practice, the wet red clay mixed with 0.75% lignocellulose and grass seeds can be employed as planting soil and is sprayed uniformly onto the slope surface after excavation using a spraying planting machine. To further improve the strength of the planting soil, 1.0% guar gum solution can be sprayed on the soil surface. The findings could provide useful guidance for the protection of red clay slopes.

Oleamide 및 아라미드 칩을 첨가한 NBR 고무재료의 내소음성 및 물성 연구

김현묵 ( Hyun Muk Kim ),이창섭 ( Chang Seop Lee ) 한국고무학회 2006 엘라스토머 및 콤포지트 Vol.41 No.2

내소음성과 내균열성을 가진 고무재료의 개발을 목적으로 NBR에 oleamide와 아라미드를 첨가하여 함량에 따른 가황특성, 물리적 성질, 내열성, 내유성, 내마모성, 내균열성 및 내소 음성을 조사하였다. 가황특성과 Mooney 점도를 측정한 결과, 미가황고무의 가황특성은 oleamide의 양이 증가할수록 torque가 감소하였다. oleamide의 함량이 3 phr까지 증가함에 따라 경도 및 모듈러스 값은 조금씩 감소하였고 신장률은 감소하는 경향을 나타내었으며 인장강도는 거의 변화가 없었다. 내열성 시험(70시간, 120℃) 및 내유성 시험(70시간, 40℃)을 수행한 결과, 인장강도와 신장률이 모두 감소하였으며, TGA/DSC 분석 결과 첨가제에 따른 배합고무재료의 열적 특성은 변화가 없었다. 기본물성, 내마모성, 내소음성 및 내균열성을 종합한 결과, NBR 22700l 고무재료에서 내마모성과 내소음성에 대한 oleamide의 최적배합비는 3 phr였으며, 내균열성에 대한 아라미드의 최적배합비는 l phr로 나타났다. This study are conducted for the purpose of developing rubber material with noise and crack resistance. Cure characteristics, physical properties, thermal resistance, fuel resistance, abrasion resistance, crack resistance and noise resistance of NBR compounds with the various amounts of oleamide and aramid chip were investigated. From the measurements of cure characteristics and Mooney viscosities, cure characteristics of uncured rubber showed that a torque was decreased as the amount of oleamide increased. Hardness, modulus and elongation of rubber specimens tended to be reduced gradually, however, tensile strength remained unchanged as the amount of the oleamide increased. As a testing results of heat resistance for 70 hours at 120°C and oil resistance for 70 hours at 40°C, tensile strength and elongation were all reduced. From the TGA/DSC analysis, there was no such a change observed in thermal characteristics of rubber materials. As a result of testing basic physical properties, abrasion resistance, noise resistance and crack resistance, the optimum ratio of oleamide to NBR was found to be 3 phr, while that of aramid to NBR 227001 was 1 phr.

Investigation of Temperature Dependent Cracking Behaviors of Asphalt Mixtures using the Modified Overlay Tester

Christopher Jabonero,곽평진,조윤호 한국도로학회 2017 한국도로학회 학술대회 발표논문 초록집 Vol.2017 No.10

The discontinuity movements of the Portland cement concrete (PCC) layer due to temperature fluctuations and traffic loading are primary causes of the reflection cracking in asphalt overlays. The thermal expansion and contraction of the discontinuities at the PCC layer induces tension at the bottom of the asphalt overlay layer creating excessive strains which causes cracking. The additional cyclic discontinuity movements from the thermal fluctuations and traffic loads propagates the cracks initiated until failure of the overlay layer. However, the crack behaviors of asphalt mixtures varies with temperature due to its viscoelastic property. As such, there is a need to investigate the cracking behavior of asphalt mixtures with varying temperatures and loading conditions. A modified overlay tester developed to evaluate the cracking resistance of asphalt mixtures in various loading directions and different confining temperatures was used to investigate the behavior of asphalt materials with various temperatures and loading conditions. The laboratory test was conducted in 2 segments. The first segment investigates the asphalt cracking behavior subjected to horizontal loading in 3 varying temperatures (10, 25 and 40C) which simulates the cyclic thermal contraction and expansion at the discontinuity. The second segment examines the cracking propagation of the asphalt mixture subjected to vertical loading in 3 varying temperatures. A load dissipation curve per loading cycle is generated in each test along with the images taken on the face of the specimen to monitor the crack propagation. Results have shown that asphalt mixtures undergo a 3-phase cracking behavior: initiation, propagation and failure. This is evident in the load dissipation curve when the initiation phase shows a rapid reduction of peak loads in first series of loading cycles which is followed by a slow and constant load reduction over a certain number of cycles. Failure occurs when there is a sudden decline in peak load and the percent reduction of the load is achieved. Figure 1 shows a fine dense grade asphalt mixture subjected to horizontal movement at 10C. Meanwhile, the load dissipation curve is further investigated by analyzing the images captured during testing. It can be seen that the first visible crack can be identified after 40 cycles which steadily propagates up to 600 cycles. However, between 600 and 700 loading cycles, there is a sudden dip in peak load which shows that at that the stage the crack has already propagated to the top of the test specimen as shown in Figure 2. Other tests have shown that the cracking patterns and load dissipation curves vary with different testing temperatures signifying that low temperature is more susceptible to early failure with constant differential movement. Further tests signify that using a general formula, parameters are calculated which refer to fracture properties of the material.

열간단조 금형 육성용접부 내균열성 및 내열충격성 평가방법에 관한 연구

조상명,김성호,정연호,백승희,장종훈,박철규,우희철,정병호,Cho, Sang-Myung,Kim, Sung-Ho,Jung, Yun-Ho,Baek, Seung-Hui,Jang, Jong-Hun,Park, Chul-Gyu,Woo, Hee-Chul,Jung, Byong-Ho 대한용접접합학회 2010 대한용접·접합학회지 Vol.28 No.3

Hardfacing is one of the frequently applying method to increase surface hardness in hot forging die. Recently, hardfacing receives great attention due to it's repair availability and low cost. In hot forging die, crack resistance and thermal shock resistance have been considered as major properties, However there are few studies for the assessment of these properties. So, it is necessary to establish the assessment method for crack resistance and thermal shock resistance in hardfacing for hot forging die. In this study, flux cored arc welding was applied to make hardfacing welds. Three point bending test was carried out to assess hardfacing weld's crack resistance, and high temperature bending test using salt bath was developed for thermal shock resistance. Consequently, it was possible to assess crack resistance and thermal shock resistance of hardfacing welds for hot forging die quantitatively.

인장에너지를 이용한 아스팔트 포장의 균열저항성 평가 방법

정규동,이문섭,김제원,권수안,김광우 한국아스팔트학회 2022 한국아스팔트학회지 Vol.12 No.2

As a result of research on the crack resistance evaluation test of asphalt mixtures, an improved evaluation method was suggested compared to indirect tensile strength and toughness, which are domestic standards. Indirect tensile strength was associated with an increase in asphalt mixture stiffness rather than crack resistance, and toughness did not show a clear trend. Using tensile energy that reflects indirect tensile strength and strain, the problem of evaluating toughness without considering the thickness and diameter of the specimen was improved. Tensile energy was divided into three types: 1st TE, 2nd TE, and 3rd TE, and each characteristic was evaluated. 1st TE, the tensile energy up to the maximum stiffness limit, was judged to be able to effectively evaluate the change in initial stiffness with the use of PG64-22 and PG76-22 asphalt. In addition, since 1st TE is a dissipation energy that can withstand almost no cracks, it was judged that the higher value, the higher crack resistance. In the process of developing cracks, 2nd TE, which is the dissipation energy up to the maximum load, was a value of a trend that increased with the asphalt content. It was judged that the ductility of the asphalt mixture was highly correlated. After 2nd TE, 3rd TE, the dissipation energy of up to 90% of the maximum indirect tensile strength, rose and fell with increasing asphalt content when PG64-22 was used, but in the case of modified asphalt mixtures, it was on the decline with increasing asphalt content.

고강도 탄소강 FCA 용착금속의 고온균열 저항성과 저온 충격인성에미치는 보론과 망간의 영향

박수길,조영호,지춘호,이정훈,서성문,강남현 대한금속·재료학회 2019 대한금속·재료학회지 Vol.57 No.1

The hot crack resistance and mechanical properties of flux cored arc (FCA) welds were investigated with three kinds of welding consumables having different boron (B) and manganese (Mn) contents for high strength carbon steel. The hot crack resistance, measured from self-restraint testing, strongly depended on the amount of B in the welding consumable. Welding consumables with higher B contents resulted in longer total crack length and an increased number of cracks. Boron was intensely detected near the grain boundary of the weld centerline by secondary ion mass spectrometry (SIMS) analysis, and precipitated with boron carbide (Fe23(C,B)6), as analyzed by transmission electron microscopy (TEM). This promoted hot crack propagation in the high strength carbon steel welds. However, removing B from the welding consumable decreased the low temperature toughness for root and face weld metals, due to the growth of ferrite side plate (FSP), compared with welding consumables having more B or Mn contents. The addition of Mn in the weld metal suppressed the formation of FSP and increased low temperature toughness. Therefore, the minimization of B and the supplement of Mn successfully achieved hot crack resistance and low temperature toughness for high strength carbon steel welds of 550 MPa tensile strength.

Improvement of Resistance to Hydrogen Induced Cracking in Electric Resistance Welded Pipes Fabricated with Slit Coils

홍현욱,최호진,이종봉 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.1

The optimization of electric resistance welding (ERW) conditions was studied to improve the resistance to hydrogen induced cracking (HIC) at the bondline in small diameter API X60 ERW pipes fabricated with slit coils. The results show that HIC is initiated preferentially at the elongated Si, Mn and Al-rich oxide inclusions, normally known as a penetrator on the bondline. However, no evidence was found of any centerline segregation effect. The HIC ratio increases with the fraction of penetrators at the bondline, regardless of the degrees of center segregation. Furthermore, for a satisfactory level of HIC resistance, the fraction of penetrators must be less than 0.03 % and most of the penetrators should be circular-shaped. The design of experimental (DOE) method was used to determine the optimum ERW condition for minimization of the penetrator ratio. Finally, guideline is suggested for the optimum ERW condition for achieving excellent HIC resistance. The optimization of electric resistance welding (ERW) conditions was studied to improve the resistance to hydrogen induced cracking (HIC) at the bondline in small diameter API X60 ERW pipes fabricated with slit coils. The results show that HIC is initiated preferentially at the elongated Si, Mn and Al-rich oxide inclusions, normally known as a penetrator on the bondline. However, no evidence was found of any centerline segregation effect. The HIC ratio increases with the fraction of penetrators at the bondline, regardless of the degrees of center segregation. Furthermore, for a satisfactory level of HIC resistance, the fraction of penetrators must be less than 0.03 % and most of the penetrators should be circular-shaped. The design of experimental (DOE) method was used to determine the optimum ERW condition for minimization of the penetrator ratio. Finally, guideline is suggested for the optimum ERW condition for achieving excellent HIC resistance.