• Title/Summary/Keyword: Chemical/Mechanical degradation

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Development of a Numerical Model for Evaluation of Long-Term Mechanical Degradation of Shotcrete Lining in Tunnels (터널 숏크리트 라이닝의 장기 내구성 저하 평가를 위한 수치모델의 개발)

  • Shin Hyu-Soung;Lim Jong-Jin;Kim Dong-Gyu;Lee Gyu-Phil;Bae Gyu-Jin
    • 한국터널공학회:학술대회논문집
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    • 2005.04a
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    • pp.251-258
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    • 2005
  • In this study, a new concept for simulating a long-term mechanical degradation mechanism of shotcrete in tunnels has been proposed. In fact, it is known that the degradation takes place mainly by internal cracks and reduced stiffness, which results mainly from volume expansion of shotcrete and corrosion of cement materials, respectively. This degradation mechanism of shotcrete in tunnels appears similar to those of the most kinds of chemical reactions in tunnels. Therefore, the mechanical degradation induced by a kinds of chemical reaction was generalized and mathematically formulated in the framework of thermodynamics. The numerical model was implemented to a 3D finite element code, which can be used to simulate behaviour of shotcrete structures undergoing external forces as well as chemical degradation in time. A number of illustrative examples were given to show the feasibility of the model in tunnel designs with consideration of long-term degradation effect of shotcrete quantitatively for increase of long-term safety of tunnels.

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Correlation Analysis Between Chemical Degradation Characteristics of Grease and Degradation Characteristics of Bearing Through Durability Test (내구시험을 통한 베어링의 열화 특성과 그리스의 화학적 열화 특성 연관성 분석)

  • Kang, Bo-Sik;Lee, Choong-Sung;Ryu, Kyung-Ha
    • Journal of the Korean Society of Industry Convergence
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    • v.25 no.6_3
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    • pp.1239-1246
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    • 2022
  • This paper introduces the effect of grease on the degradation characteristics of bearings used as key components of packaging equipment and automation systems. Bearings parts are installed to fix and support the rotating body of the system, and performance degradation of the bearings has a great effect on the life of the system too. When bearings are used in various devices and systems, the grease is applied to reduce friction and improve fatigue life. Determining the type of lubricant (grease) is important because it has a great influence on the operating environment and lifespan and ensures long lifespan of systems and facilities. However, studies that simultaneously compared and analyzed the change in mechanical degradation characteristics and the comparison of chemical degradation characteristics according to grease types under actual operating conditions are insufficient. In this paper, three types of small harmonic drive, high-load reducer, and low-load reducer grease used in power transmission joint modules are experimentally selected and finally injected into ball bearings with a load (19,500N) to improve bearing durability. Degradation characteristics were tested by attaching to test equipment. At this time, after the durability test under the same load conditions, the mechanical degradation characteristics, that is temperature, vibration according to the three greases types. In addition, the chemical degradation characteristics of the corresponding grease was compared to present the results of mutual correlation analysis.

DC Potential Drop Method for Evaluating Material Degradation

  • Seok, Chang-Sung;Bae, Bong-Kook;Koo, Jae-Mean
    • Journal of Mechanical Science and Technology
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    • v.18 no.8
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    • pp.1368-1374
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    • 2004
  • The remaining life estimation for the aged components in power plants as well as chemical plants are very important because mechanical properties of the components are degraded with in-service exposure time in high temperatures. Since it is difficult to take specimens from the operating components to evaluate mechanical properties of components, nondestructive techniques are needed to evaluate the degradation. In this study, test materials with several different degradation levels were prepared by isothermal aging heat treatment at $630^{\circ}C$. The DC potential drop method and destructive methods such as tensile and fracture toughness were used in order to evaluate the degradation of 1Cr-1Mo-0.25V steels. In this result, we can see that tensile strength and fracture toughness can be calculated from resistivity and it is possible to evaluate material degradation using DC potential drop method, non-destructive method.

An Electro-chemical Combined-stress Degradation Test of Rubber for Automotive Radiator Hoses (자동차 냉각기 호스용 고무의 전기화학적 복합노화시험)

  • Kwak, Seung-Bum;Seo, Boo-Seok;Choi, Nak-Sam
    • Transactions of the Korean Society of Automotive Engineers
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    • v.19 no.4
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    • pp.107-113
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    • 2011
  • Coolant rubber hoses for automotive radiators under thermal and mechanical loadings can be degraded and thus failed due to the influences of the locally formed electricity. In this study, an advanced test method was developed to simulate the failure problem of the rubber hose. For carbon black filled EPDM (ethylene-propylene dine monomer) rubber used as a radiator hose material the ageing behaviors by the electro-chemical stresses combined with a tensile strain were analyzed. As the tensile strain increased, the current of the rubber specimen reduced indicating an increase of the internal defects and electrical resistance of the rubber specimen. Elongation at break and IRHD hardness rapidly decreased with increasing the ageing time. Both electro-chemical stress and mechanical tensile stress clearly accelerated the degradation of EPDM rubber.

Mechanical Degradation of Polystyrene by Mastication (Mastication에 의한 Polystyrene의 機械的分裂)

  • Ki Hyun Chung;Chwa Kyung Sung
    • Journal of the Korean Chemical Society
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    • v.17 no.4
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    • pp.298-305
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    • 1973
  • Following results were obtained for the mechanical degradation of polystyrene (for polystyrene itself and when blended with rubber) by roll mastication. 1) The rate of mechanical degradation for polystyrene itself can be represented by the second-order rate equation proposed by Goto. $-\frac{dP_t}{dt} = k_s(P_t-P_{\infty})^2$ Where Pt is the degree of polymerization of the degraded polymer at t minutes and $P{\infty}$ is the final degree of polymerization. 2) The mechanical degradation of polystyrene component in the polystyrene-rubber (SBR, BR) blend system occurred similarly as that of polystyrene itself. 3) Under the experimental conditions the mechanical degradation rate of the polystyrene component of the polystyrene-rubber, (SBR, BR) blend system followed approximately the same second-order equation as that for polystyrene itself.

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Reducing the Test Time for Chemical/Mechanical Durability of Polymer Electrolyte Membrane Fuel Cells (고분자연료전지의 화학적/기계적 내구성 평가 시간 단축)

  • Sohyeong Oh;Donggeun Yoo;Kim Myeonghwan;Park Jiyong;Choi Yeongjin;Kwonpil Park
    • Korean Chemical Engineering Research
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    • v.61 no.4
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    • pp.517-522
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    • 2023
  • A chemical/mechanical durability test of polymer membrane evaluation method is used in which air and hydrogen are supplied to the proton exchange membrane fuel cell (PEMFC) and wet/dry is repeated in the open circuit voltage (OCV) state. In this protocol, when wet/dry is repeated, voltage increase/decrease is repeated, resulting in electrode degradation. When the membrane durability is excellent, the number of voltage changes increases and the evaluation is terminated due to electrode degradation, which may cause a problem that the original purpose of membrane durability evaluation cannot be performed. In this study, the same protocol as the department of energy (DOE) was used, but oxygen was used instead of air as the cathode gas, and the wet/dry time and flow rate were also increased to increase the chemical/mechanical degradation rate of the membrane, thereby shortening the durability evaluation time of the membrane to improve these problems. The durability test of the Nafion 211 membrane electrode assembly (MEA) was completed after 2,300 cycles by increasing the acceleration by 2.6 times using oxygen instead of air. This protocol also accelerated degradation of the membrane and accelerated degradation of the electrode catalyst, which also had the advantage of simultaneously evaluating the durability of the membrane and the electrode.

Evaluation of Material Degradation Using Electrical Resistivity Method (전기비저항법을 이용한 재료열화 평가)

  • Kim, Jeong-Pyo;Bae, Bong-Kook;Kim, Dong-Joong;Seok, Chang-Sung
    • Proceedings of the KSME Conference
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    • 2001.11a
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    • pp.129-136
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    • 2001
  • The remaining life estimation for the aged components in power plants as well as chemical plants are very important beacuse mechanical properties of the components are degraded with time of service exposure in high temperature. Since it is difficult to take specimens from the operating components to evaluate mechanical properties of components, nondestructive techniques are needed to estimate the degradation. In this study, test materials with 4 different degradation levels were prepared by isothermal aging heat treatment at $630^{\circ}C$. And the DC potential drop method and destructive methods such as tensile, $K_{IC}$ and hardness tests were used in order to evaluate the degradation of 1Cr-1Mo-0.25V steels. The objective of this study is to investigate the possibility of the application of DCPD method to estimate the material degradation, and to analyse the relationship between the electrical resistivity and the degree of material degradation.

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Mechanical Degradation of Polymers in Dilute Solutions. The Influence of the Temperature on the Scission (稀薄溶液에서의 polymer의 機械的切斷. 切斷에 미치는 온도의 영향)

  • Won, Yeong-Moo;Takashi Fukutomi;Toshio Kakurai;Tatsuya Noguchi
    • Journal of the Korean Chemical Society
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    • v.15 no.3
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    • pp.109-116
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    • 1971
  • The mechanical degradation of poly (${\alpha}$-methyl styrene) in several mixed solvents (toluene-n-butyl alcohol, toluene-sec-butyl alcohol, toluene-kerosene, toluene-methyl ethyl ketone), from $1^{\circ}C to $45^{\circ}C$, was studied using the capillary flow method. The velocity constant of scission reaction (k) and the limited degree of polymerization (g) were compared at the same value of [${\eta}$] at each temperatures. As results, mechanical degradation of polymer in dilute mixed solutions is affected by composition of solvents around the polymer chains.

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Evaluation of Material Degradation Using Electrical Resistivity Method (전기비저항법을 이용한 재료열화 평가)

  • Seok, Chang-Seong;Kim, Dong-Jung;Bae, Bong-Guk
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.12
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    • pp.2995-3002
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    • 2000
  • The remaining life estimation for the aged components in power plants as well as chemical plants are very important beacuse mechanical properties of the components are degraded with time of service exposure in high temperature. Since it is difficult to take specimens from the operating components to evaluate mechanical properties of components nondestructive techniques are needed to estimate the degradation. In this study, test materials with 4 different degradation levels were prepared by isothermal aging heat treatment at 630$\^{C}$. And the DC potential drop method and destructive methods such as tensile, K(sub)IC and hardness tests were used in order to evaluate the degradation of 1-Cr-1Mo-0.25V steels. The objective of this study is to investigate the possibility of the application of DCPD method to estimated the material degradation, and to analyse the relationship between the electrical relationship between the electrical resistivity and the degree material degradation.

Reliability Analysis and Feilure Mechanisms of Coolant Rubber Hose Materials for Automotive Radiator (자동차 냉각기 고무호스용 재질에 대한 신뢰성 평가 및 고장메커니즘규명)

  • Kwak Seung-Bum;Choi Nak-Sam;Kang Bong-Sung;Shin Sei-Moon
    • Transactions of the Korean Society of Automotive Engineers
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    • v.13 no.5
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    • pp.152-162
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    • 2005
  • Coolant rubber hoses for automobile radiators can be degraded and thus failed due to the influence of contacting stresses of air and coolant liquid under the thermal and mechanical loadings. In this study, test analysis was carried out for evaluating the degradation and failure mechanisms of coolant hose materials. Two kinds of EPDM rubber materials applicable to the hoses were adopted: commonly-used ethylene-propylene diene monomer(EPDM) rubbers and EPDM rubbers with high resistance against electro-chemical degradation (ECD). An increase of surface hardness and a large reduction of failure strain were shown due to the formation of oxidation layer for the specimens which had been kept in a high temperature air chamber. Coolant ageing effects took place only by an amount of pure thermal degradation. The specimens degraded by ECD test showed a swelling behavior and a considerable increase in weight on account of the penetration of coolant liquid into the skin and interior of the rubber specimens. The ECD induced material softening as well as drastic reduction in strength and failure strain. However EPDM rubbers designed for high resistance against ECD revealed a large improvement in reduction of failure strain and weight. This study finally established a procedure for reliability analysis and evaluation of the degradation and failure mechanisms of EPDM rubbers used in coolant hoses for automobile radiators.