• Title/Summary/Keyword: mechanical resistance

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Analysis on an improved resistance tuning type multi-frequency piezoelectric spherical transducer

  • Qin, Lei;Wang, Jianjun;Liu, Donghuan;Tang, Lihua;Song, Gangbing
    • Smart Structures and Systems
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    • v.24 no.4
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    • pp.435-446
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    • 2019
  • The existing piezoelectric spherical transducers with fixed prescribed dynamic characteristics limit their application in scenarios with multi-frequency or frequency variation requirement. To address this issue, this work proposes an improved design of piezoelectric spherical transducers using the resistance tuning method. Two piezoceramic shells are the functional elements with one for actuation and the other for tuning through the variation of load resistance. The theoretical model of the proposed design is given based on our previous work. The effects of the resistance, the middle surface radius and the thickness of the epoxy adhesive layer on the dynamic characteristics of the transducer are explored by numerical analysis. The numerical results show that the multi-frequency characteristics of the transducer can be obtained by tuning the resistance, and its electromechanical coupling coefficient can be optimized by a matching resistance. The proposed design and derived theoretical solution are validated by comparing with the literature given special examples as well as an experimental study. The present study demonstrates the feasibility of using the proposed design to realize the multi-frequency characteristics, which is helpful to improve the performance of piezoelectric spherical transducers used in underwater acoustic detection, hydrophones, and the spherical smart aggregate (SSA) used in civil structural health monitoring, enhancing their operation at the multiple working frequencies to meet different application requirements.

Evaluation of Structural Stability of Fire Resistant Steel Produced by Thermo-Mechanical Control Process at High Temperature (TMCP 내화강재의 고온 내력 평가 연구)

  • Kwon, In-Kyu
    • Fire Science and Engineering
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    • v.27 no.6
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    • pp.21-25
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    • 2013
  • Fire resistance steel, grading 490 MPa, had developed by using Thermo-mechanical control process (TMCP) and it has better performance at welding, seismic resistance than those of the ordinary structural steel, But the fire resistance performance is required to verify against the ordinary fire resistance, FR 490. Therefore this study was done to make database of mechanical properties at high temperature and to evaluate the structural stability at high temperature in terms of materials and structural member such as H-section from that of FR 490. The result of this study was that the structural stability of TMCP was lower than that of ordinary FR 490 at the range up about 700C.

Performance of Hybrid Fiber Reinforced Concrete at Elevated High Temperature (고온에서 하이브리드 섬유보강 콘크리트의 성능)

  • Won, Jong-Pil;Park, Kyung-Hoon;Park, Chan-Gi
    • Journal of the Korea Concrete Institute
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    • v.20 no.3
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    • pp.325-333
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    • 2008
  • This study evaluated the mechanical performance, shrinkage crack and fire resistance of hybrid fiber (blended steel and polypropylene fiber with different diameter and length) reinforced concrete at elevated temperature. The compressive, splitting tensile, flexural, plastic shrinkage test were conducted to the evaluate the mechanical properties and the resistance of shrinkage crack. Also, the surface investigation, reduction rate of mass and residual compressive test were performed to evaluate the physical and mechanical properties after 400C, 600C, 800C and 1,200C exposure. Test results showed that the hybrid fiber reinforced concrete improved the mechanical performance, shrinkage crack and fire resistance. The reduction of performance with a temperature change were high at the temperature of 600800C.

A Study on the Strength Evaluation and Defect Detection Capability of Adhesive Joint with CNTs (CNT를 첨가한 접착조인트의 결함탐지능 및 강도 평가에 관한 연구)

  • Kim, Tae-Hyeong;Kim, Cheol-Hwan;Choi, Jin-Ho
    • Composites Research
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    • v.31 no.4
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    • pp.151-155
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    • 2018
  • Mechanical joint and adhesive joint are two typical joining methods for structures. The adhesive joints distribute the load over a larger area than mechanical joints and have excellent fatigue properties. However, the strength of adhesive joint greatly depends on the environmental conditions and the skill of the operator. Therefore, there is a need for techniques to evaluate the quality of the adhesive joints. The electric resistance method is a very promising technique for detecting defects by measuring the electrical resistance of an adhesive joint in which CNTs are dispersed in an adhesive. In this study, Aluminium-Aluminium adhesive single lap joint specimens were fabricated by using the adhesive dispersing CNTs using a sonicator and a 3-roll mill, and the static strengths and defect detection capabilities of the joints using the electrical resistance method were evaluated according to the CNTs content.

A Study on Behaviour and Characteristics of Spark Discharge in Spark Ignition System (스파크 점화 시스템의 방전 거동 및 특성에 관한 연구)

  • Lee Myung Jun;Hall Matt;Ezekoye Ofodike A.;Matthews Ron;Chung Sung Sik
    • Transactions of the Korean Society of Automotive Engineers
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    • v.14 no.1
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    • pp.100-108
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    • 2006
  • Time-resolved current and voltage measurements for an inductive automotive spark system were made. Also presented are measurements of the total energy delivered to the spark gap. The measurements were made in air for a range of pressures from 1-18atm, at ambient temperatures. The measured voltage and current characteristics were found to be a function of many ignition parameters; some of these include: spark gap distance, internal resistance of the spark plug and high tension wire, and pressure. The voltages presented were measured either at the top of the spark plug or at the spark gap. The measurements were made at different time resolutions to more accurately resolve the voltage and current behavior throughout the discharge process. This was necessary because the breakdown event occurs on a time scale much shorter than the arc and glow phases. The breakdown, are, and glow voltages were found to be functions of spark plug resistance, gas density, and spark plug gap as expected from the literature. Spark duration was found to decrease as either pressure or gap was increased. The transition from the arc to glow phase is usually distinguished by a sudden rise in the voltage across the gap. At pressures above about 7atm this transition was not observed suggesting that a glow phase was not present. Energy delivered to the gap increased with increasing pressure. The effective resistance of the spark gap during discharge was about twice as large for the glow phase as the arc phase.

An Experimental Study on the Mechanical and Fire Resistance Properties of ECC Fire Resistance Panel (ECC내화패널의 역학 및 내화특성에 관한 실험적 연구)

  • Lee, Sang-Soo;Kang, Hoon
    • Journal of the Korea Institute of Building Construction
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    • v.10 no.2
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    • pp.89-96
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    • 2010
  • This study was based on an experiment that examines the manufacture and performance of fiber-reinforced cement composite panels. The conclusions were drawn after testing the mechanical properties and durability characteristics of fiber-reinforced mortar, and the mechanical properties and fire resistance of ECC fire resistant column panels. It was found that the fluidity of CEL fiber was lower than that of PVA and NY fiber. The amount of air increased slightly as the combination of fibers caused the number of fine pores to increase. It was found that the mechanical performance and deformability of high strength concrete could be improved through the confinement effect of ECC fire resistant column panels. Through continuous studies on the manufacturing and field construction methods of fire resistant column panels, a new PC method that eliminates weakness in the existing processes may be developed for skyscrapers.

Effects of ZrO2 Addition on Mechanical Strength and Thermal Shock Resistance of Cordierite-Mullite Ceramics (ZrO2가 코디어라이트-뮬라이트 세라믹스의 기계적 강도 및 내열충격성에 미치는 영향)

  • Lim, Jin-Hyeon;Kim, Shi Yeon;Yeo, Dong-Hun;Shin, Hyo-Soon;Jeong, Dae-yong
    • Korean Journal of Materials Research
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    • v.28 no.12
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    • pp.719-724
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    • 2018
  • Cordierite composed of an alumina-silica-magnesia compound has a low coefficient of thermal expansion(CTE) and excellent thermal shock resistance. It also has a low dielectric constant and high electrical insulation. However, due to low mechanical strength, it is limited for use in a ceramic heater. In this study, ZrO2 is added to an 80 wt% cordierite-20 wt% mullite composition, and the effect of ZrO2 addition on the mechanical strength and thermal shock resistance is investigated. With an increasing addition of ZrO2, cordierite-mullite formed ZrO2, ZrSiO4 and spinel phases. With sintering conducted at 1400C with the addition of 5 wt% ZrO2 to 80 wt% cordierite-20 wt% mullite, the most dense microstructure forms along with an excellent mechanical strength with a 3-point flexural strength of 238MPa. When this composition is quenched in water at ΔT=400C, the 3-point flexural strength is maintained. Moreover, when this composition is cooled from 800C to air, the 3-point flexural strength is maintained even after 100 cycles. In addition, the CTE is measured as 3.00×106K1 at 1000C. Therefore, 80 wt% cordierite-20 wt% mullite with 5 wt% ZrO2 is considered to be appropriate as material for a ceramic heater.

Buckling resistance behavior of WGJ420 fire-resistant weathering steel columns under fire

  • Yiran Wu;Xianglin Yu;Yongjiu Shi;Yonglei Xu;Huiyong Ban
    • Steel and Composite Structures
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    • v.47 no.2
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    • pp.269-287
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    • 2023
  • The WGJ420 fire-resistant weathering (FRW) steel is developed and manufactured with standard yield strength of 420 MPa at room temperature, which is expected to significantly enhance the performance of steel structures with excellent fire and corrosion resistances, strong seismic capacity, high strength and ductility, good resilience and robustness. In this paper, the mechanical properties of FRW steel plates and buckling behavior of columns are investigated through tests at elevated temperatures. The stress-strain curves, mechanical properties of FRW steel such as modulus of elasticity, proof strength, tensile strength, as well as corresponding reduction factors are obtained and discussed. The recommended constitutive model based on the Ramberg-Osgood relationship, as well as the relevant formulas for mechanical properties are proposed, which provide fundamental mechanical parameters and references. A total of 12 FRW steel welded I-section columns with different slenderness ratios and buckling load ratios are tested under standard fire to understand the global buckling behavior in-depth. The influences of boundary conditions on the buckling failure modes as well as the critical temperatures are also investigated. In addition, the temperature distributions at different sections/locations of the columns are obtained. It is found that the buckling deformation curve can be divided into four stages: initial expansion stage, stable stage, compression stage and failure stage. The fire test results concluded that the residual buckling capacities of FRW steel columns are substantially higher than the conventional steel columns at elevated temperatures. Furthermore, the numerical results show good agreement with the fire test results in terms of the critical temperature and maximum axial elongation. Finally, the critical temperatures between the numerical results and various code/standard curves (GB 51249, Eurocode 3, AS 4100, BS 5950 and AISC) are compared and verified both in the buckling resistance domain and in the temperature domain. It is demonstrated that the FRW steel columns have sufficient safety redundancy for fire resistance when they are designed according to current codes or standards.

Study of Specific Resistance of Conductive Ink According to Temperature During Laser Sintering Process (전도성 잉크의 레이저 열경화 공정 시 온도에 따른 비저항 연구)

  • Lee, Dae-Geon;Park, Yong-Han;Park, Ji-Young;Kim, Dong-Keun;Moon, Yoon-Jae;Moon, Seung-Jae;Hwang, Jun-Young;Kang, Heui-Seok
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.37 no.2
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    • pp.119-124
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    • 2013
  • In this study, the two-dimensional transient temperature of printed Ag nanoparticle ink during continuous wave laser sintering was calculated. Ag nanoparticle ink was printed on a glass substrate by inkjet printing. Then, a 532-nm continuous wave laser with different laser intensities was irradiated on the printed Ag nanoparticle ink for 60 s. During laser irradiation, the in-situ specific resistance of the sintered ink was measured. To obtain the transient temperature of the sintered ink during the laser sintering process, a two-dimensional transient heat conduction equation was derived by applying the Wiedemann-Franz law. It was found that the specific resistance of the sintered ink decreased with an increase in the sintering temperature of the printed ink.

The Characteristics of Mechanical Properties and Fatigue Crack Propagation of Fire Resistance Steel for Frame Structure (구조용 내화강의 기계적 성질과 피로균열전파 특성에 관한 연구)

  • Kim, Hyeon-Su;Nam, Gi-U;Gang, Chang-Ryong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.1
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    • pp.54-60
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    • 2001
  • This study is to investigate the mechanical properties and the fatigue crack propagation of fire resistance steel for frame structure as the chemical composition was changed by addition of N, B and rolled end temperature was varied. We used two kinds of specimen, the one is parallel and the other is perpendicular to the rolling directions. As rolled end temperature increased, volume fraction of ferrite and pearlite decreased, but volume fraction of baintie and grain size increased. Micro-hardness decreased as rolled end temperature increased, but tensile and yield strength increased. Volume fraction of ferrite and pearlite decreased by addition of N. But volume fraction of bainite, tensile and yield strength increased. Microstructure was changed to martensite by addition of B, and tensile and yield strength increased. Fatigue life of TL direction specimen was shorter than that of LT direction specimen. There was no significant effect to fatigue crack propagation rate by addition of N and changing rolling condition, but fatigue life was increased by addition of B.