• Structural Engineering and Mechanics
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• v.65 no.2
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• pp.163-171
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• 2018

Plain concrete is a brittle material with a very low tensile strength compared to compressive strength and critical tensile strain. This study analyzed the dynamic characteristics of high-performance fiber-reinforced cementitious composites based on slurry-infiltrated fiber concrete (SIFCON-based HPFRCC), which maximizes the steel-fiber volume fraction and uses high-strength mortar to increase resistance to loads, such as explosion and impact, with a very short acting time. For major experimental variables, three levels of fiber aspect ratio and five levels of fiber volume fraction between 6.0% and 8.0% were considered, and the flexural strength and toughness characteristics were analyzed according to these variables. Furthermore, three levels of the aspect ratio of used steel fibers were considered. The highest flexural strength of 65.0 MPa was shown at the fiber aspect ratio of 80 and the fiber volume fraction of 7.0%, and the flexural strength and toughness increased proportionally to the fiber volume fraction. The test results according to fiber aspect ratio and fiber volume fraction revealed that after the initial crack, the load of the SIFCON-based HPFRCC continuously increased because of the high fiber volume fraction. In addition, sufficient residual strength was achieved after the maximum strength; this achievement will bring about positive effects on the brittle fracture of structures when an unexpected load, such as explosion or impact, is applied.

• Smart Structures and Systems
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• v.25 no.3
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• pp.323-335
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• 2020

Magnetorheological elastomer (MRE), a smart material, is an innovative material for base isolation system. It has magnetorheological (MR) effect that can control the stiffness in real-time. In this paper, a new hybrid base isolation system combining two electromagnetic closed circuits and the roller bearing is proposed. In the proposed system, the roller part can support the vertical load. Thus, the MRE part is free from the vertical load and can exhibit the maximum MR effect. The MRE magnetic loop is constructed in the free space of the roller bearing and forms a strong magnetic field. To demonstrate the performance of the proposed hybrid base isolation system, dynamic characteristic tests and performance evaluation were carried out. Dynamic characteristic tests were performed under the extensive range of strain of the MRE and the change of the applied current. Performance evaluation was carried out using the hybrid simulation under five earthquakes (i.e., El Centro, Kobe, Hachinohe, Northridge, and Loma Prieta). Especially, semi-active fuzzy control algorithm was applied and compared with passive type. From the performance evaluation, the comparison shows that the new hybrid base isolation system using fuzzy control algorithm is superior to passive type in reducing the acceleration and displacement responses of a target structure.

• The korean journal of orthodontics
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• v.25 no.2 s.49
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• pp.187-200
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• 1995

To estimate the characteristics of Korean Ni-Ti alloy orthodontic wire, this study investigated compositions, tensile properties, bending properties, heat treatment effects, and ion releasing degrees, and compared these characteristics to those of the imported Ni-Ti alloy wire. The results obtained are as follows ; 1. Ti and -Ni elements in ORTHOLLOY were in a range showing superelasticity, and there was a little difference in the Ni and Ti contents of ORTHOLLOY as compared with those of SENTALLOY. 2. The results of the tensile test concerning ORTHOLLOY exhibited a superelastic effect, indicating an area of a definite amount of stress in spite of the changes in the range from $2\%\;to\;8\%$ in the strain rate. 3. ORTHOLLOY presented higher load values than SENTALLOY in the same deflection values when the wire was tested in three-point bending. A load range displaying a superelastic effect was 80-l00g, 140-l80g, and 130-200g respectively, in wire diameters of 0.014', 0.016', and 0.018' 4. By heat treatments at $400^{\circ}C$ and at $500^{\circ}C$, a load range showing the effect of superelasticitly was lessened by the duration of the heat treatment time. The superelastic effect was destroyed as a result of the 10 minutes heat treatment at $600^{\circ}C$. 5. The quantity of the Ni ion released from ORTHOLLOY, tended to be greater than the amount of released Ni ion in SENTALLOY. The Co ion released was very little(<0.01ppm) in SENTALLOY and ORTHOLLOY irrespective of the lapse of time. Released Ni ions on the 1st day were at the maximum, and the releasing rate showed plateaus after three days. 6. The surface morphology of SENTALLOY was relatively regular irrespective of the lapse of rime, and the corrosion tendency was not observed. However, the surface morphology of ORTHOLLOY was rather irregular and shelved fitting corrosion after immersion.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.531-537
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• 2016

The damage and fracture of machine or structure are caused by the crack happened from the defect existed at the inside of material. The properties of crack propagation and growth characteristic must be considered because there are many cases at which these cracks are densely existed. Therefore, this study investigates the fracture property due to the position of crack and hole inside the standard compact tension (C. T.) specimen. When the concentrated load is applied eccentrically at the standard C. T. specimen, the fracture mechanical behavior due to the existence or non-existence and the position of hole near crack is investigated. As the result of analysis study, model 3 (in case of the distance of 2mm on the horizontal direction between the end part and hole as the specimen model existed with one hole near the crack) has the maximum deformation, stress and deformation energy of the most values among three models. As the distance between the crack and hole inside the specimen becomes nearer, the maximum stress becomes higher in cases of three models. Apart from the number of holes, it is seen that the maximum stress becomes higher near the crack when the hole exists near the crack inside the specimen. If the hole inside the machine or the mechanical structure is punctured by using the result of this study, it is thought that the occurred breakage or breakdown can be prevented by reducing the fracture stress happened at the specimen.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.1
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• pp.62-68
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• 2001

In order to characterize the microscopic fracture behaviour of the weldment din stress corrosion cracking(SCC) phenomena, SCC and acoustic emission(AE) tests were carried out simultaneously and the correlation between mechanical paramenters obtained from SCC and AE tests was investigated. In the case of base metal, much more AE events were produced at -0.5V than at -0.8V because of the dissolution mechanism before the maximum load. Regardless of the applied voltages to the specimens, however, AE events decreased after the maximum load. In the case of weldment, lots of AE events with larger amplitude $range(40{\sim}100dB)$ were produced because of the singularities of weld HAZ in comparision to the base metal and post-weld heat-treated(PWHT) specimens. Numerous and larger cracks for the weldment were observed on the fractured surfaces by SEM examination. From these results, it was concluded that SCC for the weldment appeared most severely in synthetic seawater. Weld HAZ was softened by PWHT which also contributed to the reduced susceptibility to corrosive environment in comparison to the weldment.

• Journal of Magnetics
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• v.16 no.3
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• pp.211-215
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• 2011

The dynamic magnetostriction characteristics of an Fe-based nanocrystalline FeCuNbSiB alloy are investigated as a function of the dc bias magnetic field. The experimental results show that the piezomagnetic coefficient of FeCuNbSiB is about 2.1 times higher than that of Terfenol-D at the low dc magnetic bias $H_{dc}$ = 46 Oe. Moreover, FeCuNbSiB has a large resonant dynamic strain coefficient at quite low Hdc due to a high mechanical quality factor, which is 3-5 times greater than that of Terfenol-D at the same low $H_{dc}$. Based on such magnetostriction characteristics, we fabricate a new type of transducer with FeCuNbSiB/PZT-8/FeCuNbSiB. Its maximum resonant magnetoelectric voltage coefficient achieves ~10 V/Oe. The ME output power reaches 331.8 ${\mu}W$ at an optimum load resistance of 7 $k{\Omega}$ under 0.4 Oe ac magnetic field, which is 50 times higher than that of the previous ultrasonic-horn-substrate composite transducer and it decreases the size by nearly 86%. The performance indicate that the FeCuNbSiB/PZT-8/FeCuNbSiB transducer is promising for application in highly efficient magnetoelectric energy conversion.

• 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.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.4
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• pp.23-29
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• 2017

The packaged optical fiber Bragg grating sensors which were networked by multiplexing the Bragg grating sensors with WDM technology were investigated in application for the structural health monitoring of the marine trestle structure transporting the ship. The optical fiber Bragg grating sensor was packaged in a cylindrical shape made of aluminum tubes. Furthermore, after the packaged optical fiber sensor was inserted in polymeric tube, the epoxy was filled inside the tube so that the sensor has resistance and durability against sea water. The packaged optical fiber sensor component was investigated under 0.2 MPa of hydraulic pressure and was found to be robust. The number and location of Bragg gratings attached at the trestle were determined where the trestle was subject to high displacement obtained by the finite element simulation. Strain of the part in the trestle being subjected to the maximum load was analyzed to be ${\sim}1000{\mu}{\varepsilon}$ and thus shift in Bragg wavelength of the sensor caused by the maximum load of the trestle was found to be ~1,200 pm. According to results of the finite element analysis, the Bragg wavelength spacings of the sensors were determined to have 3~5 nm without overlapping of grating wavelengths between sensors when the trestle was under loads and thus 50 of the grating sensors with each module consisting of 5 sensors could be networked within 150 nm optical window at 1550 nm wavelength of the Bragg wavelength interrogator. Shifts in Bragg wavelength of the 5 packaged optical fiber sensors attached at the mock trestle unit were well interrogated by the grating interrogator which used the optical fiber loop mirror, and the maximum strain rate was measured to be about $235.650{\mu}{\varepsilon}$. The modelling result of the sensor packaging and networking was in good agreements with experimental result each other.

• Proceedings of the KOSOMBE Conference
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• v.1994 no.12
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• pp.71-74
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• 1994

In cementless total hip arthroplasty(THA), an initial stability of the femoral component is mandatory to achieve bony ingrowth and secondary long term fixation. Bone ingrowth depends strongly on relative micromotion and stress distributions at the interface. Primary stability of the femoral component can be obtained by minimizing the magnitude of relative micromotions at bone-prosthesis interface, Hence an accurate evaluation of interface behavior and stress/strain fields in the bone implant system may be relevant for better understanding of clinical situations and improving THA design. However, complete evaluation of load transfer in the bone remains difficult to assess experimentally, Hence, recently finite element method (FEM) was introduced in orthopaedic research field to fill the gap due to its unique capacity to evaluate stress in structure of complex shape, loading and material behavior. The authors developed the 3-dimensional numerical finite element model which is composed of totally 1179 elements off and 8 node blick. We also analyzed the micromotions at the bone-stem interface and mechanical behavior of existing bone prosthesis for a loading condition simulating the single leg stance. The result indicates that the values of relative motion for this well fit Multilock stem were $150{\mu}m$ in maximum, $82{\mu}m$ in minimum, and the largest relative motion developed in medial region of proximal femur with anterior-posterior direction. The proximal region of the bone was much larger in motion than the distal region and the stress pattern shows high stress concentration on the cortex near the tip of the stem. These findings indicates that the loading in the proximal femoral bone in the early postoperative situation can produce micromotions on the interface and clinically cementless TEA patient should not be allowed weight bearing strictly early in the postoperative period.

• Journal of Biomedical Engineering Research
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• v.17 no.1
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• pp.61-70
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• 1996

In cementless total hip arthroplasty(THA), an initial stability of the femoral component is mandatory to achieve bony inyowth and secondary long term fixation. Primary stability of the femoral component can be obtained by minimizing the magnitude of relative micromotions at bone stem interface. An accurate evaluation of interf'ace micromotion and stress/strain fields in the bone-implant system may be relevant for better understanding of clinical situations and improving THA design. Recently finite element method(FEM) was introduced in'orthopaedic research field due to its unique capacity to evaluate stress in structure of complex shape, loading and material behavior. The authors developed the 3-dimensional finite element model of proximal femur with $Multilock^{TM}$ stem of 1179 blick elements to analyse the micromotions and mechanical behaviors at the bone-stem inteface in early post-operative period for the load simulating single leg stance. The results indicates that the values of relative motion for this well fit stem were $150{\mu}m$ in maximum $82{\mu}m$ in minimum and the largest relative motion was developed in medial region of Proximal femur and in anterior-posterior direction. The motion in the proximal bone was much greater than in the distal bone and the stress pattern showed high stress concentration on the cortex near the tip of the stem. These findings indicate that the loading on the hip joint in the early postoperative situation before achieving bony ingrowth could produce large micromotion of $150{\mu}m$ and clinicaly non-cemented THA patient should not be allowed weight bearing strictly early in the postoperative period.