• Progress in Superconductivity and Cryogenics
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• v.18 no.4
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• pp.21-24
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• 2016

The mechanical properties of REBCO coated conductor (CC) wires under uniaxial tension are largely determined by the thick component layers in the architecture, namely, the substrate and the stabilizer or even the reinforcement layer. Depending on device applications of the CC tapes, it is necessary to reinforce thin metallic foils externally to one-side or both sides of the CC tapes. Due to the external reinforcement of brass foils, it was found that this could increase the reversible strain limit from the Cu-stabilized CC tapes. In this study, the effects of differently hardened brass foil laminate on the electromechanical property of CC tapes were investigated under uniaxial tension loading. The tensile strain dependence of the critical current ($I_c$) was measured at 77 K and self-field. Depending on whether the $I_c$ of CC tapes were measured during loading or after unloading, a reversible strain (or stress) limit could be determined, respectively. The both-sides of the Cu-stabilized CC tapes were laminated with brass foils with different hardness, namely 1/4H, 1H and EH. From the obtained results, it showed that the yield strength of the brass laminated CC tapes with EH brass foil laminate was comparable to the one of the Cu-stabilized CC tape due to its large yield strength even though its large volume fraction. It was found that the brass foil with different hardness was mainly sensitive on the stress dependence of $I_c$, but not on the strain sensitivity due to the residual strain induced in the laminated CC tapes during unloading.

• Composites Research
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• v.35 no.4
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• pp.283-287
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• 2022

Stretchable strain sensors have been developed for potential future applications including wearable devices and health monitoring. For practical implementation of stretchable strain sensors, their stability and repeatability are one of the important aspects to be considered. In this work, we utilized 3D printed polymer structures having kirigami patterns to improve the stretchability and reduce the hysteresis. The polymer structures were coated with graphene/carbon nanofiber hybrids to make a robust electrical network. The stretchable strain sensors showed a high gauge of 36 at a strain of 32%. Because of the kirigami structures and the robust graphene/carbon nanofiber coating, the sensors also exhibited stable resistance responses at various strains ranging from 1% to 30%.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.1
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• pp.127-132
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• 2001

By the use of a similar numerical method as the forming limit strain by coating method of coated sheet metals is investigated, in which the FEM is applied and J2G(J2-Gotohs Corner Theory) is utilized as the plasticity constitutive equa-tion. Circular bonded sheet metals with dissimilar sheets on both surface planes are stretched in a plane -strain state, with various work-hardening exponent n-values and thicknesses of each layer. Processes of shear-band formation in such com-posite sheets are clearly illustrated. It is concluded that, it the bonded state, the higher limiting strain of one layer is reduced due to the lower limiting strain of the other layer and vice versa, and does not necessarily obey the rule of linear combination of the limiting strain of each layer weighed according thickness.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.04a
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• pp.340-345
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• 2003

By the use of a similar numerical method as that in the previous paper, the forming limit strain by coating method of clad sheet metals is investigated, in which the FEM is applied and J2G(J2-Gotoh's corner theory) is utilized as the plasticity constitutive equation. Clad two-layer sheets and sheets bonded with dissimilar sheets on both surface planes are stretched in a plane-strain state, with various work-hardening exponent n-values and thicknesses of each layer. Processes of shear-band formation in such composite sheets are clearly illustrated. It is concluded that, in the clad state, the higher limiting strain of one layer is reduced due to the lower limiting strain of the other layer and vice versa, and does not necessarily obey the rule of linear combination of the limiting strain of each layer weighted according thickness.

• Progress in Superconductivity and Cryogenics
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• v.14 no.2
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• pp.8-11
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• 2012

In order to recognize the allowable bending diameter in coils, the strain as function of diameters is evaluated. The irreversible strain limits of $I_c$ in the easy and hard bending modes were measured. Strains were calculated at the coating film in the easy bending and at outer edge or inner edge in the hard bending of the CC tape, respectively. The tape geometry subjected to bending procedures is considered from the current industrial spool winding operation. Through the linear superposition of strain induced in different bending modes regarding the expressions, the appropriate design for critical bending diameter is suggested. Results proved that the existence of buckling resulting from bending in hard direction when applied strain exceeded 0.6% is possible. The depicted results showed that the strain limit as a viable parameter should be considered for future purposes.

• Journal of Sensor Science and Technology
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• v.9 no.2
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• pp.96-105
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• 2000

Fiber optic TR-EFPI(total reflected extrtinsic Fabry-Perot interferometric) sensor was developed to measure the strain of structures, such as building, bridge, aircraft, etc. It has been difficult to distinguish the increase and decrease of the strain from the conventional fiber optic EFPI sensor because their signals only have a sinusoidal wave pattern related to the change of strain. Also, the absolute strain could not be measured by the simple fiber optic EFPI sensor. In this study, in order to measure the magnitude of strain with the direction of strain, the fiber optic sensor was simply constructed with the total reflected EFPI sensor probe. This probe was manufactured with a single mode fiber and a mirror coated fiber in a silica glass capillary tube. The output signal of this fiber optic TR-EFPT sensor can give the information about the magnitude and the direction of strain. The loading-unloading test was performed by the universal testing machine with alluminum beam specimen to compare the strain from fiber optic TR-EFPI sensor with the value from electrical strain gauge. In the result of this experiment. the strain from fiber optic TR-EFPI sensor had a good agreement with the values from the electrical strain gauge.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.27 no.1
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• pp.9-14
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• 2001

With the object of providing a temporary artificial periodonal ligament-like membrane around the dental implant, 10 Branemark type implants were coated with commercially available chitosan(Fluka Co., Buchs, Switzerland) which has a molecular weight of 70,000 and 80% deacetylation degree. Once this bioactive hydrophillic polymer(chitosan) contacts with blood or wound fluids, it becomes swollen and penetrates into the adjacent cancellous bone. Thus the interface between implant and surrounding bone is completely filled with chitosan. This tight junction in early healing phase enhances primary stability. The chitosan coated dental implants were implanted into the fresh patella bones from porcine knees, since the thickness of cortical bone is relatively even and their cancellous structure is homogenous. To test the shock absorbing effect, 1mm delta-rogette strain gage was installed behind the implant. The results showed 1. The principal strain peak value directed to the impact of coated implant was 0.064 0.018(p<0.05) and that of uncoated implant was 0.095(0.032 p<0.05). 2. The peak time delay of coated implant was 0.056sec(0.011 p<0.05) and that of uncoated implant was 0.024sec(0.009 p<0.05). It can be reasoned from this results that the chitosan coating has a shock absorbing effect comparable with a temporary artificial periodontal ligament.

• Steel and Composite Structures
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• v.16 no.6
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• pp.703-718
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• 2014

The initial clamping forces of high strength bolts subjected to different faying surface conditions drop within 500 hours regardless of loading, any other external force or loosening of the nut. This study develops a mathematical model for relaxation confined to creep on a coated faying surface after initial clamping. The quantitative model for estimating relaxation was derived from a regression analysis for the relation between the creep strain of the coated surface and the elapsed time for 744 hours. This study establishes an expected model for estimating the relaxation of bolted joints with diverse coated surfaces. The candidate bolts are dacro-coated tension control bolts, ASTM A490 bolt, and plain tension control bolts. The test parameters were coating thickness, species of coating. As for 96, 128, 168, and $226{\mu}m$ thick inorganic zinc, when the coating thickness was increased, relaxation after the initial clamping rose to a much higher range from 10% to 18% due to creep of the coating. The amount of relaxation up to 7 days exceeded 85% of the entire relaxation. From this result, the equation for creep strain can be derived from a statistical regression analysis. Based on the acquired creep behavior, it is expected that the clamping force reflecting relaxation after the elapse of constant time can be calculated from the initial clamping force. The manufacturer's recommendation of inorganic zinc on faying surface as $75{\mu}m$, appears to be reasonable.

• Journal of Sensor Science and Technology
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• v.24 no.4
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• pp.215-218
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• 2015

As several innovative technologies for flexible electric devices are being realized, demand for in-situ strain monitoring for flexible electric devices is being emphasized. Because flexible devices are commonly influenced by substrate strain, suitable strain sensors for flexible devices are essential for the sophisticated maneuvering of flexible devices. In this study, a flexible strain sensor based on an Ag electrode is prepared on a polyimide substrate using the LDW (laser direct writing) process. In this process, first, the Ag nanoparticles are coated on the substrate and selectively sintered using a focused laser. Because of the advantages of the LDW process (such as being mask-less, using low temperatures, and having non-vacuum characteristics), the entire fabrication process has been dramatically simplified; as a final outcome, a highly reliable strain sensor has been fabricated. Using this strain sensor, various strain conditions that arise from different bending radii can be detected by measuring real-time electrical signals.

• Progress in Superconductivity and Cryogenics
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• v.11 no.4
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• pp.12-15
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• 2009

The $I_c$ degradation behavior of critical current in differently processed YBCO and SmBCO CC tapes with IBAD template has been investigated. It has been known that the residual strain in the CC tape will influence the shape of the $I_c$-strain window; $I_c$ may show a peak value if there exist a residual strain induced in the tape during manufacturing. The difference of residual strain may be resulted from the adopted different deposition techniques. In this study, bending test of CC tapes has been done using the Goldacker bending test rig which can produce both compressive and tensile bending strain continuously or alternately to the sample. For SmBCO CC tapes, in continuous compressive bending test, $I_c$ showed a minimal increase and did not degrade up to the largest strain that can be applied using the bending rig equivalent to 1.15% based on the sample thickness. However, in the case of alternate application of compressive and tensile bending strain, $I_c$ showed a larger degradation and a lower reversible limit when compared with the case of continuous application of the bending strain. When $I_c$ started to degrade significantly at the tension side, the reversibility ended, also at the compression side which is resulted from the permanent deformation like delamination or cracks that was induced due to tensile bending strain.