• Proceedings of the KSME Conference
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• 2001.06a
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• pp.419-423
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• 2001

It is important to know the mechanical properties of the materials under dynamic load. The mechanical properties of most materials are influenced to some extent by strain rate. One of the reliable test device for determining the mechanical properties of materials at high strain rate is Split Hopkinson Pressure bar. In this paper, we conducted the mechanical properties test for the aluminium alloy 6063 and 6061 using the SHPB device.

• Structural Engineering and Mechanics
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• v.75 no.6
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• pp.659-674
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• 2020

The present paper employs nonlocal strain gradient theory (NSGT) to study buckling behavior of functionally graded magneto-electro-thermo-elastic (FG-METE) nanoshells under various physical fields. NSGT modeling of the nanoshell contains two size parameters, one related to nonlocal stress field and another related to strain gradients. It is considered that mechanical, thermal, electrical and magnetic loads are exerted to the nanoshell. Temperature field has uniform and linear variation in nanoshell thickness. According to a power-law function, piezo-magnetic, thermal and mechanical properties of the nanoshell are considered to be graded in thickness direction. Five coupled governing equations have been obtained by using Hamilton's principle and then solved implementing Galerkin's method. Influences of temperature field, electric voltage, magnetic potential, nonlocality, strain gradient parameter and FG material exponent on buckling loads of the FG-METE nanoshell have been studied in detail.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.4
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• pp.148-153
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• 2004

It is well-known that the mechanical behavior of fiber-reinforced composites under hydrostatic pressure environment is different from that of atmospheric pressure environment. It is also known that the mechanical behavior of fiber-reinforced composites is affected by a strain rate. In this work, we investigated the effect of strain rate on the compressive elastic modulus, fracture stress, and fracture strain of carbon/epoxy composites under hydrostatic pressure environment. The material used in the compressive test was unidirectional carbon/epoxy composites and the hydrostatic pressures applied was 270㎫. Compressive tests were performed applying three strain rates of 0.05％/sec, 0.25％/sec, and 0.55％/sec. The results showed that the elastic modulus increased with increasing strain rate while the fracture stress was little affected by the strain rate. The results also showed that the fracture strain decreased with increasing strain rate.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.191-191
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• 2003

It is well-known that the mechanical behavior of fiber-reinforced composites under hydrostatic pressure environment is different from that of atmospheric pressure environment. It is also known that the mechanical behavior of fiber-reinforced composites is affected by strain rate. In this work, we investigated the effect of strain rate on the compressional elastic modulus and fracture stress of fiber-reinforced composites under hydrostatic pressure environment. The material used in the compressional test was unidirectional carbon/epoxy composites and the hydrostatic pressures applied was 250 MPa. Compressional tests were performed applying various strain rates of 0.05 %/sec, 0.25 %/sec, 0.45 %/sec, and 0.75 %/sec. The results showed that the elastic modulus increased with increasing strain rate while the fracture stress was little affected by the strain rate.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.107-112
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• 2003

Mechanical properties of the materials used for transportations and industrial machinery under high strain rate loading conditions such as high impact loading are required to provide appropriate safety assessment to varying dynamically loaded mechanical structures. The Split Hopkinson Pressure Bar(SHPB) technique with a special experimental apparatus can be used to obtain the material behavior under high strain rate loading conditions. In this paper, the dynamic deformation behavior of a brass under both high strain rate compressive loading conditions has been determined using the SHPB technique.

• 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.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.268-273
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• 2000

Mechanical properties of the materials used for transportations and industrial machinery under high strain rate loading conditions are required to provide appropriate safety assessment to these mechanical structures. The Split Hopkinson Pressure Bar(SHPB) technique, a special experimental apparatus, can be used to obtain the material behavior under high strain rate loading condition. In this paper, dynamic deformation behaviors of the aluminum alloys, Al2024-T4, Al6061-T6 and Al7075-T6, under high strain rate compressive and tensile loading are determined using SHPB technique.

• Journal of Sensor Science and Technology
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• v.30 no.3
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• pp.181-184
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• 2021

Interest in healthcare and wearable devices has been increasing recently. A strain sensor is required in various wearable devices. With respect to such devices, studies on resistance changes in strain sensors using flexible materials are in progress. However, the resistance of the rest area in a strain sensor should not change according to the applied strain. So, an electrode with resistance to stretching, bending, and torsion is required in such strain sensors. Tension, bending, and torsion can be realized through structural shape control, rather than by using flexible materials. Further, such an electrode that maintains electrical properties has been developed and manufactured. This electrode can be used in various applications such as foldable devices, e-papers, batteries, and multifunctional wearable devices.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.1145-1150
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• 2000

Concrete behaves as ductile material at high temperature. The existing stress-strain relationship is not valid at high temperature condition. Thus, stress-strain curve of concrete at high temperature is re-established by modifying Saenz's suggestion in this study. A constitutive model of concrete subjected to elevated temperature is also suggested. The model consists of three components; free thermal stain, mechanical strain and thermal creep strain. As the temperature increase, the thermal creep becomes more critical to the failure of concrete. The thermal creep strain of concrete is derived from the modified power-law relation for the steady state creep. The proposed equation for thermal creep employs a Dorn's temperature compensated time theorem

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.640-643
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• 2006

In this paper, electro-mechanical coupling of cellulose-based Electro-Active Paper (EAPap) actuator is investigated by measuring induced strain and mechanical properties with and without electric excitation. The maximum induced in-plane strain is measured at the orientation angle of 45? samples. The elastic modulus and strength of EAPap are increased with electric excitation and the orientation angle of $45^{\circ}$ samples shows the largest increment of mechanical properties. From the observations, shear piezoelectricity is considered as the major piezoelectric mode of EAPap.