• Coupled systems mechanics
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• 제13권2호
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• pp.153-170
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• 2024

The problem considered in this theoretical paper is the delamination of a multilayered inhomogeneous beam structure that has viscoelastic behaviour under angle of twist, horizontal and vertical displacements which vary smoothly with time according to prescribed laws. The cross-section of the beam is a rectangle. The layers are made of different materials which are smoothly inhomogeneous along the length of the beam. The beam under consideration represents statically undetermined structure since it is clamped in its two ends. The problem of the strain energy release rate is solved. For this purpose, the strain energy stored in the beam structure is analyzed. In order to verify the solution obtained, the strain energy release rate is found also analyzing the time-dependent compliances of the beam under prescribed angle of twist and displacements. A parametric investigation is carried-out by applying the solution obtained. Special attention is paid to the effect of the parameters which control the variation of the angle of twist and the displacements with time on the strain energy release rate.

• 한국습지학회지
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• 제19권1호
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• pp.63-68
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• 2017

노후화된 하수관거가 증가함에 따라 친환경적이며 효율적인 하수관거의 보수가 필요하다. 본 연구에서는 유리섬유와 뒤틀림 방지 밴드를 이용한 하수관거의 강도 및 뒤틀림을 방지 할 수 있는 하수관거 보수 공법의 성능을 평가하였다. 기존의 하수관거 부분 보수 공법과 비교하여 인장 강도, 압축 강도 및 파괴하중이 증가하였다. 또한 기존에 고려되지 않던 뒤틀림 방지 효과도 확인하였으며, 경제성도 우수한 것으로 나타났다. 향 후 본 연구를 통해 검증한 유리섬유와 뒤틀림 방지 밴드를 이용한 하수관거 보수 공법은 친환경적 및 효과적인 하수관거 보수 공법으로 활용 가능할 것으로 판단된다.

• Structural Engineering and Mechanics
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• 제23권4호
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• pp.339-352
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• 2006

Observing the unique stress-strain curves of the superelastic shape memory alloy (SMA) in tension and compression, the primary intention of this study is to investigate the behavior of the shafts made of the same material, under torsional loading-unloading cycles for large angle of twist. Experiments have been performed for the superelastic SMA shafts with different unsupported lengths and angles of twist and the results are compared with those of stainless steel (SUS304) shafts under similar test conditions. As expected for the superelastic SMA, the residual strains are small enough after each cycle and consequently, the hysteresis under loading-reverse loading is much narrower than that for the SUS304. For large angle of twists, the torsional strength of the superelastic SMA increases nonlinearly and exceeds that of SUS304. Most interestingly, the slender solid superelastic SMA shafts are found to buckle when acted upon torsion for large angle of twist.

• International Journal of Aeronautical and Space Sciences
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• 제9권2호
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• pp.18-33
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• 2008

This paper presents design optimization of a new Active Twist Rotor (ATR) blade and conducts its aeroelastic analysis in forward flight condition. In order to improve a twist actuation performance, the present ATR blade utilizes a single crystal piezoelectric fiber composite actuator and the blade cross-sectional layout is designed through an optimization procedure. The single crystal piezoelectric fiber composite actuator has excellent piezoelectric strain performance when compared with the previous piezoelectric fiber composites such as Active Fiber Composites (AFC) and Macro Fiber Composites (MFC). Further design optimization gives a cross-sectional layout that maximizes the static twist actuation while satisfying various blade design requirements. After the design optimization is completed successfully, an aeroelastic analysis of the present ATR blade in forward flight is conducted to confirm the efficiency in reducing the vibratory loads at both fixed- and rotating-systems. Numerical simulation shows that the present ATR blade utilizing single crystal piezoelectric fiber composites may reduce the vibratory loads significantly even with much lower input-voltage when compared with that used in the previous ATR blade. However, for an application of the present single crystal piezoelectric actuator to a full scaled rotor blade, several issues exist. Difficulty of manufacturing in a large size and severe brittleness in its material characteristics will need to be examined.

• 한국염색가공학회지
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• 제16권1호
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• pp.5-9
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• 2004

This research surveys the threadline instability on the belt texturing machine according to the 1st heater temperature, draw ratio and velocity ratio. the threadline instability to the time, which is called surging phenomena, is analysed with variations of draw ratio and velocity ratio. In addiction, the surging phenomena is investigated with the variation of the untwisting tension and false twist mechanism on the belt texturing machine. The breaking strain, modulus and yam unevenness of the DTY along the yarn length are measured and analysed with the surging phenomena which is due to untwisting tension variation on the threadline according to the draw ratio, 1st heater temperature and velocity ratio.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.221-225
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• 2000

The effect of twisting on the microstructural evolution and critical current of BSCCO superconductor tape has been evaluated. Twisting pitches of the tapes are in the range of 8-70 mm and uniformly deformed. The critical current of twisted tape was dependent on the twist pitch. Specifically, it was observed that the critical current decreased with decreasing twist pitch, and only 50% of critical current was retained when the tape was twisted to a pitch of 8 mm. This reduction of the critical current may be related to the interface irregularity, smaller grain size, worse texture and the presence of cracks due to the induced strain during the twisting processing.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 1991년도 제2차 학술발표초록집
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• pp.75-75
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• 1991

• Structural Engineering and Mechanics
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• 제68권3호
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• pp.377-384
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• 2018

Bi-stable structure can be stable in both its extended and coiled forms. For the un-stressed thin cylindrical shell, the strain energy expressions are deduced by using a theoretical model in terms of only two parameters. Based on the principle of minimum potential energy, the bi-stable behaviors of the cylindrical shells are investigated. The results indicate that the isotropic cylindrical shell does not have the second stable configuration and laminated cylindrical shells with symmetric or antisymmetric layup of fibers have the second stable state under some confined conditions. In the case of antisymmetric laminated cylindrical shell, the analytical expressions of the stability are derived based on the extremal principle, and the shell can achieve a compact coiled configuration without twist deformation in its second stable state. In the case of symmetric laminated cylindrical shell, the explicit solutions for the stability conditions cannot be deduced. Numerical results show that stable configuration of symmetric shell is difficult to achieve and symmetric shell has twist deformation in its second stable form. In addition, the roll-up radii of the antisymmetric laminated cylindrical shells are calculated using the finite element package ABAQUS. The results show that the value of the roll-up radii is larger from FE simulation than from theoretical analysis. By and large, the predicted roll-up radii of the cylindrical shells using ABAQUS agree well with the theoretical results.

• Structural Engineering and Mechanics
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• 제37권3호
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• pp.297-307
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• 2011

Meck Plot is an adapted version of the well-known Southwell method to the case of lateral-torsional buckling, which indeed reflects the physical inter-dependence of lateral flexure (lateral displacement) and torsion (rotation) in the structure. In the recent reported studies, it has been shown experimentally and theoretically that lateral displacement of an I-beam undergoing elastic lateral-distortional mode of buckling is interestingly directly coupled with other various deformation characteristics such as web transverse strain, web longitudinal strain, vertical deflection, and angles of twist of top and bottom flanges, and consequently good results have been obtained as a result of application of the Meck's method on lateral displacement together with each of the aforementioned deformation variables. In this paper, it is demonstrated that even web transverse and longitudinal strains, vertical deflection, and angles of twist of top and bottom flanges of an I-beam undergoing elastic lateral-distortional buckling are two-by-two directly coupled and the application of the Meck Plot on each pair of these deformation variables may still yield reliable predictions for the critical buckling load.

• Advances in nano research
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• 제16권2호
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• pp.175-186
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• 2024

Dynamical behaviors of one-dimensional (1D) nano-sized structures are of great importance in nanotechnology applications. Therefore, the torsional dynamic response of functionally graded nanorods which could be used to model the nano electromechanical systems or micro electromechanical systems with torsional motion about the center of twist is examined based on the theory of strain gradient nonlocal elasticity in this work. The mathematical background is constructed based on both strain gradient theory and Eringen's nonlocal elasticity theory. The equation of motions and boundary conditions of radially functionally graded nanorods are derived using Hamilton's principle and then transformed into the eigenvalue analysis by using Fourier sine series. A general coefficient matrix is obtained to assemble the Stokes' transformation. The case of a restrained functionally graded nanorod embedded in two elastic springs against torsional rotation is then deeply investigated. The effect of changing the functionally graded index, the stiffness of elastic boundary conditions, the length scale parameter and nonlocal parameter are investigated in detail.