• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.1
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• pp.46-51
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• 2019

Intermittent CSR testing was used to investigate the degradation of a NBR O-ring, and also the prediction of its life-time. An intermittent CSR jig was designed taking into consideration the O-ring's environment under use. Degradation of O-rings by thermal aging was observed between $40^{\circ}C$ and $120^{\circ}C$. O-rings showed non-linear degradation behavior under $80^{\circ}C$. At 20% of failure condition, predicted life-times were 32.5 years by Arrhenius plot and 22.6 years by WLF plot.

• The Journal of the Acoustical Society of Korea
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• v.17 no.2E
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• pp.53-58
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• 1998

In this paper, we study the response of several anisotropic systems to buried transient line loads. The problem is mathematically formulated based on the equations of motion in the constitutive relations. The load is in form of a normal stress acting with arbitrary axis on the plane of monoclinic symmetry. Plane wave equation is coupled with vertical shear wave, longitudinal wave and horizontal shear wave. We first considered the equation of motion in reference coordinate system, where the line load is coincident with symmetry axis of the orthotrioic material. Then the equation of motion is transformed with respect to general coordiante system with azimuthal angle by using transformation tensor. The load is first described as a body force in the equations of the motion for the infinite media and then it is mathematically characterized. Subsequently the results for semi-infinite spaces is also obtained by using superposition of the infinite medium solution together with a scattered solution from the free surface. Consequently explicit solutions for the displacements are obtained by using Cargniard-DeHoop contour. Numerical results which are drawn from concrete examples of orthotropic material belonging to monoclinic symmetry are demonstrated.

• Composites Research
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• v.13 no.1
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• pp.11-24
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• 2000

In this paper, finite thickness and tow phase effects on the mechanical behavior were studied numerically for plain weave textile composites. Unit cell analysis based on a superposition method was employed to simulate uniaxial tensile loading condition and macro-element post-processor was used to reduce computer resource requirement. The effective moduli and micro-stress distribution were calculated for finite thick plain weave composites with phase shifts. Single layer and infinitely thick configurations were also considered for comparison.

• Structural Engineering and Mechanics
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• v.31 no.6
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• pp.663-678
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• 2009

An exact solution is obtained for forced torsional vibration of a finite class 622 piezoelectric hollow cylinder with free-free ends subjected to dynamic shearing stress and time dependent electric potential at both internal and external surfaces. The solution is first expanded in axial direction with trigonometric series and the governing equations for the new variables about radial coordinate r and time t are derived with the aid of Fourier series expansion technique. By means of the superposition method and the separation of variables technique, the solution for torsional vibration is finally obtained. Natural frequencies and the transient torsional responses for finite class 622 piezoelectric hollow cylinder with free-free ends are computed and illustrated.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.884-889
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• 2003

Based on the reinterpretation of the well-known relationship between shear and the rate of change of bending moment in a reinforced concrete beam subject to combined shear and moment loads, the shortcomings of present truss models are discussed. The core of the theory is that a new perspective on the shear strength can be gained by viewing the internal stress filed in terms of the superposition of two base components of shear resistance; arch action and beam action. The arch action can be designed using the simple truss having curved compression chord, while the beam action between the two chords can be modeled using a parallel chord truss with MCFT or RA-STM. The compatibility of deformation associated to the two action is taken into account by employing a characteristic factor a. The new model was examined by the Stuttgart beam shear tests, and the results show that the present approach provides good estimates of stirrup contribution and concrete contributions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.913-920
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• 1996

In this study, the counting method for multi-axial and multi-point load states was proposed. Using this counting method, the load spectrum is generated from the service load history which is measured for boom structure of excavator. Loading state for loading points of boom structure is described as a multi-dimensional state space. From this load spectrum, the stress spectrum was generated by FEM analysis using the superposition of the unit load. The cumulated damage at the severe damage point of In nm structure by the failure example is calculated by Palmgren-Miner's rule. As a result of this study, the fatigue life estimation using the multi-axial and multi-point load counting method is useful.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.04a
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• pp.98-105
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• 1998

In this study, the boundary element analysis in dynamics for the multilayered semi-infinite plane is developed using the fundamental solution for moving loads. Also the indirect method and superposition method are introduced to consider the multilayered systems and moving loads. At each layer the fundamental solution can be obtained by solving the governing equation which is transformed by the Fourier transform. The governing equation can be solved by three conditions; continuity conditions of displacement and stress, the traction free condition at the surface and the radiation condition at the surface and the radiation condition at the infinite distance. To verify the solution and the developed algorithm, the theoretical solution for the homogeneous layer and commercial FEM program is compared with the results of this study.

• Bulletin of the Society of Naval Architects of Korea
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• v.12 no.1
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• pp.9-22
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• 1975

As a second step of a thermal stress analysis in a watertight bulkhead plate during welding of a spool type penetration piece, is idealized as a thin circular disk with a clamped boundary. The exact solution for the transient temperature distribution and associated quasi-static thermal stresses which arise in a circular disk subjected to an instantaneous point source of heat acting in its interior has been obtained. And the solutions have been extended to the case of moving source of heat with the aid of the Duhamel's superposition integral and the results finally derived have been compared with the other results from the typical cases. The solutions can be applied to the problem such as a welding of a penetration piece on the watertight bulkhead and also applicable to the problems which occur in cutting or welding.

• Transactions of Materials Processing
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• v.25 no.6
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• pp.373-378
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• 2016

Recent researches have reported that the superposition of ultrasonic vibrations in metal forming provides beneficial effects such as the reduction of forming load, flow stress and interfacial friction which improves the surface quality of end products. This paper presents experimental investigations on the effects of ultrasonic vibrations in upsetting tests of aluminum. The ultrasonic exciting system consists of piezoelectric transducer and resonator was designed and constructed to superimpose high frequency oscillation on the forming tools. Ultrasonic vibration-assisted upsetting tests were performed for three vibration modes five amplitudes, and the results were compared with those of conventional upsetting tests. The results showed that the superimposition of ultrasonic vibration reduces the upsetting load, and the load reduction is only dependent on the amplitude of the applied vibration regardless of deformation histories and vibration modes.

• Composites Research
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• v.32 no.1
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• pp.78-84
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• 2019

This study focused on the prediction of the long-term performance of carbon fiber/epoxy composites using Dynamic Mechanical Analysis (DMA) and Time-Temperature Superposition (TTS). Single-frequency test, multi-frequency test, and creep TTS test were performed. A sinusoidal load of $20{\mu}m$ amplitude was applied while increasing the temperature from $-30^{\circ}C$ to $240^{\circ}C$ at $2^{\circ}C/min$ for the single-frequency test and the multi-frequency test. The frequencies applied to the multi-frequency test were 0.316, 1, 3.16, 10 and 31.6 Hz. In the creep TTS test, a stress of 15 MPa was applied for 10 minutes at every $10^{\circ}C$ from $-30^{\circ}C$ to $230^{\circ}C$. The glass transition temperature was determined by single-frequency test. The activation energy and the storage modulus curve for each temperature were obtained from glass transition temperature for each frequency by the multi-frequency test. The master curve for the reference temperature was obtained by applying the shift factor using the Arrhenius equation. Also, TTS test was used to obtain the creep compliance curves for each temperature and the master curve for the reference temperature by applying the shift factors using the manual shift technique. The master curve obtained through this process can be applied to predict the long-term performance of carbon fiber/epoxy composites for a given environmental condition.