• The Journal of Korean Academy of Prosthodontics
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• v.33 no.4
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• pp.780-806
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• 1995

The purpose of this study was to describe the application of 3D finite element analysis to determine resultant stresses on the bone anchored fixed prosthesis, implants and supporting bone of the mandible according to fixture numbers and load conditions. 4 or 6 fixtures and the bone anchored fixed prosthesis were placed in 3D finite element mandibular arch model which represents an actual mandibular skull. A $45^{\circ}$ diagonal load of 10㎏ was labiolingually applied in the center of the prosthesis(P1). A $45^{\circ}$ diagonal load of 20㎏ was buccolingually applied at the location of the 10mm or 20mm cantilever posterior to the most distal implant(P2 or P3). The vertical distribution loads were applied to the superior surfaces of both the right and the left 20mm cantilevers(P4). In order that the boundary conditions of the structure were located to the mandibular ramus and angle, the distal bone plane was to totally fixed to prevent rigid body motion of the entire model. 3D finite element analysis was perfomed for stress distribution and deflection on implants and supporting bone using commercial software(ABAQUS program. for Sun-SPARC Workstation. The results were as follows : 1. In all conditions of load, the hightest tensile stresses were observed at the metal lates of prostheses. 2. The higher tensile stresses were observed at the diagonal loads rather than the vertical loads 3. 6-implants cases were more stable than 4-implants cases for decreasing bending and torque under diagonal load on the anterior of prosthesis. 4. From a biomechanical perspective, high stress developed at the metal plate of cantilever-to-the most distal implant junctions as a consequence of loads applied to the cantilever extension. 5. Under diagonal load on cantilever extension, the 6-implants cases had a tendency to reduce displacement and to increase the reaction force of supporting point due to increasing the bendign stiffness of the prosthesis than 4-implants cases. 6. Under diagonal load on cantilever extension, the case of 10mm long cantilever was more stable than that of 20mm long cnatilever in respect of stress distribution and displacement. 7. When the ends of 10mm or 20mm long cantilever were loaded, the higher tensile stress was observed at the second most distal implant rather than the first most distal implant. 8. The 6-implants cases were more favorable about prevention of screw loosening under repeated loadings because 6-implants cases had smaller deformation and 4-implants cases had larger deformation.

• Journal of the Korean Geotechnical Society
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• v.21 no.3
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• pp.55-63
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• 2005

In this research, we have compared and analyzed the value driven from theoretical equation of Boussinesque, Westergaard, Newmark and K$\"{o}$ogler with our experimental value from the model test on the underground stress distribution condition. As a result of conducting the Model Test, a change in the underground stress according to the loading was proven to be very similar to the tendency shown in the theories of Westergaard. A tendency of increasing in a straight line was shown in the underground stress according to the increase of loading. When compared to that of the theoretical equation, underground stress values were great until the depth of 15cm. However, after that depth, a tendency of showing smaller value than that of the theoretical equation was shown. Correlations between Moving Repeated Load (or) and Underground Stress ($\Delta\sigma$) show $\Delta\sigma\;=\; 0.009\cdot{\sigma}r-0.1$(depth 60 cm).

• Journal of the Korean Society of Safety
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• v.21 no.2 s.74
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• pp.15-21
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• 2006

The railroad bogie's components experience repeated loading during service. Especially, oil damper bush has been fatigue fractured on the plane between rubber and steel stem during service, and which results in inferior of performance of the bogie. In this study, in order to offer a proper maintenance method of the bush, bubber bush used for the oil damper was fatigue tested and its damage fraction during service was estimated. Also, FEM analysis on the bush was conducted. When 1400, 1200, and 1000kgf of repeated loads were applied to the oil damper bush, final damage fraction exhibited 63.7%, 50% and 40%. From the results of FEM analysis, deformation energy density was found to be $0.5452kgf/mm^{2}$ at an applied load of 1400kgf and the location with maximum value coincided with the fractured location of the bush. Finally, it will be desirable to adopt the normalized damage fraction rather than absolute damage fraction in estimating remaining service lifetime of the bush.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.1
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• pp.91-96
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• 2012

The retract actuator makes the landing gear retract or extend during take-off and landing of an aircraft. To prevent folding of landing gear that has remained in the extended state because of an unexpected external disturbance, an internal locking device is applied to the retract actuator. The locking device is restrained with another internal component by oil pressure supplied to the retract actuator, and this restraint makes the locking of the actuator possible. Because locking and unlocking are repeated during retraction and extension of the landing gear, the locking device takes repeated identical loads, and the possibility of fatigue failure exists. In this study, the process and results of fatigue analysis for the locking device are presented, and the appropriateness of the analysis result is verified using a fatigue test.

• Journal of the Korean Geotechnical Society
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• v.24 no.6
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• pp.101-116
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• 2008

The use of reinforced earth walls id permanent structures is getting its popularity. Despite a number of advantages of reinforced earth walls over conventional concrete retaining walls, there exists concerns over long-term residual deformations when subjected to repeated and/or cyclic loads, during their service period. In this investigation, the effects of pre-loading in reducing long term residual deformation of reinforced soil structures under sustained and/or repeated loading environment are investigated using a series of reduced-scale model tests. A model pier and a back-to-back (BTB) reinforced soil structures were constructed and tested under various loading and backfilling conditions. The results indicate that the pre-loading technique can be an effective means of controlling residual deformations of reinforced soils under various loading conditions.

• Journal of Ocean Engineering and Technology
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• v.22 no.5
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• pp.87-93
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• 2008

The objective of this paper is the investigation of the statistical properties of Vickers hardness (HV) of friction welded parts in nickel based super resisting steel, alloy 718 steel. First, we examine the statistical properties on the case of as-welded parts. Several Virkers indentations were made under same nominal conditions. This was repeated for three different applied loads, 100, 200 and 300g with a duration time, 10 second. The arithmetic mean of Vickers hardness in base metal (BM) materials is larger than that of HAZ in all applied loads. The measure of dispersion, that is, the coefficient of variation (COV) for BM and HAZ is decreased by increasing with the applied load. The distribution of Vickers hardness was not found to be symmetric type. The probability distribution of Vickers hardness was well followed Weibull distribution. The shape parameter and the scale parameter (characteristic hardness) are increased by increasing with the applied load, as both BM and HAZ.

• Smart Structures and Systems
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• v.4 no.5
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• pp.605-628
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• 2008

In bridge structures, damage may induce an additional deflection which may naturally contain essential information about the damage. However, inverse mapping from the damage-induced deflection to the actual damage location and severity is generally complex, particularly for statically indeterminate systems. In this paper, a new load concept, called the positive-bending-inspection-load (PBIL) is proposed to construct a simple inverse mapping from the damage-induced deflection to the actual damage location. A PBIL for an inspection region is defined as a load or a system of loads which guarantees the bending moment to be positive in the inspection region. From the theoretical investigations, it was proven that the damage-induced chord-wise deflection (DI-CD) has the maximum value with the abrupt change in its slope at the damage location under a PBIL. Hence, a novel damage localization method is proposed based on the DI-CD under a PBIL. The procedure may be summarized as: (1) identification of the modal flexibility matrices from acceleration measurements, (2) design for a PBIL for an inspection region of interest in a structure, (3) calculation of the chord-wise deflections for the PBIL using the modal flexibility matrices, and (4) damage localization by finding the location with the maximum DI-CD with the abrupt change in its slope within the inspection region. Procedures from (2)-(4) can be repeated for several inspection regions to cover the whole structure complementarily. Numerical verification studies were carried out on a simply supported beam and a three-span continuous beam model. Experimental verification study was also carried out on a two-span continuous beam structure with a steel box-girder. It was found that the proposed method can identify the damage existence and damage location for small damage cases with narrow cuts at the bottom flange.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.6
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• pp.567-573
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• 2017

The drive shaft of passenger vehicle has an important role in transmitting the torque between the power train system and the wheels. Torsional fatigue failures occur generally in the connection parts of the spline edge of the drive shaft, when there is significant fatigue damage under repeated twisting loads. A heat treatment, an induction hardening process, has been adopted to increase the torsional strength as well as the fatigue life of the drive shaft. However, it is still unclear how the extension of the induction hardening process in a used material relates to its shear-strain fatigue life range. In this study, a shear-strain controlled torsional-fatigue test with a specially designed specimen was conducted by an electro-dynamic torsional fatigue test machine. A finite element analysis of the drive shaft was carried out using the results obtained by the fatigue experiment. The estimated fatigue life was verified through a twisting load test of the real drive shaft in a test rig.

• Physical Therapy Korea
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• v.5 no.1
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• pp.30-43
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• 1998

The purposes of this study were to examine the effect of two different pelvic alignments and the Valsalva maneuver on electromyographic (EMG) activity of the erector spinae during squat lifting and lowering, and to find an efficient method for squat lifting and lowering. Twenty hea1thy men in their twenties lifted and lowered loads using four different methods: 1) anterior pelvic tilt position with the Valsalva maneuver, 2) anterior pelvic tilt position without the Valsalva maneuver, 3) posterior pelvic tilt with the Valsalva maneuver, 4) posterior pelvic tilt without the Valsalva maneuver. The EMG activity of erector spinae was recorded during both lifting and lowering with each method. The EMG activity of each individual was normalized to EMG activity produced by muscle during maximal voluntary contraction. Two-way analysis of variance for repeated measures ($2{\times}2$) was used to analyze the effect of the two factors: 1) pelvic tilt position (anterior pelvic tilt, posterior pelvic tilt), 2) the Valsalva maneuver (with and without). Analysis was performed separately for the lifting and lowering. The results were as follows: 1) EMG activity of erector spinae was greater when the pelvis was tilted anteriorly than when the pelvis was tilted posteriorly during squat lifting and squat lowering. 2) There was no difference between EMG activity of erector spinae with the Valsalva maneuver and EMG activity of erector spinae without the Valsalva maneuver during squat lifting and squat lowering. These results suggest that the greater EMG activity of erector spinae with an anterior pelvic tilt position during squat lifting and squat lowering may ensure optimal muscular support for the spine while handling loads, but the Valsalva maneuver may have less effect on erector spinae.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.11
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• pp.1157-1162
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• 2011

The parking brake is an essential unit embedded in the track-driving motor of an excavator. The parking brake plays an important role in keeping the excavator in place not only when it is parked, but also during the digging operation. In fact, the load placed on the parking brake during the digging operation is significantly higher than the parking load, because the impact and rating loads caused by the bucket digging force cycle frequently and have very high load ranges. Therefore, the load conditions during the digging operation should be taken into account in the parking brake certification test. In this study, a series of experiments was carried out in which various operating pressures were applied to the parking brake, where repeated loads were reciprocally placed on the brake by locking the multifriction disc and releasing the hydraulic cylinder. The characteristics of the parking brake were investigated by comparing the obtained experimental results and the theoretical design specifications.