• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.3
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• pp.37-42
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• 2010

Plastic region tightening is widely used in critical bolted joints in internal combustion engines in order to reduce the engine weight by maximizing the use of load-carrying capacity of bolt. Mechanical behavior of bolt tightened in plastic region under external axial tensile load is investigated for various friction conditions using three dimensional finite element analysis. The behavior of bolt tightened in elastic region as well as that in tensile test are investigated for comparison. Tightening process is simulated by rotating the bolt in order to examine the friction effect realistically. It is revealed that the bolt tightened in plastic region can carry more external load until the joint is opened, and yields at lower bolt load than the bolt tightened in elastic region. The friction coefficient has effect on the yield load, but not on the load-carrying capacity. Moreover, the scatter in the bolt preload due to friction begins with plastic deformation of bolt in the angle tightening control, whereas it begins with the onset of tightening in the torque tightening control. The observations are interpreted with the residual torsional stress in the bolt generated during the tightening.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.835-845
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• 1994

In this paper, the effects of the adhesive thickness and adherend roughness on the static and fatigue strengths of the adhesively bonded circular single lap joints has been investigated by an experimental method. The stacking sequence effect of the composite adherend on the static and fatigue strength and the fracture patterns of the adhesive failure were also observed. Since the circular single lap joint fails catastrophically beyond the static strength of fatigue limit, the tubular polygonal adhesively bonded joints such as triangular, tetragonal, pentagonal, hexagonal as well as elliptical joints were manufactured in order to give partial mechanical characteristics to the adhesively bonded tubular joints. These joints were tested both in static and fatigue modes. From the experimental investigations, it was found that the fatigue strength of the circular adhesively bonded joints was much dependent on the arithmetical average surface roughness of the adherends and the polygonal adhesively bonded joints had better fatigue strength characteristics than the circular adhesively bonded joints.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.7
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• pp.694-701
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• 2013

The gear-reduction units of Korean high-speed trains consist of a motor reduction unit, an axle gear box reduction unit, and a tripod joint shaft. A reduction gear unit is a gearbox used to reduce the rotational speed of the input shaft to a slower rotational speed on the output shaft. This reduction in output speed helps to increase torque. Defective reduction gear units in high-speed trains are caused by damage to the gear or by gear fatigue. To diagnose potential problems, it is important to know the vibration characteristics of the reduction gear units. In this study, we analyzed the vibration characteristics of reduction gears under various conditions. The test setup included a full-scale test rig to evaluate reduction gear under both normal and extreme operating conditions.

• Journal of Korean Society of Steel Construction
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• v.8 no.3 s.28
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• pp.139-150
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• 1996

H/T(High Tension) bolt is generally being used in joining the members of steel structure. It has some difficulties in management such as an adequate fastening force and a selection of proper instrument for fastening. T/S(Torque Shear Type High Tension) bolt which is more convenient and easier than H/T bolt in quality control has recently been developed. T/S bolts are produced and widely used these days in domestic, but those have not a detail regulation for their on. Those are only being used according to the specification for the H/T bolts. In this study, we tried to confirm the soundness of T/S bolts by the fatigue test of the modified specimens. First, we measured the reduction rate of the initial axial force with time at bolts. Second, we investigated the slip forces of bolts when the test specimen is loaded in tension. Third, we implemented the fatigue tests. During the test, we measured the variation of the axial forces of bolts under the cyclic loading. Finally, we compared and analyzed the fatigue behavior of H/T and T/S bolt, by S-N curve diagrams that are obtained in this study.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1461-1466
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• 2008

In the case of Posterior Cruciate Ligament (PCL), the most frequent mechanism is the dashboard injury, which is directly pressurized to the anterior of the proximal tibia in the state of the knee hyperflexion. The PCL associated ligament damage happens when the posterior injury, the varus, the valgus, the hyperextension and the severe vagus torque are out of the critical value of PCL. After the successful operation cases of Anterior Cruciate Ligament (ACL) reconstruction using the allograft were informed from 1986, a number of results kept over the maximum 10 years were reported. Unfortunately, PCL reconstruction are crowded the surgery techniques such as the graft, the tibia fixing method, the fixation device, the location of the femoral tunnel, the number of the graft bundles and PCL reconstruction to access to the stability of the normal joint is being developed. Therefore, this study is the basic research of these above facts. The current transtibial tunnel surgery using the cadaveric Achilles tendon grafts is chosen for the various PCL reconstruction. The initial extension of the Achilles tendon by the fixing device and its location under the cyclic loading, were observed.

• The Journal of Korean Physical Therapy
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• v.22 no.1
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• pp.1-7
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• 2010

Purpose: Stretching exercises are commonly used in conjunction with sports and rehabilitation. Weassessed the immediate effects of stretching on passive stiffness of the hamstring muscles and knee range of motion (ROM) using three stretching techniques. Methods: A total of 45 participants were recruited. Isokinetic equipment was used to measure the passive stiffness of hamstring muscles and an inclinometer was used to measure active and passive ROM of the knee joint pre and post stretching. Stiffness was then calculated based on the incline of the torque-angle relationship. The test conditions for Group I were $3{\times}30$ seconds of static stretches using the hamstring muscle, Group II were $3{\times}30$ seconds of static stretches using the hamstring muscle with ankle dorsiflexion, and Group IIII had $3{\times}30$ seconds of active stretching. Results: Group II had significantly higher excursion of active ROM and Group IIIhad significantly higher excursion of passive muscle stiffness. All of the groups had significantly higher active and passive ROM and significantly lower muscle stiffness after stretching. The participants showed no change in hamstring muscle stiffness on the following day. Conclusion: Stretching has significant acute effects on ROM and muscle stiffness and canbe used in warm-up protocols for reducing muscle stiffness before a variety of exercise programs.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.478-485
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• 2003

Today, although there have been high technical developments of a compressor in the respect of its capacity, it has been so hard to develop in the respect of vibration and noise because mechanical structure of it has originally numerous vibration and noise. However, if we can grasp the point of systematic phenomena of vibration and noise through the understanding of dynamic characteristics in mechanical equipment, it may be possible to consider countermeasures. In this study about a reciprocal compressor, the part of its machinery is modeled as rigid body, and the part of its spring is modeled as flexible body, and then they are analyzed by DADS. Each rigid body and spring are connected with joint torque of a motor is applied to shaft, and pressure is applied to a piston so that a compressor can be revolved. Based on this modeling, influence of a compressor's vibration is analyzed through changes of offset, connecting rod and crank radius In the case of weight balance, it I produced after re-design, and then changes of vibration of a compressor's inside are checked through experiments. These analysis data may help set measures of reducing vibration of a reciprocal compressor.

• The Journal of Korea Robotics Society
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• v.10 no.4
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• pp.179-185
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• 2015

The versatility of a human hand is what the researchers eager to mimic. As one of the attempt, the redundant degree of freedom in the human hand is considered. However, in the force domain the redundant joint causes a control issue. To solve this problem, the force control method for a redundant robotic hand which is similar to the human is proposed. First, the redundancy of the human hand is analyzed. Then, to resolve the redundancy in force domain, the artificial minimum energy point is specified and the restoring force is used to control the configuration of the finger other than the force in a null space. Finally, the method is verified experimentally with a commercial robot hand, called Allegro Hand with a force/torque sensor.

• Journal of the Korean Society of Industry Convergence
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• v.19 no.2
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• pp.88-94
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• 2016

In this paper, we describe a new approch to control method of a four joints-robot gripper for the purpose of parts assemblying. The robot gripper is specifically modeled by using a 3D CAD program (ANSYS), considering artificial grippers, and then the proposed control method is illustrated through the dynamic simulation tool (Adams). Each gripper finger is individually controlled to be located at the optimal positions where the maximal joint torque can be calculated. To verified the effectiveness of the proposed control method, we proposed two cases for the reference position of gripper. By comparing the control performance of two method, the performance of the proposed control method was verified.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.9
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• pp.1341-1349
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• 2001

In this paper, 3 D.O.F. actuator, which has three degrees of freedom in one joint, is proposed. The proposed 3 D.O.F. spherical actuator is composed of the rotor and atator. The upper plate of the stator supports the rotor and five electromagnets are located at the base of the stator. The rotor has two permanent magnets, and each rotational axis of the rotor gimbal system is supported by the bearing. To find out the governing equations for the torque generation, Coulombs law and Lorentz force with respect to magnetism is applied. As the experimental results, if the distance between electromagnet and permanent maget is far enough, the force between these magnets can be expressed from current of coils and z-axial distance. For the purpose of control 3 D.O.F. actuator, PID control law is applied. The experimental results are presented to show the validity of the proposed 3 D.O.F. actuator.