• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.725-730
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• 1998

Recently, non-destructive tests are getting popular in evaluating concrete properties without braking specimens. Among several NDT methods, P-wave velocity measurement technique has been widely used to evaluate the stiffness and strength of concrete. The purpose of this study is to investigate factors influencing P-wave velocity measured by impact-resonant method and ultrasonic pulse velocity method, such as moisture content of concrete, existence and size of coarse aggregates, sensor and sampling rate. Test results show that rod-wave velocity measured by impact-resonant method and ultrasonic pulse velocity are significantly affected by the moisture content of concrete, i.e., the lower moisture content, the lower velocity. Moisture content influences rod-wave velocity stronger than ultrasonic pulse velocity. Rod-wave velocity is faster in concrete than in mortar and is also faster in concrete containing small size aggregates. Sensor and sampling rate have little influence on velocity.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.4
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• pp.108-112
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• 2007

This study analyzes the dynamic fracture phenomenon that aluminum rod impacts aluminum plate or rigid plate and deforms. The value of von-Mises stress in the instance that aluminum rod deforms on rigid plate after contact becomes 1.3 times as large as that in the instance of contact. On the contrary, the value of von-Mises stress in the instance that aluminum rod goes through aluminum plate after contact becomes 0.7 times as small as that in the instance of contact. The value of internal energy in the instance that aluminum rod contacts aluminum plate becomes 2.3 times as large as that in the instance that aluminum rod contacts rigid plate. But the value of kinetic energy in the instance that aluminum rod contacts aluminum plate becomes 0.9 times as small as that in the instance that aluminum rod contacts rigid plate. The value of internal energy in the instance that aluminum rod goes through aluminum plate after contact becomes 0.7 times as small as that in the instance that aluminum rod impacts rigid plate and deforms. And the value of sliding energy in the instance that aluminum rod contacts aluminum plate becomes 0.2 times as small as that in the instance that aluminum rod contacts rigid plate. The value of total energy in case that aluminum rod impacts aluminum plate becomes 0.9 times as small as that in the case that aluminum rod impacts rigid plate.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.5
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• pp.1562-1572
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• 1996

The rigid-plastic finite element formulation including the inertia force is derived and then the rigid-plastic finite elemnt program considering the inertia effect is developed. In order to consider the strain hardening, strain rate hardening and thermal softening effects which are frequentrly observed in high-velocity deformation phenomena, the Johnson-Cook constitutive odel is applied. The developed program is used to simulate two high-velocity deformation problemss ; rod impact test and hdigh-velocity compression precess. As a result of rod impact test simulation, it is found that the siulated result has a good agreement with the experimental observation. Through the high-velocity compression process simulation. it is also found that the accuracy of the simulated results is dependent upon the time increment size and mesh size.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.78-89
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• 1993

A new theory based on the modified momentum and energy conservation has been proposed in order to overcome the drawbacks included in previous theories which are used for the determination of dynamic yield stresses and the investigation of dynamic behavior of metals. Then the improvements suggested by the new theory have been manifested through the analysis of the error included in the measurement of deformed length and through the comparison between the new theory, existing theories, and experimental results performed by previous workers. Meanwhile rod impact test has been performed which uses a compressed- air system for the acceleration of flat-ended cylindrical free-cutting brass rods. From the geomtrical measurements of deformed length, the dynamic yield stress of free-cutting brass has determined.

• Nuclear Engineering and Technology
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• v.28 no.1
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• pp.17-26
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• 1996

The in-reactor fuel rod support conditions against the fretting wear-induced damage can be evaluated by residual spacer grid spring deflection or rod-to-grid gap. In order to evaluate the impact of fuel design parameters on the fretting wear-induced damage, a simulation methodology of the in-reactor fuel rod supporting conditions as a function of burnup has been developed and implemented in the GRIDFORCE program. The simulation methodology takes into account cladding creep rate, initial spring deflection, initial spring force, and spring force relaxation rate as the key fuel design parameters affecting the in-reactor fuel rod supporting conditions. Based on the parametric studies on these key parameters, it is found that the initial spring deflection, the spring force relaxation rate and cladding creepdown rate are in the order of the impact on the in-reactor fuel rod supporting conditions. Application of this simulation methodology to the fretting wear-induced failure experienced in a commercial plant indicates that this methodology can be utilized as an effective tool in evaluating the capability of newly developed cladding materials and/or new spacer grid designs against the fretting wear-induced damage.

• Nuclear Engineering and Technology
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• v.54 no.3
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• pp.803-810
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• 2022

The small modular liquid-metal fast reactor (SMFR) is an important component of advanced nuclear systems. SMFRs exhibit relatively low breeding capability and constraint space for control rod installation. Consequently, control rods are deeply inserted at beginning and are withdrawn gradually to compensate for large burnup reactivity loss in a long lifetime. This paper is committed to investigating the impact of control rod compensation operation on core neutronics characteristics. This paper presents a whole core fine depletion model of long lifetime SMFR using OpenMC and the influence of depletion chains is verified. Three control rod position schemes to simulate the compensation process are compared. The results show that the fine simulation of the control rod compensation process impacts significantly the fuel burnup distribution and absorber consumption. A control rod equivalent position scheme proposed in this work is an optimal option in the trade-off between computation time and accuracy. The control position is crucial for accurate power distribution and void feedback coefficients in SMFRs. The results in this paper also show that the pin level power distribution is important due to the heterogeneous distribution in SMFRs. The fuel burnup distribution at the end of core life impacts the worth of control rods.

• Journal of the Korea Concrete Institute
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• v.11 no.4
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• pp.157-167
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• 1999

Among several non-destructive testing methods, ultrasonic pulse velocity method and rebound index method have been widely used for the evaluation of concrete strength. However, such methods might not provide accurate estimated results since factors influencing the relationship between strength and either ultrasonic pulse velocity or rebound index are not considered. In this paper, the evaluation method of concrete strength using rod-wave velocity measured by impact-resonance method is proposed. A basic equation is obtained by the linear regression of velocity vs, strength data at specific age and then, aging factor is employed in the equation to consider the difference of the increasing rate between wave velocity and strength. Strengths predicted by the proposed equation agree well with test results. Furthermore, the combined method of rod-wave velocity and rebound index is proposed.

• Geomechanics and Engineering
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• v.28 no.1
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• pp.25-33
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• 2022

The energy transferred on drill rods by dynamic impact mainly determines the penetration depth for in-situ tests. In this study, the dynamic response and transferred energy of drill rods are determined from the frequency of the stress waves. AW-type drill rods of lengths 1 to 3 m are prepared, and strain gauges and an accelerometer are installed at the head and tip of the connected rods. The drill rods are hung on strings, allowing free vibration, and then impacted by a pendulum hammer with fixed potential energy. Increasing the rod length L increases the wave roundtrip time (2L/c, where c is the wave velocity), and hence the transferred energy at the rod head. At the rod tip, the first velocity peak is higher than the first force peak because a large and tensile stress wave is reflected, and the transferred energy converges to zero. The resonant frequency increases with rod length in the waveforms measured by the strain gauges, and fluctuates in the waveforms measured by the accelerometer. In addition, the dynamic response and transferred energy are perturbed when the cutoff frequency is lower than 2 kHz. This study implies that the resonant frequency should be considered for the interpretation of transferred energy on drill rods.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.55-60
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• 2011

For the bolster type bogie, bolster anchor body connections are proviede to transmit the longitudinal loads for traction or braking between the carbody and the truck. The bolster anchor body connection is generally composed of anchor rod bracket, anchor rod and its fastening devices. The bolster anchor body connection shall be basically capable of withstanding a longitudinal load resulting from excessive braking case or impact. Additionally the north America standard requires that the anchor rod bracket shall be frangible, I.e. the anchor rod bracket shall fail and fall away under load before the carbody structure is damaged since to protect the cabody structure in the event of unexpected accident. This paper describes the shear connection design using the optimized mechanical fasteners in the bolster anchor body connection to satisfy these Northe America requirements.

• Journal of the Korea Institute of Military Science and Technology
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• v.9 no.1 s.24
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• pp.127-134
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• 2006

The protection capability against an enhanced long rod(L/D=30) with yaw is investigated numerically and compared with that of shorter one(L/D=15). In addition details of interactions between yawed long rods and oblique plate velocity are examined. Through the simulation results, we find that dual flying plates system is more effective with longer rod due to the elongated disturbance. The protection performance is more effective for the penetrator with $+6^{\circ}$ of yaw angle than that with a yaw angle of $-6^{\circ}$.