Abstract: This paper presents design concepts of a reconfiguration mobile robot developed in
Hannam University and experimental results of position estimation by multiple sensors. In order to
achieve high reliability and mobility in maneuver, driving motors of the mobile robot are assembled
inside the wheels of the mobile robot, and the rhombus-shaped structure of the mobile robot with
four wheels yields as good adaptability to rough terrain as a six-wheel mobile robot. Since the
proposed mobile robot receives multiple sensor signals from odometers and an orientation sensor,
states related to position and orientation of the mobile robot are optimally calculated by the
extended Kalman filter. Experimental results show that tracking errors of the mobile robot can be
reduced remarkably by the optimal state observer.
Abstract: In this paper, transparent dynamic photoelastic experimental hybrid method for
propagating cracks in orthotropic material was developed. Using transparent dynamic photoelastic
experimental hybrid method, we can obtain stress intensity factor and separate the stress
components from only isochromatic fringe patterns without using isoclinics. When crack is
propagated with constant velocity, the contours of stresses components in the vicinity of crack tip in
orthotropic material are similar to those of isotropic material or orthotropic material with stationary
crack under the static load. Dynamic stress intensity factors are decreased as crack growth. It was
certified that the dynamic photoelastic experimental hybrid method was very useful for the analysis
of the dynamic fracture mechanics.
Abstract: In this research, conventional boronizing process (CB) and a new method of boronizing
process under compression load condition (LB) were conducted and compared in order to study the
effect of superplasticity on boronized substrate. Both processes were conducted on duplex stainless
steel (DSS) with two different microstructures; as-received DSS with coarse grain microstructure
(CDSS); and thermo-mechanically treated DSS with fine grain microstructure (FDSS) which can
show superplastic behavior at high temperatures. Both processes were conducted at duration of 6
hours and temperatures between 1123 and 1223 K. All of boronized specimens demonstrated thin,
smooth and compact morphology of boride layer. For CDSS, both CB and LB processes produced
about similar surface hardness values within the range of 1425 – 2330 HV. For FDSS, CB process
produced surface hardness between 1522 and 2601 HV, while under LB, the highest surface
hardness values in the range of 1659 - 2914 HV were obtained. The result shows that introduction
of load during boronizing has initiated superplastic deformation on FDSS thus accelerated diffusion
of boron atoms into surface which finally lead to significantly higher surface hardness.
Abstract: Tensile failure behavior of ceramic matrix composites (CMCs) was characterized with
nondestructive evaluation (NDE) techniques. Prior to the mechanical testing, infrared (IR)
thermography was employed to obtain thermal diffusivity maps for CMC specimens. IR
thermography also was used for quantitative analyses of the progressive damage and in-situ
monitoring of the damage during tensile tests, while ultrasonic (UT) C-scans were used to present
defect distributions of the composites. The thermal diffusivity map showed good consistency with
ultrasonic C-scan results of CMC specimens. In this investigation, qualitative relationship
between UT signatures and thermal diffusivity has been introduced, and the temperature changes of
CMC specimens during tensile test have been measured. Moreover, the correlation between NDE
results and fracture behavior of CMCs has been presented to understand tension fracture behavior of
Abstract: Fretting can be defined as the oscillatory motion with very small amplitudes, which
usually occur between two contacting surfaces. Fretting wear is the removal of material from
contacting surfaces through fretting action. This fretting wear, which occurs between cladding
tubes of nuclear fuel rod and grids, causes in damages the cladding tubes by flow induced
vibration in a nuclear reactor. In this paper the fretting wear tests were performed with two
types of cladding tubes and three types of supporting grids in water. Fretting wear tests were
done using various applied loads. From the results of fretting tests, the wear amounts of tube
materials can be predictable by obtaining the wear coefficient using the work rate model.
Depending on various normal load, tube materials, and supporting grid shapes, distinctively
different wear scar of fretting and stick-slip mechanism can occur.
Abstract: Dissimilar weld region located at the cooling tube of pump was damaged and failed.
We performed a root cause analysis using the Scanning Electron Microscopy (SEM) and Energy
Dispersive X-ray Spectroscopy for the fractured surface. Many internal defects were shown in the
fracture section. Root cause analysis shows that the failure is due to welding at higher temperature
over 1000. This was confirmed by high-temperature cracks observed with SEM. In this study
Failure scenario including initial crack generation, propagation of corrosion cracks and final failure,
has been constructed and verified.
Abstract: Fretting wear generated by flow induced vibration is one of the important degradation
mechanisms of steam generator tubes in the nuclear power plants. Understanding of tube wear
characteristics is very important to keep the integrity of the steam generator tubes to secure the
safety of the nuclear power plants. Experimental examination has been performed for the purpose of
investigating the impact fretting. Test material is alloy 690 tube and 409 stainless steel tube
supports. From the results of experiments, wear scar progression is investigated in the case of
impact-fretting wear test of steam generator tubes under plant operating conditions such as pressure
of 15MPa, high temperature of 290C and low dissolved oxygen. Hammer imprint that is actual
damaged wear pattern, has been observed on the worn surface. From investigation of wear scar
pattern, wear mechanism was initially the delamination wear due to cracking the hard oxide film
and finally transferred to the stable impact-fretting pattern.
Abstract: The experiments of the shielded charge initiated by the high speed half- prefabricated
steel fragment has been studied in this paper. The damage way of half- prefabricated steel fragment
to the shielded charge is hit, burning or detonation action. And the damage effect is structure
damage or function damage. The result shows that toward Comp. B explosive with 1.62g/cm3 dense
behind 6mm Q235 steel and of φ 200 mm×100mm size, the fragment’s critical detonation speed is
about 2 400~2 600m/s.
Abstract: Small Butterfly valve is specially designed for use in industry field and ship. The
important parts of butterfly valve are composed of disk, stem and body. But, like LNG ship, in
enviroment of low temperature, as working condition deteriorates, important of sealing more
increased. In this study, we examine sealing mechanism of butter valve on the base of FEM and
investigate sealing life by measurement. The finite element analysis was carried out to study the
effect of the seal ring shape on bi-directional sealing force of valve. The sealing mechanism was
evaluated by 2-dimensional model in order to save the analysis time. And these analyses used by
material non-linearity and contact element were implemented.
Abstract: Tubes in nuclear steam generators are held up by supports because the tubes are long and
slender. Fluid flows of high-pressure and high-temperature in the tubes cause oscillating motions
between tubes and supports. This is called as FIV (flow induced vibration), which causes fretting wear
in contact parts of tube-support. The fretting wear of tube-support can threaten the safety of nuclear
power plant. Therefore, a research about the fretting wear characteristics of tube-support is required.
This work is focused on fretting wear transitions from mild wear to severe wear of tube-support
materials by various loads and relative displacements. The transition is defined on the basis of the
changes in wear amount. To investigate the transition, the fretting wear tester was contrived to
prevent the reduction of relative displacement between tube and support by increasing the load. The
tube and support materials were Inconel 690 and 409 SS, respectively. The results show that the
transition of tube-support wear is caused by the changes of the dominant wear mechanism depending
on the applied load and the relative displacement.