Dong Joon Oh

Development of 3-dimension controllable catheter to show the immediate response using both the thermoelectric module and the shape memory alloy (SMA)

Today, the highlighted actuators such a Shape Memory Alloy (hereafter, it is called SMA), will change greatly the next medical device market since their energy integration, lightness and simple structure are superior to those of the conventional electromechanical actuator. Especially, the reason why the SMA actuator system becomes the most important technique for the medical device market of the next generation is that the minimally invasive technique can be applied to the in-vivo lesion due to the superior flexibility of SMA actuator system such a hand. In spite of this advantage, the current SMA actuator is not widespread. The reason is that the non-linear dynamic characteristics of the SMA original hysteresis have not yet been solved. Therefore, to evaluate the thermoelectric characteristics of our developed thermoelectric module for our first basic study, we investigated the temperature variation by stage 1) according to the current increase of the consecutive current and 2) according to the countercurrent of the discontinuous static current.

Fatigue Crack Growth of Glass Fiber Reinforced Aluminum Alloy Laminate (Al/GFRP) According to the Micro Hole Location

The diverse studies on Al/GFRP laminates with the circular holes, therefore, have been carried out recently. The recent studies just focused on the behavior of the fatigue crack propagation and the delamination when the shape and the size of the notches were changed. Therefore, this study evaluated the location effect of the defects in the vicinity of the circular notch of the high strength monolithic aluminum and Al/GFRP laminates on the initiation life (Ni) of the fatigue cracks, the relationship between the crack length (a) and the fatigue life (N). In addition, the fatigue crack behavior of Al/GFRP laminates was studied when the fatigue loading and the interlaminar delamination took place at the same time during crack propagation. In conclusions, (1) for the monolithic aluminum, 10% of the failure life at θ2=30° was more increased than that at θ3=60°. (2) The crack length and the fatigue life behavior of Al/GFRP laminates according to the location of the artificial defect were different from those of the monolithic aluminum. Namely, the fatigue life of θ1=0° and θ2=30° were remarkably shorter than those of θ3=60° and θ4=90°.

Irradiation and Operating Temperature Effects on the Tensile Characteristics of CANDU Pressure Tube Material

To investigate the degradation of mechanical properties induced mainly by neutron irradiation and operating temperatures, tensile tests were conducted from room temperature to 300°C using irradiated and unirradiated Zr-2.5Nb pressure tube materials. The irradiated longitudinal and transverse specimens collected from the coolant inlet, middle and outlet parts of the tube which had been operated in the CANDU reactor and showed different operating temperatures and irradiation fluence. The different tensile behavior was characterized by the tensile loading direction in the unirradiated tube. The transverse specimen showed higher strength and lower elongation than those of the longitudinal one. The increased strength hardening and the decreased elongation embrittlement of the irradiated material were compared to those of the unirradiated one. While the tensile strength of the inlet was higher than that of the outlet, the elongation of the inlet was lower than that of outlet. Considering the operation condition, it was proposed that the operating temperature could be a more effective parameter than the irradiation fluence for long-time life. Through TEM observation, it was also found that while the a-type dislocation density was increased, the c-type dislocation was not changed in the irradiated material. The fact that the higher dislocation density was sequentially distributed over the inlet to the outlet parts was consistent with the distribution of the tensile strength.

Microstructure and mechanical property of irradiated Zr−2.5Nb pressure tube in Wolsong unit-1

With the aim of assessing the degradation of Zr−2.5Nb pressure tubes operating in the Wolsong unit-1 nuclear power plant, characterization tests are being conducted on irradiated Zr−2.5Nb tubes removed after 10-year operation. The examined tube had been exposed to temperatures ranging from 264 to 306°C and a neutron fluence of 8.9×1021 n/cm2 (E>1 MeV) at the maximum. Tensile tests were carried out at temperatures ranging from RT to 300°C. The density of a-type and c-type dislocations was examined on the irradiated Zr-2.5Nb tube using a transmission electron microscope. Neutron irradiation up to 8.9×1021 n/cm2 (E>1 MeV) yielded an increase in a-type dislocation density of the Zr−2.5Nb pressure tube to 7.5×1014 m−2, which was highest at the inlet of the tube exposed to the low temperature of 275°C. In contranst, the c-component dislocation density did not change with irradiation, keeping an initial dislocation density of 0.8×1014 m−2 over the whole length of the tube. As expected, the neutron irradiation increased mechanical strength by about 17–26% in the transverse direction and by 34–39% in the longitudinal direction compared to that of the unirradiated tube at 300°C. The change in the mechanical properties with irradiation is discussed in association with the microstructural change as a function of temperature and neutron fluence.

Biomechanical Approach of Radius of Curvature on the UHMWPE Core in Artificial Intervertebral Disc Using FE Analysis

The research of stress distributions and the structural deformation at the sliding core in artificial intervertebral disc under the dorsiflexion is becoming more significant. This research analyzes the finite element model of sliding core and evaluates the effect of radius of curvature and the friction coefficient at the sliding core on von-Mises stress and the contact pressure. New Models of the artificial intervertebral disc are suggested by the results of the sliding core is evaluated by the comparison of that of SB Charité III. Based on the above facts, the optimized radius curvature of the sliding core is also suggested.

Evaluation of Un-Cracking Delamination by Pseudo Crack Model (PCM) in FRMLs

If Fiber Reinforced Metal Laminates (FRMLs) were delaminated, the decrease of stiffness and fiber bridging effect would result in the sudden aggravation of fatigue characteristics. It was reported that the delamination of FRMLs resulted from the crack of Al alloy layers and that it depended on the crack growth. When FRMLs with circular holes was un-cracked but was delaminated, it was impossible to analyze them by conventional fracture parameters expressed as the function of cracks. Therefore, a new analytical model called Pseudo Crack Model (PCM) was suggested to compare the delaminations whether cracks were made or not. The relationship between the crack consumption rate (Ccrack) and the delamination consumption rate (Cdel) was discussed and it was also known that the effect of the Ccrack was larger than that of the Cdel.

The Effect of Defect Locations on the Stress Distribution and Crack Initiation in Monolithic Aluminum vs. GLARE Hybrid Composite

This paper investigates the effect of the defect location on the stress concentration, the stress distribution, and the crack initiation behavior when the defects were made in the vicinity of the circular hole in the monolithic aluminum and the glass fiber reinforced laminates (GLARE). As the defect location in the vicinity of the circular hole was changed from ° = 90 4 q to ° = 0 1 q , the stress concentration was increased. Generally, the stress concentration of GLARE was about 15% greater than that of the monolithic aluminum. When the defect was at ° = 30 2 q , Multi Site Damage (MSD) crack was found in the monolithic aluminum, but just the main cracks existed in GLARE. The delamination instead of MSD crack was made in GLARE, and it resulted in the prevention against the second crack initiation.

Influences of Fiber Orientation on the Progressive Damage in Glass Reinforced Hybrid Composite

The anisotropy of hybrid composite such as Al/GFRP laminates made it possible to control the fiber orientation according to the loading patterns. Therefore, it is important to study the fatigue and delamination behaviors of Al/GFRP laminates by fiber orientation. Al/GFRP laminates of three different fiber orientations (0°, 45°, 90°) were chosen, and the progressive delamination behavior was examined through the fatigue tests. The effects of the fiber orientation on the crack length, the fatigue life, the delamination, the crack growth rate (da/dN), and the stress intensity factor range ( ΔK) were investigated and discussed. The findings led to a conclusion that the effect of fiber orientation should not be ignored in analyzing the progressive damage of Al/GFRP laminates.

Evaluation of Eddy Current Inspection on the Defects of Unloading vs. Loading Conditions in the Fiber Reinforced Composite Materials

It had been impossible to inspect the Eddy Current (EC) since the Fiber Reinforced Composite Materials (FRCM) had the low electric conductivity of resin layer. However, it has been successful for our previous research to inspect the defect using the EC. In the case of loading to FRCM, the researches of relationship between the failure behavior and the variation of EC signals have not been carried out. Therefore, this research focused on the comparison and the evaluation of the EC signals according to the variation of the defect depth using the unloading and the radial-loading FRCM tube. We obtained results are as follow. Firstly, The EC signals similar to that of the unloading specimens could be obtained from the loading specimen of 80% defect. Secondly, Regardless of the unloading and the loading specimens, the defect of 100% and 80% depths had the similar phase angles and Lissajous figures. Finally, it was guessed that the length of micro-cracks distributed at the whole specimens under the loading was less than 60% of the specimen thickness.

Proposal of Pseudo Crack Model for the Un-Cracking Delamination Behavior of Fiber Reinforced Metal Laminates

If Fiber Reinforced Metal Laminates (FRMLs) were delaminated, the decrease of stiffness and fiber bridging effect would result in the sudden aggravation of fatigue characteristics. It was reported that the delamination of FRMLs resulted from the crack of Al alloy layers and that it depended on the crack growth. When FRMLs with circular holes was un-cracked but was delaminated, it was impossible to analyze them by conventional fracture parameters expressed as the function of cracks. Therefore, a new analytical model called Pseudo Crack Model (PCM) was suggested to compare the delaminations whether cracks were made or not. The relationship between the crack consumption rate (Ccrack) and the delamination consumption rate (Cdel) was discussed and it was also known that the effect of the Ccrack was larger than that of the Cdel.