• Journal of the Korean Society for Nondestructive Testing
• /
• v.20 no.5
• /
• pp.381-389
• /
• 2000

Metal matrix composite(MMCs) have been rapidly becoming one of the strongest candidates for structural materials for high temperature application. It is well recognized that MMCs always experience at least one large cool-down from processing temperature before my significant applied service loading. Due to the large difference in thermal expansion coefficient between the fiber and matrix, large thermal residual stresses generally develop in composites. It was reported from many previous studies that the effects of thermal residual stress on mechanical properties and fracture behavior were much more complex and dramatic than conventional engineering materials. Therefore it is crucial to evaluate the effect of heat treatment which changes the characteristic of distribution of thermal residual stress in MMCs. Single fiber composite(SFC) test based on the balance in a micromechanical model is a quite convenient method to evaluate interfacial shear strength(IFSS) and the failure mode of composite. In this study the effect of heat treatment on IFSS and the microscopic failure mechanism of MMC is investigated by combining acoustic emission(AE) technique with SFC test. The characteristic of AE signal, IFSS and microscopic failure mechanism due to heat treatment condition is discussed.

• Journal of the Korean Society of Radiology
• /
• v.18 no.3
• /
• pp.309-315
• /
• 2024

The Study In order to obtain a Clear Image of fractures in Atlas and Axis of Cervical Spin, this Study obtained Images examined using a Cervical Spin Pantom and a Radiation device, and then Commissioned five Radiologists and three Orthopedic Regent Doctors for Subjective Psychological ROC (Receiver, Operation, Characteristic) Evaluation. As aRresult, the X-ray Tube was Tilted 15° toward the leg to Receive a high score of 29 Points during the Eamination, and the Objective Evaluation Signal-to-noise Ratio (SNR) was 6.032 points, which was high. In Addition, by Tilting the X-ray tube 10° toward the head, it received a high score of 33 points during the Examination, and a high score of 7.840 Points in the objective evaluation. And as a result of Subjectively and Objectively Statistically Evaluating the Examined Images, the Cronbach Alpha value was Calculated as 0.791. Since the Cronbach Alpha value was 0.7 or higher, the Reliability could be Evaluated as 'very good', and the significance probability (p) was Statistically Significant at 0.042 points.

• Journal of the Korea Concrete Institute
• /
• v.23 no.5
• /
• pp.675-682
• /
• 2011

Recently, in retrofit of RC structures using FRP (Fiber Reinforced Polymer), researches about Near-Surface-Mounted Rertofit (NSMR) method have been widely performed. In NSMR, FRP bar is normally inserted in the slit formed in the cover concrete and then bonded by using epoxy mortar. In this paper, the bond characteristic of NSMR using FRP plate instead of bar was studied experimentally. Fracture behavior is observed from bond test using the parameters of embedment length, shear key, and FRP plate layer. In addition, an equation to predict the splitting strength of NSMR using FRP is proposed using the test result. The results showed that when the longer embedment length and more layers of FRP are used, the higher bond strength is achieved. There was a good co-relationship between the test and calculated results using the proposed equation.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2003.10a
• /
• pp.138-144
• /
• 2003

Rencentely, the request for the light weight is more incresed in the area of industrial environment and machinery and consistent effort is needed to accomplish high strength of material for the direction of light weight. we got the following characteristic from crack growth test carried out in the range of stress ration of 0.1, 0.3 and 0.6 by means of opening mode displacement. At the content stress ratio, the threshold stress intensity factor crack range ${\Delta}K_{th}$in the early stage of fatigue crack growth (Region I) and dtress intensity factor range ${\Delta}K$ in the stable of fatigue crack growth (Region II) with an increase in ${\Delta}K$. Fatigue life shows more improvement in the Shot-peened material than in the Un-peening material. And compressive residual stress of surface on the Shot peening processed operate resistance force of fatigue. So we can obtain fallowings. (1) The fatigue crack growth rate on stage II is conspicuous with the size of compressive residual stress and is depend on Paris equation. (2) Although the maxium compressive residual stress is deeply and widely formed from surface, fatigue life does not improve than when maxium compressive residual stress is formed in surface. (3) The threshold stress intensity factor range is increased with increasing compressive residual stress.

• Journal of Biomedical Engineering Research
• /
• v.30 no.5
• /
• pp.444-451
• /
• 2009

Purpose: The aim of present study is to detect longitudinal alterations of mechanical characteristic determined by bone quality (microarchitecture and degree of mineralization) on femur trabecular bone due to metastatic bone tumor Materials and Methods: Each 6 female SD rats (12 weeks old, approximate 250g) were allocated in SHAM and TUMOR Group. W256 (Walker carcinosarcoma 256 malignant breast cancer cell) was injected into the right femur (intraosseous injection) in TUMOR Group, whereas 0.9% NaCl (saline solution) was injected in SHAM Group. The right hind limbs of all rats were scanned by in-vivo micro-CT to acquire structural parameters, bone mineral density, X-ray attenuation and bone mineralization distribution at 0 week and 4 weeks after surgery. Results: BMD, BV/TV and Tb.N of trabecular bone in TUMOR group were markedly decreased (26%, 11% and 23%) while those in SHAM group were significantly increased (34%, 48% and 11%) (p<0.05). BS/BV, Tb.Sp and SMI in TUMOR group were significantly increased (-16%, 38% and 2%) compared with those in SHAM group (-33%, 12% and -16%) (p<0.05). Additionally, bone mineralization in TUMOR group significantly decreased while those in SHAM group was significantly increased (p<0.05). Conclusion: It is identified that how much bone microarchitecture and mineralization are diminished due to the metastatic bone tumor. The results may be helpful to prediction of fracture risk by metastatic bone tumor.

• Journal of the Korean Society of Radiology
• /
• v.12 no.3
• /
• pp.397-402
• /
• 2018

The study best image for diagnosis of fracture, dislocation and unilateral degenerative arthritis of the Sacroiliac joint, this study was performed to obtain the best image of the joint space of the hip joint by giving angle change to the pelvis phantom and the x-ray tube. I received evaluation. The results of the Receiver Operating Characteristic that in the case of simple photographs for the detection of joint arthritis and degenerative arthritis in the prone position, the photograph taken in the prone position raises the buttocks of the opposite side of the test by $25^{\circ}{\sim}30^{\circ}$ and the x-ray tube is perpendicular to the sagittal plane passing 2.5 cm inward from the thorny vertebra In the lying position, lift the Sacroiliac joint of the test side by $25^{\circ}{\sim}30^{\circ}$, and take a $5^{\circ}$ angle of the x-ray tube angle toward the foot toward the center of the upper bruch spine from it will be helpful to diagnose arthritis. the center of the upper bruch spine to the side of the ankle joints in the transverse direction And posterior direction, it will be helpful to diagnose arthritis.

• Economic and Environmental Geology
• /
• v.32 no.3
• /
• pp.217-225
• /
• 1999

Nine cauldrons have been recognized in the PVD (Pusan- Taegu Volcano-tectonic Depression) zone covering an area of nearly 7,000 $km^{2}$. They form characteristic landscape features with various mountains in the southeastern Kyongsang basin. Economically important ore deposits are also developed either in the ring fracture zone or the central pluton within the resurgent cauldrons or in the marginal area of the PVD, suggesting that these cauldrons played a major role in the distribution of ore deposits in the southeastern Kyongsang basin. Furthermore, the cauldron subsidences were more frequent with the more felsic volcano-plutonic complex, possibly indicating that the amounts of water and volatile components also acted as a controlling factor to cause the caldera subsidence and to concentrate the ore-forming elements in economic concentrations. The review of the relationship and variations of ore mineralization and cauldron subsidence is rather sketchy, but it provides a skeleton to carry out more detailed and quantitative studies related to temporal and spatial relationships between each cauldron subsidence accompanying its own ore mineralization. In the southeastern Kyongsang basin, additional calderas and associated ore deposits undoubtedly can be discovered through future detailed studies. The concept that cauldron subsidence are an important control for the formation of ore deposits will appear to be vindicated.

• Journal of the Korean Society for Heat Treatment
• /
• v.19 no.1
• /
• pp.30-36
• /
• 2006

Fretting fatigue behavior of SCM420 steel commonly used in the automotive industry for structural applications was investigated in this study. In addition, the effect of bridge pad on the fretting fatigue test was evaluated from different pad materials and following conclusions were drawn. Simple fatigue limit of SCM 420 steel was determined to be 350 MPa while this value was 225 MPa and 285.5 MPa with SCM420H and with SM45C pad, respectively. Reduction in fatigue limit was, thus found to be 35.7% and 17.9% with SCM 420H pad and SM45C pad, respectively. Results of fracture surface observation revealed that typical striation pattern of fatigue failure existed as well as dimpled and cleavage frature appearance was found in final fractured region. From the EDS compositional analysis, test sample and pad part all had high signals for oxygen and iron, suggesting that worn particles might be iron oxide, although exact chemical composition has to be confirmed. Considerable reduction in fatigue life was apparent in SCM 420 steel under fretting fatigue against simple fatigue. Such reduced fatigue life by fretting damage should be considered as an important factor not only in the viewpoint of repairing but also inevitably in the design stage of structural components.

• Clinical and Experimental Pediatrics
• /
• v.46 no.4
• /
• pp.404-408
• /
• 2003

Shaken baby syndrome is a serious form of child abuse, mostly involving children younger than 2 years. It results from extreme rotational cranial acceleration induced by violent shaking. The characteristic injuries include subdural hemorrhage, retinal hemorrhage, and fracture of ribs or long bones. If physicians have no recognition of, or suspicion about, shaken baby syndrome, this syndome is difficult to diagnosis because of a lack of obvious external signs and failure of the abuser to admit his or her actions. In addition to the high mortality, 60% of survivors have significant long term neurologic and developmental abnormality. The authors experienced five cases of shaken baby syndrome presented with seizures or vomiting, without external signs of trauma. All of these cases had subdural hemorrhages, and four cases had retinal hemorrahges. In our follow up, two children were found to have sequelae such as quadriplegia, monoplegia, and developmental delay. We emphasize that early recognition and prompt treament are key to overall success of case management. The incidence of shaken baby syndrome can be reduced through public awareness and education of parents not to shake a babies.

• Journal of the Society of Naval Architects of Korea
• /
• v.41 no.6
• /
• pp.75-83
• /
• 2004

Ice rubble pieces broken by the bow impact load and side hull of an icebreaking vessel usually pass along the ship's bottom hull and may hit the propeller/rudder or other stern structures causing serious damage to ship's hull . Therefore it is important to estimate the size of broken ice pieces during the icebreaking process. The dynamic interaction process of icebreaker with infinite ice sheet is simplified as a wedge type beam of finite length supported by elastic foundation. The wedge type ice beam is leaded with vertical impact forces due to the inclined bow stem of icebreaking vessels. The numerical model provides locations of maximum dynamic bending moment where extreme tensile stress arises and also possible fracture occurs. The model can predict a failure length of broken ice sheet given design parameters. The results are compared to Nevel(1961)'s analytical solution for static load and observed pattern of ice sheet failure onboard an icebreaker. Also by comparing computed failure length with the characteristic length, the meaning of ice rubble sizes is discussed.