• Tunnel and Underground Space
• /
• v.10 no.3
• /
• pp.447-456
• /
• 2000

Rock bridge in rock masses can be considered as one of several types of opening-mode fractures, and also it has been known to have a great influence on the stability of structures in rock mass. In the beginning of researching a rock bridge it used to be studied only in characteristics of its behavior, as considering resistance of material itself. However the distribution pattern of rock bridges, which can affect the stability of rock structures, is currently researched with a fracture mechanical approach in numerical studies. For investigating the effect of rock bridges on the development pattern of hydraulic fractures, the author analyzed numerically the stress state transition in rock bridges and their phenomena with a different pattern of the rock bridge distributions. From the numerical studies, a two-crack configuration could be defined to be representative of the most critical conditions for rock bridges, only when cracks are systematic and same in their length and angle. Moreover, coalescence stresses and onset of propagation stresses could be known to increase with decreasing s/L ratio or increasing d/L ratio. The effect of pre-existing crack on hydraulic fracturing was studied also in numerical models. Different to the simple hydraulic fracturing modeling in which the fractures propagated exactly parallel to the maximum remote stress, the hydraulic fractures with pre-existing cracks did not propagate parallel to the maximum remote stress direction. These are representative of the tendency to change the hydraulic fractures direction because of the existence of pre-existing crack. Therefore s/L, d/L ratios will be identical as a function effective on hydraulic fractures propagation, that is, the K$_1$ value increase with decreasing s/L ratio or increasing d/L ratio and its magnification from onset to propagation increases with decreasing s/L ratio. The scanline is a commonly used method to estimate the fracture distribution on outcrops. The data obtained from the scanline method can be applied to the evaluation of stress field in rock mass.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.25 no.2
• /
• pp.87-104
• /
• 1989

Recently, with the tendency of more lightening, high-strength and high-speed in the marine industries such as marine structures, ships and chemical plants, the use of the aluminium Alloy is rapidly enlarge and there occurs much interest in the study of corrosion fatigue crack characteristics. In this paper, the initiation of surface crack and the propagation characteristics on the base metal and weld zone of 5086-H116 Aluminium Alloy Plate which is one of the Al-Mg serious alloy(A5000serious) used most when building the special vessels, were investigated by the plane bending corrosion fatigue under the environments of marine, air and applying cathodic protection. The effects of various specific resistances on the initiation, propagation behavior of corrosion fatigue crack and corrosion fatigue life in the base metal and heat affected zone were examined and its corrosion sensitivity was quantitatively obtained. The effects of corrosion on the crack depth in relation to the uniform surface crack length were also investigated. Also, the structural, mechanical and electro-chemical characteristics of the metal at the weld zone were inspected to verify the reasons of crack propagation behavior in the corrosion fatigue fracture. In addition, the effect of cathodic protection in the fracture surface of weld zone was examined fractographically by Scanning Electron Microscope(S.E.M.). The main results obtained are as follows; (1) The initial corrosion fatigue crack sensitibity under specific resistance of 25Ω.cm% show 2.22 in the base metal and 19.6 in the HEZ, and the sensitivity decreases as specific resistance increases (2) By removing reinforcement of weldment, the initiation and propagation of corrosion crack in the HAZ are delayed, and corrosion fatigue life increases. (3) As specific resistance decreases, the sensitivity difference of corrosion fatigue life in the base metal and HAZ is more susceptible than that of intial corrosion fatigue crack. (4) Experimental constant, m(Paris' rule) in the marine environment is in the range of about 3.69 to 4.26, and as specific resistance increases, thje magnitude of experimental constant, also increases and the effect by corrosion decreases. (5) Comparing surface crack length with crack depth, the crack depth toward the thickness of specimen in air is more deeply propagated than that in corrosion environment. (6) The propagation particulars of corrosion fatigue crack for HAZ under initial stress intensity factor range of $\Delta$k sub(li) =27.2kgf.mm super(-3/2) and stress ratio of R=0 shows the retardative phenomenon of crack propagation by the plastic deformation at crack tip. (7) Number of stress cycles to corrosion fatigue crack initiation of the base metal and the welding heat affected zone are delayed by the cathodic protection under the natural sea water. The cathodic protection effect for corrosion fatigue crack initiation is eminent when the protection potential is -1100 mV(SCE). (8) When the protection potential E=-1100 mV(SCE), the corrosion fatigue crack propagation of welding heat affected zone is more rapid than that of the case without protection, because of the microfissure caused by welding heat cycle.

• Journal of the Korean Ceramic Society
• /
• v.39 no.10
• /
• pp.994-1000
• /
• 2002

Oxygen permeability and the mechanical properties of mixed ionic-electronic conductive $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_{3-{\delta}}$ perovskite-type membrane, fabricated by solid state reaction, were investigated with regard to microstructure. The microstructure of the membrane was controlled by changing the sintering temperature and holding time. The average grain size and relative density were evaluated as a function of sintering conditions. As the fraction of grain boundary decreased, oxygen permeability showed a tendency to increase. Especially the maximum oxygen flux of 0.37 ml/$cm^2$${\cdot}$min was measured for the specimen sintered at 1300${\circ}C$ for 10 h, which has high density and relatively large grain size. Fracture strength was dependent on the relative density of sintered body, while fracture toughness increased with average grain size.

• Journal of Korean Foot and Ankle Society
• /
• v.5 no.2
• /
• pp.112-119
• /
• 2001

Purpose: The purpose of this study is to analyze the clinical prognostic factors which may affect the postoperative clinical results of the unstable ankle fractures. Materials and Methods: This study is based on 62 unstable ankle fractures treated by open reduction and internal fixation from May 1994 to June 2000, with a minimum follow-up period of 12 months(range: 13 months-7 years 3 months). The 62 patients were average 39.1 years old with male: female ratio of 41:21. Based on Lauge-Hansen classification, the supination-external rotation type was the most common with 36 (58.1%) cases. The clinical results was assessed by American Orthopaedic Foot and Ankle Society(AOFAS) functional scale. The sex, age, body weight, trauma-operation interval, operation time, cause of injury, fracture type were statistically analyzed as the possible postoperative clinical prognostic factors. Results: Postoperative AOFAS functional scale was average 82.1 points with 22(35.5 %) cases excellent, 12(19.4%) good. 16(25.8%) fair and 12(19.4%) cases poor results. The age and the operation time were found to be statistically significant factors affecting the prognosis(p<0.001). The sex, weight, trauma-operation interval factors did not significantly affect the clinical results. The pronation-external rotation type showed better clinical tendency among the fracture types, but without the statistical significance. Conclusion: The surgically treated unstable ankle fractures in patients whose age was above 41 years old or operation time exceeding 90 minutes showed significantly poor clinical results.

• Journal of Korean Neurosurgical Society
• /
• v.43 no.6
• /
• pp.288-293
• /
• 2008

Objective : Bone cement leakage is a well-known potential complication of percutaneous vertebroplasty (PVP) in patients with osteoporotic compression fracture. Even though there has been a controversy in the efficacy of antecedent venography to prevent this complication, many authors have performed intra osseous venography before bone cement injection. The goal of this study was to classify the venous drainage patterns of spine before PVP, and compare their patterns at different vertebral levels. Methods : The authors retrospectively reviewed 1,042 intraosseous venographic patterns in 321 patients with 574 osteoporotic compression fractures during six-year period in one institution. To classify venogram patterns, we selected simple lateral X-ray of spine taken immediately after injection of the contrast dye. We classified the venography patterns according to contrast leakage pattern and leakage direction as follows; trabecular (TR), trabecular anterior (TA), trabecular posterior (TP), trabecular anterior-posterior (TAP), trabecular lateral (TL), venous anterior(VA), venous posterior (VP), venous anterior-posterior (VAP), soft tissue (ST). Also, we compared venogram patterns according to different spinal levels. Results : In overall, the most common pattern was TP type accounting for 37.4% (390/1042) of all intraosseous venograms. This is followed by TAP in 21.5%, TR 17.4%, TA 116%, TL 5.8%, ST 4.1%, VA 1.2%, VP 0.6%, and VAP 0.4% in descending order of frequency. According to the spinal level, TR and TAP types were most common in thoracic spine (T6-T10), TP type was most common in thoraco-Iumbar spine (T11-L2), and TP and TAP types were most common in lumbo-sacral spine (L3-S1). Contrast dye leakage to soft tissue such as psoas muscle or disc were detected in 43 (4.1%) venograms. Direct venous drainage without staining of vertebral body was found in 23 (2.2%) venograms. The 8.3% of thoracic venogram showed direct venous drainage. Thoracic level showed a more tendency of direct venous drainage than other spine levels (p<001). Conclusion : The authors propose a new classification system of intra osseous venography during PVP. The trabecular-posterior (TP) type is most common through all spine, and venous-filling (V) type was most frequent in thoracic spine. Further study would be necessary to elucidate the efficacy of this classification system to prevent bone cement leakage during PVP.

• Journal of the Microelectronics and Packaging Society
• /
• v.17 no.2
• /
• pp.41-47
• /
• 2010

The effect of PCB and BGA pad designs was investigated on the mechanical property of Pb-free solder joints. The mechanical property of solder joint was tested by three different test methods of drop impact tests, bending impact test, and high speed shear test. Two kinds of pad design such as NSMD (Non-Solder Mask Defined) and SMD (Solder Mask Defined) were applied with the OSP finished Pb-free solder (Sn-3.0Ag-0.5Cu, Sn-1.2Ag-0.5Cu). in the drop impact test and bending impact test, the characterized lifetime showed the same tendency, and SMD design showed better mechanical property of solder joint than NSMD regardless of test method, which was due to the different crack path. The fracture crack on SMD pad was propagated along the intermetallic compound (IMC) layer of solder joint, while the fracture crack on NSMD pad propagated through upper edge of land which shields pattern. In the high speed shear test, pad lift occurred on the solder joint of NSMD. SMD/SMD combination of pad design consequently illustrated the best mechanical property of BGA/PCB solder joint, followed by SMD/NSMD, NSMD/SMD, and NSMD/NSMD.

• Korean Journal of Materials Research
• /
• v.4 no.5
• /
• pp.524-534
• /
• 1994

The effects of transformation temperature and mechanical properties by thermal cycle of CuZnAl shape memory alloy with a small of misch metal and Zr contents were investigated. The addition of misch metal and Zr was very effective for reducing the grain size. After solution treatment, the specimens were post-quench aged or step quenched at $100^{\circ}C$ to $350^{\circ}C$ for variation of Rockwell hardness value. It was found that the Rockwell hareness value was very increased at $200^{\circ}C$ and $250^{\circ}C$. The fracture strength and ductility have been significantly increased with the increase of misch metal conten when tensile tested below $M_f$ temperature. Also, the fracture strength has been more increased in the case of post quench aging treatment than that of the as-quenching treatment. Aging of the $\beta$-phase decreases the $M_s$ temperature, but that of the martensite phase increases the $A_s$ temperature. The change in $A_s$ temperature with post-quench aging can be attributed to recovery of order in the $\beta$phase. The hystersis of transformation temperature ($A_s-M_s$) has an increasing tendency by thermal cycles.

• The Journal of Engineering Geology
• /
• v.6 no.2
• /
• pp.103-110
• /
• 1996

This study shows the variation of poisson's ratio according to stress for the Cretaceous sandstones and shale in the Euiseoung Subbasin. To make a mechanical experiment, samples prepared with 3.0 cm in diameter and 6.2 cm in length were used in testing stress and strain. Generally poisson's ratio has been considered as one of properties, but contrary to steel, the test result makes sure that poisson's ratio has functional relation to stress. I had used four methods to calculate poisson's ratio, Poisson's ratio shows considerable different results according to the calculating, method but it has similar tendency in an elastic limit. Poisson' s ratio increases rapidly and is distinguished clearly in internal fracture region according to the calculating method. Poisson's ratio of sandstone and shale is different from one another in low and high stress regimes,but it is linearly proportional to the stress in an elastic regimes, that is, ${\nu}_t={\;}{\nu}_0+P_{\sigma}({\nu}_0$:first stage Poisson's ratio, ${\nu}_t$:poisson's ratio, P: poisson's coefficient, $\sigma$:stress). Poisson's ratios of two kinds of rock samples show continuous variation from 0.1 to 0.21 in an elastic regime. The variation of poisson's ratio is much wider in an internal fracture regine. It varies from 0.22 to 0.45 in sandstone, which is out of elastic regime.

• The Journal of Korean Academy of Prosthodontics
• /
• v.39 no.1
• /
• pp.84-95
• /
• 2001

Titanium is widely used in dentistry for its low density, high strength, fatigue resistance, corrosion resistance, and biocompatibility. But it has a tendency of surface damage under circumstance of friction and impact for its low hardness of the surface. Coating is one of methods fir increasing surface hardness. Its effect is to improve surface physical characteristics without change of titanium. Diamond-like carbon and titanium nitride are known for its high hardness of the surface. So that this study was aimed at the wear test and the cytotoxicity test of the commercially pure titanium and Ti-6Al-4V alloy which were deposited by diamond-like carbon film or titanium nitride film to acertain improvement of the surface hardness and the biocompatibility. A disk (25mm diameter, 2mm thickness) was made of commercially pure titanium and Ti-6Al-4V alloy and these substrates were deposited by diamond-like carbon film or titanium nitride film. Diamond-like carbon film was deposited by the method of radiofrequency plasma assisted chemical vapor deposition and titanium nitride film was deposited by the method of reactive arc ion plating. Then these substrates were tested about wear characteristics by the pin-on-disk type wear tester in which ruby ball was used as a wear causer under the load of 32N, The fracture cycles were measured by rotating the substrates until their films were fractured. The wear volume was measured after 150 cycles and 3,000 cycles using surface profiler. The cytotoxicity test was peformed by the method of the MTT assay. The results were as follows : 1. In the results of the wear volume test, commercially pure titanium and titanium alloy which were coated by diamond-like carbon film or titanium nitride aim had higher resistance against wear than the substrates which were not coated by any films (P<0.05). 2. In the results of the fracture cycle test and the wear volume test, diamond-like carbon film had higher resistance against wear than titanium nitride film (P<0.05). 3. In both coatings of diamond-like carbon aim and titanium nitride film, Ti-6Al-4V alloy had higher resistance against wear than commercially pure titanium (P<0.05) 4. In the results of the cytotoxicity test, diamond-like carbon film and titanium nitride film had little cytotoxicity as like commercially pure titanium or Ti-6Al-4V alloy (P>0.05).

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.13 no.4
• /
• pp.176-181
• /
• 2003

Rapid densification of a SiC powder with additive 0.5 wt% $B_4$C was conducted by spark plasma sintering (SPS). The unique features of the process are the possibilities of using very fast heating rate and short holding time to obtain fully dense materials. The heating rate and applied pressure were kept to be $100^{\circ}C$/min and 40 MPa, while sintering temperature and soaking time varied to 1800, 1850, 1900 and $1950^{\circ}C$ and 10, 20 and 30 min, respectively. All of the SPS-sintered specimens at $1950^{\circ}C$ reached near-theoretical density. The XRD found that 3C-to-6H transformation at $1850^{\circ}C$. The microstructures of the rapidly densified SiC ceramics consisted of duplex microstructure with ultrafine equiaxed grains under 2 $\mu\textrm{m}$ and elongated grains of 0.5∼2 $\mu\textrm{m}$ wide, length 3∼10 $\mu\textrm{m}$. The biaxial strength increased with the increase of sintering time. Strength of 392.7 MPa was obtained with the fully densified specimen sintered at $1950^{\circ}C$ for 30 min, in agreement with the general tendency that strength increases with decreases pore. On the other hand, the fracture toughness shows the value of 2.17∼2.34 MPa$.$$m^{1/2}$ which might be due to the transgranular fracture mode.