• Journal of Powder Materials
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• 제25권3호
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• pp.246-250
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• 2018

In this study, we investigate the deformation behavior of $Hf_{44.5}Cu_{27}Ni_{13.5}Nb_5Al_{10}$ metallic glass powder under repeated compressive strain during mechanical milling. High-density (11.0 g/cc) Hf-based metallic glass powders are prepared using a gas atomization process. The relationship between the mechanical alloying time and microstructural change under phase transformation is evaluated for crystallization of the amorphous phase. Planetary mechanical milling is performed for 0, 40, or 90 h at 100 rpm. The amorphous structure of the Hf-based metallic glass powders during mechanical milling is analyzed using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Microstructural analysis of the Hf-based metallic glass powder deformed using mechanical milling reveals a layered structure with vein patterns at the fracture surface, which is observed in the fracture of bulk metallic glasses. We also study the crystallization behavior and the phase and microstructure transformations under isothermal heat treatment of the Hf-based metallic glass.

• Structural Engineering and Mechanics
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• 제66권5호
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• pp.569-582
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• 2018

Effects of crack separation, bridge area, on the tensile behaviour of concrete are studied experimentally and numerically through the Brazilian tensile test. The physical data obtained from the Brazilian tests are used to calibrate the two-dimensional particle flow code based on discrete element method (DEM). Then some specially designed Brazilian disc specimens containing two parallel cracks are used to perform the physical tests in the laboratory and numerically simulated to make the suitable numerical models to be tested. The experimental and numerical results of the Brazilian disc specimens are compared to conclude the validity and applicability of these models used in this research. Validation of the simulated models can be easily checked with the results of Brazilian tests performed on non-persistent cracked physical models. The Brazilian discs used in this work have a diameter of 54 mm and contain two parallel centred cracks ($90^{\circ}$ to the horizontal) loaded indirectly under the compressive line loading. The lengths of cracks are considered as; 10 mm, 20 mm, 30 mm and 40 mm, respectively. The visually observed failure process gained through numerical Brazilian tests are found to be very similar to those obtained through the experimental tests. The fracture patterns demonstrated by DEM simulations are mostly affected by the crack separation but the tensile strength of bridge area is related to the fracture pattern and failure mechanism of the testing samples. It has also been shown that when the crack lengths are less than 30 mm, the tensile cracks may initiate from the cracks tips and propagate parallel to loading direction till coalesce with the other cracks tips while when the cracks lengths are more than 30 mm, these tensile cracks may propagate through the intact concrete itself rather than that of the bridge area.

• Clinics in Shoulder and Elbow
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• 제20권4호
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• pp.222-229
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• 2017

Background: The purpose of this study was to investigate the outcomes after fixation using a 3.5-mm locking compression plate (LCP) hook plate for isolated greater tuberosity (GT) fractures of the proximal humerus. Methods: We evaluated the postoperative radiological and clinical outcomes in nine patients who were followed up at least 1 year with isolated GT fractures. Using the deltopectoral approach, we fixed the displaced GT fragments with a 3.5-mm LCP hook plate (Synthes, West Chester, PA, USA). Depending on the fracture patterns, the hook plate was fixed with or without augmentation using either tension suture or suture anchor fixation. Results: All the patient showed successful bone union. The mean time-to-union was 11 weeks. The radiological and clinical outcomes at the final follow-up were generally satisfactory. The mean visual analogue scale for pain, the University of California at Los Angeles score, the American Shoulder and Elbow Surgeons score, and the subjective shoulder value were 1.4, 30.3, 84.3, and 82.2%, respectively. The mean active forward flexion, abduction, external rotation, and internal rotation of the shoulder were $156.7^{\circ}$, $152.2^{\circ}$, $61.1^{\circ}$, and the 10th thoracic vertebral level, respectively. Only one patient presented with a postoperative complication of shoulder stiffness. The patient was treated through arthroscopic capsular release on the 5th postoperative month. Conclusions: We conclude that fixation using 3.5-mm LCP hook plates for isolated GT fractures of the proximal humerus is a useful treatment method that provides satisfactory clinical and radiological outcomes.

• Economic and Environmental Geology
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• 제3권4호
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• pp.199-222
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• 1970

One of the biggest sulfide metallic (Cu, Pb, Zn) ore deposits of South Korea is located in the area of Seo-myeon, Shiheung-gun, Gyeonggi-do. Geology of the region is mostly composed of metasediments of biotite schist, graphite schist, injection gneiss, sericite schist, limesilicate and quartzite from bottom, those are applicable to so-called Yeoncheon System of Pre-Cambrian, and granodiorite, quartz porphyry, basic dykes are outcroped in a small scope as intrusives. The origin of the ore deposit is pyrometasomatic contact deposits due to hydrothermal replacement and the ore bodies are imbedded in lower bed of limesilicate formation as impregnation and ore minerals are galena, sphalerite, marmatite, chalcopyrite, bornite, chalcocite, covellite, and the later two minerals are both hypogene and supergene. Gangue minerals are mostly skarn minerals those hornblende, diopside, epidote, hedenbergite, chlorite, garnet and quartz except primary calcite and quartz. Boundary plane (NS strike) between schists and limesilicate seemed to be primary opening of ore solution and fractures bearing $N50^{\circ}{\sim}80^{\circ}W$ are secondary structural control for localization of ore minerals and the third structural controls are both irregular gashes and schistosity in small scale. Photogeological study was carried with vertical aerial photo scaled 1: 38,000 and enlarged 1 : 10,000 under stereoscope. The study on the area convinced the fact that the geologic boundaries between rocks, limesilicates and quartzites, are traced easily by their typical topographic feature and drainage, and the main fracture patterns which derived from the result of fracture traces, that photogeologic lineament observed under stereoscope, are those bearing (1) $N20^{\circ}W$, (2) $N58^{\circ}W$, (3) $N76^{\circ}W$, (4) EW, (5) $N20^{\circ}W$, (6) $N62^{\circ}W$, (7) $N77^{\circ}W$. Among the written fractures, (5) (not schistosity, in case of fault) (6) (7) are post-mineral faults and others are pre-mineral faults and others are pre-mineral structures, and (2) (3) (6) (7) are coincided with statistical figure of 208 fractures surveyed in underground. By the result of the study, mineralized zone, are presumed to extend north and southward, total length about 4km.

• Journal of the Korean Society for Precision Engineering
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• 제22권2호
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• pp.164-171
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• 2005

This study aims to examine an effect of stacking sequence and curvature on the penetration characteristic of a composite laminated shell. For the purpose, we manufactured specimens with different stacking sequences and curvatures, and conducted a penetration test using an air-gun. To examine an influence according to stacking sequence, as flat plate and curvature specimen had more plies, their critical penetration energy was higher, Critical penetration energies of specimen A and C with less interfaces somewhat higher than those of B and D with more interfaces. The reason that with less interfaces, critical penetration energy was higher is pre-impact bending stiffness of composite laminated shell with less interfaces was lower than that of laminated shell with more interfaces, but bending stiffness after impact was higher. And it is because interface, the weakest part of the composite laminated shell, was influenced by transverse impact. As curvature increases, critical penetration energy increases linearly. It is because as curvature increases, resistance to in-plane deformation as well as bending deformation increases, which need higher critical penetration energy. Patterns of cracks caused by penetration of composite laminated shells include interlaminar crack, intralaminar crack, and laminar fracture. A 0$^{\circ}$ply laminar had a matrix crack, a 90$^{\circ}$ply laminar had intralaminar crack and laminar fracture, and interface between 0$^{\circ}$and 90$^{\circ}$laminar had a interlaminar crack. We examined crack length and delamination area through a penetration test. For the specimen A and C with 2 interface, the longest circumferential direction crack length and largest delamination area were observed on the first interface from the impact point. For the specimen B and D with 4 interface, the longest crack length and largest delamination area were observed on the third interface from the impact point.

• Journal of the Earthquake Engineering Society of Korea
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• 제10권1호
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• pp.25-32
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• 2006

In this study the seismic performance of welded steel moment connections to built-up box columns in the existing building built before 1994 Northridge earthquake was evaluated by cyclic tests. According to the test results, the pre-Northridge steel moment connections to the box columns also suffered from brittle fracture similar to that in the H-shaped column connections. However, the flange force transfer mechanism of the box column connections was substantially different from that of the H-shaped column connections, and the patterns of crack propagation may be changed due to the shape of the box column. Therefore, it is required to develop proper details for the box column connections instead of using the research results for H-shaped column connections in order to enhance the seismic performance the connections.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제35권3호
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• pp.292-296
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• 2022

(La_0.5Nd_0.2Sr_0.3)MnO₃ specimens were prepared by a solid-state reaction. In all specimens, X-ray diffraction patterns of an orthorhombic structure were shown. The fracture surfaces of (La_0.5Nd_0.2Sr_0.3)MnO₃ specimens showed a transgranular fracture pattern be possibly due to La ions (0.122 nm) as a perovskite A-site dopant substituting for Nd ions (0.115 nm) having a small ionic radius. The full-width at half maximum (FWHM) of the Mn 2p XPS spectra showed a value greater than that [8] of the single valence state, which is believed to be due to the overlapping of Mn²⁺, Mn³⁺, and Mn⁴⁺ ions. The dependence of Mn 2p spectra on the Mn³⁺/Mn⁴⁺ ratio according to sintering time was not observed. Electrical resistivity resulted in the minimum value of 100.7 Ω-cm for the specimen sintered for 9 hours. All specimens show a typical negative temperature coefficient of resistance (NTCR) characteristics. In the 9-hour sintered specimen, TCR, activation energy, and B25/65-value were -1.24%/℃, 0.19 eV, and 2,445 K, respectively.

• Journal of Technologic Dentistry
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• 제46권2호
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• pp.21-27
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• 2024

Purpose: This study aimed to analyze the stress distribution and deformation in implant abutments made from titanium (Ti-6Al-4V), zirconia, and polyetheretherketone (PEEK), including their screws and fixtures, under various loading conditions using finite element analysis (FEA). Methods: Three-dimensional models of the mandible with implant abutments were created using Siemens NX software (NX10.0.0.24, Siemens). FEA was conducted using Abaqus to simulate occlusal loads and assess stress distribution and deformation. Material properties such as Young's modulus and Poisson's ratio were assigned to each component based on literature and experimental data. Results: The FEA results revealed distinct stress distribution patterns among the materials. Titanium alloy abutments exhibited the highest stress resistance and the most uniform stress distribution, making them highly suitable for long-term stability. Zirconia abutments showed strong mechanical properties with higher stress concentration, indicating potential vulnerability to fracture despite their aesthetic advantages. PEEK abutments demonstrated the least stress resistance and higher deformation compared to other abutment materials, but offered superior shock absorption, though they posed a higher risk of mechanical failure under high load conditions. Conclusion: The study emphasizes the importance of selecting appropriate materials for dental implants. Titanium offers durability and uniform stress distribution, making it highly suitable for long-term stability. Zirconia provides aesthetic benefits but has a higher risk of fracture compared to titanium. PEEK excels in shock absorption but has a higher risk of mechanical failure compared to both titanium and zirconia. These insights can guide improved implant designs and material choices for various clinical needs.

• Geomechanics and Engineering
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• 제38권3호
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• pp.215-229
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• 2024

Because of the various patterns of deep-water inrush and complicated mechanisms, accurately predicting mine water inflows is always a difficult problem for coal mine geologists. In study presented in this paper, the water inrush channels were divided into four basic water diversion structures: aquifer, rock fracture zone, fracture zone and goaf. The fluid flow characteristics in each water-conducting structure were investigated by laboratory tests, and multistructure and multisystem coupling flow analysis models of different water-conducting structures were established to describe the entire water inrush process. Based on the research of the water inrush flow paths, the analysis model of different water inrush space structures was established and applied to the prediction of mine water inrush inflow. The results prove that the conduction sequence of different water-conducting structures and the changing rule of permeability caused by stress changes before and after the peak have important influences on the characteristics of mine water-gushing. Influenced by the differences in geological structure and combined with rock mass RQD and fault conductivity characteristics and other mine exploration data, the prediction of mine water inflow can be realized accurately. Taking the water transmitting path in the multistructure as the research object of water inrush, breaking through the limitation of traditional stratigraphic structure division, the prediction of water inflow and the estimation of potentially flooded area was realized, and water bursting intensity was predicted. It is of great significance in making reasonable emergency plans.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제13권2호
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• pp.747-754
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• 2012

The purpose of this study was to compare inter-regional accident modes using the National Hospital Discharge Patient Injury Survey. In order to determine economic status of each region, 234 cities and counties were categorized as 5 groups according to their financial self-reliance ratio. The main results are as follows. First, transport accidents had increased by the age group of 25 to 44 but decreased thereafter. Second, the frequency of car accidents was the highest among several types of transport accidents. Most common site of transport accidents was roads and highways. Third, there was significant difference in the modes of transport accident among regions. Fourth, emergency admission rate was quite different according to regional groups but it was no significant difference by economic status. Lastly, there was significant difference in injury patterns by region groups. In regions which were high economic status, there were relatively less serious injury patterns such as sprain, strain, dislocation while regions which were in low economic status had experienced serious injury including fracture, stab wound, and open fracture. We could find the difference in accident modes by regional economic status. Therefore, health authority should consider different accident prevention strategies by regional groups.