• Journal of Welding and Joining
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• 제14권4호
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• pp.99-108
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• 1996

The microstructure and bond strength are examined on the SiC/SiC and SiC/mild steel joints brazed by the Ag-Ti based alloys with different Ti contents. In the SiC/SiC brazed joints, the thickness of the reaction layers at the bond interface and the Ti particles in the brazing alloy matrices increase with Ti contents. When Ti is added up to 9 at% in the brazing alloy. $Ti_3SiC_2$ phase in addition to TiC and $Ti_5Si_3$ phase is newly created at the bond interface and TiAg phase is produced from peritectic reaction in the brazing alloy matrix. In the SiC/mild steel joints brazed with different Ti contents, the microstructure at the bond interface and in the brazing alloy matrix near SiC varies similarly to the case of SiC/SiC brazed joints. But, in the brazing alloy matrix near the mild steel, Fe-Ti intermetallic compounds are produced and increased with Ti contents. The bond strengths of the SiC/SiC and SiC/mild steel brazed joints are independent on Ti contents in the brazing alloy. There are no large differences of the bond strength between SiC/SiC and SiC/mild steel brazed joints. In the SiC/mild steel brazed joints, Fe dissolved from the mild steel does not affect on the bond strength of the joints. Thermal contraction of the mild steel has nearly no effects on the bond strength due to the wide brazing gap of specimens used in the four-point bend test. The brazed joints has the average bond strength of about 200 MPa independently on Ti contents, Fe dissolution and joint type. Fracture in four-point bend test initiates at the interface between SiC and TiC reaction layer and propagates through SiC bulk. The adhesive strength between SiC and TiC reaction layer seems to mainly control the bond strength of the brazed joints.

• Structural Engineering and Mechanics
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• 제81권1호
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• pp.81-91
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• 2022

The effects of interaction between concrete-gypsum interface and edge crack on the failure behavior of the specimens in senicircular bend (SCB) test were studied in the laboratory and also simulated numerically using the discrete element method. Some quarter circular specimens of gypsum and concrete with 5 cm radii and hieghts were separately prepared. Then the semicircular testing specimens were made by attaching one gypsum and one concrete sample to one another using a special glue and one edge crack is produced (in the interface) by do not using the glue in that part of the interface. The tensile strengths of concrete and gypsum samples were separately measured as 2.2 MPa and 1.3 MPa, respectively. during all testing performances a constant loading rate of 0.005 mm/s were stablished. The proposed testing method showed that the mechanism of failure and fracture in the brittle materials were mostly governed by the dimensions and number of discontinuities. The fracture toughnesses of the SCB samples were related to the fracture patterns during the failure processes of these specimens. The tensile behaviour of edge notch was related to the number of induced tensile cracks which were increased by decreasing the joint length. The fracture toughness of samples was constant by increasing the joint length. The failure process and fracture pattern in the notched semi-circular bending specimens were similar for both methods used in this study (i.e., the laboratory tests and the simulation procedure using the particle flow code (PFC2D)).

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.1667-1673
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• 2011

For performance evaluation of modified wide sleepers(MF-140 PSC sleepers), design moment for urban transit was calculated and then performance evaluation criteria were set up according to EN 13230-2. Next, static bend tests, dynamic tests at rail seat section of sleeper were carried out and static bend tests at center section of sleeper were fulfilled. The test results for modified wide sleepers were in excess of performance evaluation criteria and structural safety of sleepers was able to guaranteed from the results. As modifying depth of wide sleepers, construction convenience in underground will be expected to be improved and construction costs will be expected to be decreased.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1696-1701
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• 2007

This paper presents a micro-mechanical model of ductile fracture for the API X65 steel using the Gurson-Tvergaard-Needleman (GTN) model. Experimental tests and FE damage simulations using the GTN model are performed for smooth and notched tensile bars, from which the parameters in the GTN model are calibrated. As application, the developed GTN model is applied to simulate small-sized, single-edge-cracked tensile and bend bars, via three-dimensional FE damage analyses. Comparison of FE damage analysis results with experimental test data shows overall good agreements.

• 터널과지하공간
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• 제2권2호
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• pp.251-264
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• 1992

In this study, the size effect in measuring the fracture toughness of rock was investigated using the ISRM Suggested Method for Fracture toughness using Chevron Bend Specimens. Total 58 specimens were prepared with 4 different diameters, 29, 42, 54, 68mm and center cut-chevron notch. In addition to this, to evaluated the effect of anisotropy of Jecheon granite, which is the sample for this study, core drilling direction was adjusted perpendicular(short transverse) and parallel(arrester) to the rift plane in the sample and the measured fracture toughness for each direction were compared. Important results obtained from this study are as follows. Level ll test condition is more adequate than l, because of low data scattering and precision and corrected fracture toughness of Jechoen granite measured and 2.2MPa{{{{ SQRT { m} }}}} for arrester direction with minimum initial crack length 0.7cm. From the relationship between core diameter and initial crack length presented in the ISRM testing method, the specimen diameter should be bigger than 47mm. The fracture toughnesses measured for arrester and short transverse directon show 10% difference. This is to the anisotropy of Jecheon granite possessing rift plane.

• Journal of Welding and Joining
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• 제13권1호
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• pp.89-102
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• 1995

The evaluation of reheat cracking susceptibility in CrMoV turbine rotor steel was performed using thermally simulated heat affected zones. The examinations were carried out in terms of microstructural characterization, microhardness measurement and a Charpy type notch opening three point bend test. It was found that reheat cracking susceptibility increased as the peak temperature increased. This effect was due to the combined effects of the carbide dissolution and unrestricted grain growth at 1350.deg. C peak temperature. Reheat cracking susceptibility was estimated based on microhardness measurement and prior austenite grain size. It was established that for this particular material, reheat cracking in coarse grained heat affected zone can be eliminated if the microhardness is below about 360DPH and the grain size is below about 30.mu.m. It is evident that reheat cracking susceptibility can be eliminated or reduced by carefully controlling the welding parameters such that a refined structure is produced in the coarse grained heat affected zone.

• 대한기계학회논문집A
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• 제22권2호
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• pp.416-427
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• 1998

Unidirectional commingled-yarn-based carbon fiber(CF)/polyamide(PA) 6 composite was fabricated under molding pressures of 0.4, 0.6 and 1.0 MPa to study its flexural deformation and fracture behavior. Fiber/matrix interfacial bonding area became larger with an increase of molding pressure from 0.4 to 0.6 MPa. For molding pressures .geq. 0.6 MPa, good flexural performance of similar magnitudes was attained. For the fracture test, four kinds of notch direction were adopted : edgewise notches parallel (L) and transverse (T) to the major direction of fiber bundles, and flatwise notches parallel(ZL) and perpendicular(ZT) to this direction. Nominal bend strength for L and ZL specimens exhibited high sensitivity to notching. ZL specimens revealed the lowest values of the critical stress intensity factor $K_c$ which was slightly superior to those of unfilled PA6 matrix. Enlargement of the compression area for T specimens was analyzed by means of the rigidity reduction resulting from the fracture occurrence.

• 콘크리트학회지
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• 제10권6호
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• pp.203-211
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• 1998

고체내부의 미소파괴시 발생하는 탄성파 방출을 이용하는 음향방출기법은 구조물 또는 재료 내부의 미시적 변형기구를 이해하는데 매우 유익한 수단으로 최근 각 분야에서 다양하게 응용되고 있다. 따라서 본 연구에서는 모르타르 부재의 휨재하 시험시 부재 내부에 발생하는 미시적 손상거동 및 파괴특성을 시험시 연속적으로 모니터링한 AE 신호특성으로부터 평가하였다. 나아가 삼각법을 이용한 2차원 AE 발생원 위치추정으로부터 시험체 노치선단 주변에 대한 AE 발생원 위치를 명확히 하였으며 이들 결과로부터 미소균열의 성장 거동을 연속적으로 모니터링 하였다.

• International Journal of Safety
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• 제11권1호
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• pp.22-25
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• 2012

Scoliosis can be biomechanically described as a three dimensional deformity of the spine, with deviations from the physiologic curves in the sagittal and frontal planes, usually combined with intervertebral rotation. Various factors are suspected such as genetic defects, uneven growth of the vertebrae, hormonal effects, abnormal muscular activity, postural problems, or a mix of some of these elements, but its initial cause is known in only 15-20% cases. The screening test for diagnosing scoliosis is called the Adams Forward Bend Test. During the experiment, the subjects were asked to bend over, with arms dangling, until a curve could be observed. The Scoliometer was placed on the back of the subjects and used to measure the difference between the left and right apex of the curve in the thoracic, thoracolumbar and lumbar area. Then, the subjects were asked to perform Maximum Voluntary Contractions (MVCs) using the digital back muscle dynamometer in three different postures: (1) 0o (sagittally symmetric); (2) 30o from the mid-sagittal plane (clockwise); and (3) 30o from the mid-sagittal plane (counterclockwise). In addition to the experimental data, subject-dependent variables including Body Mass Index (BMI), percentage of body fat and muscle mass of left/right arms and legs were employed to reveal the cause of difference among three MVC conditions. All those variables were tested using statistical methods.

• 한국주조공학회지
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• 제34권1호
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• pp.6-13
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• 2014

The mechanical properties of low-pressure die cast (LPDC) A356-T6 automotive road wheels are evaluated and correlated with their corresponding microstructures. In this study, two types of alloy wheels processed using different LPDC gating system are investigated. The yield stress, tensile stress, and elongation values tested at room temperature are correlated with the secondary dendrite arm spacing (SDAS) with respect to the gating system, and are also compared with similar studies. The SDAS and precipitates are examined using optical microscopy, scanning electron microscopy (SEM) and energy-dispersive spectroscopy. The phase information is also investigated using X-ray diffraction. Charpy impact tests are also performed from $-100^{\circ}C$ to $200^{\circ}C$, and the fracture surfaces are examined using SEM. The impact energy is demonstrated to increase with increasing temperatures without exhibiting specific transition behaviors as in other nonferrous alloys. The fracture toughness is also evaluated using three point bend test with single-edged bend specimens. The obtained fracture toughness values are in good agreement with those in similar studies.