• Journal of Korea Foundry Society
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• v.21 no.4
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• pp.239-245
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• 2001

Microstructure and mechanical properties of Sn-3.1 wt.%Ag-6.9 wt.%Bi system solders on Cu-substrate were studied. The Sn3.1 wt.%Ag-6.9 wt.%Bi alloy was designed by phase diagram and chemical properties and was prepared by melting in argon atmosphere. The mechanical properties of solder/Cu joints were examined by shear strength test, and also creep test. The microstructure of Sn-3.1 wt.%Ag-6.9 wt.%Bi alloy consists of Bi-rich phase and $Ag_3Sn$ precipitate in {\beta}-Sn$ matrix phase. The shear strength of the joint was decreased with aging treatment. Crack path under shear test was through the solder. Similar crack path change mode was observed at the creep test of solder/Cu joint. The creep behavior of Sn-3.1 wt.%Ag-6.9 wt.%Bi alloy represented the inverse primary creep behavior at all test condition. It is suggested that the inverse primary creep behavior is induced from Bi solute atoms in Sn-matrix. The creep resistance of Sn-3.1Ag-6.9Bi alloy is better than that of Sn-3.5 wt.%Ag alloy at all test conditions.

• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.19-19
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• 1991

Fracture of Al2O3 tubes for different loading path under combined tension/torsion was investigated. Macroscopic directions of crack propagation agreed well with the maximum principal stress criterion, independent of the loading path. However, fracture strength from the proportional loading test(τ/σ= constant) showed either strengthening or weakening compared to that from uniaxial tension, depending on the ratio τ/σ. The Weibull theory was capable to predict the strengthening of fracture strength in pure torsion, but not the weakening in the proportional loading condition. The strengthening or weakening of fracture strength in the proportional loading condition was explained by the effect of shear stresses in the plane of randomly oriented microdefects. Finally, a new empirical fracture criterion was proposed. This criterion is based on a mixed mode fracture criterion and experimental data for fracture of Al2O3 tubes under combined tension/torsion. The proposed fracture criterion agreed well with experimental data for both macroscopic directions of crack propagation and fracture strengths.

• Journal of the Korean Society for Railway
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• v.14 no.2
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• pp.109-115
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• 2011

The shoe brake of the KTX is used in low speed when the electric brake is not effective. The main purpose of the shoe brake is to stop the train to a desired stop point at the station. Lots of defects have been encountered in the shoe brake unit since the KTX started its operation. To improve the reliability of shoe brake unit of the KTX power car, first of all, failure modes of the KTX shoe brake unit were analyzed. Main failure modes are cracks in the shoe friction material and fracture in the welded joints of the shoe backing steel structure. Several methods to remove the defects of the shoe brake unit were proposed and on-board tests were carried out: Increase of the strength of the shoe key and shoe cam, which decreased a little the occurrence of cracks in the shoe friction material; Redesign of the shoe backing steel structure, which eliminated the occurrence of the cracks in the backing plate but could not solve completely the crack problem in the shoe friction material; Development of a new friction material, which with redesign of the shoe backing steel structure could solve satisfactorily the crack problem in the shoe friction material.

• Geomechanics and Engineering
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• v.18 no.4
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• pp.449-457
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• 2019

Physical model tests were first performed to investigate the failure pattern of multiple pillar-roof support system. It was observed in the physical model tests, pillars were design with the same mechanical parameters in model #1, cracking occurred simultaneously in panel pillars and the roof above barrier pillars. When pillars 2 to 5 lost bearing capacity, collapse of the roof supported by those pillars occurred. Physical model #2 was design with a relatively weaker pillar (pillar 3) among six pillars. It was found that the whole pillar-roof system was divided into two independent systems by a roof crack, and two pillars collapse and roof subsidence events occurred during the loading process, the first failure event was induced by the pillars failure, and the second was caused by the roof crack. Then, for a multiple pillar-roof support system, three types of failure patterns were analysed based on the condition of pillar and roof. It can be concluded that any failure of a bearing component would cause a subsidence event. However, the barrier pillar could bear the transferred load during the stress redistribution process, mitigating the propagation of collapse or cutting the roof to insulate the collapse area. Importantly, some effective methods were suggested to decrease the risk of catastrophic collapse, and the deep-hole-blasting was employed to improve the stability of the pillar and roof support system in a room and pillar mine.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3D
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• pp.445-451
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• 2006

This study was conducted to develop the interlayer mixture that absorbs the stress between the old concrete pavement and the asphalt overlay pavement layer. The elasticity, the flexibility, the consistency and the impermeability is required for high-elastic Stress Absorbing Interlayer(HSAI) to absorb and disperse the stress that causes the flexural and horizontal movements of the joint and the crack. The HSAI developed from foreign product was satisfied with the design criteria. The specimens using the HSAI showed the significant reduction of the reflective crack compared those not using the HSAI. The significance included that the life of shear failure and horizontal displacement resistance increased 4 times. The life of the share failure increased to 5 times and the horizontal displacement increased to 9 times according to the selection of surface course material which showed the excellence of the HSAI.

• Structural Engineering and Mechanics
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• v.90 no.4
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• pp.371-390
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• 2024

Investigating the impact of openings on the structural behavior of ferrocement I-beams with two distinct types of reinforcing metallic and non-metallic meshes is the primary goal of the current study. Up until failure, eight 250x200x2200 mm reinforced concrete I-beams were tested under flexural loadings. Depending on the kind of meshes used for reinforcement, the beams are split into two series. A control I-beam with no openings and three beams with one, two, and three openings, respectively, are found in each series. The two series are reinforced with three layers of welded steel meshes and two layers of tensar meshes, respectively, in order to maintain a constant reinforcement ratio. Structural parameters of investigated beams, including first crack, ultimate load, deflection, ductility index, energy absorption, strain characteristics, crack pattern, and failure mode were reported. The number of mesh layers, the volume fraction of reinforcement, and the kind of reinforcing materials are the primary factors that vary. This article presents the outcomes of a study that examined the experimental and numerical performance of ferrocement reinforced concrete I-beams with and without openings reinforced with welded steel mesh and tensar mesh separately. Utilizing ANSYS-16.0 software, nonlinear finite element analysis (NLFEA) was applied to illustrate how composite RC I-beams with openings behaved. In addition, a parametric study is conducted to explore the variables that can most significantly impact the mechanical behavior of the proposed model, such as the number of openings. The FE simulations produced an acceptable degree of experimental value estimation, as demonstrated by the obtained experimental and numerical results. It is also noteworthy to demonstrate that the strength gained by specimens without openings reinforced with tensar meshes was, on average, 22% less than that of specimens reinforced with welded steel meshes. For specimens with openings, this value is become on average 10%.

• Magazine of the Korea Concrete Institute
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• v.7 no.6
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• pp.233-241
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• 1995

In this thesis, the fatigue tests were performed on a series of R /C beams repaired with co& crete-lmlyrner composites to investigate the fatigue bahavior. The three point loading system is used in the fatigue tests. In these tests, relations between the repeated loading cycles and mid-span deflections, number of repeated loading cycles when repaired beams were fractured, the bonding performance of repair materials were observed. On this basis, the mid-span deflections, the crack growth and failure mode of repaired R /C beams were studied. A S-N curve was drawn to present the fatigue strength of repaired beams. From the test results, it was shown that behavior of R /C beams repaired with polymer-cement series were very sirnillar to control beam about bonding performance, mid-span deflections and fatigue strength according to S-N curve drawn by the regression anlysis on the fatigue test results.

• Korean Journal of Construction Engineering and Management
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• v.5 no.6 s.22
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• pp.212-217
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• 2004

Carbon fiber reinforced plastic(CFRP) plate Is one of the alterative materials for soengthening of reinforced and prestressed connote members due to excellent strength and light weight In this paper, the behavior of beams strengthened with CFRP plate and CFS(Carbon fiber sheet) is observed and analyzed from the test results. Especially specimens with thick plate is tested when large moment and large shear lone appear in same position. The main failure mode is a peeling-off of the CFRP plate near the loading points due to flexural-shear crack, Because of this failure mode, failure load is not linearly proportional to the thickness of CFRP plates. When beam is wrapped with CFS around oかy loading point it does not influence on the failure loads. Depending on the loading pattern, it is necessary to consider different design criteria for reinforced concrete members with external reinforcement. When line moment and large shear force appear in same location, maximum thickness may limit to 0.6mm and ratio between moment of strengthened beam and moment of unstrengthened beam is proposed 1.5-2.0. In order to use the plate of thicker than 6mm, CFS may be extended to the location which moment of strengthened beam is 1.5 times than moment of unstrengthened beam.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.16-23
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• 2016

DFRCC (ductile fiber reinforced cementitious composites), which are a significantly improved ductile material compared to conventional concrete, were evaluated as a new construction material with a high potential applications to concrete structures for a range of purposes. In this study, experiments on the failure behavior of composite beams with a DFRCC and FRP (fiber reinforced polymer) plank with a rib used as permanent formwork and tensile reinforcement were carried out. A normal concrete and a fiber reinforced concrete with PVA series of RF4000 and the PP series of PP-macro were used for comparison, and each RF4000+RSC15 and PP-macro+RSC15 was tested by producing composite beams. The experimental results of the FRP plank without a sand coating showed that sliding failure mode between the FRP plank and concrete started from a flexural crack at the beam center; therefore it is necessary for the FRP plank to be coated with sand and the effect of the fiber to failure mode did not appear to be huge. The experiment of the FRP plank with a sand coating showed that both 1200mm and 2000mm allowed sufficient bonding between the concrete and FRP plank. The maximum load of the fiber reinforced concrete was higher than that of normal concrete and the case which a series of PP fiber was mixed showed the highest value. The crack latency caused by the fibers led to composite action with a FRP rib.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.565-571
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• 2016

This paper investigates macro- and microscopic fractography performed on fracture specimens from low cycle fatigue (LCF) testings through an Alloy 617 base metal and weldments. The weldment specimens were taken from gas tungsten arc welding (GTAW) pad of Alloy 617. The aim of the present study is to investigate the macro- and microscopic aspects of the low cycle fatigue fracture mode and mechanism of Alloy 617 base metal and GTAWed weldment specimens. Fully axial total strain controlled fatigue tests were conducted at room temperature with total strain ranges of 0.6, 0.9, 1.2 and 1.5%. Macroscopic fracture surfaces of Alloy 617 base metal specimens showed a flat type normal to the fatigue loading direction, whereas the GTAWed weldment specimens were of a shear/star type. The fracture surfaces of both the base metal and weldment specimens revealed obvious fatigue striations at the crack propagation regime. In addition, the fatigue crack mechanism of the base metal showed a transgranular normal to fatigue loading direction; however, the GTAWed weldment specimens showed a transgranular at approximately $45^{\circ}$ to the fatigue loading direction.