• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.129-136
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• 2018

The estimation of the fatigue design life for large welded structures is usually performed using the liner cumulative damage method such as Palmgren-Miner rule or the equivalent damage method. When a fatigue crack is detected in a welded steel structure, the residual service life has to be estimated base on S-N curve method and liner elastic fracture mechanics. In this study, to examine the 3D fatigue crack behavior and estimate the fatigue life of out-of-plane gusset fillet welded joint, the fatigue tests were carried out on the model specimens. Investigations of three-dimensional fatigue crack propagation on gusset welded joint was used the finite element analysis of FEMAP with NX NASTRAN and FRANC3D. Fatigue crack growth analysis was carried out to demonstrate the effects of aspect ratio, initial crack length and stress ratio on out-of-plane gusset welded joints. In addition, the crack behaviors of fatigue tests were compared with those of the 3D crack propagation analysis in terms of changes in crack length and aspect ratio. From this analysis result, SIFs behaviors and crack propagation rate of gusset welded joint were shown to be similar fatigue test results and the fatigue life can also be predicted.

• Restorative Dentistry and Endodontics
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• v.22 no.2
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• pp.609-621
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• 1997

The purpose of this study was to evaluate the shear bond strength of three light-cured glass ionomer cements to blood contaminated bovine dentin. The materials used in this study were Fuji II LC, Dyract and Variglass VLC. The dentin conditioners were 10% polyacrylic acid, 10% maleic acid and 10% phosphoric acid. 180 lower anterior bovine teeth were selected in this study. The teeth were embedded in acrylic resin and were grounded with 320 to 600 grit silicon carbide paper to create a flat dentin surface. The teeth were divided into SIX groups. The experimental procedures in six groups were as follows; Group l(GF) : Samples bonded to dentin surface with Fuji II LC after 10% polyacrylic acid treatment. Group 2(BGF) : Samples bonded to dentin surface with Fuji II LC after 10% polyacrylic acid treatment and blood contamination. Group 3(MD) : Samples bonded to dentin surface with Dyract after 10% maleic acid treatment. Group 4(BMD) : Samples bonded to dentin surface with Dyract after 10% maleic acid treatment and blood contamination. Group 5(PV) : Samples bonded to dentin surface with Variglass VLC after 10% phosphoric acid treatment. Group 6(BPV) : Samples bonded-to dentin surface with Variglass VLC after 10% phosphoric acid treatment and blood contamination. Group 1,3 and 5 were classified into the control groups, while group 2,4 and 6 were classified into the experimental groups. Each group contained 30 samples. After 24 hours water storage at $37^{\circ}C$, all smples were subjected to a shear load to fracture at a cross head speed of 1.0 mm/min with Instron universal testing machine(No. 4467). Debonded surfaces were observed under Scanning Electron Microscope(Hitachi S-2300) at 20kvp. The data were evaluated statistically at the 95% confidence level with Student's t-test. The following results obtained; 1. Shear bond strengths were higher in the control groups(1,3,5 group) than in the experimental groups(2,4,6 group). 2. The shear bond strength of group 5(PV) was the highest in the control groups, and the group 5 was significantly higher than the group l(GF) on the shear bond strength. 3. The group 4(BMD) was the highest on the shear bond strength, and the group 2(BGF) was the lowest in the experimental groups. The group 4(BMD) and 6(BPV) showed a significant difference with the group 2 on the shear bond strength. 4. All the groups showed an adhesive-cohesive failure. except the group 2(BGF) showing adhesive failure.

• Korean Journal of Materials Research
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• v.9 no.10
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• pp.962-969
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• 1999

Elastic and elasto-plastic stress analyses of AlN/Cu and AlN/W pints produced by active-metal brazing method using Ag-Cu-Ti insert-metal were performed with use of Finite-Element-Method(FEM). The results of stress analyses were compared with those from the pint strength tests and the observations of fracture behaviors. It was shown that a remarkably larger maximum principal stress is built in the AlN/Cu pint compared to the A1N/ W joint. Especially, the stress concentration with tensile component was confirmed at the free surface close to the bonded interface of AlN/Cu. The elasto-plastic analysis under consideration of stress relaxation effect of Ag-Cu-Ti insert possessing a so-called 'soft-metal effect' showed that the insert leads to a lowering of maximum principal stress in AlNiCu pint, even though an increase of the insert thickness above 100$\mu\textrm{m}$ could not bring its further decrease. The maximum pint strengths measured by shear test were 52 and 108 MPa for AlNiCu and AlN/W pints. respectively. Typical fractures of AlN/Cu pints occurred in a form of 'dome' which initiated from the free surface of AlN close to the bonded interface and proceeded towards the AlN inside forming a large angle. AlN/W pints were usually fractured at AlN side along the interface of AlN/insert-metal.

• Fire Science and Engineering
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• v.17 no.4
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• pp.124-130
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• 2003

This research focuses on analysis of a interaction fracture of various glasses due to contact of water sprayed curtain on hot glass surface with high temperature produced from convective heat source near glass wall. A large scaled experimental test was done in order to find the range of the glass surface temperature to be able to cause the breakage of the glasses when water droplets reach on the hot surface. This paper shows the allowable temperature of the glass surface for prevention of the cooling down breakage before water curtain droplets contact the surface. Allowable Temperature if $250^{\circ}C$ for the tempered glass but general glass is very relatively low. Therefore if the water curtain spray system was adequately activated by a thermal detector installed below ceiling adjacent glass wall with water curtain nozzle system, all hot glass would not break out by cooling water droplet's contact on the hot surface due to convective heat released by adjacent fire source near the glass wall.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.4
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• pp.48-54
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• 2020

Cracks in reinforced concrete structures are the most common type of damage and are used as important analytical data to understand the fracture behavior characteristics of structures. Currently, there is a problem that most of the crack investigation relies on visual inspection, therefore many researchers have proposed image analysis techniques to improve the problem. In this study, we proposed a crack evaluation method to be applied at an indoor experimental level using image analysis method. The image analysis technique using color is for distinguishing a boundary surface between objects existing in an image, and is a method for separating similar colors into one region based on a predefined color. In this study, to improve the accuracy of image analysis, blue paint was applied to the concrete surface and bending experiments were performed. The image analysis method was able to measure the crack width with superior accuracy compared to the crack diameter, and at the same time, it was also possible to analyze the deflection of the beam. Both the crack and deformation were able to confirm the accuracy similar to the existing measurement method, and it was found that the image analysis method was very excellent in terms of applicability.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.3
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• pp.37-42
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• 2001

The concerns of the toxicity and health hazard of lead in solders have demanded the research to find suitable lead-free solder alloys. It was discussed that effect of the intermetallic formation and structure on the reliability of solder joints. In this study, lead-free solder alloys with compositions of Sn/3.5Ag/0.75Cu, Sn/2.0Ag/0.5Cu/2.0Bi were applied to the 48 $\mu$BGA packages. Also, the lead-free solder alloys compared with eutectic Sn/37Pb solder using shear test under various aging temperature. Common $\mu$BGA with solder components was aged at $130^{\circ}C$, $150^{\circ}C$ and $170^{\circ}C$. And the each temperature applied to 300, 600 and 900 hours. The thickness of the intermetallics was measured for each condition and the activation energy for their growth was computed. The fracture surfaces were analyzed using SEM (Scanning Electron Microscope) with EDS (Energy Dispersive Spectroscopy). These results for reliability of lead-free interconnections are discussed.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.3
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• pp.55-62
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• 2001

With a spread of BGA, CSP and fine pitch devices, the need of flatter surface finish in bare board is becoming more critical in solderability. The electroless Ni/Au plating has a solution of these needs and also has being spread to apply to surface finish for bare board in many electronic goods. But, the electroless Ni/Au plating had several issues such as Ni oxidation and phosphorous contents. Before this study, we studied on the effect of BGA solderability in electroless Ni/Au plating and chose some major factors such as the oxidation property of NiP plating and warpage of board. Firstly, we made test board with various plating conditions and improved the plating property through the improvement of NiP oxidation reducing P content. Also, we minimized the warpage of board with the improvement of inner layer structure and the analysis of warpage. For the evaluation of solderability, we analyzed the warpage of board and the plating property after mounting BGA on the board with optimizing conditions. The solder joint of BGA is investigated by SEM(Scanning Electronic Microscope) and OM(Optical Microscope). The composition of joint is used by EDS(Energy Dispersive Spectroscopy). We analyzed the fracture strength and mode by ball shear teser.

• Composites Research
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• v.24 no.6
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• pp.56-63
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• 2011

The objective of this study is to investigate appropriate bonding methods of solar cells in order to apply solar cells, which have been receiving particular attention as a renewable energy due to fossil energy depletion and environment issues, to composite structures. Back-contact solar cells with approximately 24.2% energy conversion efficiency were used in this study. Since silicon-based solar cells are mechanically fragile, the secondary-bonding methods using adhesive were examined in this study. The experiment was conducted with three kinds of bonding materials such as EVA film, Resin film and elastic adhesive. The performance of solar cells for three types of adhesives under mechanical loading on test specimens is conducted. In addition, the measuring equipment was designed to evaluate the performance of the solar cells under mechanical loading in real time and the fracture characteristics depending on bonding materials were evaluated. The reason decreasing solar cells efficiency were analyzed and considered by Fractography. The results show that the solar cell performance is largely affected by bonding techniques. Moreover, the bonding method using elastic adhesive shows best solar cell efficiency.

• Journal of Dental Rehabilitation and Applied Science
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• v.29 no.4
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• pp.327-336
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• 2013

This study aimed to investigate the reinforcing effect of two kinds of glass fiber, Quarts Splint$^{TM}$ Mesh and SES MESH$^{(R)}$ and to evaluate the effect of the thermocycling on the transverse strength of the denture base and on the reinforcing effect of the reinforcements. 20 specimens of the size of $2.5{\times}10.0{\times}65.0mm$ were fabricated for each group; control group, metal mesh reinforcement group, Quarts Splint$^{TM}$ Mesh reinforcement group and SES MESH$^{(R)}$ reinforcement group. To find the difference made by the thermocycling, 10 specimens of each reinforcement group were treated by thermocycling. 3-point bending test was performed to measure the transverse strength of the denture base resin. The specimens reinforced with SES MESH$^{(R)}$ and Quarts Splint$^{TM}$ Mesh showed significantly higher transverse strength than the control group (P<.05), and significantly lower transverse strength than the specimens reinforced with the metal mesh (P<.05). Thermocycled specimens were lower in transverse strength than non-thermocycled specimens in the control group, metal mesh group, Quarts Splint$^{TM}$ Mesh group and SES MESH$^{(R)}$ group, however significant difference (P<.05) was found only in the control group.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.6
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• pp.959-972
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• 2017

In evaluation of blast-induced vibration, peak particle velocity (PPV) is generally calculated by using attenuation relation curve. Calculated velocity is compared with the value in legal requirements or the standards to determine the stability. Attenuation relation curve varies depending on frequency of test blasting, geological structure of the site and blasting condition, so it is difficult to predict accurately using such an equation. Since PPV is response value from the ground, direct evaluation of the structure is impractical. Because of such a limit, engineers tend to use the commercial numerical analysis program in evaluating the stability of the structure more accurately. However, when simulate the explosion process using existing numerical analysis program, it's never easy to accurately simulate the complex conditions (fracture, crushing, cracks and plastic deformation) around blasting hole. For simulating such a process, the range for modelling will be limited due to the maximum node count and it requires extended calculation time as well. Thus, this study is intended to simulate the elastic energy after fractured zone only, instead of simulating the complex conditions of the rock that results from the blast, and the analysis of response characteristics of the velocity depending on shape and size of the fractured zone was conducted. As a result, difference in velocity and attenuation character were calculated depending on fractured zone around the blast source appeared. Propagation of vibration tended to spread spherically as it is distanced farther from the blast source.