• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.2
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• pp.121-143
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• 2010

To investigate the effect of implant types and bone resorption on the fracture characteristics. 4 types of Osstem$^{(R)}$Implant were chosen and classified into external parallel, internal parallel, external taper, internal taper groups. Finite elements analysis was conducted with ANSYS Multi Physics software. Fatigue fracture test was performed by connecting the mold to the dynamic load fatigue testing machine with maximum load of 600N and minimum load of 60N. The entire fatigue test was performed with frequency of 14Hz and fractured specimens were observed with Hitachi S-3000 H scanning electron microscope. The results were as follows: 1. In the fatigue test of 2 mm exposed implants group, Tapered type and external connected type had higher fatigue life. 2. In the fatigue test of 4 mm exposed implants group, Parallel type and external connected types had higher fatigue life. 3. The fracture patterns of all 4 mm exposed implant system appeared transversely near the dead space of the fixture. With a exposing level of 2 mm, all internally connected implant systems were fractured transversely at the platform of fixture facing the abutment. but externally connected ones were fractured at the fillet of abutment body and hexa of fixture or near the dead space of the fixture. 4. Many fatigue striations were observed near the crack initiation and propagation sites. The cleavage with facet or dimple fractures appeared at the final fracture sites. 5. Effective stress of buccal site with compressive stress is higher than that of lingual site with tensile stress, and effective stress acting on the fixture is higher than that of the abutment screw. Also, maximum effective stress acting on the parallel type fixtures is higher. It is careful to use the internal type implant system in posterior area.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.80-85
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• 1999

Residual stress in the forged products directly affects material stability, resistance to deformation, accuracy, and fatigue life of products. It is very important to study the residual stress distributions in forged products and to monitor operating conditions for the minimum tensile or maximum compressive residual stresses. As a way to study the residual stress formation due to radial forging, a three dimensional theoretical model was developed using ANSYS finite element program. Using the developed model, residual stress distributions in forged product were calculated and selected results were compared with the published experimental data to verify the effectiveness of the developed model.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.331-332
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• 2002

Most manufacturing processes such as welding, cutting and molding generate residual stresses on the surface of manufactured parts. Tensile residual stress is harmful to the surface integrity, which results in reduced fatigue life and causes other structural failures when the service stresses are superimposed on the residual stresses. In the research, the residual stresses of the high hardness steel (over $H_{RC}60$) workpiece (SKD11) machined by the hard turning were measured using Hole-drilling Method. Residual stress in the surface of hard turned workpiece was mainly appeared to be compressive stress.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.8
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• pp.1615-1622
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• 2002

The purpose of this study is comparing cold expansion method with interference fit. Cold expansion method and interference fit of fastener hole is using in the aerospace industry. These treatment lead to an improvement of fatigue life to the compressive residual stresses developed on the hole surface. But Research is nothing to about difference effect of between cold expansion method and interference fit. So, this paper, it is shown that Comparing cold expansion method with interference fit using the finite element method. It is further shown that residual stress distribution according to plate thickness and clamping force.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.419-424
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• 2001

The purpose of this study is comparing cold expansion method with interference fit. Cold expansion method and interference fit of fastener hole is using in the aerospace industry. These treatment lead to an improvement of fatigue life to the compressive residual stresses developed on the hole surface. But Research is nothing to about difference effect of between cold expansion method and interference fit. So In this paper, It is shown that Comparing cold expansion method with interference fit. and It is further shown that residual stress distribution according to plate thickness.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.328-333
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• 2003

The purpose of this study is to analyze the impact of shot peening angle on residual stress distribution. From the residual stress analysis of perpendicular shot peening, it could be known that the residual stress in the case of high velocity is larger than low velocity, but the amount of shot size has little effect on the magnitude of compressive residual stress. The centroidal residual stress is not greatly affected by the inclined shot peening but mainly related to the unstable conditions of surface residual stress field. Therefore, this tendency may lead to reduce fatigue life of treated material.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.9
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• pp.1605-1614
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• 1992

The effects of % overload (% O.L), baseline stress intensity factor range (.DELTA. $K_{b}$) and dimension-less crack depth (a/W) are examined for the retardation behaviors after a single overload and high-low block loads in 7075-T73 aluminum alloy. And wheeler model, which is one of the fatigue life prediction models, is modified to predict retardation life using these test results. The retardation cycles( $N_{d}$) increased with a decrease in a/W and an increase in % O.L. and (.DELTA. $K_{b}$) These effects are more severe after high-low block loads than single overload. In the case of single overload, the main mechanisms of the retardation are the crack closure and the relaxation of K due to crack branching. But in the case of high-low block loads, that of the main mechanism is the crack closure caused by the accumulated compressive residual stree at the crack tip, which is related with the contact of fracture surfaces. Test results were multiple regression analyzed and got regressed shaping correction factors, (n)$_{REG}$, as function of %O.L., a/W and (.DELTA. $K_{b}$) Wheeler model is modified by using these (n)$_{REG}$. The number of delay cycles calculated by modified Wheeler model were in good agreement with the test results of this study.y.udy.y.y.y.

• Advances in concrete construction
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• v.4 no.2
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• pp.123-143
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• 2016

Use of heavy fuel fly ash (HFFA) (diesel and cracked fuel) for power generation in Saudi Arabia has generated and accumulated large quantities of HFFA as a byproduct. In this research, HFFA is studied with the emphasis on the utilization of this waste material in concrete blocks and asphalt concrete mixes. Two types of mixes, one with low and other with high cement content, were studied for concrete blocks. Different mixes having varying percentages of HFFA (0% to 25%), as cement/sand replacement or as an additive, were studied. The performance of concrete blocks is evaluated in terms of compressive strength, water absorption, durability and environmental concerns. The results showed that blocks cannot be cast if more than 15% HFFA is used; also there is a marginal reduction in the strength of all the mixes before and after being exposed to the sulfate solution for a period of ten months. HFFA is studied in asphalt concrete mixes in two ways, as an asphalt modifier (3&5%) and as a filler (50%) replacement, the results showed an improvement in stiffness and fatigue life of mixes. However, the stability and indirect tensile strength loss were found to be high as compared to the control mix due to moisture damage, indicating a need of using antistripping agents. On environmental concerns, it was found that most of the concerned elements are within acceptable limits also it is observed that lower concentration of barium is leached out with the higher HFFA concentrations, which indicates that HFFA may work as an adsorbent for this leaching element.

• Journal of Welding and Joining
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• v.30 no.6
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• pp.74-79
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• 2012

It depends on the joint configuration, dimensions and constraints of the joint whether the residual stress at the root of single-sided butt weld is tensile or not. Therefore, recommendation is generally made that high R ratio should be used in the fatigue test of welded joint in order to prevent excessively long life caused by compressive residual stress. In this research, the residual stress profile in butt weld joint was obtained through compliance method, using successive extension of a slot and measurement of the variation of strain during the slot extension. The residual stress profile was firstly assumed to be the linear summation of Legendre polynomials up to 9th order excluding 0th and 1st order. Strain variation on the surface was measured while the slot was being extended by cutting to find out the 8 unknown coefficients of each polynomial term. The cut was made by the electric discharge machine. It was concluded that the residual stress near the surface is positive valued, however, it turned into the negative value as soon as it passed through 2 or 3 mm of the depth.

• Progress in Medical Physics
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• v.20 no.2
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• pp.80-87
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• 2009

Phase transformation, superelastic characteristics and variation of surface residual stress were studied for Nitinol shape memory alloy through application of UNSM technology, and life extension methods of stent were also studied by using elastic resilience and corrosion resistance. Nitinol wire of ${\phi}1.778$ mm showed similar surface roughness before and after UNSM treatment, but drawing traces and micro defects were all removed by UNSM treatment. It also changed the surface residual stress from tensile to compressive values, and XRD result showed less intensive austenite peak and clear martensite and additional R-phase peaks after UNSM treatment. Fatigue resistance could be greatly improved through removal of surface defects and rearrangement of surface residual stress from tensile to compressive state, and development of surface modification system to improve not only bio-compatability but also resistance to corrosion and wear will make it possible to develop vascular stent which can be used for circulating system diseases which run first cause of death of recent Koreans.