• The korean journal of orthodontics
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• v.15 no.2
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• pp.163-174
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• 1985

The requirements of orthodontic wire should include chemical stability, non-discoloration and non-corrosion in oral environment. Ability to be soldered, ease of fabrication and elasticity should be also considered. The purpose of this study was to compare and analyze the physical properties of Tru-chrome wire and manufactured E.S.S. (Experimental Stainless Steel) wire similar to Tru-chrome. The results were as follows: 1. Tru-chrome wire and E.S.S. wire were SUS 304 which was 18 Cr-8Ni austenite stainless steel. There was not significant difference in each composition between two wires. 2. There were not significant differences in ultimate tensile strength, yield strength, elongation and modulus of elasticity between Tru-chrome and E.S.S. wires. 3. There was not significant difference between flexuree modulus of elasticity of Tru-chrome and E.S.S. wires. 4. Micro-hardness value of E.S.S. wire was more than that of Tru-chrome wire and they were softened significantly by solution heat reatment. 5. Micro-structure of Tru-chrome and E.S.S. wires showed fibrous interlocking grains, and an austenite structure after solution heat treatment. 6. There was significant difference between corrosion rate of Tru-chrome and E.S.S. wires.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.2
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• pp.139-146
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• 1994

In the molten state, magnesium alloys vigousey react with oxygen in the air, is protected from oxidation and burning by the addition of $SF_6$ to $CO_2$ atmosphere over the melt. The mechanical properties and metallographic examinatin have made of Mg-Al alloys containing 3, 6, 9% in the solution treated state and precipitated state, comparing mechanical properties obtained during unidirectional solidification with me chanical properties obtained during conventional casting. For a given solution treatment, a higher aluminum contents produce more or less fine grains in conventional casting. For a given artifical aging treatment, a higher aluminum contents produces much precitates at the grain boundary as well as within the grain in unidirectional solidification. As a result of this experiment, for a given heat treatment, the higher is aluminum contents the higher is the ultimate tensile strength, yield strength, hardness while the lower the elongation. Also the mechanical properties of unidirectional solidification is larger than that of conventional casting.

• Steel and Composite Structures
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• v.31 no.4
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• pp.409-417
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• 2019

The choice of individual material for industrial application is primarily based on knowledge of its behavior in similar applications and similar environmental conditions. Contemporary design implies knowledge of material behavior and knowledge in the area of structural analysis supported by large capacity computers. Bearing this in mind, this paper presents and analyzes the experimental results related to the mechanical properties of the material considered (30CrNiMo8/1.6580/AISI 4340) at different temperatures as well as its creep and fatigue behavior. All experimental tests were carried out as uniaxial tests. The test results related to the mechanical properties are presented in the form of engineering stress-strain diagrams. The results related to the creep behavior of the material are shown in the form of creep curves, while the fatigue of the material is shown in the form of stress - life (S - N) diagram. Based on these experimental results, the values of the following properties are determined: ultimate tensile strength (${\sigma}_{m,20}=696MPa$), yield strength (${\sigma}_{0.2,20}=355.5MPa$), modulus of elasticity ($E_{,20}=217GPa$) and fatigue limit (${\sigma}_{f,20,R=-1}=280.4MPa$). Results related to fatigue tests were obtained at room temperature and stress ratio R = -1.

• Advances in concrete construction
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• v.13 no.4
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• pp.291-305
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• 2022

The present investigation deals with the production of the innovative lightweight fly ash angular aggregates (FAA) first time in India using local class 'F' fly ash, its characterization, and exploring the potential for its utilization as alternative coarse aggregates in structural concrete applications. Two types of aggregates are manufactured using two different kinds of binders. The manufacturing process involves mixing fly ash, binder, and water, followed by the briquetting process, sintering and crushing them into suitable size aggregates. Tests are conducted on fly ash angular aggregates to measure their physical properties such as crushing value, impact value, specific gravity, water absorption, bulk density, and percentage of voids. Study shows that the physical parameters are significantly enhanced as compared to commercially available fly ash pellets (FAP). The developed FAA are used in concrete vis-à-vis conventional granite aggregates and FAP to determine their compressive, split tensile and flexural strengths. Although being lightweight, the strength parameters for concrete containing FAA are well compared with conventional concrete. This might be due to the high pozzolanic reaction between fly ash angular aggregates and cement paste. Also, RCC beams are cast and the load-deflection behaviour and ultimate load carrying capacity signify that FAA can be suitably used for RCC construction. Hence, the utilization of fly ash as angular aggregates can reduce the dead load of the structure and at the same time serves as a solution for fly ash disposal and mineral depletion problem.

• Composites Research
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• v.37 no.2
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• pp.94-100
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• 2024

In order to evade the premature failure of super duplex stainless steels (SDSSs) in some harsh environments, the increase of their mechanical properties is a promising approach. In this study, based on the laser powder bed fusion (LPBF) technique, SDSS matrix composites without post heat treatment were fabricated by using the powder mixture of SDSSs, super austenitic stainless steels (SASSs) and micron-sized TiC particles. Many in-situ TiC_xN_y nanoparticles were found to be formed by using micron-sized TiC particles in as-built composites, and both fine ferrite and austenite grains were generated. The as-built composites exhibited an excellent combination of high ultimate tensile strength (UTS) (~1066 MPa) and good uniform elongation (UE) (~15.6%), showing a better mechanical property compared with other reported LPBF-fabricated SDSSs, which was mainly attributed to the fine grain, Orowan and dislocation strengthening mechanisms. In particular, the successful fabrication of SDSS matrix composites can set the stage for producing high-performance metallic parts via LPBF technique.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.4
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• pp.968-980
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• 1995

Al/Al$_{2}$O$_{3}$/C hybrid metal matrix composites are fabricated by the direct squeeze infiltration method. From the microstructure of Al/Al$_{2}$O$_{3}$/C composites, uniform distribution of reinforcements and good bondings are found. Optimum processing conditions for preforms and squeeze castings are suggested. Mechanical properties, such as elastic modulus, elongation, 0.2% offset yield strength and ultimate tensile strength are obtained. Through the abrasive were test and wear surface analsis, wear behavior and its mechanism of AC2B aluminum and Al/Al$_{2}$O$_{3}$/C composites can be characterized under various sliding speed conditions. Tensile strenght elongation of Al/Al$_{2}$O$_{3}$/C composites are decreased with increasing the addition of carbon fiber. On the contrary, elastic modulus of Al/Al$_{2}$O$_{3}$/C composites is slightly improved compared with that of the unreinforced matrix alloy. The addition of carbon fiber to al/al$_{2}$O$_{3}$/C composites gives rise to improvement of the wear resistance. Specially, carbon chopped fibers play an important role in interfering sticking between the counter material and metal matirix composites. Al/Al$_{2}$O$_{3}$/C composites are suitable to high speed due to solid lubication of carbon. And wear model of Al/Al$_{2}$O$_{3}$/C composites is suggested by the examination of worn surfaces.

• Korean Journal of Materials Research
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• v.27 no.12
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• pp.652-657
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• 2017

The use of continuous welded rail is increasing because of its many advantages, including vibration reduction, enhanced driving stability, and maintenance cost savings. In this work, two different types of continuous welded rails were examined to determine the influence of repeated wheel-rail contact on the crystal structure, microstructure and mechanical properties of the rails. The crystal structure was determined by x-ray diffraction, and the microstructure was examined using optical microscopy and scanning electron microscopy. Tensile and microhardness tests were conducted to examine the mechanical behaviors of prepared specimens taken from different positions in the cross section of both newly manufactured rail and worn rail. Analysis revealed that both the new and worn rail had a mixed microstructure consisting of ferrite and pearlite. The specimens from the top position of each rail exhibited decreased lamella spacing of the pearlite and increased yield strength, ultimate tensile strength and hardness, as compared with those from other positions of the rail. It is thought that the enhanced mechanical property on the top position of the worn rail might be explained by a mixed effect resulting from a directional microstructure, the decreased lamella spacing of pearlite, and work hardening by the repeated wheel-rail contact stress.

• Computers and Concrete
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• v.30 no.5
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• pp.339-355
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• 2022

The high cost of ultra-high-performance engineered cementitious composite (UHP-ECC) is currently a crucial issue, especially in terms of the polyethylene (PE) fibers use. In this paper, cheap calcium carbonate whiskers (CW) were evaluated on the feasibility of hybrid with PE fibers. Diverse combinations of PE fibers and CW were employed to investigate the multi-scale enhancement on the UHP-ECC performance. A probabilistic-based UHP-ECC tensile strain reliability analysis approach was utilized, which was in general agreement with the experimental results. Furthermore, a multi-dimensional integrated representation was conducted for the comprehensive assessment of UHP-ECC. Results illustrated that CW improved the compressive strength and energy dissipation capacity of UHP-ECC owing to the microscopic strengthening mechanism. CW and PE fiber further promoted the saturated cracking of composite by multi-scale crack arresting effect. In particular, PE1.75-CW0.5 specimen possessed the best overall performance. The ultimate cracking width of PE1.75-CW0.5 group had 98 ㎛, which was 46.18% lower compared to PE2-CW0 group, the 28d compressive strength were slightly improved, the tensile strain capacity was comparable to that of PE2-CW0 group. The results above demonstrated that combinations of PE fiber and CW could significantly enhance the comprehensive performance of UHP-ECC, which was beneficial for large-scale engineering applications.

• The Journal of Korean Academy of Prosthodontics
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• v.52 no.2
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• pp.67-73
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• 2014

Purpose: The purpose of present study is to compare mechanical properties and microstructural characteristics of fractured surface for cast, 3-D printing laser sintered and CAD/CAM milled cobalt-chromium (Co-Cr) alloy specimens and to investigate whether laser sintered technique is adequate for dental applications. Materials and methods: Thirty six flat disc shape Co-Cr alloy specimens were fabricated for surface hardness test and divided into three groups according to the manufacturing methods; 12 specimens for casting (n=12), 12 specimens for laser sintered technology (n=12) and 12 specimens for milled technology (n=12). Twelve dumbbell shape specimens for each group were also fabricated for a tensile test. Statistical comparisons of the mechanical properties for the alloys were performed by Kruskal-Wallis test followed by Mann-Whitney and Bonferroni test. The microstructural characteristics of fractured surfaces were examined using SEM. Results: There were significant differences in the mean Vickers hardness values between all groups and the cast specimen showed the highest (455.88 Hv) while the CAD/CAM milled specimen showed the lowest (243.40 Hv). Significant differences were found among the three groups for ultimate tensile strength, 0.2% yield stress, elongation, and elastic modulus. The highest ultimate tensile strength value (1442.94 MPa) was shown in the milled group and the highest 0.2% yield strength (1136.15 MPa) was shown in the laser sintered group. Conclusion: Different manufacturing methods influence the mechanical properties and microstructure of the fractured surfaces in Co-Cr alloys. The cast Co-Cr alloy specimens showed the highest Vickers hardness, and the CAD/CAM milled specimens revealed the highest tensile strength value. All alloys represent adequate mechanical properties satisfying the ISO standards of dental alloy.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.3
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• pp.165-172
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• 2019

In this study, the shear strength of prestressed concrete deep beams is predicted using finite element analysis, and the variation in the shear strength according to the degree of prestressing is investigated. Numerical analysis results are compared with results obtained by the strut-and-tie model and associated experiments. Numerical analyses are performed on prestressed concrete deep beams with different values of concrete strength, effective prestress, ratio of tensile reinforcement, and shear span to effective depth ratio. The shear strength predicted by the numerical analysis is similar to the experimental value obtained, with an error of less than 5%. However, the strut-and-tie model highly overestimated the shear strength of prestressed concrete deep beams with a concentrated loading area. The ultimate shear capacity of prestressed concrete deep beams increased linearly with increasing prestresss applied to the tendon.