• Journal of the Korean institute of surface engineering
• /
• v.51 no.4
• /
• pp.191-196
• /
• 2018

The self-annealing which leads evolution of microstructure in copper electroplating layers at room temperature occurs after forming deposition layer. During the process, crystal orientation, size and sheet resistance of plating layer change. Lastly, it causes the change of physical and mechanical characteristics such as a tensile strength of plating layer. In this study, the variation of incorporated impurities, microstructure and sheet resistance of copper plating layer formed by electroplating are measured with and without inorganic additives during the self-annealing. In case of absence of inorganic additives, the copper layer presents strong total intensity of incorporated impurities. During the self-annealing, such width of reduction was significant. Moreover, microstructure and crystal size are increased while the tensile strength is decreased noticeably. On the other hand, in the presence of inorganic additives, there is no observable distinction in the copper plating layer. According to the observation on movements of the incorporated impurities in electrodeposition copper layer, within 12 hours the impurities are continuously shifted from inside of the plating layer to its surface after as-deposited electroplating. Within 24 hours, except for the small portion of surface layer, it is considered that most of the microstructure is transformed.

• Elastomers and Composites
• /
• v.35 no.3
• /
• pp.173-179
• /
• 2000

Cure characteristics. tensile properties, and dynamic properties were investigated on the carbon black-filled natural rubber compounds, in which three typical vulcanization types conventional vulcanization(Conv), semi-efficient(Semi-EV), and efficient(EV) vulcanizations were used. The effects of vulcanization temperature on both the mechanical property and aging resistance of rubber compounds were also investigated. The Conv cure system showed a slightly slower rate of vulcanization than those of Semi-EV and EV ones. On the other hand, it showed a higher value in the maximum torque of cure curve. Higher tensile moduli were observed in Conv system than those in Semi-EV and EV ones, while lower elongation at break were obtained in Conv one. The tensile strength at break were found to be about the same for three cute systems. Hardness, modulus, and tensile strength decreased with increasing the vulcanization temperature, and the degree of changes in the properties was found to be smaller for EV and Semi-EV systems than that in Conv one. The EV system was found to be superior in thermal-aging resistance to Conv one.

• Structural Engineering and Mechanics
• /
• v.60 no.6
• /
• pp.1021-1038
• /
• 2016

Considerable part of reinforced concrete building has suffered from destructive earthquakes in Turkey. This situation makes necessary to determine nonlinear behavior and seismic performance of existing RC buildings. Inelastic response of buildings to static and dynamic actions should be determined by considering both flexural plastic hinges and brittle shear hinges. However, shear capacities of members are generally neglected due to time saving issues and convergence problems and only flexural response of buildings are considered in performance assessment studies. On the other hand, recent earthquakes showed that the performance of older buildings is mostly controlled by shear capacities of members rather than flexure. Demand estimation is as important as capacity estimation for the reliable performance prediction in existing RC buildings. Demand estimation methods based on strength reduction factor (R), ductility (${\mu}$), and period (T) parameters ($R-{\mu}-T$) and damping dependent demand formulations are widely discussed and studied by various researchers. Adopted form of $R-{\mu}-T$ based demand estimation method presented in Eurocode 8 and Turkish Earthquake Code-2007 and damping based Capacity Spectrum Method presented in ATC-40 document are the typical examples of these two different approaches. In this study, eight different existing RC buildings, constructed before and after Turkish Earthquake Code-1998, are selected. Capacity curves of selected buildings are obtained with and without considering the brittle shear capacities of members. Seismic drift demands occurred in buildings are determined by using both $R-{\mu}-T$ and damping based estimation methods. Results have shown that not only capacity estimation methods but also demand estimation approaches affect the performance of buildings notably. It is concluded that including or excluding the shear capacity of members in nonlinear modeling of existing buildings significantly affects the strength and deformation capacities and hence the performance of buildings.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.6
• /
• pp.27-32
• /
• 2021

This study was conducted to improve the workability of cementitious composites using nano-bubble water. The used nano-bubble water contains 7% of nano-sized bubbles with an averaged bubble size of 750 nm. Various different types of cementitious composites including ultar-high performance concrete, lightweight cementitious composites, and high-strength mortar have been tested to identify the changes of material properties. From the use of nano-bubble water, it was confirmed that workability has been improved by 3-22%. On the other hand, other material characteristics such as compressive strength did not have noticeable changes. Therefore, it was proposed that the use of nano-bubble water can enhance workability of cementitious composites without having significant impact on other material properties.

• Korean Journal of Materials Research
• /
• v.28 no.12
• /
• pp.702-708
• /
• 2018

This study deals with the effect of microstructure factors on the strain aging properties of API X70 pipeline steels with different microstructure fractions and grain sizes. The grain size and microstructure fraction of the API pipeline steels are analyzed by optical and scanning electron microscopy and electron backscatter diffraction analysis. Tensile tests before and after 1 % pre-strain and thermal aging treatment are conducted to simulate pipe forming and coating processes. All the steels are composed mostly of polygonal ferrite, acicular ferrite, granular bainite, and bainitic ferrite. After 1 % pre-strain and thermal aging treatment, the tensile test results reveal that yield strength, tensile strength and yield ratio increase, while uniform elongation decreases with an increasing thermal aging temperature. The increment of yield and tensile strengths are affected by the fraction of bainitic ferrite with high dislocation density because the mobility of dislocations is inhibited by interaction between interstitial atoms and dislocations in bainitic ferrite. On the other hand, the variation of yield ratio and uniform elongation is the smallest in the steel with the largest grain size because of the decrease in the grain boundary area for dislocation pile-ups and the presence of many dislocations inside large grains after 1 % pre-strain.

• Transactions of Materials Processing
• /
• v.28 no.1
• /
• pp.34-42
• /
• 2019

In this study, various alloying elements (Cr, Sr, Ca, Cd) were added to improve the mechanical properties of ADC12 fabricated by a die casting process. The effect of alloying elements on the microstructure and mechanical properties were investigated. The phase analysis results of the modified ADC12 alloy with conventional ADC12 alloy, showed the similar characteristics of Al matrix, Si phase, $CuAl_2$ phase and the Fe intermetallic phase. As a result of the microstructure observation, the secondary dendrite arm spacing (SDAS) was shown to have decreased after the addition of the alloying elements. The eutectic Si phase, which existed as flake form in the conventional ADC12 alloy, was modified finely as a fiber form in the modified ADC12 alloy. It was observed that the $CuAl_2$ phase as the strengthening phase was relatively finely distributed in the modified ADC12 alloy. The Fe intermetallic appeared as a Chinese script shaped $Al_6$ (Mn,Fe) which is detrimental to mechanical properties in conventional ADC12 alloy. On the other hand, in the modified ADC12 alloy, polyhedral ${\alpha}-Al_{15}Si_2$ $(Fe,Mn,Cr)_3$ was observed. The tensile properties were improved in the modified ADC12 alloy. The yield strength and tensile strength increased by 12.4% and 10.0%, respectively, in the modified ADC12 alloy, and the elongation was also seen to have been increased. As a result of the pin on disk wear test, the wear resistance properties were also improved by up to about 7% in the modified ADC12 alloy. It is noted that the wear deformation microstructures were also observed, and it was found that the fine eutectic Si and strengthening phases greatly improved abrasion resistance.

• Korean Journal of Materials Research
• /
• v.29 no.6
• /
• pp.349-355
• /
• 2019

This study deals with the microstructure and tensile properties of 600 MPa-grade seismic reinforced steel bars fabricated by a pilot plant. The steel bar specimens are composed of a fully ferrite-pearlite structure because they were air-cooled after hot-rolling. The volume fraction and interlamellar spacing of the pearlite and the ferrite grain size decrease from the center region to the surface region because the surface region is more rapidly cooled than the center region. The A steel bar specimenwith a relatively high carbon content generally has a higher pearlite volume fraction and interlamellar spacing of pearlite and a finer ferrite grain size because increasing the carbon content promotes the formation of pearlite. As a result, the A steel bar specimen has a higher hardness than the B steel bar in all the regions. The hardness shows a tendency to decrease from the center region to the surface region due to the decreased pearlite volume fraction. On the other hand, the tensile-to-yield strength ratio and the tensile strength of the A steel bar specimen are higher than those of the B steel bar with a relatively low carbon content because a higher pearlite volume fraction enhances work hardening. In addition, the B steel bar specimen has higher uniform and total elongations because a lower pearlite volume fraction facilitates plastic deformation caused by dislocation slip.

• Journal of The Korean Society of Integrative Medicine
• /
• v.7 no.3
• /
• pp.51-59
• /
• 2019

Purpose : To evaluate the effect of comprehensive art therapy on physical function and activities of daily living in children with cerebral palsy (CP). Methods : Ten ambulant children with diplegic (n=8) or hemiplegic (n=2) CP participated in this study. All were randomly assigned to either the art therapy group (n=5) or the control group (n=5). Both groups received physical therapy based on neurodevelopmental techniques for 20 minutes a day, 1 day a week, for a period of 12 weeks. Children in the art therapy group received additional comprehensive art therapy for 70 minutes once a week for 3 months. Tests for various measurements-Motricity Index (MI) for strength, Trunk Control Test (TCT) for trunk ability, Gross Motor Function Measure (GMFM) and Gross Motor Function Classification System (GMFCS) for gross motor function, Denver Developmental Screening Test-II (DDST-II) for developmental milestones, Functional Independence Measure of Children (WeeFIM) for abilities to complete daily activities, Leg and Hand Ability Test (LHAT) for limb function-were performed before and after treatments. Results : The upper extremity and whole extremity strengths of MI, self-care and total scores of WeeFIM, and leg and arm functions of LHAT improved significantly only for individuals in the art therapy group after the art therapy (p<.05). The value of MI after treatment was at the upper extremity and whole extremity strengths the leg function of LHAT was also significantly improved compared to the control group (p<.05). Conclusion : This study revealed that comprehensive art therapy along with physiotherapy was effective in increasing upper extremity strength and leg ability in children with CP. This suggests that comprehensive art therapy may be a useful adjunctive therapy for children with CP.

• PNF and Movement
• /
• v.17 no.2
• /
• pp.199-206
• /
• 2019

Purpose: The purpose of this study was to evaluate the effects of a virtual upper extremity training program using the RAPAEL Smart Glove on upper extremity function in stroke survivors with chronic hemiparesis and to focus the training program development using the Smart Glove as a feasibility study. Methods: This study was conducted using a single group and pre-post test research design in the outpatient departments of local rehabilitation units. Ten chronic hemiparetic stroke survivors with a diagnosis of first stroke received therapeutic rehabilitation at the rehabilitation units. All the participants used a virtual reality program with the RAPAEL Smart Glove for 30 minutes per session 3 days a week over 8 weeks. They also received conventional occupational therapy with functional electrical stimulation for 40 minutes per session 3 days a week for 8 weeks as an additional therapy. To analyze the effects of this therapeutic intervention, four clinical measures, including the box-block test (BBT), the Wolf motor function test (WMFT), the trail-making score, the Jebsen Taylor hand function test (JTHFT), and grip strength, were used. Results: Upon completion of the intervention in week 8, all the participants demonstrated significant WMFT, JTT, BBT, grip strength, and trail-making score gains compared to the respective baselines at week 0. Conclusion: This study suggests that virtual upper extremity training using the RAPAEL Smart Glove has a reasonable and beneficial effects on upper extremity function in chronic hemiparetic stroke survivors.

• The Journal of Korean Academy of Prosthodontics
• /
• v.57 no.1
• /
• pp.88-94
• /
• 2019

Increasing demands for esthetic dental treatment, zirconia, which has high mechanical and esthetic properties, had been applied more and more in clinics. Therefore, assessment of biocompatibility of zirconia is necessary. In this article, a review of in vivo studies of zirconia compatibility was performed. In vivo studies showed zirconia had great biocompatibility both on soft and hard tissue. Studies with various animals and patients reported high biocompatibility of zirconia. In terms of bone synthesis and bone adhesion, zirconia showed similar biocompatible properties to titanium. On the other hand, zirconia could be used as implant. For using as an implant, various methods of Hydroxyapatite (HA) coating had been suggested. Since HA coating on titanium implant showed some problems such as low bonding strength and degeneration of HA, HA-zirconia composite, HA-coated zirconia, and HA-zirconia functionally graded material (FGM) or intermediate layer of alumina had been proposed. These methods showed higher bonding strength and biocompatibility.