• Journal of dental hygiene science
• /
• v.17 no.4
• /
• pp.358-367
• /
• 2017

The purpose of this study was to evaluate the influence of water infiltration and flexural strength changes in dental porcelain with glazing treatment. The block specimens were prepared as experimental materials, using feldspar type commercial dental porcelain; then, these were fired at $940^{\circ}C$ for 1 minute. The fired specimens were polished with a dimension of $40{\times}5.5{\times}5mm$. The specimens were distributed to two experimental groups: with and without glazing treatment specimens (n=5), and they were immersed in a solution of pH 7 for 3, 7, and 20 days at $40^{\circ}C$ after fabrication. To evaluate the flexural strength changes with water infiltration treatment in specimens with and without glazing, the 3-point flexural test was performed, using a universal testing machine until failure occurred. Starting powder and fired specimens consisted of amorphous and leucite crystalline phase. The Vickers hardness of fired specimens was more than 1.6 times higher than that of the enamel of natural teeth. According to porosimeter results, the specimens without glazing treatment exhibited a porosity of about 14.7%, whereas the glazed specimens exhibited the lowest porosity at about 1.1%. The average flexural strength of glazed specimens was higher than the flexural strength of specimens without glazing treatment (p<0.05). The flexural strength of all specimens with and without glazing treatment deteriorated with accelerated aging in the solution. In addition, significant differences between these two treatment groups were observed in all of the specimens treated at various water infiltration periods (p<0.05). The exposure of internal pores and micro-cracks in the surface due to polishing of the fired specimens influenced mechanical behaviors. Especially, the flexural strength in specimens without glazing treatment has shown significant degradation with the infiltration of water. Therefore, this study suggests that glazing processes can improve mechanical properties of dental porcelain.

• Journal of the Microelectronics and Packaging Society
• /
• v.17 no.3
• /
• pp.17-26
• /
• 2010

Pb-Sn solder is rapidly being replaced by lead-free solder for board-level interconnection in microelectronic package assemblies due to the environmental protection requirement. There is a general lack of mechanical reliability information available on the lead-free solder. In this study, thermo-mechanical behaviors of wire-bond plastic ball grid array (WB-PBGA) package assemblies are characterized by high-sensitivity moire interferometry. Experiments are conducted for two types of WB-PBGA packages that have Pb-Sn solder and lead-free solder as joint interconnections. Using real-time moire setup, fringe patterns are recorded and analyzed for several temperatures. Bending deformations of the assemblies and average strains of the solder balls are investigated and compared for the two type of WB-PBGA package assemblies. Results show that shear strain in #3 solder ball located near the chip shadow boundary is dominant for the failure of the package with Pb-Sn solder, while normal strain in #7 most outer solder ball is dominant for that with lead-free solder. It is also shown that the package with lead-free solder has much larger bending deformation and 10% larger maximum effective strain than the package with Pb-Sn solder at same temperature level.

• Korean Journal of Childcare and Education
• /
• v.10 no.1
• /
• pp.183-199
• /
• 2014

The objective of this study was to examine the effects of mother's perfectionism and parenting beliefs on her preschooler's social competence. The participants were 277 mothers residing in Daejeon, Korea. Basic descriptive statistics, Cronbach's ${\alpha}$, t-test, ANOVA, and multiple regression were used for statistical treatment. The results were as follows: First, a mother's perfectionism and parenting beliefs did not differ according to her educational level. One factor of perfectionism, 'holding high standards', alone showed significant difference between highschool graduates and graduate school graduates, the latter's scores being higher than the former's. There were no significant differences in preschooler's social competence by sex or age. However, a few sex and age differences were found in sub-factors of social competence. Girls scored higher than boys on 'showing affection', and 5 year olds scored lower on 'showing affection' and higher on 'leadership' than 3 years olds. Second, a mother's perfectionism and parenting beliefs were able to explain 22.8% of variance in preschooler's social competence, the former showing more predictive power than the latter. Each of the two factors of maternal perfectionism affected five factors of preschooler's social competence in a different manner. 'Holding high standards' of perfectionism positively influenced preschooler's social competence factors such as 'social capability', 'leadership', and 'showing affection', whereas maternal 'fear of failure' had a negative impact on 'showing affection', 'disturbing'(reversed), and 'instability'(reversed). These results were discussed in relation with changes in social atmosphere and value systems, changes in child-rearing behaviors, or the construct and concept of perfectionism itself, It was suggested that these results be utilized in developing parent education programs for preschoolers lacking social competence.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.24 no.2
• /
• pp.94-102
• /
• 2020

Precast concrete segment arch system has an economic and construct ability that combined with advantage of precast concrete and arch behavior. A precast concrete segment arch system with outrigger is consisted of segmented precast panels, a steel outrigger rib, and V-strip to connect precast panels with a steel outrigger rib and cast-in-place anchors in precast panels to connect V-strip should have sufficient pull-out capacity to form its arch shape by site lifting for assembled precast panels and outriggers. However, it is difficult to secure its embedment depth due to the relatively shallow thickness of precast panel. It can be also occurred that flexure deformation of precast panels caused by its pull-out behaviors. In this study, pull-out capacity of cast-in-place anchor was examined for construction of precast concrete segment arch system with outriggers. Therefore, a total of 24 precast panel specimens were fabricated to examine pull-out capacities of cast-in-place anchor in precast panels, and installation depth of anchors, diameter of anchors and wire mesh effects for the precast panel were examined. From this pull-out tests, its pull-out capacities and failure modes were evaluated and the type of the cast-in-place anchor applicable to the precast concrete segment panel arch system with outriggers was determined from comparison of the design specification values.

• Polymer(Korea)
• /
• v.31 no.5
• /
• pp.399-403
• /
• 2007

Trans-esterification behavior of polycarbonate/poly(butylene terephthalate) (PC/PBT) blends was investigated during the melt mixing process. Rheological and fracture behaviors, and fracture morphology were also investigated as a function of PC/PBT blend ratio. Based on FT-IR and $^1H-NMR$ results, a trans-esterification reaction was confirmed to occur between PC and PBT during the melt mixing process. The melt index(MI) decreased with increased PC content, indicating the higher flow resistance of PC. The storage and loss moduli were increased by increasing the PC loading, and the PC/PBT blends were rheologically incompatible based on the Cole-Cole plot. The tensile property increased linearly with the increased PC content. However, the impact strength increased until 50 wt% of PC loading, notably around $30{\sim}40wt%$, and then was levelled off at 50 wt%. Rough ridges were formed on the impact fracture surfaces above the 40 wt% of PC content, supporting the observed higher impact strength in this range.

• Journal of the Microelectronics and Packaging Society
• /
• v.12 no.2 s.35
• /
• pp.167-174
• /
• 2005

Smaller size and higher integration of electronic components make smaller gap between metal conducting layers in electronic package. Under harsh environmental conditions (high temperature/humidity), electronic component respond to applied voltages by electrochemically ionization of metal and metal filament formation, which lead to short failure and this phenomenon is termed electrochemical migration(ECM). In this work, printed circuit board(PCB) is used for determination of ECM characteristics. Copper leads of PCB are soldered by eutectic solder alloys. Insulation breakdown time is measured at $85^{\circ}C,\;85{\%}RH$. CAF is the main mechanism of ECM at PCB. Pb is more susceptible to CAF rather than Sn, which corresponds well to the corrosion resistance of solder materials in aqueous environment. Polarization tests in chloride or chloride-free solutions fur pure metal and eutectic solder alloys are performed to understand ECM characteristics. Lifetime results show well defined log-normal distribution which resulted in biased voltage factor(n=2) by voltage scaling. Details on migration mechanism and lifetime statistics will be presented and discussed.

• Journal of the Korea Concrete Institute
• /
• v.17 no.6 s.90
• /
• pp.955-962
• /
• 2005

Still no accurate theory exists for predicting ultimate shear strength of deep reinforced concrete beams because of the structural and material non-linearity after cracking. Currently, the load capacity assesment is performed for the upper structure of the bridges and containing non-reliability in the applications and results. The purpose in this study is to evaluate analytically the complex shear behaviors and normal strength for the reinforced concrete deep beams and to offer the accuracy load capacity assesment method based on the reliability theories. This paper presents a method for the load capacity assesment of reinforcement concrete deep beams using nonlinear finite element analysis. A computer program named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. Material non-linearity is taken Into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. From the results, determine the reliability index for the failure base on the Euro Code. Then, calculate additional reduction coefficient to satisfy the goals from the reliability analysis. The proposed numerical method for the load capacity assesment of reinforced concrete deep beams is verified by comparison with the others methods.

• Journal of the Korea Concrete Institute
• /
• v.14 no.3
• /
• pp.430-439
• /
• 2002

The development of reinforcing steel is required in reinforced concrete structures. The standard hooks that have been widely used for the tensile development in the beam-column joints tend to create difficulties of construction such as steel congestion as the member cross sections are becoming smaller due to the use of higher strength concrete and higher grade steel. Using the reinforcing bars with end mechanical anchoring device (headed reinforcement) provides potential economies in construction such as reduction in development lengths, simplified details, and improved responses to cyclic loadings. In this paper, the pullout strengths and behaviors of the headed reinforcement were experimentally studied. In 33 pullout tests performed using D25 deformed reinforcing bars, the test parameters were embedment depth, edge distance, head size, and the use of transverse reinforcement. The pullout strengths determined from tests closely agreed with the pullout strengths predicted using the CCD method. The pullout strengths increased with increasing embedment depths nd edge distances. The strengths tend to increase with the use of larger heads. From the experimental program where the effect of the transverse reinforcement was examined, a modification factor to the CCD was suggested to represent the effect of such reinforcement that is installed across the concrete failure plane on the pullout strengths.

• Spatial Information Research
• /
• v.22 no.6
• /
• pp.55-65
• /
• 2014

By combining the role of current GIS technology and design behaviors from the cognitive perspective, spatial conceptualization can be extended efficiently and creatively for ill-structured problems. This study elaborates the model of a conceptualization-oriented SDSS(Spatial Decision Support System) for a landscape design problem. Current information-oriented GIS technology plays a minor role in planning and design. The three attributes in planning and design problems describe how the deficiencies of current GIS technology can be seen as a failure of the technology. These are summarized: (1) Information Explosion/Information Ignorance (2) Dilemma of Rigor and Relevance (3) Ill-structured Nature of planning and Design. In order to implement the conceptualization idea in the current GIS environment, it will be necessary to shift from traditional, information-oriented GISs to conceptualization-oriented SDSSs. The conceptualization-oriented SDSS model reflects the key elements of six important theories and techniques. The six useful theories and techniques are as follows; (1) Human Information Processing (2) Tool/Theory Interaction (3) The Sciences of the Artificial and Epistemology of Practice (4) Decision Support Systems (DSSs) (5) Human-Computer Interaction (HCI) (6) Creative Thinking. The future conceptualization-oriented SDSS can provide capabilities for planners and designers to figure out some "hidden organizations" in spatial planning and design, and develop new ideas through its conceptualization capability. The facilitation of conceptualization has been demonstrated by presenting three key ideas for the framework of the SDSS model: (1) bubble-oriented design support system (2) prototypes as an extension of semantic memory, and (3) scripts as an extension of episodic memory in a cognitive pschology perspective. The three ideas can provide a direction for the future GIS technology in planning and design.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.2
• /
• pp.643-653
• /
• 2013

Recently, there are an increasing number of studies on the method of wrapping the outer wall of granular piles with geosynthetic fibers such as geotextile or geogrid that has a certain level of tensile strength as an alternative method for the ground improvement techniques. In this study, triaxial compression tests are performed on the sand and clay specimen encased with various textiles to evaluate the reinforcing effect with regard to the tensile strength of the textile. Furthermore, triaxial compression tests are performed on the clay specimen inserted by sand only and sand encased with geosynthetics to compare behavioral differences between the conventional sand compaction pile and geosynthetic encased sand pile with regard to the replacement ratio, ${\alpha}_s$ and the tensile strength of the geosynthetics. Based on the experimental results, the strength enhancement due to the textile is affected by the longitudinal tensile strength rather than the transverse one of the applied textile. The effect of the confinement by the textile encasement results in the large increase of the cohesions. The overall behaviors, such as shear strength, pore pressure parameter at failure and stress ratio, of the geosynthetic encased sand pile is quite different from those of the conventional sand compaction pile.