• Restorative Dentistry and Endodontics
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• v.25 no.3
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• pp.421-434
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• 2000

The purpose of this study was to evaluate the influences of incorporation of zirconium-silicate on diametral tensile strength, shear bond strength to the enamel, and depth of cure of 7 experimental composites. One group contained no filler(group 1 or control group), and the other 6 composites contain 75% filler in which zirconium-silicate(Zr-Si) were 0%, 2%, 4%, 6%, 8%, 10% with reduced contents of silica filler, respectively. Both of fillers were treated with 1% silane (${\gamma}$-methacryloxypropyltrimethoxy silane). Light curable monomers were prepared by mixing Bis-GMA and TEGDMA with 3:1 ratio and adding camphoroquinone(CQ) 0.6% with tertiary amine 0.3%. Diametral tensile strengths of specimens with $3mm{\times}6mm$ were measured with Instron (No.4467, USA) with 1mm/min crosshead speed. Shear bond strengths of composites which bonded to bovine enamel etched with 37% phosphoric acid were measured at Instron Testing Machine with as same speed as in diametral tensile strengths. Depth of cure were measured by a method that composite was filled in cylinder mold, illuminated at one side. and uncured composite was removed with acetone, and the residual thickness of composite was measured. Following results were obtained ; 1. Composites containing 0%, 2%, or 4% zirconium-silicate filler(group 2, 3 and 4) showed the statistically higher diametral tensile strength than the others. (p<0.05) 2. Increase of zirconium-silicate filler contents reduced the diametral tensile strength of experimental composites. ($r^2$=0.8721, p=0.0002) 3. Increase of zirconium-silicate filler contents did not affect the shear bond strength of experimental composites. ($r^2$=0.2815, p=0.4067) 4. Increase of zirconium-silicate filler contents reduced significantly the depth of cure of experimental composites. ($r^2$=0.9700, p<0.0001) These results mean that the mechanical properties of composites could not be improved by incorporation of small amount of zirconium-silicate filler. Also, the increased contents of zirconium-silicates fillers was found to reduce the diametral tensile strength and depth of cure.

• Geomechanics and Engineering
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• v.19 no.6
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• pp.499-511
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• 2019

The reliability of reinforced concrete structures is frequently compromised by the deterioration caused by reinforcement corrosion. Evaluating the effect caused by reinforcement corrosion on structural behaviour of corrosion damaged concrete structures is essential for effective and reliable infrastructure management. In lifecycle management of corrosion affected reinforced concrete structures, it is difficult to correctly assess the lifecycle performance due to the uncertainties associated with structural resistance deterioration. This paper presents a stochastic deterioration modelling approach to evaluate the performance deterioration of corroded concrete structures during their service life. The flexural strength deterioration is analytically predicted on the basis of bond strength evolution caused by reinforcement corrosion, which is examined by the experimental and field data available. An assessment criterion is defined to evaluate the flexural strength deterioration for the time-dependent reliability analysis. The results from the worked examples show that the proposed approach is capable of evaluating the structural reliability of corrosion damaged concrete structures.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2002.05a
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• pp.47-50
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• 2002

This paper presents the results of fire resistance properties of high performance concrete varying with fiber kinds and the size of metal lath in order to verify the validities of fiber on the spatting resistance by fire. Metal lath, glass fiber and carbon fiber are used to confine the concrete. According to test results, plain concrete without lateral confinement and confined concrete with glass fiber and carbon fiber show entire failure after exposed to fire, while confined concrete with metal lath take place in the form of slight surface spatting by fire, which has favorable spatting resistance of concrete. As for the effect of the size of metal lath, when the size of metal lath is more than 1.2mm of thickness, the residual strength of concrete exposed to fire maintains more than 80% of its original strength. However, glass fiber and carbon fiber does not perform desirable spatting resistance by fire due to loss of lateral confinement of fiber exposed to fire caused by melting of fiber and reducing bond strength between concrete and fiber.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05a
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• pp.70-73
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• 2004

The packaging of the integrated circuits requires knowledge of ceramics and metals to accommodate the fabrication of modules that are used to construct subsystems and entire systems from extremely small components. Composite ceramics (Al$_2$O$_3$-SiO$_2$) were tested for substrates. A stress analysis was conducted for a linear work-hardening metal cylinder embedded in an infinite ceramic matrix. The bond between the metal and ceramic was established at high temperature and stresses developed during cooling to room temperature. The calculations showed that the stresses depend on the mismatch in thermal expansion, the elastic properties, and the yield strength and work hardening rate of the metal. Experimental measurements of the surface stresses have also been made on a Cu/Al$_2$O$_3$-SiO$_2$ceramic system, using an indentation technique. A comparison revealed that the calculated stresses were appreciably larger than the measured surface stresses, indicating an important difference between the bulk and surface residual stresses. However, it was also shown that porosity in the metal could plastically expand and permit substantial dilatational relaxation of the residual stresses. Conversely it was noted that pore clusters were capable of initiating ductile rupture, by means of a plastic instability, in the presence of appreciable tri-axiality. The role of ceramics for packaging of microelectronics will continue to be extremely challenging.

• Steel and Composite Structures
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• v.43 no.1
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• pp.19-30
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• 2022

The static strength and fatigue crack resistance of the aircraft skin structures depend on the materials used and joint type. Most of the commercial aircraft's skin panel structures are made from aluminium alloy and carbon fibre reinforced epoxy. In this study, the fatigue resistance of four joint configurations (metal/metal, metal/composite, composite/composite and composite/metal) with riveted, adhesive bonded, and hybrid joining techniques are investigated with experiments and finite element analysis. The fatigue tests were tension-tension because of the typical nature of the loads on aircraft skin panels susceptible of experimenting fatigue. Experiment results suggest that the fatigue life of hybrid joints is superior to adhesive bonded joints, and these in turn much better than conventional riveted joints. Thanks to the fact that, for hybrid joints, the adhesive bond provides better load distribution and ensures load-carrying capacity in the event of premature adhesive failure while rivets induce compressive residual stresses in the joint. Results from FE tool ABAQUS analysis for adhesive bonded and hybrid joints agrees with the experiments. From the analysis, the energy release rate for adhesive bonded joints is higher than that of hybrid joints in both opening (mode I) and shear direction (mode II). Most joints show higher energy release rate in mode II. This indicates that the joints experience fatigue crack in the shear direction, which is responsible for crack opening.

• The korean journal of orthodontics
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• v.25 no.2 s.49
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• pp.223-233
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• 1995

The purpose of this study was to evaluate the effects of surface conditioning with $10\%$ polyacrylic acid, etching with $38\%$ phosphoric acid, and polishing with a slurry of pumice on shear bond strengths of light-cured glass ionomer cement, chemically cured glass ionomer cement, and a composite resin to enamel, and to observe the failure patterns of bracket bondings. Shear bond strengths of glass ionomer cements were compared with that of a composite resin. Metal brackets were bonded on the extracted human bicuspids after enamel surface treatments, and samples were immersed in the $37^{\circ}C$ distilled water bath, and shear bond strengths of glass ionomer cements and a composite resin were measured on the Instron machine after 24hrs passed, and the deboned samples were measured in respect of adhesive remnant index. Scanning electron micrographs were taken of enamel surfaces after various treatments. The data were evaluated and tested by ANOVA and Duncan's multiple range test, and those results were as follows. 1. Shear bond strength of light-cured glass ionomer cement showed statistically higher than that of chemically cured glass ionomer cement. 2. Shear bond strengths of light-cured and chemically cured glass ionomer cements to enamel treated with $10\%$ polyacrylic acid and $38\%$ phosphoric acid showed statistically higher than those with a slurry of pumice. 3. According to scanning electron micrographs, enamel surface conditioned with $10\%$ polyacrylic acid is slightly etched and cleaned, that etched with $38\%$ phosphoric acid is severely etched, and that polished with a slurry of pumice is irregulary scretched and not completely cleaned. 4. After debonding, light-cured glass ionomer cement to enamel treated with $10\%$ polyacrylic acid showed less residual materials on the enamel solace than composite resin to enamel etched with $38\%$ phosphoric acid. 5. There was no significant difference in the shear bond strength of light-cured glass ionomer cement to enamel treated with $10\%$ polyacrylic acid and that of composite resin to enamel etched with $38\%$ Phosphoric acid.

• Restorative Dentistry and Endodontics
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• v.35 no.5
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• pp.321-334
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• 2010

Objectives: The purpose of this study is to evaluate bonding efficacy by means of measuring the effect of remained solvent on Degree of conversion(DC) and ${\mu}TBS$ and FE-SEM examination. Materials and Methods: Two 2-step total etching adhesives and two single-step self etching adhesives were used in this study. First, volume weight loss of 4 dentin adhesives were measured using weighting machine in process of time in normal conditions and calculate degree of evaporation (DE). Reaction/reference intensity ratio were measured using micro-Raman spectroscopy and calculate DC according to DE. Then 2 experimental groups were prepared according to air-drying methods (under, over) and control group was prepared to manufacturer's instruction. Total 12 groups were evaluated by means of micro tensile bond strength and FE-SEM examination. Results: Degree of evaporation (DE) was increased as time elapsed but different features were observed according to the kind of solvents. Acetone based adhesive showed higher DE than ethanol and butanol based adhesive. Degree of conversion (DC) was increased according to DE except for $S^3$ bond. In ${\mu}TBS$ evaluation, bond strength was increased by additional air-drying. Large gaps and droplets were observed in acetone based adhesives by FE-SEM pictures. Conclusions: Additional air-drying is recommended for single-step self etching adhesive but careful consideration is required for 2-step total etching adhesive because of oxygen inhibition layer. Evaporation method is carefully chose and applied according to the solvent type.

• The Journal of Korean Academy of Prosthodontics
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• v.28 no.1
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• pp.165-191
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• 1990

Although a number of studies have been performed to assure that residual stress caused by a mismatch of alloy porcelain thermal expansion can contribute to clinical failure of a ceramometal restoration, the interactive influence of cooling rate on the magnitude of thermal expansion difference and on bond strength between them have not been extensively analyzed. The objective of this study was to determine the influence of cooling rate and the number of firing cycles on the expansion mismatch and the flexural failure resistance of metal porcelain strip. Tested alloys included one Pd-Ag alloy, one Ni-Cr-Be alloy with two kinds of porcelain, Vita and Ceramco. Metal specimens were cast into rods with a height of 13mm and a diameter of 5mm. Subsequently, the castings were subjected to scheduled firing cycles without porcelain. And the porcelain specimens after being fired were trimmed into a bar with a final dimension of $5{\times}5{\times}25mm$. Thermal expansions of the alloys and porcelains were measured by using a push rod or a differential dialometer respecitvely. Porcelain glass transition temperatures and expansion values were derived alloy-porcelain pairs were assessed by comparing expansion values of the components at a porcelain glass transition temperature. Calculations were made using combinations of a Ni-Cr alloy or Pd-Ag alloy with each of two porcelain products. Metal-porcelain strip specimens were subjected to four point loading in an Instron testing machine until crack occured at the metal-cramic interface at the time of sharp decrease of load on recorder. On the basis of this study, the following conclusions may be stated: 1. Regardless of the kinds of ceramometal combinations, both of calculated and experimental data revealed that the double fired specimens exhibited a significantly lower flexural strength. 2. By the rise of the amount of mismatch, bond strength were decreased. 3. Thermal expansion value of Pd-Ag alloys were higher than that of Ni-Cr alloys. 4. Expansion curves of metal were proportional to the increase of temperature and were not affected by the experimental conditions, however porcelains did not show the same magnitude of metal, and a shift of the glass transition temperature to higher temperatures was observed when cooled rapidly 5. Alloy-porcelain thermal compatibility appeared more dependent on the porcelain than the alloy.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.1
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• pp.111-137
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• 1991

Although a number of studies have been performed to assure that residual stress caused by a mismatch of alloy porcelain thermal expansion can contribute to clinical failure of a ceramometal restoratoin, the interactive influence of cooling rate on the magnitude of thermal expansion difference and on bond strength between them have not been extensively analyzed. The objective of this study was to determine the influence of cooling rate and the number of firing cycles on the expansion mismatch and the flexural failure resistance of metal porcelain strip. Tested alloys included one Pd-Ag alloy, one Ni-Cr-Be alloy with two kinds of porcelain, Vita and Ceramco. Metal specimens were cast into rods with a height of 13mm and a diameter of 5mm. Subsequently, the castings were subjected to scheduled firing cycles without porcelain. And the porcelain specimens after being fired were trimmed into a bar with a final dimension of 5 x 5 x 25mm. Thermal expansions of the alloys and porcelains were measured by using a push rod or a differential dialometer respectively. Porcelain glass transition temperatures and expansion values were derived alloy- porcelain pairs were assessed by comparing expansion values of the components at a porcelain glass transition temperature. Calculations were made using combinations of a Ni-Cr alloy or Pd-Ag alloy with each of two porcelain products. Metal- porcelain strip specimens were subjected to four point loading in an Instron testing machine until crack occured at the metal-cramic interface at the time of sharp decrease of load on recorder. On the basis of this study, the following conclusions may be stated : 1. Regardless of the kinds of ceramometal combinations, both of calculated and experimental data revealed that the double fired specimens exhibited a significantly lower flexural strength. 2. By the rise of the amount of mismatch, bond strength were decreased. 3. Thermal expansion value of Pd-Ag alloys were higher than of Ni-Cr alloys. 4. Expansion curves of metal were proportional to the increase of temperature and were not affected by the experimental conditions, however porcelains did not show the same magnitude of metal, and a shift of the glass transition temperature to higher temperatures was observed when cooled rapidly. 5. Alloy- porcelain thermal compatibility appeared more dependent on the porcelain than the alloy.

• The korean journal of orthodontics
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• v.43 no.5
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• pp.235-241
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• 2013

Objective: The purpose of this study was to investigate whether extension of the custom base is necessary for enhancement of bond strength, by comparing the debonding forces and residual adhesives of 3 different lingual bracket systems. Methods: A total of 42 extracted upper premolars were randomly divided into 3 groups of 14 each for bonding with brackets having (1) a conventional limited resin custom base; (2) an extended gold alloy custom base: Incognito${TM}$; and (3) an extended resin custom base: KommonBase${TM}$. The bonding area was measured by scanning the bracket bases with a 3-dimensional digital scanner. The debonding force was measured with an Instron universal testing machine, which applied an occlusogingival shear force. Results: The mean debonding forces were 60.83 N (standard deviation [SD] 10.12), 69.29 N (SD 9.59), and 104.35 N (SD17.84) for the limited resin custom base, extended gold alloy custom base, and extended resin custom base, respectively. The debonding force observed with the extended resin custom base was significantly different from that observed with the other bases. In addition, the adhesive remnant index was significantly higher with the extended gold alloy custom base. Conclusions: All 3 custom-base lingual brackets can withstand occlusal and orthodontic forces. We conclude that effective bonding of lingual brackets can be obtained without extension of the custom base.