• 한국세라믹학회지
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• 제35권6호
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• pp.610-618
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• 1998

Alumina were added to ceria based ceramic powders upto 9.7 vol% and composite powders were sprayed by plasma spraying process in order to improve the mechanical properties such as hardness fracture tough-ness and thermal shock resistance. The ceria based coating sprayed without alumina has the typical colum-nar and lamellar structure. Alumina addition has lowered the amount of columnar and lamellar sturcture Added alumina was segreagated in the grain boundary and grain of ceria based crystal accompanied with pore. The maximum value of density and the minimum value of porosity were observed at the sprayed coating with 4.8 vol% alumina. The hardness fracture toughness and thermal shock resistance were increased with alumina addition. The improvement of mechanical properties of plasma sparyed ceria based coatings result-ed from the disapperance of the columnar and lamellar sturcture by addition of alumina.

• 대한기계학회논문집A
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• 제26권10호
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• pp.2089-2095
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• 2002

Ceramic/metal composites have many attractive properties and great potential fur applications. Interfacial fracture properties of different layered composites are important in material integrity. Therefore, evaluation of fracture toughness at interface is required in essence. In this study, the mechanical characteristics for interface of ceramic/metal composites were investigated by indentation test of micro-hardness method. Apparent interfacial toughness of TBC system could be determined with a relation between the applied load and the length of the crack formed at the interface by indentation test.

• The Journal of Advanced Prosthodontics
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• 제12권4호
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• pp.181-188
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• 2020

PURPOSE. The effect of core design on the fracture resistance of zirconia-lithium disilicate (LS2) bilayered crowns for anterior teeth is evaluated by comparing with that of metal-ceramic crowns. MATERIALS AND METHODS. Forty customized titanium abutments for maxillary central incisor were prepared. Each group of 10 units was constructed using the same veneer form of designs A and B, which covered labial surface to approximately one third of the incisal and cervical palatal surface, respectively. LS2 pressed-on-zirconia (POZ) and porcelain-fused-to-metal (PFM) crowns were divided into "POZ_A," "POZ_B," "PFM_A," and "PFM_B" groups, and 6000 thermal cycles (5/55 ℃) were performed after 24 h storage in distilled water at 37 ℃. All specimens were prepared using a single type of self-adhesive resin cement. The fracture resistance was measured using a universal testing machine. Failure mode and elemental analyses of the bonding interface were performed. The data were analyzed using Welch's t-test and the Games-Howell exact test. RESULTS. The PFM_B (1376. 8 ± 93.3 N) group demonstrated significantly higher fracture strength than the PFM_A (915.8 ± 206.3 N) and POZ_B (963.8 ± 316.2 N) groups (P<.05). There was no statistically significant difference in fracture resistance between the POZ_A (1184.4 ± 319.6 N) and POZ_B groups (P>.05). Regardless of the design differences of the zirconia cores, fractures involving cores occurred in all specimens of the POZ groups. CONCLUSION. The bilayered anterior POZ crowns showed different fracture resistance and fracture pattern according to the core design compared to PFM.

• 대한치과보철학회지
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• 제38권6호
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• pp.791-799
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• 2000

Statement of problem. Targis/Vectris restorations provide excellent esthetics. Marginal accuracy is significantly influenced by the preparation design. There were no studies to examine the effect of preparation design on the marginal discrepancy and fracture strength of Targis / Vectris crowns. Purpose. This study evaluated the marginal accuracy before and after cementation, and the fracture strength of FRC/Ceromer(Targis / Vectris) crowns according to different preparation design. Material and method. Three metal dies with different convergence angles($6^{\circ},\;10^{\circ},\;15^{\circ}$) were prepared. Total 30 (10 for each angle) Targis/Vectris crowns were made. The restorations were evaluated for adaptation of the margin before and after cementation, then were compressively loaded to failure. Fracture surfaces of the crowns were examined using a SEM. Results. The mean marginal gap was $49{\yen}m\;for6^{\circ},\;55{\S}>for\;10^{\circ}\;and\;70{\S}>for\;15^{\circ}$ and in clinically acceptable level. The mean marginal gap increased significantly after cementation. The increasing amount during cementation was the largest in the $6^{\circ}$ group. The crowns on 60 convergence angle had a significantly higher fracture strength than the crowns on $15^{\circ}$ angle. Mean fracture strength of total crowns regardless of convergence angle was 1390 N, which was higher than all-ceramic crowns. SEM observation showed two-mode fracture pattern. Conclusion. From the results of this study, all of the FRC/Ceromer crowns had clinically acceptable marginal accuracy and could withstand the bite force. Moreover, less convergent angle than all-ceramic crown might be recommended for preparation procedure.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 춘계학술대회 논문집
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• pp.233-238
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• 1998

Recently, the uses of ceramic/metal bonded joints for structural materials have increased in various engineering fields such as automobiles, heat engines, and so on. A method of strength evaluation focussing on fracture criterion of mixed was investigated in Si3N4/metal bonded joint. Also, Fracture toughness tests of Si3N4/metal bonded joints with an interface crack were carried out and the stress intensity factors of these joints were analyzed by boundary element method. From the results, the fracture criterion and method of strength evaluation by the fracture toughness were proposed in Si3N4/metal bonded joints

• 대한치과보철학회:학술대회논문집
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• 대한치과보철학회 2005년도 추계학술대회
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• pp.80-80
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• 2005

• 한국세라믹학회지
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• 제30권12호
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• pp.993-998
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• 1993

Nicalon-fiber-reinforced SiC composites were fabricated via polymer solution infiltration/chemical vapor infiltration (PSI/CVI) and CVI. Specifically, data were taken and compared for flexural strength, fracture toughness, and processing time. The two process resulted in comparable mechanical properties, and PSI/CVI process resulted in significantly reduced infiltration time.

• 한국세라믹학회지
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• 제42권6호
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• pp.411-416
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• 2005

Y-TZP(Yttria-stabilized Tetragonal Zirconia Polycrystal) ceramics are of great interest as engineering and structural materials due to their excellent mechanical properties arising from transformation toughening, it is also reported that the 3Y-TZP($3 mol\%$ Yttria-stabilized Tetragonal Zirconia Polycrystal) has the best mechanical properties in Y-TZP ceramics. But to use widely for engineering and structural materials, it remains an important challenge to be able to improve its fracture toughness. In order to produce the 3Y- TZP ceramics showing much better mechanical properties, milling method adding monoclinic zirconia to 3Y-TZP was adopted and the resultant mechanical properties containing apparent density and fracture toughness were measured by using proper techniques. Experimental results showed that the 3Y-TZP specimen containing $33 wt\%$ of monoclinic zirconia, which was sintered at $1450^{\circ}C$, has the highest fracture toughness value of $11.38 MPa{\cdot}m^{1/2}$ which is three times higher than that of normal 3Y-TZP ceramics.

• 한국세라믹학회지
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• 제33권10호
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• pp.1177-1185
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• 1996

Y-TZP/Ce-TZP ceramics having relative sintered densities of>95% average grain sizes of 0.36$\mu\textrm{m}$ microhar-dness of 1150 kg/mm2 fracture strength of 390-830 MPa and toughness of 6.4-10.2 MPa$.$mm1/2 were prepared by conventional sintering of 3 mol% Y2O3-ZrO2 and 12 mol% CeO2-ZrO2 powders at 1400 and 1500$^{\circ}C$ The average grain sizes of Y-TZP/Ce-TZP ceramics were mainly governed by those of Ce-TZP. White increasing Ce-TZP content toughness increased while microhardness and fracture strength decreased. With comparing microhardness and toughness fracture strength was more sensitive on not only grain size but also other factors such as microstructural and compositional variations. The densification of Y-TZP/Ce-TZP cermaics was not greatly affected by composition and soaking time at temperature over 1400$^{\circ}C$ With increasing CE-TZP content the stability of t-ZrO2 decreased under thermal aging in air whereas increased in hydrothermal atmosphere and aqueous solution.

• 한국세라믹학회지
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• 제35권1호
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• pp.48-54
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• 1998

Part I에 이어서 질화규소로 코팅된 질화규소-질화붕소 시스템에 있어서 접촉하중에 의한 코팅층의 파괴에 대한 코팅층의 두께의 영향을 고찰하였다. 코팅층과 기판층간의 elastic/plastic mismatch가 큰 경우 코팅층의 균열생성을 방지하는 어느 임계 두께가 존재한다는 사실을 발견하였으며, mismatch가 감소할수록 이러한 요구 임계두께가 감소하였다. 또한 가해진 하중이 증가할수록 요구 임계두께는 증가하여야 함을 알 수 있었다. 따라서 코팅층의 파괴를 방지하기 위해서는 코팅층과 기판층간의 mismatch와 사용환경(가해지는 하중)을 고려한 적정 임계두께늬 설계가 요구된다.