• Title, Summary, Keyword: Hertzian indentation

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Studies on Damage Properties of MgO-C Refractories through Hertzian Indentation at Room and High Temperatures

  • Cho, Geun-Ho;Byeun, Yunki;Jung, Yeon-Gil
    • Journal of the Korean Ceramic Society
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    • v.56 no.1
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    • pp.77-83
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    • 2019
  • MgO-C refractories are used in basic furnaces and steel ladles due to their many desirable properties, such as excellent thermal shock resistance via low thermal expansion, and high thermal conductivity. However, the mechanical and thermal properties of the refractory continuously deteriorate by spalling phenomena and pore generation due to the oxidation of graphite, used as a carbon source, indicating that the characteristics and performance of MgO-C refractories need to be improved by using a new material or composition. In this study, the use of a Hertzian indentation test as a method for determining the damage and fracture behavior of an MgO-C refractory is described. The results highlight that Hertzain indentation tests can be one of the important evaluation tools for quasi-plastic damage accumulation of MgO-C refractories during falling process of scrap metal.

Hertzian Crack Suppression and Damage Tolerance of Silicon Nitride Bilayer

  • Lee, Kee-Sung;Kim, Do-Kyung;Lee, Seung-Kun;Lawn, Brian R.
    • The Korean Journal of Ceramics
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    • v.4 no.4
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    • pp.356-362
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    • 1998
  • Hertzian crack suppression phenomena and relatively high damage tolerance were investigated in hard/soft silicon nitride ($Si_3N_4$) bilayers. Coarse $\alpha}-Si_3N_4$ powder was wsed for the hard coating layer and fine $\alpha}-Si_3N_4$ powder was used for the soft substrate layer. The two layers were designed with a strong interface. Hertzian indentation was used to investigate contact fracture and damage tolerance property. Hertzian crack suppression has occurred with increasing applied load and decreasing coating thickness. The crack suppression contributed strength improvement, especially in the bilayers with thinner coatings. Ultimately, the combination of hard coating with soft but tough underlayer improved the damage tolerance of brittle $Si_3N_4$ ceramics.

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Microstructure and annealing effect on fracture behavior in the dental glass-infiltrated alumina (치아용 유리침윤 알루미나에서 파괴거동에 미치는 미세구조 및 어닐링 효과)

  • 정종원;최성철
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.10 no.4
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    • pp.330-336
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    • 2000
  • Effects of microstructure and indentation stress on fracture behavior of glass-infiltrated alumina composite for dental restorative application were investigated by the Hertzian and Vickers indentation method. Indentation stress-strain curve of glass-infiltrated alumina has showed the quasi-plastic behavior - deviation from linearity at high stress and the classical Hertzian cone crack, which could be confirmed the subsurface damage micrographs using bonded-interface specimen technique. The indentation stress-strain curves for the starting preforms are strongly dependent on porosity and microstructure of the preforms. On the other hand, the curves for the infiltrated composites are relatively insensitive to these factors. The failure of composite is originated at quasi-plastic deformation region. Damage and fracture behavior due to Hertzian stress field is theoretically examined, so that the indentation stress field plays a great role in material degradation. After Hertzian indentation annealing processing changes fracture behavior of alumina composite, so that stress field in material is healed through annealing.

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Indentation Damage of Porous Alumina Ceramice

  • Ha, Jang-Hoon;Lee, Chul-Seung;Kim, Jong-Ho;Kim, Do-Kyung
    • Journal of the Korean Ceramic Society
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    • v.41 no.1
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    • pp.19-23
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    • 2004
  • The Hertzian indentation contact damage behavior of porous alumina with controlled pore shape was investigated by experiments. Porous alumina ceramics containing well-defined pore shape, size and distribution were prepared by incorporation of fugitive spherical starch. Porous alumina with isolated pore structure was prepared with porosity range up to 30%. The indentation stress-strain curves of porous alumina were constructed. Elastic modulus and yield stress can be obtained from the stress-strain relationship. Impulse excitation method for the measurement of elastic modulus was also conducted as well as Hertzian indentation and was confirmed as a useful tool to evaluate the elasticity of highly porous ceramics. Elastic modulus of the inter-connected pore structure is more sensitive to porosity than that of the isolated pore structure. When the specimen had isolated pore structure, higher yield point was obtained than it had inter-connected pore structure. This study proposed that the elastic modiulus of porous ceramics is strongly related to not only porosity, but also the structure of pore.

Effects of Contact Damage and Residual Stress in Dental Layered Ceramics (치아응용을 위한 층상 세라믹스에서의 접촉손상 및 잔류응력의 영향)

  • 정종원;최성철
    • Journal of the Korean Ceramic Society
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    • v.37 no.3
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    • pp.288-293
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    • 2000
  • Effects of contact damage and residual stress for two kinds of dental restorative layered ceramics, porcelain/alumina and porcelain/zirconia bilayers, were observed with Hertzian and Vickers indentation methods. Indentation stress-strain behavior of each material, strength degradation of the coating material, and crack propagation behavior in the coating layer after Vickers indentation were examined by an optical microscope. As a result, porcelain as coating materials showed the classical brittleness. It was inferred that damage and strength in two bilayer system were dependent on thermal expansion mismatch between the coating material and the substrate, which affected the strength degradation. Residual stress resulting from thermal expansion mismtch was formed in the coating layer, and specially in the case of porcelain/zirconia, residual stress was eliminated as coating thickness decreased.

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Mechanical Propertis and Contact Damage Behavior of Ti$_3$SiC$_2$ (Ti$_3$SiC$_2$의 기계적 성질 및 접촉 손상 거동)

  • 이승건
    • Journal of the Korean Ceramic Society
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    • v.35 no.4
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    • pp.333-338
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    • 1998
  • Mechanical properties of polycrystalline{{{{ {Ti }_{3 }{SiC}_{2 } }} were investigated. Hertzian indentation test using a spher-ical indenter was used to study elastic and plastic behavior in{{{{ {Ti }_{3 }{SiC}_{2 } }} A high ratio of hardness to elastic mo-dulus indicated that mechanical properties of{{{{ {Ti }_{3 }{SiC}_{2 } }} are somehow similar to those of metals. Indentation stress-strain curve deviated from an ideal elastic limit indicating exceptional plasticity in this material. De-formation zones were formed below the contact as well as around the contact area. Intragrain slip would ac-count for high plasticity.

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A Study on Glass-Infiltrated Alumina and Spinel Composite I. Effect of Microstructure and Glass Content on Contant Damage and Strength (유리침윤 알루미나 및 스핀넬 복합체에 관한 연구 I. 미세구조 및 유리함량이 접촉손상 및 강동에 미치는 영향)

  • 정연길;최성철
    • Journal of the Korean Ceramic Society
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    • v.35 no.7
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    • pp.671-678
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    • 1998
  • Hertzian indentation tests with sphere indenters were used to study the mechanical properties of glass-in-filtrated alumina and spinel composites and evaluated the effect of preform microstructure and evaluated the effect of preform microstructure and glass con-tents on contanct damage and strength. The spinel composite showed more brittle behavior than the alumina composite which is verified from indentation stress-strain curve cone cracks and quasi-plastic deformation developed at subsurface. Failure originated from either cone cracks(brittle mode) or deformation zone(quasi-plastic mode) above critical load for cracking(Pc) and yield ({{{{ {P }_{Y } }}) with the brittle mode more dominant in the spinels and the quasi-plastic mode more dominant in the aluminas. Even though brittle mode was dominant in the spinel composites the strength degradation from accumulation of damage above these critical loads was conspicuously small suggesting that the glass-infiltrated composites should be highly damage tolerant to the blunt contacts.

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Contact Damage and Strength Degradation of Yttria doped Tetragonal Zirconia Polycrystal (Y$_2$O$_3$ 를 첨가한 정방정 지르코니아에서의 접촉손상 및 강도저하)

  • 정연길;최성철
    • Journal of the Korean Ceramic Society
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    • v.35 no.5
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    • pp.429-436
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    • 1998
  • The mechanical properties and damage mode of {{{{ {Y}_{2 } {O}_{3} }}-doped tetragonal (Y-TZP) can-didated as biomaterials were performed under indentation stress-strain curve critical load for yield and cracking strength degradation and fatigue behavior with Hertzian indentation tests. This material shows the brittle behavior which is confirmed by indentation stress-strain response. The critical load for cracking(Pc) is much higher than that for yields (Py) indicating crack resistance Strength were strongly dependant on contact area and there were no degradation when the indenter size was ${\gamma}$=3.18 mm suggesting that Y-TZP should be highly damage tolerant to the blunt contacts. Multi-cycle contact were found to be innocuous up to {{{{ {10 }^{6 } }} cycles at 500N and {{{{ {10 }^{5 } }} cycles at 1000N in water. On the other hand contacts at {{{{ {10 }^{6 } }} cycles at 1000 N in water did show some signs of incipient degradation. By contrast contacts with Vickers indenter pro-duced substantial strength losses at much lower loads suggesting that the mechanical integrity of this ma-terial would be compromised by inadvertent sharp contacts.

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Effect if Grain Size on Plasticity of Ti$_3$SiC$_2$ (Ti$_3$SiC$_2$의 소성 변형 특성에 미치는 결정립 크기의 효과)

  • 이승건
    • Journal of the Korean Ceramic Society
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    • v.35 no.8
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    • pp.807-812
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    • 1998
  • Mechanical properties of two types of polycrystlline {{{{ { { Ti}_{3 }SiC }_{2 } }} with different grain size were investigated. A fine grain {{{{ { { Ti}_{3 }SiC }_{2 } }} has a higher fracture strength and hardness. Plot of strength versus Vickers indentation load indicated that {{{{ { { Ti}_{3 }SiC }_{2 } }} has a high flaw tolerance. Hertzian indentation test using a spherical indenter was used to study elastic and plastic behavior in {{{{ { { Ti}_{3 }SiC }_{2 } }}. Indentation stress-strain curves of each material are made to evaluate the plasticity of {{{{ { { Ti}_{3 }SiC }_{2 } }} Both find and coarse grain {{{{ { { Ti}_{3 }SiC }_{2 } }} showed high plasticity. In-dentation stress-strain curve of coarse grain {{{{ { { Ti}_{3 }SiC }_{2 } }} deviated even more from an ideal elastic limit in-dicating exceptional plasticity in this material. Deformation zones were formed below the contact as well as around the contact area in both materials but the size of deformation zone in coarse grain {{{{ { { Ti}_{3 }SiC }_{2 } }} was much larger than that in fine grain {{{{ { { Ti}_{3 }SiC }_{2 } }} Intragrain slip and kink would account for high plasticity. Plastic behavior of {{{{ { { Ti}_{3 }SiC }_{2 } }} was strongly influenced by grain size.

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Strength Degradation from Contact Fatigue in Self-toughened Glass-ceramics

  • Lee, Kee Sung;Kim, Do Kyung;Woo, Sang Kuk;Han, Moon Hee
    • The Korean Journal of Ceramics
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    • v.7 no.2
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    • pp.63-69
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    • 2001
  • We investigated strength degradations from cyclic contact fatigue in self-toughened glass-ceramics. Hertzian indentation was used to induce cyclic contact load. Dynamic fatigue was also performed with changing stress rates from 0.01 to 10000 MPa/sec. After that, strength data and fracture origins were analysed. As the number of contact cycles increased or stressing rate decreased, severe strength degradation occurred by as much as 50% because of radial cracks developed from microcrack coalescence.

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