• 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.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.1
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• pp.44-49
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• 2004

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.4
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• pp.313-320
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• 1984

본 연구에서는 원형 단면 링 압인(circularcross-section ring indentation) 을 노치 주위에 주고 피로 하중하에서 발생한 균열이 성장하는 거동을 관찰하고 해석 하므로써 균열의 저지 및 지연 방법으로써 가능성을 제시하고자 한다.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.144-150
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• 2001

Considered is non-symmetric contact traction induced by the tilting of a contact body and/or by a far field bulk tensile load to the other body. The problem is under the regime of plane strain. General profile of the contact end is incorporated and partial slip condition is supposed. As an example contact configuration, an indentation of a punch with rounded corners onto a half plane is studied. The variation of the internal stress field due to the tilting and the bulk tension is investigated. An edge crack problem is analyzed to examine the influence of the non-symmetric traction. It is shown that the tilting of a punch does not influence the behaviour of the crack. Rather, the effect of the bulk tension on the cracking behaviour is found considerable.

• Composites Research
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• v.24 no.2
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• pp.9-13
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• 2011

,In this paper, the symmetric axis parameter method, which was proposed to identify defects, dislocations and stacking fault, with perfect structures in the zinc-blende materials, was introduced as a way to distinguish between elastic and plastic deformation. LAMMPS, a molecular dynamics programme of Sandia National Laboratories, was used to perform nanoindentation simulation on silicon, a zinc-blende material. Defects in silicon (111) under spherical indentation showed the threefold pattern and the slip system in the form of ring crack. Also simulation results show good agreement with experimental results and existing theoretical analyses.

• Journal of the Korean Ceramic Society
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• v.38 no.5
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• pp.454-460
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• 2001

장석, 석영, 점토와 17 wt% $Al_2$O$_3$를 함유한 알루미나질 자기 애자를 제조하였다. 분말을 ball milling으로 6시간 분쇄하였으며 성형체를 압출법으로 제조한 후 터널가마에서 130$0^{\circ}C$, 50분 동안 소결하였다. 터널가마에서 소결한 시편의 소결밀도는 이론밀도의 97%에 도달하였고, 3점 꺾임강도는 1658kgf/$ extrm{cm}^2$ 이었으며 ICL(indentation crack length) 방법으로 측정한 파괴인성은 2.3 MPa.m$^{1}$2/이었다. 기계적 성질을 향상시키기 위하여 ZrO$_2$를 첨가하여 15 wt% $Al_2$O$_3$-2 wt% ZrO$_2$와 12 wt% $Al_2$O$_3$-5 wt% ZrO$_2$를 복합체를 제조하였다. ZrO$_2$를 첨가한 시편의 꺾임강도는 1740kgf/$\textrm{cm}^2$이고 파괴인성은 2.4 MPa.m$^{1}$2/로 약 10% 기계적 성질이 향상되었다.

• Korean Journal of Materials Research
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• v.16 no.12
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• pp.743-746
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• 2006

ZTA tubes were prepared by centrifugal casting and sintered at $1600^{\circ}C$ for 2 hrs. The ZTA tubes were machined into specimens of $3{\times}4{\times}40$ mm. Molten Soda lime glass (SLG) was penetrated into the surface of ZTA at an optimized condition of $1500^{\circ}C$ for the holding time of 5 h and furnace cooled. The extra glass on the surface was removed using a resin bonded diamond wheel. The glass penetrated samples were tested for their flexural strength using four point bend test. Vickers Indentation cracks were made on the glass penetrated surface at different loads of 9.8 N, 49 N, 98 N and 196 N. The residual compression on the surface enhanced the flexural strength and crack arrest behaviour remarkably. This was attributed to the thermoelastic mismatch between the glass and ZTA matrix during cooling.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.121-126
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• 2000

Metal/Ceramic structures have many attractive properties, with great potential for applications that demand high stiffness, as well as chemical and biological stability, thermal and electrical insulation. They are currently in use for mechanical and thermal protection in cutting tool and engine parts. With all their great advantage, ceramics suffer from one major problem they are brittle, and are especially susceptible to cracking from surface contacts. Delamination at the interfaces with adjacent layers is a particularly disturbing problem, and can cause premature failure of a composite system. so determination of adhesive properties of coating is one of the most important problems for the extension of the use of coated materials. In this work, mechanical characteristics of Interface of ceramic/Metal composites are evaluated by means of hardness test, indentation test apparent interfacial toughness and bonding strength test. The interface indentation test provides a relation between the applied load(P) and the length of the crack(a) created at the interface between the coating and the substrate.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.12
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• pp.3847-3855
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• 1996

In order to study the relationship between static and cynamic behaviors of silion caride, both quasi-static indentaiton and impact experiments of spherical particle have been conducted. The difference inmaterial behavior when using the two mehtods suggests a loading rate difference in the damate pattrern and fracture strength of silicon carbide. This investigation showed some difference in damage pattern according to particla property, especially inthe case of particle impact. There was no differences in deformation behaviors according to the loading rate when the crater profiles were compared with each other at the same contact radius. From the result of residual strength evaluation, it was found that the strength degradation began at the initiation of ring crack and its behavior was colsely related to morphologies of the damage developed which was also dependent upon the extent of deformation atthe loaidng point. In the case of static indentation, there didnot exist the particle property effects onthe strength degradation behavior.

• Journal of the Korean Ceramic Society
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• v.22 no.6
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• pp.37-41
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• 1985

Several $Al_2O_3$-based polycrystalline which had different dopant ratio in the range of 0.5mol% were prepared by doping pure $Cr_2O_3$, $ZrO_2$, $HfO_3$ Single crystalline which had same composition with above polycrystalline were made by means of floating zone method. This study examined the role of each dopant for enhancing the mefchanical properties of $Al_2O_3$-based Ceramics. Optical micrographs $({\times}200)$ of $Al_2O_3-Cr_2O_3$ single crystal showing not only radial crack (rc) on the specimen surface but median crack (mc) and lateral crack (lc) under surface at the edge of indentation mark. Fracture toughness of $Al_2O_3$-based Ceramics was increased with $ZrO_2$ content. Alloying effect of $Cr_2O_3$ contributed to the hardness of $Al_2O_3$ based ceramics.