Glass-ceramics flexural strength

In addition to the initial work in the alumina and mullite matrix systems previously mentioned, SiC whiskers have also been used to reinforce other ceramic matrices such as silicon nitride,9-13 glass,14 15 magnesia-alumina spinel,16 cordierite,17 zirconia,18 alumina/zirconia,18 19 mullite/zirconia,18-21 and boron carbide.22 A summary of the effect of SiC whisker additions on the mechanical properties of various ceramics is given in Table 2.1. As shown, the addition of whiskers increases the fracture toughness of the ceramics in all cases as compared to the same monolithic materials. In many instances, improvements in the flexural strengths were also observed. Also important is the fact that these improvements over the monolithic materials are retained at elevated temperatures in many cases. 

K. M. Prewo, Tensile and Flexural Strength of SiC Fiber-Reinforced Glass-Ceramic Composite , J. Mat. Sci., 21, 3590 (1986). 

Flexural strength, psi (MPa) Fly ash, wollastonite, and 1-3% glass fiber 1300-1700(9-12) ==700 (4.9) MaCTO-encapsulation of radioactive objects, structural ceramics... 

The strength or modulus of rupture quoted for glass ceramics is determined by loading test bars in flexure. This value can vary by a factor of ten or more for a given material, depending on the surface finish of the test specimens. Fracture strength, ur, depends on the size of surface flaws c, the elastic modulus E, and the work of fracture yr ... 

The crystal phases in the glass-ceramics were determined by XRD analysis. All instruments were precisely and identically set to ensure a high precision to obtain the integral peak area. The microstructure of the fresh fractured cross section of the glass-ceramics was observed by SEM. The thermal expansion coefficient (TEC) was calculated from room temperature to 500 °C at a heating rate of 5°C/min in the dilatometry analyser (NETZSCH, DIL402PC). The flexural strength was determined in a 3-point bend test at a constant strain ratio of 0.5mm/min. 

In unsaturated polyester, a nominal 25 percent replacement of glass fiber with engineered ceramic fiber has shown improvement in flexural, tensile, and impact values. Further improvements are possible via the use of coupling agents. For example, flexural modulus of 2.3 million psi, notched Izod impact strength of 4.4 ft Ib/in., tensile strength of 5610 psi, and flexural strength of 11,200 psi are possible. 

In comparison to the IPS Empress microstructure, a different type of leucite glass-ceramic was developed by Schweiger et al. (1999). The leucite-reinforced glass-ceramic was developed as a biomaterial for dental restoration. The material can easily be machined by a CAD/CAM system. The mechanical properties are characterized by a flexural strength of 135-160 MPa and a fracture toughness as of 1.3 MPa m (section ProCAD in Section 4.4.2 dental glass-ceramics). 

Figure 4-39 Flexural strength of pressed glass-ceramic IPS EMPRESS 2 in comparison to other dental materials, natural tooth, and technical ceramics (Kappert 1998). a) ISO limit, b) tooth enamei, c) tooth dentin, d), e) ieucite-based ceramics, f) iPS EMPRESS , g) feldspar ceramic, h) mica glass-ceramic, i) sintered spinei and infiltrated glass, j) sintered AlgOg and infiltrated glass, k) IPS EMPRESS 2,1) dense sintered AI2O3.

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