Ceramics flexural strength values

Characteristic flexural strength values for several ceramic materials are given in Table 12.5. Furthermore, depends on specimen size as explained previously, with increasing specimen volume (i.e., specimen volume exposed to a tensile stress) there is an... 

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 mechanical properties of polycrystalline ZnO ceramics are of special importance for their applications as varistors (see Section 1.4.4.1). When a varistor experiences a high-current pulse, the electrical energy is quickly converted to heat. The inertia of the material, which resists its thermal expansion, and the resonances of the resultant elastic waves in the block, may lead to microcracks and finally to mechanical failure [107]. Characteristic values of mechanical properties of ZnO ceramics are 1.2-1.4 MPa m for fracture toughness, and 100-125 MPa for flexural strength. 

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. 

LCPs ease of processing gives them the ability to fill long, narrow molds, which makes them eminently suitable for such high-performance parts as electronic connectors. They may have 138,000 kPas (20,000 psi) or more in tensile strength, with flexural modulus values up to 5 x 10 psi. They are available in grades with heat deflection temperatures (HDT) of about 357°C (675°F) at 1,820 kPas (264 psi). This family of different LCPs resists most chemicals and weathers oxidation and flame, making them excellent replacements for metals, ceramics, and other plastics. 

However, flexural strength, strain-to-failine, and fracture toughness values of HA-ceramics are significantly less than those of bone, whereas the elastic modulus is much higher [8, 9], These mechanical mismatches influence the reliability of ceramics when implanted into the bone tissue. To improve the mechanical compatibility, a composite approach may be promising. The combination of different materials within a composite structure may lead to a composite material that reveals specific physical, chemical and/or mechanical properties, particularly resulted from a synergy principal. 

The impact of thermal shock on the properties of a ceramic or a CMC is assessed by means of both destructive and non-destructive testing methods. Flexural or tensile (mainly for CMCs) tests of suitably-sized thermally shocked specimens are usually employed to measure retained mechanical properties as a function of the temperature difference. The temperature differential for which a significant drop in property values is observed is the A A- For monolithic ceramics and particle- or whisker-reinforced CMCs the property under investigation is usually strength, whereas in fibre-reinforced CMCs a drop in Young s modulus is usually a better indication of the onset of damage. 

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