125 100 0750 0500 0250 000

Cold'Grips, Tgrip = 20°C Grip/tab length =40 mm

Ambient Air, To = 1260° C L = 200 mm, t = W = 6 mm

Cold'Grips, Tgrip = 20°C Grip/tab length =40 mm

z Normalized distance from center of the specimen, y/(L/2)

FIGURE 12.2 Temperature distributions in a ceramic matrix composite test specimen for various types of grips.

exhibits increasing strength with increasing temperature (e.g., SiC fiber-reinforced SiC matrix composites). Therefore, it is often necessary to define a gage section where the material is not only exposed uniformly to the test temperature but where it is also subjected to the maximum stress. This is accomplished by reducing the cross section of the specimen, thereby "forcing" the failures to occur in the uniformly heated and stressed region.

In addition, no comprehensive study addressing the reliability of temperature measurements at high temperatures for CFCCs has been reported to date. In addition, an in-depth study is required to compare optical and other contact-type temperature measuring devices and to determine their reliability especially as a function of time. It will be necessary to monitor the temperature at the extensometer contact points and along the gage section, including comparison of temperature measurements at the surface and at the interior of the specimen. Temperature control and its relation to temperature distribution in the furnace and in the specimen should be addressed, and, ideally, maximum allowed temperature differences along the gage length should be required for consistent tests. Possible recommendations of temperature uniformity are ±5°C at <500°C and ±1% of test temperature at >500°C. Finally, temperature measurement must have an accuracy of ±5°C.

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