The Monkman-Grant Method

The Monkman-Grant [henceforth MG] relation between minimum creep rate (or steady-state strain rate) and time-to-fracture, tf, is given as  

This relation is useful for industrial applications, when one knows the constants, m and C, of a material, since the above expression evaluates the fracture time on 

Originally, the MG relation was developed for alloys, but it also has the ability to predict the rupture life of ceramic materials. This MG relation was experimentally applied to various ceramics at various temperatures and stresses and an example of its use to predict their creep lifetime is shown for advanced silicon nitrides. Certain departures from the uniqueness of the MG relation, in both metals and ceramics, have been noted by previous investigators. Consequently, some improvements were suggested by Mamballykalathil et al. [62]. in order to achieve a modified MG relation for ceramics  

K and b, are constants. Note that this relation is equivalent to Eq. (6.103). The time-to-fracture (mpture), tf, may be expressed as  

Comparison of the average lines predicted by Eq. (6.105) with the unmodified data kind permission of John Wiley and Sons 

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There are parametric methods for determining the creep lifetime of materials. Such methods are based on evaluating the stress-rupture behavior. In essence, the results of short-duration, high-temperature tests are correlated with the performance of long-term tests at lower temperatures. The most popular parametric methods are (a) Larson-Miller (b) Manson-Haferd (c) Orr-Sherby-Dom and, (d) Monkman-Grant. Of these methods, the following is a discussion on the Larson-Miller and the Monkman-Grant methods to the evaluation of ceramic-material lifetimes. 

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