Arabi H., Seyedein S.h., Satari M., Tabatabaie N.,
Volume 2, Issue 4 (12-2005)
Abstract
Life assessment on the base of grain boundary creep cavitation of 1%Cr - 0.5%Mo low alloy steel has been discussed in this paper. Since microstructural degradation is one of the most important mechanisms that affects creep life, it is necessary to assess microstructural damage in order to estimate the life. Microstructural damage within the grain boundaries is a continuous phenomena starting from about the beginning of secondary stage of creep process. In this research, the amounts of damage accumulation in the form of grain boundary cavitations for various creep times up to the ends of secondary creep stage for each creep condition was found by using quantitative metallography technique, i.e. image analyser. Then from the data obtained for grain boundary area cavitated and number of cavities per unit area, which was about linear as a function of time for each of creep conditions, the amount of damage in the tertiary stage was estimated for various times. Then a creep damage parameter was proposed for the creep process. Finally, having this damage parameter (?) and using continuum damage mechanics (CDM), a new version of Rabotnov-Kachanov equation for tertiary creep rate was established.
M. Ghassemi Kakroudi,
Volume 5, Issue 4 (12-2008)
Abstract
Abstract: Refractory materials containing cordierite (2MgO.2Al2O3.5SiO2) and mullite (3Al2O3.2SiO2) are used as
support in furnaces, because of their low thermal expansion properties which confer them a very good ability to
thermal shock resistance. Composed of two phases presenting very different CTE (1.5–3×10-6 for cordierite and
4–6×10-6 K-1 for mullite), these materials can develop damage during thermal cycling due to internal stresses.
The resulting network of microcracks is well known to improved thermal shock resistance of materials, since it usually
involves a significant decrease in their elastic properties. This paper is devoted to the characterisation of the damage
generated by this CTE mismatch, thanks to the application of a specific ultrasonic device at high temperature.
