Effect of Structural Parameters on Thermal Stress Resistance

The criteria of thermal stress resistance Rfor the majority of a dense highmelting point compounds with porosity of 5–15% is within the limits of 30–100 grades, only on occasion are values ofRincreased to 400 degrees. The differences between the materials, determined by criteria R′, are more appreciable – they vary almost by two orders from 500Wm−¹ for example, for such low heat-conducting materials as Al₂O₃, up to 5,500Wm−¹ for SiC (Table 7.1). The thermal stresses σt producing emersion of the first cracks (using a test method in fluidic medium), lie over the range of values 0.45–0.57 from ultimate bend strength σb, and variation coefficients of thermal stress resistance are comparable to values Wmeasured at a force loading.

It is characteristic that the thermal stress resistance of the same materials produced by various experimental studies is not essentially equal. It is no wonder, since thermal stress resistance, a structurally sensitive characteristic similar to strength, depends on the strength bond between grains, geometry and size of flaws and pores, and content and allocation of impurities in a body, all changing with the variation of technological regimes of manufacture [14, 231].