Fatigue failure and thermal spalling tests to evaluate dynamic fatigue fracture of MgO-C bricks

Abstract

The relationship between compressive stress and loading cycles in MgO-C bricks with various carbon contents was investigated at room temperature and high temperature. The relationship between fatigue failure and thermal spalling was investigated by estimating a characteristic material constant, which represents the degree of sensitivity of crack growth, in terms of fracture mechanics. The relationship between the ratio of compressive stress for compressive strength and loading cycles in MgO-C bricks is not affected by the temperature of the atmosphere. At the same acting stress ratio, fatigue fracture life decreased as the carbon content in the MgO-C bricks decreased. In the thermal spalling test, the number of heating cycles at which small cracks and large cracks were generated decreased as the carbon content decreased. In the fatigue failure test, the ratio of the dynamic elastic modulus to the initial elastic modulus decreased gradually. This ratio also showed a gradual decrease in the thermal spalling test as the number of heating cycles increased. A characteristic material constant was obtained and compared based on the results of a fracture mechanics discussion. The characteristic material constant obtained from the fatigue failure test was substantially the same as that obtained from the thermal spalling test. From this, a relationship in which crack growth behavior leading to fatigue failure is equivalent to that of thermal spalling in MgO-C brick was recognized. © 2011 ISIJ.