Size Effects on Fracture Parameters of High Alumina Refractories

The randomness of phase compositions and their distribution as well as the micro cracks and pores in refractories result in the dependence of mechanical properties on the sample size. In this work, the size effects on fracture parameters including bending strength, elastic modulus and fracture toughness of high alumina bricks were investigated by testing samples of different sizes according to the national standard in China. The results showed that the smaller samples presented higher strength, while the larger samples possessed greater elastic modulus. Weibull modulus m of bending strength for high alumina bricks calculated for samples of two sizes, each group featured 32 samples, ranged from 11 to 12, which was higher than in other refractories such as low grade high alumina, magnesia-carbon and magnesia-chrome bricks. The scatter of the average strength and its standard deviation became stable when the sample number was more than 20. The fractal dimension of fracture surface for high alumina bricks was inversely and directly proportional to the sample size and the fracture toughness, respectively. The estimated fracture toughness of high alumina bricks was close to window glass and less than alumina and mullite.