Numerical simulation of the thermal shock of alumina disks with different surface finish

Disks of commercial alumina were fabricated by slip casting and sintering. Two surface treatments were performed: a coarse machining, using a diamond wheel (70 grit) and a fine one with SiC papers (120/320 grit). Residual stresses were measured by X-ray diffraction and the fracture strength of the specimens were determined in biaxial flexion using a ball on discontinuous ring fixture. The thermal shock resistance of the disks was evaluated by sudden cooling with a high-velocity air jet. The temperature differential between the disk and the air jet was incremented in 10°C until crack propagation was detected and the critical temperature differential (ΔTC) was determined. Temperature and stress distributions during air impinging were calculated using a finite element analysis. Three models were proposed for the calculations and the results were analysed comparatively. Experimental data (ΔTC values and crack patterns) were explained on the basis of the calculated stresses.