Fracture Analyses of Alumina Subjected to Mechanical and Thermal Shock Biaxial Stresses

Abstract

7600) Mar del Plata, ArgentinaDisks of commercial alumina were fabricated by slip casting and sintering. Two surface finishes were performed: coarse (denoted as "C") using a 70 grit diamond wheel and fine (denoted as "F") with 120 and 320 grit SiC papers. The machined surfaces were analyzed by SEM, profilometry, and residual stresses measurements. The fracture strength was evaluated in biaxial flexure, and the thermal shock resistance was tested by cooling with a high-velocity air jet. The fracture of the specimens under both conditions was studied analyzing crack patterns and fracture surfaces in relation to the surface machining and type of loading, i.e., mechanical and thermal stresses.

Machining damage analysis of alumina in relation to thermal shock behavior

“…The number of fragments was only 2-3 for C and F disks and 3-5 for thermally treated specimens. No significant differences were observed in the branching features of thermally treated disks (Ctt 3 and Ftt 2 ) with respect to those of C and F disks [10,22].…”

“…Values of mechanical strength are reported in Table 2 [10,22]. An increment in strength for C specimens (&22%) was observed compared to the mechanical strength of as-sintered disks, 243 ± 30 MPa.…”

“…Table 2 also summarizes the results obtained from the fractographic analysis of the different types of specimens [22], including those subjected to thermal treatments. In the latter, the fractographic analysis was rather hard to perform due to the irregularity of edge between the machined surface and the fracture surface of the disks.…”

“…The increment of r F of C disks with respect to that of as-sintered specimens stems from the presence of compressive residual stresses coming from the machining, which have quite higher magnitudes and greater depths than those generated during sintering. The type of defect identified as the fracture origin exhibited an approximately semi-elliptical shape, with a high degree of association, typical of machining damage [22]. The difference between fractographical flaw size and c calc is partially attributed to the high degree of association.…”

Thermal shock and post-quench strength of lapped borosilicate optical glass

“…Glasses, on the other hand, have a low thermal conductivity, and are thus liable to severe thermal shock. There is a large amount of work in the literature on thermal shock of ceramics [3][4][5][6][7][8][9], but less on thermal shock of glasses [10].…”