Ultrasonic tensile test and micro-CT defect analysis on alumina 99.5%

Abstract

The ultrasonic tensile test method recently developed by the Authors is applied with the micro-computed tomography technique aiming to correlate the failure-inducing nominal stress in alumina 99.5% with the manufacturing defect size. After characterizing the defect population, the critical defect size of each specimen is defined, and an empirical formulation for the stress intensity factors on this material is obtained.The ultrasonic tensile test, with a loading frequency of 20 kHz, is simulated with finite element analyses, to estimate with an optimization process the material properties that reproduce the experimental displacements. Evidence of negligible fatigue damage is verified to further support the validity of the ultrasonic tensile test as a method capable of providing a good estimate for the quasi-static tensile strength.The analysed alumina resulted in a density of 3969 kg/m3 and an elastic modulus of 371.2 GPa. All specimens failed in 100 cycles or less, with tensile strength values ranging from 79.5 MPa to 322.6 MPa. The reason for this large experimental variability is attributed to the dispersion of imperfection sizes, with critical sizes ranging from 92 μm to 3443 μm, proving the importance of combining the information on the defect population with the assessed tensile strength.