Thermal shock fracture by laser irradiation.

To investigate the thermal shock behaviour of modern high strength ceramic material. An experimental arrangement was developed which allows the generation of strong temperature gradients in thin circular ceramic disks by rapid heating with high power laser radiation. The temperature gradients causes large tensile stresses at the boundary of the sample. During the heating experiments the temperature along the diameter of the sample is measured by a high speed pyrometer combined with an electronically driven tilting mirror. The time dependent internal stress in the sample can be numerically calculated from the measured temperature distribution. When the stress in the sample reaches the material strength the sample will be destroyed by instable crack propagation. This moment of fracture is detected by an acoustic sensor, which is attached to the sample over a waveguide. First experimental results, which were received during thermal shock investigations on silicon nitride, are presented.