Abstract
Thermal loading of thin ceramic discs by lamp irradiation is used to study the crack propagation of radially orientated edge cracks. The sample temperature is measured by scanning the disc surface with an infrared pyrometer and used to calculate the stress intensity factor, Ki as a function of the crack length a. The crack growth is observed and recorded using a stereo-microscope connected to CCD-camera, giving a spatial resolution of about 5 μm. Stable and unstable crack growth modes are observed unambiguousely. Coarse grained alumina exhibited stable crack growth in the region of the increasing Ki-a-curve clearly revealing the stabelizing effect of an R-curve. The measurements are quantitatively evaluated in terms of fracture resistance curves up to 1000°C. The results agree with the existing theories of crack propagation in thermal stress fields. Special effects like unstable crack branching of long stably growing cracks and subcritical crack growth prior to unstable crack propagation are observed and discussed.
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