MULTIPLE SURFACE THERMAL FRACTURE OF GRADED CERAMIC COATINGS

The mechanism of multiple crack formation at the surface of graded the rmal barrier coatings subjected to transient heating and cooling loads is studied. An experimental setup was used to apply concentrated tran sient thermal loads on a beam-shaped specimen producing multiple surfa ce cracks under controlled conditions. A corresponding analytical mode l was developed to study the fracture process. It is shown that the sp acing of surface cracks can be predicted by calculating the thermal st resses generated by the temperature gradients in the coating. It is al so shown that the multiple surface cracking inhibits the interface cra cking process.