Patent ID: 6072568
Filing Date: 2000-06-06
Classification: G01L,G01N

Abstract:
A non-destructive measurement method for determining residual stress proximate a relatively thin intermediate ceramic layer in a multilayer thermal barrier coating having a relatively thick outer thermal insulating, different ceramic layer overlying said intermediate layer, and at least one of a bondcoat and superalloy substrate underlying said intermediate layer, comprising directing a laser beam to pass through said outer thermal insulating layer to illuminate said intermediate layer of said coating in a manner to cause species incorporated in said intermediate layer from at least one of said bondcoat and said superalloy substrate to fluoresce to emit light that passes back through said outer thermal insulating layer, measuring the frequency shift of the light emitted by the fluorescing species after it passes through said outer thermal insulating layer, comparing the measured frequency shift of said intermediate layer to the frequency shift determined on a reference material under controlled stress states to assess relative residual stress in the measured coating without need to remove said outer thermal insulating layer from said coating.