Wedge indicators have been proposed for measuring thermal radiation that impinges on specimens illuminated by flash lamps for thermographic inspection. Heat fluxes measured by use of these indicators would be used, along with known thermal, radiative, and geometric properties of the specimens, to estimate peak flash temperatures on the specimen surfaces. These indicators would be inexpensive alternatives to high-speed infrared pyrometers, which would otherwise be needed for measuring peak flash surface temperatures. The wedge is made from any suitable homogenous material such as plastic. The choice of material is governed by the equation given below. One side of the wedge is covered by a temperature sensitive compound that decomposes irreversibly when its temperature exceeds a rated temperature (Trated). The uncoated side would be positioned alongside or in place of the specimen and exposed to the flash, then the wedge thickness (d) at the boundary between the white and blackened portions measured. The heat flux (Q) would then be estimated by Q = (cρ/εb)(Trated–Tambient)d, where c and ρ are the specific heat and mass density, respectively, of the wedge material; εb is the emissivity of the black layer of the sheet material, and Tambient is the ambient temperature.
This work was done by Ajay M. Koshti of Boeing Co. for Johnson Space Center.