On using strain gages in electronic assemblies when temperature is not constant.

In a previous paper (TM52471-831010-01) we presented this equation for processing strain gage readings when the temperature is changing. Epsilon=Epsilon(gage reading)-Epsilon(apparent strain)+Epsilon (std. material). This paper presents second order corrections to this equation and estimates the size of the corrections and their uncertainties. Included are measurements on NBS standard reference materials (Cu and glass), which verify the accuracy of the method to within about +-60 ppm (i.e. 60 microstrain) for the range -25C to +125C.