Strain measurements at elevated temperature in components and structures in power, chemical and mechanical industries are often required to estimate their strength and serviceability. The use of electrical resistance strain gages at elevated temperature poses a variety of problems such as, change in gage factor, change in resistance of the strain gage and lead-wire, mismatch in thermal coefficient of expansion of gage backing and the material of the specimen, etc. Hence, strain measurement at elevated temperature requires special techniques and procedures. It is necessary to correctly interpret the influence of various parameters on the gage output. Temperature induced apparent strain can cause significant errors in estimating the stresses in material, if it is not properly accounted for. When carrying out strain measurement at a temperature different from the initial temperature of substrate, the indicated strain is the sum of the elastic strain due to loading and the apparent strain due to change in temperature. To compute the elastic strain of the specimen, apparent strain has to be separated from the total strain. Hence calibration curves are generated for correcting apparent strain, when strain gage bonded to aluminium and steel materials by conducting the experiments at elevated temperature. This paper describes the behaviour and performance of weldable and bondable type strain gages when used for strain measurement at elevated temperature.
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