Thermal Decoupling
Experimental mechanics uses specialized diagnostic techniques to capture the deformation of materials subjected to simultaneous changes in both mechanical load and temperature. Through non isothermal strain measurement, engineers can isolate the mechanical strain component from the substantial thermal expansion strain that occurs during temperature swings. This is essential for characterising materials under thermomechanical fatigue conditions.
Apparent Strain
Decoupling the thermal expansion from the total measured strain requires a rigorous calibration procedure using an unstressed dummy specimen of the same material. The strain sensor, such as a high temperature strain gauge or a digital image correlation system, measures the apparent strain across the thermal cycle without external load. This apparent strain profile is then subtracted from the total strain recorded during the active thermomechanical test.
Gauge Calibration
Optical and resistive sensors suffer from drift and sensitivity shifts when subjected to rapid thermal transients. For instance, the gauge factor of a foil strain gauge varies with temperature, requiring dynamic correction formulas. These corrections are verified against high purity reference specimens with known thermal expansion coefficients.
Thermal Equilibrium
Extreme temperature rates can create internal thermal gradients within the specimen that invalidate the uniform strain assumption. Consequently, heating and cooling rates must be limited to ensure thermal equilibrium across the gauge section.
