Experimental Methods for Tensile Testing of Metallic Thin Films at High Temperatures

Two methods for microscale tension experiments with microscale freestanding thin films at elevated temperatures were evaluated by means of optical microscopy/Digital Image Correlation (DIC) and Infrared (IR) imaging. The two methods employed uniform and resistive specimen heating. Optical images processed by DIC were used to calculate the strain along the specimen gauge section of specimens subjected to both experimental methods, while IR imaging was used to measure the temperature distribution along the specimens’ gauge sections. The axial strain and temperature distributions were compared qualitatively to evaluate the efficacy of each method. Uniform specimen heating provided uniform temperature and axial strain distributions that were not affected in any measurable way by the use of the “cold” external probe employed to pull on the specimens. However, the resistively heated specimens had highly non-uniform temperature and axial strain distributions along their gauge sections. The associated high temperature gradients resulted in strain localization and significant reduction in yield and ultimate strength measured during resistive heating experiments compared to uniformly heated samples. The experiments revealed that the latter method provides high fidelity measurements at elevated temperatures.