On the use of stereo‐digital image correlation for the alignment of a fatigue testing machine in accordance with international standards: A feasibility study

Stereo‐digital image correlation (SDIC) is used for the analysis and quantification of parasite bending stresses in a fatigue specimen due to its mounting in a misaligned load frame. The aim of this work is to provide an easy way to estimate the induced parasite bending stresses due to the load frame misalignment, using the out‐of‐plane displacement measurements obtained by SDIC and beam theory. Analytical solutions of parasite stresses as a function of out‐of‐plane misalignments are provided for flat fatigue specimens having (a) tangentially blending fillets between the uniform test section and the ends and (b) continuous radius between the ends. Simple procedures for aligning a commercial load frame in accordance with international standards are also provided. The bending stresses profile along the specimen main axis obtained by numerical simulations have shown a very good agreement with the results obtained by the analytical models. The proposed methodology could complement standard alignment techniques based on samples instrumented with strain gauges or, in their absence, even replace established procedures.