Cruciform specimens’ experimental analysis in ultrasonic fatigue testing
Authors: Costa, P., Montalvao, D., Freitas, M., Baxter, R. and Luis, R.
Journal: Fatigue & Fracture of Engineering Materials & Structures
Issue: Special Issue on New Trends in Fatigue and Fracture
In this work, two special aluminium cruciform specimens are designed and tested in an ultrasonic fatigue machine. They were designed based on Single-Input-Multiple-Output (SIMO) modal analysis to induce in-plane biaxial stress combinations (in-phase T-T and out-of-phase C-T) when at resonance at 20 kHz. The geometries were subjected to both numerical analysis and experimental testing to understand if they can indeed create the intended biaxial state of stresses. Both numerical and experimental results showed an impact of nearby resonant modes of non-interest on the correct functioning of the specimens, especially regarding the T-T specimen where a large deviation from the mode of interest was measured. This means that future work includes re-designing T-T specimens taking into account these mode shapes. Only out-of-phase specimens demonstrated to work properly and tests until failure were conducted. The first failure results showed to be consistent with literature when out-of-phase biaxial stress is applied cyclically.