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Cumulative nonlinearity as a parameter to quantify mechanical fatigue
Author(s) -
Hirschberg Valerian,
Wilhelm Manfred,
Rodrigue Denis
Publication year - 2020
Publication title -
fatigue and fracture of engineering materials and structures
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.887
H-Index - 84
eISSN - 1460-2695
pISSN - 8756-758X
DOI - 10.1111/ffe.13120
Subject(s) - materials science , nonlinear system , composite material , amplitude , torsion (gastropod) , dissipation , structural engineering , vibration fatigue , fatigue testing , physics , thermodynamics , engineering , optics , medicine , surgery , quantum mechanics
The cumulative nonlinearity ( Q f ) is proposed as a new parameter to quantify mechanical fatigue. The parameter Q f represents the (cycle number) integral of the ratio of the third harmonic to the fundamental one ( I 3/1 ), obtained via Fourier transform of the stress (torque), normalized by the square of the strain amplitude ( γ 0 ). The validation is performed on different polymers: polystyrene (PS) with different molecular weights, styrene‐acrylonitrile (SAN), polymethylmethacrylate (PMMA), and polytertbuthylmethacrylate (PtBMA) under strain controlled fatigue tests in a torsion rectangular set‐up. A power‐law correlation between the number of cycles to failure ( N f ) and the cumulative nonlinearity was found for N f > 1000 cycles, and the results were compared with well‐established failure criteria such as the cumulative stress and the dissipated energy density. It was found that the cumulative nonlinearity has superior prediction ability since it can quantify material changes during a test.