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Damage Precursor Detection Using Nonlinear Dynamic Parameters and Micromechanics



A nonlinear vibration methodology coupled with micromechanics is developed for detecting and estimating fatigue damage precursors in metallic alloy structures, where damage precursor is defined as detectable change in the materials properties prior to crack initiation. The proposed methodology is based on measuring the structural nonlinear response due to nonlinear base excitation. The damage precursor feature can be extracted by quantifying the reduction in the nonlinear stiffness parameter due to localized increase in the material compliance due to microstructural changes at high stress concentration sites. A case study is presented where a simple structure is subjected to various base excitations. At high response amplitudes, the structure is observed to experience three competing nonlinear response mechanisms: 1) kinematic stiffening due to high response amplitude at the fundamental mode, 2) softening due to inertial forces, and 3) softening due to localized change in the micromechanical properties of the material. Micromechanics characterization techniques are utilized to confirm the presence of fatigue damage precursors. Micromechanics techniques are employed to assess the changes in material’s properties due to damage build up. This paper demonstrates that the sensitivity of the SHM metrics can be significantly improved if one looks at nonlinear dynamic response.

doi: 10.12783/SHM2015/159

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