Dynamic acousto-elastic response of single fatigue cracks with different microstructural features: An experimental investigation

Nonlinearity of damaged materials is often assumed to be correlated with the cumulative length of micro-cracks discounting the influence of crack width and roughness. To investigate the influence of microstructural features of realistic cracks on the nonlinear elastic properties, Dynamic Acousto-Ela...

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Bibliographic Details
Published in:Journal of applied physics 2018-08, Vol.124 (7)
Main Authors: Jin, Jiang, Rivière, Jacques, Ohara, Yoshikazu, Shokouhi, Parisa
Format: Article
Language:English
Subjects:
Aluminum alloys
Aluminum base alloys
Applied physics
Crack propagation
Crack tips
Cracks
Elastic properties
Fatigue cracks
Fatigue failure
Fatigue tests
Feature extraction
Fracture mechanics
Microcracks
Nonlinearity
Roughness
Signatures
Stress intensity factors
Surface waves
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Summary:Nonlinearity of damaged materials is often assumed to be correlated with the cumulative length of micro-cracks discounting the influence of crack width and roughness. To investigate the influence of microstructural features of realistic cracks on the nonlinear elastic properties, Dynamic Acousto-Elastic Testing (DAET) is performed on two aluminum alloy samples (30 × 40 × 170 mm3) with a single fatigue-crack. The cracks on the two samples are of similar length but have dissimilar microstructural features due to the different stress intensity factors used during the fatigue tests. DAET is carried out with a surface wave probe to measure the near-surface nonlinearity at a number of locations along each crack. The geometric features of the cracks, including crack width and roughness, are extracted from a series of scanning electron microscope images. DAET results demonstrate that nonlinearity varies along the crack; both samples exhibit greater nonlinearity near the notch, where the crack is wider than near the crack tip. However, the nonlinearity parameters obtained from the sample with a smoother crack are one order of magnitude larger than those of the sample with a relatively rough crack. In addition, the nonlinearity signatures of the two cracks exhibit very different tension/compression asymmetry. This study provides valuable data that not only directly correlates the nonlinear ultrasonic signatures and crack interface features but also illuminates the micro-mechanisms and origins of the measured nonlinearities.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.5036531