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Zero-group velocity modes in plates with continuous material variation through the thickness.
1Division of Engineering Geology, Lund University, P.O. Box 118, SE-22100, Lund, Sweden.
Lamb modes with zero group velocity are useful for nondestructive evaluation of plate properties. However, material variations in concrete structures create complex relationships, potentially causing errors in property estimations.
Area of Science:
- Solid Mechanics
- Materials Science
- NonDestructive Evaluation
Background:
- Lamb modes with zero group velocity (ZGV) enable stationary resonances in isotropic plates, valuable for material characterization.
- Applications include nondestructive evaluation (NDE) of plate-like structures, such as concrete, where material properties can vary through thickness.
Purpose of the Study:
- Investigate Lamb modes in inhomogeneous, nonsymmetric plates with continuous material variations.
- Analyze the behavior and detectability of ZGV modes in such complex structures.
- Assess the impact of material inhomogeneity on the interpretation of NDE results.
Main Methods:
- Employed a semi-analytical finite element technique for analysis.
- Utilized a simulated measurement application to assess detectability.
- Focused numerical studies on the lowest ZGV mode.
Main Results:
- ZGV modes in inhomogeneous plates exhibit similar generation behavior and detectability as in isotropic plates.
- A complex, nonlinear relationship exists between mode frequency and material velocity in inhomogeneous cases.
- Standard interpretation methods for isotropic plates are hindered by these complex relationships.
Conclusions:
- While ZGV modes remain detectable in inhomogeneous plates, their utility for precise property estimation is compromised.
- The complex frequency-material velocity relationship complicates the interpretation of cross-sectional mean values.
- Practical NDE applications on structures with through-thickness material variations require revised interpretation strategies to avoid errors.

