Localization of Ultrasound in Thick Composites
Abstract
The propagation of ultrasound in fiber-reinforced composites is controlled by the relative magnitudes of characteristic length variables. These length variables are the wavelength (Lambda), the fiber diameter (a), the thicknesses of plies (h), and the overall thickness of the component (H). In this paper we consider the propagation of longitudinal waves in a cross-ply fiber-reinforced composite. Since Lambda>>a, we will use an effective modulus representation for the mechanical behavior of the plies. This means that in the direction normal to the plies longitudinal waves will propagate with a wave speed which is independent of the fiber direction. Hence the problem considered here is a one dimensional problem of wave propagation through layers with identical mechanical impedances which are separated by interfaces. Since the interfaces of the plies and/or laminates may reflect sound, a composite may display some of the features that are characteristic of the propagation of ultrasound in periodic media, such as passing and stopping bands in the frequency spectrum. Strict structural periodicity is, however, an idealization. In reality there will be random deviations from periodicity, which will in fact destroy the passing bands, and will give rise to attenuation at all frequencies. This attenuation is often referred to as localization. The present paper analyzes such localization.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 15, 1989
- Accession Number
- ADA212994
Entities
People
- Jan D. Achenbach
- Yichi Lu
Organizations
- Northwestern University