Location

Williamsburg, VA

Start Date

1-1-1988 12:00 AM

Description

The presence of porosity in a fiber-reinforced composite may have a critical effect on the composite’s mechanical properties and service performance. Detection and characterization of porosity by ultrasonic means have, therefore, received considerable attention in recent years. The frequency dependence of ultrasonic attenuation has been used to find the volume fraction and pore size of gas porosity in aluminum alloys, [1]–[3], and in graphite-epoxy composites [4], The use of ultrasonic backscatter measurements to characterize the volume fraction has been reported in Refs. [5]–[6]. A theoretical model to analyze the backscatter from a porous unidirectionally fiber-reinforced composite has been established in [7]. In the present paper, the approach of Ref. [7] is extended to multi-ply fiber-reinforced composites. It has been shown experimentally by several investigators, [8]–[9], that polar backscatter from a multi-ply composite shows an amplitude dependence on the azimuthal angle, which is characterized by a pattern of peaks and valleys. The peaks occur when the propagation vector of the incident pulse is normal to the direction of the fibers in one of the plies of the multi-ply layup.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

7B

Chapter

Chapter 5: Adhesive Bonds and Composites

Section

Composites—Defects

Pages

1029-1036

DOI

10.1007/978-1-4613-0979-6_18

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Backscatter from Porosity in Cross-Ply Composites

Williamsburg, VA

The presence of porosity in a fiber-reinforced composite may have a critical effect on the composite’s mechanical properties and service performance. Detection and characterization of porosity by ultrasonic means have, therefore, received considerable attention in recent years. The frequency dependence of ultrasonic attenuation has been used to find the volume fraction and pore size of gas porosity in aluminum alloys, [1]–[3], and in graphite-epoxy composites [4], The use of ultrasonic backscatter measurements to characterize the volume fraction has been reported in Refs. [5]–[6]. A theoretical model to analyze the backscatter from a porous unidirectionally fiber-reinforced composite has been established in [7]. In the present paper, the approach of Ref. [7] is extended to multi-ply fiber-reinforced composites. It has been shown experimentally by several investigators, [8]–[9], that polar backscatter from a multi-ply composite shows an amplitude dependence on the azimuthal angle, which is characterized by a pattern of peaks and valleys. The peaks occur when the propagation vector of the incident pulse is normal to the direction of the fibers in one of the plies of the multi-ply layup.