Presenter Information

David K. Hsu, Iowa State University

Location

Williamsburg, VA

Start Date

1-1-1988 12:00 AM

Description

A method for evaluating the porosity volume content in composite laminates using the slope of the ultrasonic attenuation with respect to frequency has been reported before in these proceedings1,2. The method was first applied to laminates laid up from unidirectional prepreg tapes and has now been extended to the case of woven composite laminates. It was found that a linear relationship still holds between the porosity volume fraction and the attenuation slope; however, the constant of proportionality is quite different for the case of woven laminates. This difference is attributed to the differences in pore morphology in the woven and nonwoven laminates. Qualitatively, the voids are flatter and longer (needle-like or strip-crack-like) in the interlaminar region of nonwoven laminates of unidirectional prepregs and are very effective in blocking the sound energy. On the other hand, voids tend to be localized in the resin-rich pockets of woven laminates and remain spherical, as shown in Fig. 1. The attenuation and the slope of the attenuation are therefore lower (by about a factor of 2) in the woven composite for the same amount of porosity content. Quantitatively, the “void content-attenuation slope” relationship is modeled for both woven and nonwoven laminates in terms of the scattering amplitude of P-waves from voids of different shapes.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

7B

Chapter

Chapter 5: Adhesive Bonds and Composites

Section

Composites—Defects

Pages

1063-1068

DOI

10.1007/978-1-4613-0979-6_22

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Ultrasonic Measurements of Porosity in Woven Graphite Polyimide Composites

Williamsburg, VA

A method for evaluating the porosity volume content in composite laminates using the slope of the ultrasonic attenuation with respect to frequency has been reported before in these proceedings1,2. The method was first applied to laminates laid up from unidirectional prepreg tapes and has now been extended to the case of woven composite laminates. It was found that a linear relationship still holds between the porosity volume fraction and the attenuation slope; however, the constant of proportionality is quite different for the case of woven laminates. This difference is attributed to the differences in pore morphology in the woven and nonwoven laminates. Qualitatively, the voids are flatter and longer (needle-like or strip-crack-like) in the interlaminar region of nonwoven laminates of unidirectional prepregs and are very effective in blocking the sound energy. On the other hand, voids tend to be localized in the resin-rich pockets of woven laminates and remain spherical, as shown in Fig. 1. The attenuation and the slope of the attenuation are therefore lower (by about a factor of 2) in the woven composite for the same amount of porosity content. Quantitatively, the “void content-attenuation slope” relationship is modeled for both woven and nonwoven laminates in terms of the scattering amplitude of P-waves from voids of different shapes.