Location

Seattle, WA

Start Date

1-1-1996 12:00 AM

Description

Advanced fibers used to reinforce composite materials exhibit complicated morphology. Typically, the fiber consists of a cylindrical core embedded in a cladding region followed by a distinct interface zone separating the fiber system from the matrix region. In addition, the cladding region itself often consists of subregions which can be identified as more or less distinct layers. According to the simplest micromechanical models these coaxial layers are assumed to be isotropic and homogeneous. At low frequencies when the acoustic wavelength is much larger than the radius of the fiber, such a composite fiber exhibits significant anisotropy of transversely symmetric nature manifested by higher axial stiffness relative to the radial one. This macroscopic anisotropy is caused by the coaxial structure and the possibly imperfect interfaces between the layers. The main goal of this study was to determine whether this structural anisotropy produced by the presence of microscopically isotropic and homogeneous constituents is sufficient to account for all of the macroscopic anisotropy observed in real fibers or, in addition, microscopic anisotropy caused by some texturing in the constituents themselves is needed to properly model the fiber at ultrasonic frequencies. Apparent texturing in the constituents can be caused by either real microscopic anisotropy due to preferred crystallographic orientation of grain growth during manufacturing or by additional structural anisotropy due to strong radial inhomogeneity in the material composition, e.g., increasing carbon content in the silicon carbide caladding.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

15B

Chapter

Chapter 6: Material Properties

Section

Residual Stress and Texture

Pages

1701-1708

DOI

10.1007/978-1-4613-0383-1_222

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Texture Assessment in SCS-6 Fibers from Ultrasonic Dispersion Measurements

Seattle, WA

Advanced fibers used to reinforce composite materials exhibit complicated morphology. Typically, the fiber consists of a cylindrical core embedded in a cladding region followed by a distinct interface zone separating the fiber system from the matrix region. In addition, the cladding region itself often consists of subregions which can be identified as more or less distinct layers. According to the simplest micromechanical models these coaxial layers are assumed to be isotropic and homogeneous. At low frequencies when the acoustic wavelength is much larger than the radius of the fiber, such a composite fiber exhibits significant anisotropy of transversely symmetric nature manifested by higher axial stiffness relative to the radial one. This macroscopic anisotropy is caused by the coaxial structure and the possibly imperfect interfaces between the layers. The main goal of this study was to determine whether this structural anisotropy produced by the presence of microscopically isotropic and homogeneous constituents is sufficient to account for all of the macroscopic anisotropy observed in real fibers or, in addition, microscopic anisotropy caused by some texturing in the constituents themselves is needed to properly model the fiber at ultrasonic frequencies. Apparent texturing in the constituents can be caused by either real microscopic anisotropy due to preferred crystallographic orientation of grain growth during manufacturing or by additional structural anisotropy due to strong radial inhomogeneity in the material composition, e.g., increasing carbon content in the silicon carbide caladding.