Acoustic Characterization of Morphologically Textured Short-Fiber Composites: Estimation of Physical and Mechanical Properties

Published

November 1, 1999

Author(s)

Martin Dunn, H M. Ledbetter

Abstract

Short-fiber composites are increasingly being used in a wide range of applications spanning the automotive, computer, communications, aerospace, and home-appliance industries to name a few. They are most often fabricated in the form of short glass or ceramic fibers embedded in a polymer, metal, or ceramic matrix. It is widely accepted that the microstructure of the composite plays a tremendous role on its overall physical and mechanical properties. For a prescribed fiber/matrix system, perhaps the most significant microstructural variable in a short-fiber composite is the fiber composite is the fiber-orientation distribution: it dominates the aspect ratio effect. It dictates the overall symmetry of the composite and it strongly affects almost all macroscopic material properties: stiffness, strength, thermal expansion, thermal conductivitiy, dielectric constant, plastic-deformation behavior, processing-induced residual stresses, and fracture toughness. The fiber orientation distribution is predominately controlled by processing and forming operations.There are numerous ways to describe the orientation distribution of short fibers in composite materials: however, a comprehensive review is not presented here. Interested readers may find details in numerous studies^1-14 and the many references contained therein . Regardless of the way the orientation distribution function (ODF) is described mathematically, the most challenging problem to date is its measurement. Currently, techniques for the measurement of the orientation distribution of short-fiber composites consist of two general approaches: (i) measurement by x-ray or neutron diffraction in the same way that crystallite orientations are measured in textured polycrystals:¹⁵ (ii) measurement by a repeated slice-polish-image procedure. The former is quite accurate but only applicable to composites with crystalline fibers (glass does not diffract), and there must be a unique relationship between the crystalline axes and the fiber axis. In particular, the technique can not be used when the fibers are polycrystalline. The technique is also expensive, requiring careful specimen preparation and x-ray or neutron diffraction facilities. The latter technique is based on the repeated polishing and imaging of a cross-section of the composite. Ideally the sectioned fibers appear as ellipses on the cross section. After measurement of the elliptical shape of numerous fibers at numerous cross sections, the orientation distribution of the fibers can be inferred. This method has numerous drawbacks including the fact that great care must be taken in surface preparation, it is destructive, and it is time-consuming. Nevertheless, it is the state of the art.

Citation

Nondestructive Testing and Evaluation

Volume

VIII

Pub Type

Journals

Keywords

composites, fiber-reinforced composites, mechanical properties, physical properties, texture

Citation

Dunn, M. and Ledbetter, H. (1999), Acoustic Characterization of Morphologically Textured Short-Fiber Composites: Estimation of Physical and Mechanical Properties, Nondestructive Testing and Evaluation (Accessed November 8, 2024)