Effect of moisture absorption on the micromechanical behavior of carbon fiber/epoxy matrix composites

• Published in: Journal of materials science 2011-10, Vol.46 (20), p.6664-6672
• Main Authors: Cauich-Cupul, J. I., Pérez-Pacheco, E., Valadez-González, A., Herrera-Franco, P. J.
• Format: Article
• Language: English
• Subjects: Acoustic emission; Acoustic emission testing; Acoustic propagation; Acoustic waves; Acoustics; Carbon fiber reinforced plastics; Carbon fibers; Carbon-epoxy composites; Characterization and Evaluation of Materials; Classical Mechanics; Composite materials; Composite materials industry; Crystallography and Scattering Methods; Epoxy matrix composites; Failure mechanisms; Fiber-matrix adhesion; Fibers; Fragmentation; Glass transition temperature; Interfacial shear strength; Materials Science; Mechanical components; Mechanical properties; Moisture; Moisture absorption; Optics; Polymer matrix composites; Polymer Sciences; Residual stress; Shear properties; Shear strength; Solid Mechanics; Unidirectional composites; Wave propagation
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-011-5619-0

Carbon fiber/epoxy material in the form of a single fiber unidirectional composite was subjected to controlled humidity environments. Moisture uptake in polymer composites has significant effects on the mechanical properties of the matrix as well as on the final performance of the composite material. Diminishing of the mechanical properties of the matrix is attributed to a decrease of its glass transition temperature ( T g ). The quality of the fiber–matrix interphase was assessed using the single fiber fragmentation test and the fiber-fragment length, considered as an indicator of interfacial quality. In order to measure the fiber fragment lengths and indentify failure mechanism at the interface optical observation and acoustic emission technique were used. The speed of propagation of an acoustic wave in the material was also determined. A comparison is made of interfacial shear strength values determined by acoustic emission and optical techniques. Excellent agreement between the two techniques was obtained. By means of a micromechanical model, it was possible to determine from the fragmentation lengths a measure of the interfacial shear strength between the fiber and the matrix. The role of moisture uptake swelling of the matrix on the residual stresses is considered to be important when considering the effect deterioration of interfacial shear properties. Both the contribution of the radial stresses and the mechanical component of fiber–matrix adhesion are seen to decrease rapidly for higher moisture contents in the matrix and/or interface.