Fiber-Matrix Interphase Structure and Its Effect on Adhesion and Composite Mechanical Properties

Abstract

“Good” adhesion between fiber and matrix has been treated as a necessary condition for acceptable composite mechanical properties in polymeric matrix composites. Quantification of the level of adhesion has been difficult to attain by composite testing alone. Recent advances in single fiber techniques for the measurement of fiber-matrix adhesion using the embedded single fiber fragmentation technique have resulted in the establishment of a mechanical parameter characteristics of and sensitive to fiber-matrix interfacial shear strength. In addition direct observation of the fracture process has allowed the failure mode to be identified. This failure mode changes depending on the degree of adhesion.

Experimental measurements of composite axial and transverse properties as well as single fiber studies have been completed on samples with three different levels of adhesion and interfacial failure modes. Care was taken to preserve continuity between samples and processing conditions for both sets of samples. A direct relationship between increasing levels of fiber-matrix adhesion and increasing composite mechanical properties has been detected for off-axis properties. An effect on composite axial properties was also noted but to a lesser degree. Comparison of the fracture surfaces of tested composite specimens shows that the level of adhesion and the failure mode are necessary to explain composite behavior. Optimum composite properties depend on the combination of both factors.