Fiber-matrix interfacial properties testing

The strength of the fiber-matrix interface is one of the key parameters responsible for the stress-strain behavior and damage tolerance of ceramic composites. Two different types of tests are available to measure the fiber-matrix interfacial properties in fiber-reinforced ceramic composites. The first is based on an indentation technique to either push the individual fiber into or through the matrix. The second test method relies on pulling a single fiber out of a matrix. These methods have been compared59 to one another for a glass matrix material, and yield similar results. 

Testing of the composites themselves, or portions of them, are only one part of elevated temperature testing. Other areas requiring attention include failure analysis, damage accumulation, nondestructive evaluation, micro-structural evaluation, and information needed to validate predictive models. Chapter 4 refers to modeling efforts which require the collection of data on the constituents of the composites, i.e., the starting fibers, the matrices, and the fiber-matrix interfacial materials, to make predictions for properties of real composites. To use the models described previously, one must also know about the properties of the individual components. These issues are addressed in this section. 

Interlaminar shear strength (ILSS) depends primarily on the matrix properties and fiber-matrix interfacial adhesion rather than on the fiber properties [141]. The ILSS, measured by the short-beam shear test, can be enhanced by increasing the tensile strength and volume fraction of the matrix as well as by increasing the interfacial adhesion in the laminates. 

The increase in ILSS for the epoxy-sized fibers over the bare fibers is 12.4%, approximately 50% of the increase observed in the interfacial shear strength as measured by ITS testing. Changes in the failure mode at the fiber-matrix interface may account for the differences. The sized fibers produced large matrix cracks that grew quickly to catastrophic size under load. This would tend to limit the increase in composite shear properties if at every fiber break in the tensile surface of the coupon a matrix crack was created. The presence of these matrix cracks... 

The interaction of two substrates, the bond strength of adhesives are frequently measured by the peel test [76]. The results can often be related to the reversible work of adhesion. Due to its physical nature such a measurement is impossible to carry out for particulate filled polymers. Even interfacial shear strength widely applied for the characterization of matrix/fiber adhesion cannot be used in particulate filled polymers. Interfacial adhesion of the components is usually deduced indirectly from the mechanical properties of composites with the help of models describing composition dependence. Such models must also take into account interfacial interactions. 

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