Study of the Carbon Fiber-Poly( Ether-Ether-Ketone) (PEEK) Interfaces, 2: Relationship Between Interfacial Shear Strength and Adhesion Energy

In the second part of this general study, the carbon fiberPEEK interfacial shear strength is measured by means of a fragmentation test on single-fiber composites. Different thermal treatments ( continuous cooling from the melt, isothermal treatments and long melting temperature time) are applied to these model composites prior to testing. The results are systematically compared with the previously determined reversible work of adhesion between carbon fiber and PEEK. It is shown that physical interactions at the interface determine, to a large extent, the magnitude of the interfacial shear strength between both materials. However, it appears that the magnitude of the stress transfer from the matrix to the fiber is affected either by the existence of an interfacial layer or by a preferential orientation of the polymer chains near the fiber surface. The results obtained on systems that have been subjected to isothermal treatments ( isothermal crystallization of PEEK) seem to confirm the existence of a transcrystalline interphase, the properties of which are dependent upon the cystallization rate of the matrix and the interfacial adhesion energy.