Study of the carbon fiber–poly(ether–ether–ketone) (PEEK) interfaces, 2: relationship between interfacial shear strength and adhesion energy

Abstract

In the second part of this general study, the carbon fiber–PEEK 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 crystallization rate of the matrix and the interfacial adhesion energy.

Effect of preheat treatment on carbon fiber surface properties and fiber/PEEK interfacial behavior

“…However, for PEEK matrix in this work, the interfacial adhesion showed different tendency compared with that of thermoset composites. Actually, in terms of PEEK matrix, there is no theoretical evidence of chemical bonding between sizing agents and polymer matrix, because PEEK matrix does not have functional groups to interact chemically with sizing agents [14,48,49]. Poor in chemical bonding, the sizing layer has become weak interface region which can also be confirmed by the information in Fig.…”

Study of the carbon fiber–Poly(Ether–Ether–Ketone) (PEEK) interfaces, 3: influence and properties of interphases

“…The results of fragmentation tests on single-fiber composites, obtained in the preceding study [2], are now examined precisely, and therefore no new experimental conditions concerning this test have to be presented. Nevertheless, it is worth noting that both strength-strain curve and variation of the number of acoustic events versus strain were simultaneously recorded, thus making it possible directly to determine the strain at which the fragmentation process just starts.…”

“…As described in the previous paper [2], the measurement of the critical length is performed by counting the acoustic events corresponding to the fragmen-tation process of the fiber, using an acoustic emission measuring device. It has been observed in PEEK matrices that, while the load is increasing, the acoustic emission starts at a strain E~ and stops at a strain just above the yield point of the matrix.…”

Effects of thermal histories on interfacial properties of carbon fiber/polyamide 6 composites: Thickness, modulus, adhesion and shear strength

“…Micro-mechanical techniques such as fiber fragmentation [6,22,23], fiber pull-out [6,24,25] and micro-debonding [24,[26][27][28][29] have certain limitations to their use, and have not yet been standardized [30]. Alternatively, macromechanical testing methods can be used to indirectly assess fiber/ matrix interfacial adhesion, but they require the production of bulk composite laminates, which is time-consuming and costly.…”