The dependence of interfacial shear strength on matrix and interphase properties

Abstract

Experiments were conducted to determine the dependence of the interfacial shear strength on the bulk material matrix properties using model compounds based on epoxy/amine chemistry. AS4, carbon fibers were used as the subject for these measurements with both a difunctional epoxy (DGEBA) system as well as a tetrafunctional epoxy (MY720) system. Amine curing agents were carefully chosen to produce matrices which produced a range of matrix properties from brittle, elastic to ductile, plastic. The fiber-matrix interfacial chemistry was constant throughout this study by always using a stoichiometric amount of curing agent.The results indicate that, for both the difunctional a s well as the tetrafunctional epoxy system, the interfacial shear strength (as determined by the fragmentation test) decreases nonlinearly with decreasing modulus of the matrix. Linear elastic analysis yields a nearly linear relationship, for both systems, between the interfacial shear strength and the product of strain to final break and the square root of the matrix shear modulus. A linear relationship is also found between the difference in test temperature and glass transition temperature of the cured matrix and the interfacial shear strength. Additionally, the failure mode is seen to remain interfacial as the ductility of the matrix changes.

Glass fiber 'sizings' and their role in fiber-matrix adhesion

“…Rosen [20], Cox [21], and Whitney and Drzal [22] have shown that the square root of the shear modulus of the matrix appears explicitly in any model of the interfacial shear strength. It has been demonstrated experimentally [23,24] that the fiber-matrix interfacial shear strength has a dependence on both the product of the strain-to-failure of the matrix times the square root of the shear modulus and on the difference between the test temperature and Tg when the interfacial chemistry is held constant.…”

Nanoindentation of polymeric thin films with an interfacial force microscope

“…The interphase is the region between the surface of the reinforcement and the polymer matrix where the chemistry is di erent from that of the bulk matrix (Drzal, 1990;Rao and Drzal, 1991;Madhuka and Drzal, 1991). The mechanical properties in the interphase are a direct re ection of the interphase chemistry.…”

Fibre/resin interaction in fragmentation tests: coaxial vs. simple specimens comparison

“…It is to be pointed out that in their analysis Skourlis & McCullough take care to say that 'no major interfacial debonding appears even up to the saturation point'. Rao & Drzal (1991), who also derived a quasi-elastic model, do the same when they specify that the comparisons of systems are of value only if 'all other things (are) equal'.…”

“…The demonstration was given as early as 1978 for glass fibres in epoxy or polyester resins tested up to 100-120 ЊC by Ohsawa et al (1978) who concluded that 'if the interfacial strength is greater than the matrix shear strength, the apparent strength calculated from the fragmentation test is merely the matrix shear strength'. Other authors conducted fragmentation tests on the (necessarily) same limited range of temperatures with glass (DiBenedetto & Lex, 1989;DiBenedetto, 1991) or carbon fibres (Wimolkiatisak & Bell, 1989;Skourlis & McCullough, 1993;Detassis et al, 1995) or with resin mixtures of variable stiffness associated with carbon (Rao & Drzal, 1991) or Nicalon SiC fibres (Ho et al, 1995); they all observed an increase of the fragment length with temperature or the reduction of the matrix modulus. In the last two studies, the authors point out that the extension of the fibre/matrix debonding process does not change very much from one resin system to the other and thus the comparison of the elastic reloading modes is quite relevant.…”

“…When one wants to examine the resin contribution, resins of very high ultimate fracture strain are called on in order to extend the experimental range of stress transfer conditions, for example by Netravali et al (1989) and Rao & Drzal (1991) with carbon fibres or Ho et al (1995) with Nicalon SiC fibres. However, with ductile resins, stress transfer may be limited by the plastic yield of the matrix and a pseudosaturation state observed (Fig.…”