Adhesion fiber-matrix

Another major drawback of polysaccharides is their hydrophilic nature leading to low degrees of adhesion between fiber and matrix [11]. Moisture absorption takes place by three types of mechanisms namely diffusion, capillarity, and transport via micro cracks [2]. Among the three, diffusion is considered to be the major mechanism. Water absorption largely depends on the water-soluble or hygroscopic components embedded in the matrix, which acts as a semipermeable membrane. While, fiber/matrix adhesion and fiber architecture also affect the moisture absorption. The results of the water sorption experiment showed an interesting trend. The extent of water uptake was not very significant and also did not increase linearly with amount of filler (Table-2). 

The aspect ratio, i.e., the length/diameter ratio (L/D) of the fibers is a major parameter that controls the fiber dispersion, fiber-matrix adhesion and optimum performance of short fiber-mbber... 

Proper reinforcement of rubber matrix using hllers can be achieved only if there exists adequate adhesion between the hller and the mbber. Rubber-mbber adhesion and rubber-hller adhesion both without and with adhesion promoters have been studied extensively [125-127]. Fiber-matrix adhesion in short fiber-rubber composites is always a field of extensive research. If the fibers are not bonded properly with the rubber matrix, fibers will shde past each other under tension deforming the matrix, thereby reducing the strength properties. In the case of short fiber-reinforced rubber composites, loads are not directly applied to the fibers, but are apphed to the matrix. To obtain a high-performance composite, the load must be effectively transferred to the fibers, which is possible only when the fiber-matrix interphase is sufficiently strong. In addition, the adhesion between the fiber and the matrix should be such that the failure occurs in the matrix rather than at the interphase [92]. 

Drzal, L.T. and Madhukar, M. (1993). Fiber-matrix adhesion and its relationship to composite mechanical properties. J. Mater. Sci. 28, 569-610. 

Bucher, R.A, and Hinkley, J.A. (1992). Fiber/matrix adhesion in graphite/peek composites. J. Thermoplastic Composite Mater. 5, 2-13. 

Gutowski, W. (1990). Effect of fiber-matrix adhesion on mechanical properties of composites. In Controlled Interfaces in Composite Materials (Proc. ICCI-III) (H. Ishida ed.), Elsevier, New York, pp. 505-520. 

Herrera-Franco, P.J. and Drzal, L.T. (1992). Comparison of methods for the measurement of fiber/matrix adhesion in composites. Composites, 23, 2-27. 

Madhukar, M.S. and Drzal, L.T. (1991). Fiber-matrix adhesion and its effects on composite mechanical properties II. Longitudinal (0°) and transverse (90°) tensile and flexural behaviour of graphite/epoxy composites. J. Composite Mater. 25, 958-991. 

Biro, D.A., Pleizeier, G, and Deslandes, Y. (1993b). Application of the microbond technique. IV. Improved fiber matrix adhesion by RF plasma treatment of organic fibers. J. Appl. Polym. Sci. 47. 883-894. 

Drown, E.K., Al-Moussawi. H. and Drzal, L.T. (1991). Glass fiber sizings and their role in fiber-matrix adhesion. J. Adhesion Sci. Techno . 5, 865-881. 

Different kinds of carbon-intense fibers are used, the most common being carbon and graphite fibers, and carbon black. As is the case with fibrous glass, surface voids are present. Carbon-intense fibers are often surface-treated with agents such as low molecular weight epoxy resins. Such surface treatments also aim at increasing the fiber-matrix adhesion. 

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

IFSS are much more striking, emphasizing the fact that the effectiveness of silane treatment is more important in retaining fiber-matrix adhesion under conditions of exposure to moisture. 

IFSS of the sized fibers vs. the bare. These results indicate that the application of the sizing and the consequent formation of the interphase have resulted in an increase in the level of fiber-matrix adhesion. It could reasonably be expected that under the multiaxial state of stress at the fiber-matrix interphase, stronger fiber-matrix adhesion would reduce the tendency to grow an interfacial crack, thereby placing more energy into driving the matrix crack as observed for the sized fiber. 

Effect of fiber-matrix adhesion and the interphase on composite mechanical properties... 

Both fiber-matrix interphase-sensitive mechanical tests (interlaminar shear strength, 90° flexure) and interphase-insensitive tests (0° flexure) were conducted on high volume composite samples fabricated from the same materials and in the same manner as discussed above to see if the interphase and its properties altered the composite mechanical properties and in what manner. A summary of the data is plotted as a bar graph in Fig. 7. The first set of bars represents the difference in fiber-matrix adhesion measured between the bare fibers and the sized fibers by the ITS. The composite properties plotted on the figure also show increased values for the epoxy-sized material over the bare fiber composite. 

An alternative approach to understanding the role which silane-based fiber sizes play in fiber-matrix adhesion has been proposed in which the three-dimensional nature of the interphase formed by the interaction of the sizing agent with the bulk matrix has been shown to be a potential key factor in understanding the role that fiber sizings have in affecting fiber-matrix adhesion and composite mechanical properties. 

The mechanical properties of a fiber-matrix interphase composed of high concentrations of sizing, exclusive of the presence or absence of specific chemical interactions between the fiber surface and the surrounding matrix, have been demonstrated to be potentially responsible for the level of fiber-matrix adhesion. 

The modulus and toughness of this interphase combined with the increased fiber-matrix adhesion can be used to explain the resulting mechanical properties of these composite materials. For both interphase-sensitive and -insensitive mechanical properties, it has been concluded that the strength of the interphase and the failure mode initiated by the interphase properties can be responsible for composite mechanical properties. 

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