Matrix interface epoxy

The mechanical properties of the blend of silane/size and bulk epoxy matrix (at concentrations representing likely compositions found at the fiber-matrix interface region) also suggest that the interaction of size with epoxy produces an interphase which is completely different to the bulk matrix material (Al-Moussawi et al., 1993). The interphase material tends to have a lower glass transition temperature, Tg, higher modulus and tensile strength and lower fracture toughness than the bulk matrix. Fig. 5.4 (Drown et al., 1991) presents a plot of Tg versus the amount of... 

Janssens, W., Doxsee Jr., L., Verpoest, I. and de Meester, P. (1989). Influence of the fiber-matrix interface on the transverse bending strength of dry and moist aramid-epoxy composites. In Proc. Interfacial Phenomena in Composite Materials 89, (F.R. Jones ed.), Butterworths, London, pp 147-154. 

Bader M.G., Bailey J.E. and Bell 1. (1973). The effect of fiber-matrix interface strength on the impact and fracture properties of carbon fiber-reinforced epoxy resin composites. J. Phys. D Appi. Phvs. 6, 572-586. 

Consider the same unidirectional lamina with the stresses now applied perpendicular to the fiber axis as shown in Fig. 12. The local stress at the fiber matrix interface can be calculated and compared to the nominally applied stress on the whole lamina to give K, the stress concentration factor. The plot of the results of this analysis shows that the interfacial stresses at the point of maximum principal stress can range up to 2.6 times the applied stress depending on the moduli of the constituents and the volume fraction of the reinforcement. For a typical graphite-epoxy composite, with a modulus ratio of 70 and a volume fraction of 70 % the stress concentration factor at the interface is about 2.4. That is, the local stresses at the interface are a factor of 2.4 times greater than the applied stress. 

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 results reported here are similar to a study recently completed in which the adhesion of carbon fibers to epoxy matrices was varied [25, 26]. Over three different levels of adhesion and three different failure modes, composite properties both in the fiber direction and perpendicular to the fiber-matrix interface were shown to be dependent both on the level of adhesion and on the interphase properties and failure modes. 

In previous work (30-321. it has been suggested that the adhesion between a carbon fibre and an epoxy matrix is essentially the result of physical bonds, either dispersive or polar. It is clear from the results in the last column of Table VI that there is no correlation between x and the reversible energy of adhesion WA, calculated as the sum of the dispersive and polar interactions at the fibre-matrix interface. 

However, little or no significant benefit of rubber modification has been seen in the few epoxies examined, even though the rubber improved the impact strength. The cause of this paradoxical behavior has not been established, but Manson et al. (22) proposed that the rubber-matrix interface may fail well ahead of the advancing crack, thus limiting the already low capacity for shear deformation in the matrix. 

Tillie et al. (1998) examined the effect of the fibre/matrix interface on the cure of glass-fibre-filled epoxy-resin systems. They found that the introduction of a lower-Tg interphase based on hydroxylated PDMS oligomers allowed an increase in toughness without a reduction in modulus or Tg. This was due to a modification of the stress field under load due to the elastomeric interphase. 

Hexcel T2C145 carbon fibre/F263 TGDDM-DDS epoxy Matrix Interface... 

Particle pull-out, which leaves hemispherical holes on the fracture surface, is due to the debonding of nanoparticles. The strong interface between treated Al Oj and matrix in epoxy nanocomposites is debonded during tensile testing. Voids are also formed aroimd both treated and non-treated Al O particles. Plastic void formation is also a toughening mechanism. The voids deform more in APTES-Al O /epoxy nanocomposites than NT-Al Oj/epoxy nanocomposites. 

For systems involving, on the one hand, poorly polar matrices, such as polyethylene, polyvinylchloride and polyurethane and, on the other hand, untreated and surface treated glass or carbon fibres, it has been shown in our laboratory [12,13] that a linear relationship can be established to a first approximation between t and the reversible work of adhesion W defined by equation (5). However for more polar matrices, like epoxy resin for example, such a relationship is no longer valid, since strong specific interactions are now established at the fibre-matrix interface. 

The plasma treatment also reduced the water absorption of the composite by a factor of 3 and converted it from capillary (wicking along the fiber-matrix interface) to Pick s law absorption through the body of the matrix. The rate of water absorption in the composite was less than it was in a block of neat epoxy the same size as the composite. The difference in absorption rate was the same as the volume fraction of epo in the composite. This change in absorption mechanism would predict that there should be a great improvement in the hydrothermal stability of plasma treated composites. 

The mechanical properties of fiber-reinforced polymer composites are cmitroUed by factors such as nature of matrix, fiber—matrix interface, fiber volume or weight fraction, fiber aspect ratio, etc. Due to the hydrophilic nature, the fibers pulled out from polyester and polyethylene matrices, they were compared with the fibers pulled out from the epoxy matrix, which carry polymer particles on their surfaces. On the other hand, fracmre of the fibers occurs at the crack plane in phenolic composites. From SEM microstructures of different composites, it was observed that the bonding of sisal fiber with the four matrices are found to be in the order of phenolic > epoxy > polyester > polyethylene [58, 59]. 

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