Mechanical properties of composites

The mechanical properties of composites based on the fibers discussed depend not only on the characteristics of the fibers but also on those of the matrix itself as well as on the fiber—matrix interface. 

The mechanical properties of composites reinforced with wood fibers and PVC or PS as resin can be improved by an isocyanate treatment of those cellulose fibers [41,50] or the polymer matrix [50]. Polymethylene-polyphenyl-isocianate (PMPPIC) in pure state or solution in plasticizer can be used. PMPPIC is chemically linked to the cellulose matrix through strong covalent bonds (Fig. 8). 

C. Influence of Coupling Agents on the Mechanical Properties of Composites... 

The mechanical properties of composites are mainly influenced by the adhesion between matrix and fibers of the composite. As it is known from glass fibers, the adhesion properties could be changed by pretreatments of fibers. So special process, chemical and physical modification methods were developed. Moisture repel-lency, resistance to environmental effects, and, not at least, the mechanical properties are improved by these treatments. Various applications for natural fibers as reinforcement in plastics are encouraged. 

However, in composites, fiber ruptures result in development of mainline cracks even at lower stresses. It is therefore necessary to know the so-called attainment coefficient in order to predict the mechanical properties of composites. The fiber strength in a PCM [Pg.20]

It should be noted that for polymerization-modified perlite the strength parameters of the composition algo go up with the increasing initial particle size. [164]. In some studies it has been shown that the filler modification effect on the mechanical properties of composites is maximum when only a portion of the filler surface is given the polymerophilic properties (cf., e.g. [166-168]). The reason lies in the specifics of the boundary layer formation in the polymer-filler systems and formation of a secondary filler network . In principle, the patchy polymerophilic behavior of the filler in relation to the matrix should also have place in the failing polymerization-modified perlite. 

Physico-Mechanical Properties of Composites with Polymerization-Modified Fillers (PMF)... 

Table 14. Thermal effect (dH) of interaction of chalk coated with different polymeric materials with the PVC matrix and the mechanical properties of compositions with 40% by mass of chalk [210]...

All theoretical models, describing the physical and mechanical properties of composites, consider the surfaces of the inclusions as perfect mathematical surfaces. In this way, the transition of the mechanical properties from the one phase to the other is done by jumps in the characteristic properties of either phase. This fact introduces high-shear straining at the boundaries, which is an unrealistic fact. 

In order to evaluate the effect of hygrothermal fatigue on the physical and mechanical properties of composites in actual service, it is crucial to resolve the basic phenomena driving the complex water sorption behaviour and degradation mechanisms in various combinations of moist environment and temperature. 

Fig. 2. Summary of mechanical properties of composites containing various fillers...

M. Fang, K. G. Wang, H. B. Lu, Y. L. Yang, S. Nutt, Covalent polymer functionalization of graphene nanosheets and mechanical properties of composites, Journal of Materials Chemestry, vol. 19, pp. 7098-7105, 2009. 

Other than in polymer matrix composites, the chemical reaction between elements of constituents takes place in different ways. Reaction occurs to form a new compound(s) at the interface region in MMCs, particularly those manufactured by a molten metal infiltration process. Reaction involves transfer of atoms from one or both of the constituents to the reaction site near the interface and these transfer processes are diffusion controlled. Depending on the composite constituents, the atoms of the fiber surface diffuse through the reaction site, (for example, in the boron fiber-titanium matrix system, this causes a significant volume contraction due to void formation in the center of the fiber or at the fiber-compound interface (Blackburn et al., 1966)), or the matrix atoms diffuse through the reaction product. Continued reaction to form a new compound at the interface region is generally harmful to the mechanical properties of composites. 

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. 

Termonia, Y. (1992). Effect of strain rate on the mechanical properties of composites with a weak fiber/ matrix interface, J. Mater. Sci. 27, 4878-4882. 

The interaction of two substrates, the bond strength of adhesives are frequently measured by the peel test [76]. The results can often be related to the reversible work of adhesion. Due to its physical nature such a measurement is impossible to carry out for particulate filled polymers. Even interfacial shear strength widely applied for the characterization of matrix/fiber adhesion cannot be used in particulate filled polymers. Interfacial adhesion of the components is usually deduced indirectly from the mechanical properties of composites with the help of models describing composition dependence. Such models must also take into account interfacial interactions. 

The final step of thermoplastic composite consolidation is to cool and solidify the consolidated parts. It is well known that the physical and mechanical properties of composites are determined by the microstructure of the matrix in addition to the reinforcement, whereas the morphology of the thermoplastics is determined by its thermal history [14-17]. 

Rusakov, V. V., in Structural and Mechanical Properties of Composite Materials, pp. 37-48, Sverdlovsk, Sci. Papers of Ural Sci. Center of Akad. Nauk USSR 1984... 

The U.S. Navy has sponsored research at Virginia Tech to look at structural performance of FRP for the previously mentioned deck applications. This included work on determining the postftre structural properties. This work was reported in detail in the doctorate dissertation of Steven Boyd in 1996.27 Gibson et al.28 did work on modeling the residual mechanical properties of composites after fire. There have been recent studies on the mechanical properties of composites after fire,29-31 some of which have been cited previously in this chapter.1314 The requirements for the Navy applications have been described by Sorathia.19 20 32... 

Another acid-base study on carbon fiber (supplied by Courtaulds Co.) surfaces accompanied with the results of mechanical properties of composites is shown in Table 11, with 90% confidence level in arbitrary units [107,110,159]. 

In simple cases the mechanical properties of composites can be estimated. 

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