Polymer matrix ductility

The stress-strain curves for cortical bones at various strain rates are shown in Figure 5.130. The mechanical behavior is as expected from a composite of linear elastic ceramic reinforcement (HA) and a compliant, ductile polymer matrix (collagen). In fact, the tensile modulus values for bone can be modeled to within a factor of two by a rule-of-mixtures calculation on the basis of a 0.5 volume fraction HA-reinforced... 

Ang Angola, J., Fujita, Y., Sakai, T., Inoue, T. Compatibilizer-aided toughening in polymer blends consisting of brittle polymer particles dispersed in a ductile polymer matrix. J. Polym. Sci. Part B Polym. Phys. 26 (1988) 807-816. 

Very recently, in our group, enhanced self-reinforced PP composites based on commercial PP fabrics were obtained by the film stacking method followed by compression molding introducing different contents of micron-sized quartz particles in the matrix films (unpublished results). Simultaneous improvements of composite tensile strength, ductility and fracture toughness were observed from the addition of quartz to the polymer matrix (Table 14.1). Enhanced degree of consohdation was obtained for the composites with quartz as evidenced from the improved mechanical properties and by SEM observations. This was also confirmed by acoustic emission analysis in situ in tensile tests. 

In their function as fillers, the organic spheres share the performances and benefits of the spherical form, similar to glass and ceramic spheres. However, their effect on a polymer matrix is normally not the enhancement of mechanical strength, such as tensile strength and abrasion resistance. Instead, they can impart new features to thermoplastics and thermosets, such as reduced density, improved resilience and ductility, mechanical and thermal stress absorption, or enhanced thermal and electrical insulating properties. When added to binders and plastisols for coatings, the function of the spheres can be surface modification of the coated surface this may include the creation of a visual effect or antislip properties, or to make a protective coating [2, 3]. 

Because fibre composites frequently fail in this statistical manner by accumulating local damage, the methods of fracture mechanics are often not too useful. If, on the other hand, a sufficiently long crack in a fibre composite forms, it may propagate. In this case, the fracture toughness Kic of composites with ductile matrix is often smaller than in the pure matrix material because the fibres cause the stress state to be triaxial (see section 3.5.3). This happens in some polymer matrix composites, but mostly in metal matrix composites in which the fracture toughness may be halved compared to the matrix material [62]. 

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