Some limits of the equation H kTg

A peculiarity of polymeric composites that makes them very attractive is that their structure and thus their mechanical property profile can be tailored to given requirements and service conditions. Composite materials have been classified in many ways depending on the ideas and concepts that need to be identified. For the 

Both thermoset and thermoplastic resins and CF composites have been examined using microhardness techniques. The thermoset resin used was an epoxy, both with and without PA6 particles that served as a toughening agent. 

Firstly, we discuss the microhardness values obtained for the epoxy materials first. The addition of the CFs greatly increased the microhardness ( 740 MPa) with respect to that of the resin ( 314 MPa). This difference reflects the tremendous improvement in mechanical properties resulting from the presence of reinforcing CFs. In addition, the PA6 particles added for toughening induce a much higher increase in the microhardness in the composite. 

This increase in the microhardness resulting from CF reinforcement has been also seen in thermoplastic TPI resin. In addition, microhardness is also influenced by the presence of crystallinity. 

The high microhardness values found for these composites illustrate that the gap in microhardness between polymers and hard metals has been narrowed (see Fig. 1.2). While no microhardness values are available for CFs, the microhardness values for reinforced materials, especially high local values for areas with little resin, indicate the microhardness of CFs should be at least 1000 MPa. This agrees with the published microhardness for graphite (1 GPa) (Skinner Gane, 1973), which 

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