Basic Theory of Fiber-Reinforced Composite Materials

Basic Theory of Fiber-Reinforced Composite Materials 

It should be stressed that an increase of Young s modulus can be achieved by increasing the nanotube content and using high aspect ratio fillers, namely, longer and thinner nanotubes (for l/D 15, tji 1). 

It is well documented [78] that there is a critical length that the fibers must have to strengthen a material to their maximum potential. The stress transferred to the fiber reaches the maximum value (cTf) at a length from the end of the fiber. This means that short fibers can carry stresses less effectively than the long ones and they seem to have a smaller effective modulus for reinforcement purposes. The critical length Ic is given in Eq. (10.6)  

Concerning the composite strength Jc, Eq. (10.2) holds for quite long aligned fibers. For midlength fibers, Eq. (10.2) is modified to the following  

Equation (10.9) shows that the composite strength depends on the strength of matrix-fiber interface, r, and not on the fiber s strength. The above-mentioned relations should be used as a benchmark to calculate the composite strength and modulus. Modulus can be determined if the external and inner diameters of CNTs 

---