In this paper, a set of numerical and experimental studies are performed to improve mechanical and vibrational properties of carbon nanotubes-reinforced composites. First, at a design concept level, linear distribution patterns of multi-walled carbon nanotubes through the thickness of a typical beam is adopted to investigate its fundamental natural frequency for a given weight percent of multi-walled carbon nanotubes. Both Timoshenko and Euler-Bernoulli beam theories are used in the derivation of the governing equations. The finite element method is employed to obtain a numerical approximation of the motion equation. Next, based on the introduced distribution patterns, laminated multi-walled carbon nanotubes-reinforced polystyrene-amine composite beams are fabricated. Static and experimental modal tests are performed to measure the effective stiffness and fundamental natural frequencies of the fabricated composite beams. Also, in order to generate realistic model to investigate the material properties of fabricated composite beams, the actual tensile specimens of multi-walled carbon nanotubes/polystyrene-amine composites are successfully fabricated and the tensile behaviors of both pure matrix and composites are investigated. To better interfacial bonding between carbon nanotubes and polymer, a chemical treatment is performed on carbon nanotubes. It is seen that the addition of a few wt. % of multi-walled carbon nanotubes make considerable increase in the Young's modulus and the tensile strength of the composite. It is observed from the free vibration tests that the uniform distribution of multi-walled carbon nanotubes results in an increase of 9.5% in the fundamental natural frequency of the polymer cantilever beam, whereas using the symmetric multi-walled carbon nanotube distribution increased its fundamental natural frequency by 17.32%.
Theoretical and Experimental Studies of Timber Composite Beams Reinforced by Cold Formed Steel Sheets
