Mechanical properties of Carbon Nanotube (CNT) reinforced composites are obtained utilizing finite element (FE) method-based indentation simulations considering large strain elasto-plastic behavior of elements. This study includes nanoindentation simulations for chemically non-bonded CNT/matrix interface, including the length scale effect of nanocomposites. In order to investigate the mechanical properties of CNT reinforced nanocomposites, a number of FE models for nanoindentation tests have been simulated. Sample nanocomposites are examined to determine the suitable types of CNTs and their effectiveness as a reinforcement of different potential matrices. The Parametric study is conducted to obtain the influence of wall thickness, relative positioning, and volume fraction of CNT and strain hardening parameter of matrix on the mechanical properties of nanocomposites. The obtained results indicate that, properties such as modulus of elasticity and hardness of the nanocomposites are largely dependent on wall thickness of CNT and strain hardening parameter of the matrix. This study also suggests, the minimum wall thickness of CNT to avoid local buckling in nanocomposite which is required to be at least 0.2 nm for a diameter to thickness ratio of 5.0. Moreover, a matrix having a value of strain hardening parameter near 0.1 is expected to be significantly effective for nanocomposite.

Indentation analyses are conducted to investigate the CNT’s wall thickness dependencies of the mechanical properties of nanocomposites. This study incorporates Berkovich nanoindentation analyses for chemically non-bonded CNT/matrix interface, including the size effects of nanocomposites. For non-bonded interface, the properties of nanocomposite are generally controlled by mechanical interlocking, thermal residual stress, Poisson’s contraction and van der Waal’s (vdW) interaction between CNT and matrix. Considering all these parameters, a series of finite element models for nano-indentation tests have been constructed, aiming to investigate the mechanical properties of CNT reinforced nanocomposites. The model is validated and numerical results are compared with that of existing experimental indentation test. Analysis has been run for ten different wall thicknesses of CNTs in a range of wall thickness starting from 0.034 nm to 0.334 nm. Elasto-plastic behavior of steel and CNT including strain gradient is considered in the program. The study on wall thickness dependencies of CNTs in nanocomposite shows that mechanical properties of nanocomposites largely depends on the wall thickness of CNTs. A minimum wall thickness for a particular tube diameter to achieve a pick value of hardness and modulus of elasticity of nanocomposites is determined. The minimum wall thickness of CNTs is suggested to be 0.2 for an outer diameter of 1nm in order to achieve the maximum value of composite properties. In addition, a wall thickness smaller than 0.05 nm may even reduce the hardness and modulus of elasticity of CNT reinforced composites compare to that of pure matrix.

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