Effects of adding carbon nanofibers on the reduction of matrix cracking in laminated composites: Experimental and analytical approaches

The main purpose of the present study is to investigate the effect of adding carbon nanofibers (CNFs) in fibrous polymeric composites on the reduction of matrix cracking. A tensile testing machine was used to apply five loading steps and induce different crack densities in [02/906]s composite specimens with and without CNF fillers. After each loading step, the elastic modulus of specimens was measured. The crack density of damaged specimens was also measured by an optical microscope after each loading step. The Lamb wave propagation method was used to assess the elastic modulus of specimens at different crack densities. It was demonstrated that the addition of CNF fillers into the composite specimens resulted in lower crack densities and less stiffness reduction at certain applied stress levels. Moreover, Hashin and Andersons et al. micromechanical models were assessed by the experimental results for the analysis of matrix cracking in cross-ply laminated composites. For composite specimens with and without CNFs, the stiffness reduction at different crack densities was in good agreement with the predictions of the Hashin model, and the induced crack density at each applied loading step was in good agreement with the predictions of the Andersons et al. model. •The Lamb wave propagation method offers a strong tool for nondestructive evaluation of hybrid composite materials.•The matrix crack density and the stiffness reduction decreased by adding carbon nanofiber into the matrix of the specimens.•The stiffness reduction after each loading step was in good agreement with the predictions of the Hashin model.•The induced crack density after each loading step was in good agreement with the predictions of the Andersons et al. model.•The enhancement of the strength of the 90-degree layers was the major factor in decreasing the matrix crack density.