High strain rate behavior of multi-walled carbon nanotubes–polycarbonate composites

Multi-walled carbon nanotubes–polycarbonate composites (MWCNT–PC) were prepared by a two-step method of solvent casting followed by compression molding and their dynamic impact strength was studied. Split Hopkinson Pressure Bar (SHPB) was deployed as the instrument for impact testing of the composite samples. The impact tests were performed under varying strain rates ranging from 1096 to 4017/s. The present studies report the stress–strain behavior of MWCNT–PC composites under a high strain rate of 2000–2600/s. A comparison of stress at various strains ranging from 5% to 20% was done by varying MWCNT concentration in the range 0.1, 0.5, 1, 2 and 5 wt.% in PC. Stress tolerance of these composites was studied to analyze effectiveness of small amounts of carbon nanotubes (CNTs) for impact/stress absorption in comparison to pure PC samples. It was found that the stress behavior for specific strains varies with concentration of CNTs in polycarbonate. At very low (about 0.1 wt.%) and high concentrations (about 5 wt.%) of carbon nanotubes the stress did not vary much as compared to pure PC for the above mentioned strain range. At concentration levels of 0.5, 1 and 2 wt.% CNTs, the impact absorption (nearly 105 MPa) increased by 10–20% as compared to pure PC (nearly 90 MPa) depending upon the amount of strain in the samples. The role of functionalized CNTs in impact studies was also studied by using 0.5 wt.% and 2 wt.% functionalized MWCNT. The use of functionalized CNTs was found to result in reduced impact absorption (nearly 95 MPa) as compared to as-synthesized CNTs (nearly 105 MPa). The effect of concentration of CNTs on impact strength of MWCNT–PC composites was analyzed by studying the SEM images of composite samples after impact.