Investigation on delamination and flexural properties in drilling of carbon nanotube/polymer composites

The drilling of composite laminates is difficult to control and often leads to delamination that significantly affects the strength of the structure. Of the mechanical properties of composite materials affected by drilling-induced damage, flexural strength has received very little attention. In the present paper, experiments were conducted to analyze the thrust force, delamination factor and residual flexural strength in the drilling of woven E-glass fiber-epoxy composites reinforced with functionalized multi-walled carbon nanotubes. The process parameters considered for the experiments are the feed rate, spindle speed, drill diameter, and the weight percentage of carbon nanotubes present in nanocomposite laminates. Drilling experiments were conducted based on Taguchi design of experiment and three-point bending tests were then done to assess the residual flexural strength of drilled specimens. Analysis of variance and Taguchi S/N ratio analysis were performed to investigate the influence of input parameters on each individual drilling characteristics. In addition, the orthogonal array with grey relational analysis was employed to simultaneously optimize the multiple performance characteristics of the drilling process. According to the results, the feed rate is the factor which has the greatest influence on the thrust force and delamination factor, followed by spindle speed. Residual flexural strength, however, is mostly influenced by nano content, followed by feed rate.