Post-indentation compression behavior of S2-glass/epoxy composite tubes with nanofillers

The goal of the investigation reported in this paper is to determine the influence of carbon nanotube (CNT) and carbon nanofiber (CNF) fillers on the damage tolerance of S2-glass/epoxy laminated tubes by using compression-after- indentation (CAI) tests. Laminated [(±45)1/(±2)2/(±45)2] tubes were manufactured by the filament winding method. The nanofillers were added by one of two approaches: (1) adding nanofiller in the resin bath and continuously wetting the tow with nanofilled resin during filament winding; and (2) adding nanofilled epoxy as an interlayer in between wet or dry glass fiber/epoxy plies. The best percent improvement in non-indented compressive strength versus the unfilled control case was 21% in a composite made with 0.5 wt% short COOH-CNTs throughout the matrix of the composite. The best improvement in compressive strength after indentation versus the unfilled control case was 15% in a composite made with the baseline epoxy resin in the plies and 0.5 wt% CNFs in the interlayer regions. Reduction in compressive strength due to indentation, as a percentage of nonindented tube strength, was mostly a function of the maximum indentation force and did not depend as strongly on the presence or type of nanofiller or the method of introducing the nanofiller. These reductions were 29 to 33% for the 1500 N indentation force and 37 to 45% for the 2400 N indentation force. Little change in the modulus of elasticity of the tubes was observed due to the dominating influence of the continuous glass fibers.