Non-destructive health monitoring of glass fibre epoxy composites under fatigue loading using electrical resistance change method

This study investigates the effect of stress amplitude on the damage sensing characteristic of glass fibre reinforced (GFRP) composites under fatigue loading using the electrical resistance change (ERC) method. The electrical conductivity of GFRP composites was achieved by incorporating 0.3 wt.% multi-walled carbon nanotubes (MWCNTs) into epoxy resin by ultrasonication method. In-situ electrical resistance measurements during fatigue tests of MWCNT-filled GFRP (MWNCT/GFRP) composites were conducted at two different stress amplitudes, S = 0.6 and S = 0.5. The average stiffness losses at failure were observed as 28% and 25% for S = 0.6 and S = 0.5 respectively. The corresponding ERC ratios at failure were found as 153% and 59% for S = 0.6 and S = 0.5, respectively. A two-parameter Weibull analysis, based on the ERC ratios corresponding to 40%, 60%, 80%, and 100% (failure) fatigue life, was implemented to establish reliability curves at the two stress amplitudes. The ERC ratios at failure with a 95% reliability for S = 0.6 and S = 0.5 were determined as 64% and 23%, respectively. Finally, the remaining fatigue life and the stiffness loss of composite specimens at the ERC ratios corresponding to various Weibull reliability were found for both stress amplitudes.