The effect of debonding on the vibration behaviour of CFRP/Epoxy sandwich panels

Abstract

Fibre composite materials are widely used because they are light but strong. This work discusses two topics of composites: 1. Vibration behaviours of debonded sandwich structures. 2. The fracture and fatigue behaviours of carbon fibre reinforced polymers (CFRPs) with nanoparticle-modified sizing. Debonds between the facesheets and the core of sandwich structures can weaken the structures, whilst affecting its vibration response. The vibration behaviours of sandwich structures were analysed by conducting hammer impact tests and finite element simulations on the structures with different debond configurations, facesheet stacking, matrix modifiers and curvatures. For the flat structure using the [0°]4 facesheets, the natural frequency significantly decreased by 57 % when there was an 80 mm debonded region due to the reduction in the stiffness. The natural frequencies of the bending modes dropped most significantly when two debonds were present in the same location for both upper and lower facesheets. The curvature had more effect on the lateral modes than other modes since the mode shapes involved torsional movements. Reduction in the natural frequencies can cause a structure to vibrate at resonance and hence cause structural failure, which is critical for the applications of sandwich structures. Fibre composites with thermoset polymer matrices are widely used, but the brittleness of thermoset polymers used as the matrix can limit their applications. In this work, silica nanoparticles (SNPs) were used to modify two carbon-fibre sizings. Mode I interlaminar fracture tests and fatigue crack growth tests were conducted on the sizing-modified CFRPs. Although there was no significant change in the fatigue crack growth rate, the fracture energy was significantly increased from 166 J/m2 to 220 J/m2 with the addition of only 0.89 wt% on fibre weight of SNPs. This is significantly more efficient than directly adding SNPs into the matrix to achieve the same improvement.