Effect Of Peel Plies On Bonding Quality For Composites

The co-bonding technology has been used widely in the manufacture of composite structures in the field of aerospace.However,the performance of the co-bonding of composites has intimate relationship with surface treatment of composites.Boeing and Airbus have used the peel ply surface-treatment instead of sanding since 2008,which was the traditional process for the surface treatment of composites.It was also found that varied bonding properties were observed on the surfaces of composites with different peel plies after treatments during development of China's commercial aircraft.Nevertheless,the effect of peel plies on the bonding properties was not yet clear.In order to study the effects of the bonding quality on different surfaces of composites with different peel plies,the typical pregreg systems and peel plies used by the commercial aircraft were chosen for surface treatment.It is anticipated that the research results will provide theoretical basis for the co-bonding of composites.The composites were fabricated using the autoclave process with 970/T300 woven prepreg and 3900/T800 unidirectional prepreg.And four kinds of peel plies(P60001,EA9895,R60 and R60S)and traditional way of sanding were chosen for surface treatment and bonding respectively.Then,Contact Angle test,Scanning Electron Microscopy(SEM)and X-Ray Photo Spectroscopy(XPS)were applied to characterize the surface wettability,microscopic morphology and surface chemical form for composites and peel plies.Finally,the stripping tests and single lap shear test specimens of composite laminate were prepared by the ASTM standards.According to the results of mechanical properties,the varied bonding quality of composite surface with different peel plies after treatments was analyzed.The results show that the residual of peel plies was not observed on the 970/T300 and 3900/T800 composite surfaces treated with R60 and R60 S peel ply by SEM,but the transfer of nylon and silicone coating was detected by XPS analysis on R60 and R60 S,respectively.The co-bonding with the surface treatment of both peel plies exhibits poor bonding properties and the failure modes are adhesive.This could be explained that the residual and coating of peel plies on the composite surface have negative effect on the bonding performance of 970/T300 and 3900/T800 composites.The peel ply fibers were found on the 970/T300 composite surface treated with P60001 peel ply with SEM and typical of a ductile fiber fracture was also observed on the removed P60001 peel ply.As a result,the bonding quality was poor and the failure mode was adhesive.By contrast,no residual of P60001 peel ply was observed on the 3900/T800 composite surface,which possessed better bonding quality than 970/T300 composite due to the absent of P60001 peel ply residual.The residual of peel plies was not observed on the 970/T300 and 3900/T800 composite surfaces treated with EA9895,and the types of failure modes are cohesion.It is indicated that P60001 peel ply possessed better matching properties with 3900/T800 composite laminate than 970/T300 composite laminate,and EA9895 peel ply matched well with both.