Effect Of Polyurethane Coating On Anti - Repeated Low - Speed Impact Performance Of Composite Laminates

Carbon fiber composite laminated structure which has been widely used in aerospace, transportation, construction and other fields, owns the properties of light weight, high strength, good resistance to fatigue and good designability and other unique advantages, but some other limited properties which refer to the internal delamination and the matrix cracking and damage under the low energy impacting, have becoming the fatal factors for the composite materials. Even though single impact may not cause a lot of damage to composite material, after repeated impact, the damage accumulation will greatly reduce the compression strength of laminated structure. In order to improve the composite laminated structure of repeated impact resistance and damage tolerance, this article will coat polyurethane on the surface of composite materials, the composite laminates coated with PU can affect the performance of repeated impact resistance, and then compared the laminates coated with PU and the pure laminates, we can analyze the damage forms under the low-velocity impacting and accumulate the compression strength after impact. Finally we can find it can obviously improve the property of anti-repeated resistance and damage tolerance to coat the PU on the surface of the composites laminates, which has the important value of engineering application.Firstly, the composite laminates with different stacking sequences and thickness were prepared in this article, and sand blasting, sand preparing and brushing adhesive were used to treat the surface of laminates, and finally PU low pressure solvent-free coating technology was used to coat on the surface of the composite laminates, after finishing the treatments processes, the coating pressure, coating velocity and the original temperature of the PU which coated on the surface and other coating processes were studied which can affect the surface quality of laminates coated with PU. When the coating technics was finished, he peeling testing was used to study the property of interfical strength between the coated PU and the laminate, after this we can find the excellent surface treatments.Secondly, the anti-repeated impact testing was used to analyze and compare the laminated coated with PU and the pure composites, these following testing aspects were compared, they are the impact response and the fracture area via the C-scan after repeated impact, the damage form and dent depth, respectively.In addition, these factors referring to the thickness of PU coat, the thickness of composites, different stacking sequence and various structures of composites can affect the anti-repeated impact of laminates.Finally, the compression after impact (CAI) testing was used to analyze the residual compression strength,this conclusion can be found:the inflection point shows up on the curve of residual compression strength with the increase of damage area of composite laminates, and the residual compression strength is small before the inflection point showing up, and also the thickness of PU coating and the thickness of composites laminates acting on the compression after impact were analyzed, at the same time, the DIC was applied to observe the damage style, and then the compression damage mechanism and model can be acquired.