| Carbon fiber reinforced polymer composites(CFRPs)are widely used in various fields such as aerospace,automotive and shipbuilding,and wind power generation because of their high specific strength,high specific modulus,and designability.The requirement for durability of the products is increasing at the same time that the demand for the production of CFRPs increases dramatically.However,CFRPs are subject to delamination due to low-energy impact or mechanical processing.The high stiffness of CFRPs components limits the opening of the crack surface and the sharp opening could not be observed by naked eye.So,the high-viscosity epoxy is hard to penetrate into the delamination cracks for repair.The infinite stress concentration from delamination cracks leads to premature failure of the CFRPs structure and reduces the service life of the CFRPs components.In order to repair the delamination cracks in CFRPs damage,two mixed solutions,namely acetone-diluted resin and acetone-diluted selfcuring resin,were adopted in the current study and were analyzed in terms of their feasibility and effectiveness.The mechanical properties of the epoxy resin treated by acetone were investigated using compression and three-point bending tests,and the results showed that acetone could fully evaporate from the solution without affecting the mechanical properties of the epoxy resin,indicating that the epoxy-acetone solution can be safely applied to the repair of delaminated cracks in CFRPs.In comparison to repairing by raw epoxy system,repairing by the epoxyacetone solution substantially increases the amount of resin penetration inside the crack,and the resin penetration process do not need any applied pressure.The repair mechanism of epoxyacetone solution was revealed by analyzing the capillary action of epoxy-acetone solution and the curing behavior of epoxy resin after acetone evaporation,which applied the epoxy-acetone solution to penetrate spontaneously into the delamination cracks in CFRPs,and then the curing of epoxy resin deposited inside the cracks was achieved by diffusion of hardener after acetone fully evaporating,which effectively fills the delamination cracks.An epoxy-acetone solution with epoxy resin content of 5 wt%-45 wt%was prepared to repair delamination cracks in CFRPs.The repair performance of the epoxy-acetone solution was evaluated by in-plane compression testing,and the repair effectiveness was calculated based on the ratio of the strength recovered from the repaired specimens to the strength of the damage before repair,and the failure behavior of the specimens and resin penetration within the delaminated cracks were characterized on multiple scales.When the curing time was 7 days,the repair effectiveness of the specimens repaired by epoxy-acetone solution with resin content of 30 wt%reached 37%,which was 32%higher than that of the raw epoxy-system repair.The epoxy-acetone solution mixing with carbon nanotubes to repair CFRPs delamination was presented,Futher increase of repair performance was achieved in epoxy-acetone solution with resin content of 5 wt%by adding of carbon nanotubes,and the repair effectiveness increased by 22%and the fracture absorption energy increased by 59%compared with the repair of epoxy-acetone solution without carbon nanotubes.SEM results located on the fracture surface of the delaminated cracks showed carbon nanotubes played a bridging role in the repair process,impeding crack propagation and ensuring structural integrity of CFRPs.When the curing time futher increased,the repair performance of the epoxy-acetone solution reaches the best with the repair effectiveness reaching 65%.The experimental results showed that the specimens with high repair effectiveness had less delamination at failure and higher resin infiltration within the delamination cracks than the raw epoxy-system repair,revealing that the delamination cracks in CFRPs could be repaired by epoxy-acetone solution.Self-curing epoxy resin under high temperature mixed with acetone solution was used to repair delamination cracks in CFRPs for improving repair property and reduce the repair time.The capillary properties of the self-curing epoxy-acetone solution with resin content of 5 wt%-30 wt%were investigated by the surface properties testing,the results showed that the capillary properties of the self-curing epoxy-acetone solution with low resin content were stronger and was able to penetrate deeply into the crack interior.The curing behavior of the self-curing epoxy resin after acetone evaporation was analyzed by DSC testing result,and it was found that the acetone in the solution could be completely evaporated and the curing products structure of the self-curing epoxy resin after acetone evaporation was not changed.The characteristic temperature and activation energy of the curing reaction of the self-curing epoxy resin were significantly reduced,indicating that the acetone treatment promoted the occurrence of the curing reaction.The effects of resin content of solution and penetration times on the repair performance of self-curing epoxy-acetone solution repairing CFRPs delamination were studied,and the experimental results showed that the specimens repaired by self-curing epoxy-acetone solution with 20 wt%of resin content and 4 penetration times had 87%of repair effectiveness,which was 22%higher than the repair effectiveness of epoxy-acetone solution.The damage area of the repaired specimens was recovered extensively by X-ray tomography detection,especially at the crack openings and crack tips,revealing that the self-curing epoxyacetone solution achieved effective repair of delaminated cracks in CFRPs through capillary action.Likewise,adding carbon nanotubes into self-curing epoxy-acetone solution to repair CFRPs delamination,the repair effectiveness of the solution increased to 103%and the strength of repaired sample even exceeds original CFRPs.The fracture mode and morphology of the fracture surface were scanned by SEM and revealed the mechanism of action of carbon nanotubes to inhibit crack propagation. |
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