Research On Process And Properties Of Epoxy Resin Composite Repaired By Scanning Microwave Irradiation

With rapid repair of large wind turbine blades as the research background, this paper conducted a study on scanning microwave repair technology for epoxy composites. Glass fiber reinforced epoxy composites with good thermal and mechanical properties was manufactured under scanning microwave radiation. By investigated on the effects of microwave absorbent on cure speed and mechanical properties, the optimal adhesive system as well as scanning curing process for microwave scanning curing was obtained. Repair parameters such as scarf angle, stacking sequence and whether to add cover layer were evaluated synthetically and an optimum repair scheme was obtained eventually. Repaired samples with high property retention were prepared successfully and a solid technology foundation was laid for microwave scanning repair.（1）Basic research was conducted on curing characteristics of E51+DDM epoxy resin system, which was applied to the scanning microwave curing technology. Glass fiber reinforced composite with stable resin content was prepared successfully. Experimental measurements of glass transition temperature（Tg）, short beam shear properties, tensile and flexural properties of the composite were conducted and microstructure was analyzed by SEM. The obtained results were compared with those of conventional thermally cured counterparts and microwave cured counterparts in closed cavity. Analysis reveals that the glass transition temperature of scanning microwave cured composites is equivalent to that of microwave cured counterparts in closed cavity and 5.1℃ higher than thermally cured counterparts. Mechanical testing shows that the short beam shear strength and bending strength of microwave cured composites are improved in different levels compared with those of conventional thermally cured counterparts and microwave cured counterparts in closed cavity. The tensile strength and tensile modulus of scanning microwave cured composites increased by 7.8% and 4.5% respectively compared to thermally cured composites, but lower than the microwave cured composites in closed cavity by 9.8% and 4.3% respectively. In terms of curing time, scanning microwave technology saved nearly 70% of curing time, whereas a 32% decrease in cure time is observed for microwave cured composites in closed cavity.（2）Fe₃O₄ was added to the E51+DDM resin system as microwave absorber to further improve the curing rate of microwave scanning. The effect of Fe₃O₄ dosage on curing rate was studied and the optimum dosage of Fe₃O₄ was determined. Finally the preparation of composites with E51 + DDM + Fe₃O₄ system using scanning microwave curing technology was achieved. Experimental study was carried out on the prepared composites. Results show that Fe₃O₄ can improve the absorbing capacity of the system and thus accelerated the reaction rate system. And the highest growth rate is achieved with 1% dosage of Fe₃O₄. Compared with the pure system cured composites without Fe₃O₄, the glass transition temperature of the counterparts with 1% dosage of Fe₃O₄ increased by 1.5℃, short beam shear strength and bending strength were improved by 6.5% and 9.0% respectively and tensile modulus improved by 5.8%, whereas the tensile strength are almost the same. Furthermore, the 1% dosage of Fe₃O₄ saved curing time by 24% and its cure rate equaled to that of pure system in closed cavity microwave curing.（3）The 1% Fe₃O₄ composite system was applied to repairing composites. A parametric study into the influence of repair parameters on the performance of repaired composites was performed. Experimental study was carried out on the repaired composites to determine to optimum repair scheme. Further comparison between scanning microwave curing technology and thermal curing method was conducted. Results show that scarf of tangent angle at 1:20 and sequential pattern stacking sequence with cover layer was the optimum repair scheme. The performance of repaired composites maintained 90% of pristine counterparts, which meet the general engineering performance requirements for repaired composites. Samples repaired by scanning microwave technology had equal tensile properties and slightly superior flexural properties to thermally cured samples.