Fundamental Research On Microwave Curing Technology Of Hybrid Fiber Composites Shaft Reinforced By Al₂O₃ Particles

The composite shaft has the advantage of high trust-weight ratio,anti-vibration and high fatigue life.Replacing the metal shaft by composite shaft to manufacture the helicopter transmission shaft has become a trend.However,the tradition heat curing would cause many problems,such as the thermal gradient,residual stress and deformation and so on.Microwave curing technology,particle enhancement technology and fiber hybrid technology were applied to the manufacture of helicopter transmission composite shaft simultaneously in this paper.The fundamental research on microwave curing technology of hybrid fiber composites shaft reinforced by Al2O3 particles has been done.The main research work and results are as follows:Microwave curing kinetics model of epoxy resin reinforced by Al2O3 particles was established.The microwave curing activation energy and reaction constant were affected by the Al2O3 amount and could be utilized to predict the curing process based on Avrami method.The relationship between activation energy,reaction constant and Al2O3 amount was acquired by the DSC and DMA method,which provides the basis of finite element analytical predicting the microwave curing process of epoxy resin reinforced by Al2O3 particles.The reinforcing mechanism of matrix resin strength by adding Al2O3 particles was revealed.By the observation of fracture surface of epoxy resin with different amounts of Al2O3,it could be found that compared with the smooth cross-section of resin with no Al2O3 addition,the cross-section of fracture morphology with Al2O3 addition showed more ladder-like fringe.The reason could be due to the higher elastic module of Al2O3 particles than E51/DDS.When the Al2O3 particles was dispersed in the resin,it would hinder the propagation of crack and consume more energy,so as to the improve of resin strength.However,excessive Al2O3 particles has a reverse effect to reduce the strength due to higher porosity.The uniformity heating technology based on double rotation was proposed.The microwave in a resonant cavity exits in the form of standing wave,which causes the non-uniformity of microwave energy,resulting in the non-uniformity of heating.The hypothesis theoretical model of standing wave field was established.By analyzing the effect of three different methods of static,single rotation and double rotation(namely rotation + revolution),combing the experiment of heating water by microwave,the heat effect of double rotation was proven to be the best.From the perspective of kinematics,by analyzing the trajectory of radiation heat zone by the microwave energy strong point,the requirements about the rotational and revolutional speed were obtained to assure the uniformity heating with microwave.This method could provide the technical support of improvement of microwave curing uniformity for composite shaft.A new microwave curing method with low-power pre-heating and high-power curing was proposed.By finite element analysis,when the resin heated by low-power,both the temperature/curing degree fields were more uniformity,but the curing reaction is slow and even no curing reaction occurs.While the resin heated by high-power,the reaction is sufficient but the uniformity of temperature/curing degree fields were worse.Therefore,by complement these two ways' advantage,namely on the basis of low power to pre-heat the resin,high-power was utilized to cure the resin completely to realize the high uniformity of temperature/curing fields and curing degree.The feasibility of new method was verified by experiment to provide the guide of microwave curing of composite shaft.