Study On Monitoring Curing Process Of Epoxy Resin Under Medium Temperature Condition By Ultrasonic Technique

Epoxy resin composites are widely used in the transportation,petrochemical and aerospace due to their excellent properties such as good adhesion,low density,corrosion resistance and outstanding designability.The excellent performance of composite materials depends to a large extent on the matrix resin and the curing process.However,the research of the curing process of the matrix resin is greatly focused by the engineering field and a key issue to improve the performance of composite materials.In this paper,ultrasonic transmission technique was successfully used to monitor the curing process of epoxy resin under different conditions.The relationship between ultrasonic amplitude attenuation and curing time as well as the effect of mold thickness and glass fiber on the curing reaction process of epoxy resin under medium temperature were investigated,respectively.In addition,curing mechanisms of epoxy resin were discussed.The results indicated that ultrasonic amplitude attenuation firstly increases and then decreases and tends to be stable.With the curing reaction proceeding,the appeared time of gel point and the phase change process transformed from viscous-gel state to gel-glass state can be accurately distinguished by ultrasonic attenuation.It is also showed that the curing time can be shorten by raising temperature,the appeared time of gel point can be delayed by adding mold thickness and glass fiber in some degree.The relationship between the resistance of carbon fiber(CF)and length(L),cross-sectional area(S),temperature(T)as well as whether accorded with the linear resistance formula were studied by voltmeter-ammeter method.The experiment results showed that the resistance of CF is linear increasing with L,and inversely proportional to S,which is different from that of ordinary conductors.Moreover,the relationship between resistance and T is negative temperature coefficient(NTC)effect,which makes CF can be a heating source that achieves a good effect of uniform heating.Based on the Joule heating effect of CF,the effect of temperature on the curing process of epoxy resin was investigated by ultrasonic transmission technique.The results indicated that the curing temperature can be controlled by changing the current of CF and the appeared time of gel point can be advanced by raising temperature,which accelerates the curing reaction time and improves the curing efficiency effectively.In short,ultrasonic transmission technique can be used to monitor and quantify the curing process of epoxy resin under different conditions,which provides theoretical foundation for studying the curing reaction process of polymers and important technical means for the curing process of composite materials.