Investigation On The Forming Mechanism Of Co-curing-injection Molded Fiber Reinforced Thermoset-thermoplastic Hybrids

The development and application of lightweight materials has attracted more and more attention.Fiber reinforced thermoset-thermoplastic（TSC-TP）hybrid structure,as a new star in lightweight material system,combines the flexible process,strong design freedom,easy repair and recycling of thermoplastic resin,with the high specific strength,good heat resistance and excellent creep resistance of thermoset composite,maximize the advantages of their respective materials.Overmolding is an efficient molding process for the preparation of multi-material structural parts,however,the heterointerface bond strength of TSC-TP hybrid structures molded by this method is relatively weak.To this end,this paper optimizes and expands the overmolding process,and firstly proposing a co-curing-injection molding process,which effectively improves the bond strength between heterogeneous interfaces.The main work of this paper is as follows:（1）The overmolding injection molding test platform was built,and the experiment of fabricating TSC-TP hybrid structure by overmolding was carried out.The effects of different pretreatment methods（silane surface treatment,plasma pretreatment and CO₂ laser ablation）on the surface physicochemical properties of TSC composites,the bonding interface morphology and shear strength of TSC-TP hybrid structures were analyzed.The results show that silane surface treatment has little effect on the interface strength of the TSC-TP hybrid structure;plasma treatment can significantly improve the surface functional groups of the TSC composite material,and at the same time has an etching effect on the surface,which can significantly improve the interface strength of the hybrid structure;after laser treatment of TSC composite,the interface strength of the hybrid structure is greatly improved,reaching 6.1 MPa.（2）The co-curing-injection process of TSC-TP hybrid structure was proposed,and the influence of the surface properties of thermoplastic films on the bond strength of heterogeneous interfaces in the TSC co-curing process was studied.The results show that enhancing the polarity of the thermoplastic film can significantly improve the physical adsorption properties of its surface,thereby improving the co-cured interfacial shear strength;the surface microstructure of the thermoplastic film can effectively increase the contact area between the co-curing structure interfaces and improve the loads transfer ability of heterogeneous interfacial;the thermoplastic film with low melting point melts during the co-curing process,and the thermoplastic film in a viscous flow state and the uncured epoxy resin penetrate each other to form an interface with a gradient along the thickness direction,and the expansion of the interface in the thickness direction changes the distribution of the interface load,which greatly improves the co-curing interface strength.（3）The influence of the process parameters of the injection process on the interfacial strength of the TSC-TP hybrid structure fabricated by the co-curing-injection process was studied.Based on the healing degree theory,the interfacial strength of the hybrid structure was studied under different injection process parameters.The study found that the degree of healing has a strong positive correlation with the interfacial shear strength.Taking the healing degree as the characterization method of the interface bond strength,the injection molding process of the TSC-TP hybrid structure was optimized by the orthogonal experiment method.The interfacial bond strength of the optimized TSC-TP hybrid structure reaches24.4 MPa,which is 3 times higher than that of the TSC-TP hybrid structure after laser pretreatment in Chapter 3.To sum up,this paper innovatively explores the efficient and high-quality fabricating methods of TSC-TP hybrid structures.The proposed new co-curing-injection process not only improves the molding efficiency,but also greatly improves the connection strength of the heterogeneous interface.It is of great significance to the development of high-performance lightweight manufacturing technology and the practice of new lines of energy conservation and emission reduction.