| Bismaleimdes(BMIs)with distinguished processing characteristics,excellent heat resistance and hot/wet properties is developed quickly and applied in many fields. However,the application of graphite laminates based on BMI matrix in the primary structure has been limited to some degree by their poor damage resistance and the reduction in compression strength after impact(CAI).A traditional method to improve the toughness of composites is to incorporate toughener component into the matrix system to form a two-phase structure.Unfortunately,many problems such as the low efficiency of toughening,the changing original process of matrix resin are followed by this method.According to the problems of composites,the interlaminar toughening technology-interleaf-is proposed by American Cyanamid company.The concept of interleaved composites is selectively toughening the interlaminar region of composites and the efficiency shows perfect.However,the major disadvantage of interleaved composites is a weight penalty.The tough layers of resin have low stiffness and strength which proportionately reduce the stiffness and strength of the laminate,requiring additional plies to maintain design properties.To this question,the Ex-situ concept is firstly proposed by Prof.Xiaosu Yi in national 973 program application in 2001.The principle of Ex-situ concept is to distinguish all kinds of physical and chemical process and break up the unitive process into some little issues based on structure and functions and solve them respectively.Further explanation is to start from the laminated structure of thermoplastic(TP)/thermosetting(TS)resin and the TP/TS co-continuous phase structure is formed by phase decomposition and phase inversion induced by curing reaction.The basic static mechanical properties and hot/wet properties of composites are kept by single thermosetting phase and the impact resistance and damage tolerance of composites is improved by the TP/TS co-continuous phase structure.The Ex-situ toughening technique has been successfully applied in prepreg/autoclave composites based on epoxy matrix. In this dissertation,The Ex-situ toughening technique will be introduced into composites based on BMI matrix,including prepreg/autoclave and resin transfer molding process.Firstly,the cure kinetics of BMI resin system suitable for autoclave and RTM process was investigated respectively,then the time-temperature-transformation diagrams were built,which standed for the characteristics of curing process.Secondly,the phase separation mechanism,phase evolution and mechanical properties of toughener/BMI diphase system were investigated to prepare for toughening composite with Ex-situ technique.The Ex-situ toughening technique was applied to toughen the T700/BMI composites manufactured with prepreg/autoclave process.The CAI(compression after impact)strength was improved by 61%,and the static mechanical properties of T700/BMI composites were well kept.The Ex-situ toughening technique was also transferred to RTM process to further validate the applicability of Ex-situ toughening technique.The experimental results showed that the process of RTM was not influenced by Ex-situ toughening technique. The Modeâ… fracture toughness of composites toughened with Ex-situ technique was improved from the 215J/m~2 to 627J/m~2,nearly two times improvement.The Modeâ…¡fracture toughness of composites toughened with Ex-situ technique was improved from 510J/m~2 to 905J/m~2,nearly one times improvement.The CAI strength increased from 155MPa to 277MPa,nealy 80%improvement.The basic static mechanical properties of composites were well kept,Finally,the mechanical properties of RTM composites toughened with Ex-situ technique was systemically investigatied,including the cryogenic temperature,high temperature and hot/wet properties.The experimental results showed that the mechanical properties of composites toughened with Ex-situ technique were well kept. Some properties such as open hole tension,open hole compression were significantly improved.
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