Manufacture And Connection Performance Of Continuous Fiber Reinforced PCBT Composites

Compared with thermoset composites,thermoplastic composites have been attracting increasing attention over last years in many fields such as aerospace,shipbuilding,automobile and architectural industry,owing to these advantages including improved toughness,impact resistance,rapid fabrication cycle,low manufacturing cost and added recycling options through reprocessing.However,due to the characteristics of molecular structure,one of the main issues that are frequently raised in using thermoplastics as polymer matrices is their high melt viscosities,which hampers the flow of resin and has an undesirable effect on wetting reinforced fibers.Therefore,this limits its application on large size and primary load-carrying structures.A recently developed new thermoplastic material cyclic butylene terephthalate(CBT)is considered to be a promising alternative to solve this dilemma.CBT is a cyclic oligoester,which has a low processing viscosity.It can be transformed into poly(cyclic butylene terephthalate)(PCBT)via entropically driven ring-opening polymerization in a short time scale,and there are no chemical and heat emissions during their processing.Based on the characteristics of CBT resin,the continuous fiber reinforced PCBT composites were prepared by in-situ polymerization in this paper,and the process parameters of liquid composite molding were researched.In addition,the mechanical properties and failure modes of thermoplastic composite fusion-bonded joints with different structures were investigated by the method of combining the experiment and the finite element simulation.The following aspects have been researched in detail:1.The viscosity variation of molten CBT was analyzed using rheological measurements to determine the best impregnation time of fiber reinforcement with resin.The polymerization temperature and catalyst addition way were determined through the differential scanning calorimetry,thermal gravity analysis and mechanical property test,and the basic performance parameters were supplied for the preparation technology of fiber reinforced PCBT composites.2.Owing to the characteristic of low processing viscosity,the ring-opening polymerization was reacted during the wetting fiber process,which can develop the liquid thermoplastic composite molding technology for manufacture of complex structure and primary load-carrying components.Based on the RTM and VARIM technology,the GF/PCBT composite laminates with high fiber volume fraction were prepared,and the influence of catalyst content and fiber volume fraction on the mechanical properties and failure modes of laminates were evaluated.3.The manufacture of large size PCBT composite components needs the joints technology,that the resin of composite surface to be jointed melts locally by heating,then cooling down and consolidate.The groove coupling butt joints of GF/PCBT were prepared.Furthermore,the ultimate bearing capacities and damage patterns were researched with the number of connection layers and length as variables of fusion-bonded joints,and the structures of fusion-bonded joints were designed.4.A series of tests were performed to study the mechanical behavior of GF/PCBT composites at different high temperature.Experimental results showed that the mechanical properties of laminates and joints decreased with temperature increase,and decreased sharply at the glass transition temperature of the PCBT matrix.Results also showed that the mechanical properties of joints was nearly a constant undergoing high temperature and cooling process,and the properties of laminates increased slightly when the heating temperature exceeded the vicat softening temperature,because this process corresponded to annealing treatment.5.The extended finite element method was used to predict the progressive damage of fusion-bonded composite joints.In numerical analysis,BK criterion was chosen to simulate the interface delamination damage using cohesive element,and 3D Hashin failure criterion was selected to emulate the fiber and matrix failure applying subroutine USDFLD of ABAQUS.Compared with experimental results,the numerical results are well agreement with experiments,which demonstrates that the simulation method is feasible for designing and optimizing the structure of GF/PCBT fusion-bonded joints.