Preparation And Mechanical Properties Of Thermoplastic Composite Curved Beam

The superior performance and designable ability of structure as well as function have ensured that composites must feature in the first rank of materials' options available in such fields as aeronautics,astronautics,automobile and shipbuilding industry.Resin matrix composites,combining the advantages of polymer matrix and fiber reinforcement,can meet the requirements of high-strength,light-weight,integrated structure and function and low cost and have drawn widely attention of many industries.As a result,the utilization ratio of resin matrix composites has kept sustainable growth in the developing period of industrial.However,thermosetting composites have several obvious drawbacks,such as poor toughness and crack propagation properties of impact.Although thermoplastics possess high toughness,recyclable and short manufacturing time,thermoplastic composites are used as structural composites seldomly.The basic reason is that high melting viscosity cannot afford high reinforcement volume fraction.In addition,curved composite beams,which are indispensable to engineering structure,are made of thermosetting resins via autoclave or resin transfer molding process.This thesis centered on the Cyclic Butylene Terephthalate resin(CBT)to set up the preparation system for thermoplastics composites and curved composite beam through post-processing.The corresponding mechanical properties were investigated in three aspects:theoretical analysis,numerical simulation and experimental investigations.The main contents are given as below:The rheological behavior during CBT ring-opening polymerization was studied,and the initiation and termination of polymerization can be monitored.The effects of temperature and nano-particle on the polymerization process were discussed.The concept of impregnation region was introduced to characterize the fiber impregnation quality.The viscosity equation was given dependent on temperature and nano-particle.The thermal properties and dynamical thermo-mechanical properties were also investigated.Considering the polymerization characteristics,the preparation system for thermoplastics composites based on pCBT is established via in-situ polymerization with hot-pressing technology.The reinforcement volume fraction of thermoplastics composites obtained in this thesis is up to 70%,guarantying perfect fiber impregnation.The post-processing was also developed to prepare the curved composite beam with feasible laboratory-used mould.The effects of temperature,holding time and pressure on the curved beam were explored.The impact performance of laminated composites was investigated and the failure modes under different impact energy were provided.The features of saturation and perforation failure are summarized through relationships between deflection,velocity,contact force,energy and time.The four-point bending test was employed to characterize the mechanical properties of curved composite beam.The manufacturing parameters have influenced the curved beam strength deeply.Commercial finite element software ABAQS was used to simulate the four-point bending test,and the simulation results had good agreement with experimental results.The curved beam based on an elastic foundation was analyzed theoretically.The numerical solutions of circumferential and radial stress were given considering the curvature change under pure bending.The theoretical method was further extended to multi-ply laminated curved structures composed of different materials.The radial stress at the interface could be regarded as normal tension stress and the displacement and radial stress were set to be continuous acted as boundary condition.Then the stress function of multi-ply laminated curved beams could be obtained which is an effective calculation method for interlaminar stress.