Crystallization Behavior Of Matrix In T700/PEEK Composites And Its Influence On Properties

Automatic Fiber Placement(AFP)of fiber reinforced thermoplastic resin matrix composites combined with in-situ solidification technology can improve the manufacturing efficiency and reduce the cost,because of ignoring the autoclave curing.In this process,the crystallization of the matrix of composites is controlled by processing,and affect the performance of the products.In this paper,T700continuous carbon fiber reinforced poly(ether ether ketone)matrix composites(T700/PEEK)is chosen to study the relationship between processing,crystallization and performance.The result can be a guide to the practice.The following tasks are carried out:Non-isothermal crystallization behaviors of PEEK and matrix in 20%and 57%weight percent T700/PEEK composites were studied by Avrami,Ozawa and Mo theories through DSC test.The results showed that Mo equation was suitable to characterize non-isothermal crystallization behaviors of the matrix in T700/PEEK composites.T700 carbon fibers can act as nucleant to increase the overall crystallization rate and restricted the space for growing,which made the initial relative crystallinity for the secondary crystallization shift ahead and the absolute crystallinity decline.T700/PEEK composites plate specimens of 20.0,24.5 and 38.8 weight percent crystallinity were obtained through different heat treatment and were tested by tensile test,short-beam shear test and pendulum impact experiment.The results showed that the tensile strength was not sensitive to the crystallinity and crystallization of the matrix contributed much less to strength than the fibers,the tensile strength was around 1.7 GPa.The interlaminar shear strength(ILSS)increased with the absolute crystallinity increasing,interlaminar shear strength of 24.5 wt%and 38.8 wt%crystallinity increased by 10%and 27.4%compared with 54.6 MPa for specimens of 20.0 wt%crystallinity.Simply supported beam compact strength present the opposite trend from ILSS due to great ductility of amorphous phase,the result were 145.8kJ/m~2,174.7kJ/m~2 and 177.4kJ/m~2 respectively.Based on process of ultrasonic-assisted placement with in-situ consolidation technique,T700/PEEK laminates were manufactured and compared with straight hot-pressing and post-consolidated specimens according to their mechanical properties,which can offer reference for ATP of thermoplastics composites.The results show that the ultrasonic heat source can meet the energy requirement for CF/PEEK placement;High power of heat source and low placement speed help layers combine;The specimens manufactured by ultrasonic-assisted placement show the character of low crystallinity,high porosity and some fiber injury;In the case of saving over 12 hours for a post-curing cycle,the tensile strength,modulus and interlaminar shear strength are 1.32GPa,113.8GPa and39.2MPa respectively,reaching 80.4%,84.8%and 65.1%of hot-pressing specimens'properties;After post-consolidation,the tensile strength,modulus and ILSS raise to 92.1%,92.6%and 82.5%of hot-pressing ones.The failure forms of pendulum impact failure of hot-pressing specimens is delamination,and it changes into fracture after post-consolidation as same as the straight hot-pressing ones.