Molding Process And Double-Position Impact/Compressive After Impact Behavior Of CFF/PEEK Composites

As one of the preferred materials for lightweight structures,advanced carbon fiber reinforced thermoplastic composites have been widely used in many engineering fields such as aerospace,military and national defense due to their excellent comprehensive performance and excellent designability.However,molding process and impact properties are the basic and key scientific issues in the research field of composites.Up to now,there are still some problems such as the explanation of the influence mechanism of process parameters on mechanical properties is not rigorous,and the research on low-velocity impact(LVI)and compression after impact(CAI)focuses on a single impact position.For this reason,this paper carried out research on the plain carbon fiber fabric reinforced high-performance polyetherether ketone(CFF/PEEK)thermoplastic composites,including the molding process parameters and internal influence mechanism,mechanical response and damage failure mechanism of double-position LVI and CAI.The specific research contents are as follows:(1)The CFF/PEEK thermoplastic composites are fabricated by hot-pressing process.Based on the analysis of the thermophysical properties of PEEK resin,the process plan of three key parameters,including the molding temperature,molding pressure and holding time,was developed.Taking the tensile,flexural and short-beam shear properties of CFF/PEEK thermoplastic composites as evaluation indicators,the influence of process parameters on its mechanical properties was analyzed.In addition,the high temperature contact angle between PEEK and CFF and the viscosity-temperature characteristics of PEEK resin were tested and analyzed.The molding quality and microscopic failure modes of CFF/PEEK composites were observed using optical microscopy,metallographic microscopy,and scanning electron microscopy(SEM),thereby revealing the inherent influence mechanism of the effects of various process parameters on mechanical properties.(2)The double-position LVI behavior of CFF/PEEK thermoplastic composites were investigated.A set of movable experimental fixture is designed to ensure the successful implementation of the double-position LVI test.And the typical LVI response of CFF/PEEK composite laminates under different impact spacing(0,10,20 and 40 mm)and impact energy(10,20 and 30 J)is comprehensively analyzed,and the impact damage including impact dent,crack and internal delamination damage is comparatively analyzed,thus revealing the internal interference mechanism between the double impact positions related to impact spaci ng and impact energy.(3)The compressive properties of CFF/PEEK thermoplastic composites after double-position LVI were investigated.The synergistic effects of impact spacing and impact energy on compressive after impact(CAI)strength,local buckling load a nd local buckling stiffness are compared and analyzed.Combining digital image correlation(DIC)measurement technology,ultrasonic C-scan and micro-focus computed tomography(micro-CT),the influences of impact energy and impact spacing on the damage evolution characteristics and failure mechanism of CAI are deeply revealed.In addition,based on various damage characteristics of CFF/PEEK thermoplastic composites after double-position LVI,an evaluation model was constructed using the fuzzy comprehensive evaluation method,and then the damage degree of CFF/PEEK thermoplastic composites was judged according to the membership level.Finally,the reliability of the fuzzy comprehensive evaluation model is verified by the experimental results of residual compres sion performance.(4)Based on continuum damage mechanics,a damage model considering tensile damage,compressive damage and shear nonlinear failure of materials is established.A simulation model integrating double-position LVI and CAI was created using ABAQUS to predict the mechanical response and failure behavior of CFF/PEEK thermoplastic composites under double-position LVI and CAI loads.The prediction accuracy of the simulation model is verified by the experimental results.On this basis,the effects of impact position arrangement and impactor shape on the double-position LVI and CAI behavior of CFF/PEEK thermoplastic composites were further investigated,and the damage evolution and internal failure mechanism were revealed.