Research On Fiber Deformation And Defects Control Constrained By Incompletely Contact During Automated Laying Process

Fiber reinforced resin matrix composites have many advantages of high specific strength and modulus,great designable and processibility,however its application has been limited by high manufacture costs.Automated laying technology can enhance the manufacture efficiency of composites,and reduce the costs,which makes it to be the typical representative of composite low-cost manufacturing technologies.The improvement of layup quality and efficiency is crucial to the further application of composites into large complex bearing components.However,for the layup of complex component,on one hand the incompletely contact phenomenon caused by the strong geometric constraints between compaction device of laying head and mould would result in the interfacial defect due to the lack of pressure.On the other hand,the deformability of prepreg tow is limited and the overlarge change of mould’s curvature would cause the excessive fiber deformation,resulting in the occurrence of fiber out-of-plane waviness.Besides,the cooperation deformation between compaction devices and flexible mould in the condition of flexible mould support for the integrated manufacturing would also result in the fiber deformation and cause the occurrence of layup defects such as fiber waviness.Therefore,in order to realize the high layup efficiency and quality of large composite complex bearing component,the research on fiber deformation regulation and defect control with constraint of incompletely contact during the automated laying process was carried out in this paper.Corresponding control and regulation methods were proposed for the interlaminar defects and fiber deformation,respectively,and were verified by the layup experiment on typical component.The main research work in this paper includes:(1)The placeability for the curved surface restricted by incompletely contact was theoretically analyzed.Based on the incompletely contact between compaction device and mould,the definition of incompletely contact was proposed by the differential geometry analysis of curved mould and the trajectory.The criteria of placeability on the curved mould were established in two aspects: completely contact and layup pressure’s uniformity on the mould.The model of pressure distribution along the width direction of tows was verified by the experiment and the influence law of pressure distribution’s uniformity was acquired.The effect of incompletely contact constraint on the placeability was acquired in theory.(2)The constraints on the deformability of typical compaction device were analyzed systematically.To satisfy the requirement of completely contact,the deformability of two typical compaction devices---segmented boots and soft roller were defined based on the geometry and fit mechanism,respectively.The influence rule of the segment boots’ deformability restricted by the fitting degree and boot’s stability was acquired and the quantitative relationship between geometric parameters,material properties and laying boots’ deformability was studied theoretically.Based on the Gaussian statistical theory,the constitutive equation of soft roller’s rubber was established by the quasi-static compression test,and the effect of geometric parameters and material properties of soft roller on its deformability was studied.(3)The theoretical model of fiber out-of-plane deformation restricted by mould’s geometry was established.The deformation rate of out-of-plane was defined by combining the influence of normal curvature change along the trajectory and layup parameters.The theoretical model based on the fiber’ out-of-plane waviness was established by taking interply slippage into consideration and was verified by designing the out-of-plane deformation experiment.Based on this model,the quantitative relationship between the stiffness retention of composite and deformation rate and temperature was predicted,and the effect rule of out-of-plane parameters on the properties of composites was acquired to provide the theoretical basis for the regulation of fiber waviness induced by out-of-plane deformation.(4)The finite element model of fiber deformation with the support of flexible mould was established.The normal compression of flexible mould and the equivalent strain of fiber were defined to character the layup quality quantitatively.The normal compression test of flexible mould was conducted to verify the validity of finite element model.On this basis of finite element model,the effect of layup pressure,flexible mould’s material proprety and geometric parameters and ply stacking’s property on the normal compression of flexible mould and equivalent strain of fiber were simulated to provide the theoretical basis for the regulation of fiber waviness for the Hat-type reinforced wall plate structure.(5)The theoretical model of fiber in-plane deformation restricted by mould’s geometry and viscoelastic resin was established.According to the fiber’s in-plane deformation caused by the change of geodesic curvature along the trajectory,the model of geometric constraint on fiber’s in-plane deformation was established to study the effect of the characteristics of laying mould and trajectory on the in-plane deformation,and verified by the layup experiment with variable curvatures.The meso-scale model of the ability of fiber’s in-plane deformation based on the viscoelastic resin matrix by taking the constraint of resin into consideration.The relationship between in-plane deformability and layup parameters was acquired.The theoretical basis for the regulation of fiber wrinkle induced by in-plane deformation was provided.(6)Different control methods were proposed to regulate the layup defects and fiber deformation.For the interfacial defects,such as delamination,entrainment and fiber bridging,the inhibition of defects could be realized by on-line detection and recognition and adjusting the laying parameters with timely feedback.The on-line detection of defects was realized by the infrared thermal imaging method: the recognition of typical defects in the static condition and the detection accuracy of quantitative defects’ analysis in the dynamic condition were studied by artificial defects.For the fiber’s deformation,the control method was proposed by optimizing the laying tows’ width,speed and temperature to satisfy the constraints of fiber’s in-plane and out-of-plane deformation according to the curvature variation characteristics on the basis of guarantee the layup efficiency.This method was verified by the automated laying process of typical hat-stiffened panel structure.