Finite Element Simulation And Online Monitoring Of Curing Deformation Process Of Fiber-reinforced Composite Structures

Fiber-reinforced resin-based composites are widely used due to the advantages of light weight,high strength,and good designability,the development of molding technology,especially the integrated molding technology,has greatly reduced the number of fasteners,cutting down the cost while improving the structural bearing capacity and sealing performance.It can be said that the realization of efficient composite materials depends on the integration of the structures.And this technique is often used to make the familiar stiffened panels,honeycomb sandwich structures,engine cowlings,etc.However,the curing deformation is more serious when manufacturing integrated large-scale composite structures,and exploring the curing deformation mechanism of composite structures can lay a solid foundation for improving the molding quality and assembly precision,which is beneficial for the low-cost,high-quality manufacturing and wide application of composite materials,and has crucial research significance and value.In this paper,the curing process of composite structures was simulated by using ABAQUS software and its subroutines,through the sequential coupling of heat transfer-chemical reaction models and three-dimensional viscoelastic constitutive models,the time evolution and spatial distribution rules of temperature,curing degree,stress,strain and deformation were analyzed,and the model was verified by comparison with the results of literatures and experiments.Firstly,starting with a simple honeycomb sandwich panel,in order to monitor its curing process,fiber Grating online monitoring technology was adopted,as well as adding a pre-curing process on the precondition of initial molding process,it turned out that adding the pre-curing process would enable the fiber Bragg grating(FBG)sensors capture the strains in the heating stage to a certain extent.Besides,FBG sensors were implanted at different positions on the 0° and 90° layers of the composite upper panel so as to explore the strain evolution and distribution of different layers.From the strain results monitored by sensors,it can be seen that the strain at different positions of the same layer are almost the same,and the difference in strain between 0° and 900 plies is about 50??,the strain field of the panel is relatively uniform as a whole.And the strain results of finite element simulation corresponding to the above experiments and those monitored by the FBG sensors can be matched to an extent of 83?93%,and no deformation of the honeycomb sandwich panel was observed from the finite element analysis even if the upper and lower panels were asymmetrically laid,the main reason can be attributed to that the honeycomb core has an constraint effect on the deformation of the composite panel.Secondly,the validated finite element model was used to explore the combined effect of the stiffener stacking sequence and geometric dimensions(fillet radius R,flange length Lf and web height H)on residual stress and deformation of T-shaped structures,the influence level of the above factors on maximum stress and deformation was quantitatively analyzed.Within the investigated range,the main influence factors of residual stress are the fillet radius and stacking sequence of the stiffener,and the change of the stiffener stacking sequence doesn't make a difference to the evolution of the maximum stress with geometric dimensions;as for the maximum deformation,the flange lengths and stacking sequences have the greatest impact,followed by fillet radii,moreover,the evolution of the maximum deformation with the flange lengths will be affected significantly once the stacking sequence of the flange is different.Therefore,when it comes to stress and deformation analysis of composite structures,it is necessary to consider the effect of the stacking sequences and geometric dimensions at the same time and the two cannot be separated.Finally,based on the above research,the FBG sensors were applied to monitor the curing process of root tile mold of large-scale wind power blades(tile-shaped glass fiber reinforced plastic structures),and the corresponding finite element analysis was carried out as well,the simulated and monitored strain curves were in good agreement.It was found that the strain along the circumferential direction was not uniform,mainly owing to the constraint of the steel structure that changes the strain distribution;as a result of large size,complex curved shape and asymmetric stacking sequence of the tile-shaped glass fiber reinforced plastic structure,the obvious axial shrinkage deformation and flange warpage deformation of the blade root tile mold can be noticed,of which the flange warpage deformation is more serious,so the key to control the profile precision of the tile-shaped glass fiber reinforced plastic structure is to improve the surface flatness of the flange.Further research has discovered that adding rigid constraints can significantly reduce deformation of the tile-shaped glass fiber reinforced plastic structure.When designing the rigid constraint,the constraint area should be distributed as evenly as possible,and it is necessary to appropriately increase the area of rigid constraints where the deformation is obvious.In addition,different from carbon fiber composites,the strain of the glass fiber composites at the second constant temperature stage is often greater than that at the end of the curing process,utilizing this characteristic rationally to design the curing process is of great significance to reduce the residual stress and strain of the glass fiber composites during the curing process.