Study On The Time Dependence Of Deformation Of 3D Thin Shell Composite

Weft-knitted biaxial multilayer lined yarn(MBWK)fabric has been widely used as reinforcement of textile structural composites because of its good formability and designability.However,the three-dimensional textile composite curing molding process,in the process of MBWK fabric lining happens in curved surface forming yarn bending and shearing slip mesoscopic structure change of internal residual stress,after curing due to the influence of various factors such as resin shrinkage strain caused by residual stress stored in the composite material parts,makes the component inevitably produce after demoulding curing deformation.At the same time,in the process of service or storage of composite materials,natural aging and gradual release of residual stress will make the dimensional accuracy of composite materials gradually deviate from the quality requirements.In order to improve the working efficiency and safety level of 3D thin shell composite material,this paper carried out a study on the time correlation of 3D thin shell composite material deformation.3D thin shell composites and hemispherical composites were prepared using MBWK fabric as reinforcement and vinyl ester resin(VER)as matrix.Through the change of fiber orientation on the curved surface of shell composite structure,the shear Angle distribution was divided into 10° span.Vacuum assisted resin transfer molding(VARTM)process was used to prepare equivalent composite plates.Then,thermal and oxygen aging experiments were carried out on the structural parts and samples.The changes of physical and chemical properties of VER castable before and after aging were tested by FTIR,DSC and DMA,and the thermal and oxygen aging mechanism of the resin matrix was characterized.Secondly,the mechanical properties of the composite plate were measured,and the stiffness attenuation of the composite with different shear angles after aging was obtained.Finally,a CMM laser scanner was used to collect the point cloud data of shell composite materials aged at different time nodes.By comparing the point cloud data,the deformation amount of shell composite materials changed with time was obtained.Combined with the degree of shear deformation,the time effect of warping deformation was analyzed.The results show that the local fiber volume difference caused by shear deformation is an important parameter affecting the deformation of shell composite materials,and the three-dimensional laser scanning analysis method is accurate and effective to study the warping deformation.The chemical structure,curing degree and thermo-mechanical properties of VER castable before and after thermo-oxygen aging were tested and analyzed.The results showed that the curing degree of the resin gradually increased with the aging time,and the rate of improvement was high due to the post curing effect within 3.5h before aging.The vitrification temperature(Tg)also increased gradually,and the peak value of energy storage modulus increased at the early stage of aging due to molecular crosslinking,while the peak value decreased gradually due to the main role of molecular chain fracture at the later stage of aging.In the tensile test,the shear Angle makes a significant difference in the elastic modulus of the composite and changes its failure mode.Thermal and oxygen aging results in the free volume shrinkage of the resin matrix,and with the extension of aging time,the aging of the resin matrix and the weakening of the yarn/matrix interface become the main mechanism affecting the tensile properties of MBWK fabric reinforced composites due to the different temperature sensitivity of the fiber and the resin.In the bending experiment,the shear Angle of the bending sample determines the number of yarn providing mechanical load along the span direction,and the vector component of resistance along the span direction also changes accordingly.The bending modulus fluctuates greatly under the influence of the precast structure.After curing of resin,the bending properties of composites are temporarily improved,but the damage of the interface between fiber and resin causes the bending properties of composites to decrease during the whole aging stage.Finally,based on the stiffness attenuation characteristics of composite materials,the Geomatic Studio software was used to make a comparative analysis with the composite design drawing of the shell.The results show that the warping deformation caused by the release of residual stress is correlated with the shear Angle distribution area on the surface,and the bending moment formed by the tension-bending coupling leads to the out-of-plane deformation.The results of this study illustrate the time-dependent deformation of 3D thin shell composites and consider the stiffness differences caused by different shear deformation degrees at various places on the surface.It provides theoretical basis for long-term service,structure design and storage life prediction of MBWK composite materials.The research has certain guiding significance for the structural design and engineering application of 3D thin shell composites with high quality and high precision.