Mechanical Properties Of F-12 Envelope Materials And Full-field Deformation Test Method In Air-inflated Capsule Structrue

Air-inflated capsule structure,such as airship,is a kind of closed pneumatic structure which maintains the configuration and bears the external load rely on the air pressure.Increase the strength utilization efficiency of the envelope material is the key to improve the voltage capacity and structure mechanical performance.Deformation test and assessment is the powerful tool to evaluate the safety of three-dimensional surface capsule structures.The research focuses on the mechanical test method,theory and numerical analysis of F-12 aramid fabric and the envelope material.A strain field measurement method applied to the large size 3D surface is processed.The research provides a support on the improvement of the pressure endurance capability of the capusle structure.The details are as follows.The basic mechanical properties of the F-12 envelope material are test at first.The stress-strain relationship,tensile strength and Poisson’s ratio of the F-12 fibers,fabric and envelope materials with different off-axis angles are obtained.The stress-strain characteristics in warp and weft directions are analyzed and compared.The performance shows strong nonlinear in warp direction.The characteristics under cyclic loading of F-12 fabric and envelope material are studied.Cyclic hardening and large residual strain phenomenon is find.The shear performance of F-12 fabric and envelope material are studied by picture frame test and bias tensile test.The influence of the clamp part and the coating on the shear performance and lock angle is discussed.The quantitative differences between the picture frame test and bias tensile test is given through regularization method.Based on digital image correlation method,an situ test method with envelope material performance in actual working state is proposed through applying normal uniform load.A bulge test system is built which can supply air pressure load.Multipoint with no slip clamp and seal proplem is solved.The equip biaxial tensile modulus of F-12 envelope material under air pressure is obtained.Furthermore,influence of material properties to deflection in bulge test is studied through finite element analysis.The mechanical properties of the envelope material is investigated by numerial method in macroscale and mesoscale.At mesoscale,a actual unit cell model is established based on optical images.In this model,the crimp amplitude and cross-section profile in warp yarn and weft yarn are different.The stiffness is changed during the deformation because of crimp change and yarn rotation.The material coordinate system fixed on the yarn path is tracked.So,a numerical model in which the material direction changed is established.The tensile material is analyzed by this model.At macroscale,a non-orthogonal anisotropic hypoelastic numerical model is established.In this model,the mesoscale structrue and fabric deformation mechanism is considered.A user subroutine in which the yarn direction and material stiffness matrix are updated in each increment step is writen.The fabric shear performance and the yarn angle change is modeled.The results are varified with test results.A method based on finite element method and Delaunay triangulation is proposed to measure the strain fields.This method takes into consideration the complex surface profile and geometrical nsituarity and is suitable for large inflatable structures for which strain fields can be obtained using only digital photogrammetry.The spatial locations of the discrete points on the capsule structure are tracked by photogrammetry method.The same targets are matched by epipolar intersect theory.Then,the point cloud of the structure is obtained.The surface reconstruction with this point cloud is conducted by Delaunay triangularization.The coordinate transformation matrix between the global coordinate system and the local coordinate system is given.Then,the element strain can be calculated by the geometry equation.Combine the coordinate transformation matrix,the strain field can be calculated.A bulge test for a circular fabric sheet is performed to verify the validity of the proposed method.The strain fields calculated from this method are compared with results from digital image correlation(DIC).Good agreement is found between the photogrammetry and DIC measurement results.The influence of the point density to the measurement accuracy is analyzed.At last,the strain field on airship and balloon model are measured by this method.The strain distribution against the pressure is obtained.