Bearing Capacity Analysis And Optimum Design Of Spiral Winding Structures With Variable Winding Corner

Fiber reinforced plastics have been widely used in aerospace, automotive industry, machinery manufacturing, chemical industry, textile, medicine, building materials and sports goods because of its light weight, high strength, corrosion resistance and many other advantages. Fiber reinforced vessel is a typical composite material application. In addition to finite element method, the structural analysis and strength design of filament-wound thick vessels are still lack of simple and accurate analytical method.Filament-wound thick vessels are made of core and winding layers. The fiber tension of the outer layer relaxes the tension of the inner layer and lead to non-uniform strength ratio via thickness. Varied winding angle may lead to more uniform distribution of strength ratio along thickness, and improve the vessel’s pressure capacity.With constitutive relation of orthotropic material, and coordinate transformation in on-axis and off-axis coordinate systems of the stress and that of the strain, the relationship between on-axis stress-strain and off-axis stress-strain is derived. Based on the relationship of forces equilibrium and deformation consistency between the global unit and the alternate-ply, analytical formulae of 3D fiber stresses are derived. The degradation is equivalent to 2D formulae in the references. The influence to strength ratio of 3D formulae and 2D formulae are compared with Hoffman and Tsai-Wu failure criteria. A finite element model of a filament T300/934 winding vessel with aluminum liner under internal pressure is calculated and perfect agreement of fiber stresses in fiber directions and strength ratio between the FEM and the theory is achieved.Using 3-D orthotropic elasticity and axisymmetric thick-walled cylinder theory, the formulae of deformation and stresses of a thick cylinder of multi-angle winding with different kind of filament with any number of layers under internal, external pressure and axial force are proposed analytically. Longitudinal stress along fiber direction, transverse stresses perpendicular to the fiber direction and shear stress is present. Degenerated case led to isotropic constitutive relation for any layer makes the model capable of simulating deformation and stresses response for sandwich pipe and filament vessel with a liner. Perfect agreement of the results of FE models and that of the theory formulae is achieved.An optimization model of FW vessel to maximize the lowest strength ratio through thickness with optimal variation of the winding angle is built. The optimization design of a varied winding angle thick-walled cylinder under internal pressure is carried out to achieve a uniform distribution of strength ratio through thickness. An improved optimization algorethm derived from two traditional methods is proposed and the optimization efficiency is greatly improved. In three cases of pure hoop stress, hoop stress to axial stress of 2:1 and 1:1 are illustrated to evaluate the improvement of the minimum strength ratio and the uniform strength ratio of the optimized winding angle under different ratio of thickness to radius, respectively. It is found that the material property has great influence on strength ratio distribution via thickness. Large difference in elasticity coefficients in different directions and thicker wall thickness, more difficult and evident variation of the winding angle should be adopted to achieve uniform strength ratio. The optimization effect and the optimized winding angle are quite different for different thickness to radius ratio cylindrical vessels made of E-glass/epoxy and T300/934. Very uniform strength ratio can be achieved for thicker E-glass/epoxy pipe, while uniform strength ratio can probably be realized for very thin T300/934 pipe by optimization of winding angle.