The Mechanics Research Of Filament Wound Composite Shells

In order to improve the flying performance, maintenance and reliability of the aircraft, many advanced materials and structures are applied. Because of the high strength weight ratio, stiffness weight ratio, fatigue resistance, vibration resistance, good performance on high temperature, designable ability, fiber reinforced composite materials are widely used in astronautics, aeronautics, energy, transportation, construction, mechanisms, medicine and sports, etc. The filament wound composite plays a more and more important role in the composite materials, due to the designable capability of its filament rule, the filament pattern, the braided angle, high reliability, high working efficiency, low cost, etc.The filament wound pattern and its affecting parameters on ultimate materials are briefly presented in this paper. The emphasis is placed on the strength, stiffness, non-linearity and damage of the filament wound composites. The effects of filament wound patterns that affect on the composite material are detail studied. The research work of this thesis is mainly summarized as following:(1) Introduced the filament winding parameters that influence the filament wound pattern; the relationships of these parameters are reduced; the calculating flow chart is given; The APDL macro program is developed based on ANSYS APDL program language, which can be afforded as a standard sub-program for the rest chapters. By using sinusoid to simulate the undulation, the ellipse to simulate the fiber section profile, the fiber volume fraction expression is deduced. Based on the work above, the two typical RVE model are established by using UG GRIP language.(2) Using FEM and the commercial finite element software ANSYS, six groups of loadings and constraints are applied on the RVE which can attribute the fiber undulation and crossover, calculated the equivalent mechanical properties in considering of the undulation of the fibers. The results of the numerical calculation show that the method is an effective method for studying the equivalent mechanical properties and agree well with the experiments results. A new finite element approach for studying the equivalent mechanical properties, the"sub-RVE"which can significantly decrease the calculation time, increase the calculation precision is put forward during the calculation. The RVE mechanical properties E11 and E22 increase when the undulation increases. This result is conflict with the reference [1～4], but agrees well with the testing result [5]. This can be interpreted as: when the undulation is increasing; the contacting area between the fibers is increasing, so the friction force between the fiber is increasing; then the fiber can withstand the axial load by the axial extension like the straight fiber and the friction force; so the axial loading capability or the axial stiffness is increasing. The mechanical property E33 has no variation when the undulation is changing. The shear module G12 has no variation when the undulation changes too. But the shear modules G23 increase when the undulation increases. When there is no undulation in the composite like the laminates, the shear are usually very small because the shear force between the fiber and the base interface is small. When there is undulation in the composite, the component of force along the thickness direction can afford a part of the shear force, so the shear strength will increase when the undulation increases; G13 increase at first, then decrease, when the undulation increases. Poisson ratio u12 will increase when the interweave number increases; Poisson ratio u23,u13 decrease when the undulation increases.(3) Studied the stress and strain distribution along the radius in elastic stage by inputting the anisotropy mechanics properties obtained from (2) on the filament would composite shell.(4) The total Lagrangian control equation and virtual energy principal are introduced. The nonlinearly properties of the AL tube are analyzed, combined with the ANSYS nonlinearly solution. The ANSYS APDL program is developed and the theoretical value is used to calibrate the calculation. Input the anisotropy composite mechanical properties into the APDL program to calculate the nonlinearly properties of the composite material. Compared it with the linearly results from (3).(5) Studied the pre-stress properties of the filament wound composites originated from the filament winding process. The stress distribution along the radius is given. The hoop stress decreases at first and then increases compared with the stress distribution without considering the pre-stress. Radial stress is always bigger along the radius than the stress distribution without considering the pre-stress. The radial displacement is always smaller along the radius than the displacement distribution without considering the pre-stress.(6) Some deficiencies by using the prevalent progressive failure method for simulating the damage evolution of the composite are illustrated and discussed in the existing failure method. A new approach, based on the solid element to simulate the damage progress is introduced. Investigated the damage progressive property by using the Hashin criteria and 3-D stiffness degradation criteria. The composite loading-displacement curve when consider the damages of the composite is afforded.