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Key design principles to follow for filament winding

Introduction to Filament Winding and Composite Design

Filament winding is a manufacturing process that involves applying continuous fiber roving, impregnated with resin, onto a rotating mandrel along predetermined patterns. This process is often used to create composite structures that have high specific stiffness and strength, as well as excellent corrosion resistance. The main advantage of composites is their anisotropy, meaning they are much stronger and stiffer in the fiber direction than perpendicular to the fibers. This allows designers to tailor their designs to meet performance requirements optimally. However, the filament winding process has limited design freedom, making it difficult to approach the optimal laminate lay-up in all given geometrical scenarios.

Designing with Composites: Material design before shape design

Designing with composites involves selecting the appropriate material, defining an appropriate configuration, and finding a suitable way to manufacture it. In the case of metal components, the geometry is typically defined independently from the material, and the material only comes into play during the final dimensioning stage. With composites, however, the material must be designed along with the structure. This requires several iterations, as there are no closed formulas for designing optimal laminates. Designers have a range of tools at their disposal, from simple laminate software in the preliminary design stage to more advanced analysis techniques like finite element analysis as the design progresses.

What needs to be considered with Filament Winding Design?

There are several factors to consider when designing filament winding. These include the manufacturing aspects and limitations of the winding process, the design tools available, and the process parameters that can significantly impact material properties and composite performance. The key limitations of conventional filament windings to keep in mind are

  • It is limited to producing closed and convex structures e.g. pipes, fittings sleeves, tanks, etc.

  • Low fiber angles (0 to 15 deg) are not easily produced. Where 0 degrees is considered along the axis of the tank/pipe.

Some of the key process parameters to consider include the resin compound, mixing and distribution within the composite, the required resin viscosity and its evolution during winding, the feasible and allowable temperature variations and gradients during curing, and the environmental conditions during manufacture. Additionally, the winding tension in the fiber and the fiber positioning accuracy should be taken into account.

What are the key steps in Designing and Optimizing for the Filament Winding of a Tank?

There are several approaches to designing with filament winding, including optimizing the laminate lay-up, combining shape and lay-up optimization, and using semi-geodesic winding to increase design freedom. A standard workflow can be seen below image. The process involves providing key inputs i.e. Pressure, polar opening radius, etc to arrive at an initial fiber angle distribution in dome and hoop regions. This approach helps with designing the first draft.

As the initial design is ready, the design can be optimized in the following ways. One method of lay-up optimization involves using stress analysis to determine the ideal fiber orientations and ply thicknesses and then adapting the lay-up to meet the strength requirements while taking into account the limitations of the winding process.

Another approach is to combine shape and lay-up optimization, using analysis software and optimization algorithms to determine the optimal shape and lay-up that will meet performance requirements. This can be done using either geodesic or semi-geodesic winding. Semi-geodesic winding allows for more advanced design optimization, and can also be used to wind previously unwindable shapes or incorporate inserts that distribute the loads.

Manufacturing Aspects and Limitations to Consider

Filament winding with AddPath