The sphere parametric automatically creates multiple winding programs for providing a mufti-angle layup on spherical components. The programs give near uniform thickness distribution particularly if the filament bands are thin and a large number of layers are used. Because multiple wind angles are used the resulting composite is effectively in-plane quasi-isotropic and this gives maximum efficiency for a spherical pressure vessel. Ultra-high performance pressure vessels have been produced and tested using this method.
QuickCAD Sphere Winding Parameter
The user defines the sphere geometry (radius and end opening radius) and material parameters such as the band width and the number of individual winding angle that are required. The program then creates all the necessary winding path information and transition paths that wind from the end point of one path to the start point of the next. The parametric program is invokes from the QuickCAD options of the Cadfil main menu. This is documented elsewhere in this manual. A sample file call SP1.PAR is supplied in the EXAMPLES directory.
The program generates a series of .PAY files for example if the parametric data was in the file SP.PAR the software would generate SP01.PAY, SP02.PAY, SP03.PAY....... A maximum of 99 payout files can be created. Note that on DOS systems the maximum filename before the extension is 8 characters and hence the stem name the user supplies should not exceed 6 characters. A special control file SP.CTL would also be created. When the data is post-processed the .CTL file identifies all the individual .PAY files such that they can be automatically processed in sequence to create a single NC data file.
There are currently three possible variations on the Sphere parametric these are shown on the parametric menu as SPHERE1, SPHERE2 and SPHERE3.
SPHERE2-Equal Openings with user specified wind angles
This parametric is for vessels with equal polar end openings the users specified the number of layers and the ply angles required for each layer. The clearance envelope is spherical with a cylindrical clearance around the shaft(s)
SPHERE3-Equal or unequal openings with automatic wind angles
This parametric is for vessels with equal or unequal polar end openings the users specified the end openings and the number of layers. The ply angles required for each layer are calculated automatically. The clearance envelope is spherical with separate cylindrical clearances for each shaft. The polar opening at one end can be zero or can be specified that the band crosses partially over the pole.
The parametric data for the SPHERE1 parametric follows. Data entry for the other sphere parametric is similar. The parameters are:
Sphere Radius Filament Band Width Polar end opening radius Number of band setsNumber of points per circuit Spherical clearance radius End shaft clearance radius
The Sphere radius and polar end opening define the winding geometry. The polar end opening is at both ends and the inner edge of the fibre band for the lowest wind angle should just touch the opening diameter. The highest wind angle is 90 degrees and this is a single band around the equator. A number of winding angles (layers) are created equal to the number of bands sets with constant changes in wind angle between the highest and lowest angles layers described above. Each program is a separate standard axisymmetric program with the number of cycles required to complete the layer automatically calculated. The wind angles, numbers of bands in the layer and the name of the particular PAY file are tabulated on the screen when the Sphere program is invoked. If the basic thickness of a filament band was say 0.18mm and a composite 4mm thick is required then 4/(2*0.18)=11.1 layers are required and the number of band sets would be specified as 11. In practice the actual thickness of the part will vary a little. We have found that the composite is often a little thinner at the poles and the lower angle winding programs can be repeated (by changing the number of cycles in the NC data) to thickness the composite at the ends.
Each winding program has a number of data points on it and this is the number of points per circuit. A value of 20 works well in most applications. This is a compromise between accuracy and the amount of data created.
The spherical clearance radius and end shaft clearance radius define a control surface on which the payout points will lie. This consists of a sphere intersected with a cylinder, the cylinder being bigger than the mandrel shafts(s) and the sphere being bigger than the mandrel (plus the thickness of the winding). Thus the values supplied must be bigger than the shaft and mandrel radii.
When post processing the payout data from the sphere program the user should note that the band pattern has automatically been calculated in producing the payout file data.