efficient design and automated production of composite pressure

Michael L. Skinner Managing Associate

Seifert and Skinner & Associates

Composicad CPV™ for pressure vessels

Composicad models the whole part – all lamina – at the same time. This allows for very fast changes to the design, which combined with the new design & analysis tools, lets us move quickly to an optimized design.

The new features in CPV (silver) package (except as noted): New Design Tab to calculate the required helical and hoop thicknesses using netting analysis New Burst Pressure tool to calculate the burst pressure of the actual laminate using netting analysis New export to ESAComp – a tightly integrated export to an inexpensive FEA tool Expanded support for FEA – Abaqus shell and brick elements, Nisa shell and brick elements, Ansys shell elements, Strand 7 shell elements and others (included in FEA Output Option only) New export to the Abaqus Wound Composite Module

1. Define the mandrel (liner shape) based on design 2. Use the Design tab to calculate the required Helical and

Circumferential winding thicknesses 3. Build (modify) the laminate 4. Use the Burst Pressure calculation to check for the

desired burst pressure and helical to circumferential fiber stress ratios

5. Export the part to ESAComp for FEA 6. Export the part to your favorite FEA program 7. Look at the results of the FEA

8. Make the machine motions for your winding machine 9. Make a test specimen 10.Test the specimen

The typical pressure vessel design and analysis process using Composicad:

Expensive (both time and materials)

Low cost

Build the mandrel

The mandrel shape (the liner outer contour) can be defined by the built in mandrel generator.

Build the mandrel

The mandrel parameters are specified and the dome shape – Isotensoid or Elliptical.

Build the mandrel

Mandrel parameters

Build the mandrel

Isotensoid dome

Elliptical dome

Correct dome geometry is crucial to CPV performance

Or the mandrel contour can be described by a mandrel file – a list of the axial positions and diameters.

Note the increased number of radial segments in the crucial dome transition region.

Netting Analysis

Netting analysis

Netting analysis only considers the fiber stresses and neglects any contribution of the resin matrix. Any shear strains are also neglected. Consider a section of a filament wound tube of radius R. At a given point, by selecting an appropriate unit cross section and summing fiber stresses, it can be shown that the components of force are:

𝑁𝑎𝑎𝑎𝑎𝑎 = 𝜎ℎ𝑒𝑎 𝑡ℎ𝑒𝑎 𝑐𝑐𝑐2𝛼 = 𝑃ℎ𝑒𝑎𝑅 2⁄ 𝑁𝑟𝑎𝑟𝑎𝑎𝑎 = 𝜎ℎ𝑒𝑎 𝑡ℎ𝑒𝑎 𝑐𝑖𝑖2𝛼 + 𝜎𝑐𝑎𝑟𝑐 𝑡𝑐𝑎𝑟𝑐 = 𝑃𝑐𝑎𝑟𝑐𝑅

where α is the angle to the helical axis (the winding angle), thel is the thickness of the helical material, tcirc is the thickness of the circumferential material , 𝜎ℎ𝑒𝑎 is the helical fiber stress , 𝜎𝑐𝑎𝑟𝑐 is the circumferential fiber stress, 𝑃ℎ𝑒𝑎 is the helical pressure, 𝑃𝑐𝑎𝑟𝑐 is the circumferential pressure and the N values are the axial and radial forces in the section.

α -α

0.5 𝜎ℎ𝑒𝑎 𝑡ℎ𝑒𝑎 𝑐𝑖𝑖2𝛼 0.5 𝜎ℎ𝑒𝑎 𝑡ℎ𝑒𝑎 𝑐𝑖𝑖2𝛼

0.5 𝜎ℎ𝑒𝑎 𝑡ℎ𝑒𝑎 𝑐𝑐𝑐2𝛼 0.5 𝜎ℎ𝑒𝑎 𝑡ℎ𝑒𝑎 𝑐𝑐𝑐2𝛼

𝜎𝑐𝑎𝑟𝑐 𝑡𝑐𝑎𝑟𝑐

𝑁𝑎𝑎𝑎𝑎𝑎 = 𝑃ℎ𝑒𝑎𝑅 2⁄

𝑁𝑟𝑎𝑟𝑎𝑎𝑎 = 𝑃𝑐𝑎𝑟𝑐𝑅

Netting analysis

Circumferential Fibers

Helical Fibers

Forces due to the internal pressure P at radius R

α is the winding angle, σ is the fiber stress and t is the fiber thickness

Netting analysis

By setting the helical and circumferential pressures to the burst pressure and by setting the helical and circumferential fiber stress to the fiber ultimate tensile stress, we can solve for the required helical and circumferential thicknesses:

𝑡ℎ𝑒𝑎𝑎𝑐𝑎𝑎 = 𝑃𝑏𝑏𝑏𝑏𝑏𝑅2𝜎𝑓𝑐𝑐𝑐2𝛼

𝑡𝑐𝑎𝑟𝑐 = 𝑃𝑏𝑏𝑏𝑏𝑏𝑅2𝜎𝑓

2 − 𝑡𝑡𝑖2𝛼

These equations are used by Composicad to calculate the required helical and circumferential thicknesses for the desired burst pressure.

References: 1. R.P. Willardson, D.L. Gray & T.K. DeLay, Improvements in FEA of Composite Overwrapped Pressure Vessels, SAMPE 2009 2. S.T. Peters, W.D. Humphrey, and R.F. Foral, Filament Winding Composite Structure Fabrication, 2nd ed. Covina, CA: SAMPE

Specify the desired operating pressure and safety factor – common safety factors can be selected for carbon 2.35 or glass 3.65 – to get the desired burst pressure. Pressures are shown in Mpa, bar and psi.

Using the Design Tab, specify the winding angle to be used for the helical winding. Composicad calculates the Geodesic angle, which can be used or you can specify another angle.

Composicad Design Tab

Select the appropriate material for the Helical layers from the Composicad material database. The Fiber Fraction (by volume) and the Ultimate Fiber Stress and Elongation (strain) at failure will be pulled from the material parameters (if defined). These parameters can be changed if desired.

Specify the desired Helical to Circumferential fiber stress ratio at burst.


Composicad Material DB

Composicad uses a material data base for materials. The data base stores the material properties. The materials can then be selected for the lamina. Material TEX (or yield), number of rovings,

resin and fiber densities, fiber fraction (by weight or volume), costs, and band thickness or width are specified.

Material properties which are used by the Design Tab – UFTS & UFE – as well as other properties used by the FEA output are specified.

Select the appropriate material for the Circumferential layers from the Composicad material database material. The Fiber Fraction (by volume) and the Ultimate Fiber Stress and Elongation (strain) at failure will be pulled from the material parameters (if defined). These parameters can be changed if desired.

The Circ material can be set to the same material as the Helical layers if desired.


The required thickness of helical material for the desired burst pressure is calculated. The number of Helical layers required is calculated based on the required thickness and the material thickness. Note that helical layers are always two plies – a plus and a minus ply.

The required thickness for the circumferential material and the required number of circumferential layers is calculated. Note that the circ layers are a single ply (assumed at 90 degrees).


Fraction layers are not possible. To achieve the optimum amount of material, the material thicknesses should be adjusted.

The cylinder Outside Diameter is calculated based on the required helical and circ thicknesses. At room and operating pressures.

The liner thickness in the cylinder and in the domes is specified along with the liner density to get an approximate liner weight. The model is based on an elliptical contour in the domes.

The approximate volume of the vessel is calculated (based on the liner dimensions entered) at room and operating pressure.


Typically, there may be constraints on OD and/or length of the CPV. The larger size at operating pressure must be considered.

Build the desired laminate


The appropriate sequence of helical and circumferential windings is created.

Each lamina’s thickness, weight & cost, as well as the part OD after each lamina, is calculated.


Circumferential, Helical, Connector and Other Lamina can be defined.

The total laminate thickness, weight & cost is calculated. If a machine definition is selected, then the Total Winding Time is also calculated.

Circumferential Lamina

Start and end positions of the circ winding are relative to the start or end of the cylinder section. Completely parametric.

Step in or out with each layer to mitigate the stress riser at the circ edge.

Dwell control before the start of the circ winding, between layers and at the end.

Helical Lamina

The winding can be specified by the pole diameter (or geodesic diameter).

The number of circuits for complete coverage (100%) is calculated, as well as the lap/gap of the band, coverage %, and thickness.

Or by the winding angle (or both). The required friction (slip potential) is calculated.

Connector

Connectors (or transitions) are used to make a transition from a circumferential to a helical winding or vice versa, so the roving band does not have to be cut and restarted during winding. Connectors are typically neglected for analysis – both netting and FEA.

Other Other is used to model the liner, cores or other non-wound materials.

The liner is modeled here as the area from the red line (inside of liner) to the black (outside of liner).

Next mandrel generation

Composicad calculates the thickness of each lamina. The next mandrel contour can be generated by adding the calculated thickness of the layer to the last mandrel. The next mandrel is then smoothed, made monotonic and/or made symmetrical.

Thickness cross section

Results from non-Monotonic mandrel generation – best for FEA

Results from Monotonic mandrel generation – better for winding

Thickness cross section

Burst Analysis

Burst analysis

Composicad will use the given Fiber Stresses to calculate the burst pressures in the circ and helical directions. Stress can be given in Mpa or ksi.

Composicad looks at all of the lamina in the part, using the winding angles and netting analysis to calculate the burst pressures.

Composicad will calculate the Helical to Circ fiber stress ratio. Typically, this value is in the range of 0.6 to 0.9.

Burst analysis

With the Calculate Helical stress checkbox checked, Composicad will use the given Circ Fiber Stress to calculate the burst pressure where both the Helical and Circ burst pressure are the same (a typical netting analysis) and then calculate the resulting Helical Fiber Stress.

Burst analysis

Composicad calculates the helical and circ burst pressure based on the given fiber stresses. The percentage of the design value is also given. The circ/helical burst pressure ratio is calculated (in this case 1.00 since the pressures are the same).

Burst analysis

By using the “Use Design Values” checkbox – Composicad will use the Design Tab values for the helical and circ fiber stresses including the Hel/Circ Fiber Stress Ratio factor.

Composicad calculates the helical and circ burst pressure based on the given fiber stresses. The Circ/Hel Burst Ratio is below one, since based on the allowable fiber stress, the circ burst pressure is lower than the helical burst pressure.

Burst analysis By using the “Use Material Properties” checkbox – Composicad will use the Ultimate Fiber Stress from the Material Database as the design allowable. The Ultimate Fiber Stress must be defined for each material used. This mode can be used if different materials (with different Ultimate Fiber Stresses) are used.

Composicad calculates the helical and circ burst pressure based on the given fiber stresses.

Export to ESAComp, WCM and FEA

Export to ESAComp

www.esacomp.com

Export to ESAComp

You can use the original mandrel segments or specify the number of axial (equally spaced) and radial segments.

The Full Part or only the Headstock or Tailstock end can be used.

For ESAComp we always use the inside of the part (the mandrel surface) since it is a shell model.

ESAComp export generates several files that are then imported into ESAComp. The mesh.elements, mesh.nodes and section.data files contain the nodes, elements and section information for the model.

Export to FEA The Composicad FEA output option allows for the export of the laminate data in a wide variety of formats to accommodate all FEA program input deck styles. Composicad uses scripts and meta commands to generate the FEA output.

Composicad has predefined templates for many popular FEA packages and more are in development. The user can modify the templates as needed.

Export to FEA

Composicad generates the appropriate input deck for the selected FEA program. The meshing is complete with the appropriate material parameters for each section of the model. In filament winding the thicknesses and the winding angles are changing continuously along the length of the part. For figures of revolution (pressure vessels) the material is the same radially around the part.

Thicknesses for each lamina

Composicad supports both shell and 3D brick elements. With shell elements 90/180/360 radial sweeps can be used and the number of segments can be specified. For 3D Bricks a single element is generated in the radial direction. The width of the element in degrees is specified.

Export to FEA

Axial elements can be equally spaced or can follow the original mandrel segments.

The generated data can be displayed to verify correctness before import into the FEA package.

Export to FEA

NISA shell model

Shell model with equally spaced axial segments and a 90 degree sweep.

Abaqus 3D brick elements

Detail of critical dome transition region showing triangular elements as the circumferential layers terminate

Export to Wound Composite Module (Abaqus)

You can use the original mandrel segments or specify the number of axial (equally spaced) and radial segments.

In WCM export the Full Part is used.

For WCM we always use the inside of the part (the mandrel surface). Each individual lamina contains the position and thickness information for that layer.

The mandrel zero point can be shifted to the middle of the mandrel.


The export to WCM is a XML file that is read by the WCM. The file consists of the mandrel (the liner) and all of the lamina (patterns).


The points in each pattern (lamina) designate the axial position, the radius, the winding angle and the thickness.

In Europe: Axel Seifert

Managing Associate Seifert and Skinner & Associates, BVBA

Mobile: +32 475 426 814 email: [email protected]

In the North America: Michael Skinner

Managing Associate Seifert and Skinner & Associates, Inc.

Phone: +1 801-809-2886 email: [email protected]

In South America: Franco Stupenengo Managing Associate

Seifert and Skinner & Associates Argentina, SRL Mobile: +54 9 (223) 591.4287

email: [email protected]

Thank You! Any Questions?

www.Seifert-Skinner.com

mailto:[email protected]






efficient design and automated production of composite pressure

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