Description:The present invention relates to the design of Type IV Composite Overwrapped Pressure Vessels (COPVs), particularly those used for the storage of compressed natural gas (CNG) or gaseous hydrogen (H₂) at high pressure. More specifically, the invention pertains to a dome-shaped geometry at both ends of the polymeric liner that provides structural and geometric support for axial and helical filament winding, while also optimizing performance under high internal pressure.
Background of the Invention:
Type IV cylinders are composite pressure vessels used for the storage of compressed natural gas (CNG) or gaseous hydrogen (H₂) at high pressure typically constructed with a polymeric liner that is overwrapped with continuous filament fibers (such as carbon or glass) in a resin matrix. These cylinders are designed to hold high-pressure gas, and the structural integrity of the liner is critical to their safe operation. A key manufacturing process is filament winding, which involves applying fibers in both axial and circumferential patterns over the liner surface to ensure uniform coverage and strength.
However, conventional dome shapes of polymeric liner, whether hemispherical or elliptical, do not always optimize the fibre tension distribution of the winding process or the long-term mechanical stability of the pressure vessel. Particularly, stress concentrations often arise at the dome ends, resulting in suboptimal performance under internal pressure. Moreover, the winding tension can cause fiber slippage or distortion if the liner's geometry does not support a smooth, uniform application.
This invention addresses these issues by introducing a specifically designed dome-shaped end to the polymeric liner. These optimized dome geometries ensure that the fiber winding process is controlled and efficient while also enhancing the pressure vessel's overall stability and performance during service life.

PRIOR ART SEARCH

1. US 9376049 B2 – Type IV cylinder fabrication with geodesic profile domes
Describes polymeric liners with domed ends featuring a geodesic section profile designed to ensure iso tensoid fiber stress during service. Domes transition smoothly to the cylinder, supporting uniform fiber stress distribution.
2. US 5,499,739 (A) – Thermoplastic liner with high angle helical windings across the cylinder–dome transition
Introduces a method of overwrapping a thermoplastic liner (e.g. nylon 11) with high-angle helicals (60°–88°) through the cylinder-to-dome transition to prevent filament slippage and improve structural integrity.

3. EP 4 067 724 A1 – Composite high pressure tank with twist portion helical layer at junction
Discloses a pressure vessel where the helical layer includes a twist portion at the junction of cylinder and dome. This twist presses over the end of the hoop layer to prevent voids and improve adhesion at the cylinder dome interface.

4. EP 4 215 796 A1 – Ellipsoidal/elliptical domes and specific helical angles
The invention discloses the Features metallic liners with ellipsoidal domes and specific winding sequences using hoop plus helical layers.
Defines precise helical angles at the dome–cylinder intersection to distribute stress uniformly.
5. US 10,543,651 B2 – Polymer end cap design optimizing fiber distribution
The invention Describes end cap or dome shapes for Type IV pressure vessels that are engineered to optimize fiber distribution during injection or compression molding. The structure includes geometries to mechanically protect reinforcement edges.
6. Recent modeling and numerical studies (2022–2024)
• Academic research highlights: the dome region modeling challenges, winding angle sequencing, and layer thickness optimization in Type IV COPVs.
• Emphasizes the importance of smooth transitions and accurate FEA in dome geometries to avoid stress concentrations
 

Summary of the Invention:
This invention introduces an innovative dome-shaped design at both ends of the polymeric liner of a Type IV cylinder used for the storage of compressed natural gas (CNG) or gaseous hydrogen (H₂) at high pressure. The dome shapes are integrally molded with the liner, creating a seamless and continuous curvature from the cylindrical body to the apex of each dome. This unique design serves multiple functions:
1. Enhanced Fiber Winding: The domes provide optimized support for both axial and helical fiber winding, ensuring consistent fiber tension and placement, preventing slippage or bunching.

2. Improved Stress Distribution: The curved geometry of the domes minimizes localized stress concentrations, particularly during internal pressurization, leading to a more durable and fatigue-resistant vessel.

3. Uniform Structural Performance: The symmetrical design of the domes ensures that both ends of the cylinder experience similar stress loading, improving the vessel's overall structural integrity and uniformity.
By optimizing the dome shape, the invention contributes to both manufacturing efficiency and the long-term reliability of Type IV cylinders.
Brief Description of the Drawing:
Referring to Figure 1 (attached image), the drawing shows a longitudinal sectional view of a Type IV cylinder. The polymeric liner is depicted with two dome-shaped ends. The domes are integrally molded with the cylindrical body, providing continuous curvature that optimizes the filament winding process and ensures uniform stress distribution under internal pressure.
Detailed Description of the Invention:
This invention provides a mandrel geometry for a Type IV composite pressure vessel, wherein the polymeric liner is designed with a cylindrical body and two dome-shaped ends that offer significant benefits both in terms of manufacturing and operational performance.
Dome Geometry:
The dome shapes are carefully engineered to minimize stress and deformation during both the winding and pressurization processes. The continuous curvature of the dome transitions smoothly from the cylindrical section to the apex of the dome, reducing localized stress concentrations that typically arise at sharp angles or flat interfaces. This design also ensures that the fibers, laid in axial and helical patterns, remain in constant contact with the liner surface, preventing issues such as fiber lifting, bunching, or distortion.
The dome shapes are optimized based on stress analysis and winding simulations to ensure minimal critical stresses during both the winding process and the vessel's service life. In particular, the geometries of the dome ends are designed to optimize the distribution of hoop and axial stresses, which are crucial for the vessel’s ability to withstand high internal pressures.
Manufacturing and Structural Benefits:
The optimized dome design offers multiple advantages during manufacturing. The smooth, continuous curvature facilitates the filament winding process by providing a consistent surface for the fibers to adhere to, ensuring that the winding tension is evenly distributed across the entire surface. This improves the consistency of the composite overwrap and results in a more structurally sound pressure vessel.
From a structural perspective, the dome geometry naturally distributes internal stresses more evenly, preventing localized stress concentrations that could compromise the vessel's integrity. This is particularly important during pressurization, where the vessel is subjected to both hoop and axial stresses. The dome shape minimizes these stresses, improving the fatigue life and pressure stability of the vessel.
The symmetrical design of the domes ensures balanced loading on both ends of the cylinder, which is critical for maintaining uniform thickness of the composite overwrap. This symmetry also simplifies manufacturing processes by allowing the same dome geometry to be used on both ends of the vessel.
Additional Design Features:
● Optimized Fiber Engagement: The dome shape ensures that fibers applied during filament winding maintain consistent tension and placement, preventing any fiber deformation or misalignment during the manufacturing process.

● Leak-Proof Integrity: The neck region of the polymeric liner, where the metallic boss is attached, is designed with threads that ensure a secure, leak-proof connection. This is critical for high-pressure applications, and the smooth transition of the liner's dome shape contributes to this feature.

● Cyclic Pressure Durability: The optimized dome geometry improves the vessel's ability to withstand the cyclical pressure variations experienced during normal operation, ensuring long-term durability and safety.
Compatibility with Manufacturing Processes:
The dome design is compatible with both wet and dry filament winding processes and can be adapted to different cylinder sizes and liner materials. The symmetry of the dome shapes simplifies tooling and automation, ensuring repeatable and efficient production processes.
Sealing and Pressure Containment:
The polymeric liner includes a threaded neck region designed to be securely connected to a metallic boss. This threaded connection, combined with the placement of an O-ring in a circular groove inside the metallic boss, ensures a leak-proof assembly, even under high internal pressure. The careful design of the liner's neck and boss interface reduces the risk of stress concentrations, which are common failure points in pressure vessels. 
, Claims:1. A Type IV composite pressure vessel comprising:

○ a polymeric liner having a cylindrical body and two integrally molded dome-shaped ends;

○ the dome-shaped ends being designed to support helical or axial fiber winding and minimize stress concentration during pressure containment.

2. The pressure vessel of claim 1, wherein the dome shape at each end transitions smoothly from the cylindrical portion, forming a continuous surface for winding.

3. The pressure vessel of claim 1, wherein the dome shape is geometrically optimized based on critical stress minimization under internal pressure and winding load.

4. The pressure vessel of claim 1, wherein the dome geometry allows for uniform tension and placement of composite fibers during filament winding.

5. The pressure vessel of claim 1, wherein the dome shape is symmetrical at both ends of the liner to provide structural and winding uniformity.