Description:The present invention relates to the structural design of Type IV Composite Overwrapped Pressure Vessels (COPVs), specifically to the selection and arrangement of fiber winding angles and patterns used in the manufacturing process to enhance mechanical strength, reduce material usage, and optimize stress distribution under high internal pressure.

Background and Prior Art (State of the Art)
1 General Background
Composite Overwrapped Pressure Vessels (COPVs), particularly Type IV, are widely used in industries such as automotive, aerospace, and energy for the storage of compressed gases (e.g., CNG, hydrogen). These vessels feature a non-load-bearing polymeric liner overwrapped with structural composite fibers, such as carbon or glass fiber, impregnated with resin.
The fiber winding patterns and angles are pivotal in achieving the required mechanical performance. The vessel must withstand hoop and axial stresses induced by high-pressure fluids while maintaining structural integrity and reducing weight.
2 Existing Techniques and Their Limitations
• US Patent 6,805,243 B2 describes the general methodology for composite fiber winding in pressure vessels but does not provide detailed optimization strategies for mixed winding angles to reduce weight while maintaining burst strength.
• US Patent 7,497,933 B2 discusses helical winding for COPVs but does not integrate FEA-based optimization or discuss angle variation for combined performance against hoop and axial stresses.
• US Patent 9,765,123 B1 discloses vessel constructions using geodesic windings but fails to compare the efficacy of geodesic vs. non-geodesic paths for irregular dome geometries.
These prior arts neither combine multiple winding types in a mathematically optimized structure nor account for FEA simulation in choosing winding angles and patterns.

Summary of the Invention (Overview)
The invention provides a comprehensive system for selecting and applying fiber winding layer patterns and angles in the manufacture of Type IV COPVs. The technique utilizes a combination of hoop, helical, and polar windings at optimized angles (ranging from 0° to 90°) and layer sequencing to:
• Manage both hoop and axial stress distributions.
• Maximize burst pressure.
• Minimize total weight and material cost.
• Enable adaptability for varied geometries and applications.
• Incorporate Finite Element Analysis (FEA) simulations to pre-calculate stress fields and winding efficiency.
The integration of mixed winding strategies and angle combinations (e.g., +θ and –θ helical layers) enables manufacturers to reduce local stress concentrations and enhance vessel reliability.

Detailed Description of the Invention
The present invention relates to the structural design and optimization of winding layer patterns and winding angles in the manufacture of Type IV Composite Overwrapped Pressure Vessels (COPVs). These vessels are widely used for the storage of compressed gases such as hydrogen, natural gas (CNG), and oxygen in a variety of industries including aerospace, defense, transport, and energy. Type IV COPVs feature a non-load-bearing polymeric liner overwrapped with fiber-reinforced resin composite materials. The overwrapped fibers bear the structural load, particularly under high internal pressures. The selection of winding angles, winding sequence, and winding patterns plays a vital role in determining the vessel’s mechanical performance, safety, and manufacturing efficiency.
The structural integrity of COPVs under internal pressure is governed by the vessel’s ability to withstand two major stresses—hoop stress and axial stress. Hoop stress refers to the circumferential stress acting perpendicular to the cylinder’s axis, while axial stress acts parallel to the axis. These stresses are primarily induced by the internal pressure of the stored gas. The current invention provides a comprehensive method for selecting and arranging winding angles and patterns to distribute these stresses uniformly across the vessel body and dome, thereby maximizing the vessel’s strength-to-weight ratio while minimizing material cost.
Winding Types and Functional Roles
Three primary winding strategies are used in composite pressure vessels—hoop winding, helical winding, and polar winding. Each type of winding serves a specific mechanical function and is implemented in different regions of the vessel.
Hoop Winding (85°–90°)
Hoop windings are fibers wrapped circumferentially, approximately perpendicular to the longitudinal axis of the cylinder (typically at angles ranging from 85° to 90°). These fibers provide resistance against circumferential or hoop stresses that dominate the cylindrical mid-section of the vessel. A higher number of hoop layers increases the burst pressure capacity in the central region, which typically experiences the maximum radial expansion due to internal pressure.
Helical Winding (±10° to ±45°)
Helical windings are applied in a crisscross manner with fibers oriented diagonally along the vessel’s surface at angles between ±10° and ±45°. These fibers primarily resist axial stress but also provide some circumferential support. Alternating between positive and negative angles (e.g., +30° followed by –30°) helps neutralize internal torsional loads, enhances structural balance, and improves the overall fatigue life of the pressure vessel. Helical windings are spread across both the cylindrical body and transition zones of the dome.
Polar Winding (0°–10°)
In the dome or hemispherical regions at the ends of the vessel, polar windings are applied with fibers oriented nearly parallel to the longitudinal axis (0°–10°). These are critical for strengthening the domes against axial stress concentrations that arise due to the geometric discontinuity and pressure concentration near the openings (necks) of the liner. Polar windings also provide structural stiffness around boss-to-liner interfaces, reducing the risk of localized deformation and delamination in those regions.
Geodesic and Non-Geodesic Winding Paths
The invention further distinguishes between geodesic and non-geodesic winding paths. Geodesic windings represent the shortest and most tension-optimized path across the curved dome regions. These paths help in uniformly distributing tension and minimizing fiber slippage or resin pooling. Geodesic windings are ideal for vessels with simple dome geometries. However, the present invention also supports non-geodesic paths, which allow for more complex layering strategies in cases where additional reinforcement is required in irregular geometries or non-standard domes. Non-geodesic winding requires precise control of tension, placement, and angle modulation but allows the designer to place fibers exactly where stress concentrations are predicted, offering custom reinforcement profiles.
Layer Configuration and Sequencing
The invention proposes a multi-layered configuration, with each layer tailored for a specific mechanical purpose. A typical sequence starts with a base layer of helical fibers oriented at +θ followed by –θ (e.g., +25°, –25°), which provides foundational axial strength. This is followed by one or more hoop winding layers at 90°, enhancing the circumferential load-bearing capacity. Finally, polar windings are applied at the dome ends to reinforce axial strength at critical zones. This sequence may be repeated in multiple cycles to achieve the desired wall thickness and mechanical properties.
Each winding layer is designed based on the expected internal pressure, vessel dimensions, fiber and resin material properties, and required burst strength. The number of cycles and sequence of layers is determined through Finite Element Analysis (FEA) simulations, ensuring that stresses remain below allowable limits at every point in the structure.
Winding Angle Effects on Stress Distribution
The winding angle significantly influences how stress is distributed within the composite material. Hoop windings at 90° provide maximum resistance to hoop stress but contribute little to axial stress. Conversely, helical windings at ±30°–45° provide a compromise between resisting axial and hoop stresses. This dual-role capacity allows the vessel to withstand multiaxial loads with a reduced number of layers. Polar windings at 0°–10°, while offering less hoop resistance, provide excellent axial strength in the dome ends.
By varying the angle and number of layers in each region of the vessel, the designer can “tune” the stress profile to match application-specific pressure profiles. For example, a hydrogen storage vessel designed for 700 bar pressure would need more hoop and polar reinforcement compared to a CNG tank rated for 250 bar. The FEA-based optimization further ensures that the load path through each fiber layer aligns with the principal stress directions, reducing fiber wastage and improving performance.
Finite Element Analysis for Optimization
Finite Element Analysis (FEA) plays a critical role in the invention. A full 3D model of the COPV is created with material properties assigned to each layer based on fiber direction, resin properties, and expected temperature/pressure conditions. The model simulates internal pressure loads and evaluates stress distribution across each layer and region. Using this data, the system recommends optimal winding angles, fiber orientations, and layer thicknesses.
Stress concentrations, displacement fields, and failure indices (e.g., Hashin failure criteria) are used to detect weak zones. The process iterates between the model and design table until all regions of the vessel satisfy strength, fatigue, and safety margin requirements with minimal material use.
Material Selection and Considerations
The fibers used in this invention are typically high-strength carbon fibers due to their high modulus and low density. In some cases, hybrid combinations with glass fiber are used to reduce cost or improve damage tolerance. The resin matrix may be epoxy, vinyl ester, or a thermoplastic depending on the curing process and final application temperature.
The liner used is a thermoplastic (HDPE, PA6, or similar) that is gas-tight and chemically compatible with the stored fluid but does not carry any mechanical load. The overwrap is applied using filament winding machines under controlled tension and temperature, followed by resin curing or consolidation in an autoclave or oven.
Benefits and Advantages of the Invention
• Weight Reduction: By selectively applying fibers at optimized angles, material usage is minimized while meeting safety margins.
• Stress Uniformity: Strategic placement of ±θ and 90° windings distributes loads evenly, reducing delamination and micro-cracking.
• Burst Pressure Optimization: Mixed-angle layers allow higher burst resistance with fewer total layers compared to conventional winding.
• Dome Strength Enhancement: Polar windings at the ends provide axial strength where traditional hoop windings are ineffective.
• Custom Geometry Accommodation: Non-geodesic winding supports custom dome shapes, valves, and nozzles.
• Simulation-Based Design: Integration with FEA allows predictive design, faster prototyping, and verification before production.
Example Implementation
A hydrogen vessel designed to withstand 700 bar internal pressure may include the following winding pattern:
• Layer 1: Helical +35°
• Layer 2: Helical –35°
• Layer 3: Hoop 90°
• Layer 4: Polar 5° (dome regions only)
• Layer 5: Helical +20°
• Layer 6: Helical –20°
• Layer 7: Hoop 90°
• Layer 8: Polar 0° (reinforced dome section)
This 8-layer sequence ensures balanced axial and hoop strength while minimizing material waste. The polar layers are only applied in dome areas, allowing the cylindrical body to remain lightweight.

, Claims:1. A fiber winding configuration for Type IV COPVs comprising multiple layers of composite fibers at optimized angles to resist hoop and axial stresses.
2. The configuration of claim 1, wherein hoop winding fibers are oriented between 85° and 90° relative to the vessel's longitudinal axis.
3. The configuration of claim 1, wherein helical winding fibers are oriented between ±10° and ±45° relative to the longitudinal axis.
4. The configuration of claim 1, wherein polar winding fibers are laid between 0° and 10° in the dome region to enhance axial strength.
5. The configuration of claim 1, wherein winding patterns include alternating positive and negative helical angles to balance torque.
6. The configuration of claim 1, wherein the winding angle and pattern are determined using finite element analysis based on stress prediction under internal pressure.
7. The configuration of claim 1, wherein a geodesic winding is applied for efficient coverage of dome sections, minimizing waste.
8. The configuration of claim 1, wherein a non-geodesic winding is selectively applied for structural reinforcement in non-uniform geometries.
9. The configuration of claim 1, wherein the vessel comprises at least one inner polymer liner and external composite overwrap impregnated with thermoset or thermoplastic resin.
10. The configuration of claim 1, wherein the winding sequence is helical → hoop → polar, repeated across multiple layers to optimize burst pressure and reduce weight.