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Filament Winding: Materials, Patterns, and Roving Dimensions for Pressure Vessels

Updated: Oct 4, 2023


Dive into the technical world of filament winding, a pivotal process in the composites industry. This blog sheds light on the intricacies of designing cylindrical composite pressure vessels, the significance of winding patterns, and the challenges faced in achieving optimal results. Drawing from expert insights and research findings, we provide a detailed breakdown of the art and science behind filament winding. Whether you're in the industry or just starting out, this guide offers valuable knowledge for all. Let's get started.

The Pressure Vessel Blueprint

Visualizing the Vessel:

Schematic representation of a pressure vessel and definition of the winding angle
Schematic representation of a pressure vessel and definition of the winding angle

  • Shell of Revolution: A composite pressure vessel is visualized as a shell of revolution, adorned with a specific winding pattern. This shell is formed by revolving a meridian profile, which can be represented by a function, for instance, z(Φ).

  • Load Factors: The vessel typically faces internal pressure, denoted as P. In certain scenarios, like lifting bags, there's an externally applied axial load, Fa.

Decoding the Winding Angle:

Geometry of a pressure vessel
Geometry of a pressure vessel
  • Definition: In filament-wound structures, the winding angle is conventionally measured with reference to the centerline through the polar bosses, which is the axis of rotation. This angle is crucial as it determines the path of the filament on the vessel.

  • Significance in Pipes: For pipes, the winding angle is the angle between the fiber direction on the mandrel surface and the axis of mandrel rotation. Here, 0° is axial, and 90° is circumferential, often termed as the hoop direction. This angle plays a pivotal role in optimizing the performance of the composite.

  • Influence on Design: The winding angle is not just a measure; it's a determinant of the product's design and performance. A specific winding angle is essential to achieve the desired strength and durability of the vessel.

Crafting the Perfect Vessel: The Art & Science Behind It

Filament winding is both an art and a science, and crafting the perfect vessel requires a deep understanding of both aspects. Let's delve into the intricacies of designing cylindrical composite pressure vessels and the significance of laminate thickness approximation.

Designing with Precision: The nuances of designing cylindrical composite pressure vessels.

  • Integral Approach: The design methodology for cylindrical pressure vessels is rooted in an integral approach. This method emphasizes the interplay between the real fiber bed geometry, which has finite roving dimensions, and the theoretical one.

  • Shell Stresses & Geometry: When visualizing a composite pressure vessel, think of it as a shell of revolution. This shell is adorned with a specific winding pattern and is formed by revolving a meridian profile. This profile can be influenced by various factors, including internal pressure and externally applied axial loads.

  • Thickness Distribution: One of the critical aspects of designing a pressure vessel is understanding the laminate thickness distribution. As you move from the vessel's equator to the polar areas, the laminate thickness tends to increase rapidly. This is because the same number of rovings is distributed over a smaller periphery, leading to more overlap and, consequently, increased thickness.

Thickness Matters: Delving into the influence of laminate thickness approximation.

  • Classic Method: Traditionally, the laminate thickness is determined by considering the vessel as a shell of revolution. The thickness at the equator is influenced by the winding process. However, as you move towards the polar areas, the thickness increases rapidly.

  • Polynomial Approximation: Another approach combines the benefits of the classic methods with polynomial approximations. This method uses a polynomial to approximate the thickness distribution over a specific domain, ensuring both continuity and equivalence.

  • Real-world Considerations: In practice, achieving the ideal thickness distribution can be challenging. Factors such as compaction, consolidation effects, fiber slipping, and air entrapment can influence the final thickness of the laminate in the vessel.

Patterns that Mesmerize: The Beauty of Winding

Schematic representation of a leading pattern: (p  + 1)k = 126,  nd = 125
Schematic representation of a leading pattern: (p + 1)k = 126, nd = 125

Filament winding is not just about wrapping fibers around a form; it's about creating intricate patterns that are both functional and aesthetically pleasing. Let's explore the journey of creating these mesmerizing patterns and the role of roving dimensions in this process.

Creating the Pattern: The journey from angular differences to the perfect winding pattern.

  • Angular Differences: The winding pattern on a pressure vessel is significantly influenced by the angular difference between two consecutive windings. This difference dictates the path the fibers will take on the vessel's surface.

    • Equations to Consider: The total number of rovings is represented by nd, where d denotes the number of closed layers. For d = 1, n becomes a multiple of 1/d:

  • For a lagging pattern

  • Significance of the Winding Angle: The winding angle, measured in relation to the centerline through the polar bosses (axis of rotation), is pivotal in determining the winding pattern. A repeating pattern of the filament path after a certain number of mandrel revolutions ensures complete coverage of the mandrel.

Roving Dimensions: The unsung hero of winding patterns.

  • Role of Roving Dimensions: The dimensions of the roving, especially its width and thickness, play a crucial role in determining the winding pattern. The effective roving width at the equatorial periphery is influenced by the winding angle and is given by:

  • Thickness Distribution: The desired thickness distribution across the vessel's profile is determined by the number of windings running over the vessel's surface. At the equatorial periphery, a number n of roving widths will fit in a single layer. The effective width is influenced by the roving's crossing angle at the equatorial periphery.

    • Equations to Reflect Upon: The dimensionless cross-sectional area of a single roving for dry winding is:

For wet winding, adjustments are made based on the resin content.

Beyond the Basics: Diving Deeper

Challenges in the Spotlight: Addressing the winding angle and roving overlap.

  • Angular Differences in Winding: The winding pattern of a pressure vessel is influenced by the angular difference between two neighboring windings. This angular difference determines the path the fibers take on the vessel's surface.

  • Roving Overlap: As the winding evolves, it returns to the starting position, leading to overlaps. This overlap can lead to increased thickness, especially at the polar periphery where the winding angle changes.

The Perfect Solution: Introducing the exact solution and its significance.

  • Exact Solution for Thickness Distribution: The exact solution considers the effects of winding angle and roving overlap. It provides a more accurate representation of the laminate thickness distribution over the vessel's profile.

    • Equations to Ponder:

      • The exact solution for thickness distribution is given by:

  • The exact solution shows a sharp peak at Y = 1 + B, indicating a rapid increase in thickness at the polar periphery.


The Winding Road Ahead: A recap and reflection on the wonders of filament winding.

  • A Journey of Evolution: Filament winding has come a long way from its early days. From purely mechanical machines focused on manufacturing pipes to the state-of-the-art filament winding facilities we see today, the process has seen significant modernization.

  • The Art and Science: The winding pattern, influenced by angular differences, and the role of roving dimensions showcase the intricate balance of art and science in filament winding. The exact solutions and methodologies discussed highlight the depth of research and understanding in the field.

Standing on the Shoulders of Giants: Learning from the Best

A Treasure Trove of References: Highlighting key conferences, publications, and research papers.

Books and Publications:

Conferences and Research:

  • The SAMPE (Society for the Advancement of Material and Process Engineering) International Business Office in Covina, CA, has been a hub for discussions and advancements in filament winding.

  • Research from Canada has been pivotal in the realm of reinforced piping, showcasing global contributions to the field.

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