Using multidisciplinary simulation, real-time process monitoring to improve composite pressure vessels
Multi-pronged approach closes the loop between design and production of Type 3, 4 and 5 pressure vessels, enabling simulation of as-built composite tanks to improve performance and storage capacity while reducing weight and cost.
Source (All Images) | CIKONI
The use of fiber-reinforced composites in Type 3, 4 and linerless Type 5 pressure vessels is growing, used to store compressed/renewable natural gas (CNG/RNG) and hydrogen as part of the global transition to cleaner and more efficient energy and transportation, but also to store rocket fuel and other gases in the rapidly expanding production of space vehicles. One of the issues, however, is the high cost of the carbon fiber used in these storage tanks and the need to develop designs that meet demanding performance, safety, volume, weight and cost requirements.
Local dome reinforcements enable tailoring a composite pressure vessel’s laminate in the dome and transition zones (shoulders), removing non-load carrying helical/polar winding layers, which reduces weight and cost while increasing storage capacity.
Composites engineering firm CIKONI (Stuttgart, Germany) has worked for more than a decade on projects to optimize such pressure vessel designs, developing a range of tools and approaches that have achieved improved performance and significant material and cost savings. For example, a recently completed design together with Cevotec (Unterhaching, Germany) for a pressure vessel OEM integrated local dome reinforcements, optimizing the layup to obtain a 15% reduction in carbon fiber use while maintaining equivalent mechanical properties. Because the tank wall thickness could be reduced slightly without loss of strength, usable storage capacity in the same volume was also increased by 17%.
The main approach used to achieve this is high-fidelity simulation that combines multiscale modeling, compaction analysis, process integration and crash/impact prediction. This dramatically reduces the number of required physical tests while increasing confidence in the optimized design, lowering development costs and enabling faster certification while ensuring product safety. However, such simulation-driven optimization cannot be done in isolation, but relies on accurate material and manufacturing data. CIKONI has developed a multi-pronged approach to close the loop between design and production, producing models that don’t just represent a nominal ideal, but mirror real tanks.
Multidisciplinary, multiscale simulation
One major advancement in advanced simulation methods is the use of multiscale simulation for composite pressure vessels made with filament winding or towpreg winding, as well as composite-overwrapped pressure vessels (COPVs) traditionally used in space applications. In this approach, the material’s microstructure — including fiber, matrix and behavior at the fiber-matrix interface — is characterized at the mesoscale and fed into a macroscale tank model. This enables the finite element (FE) simulation to account for critical manufacturing effects such as fiber volume fraction (FVF) gradients, resin-rich zones, and fiber overlaps and misalignments, especially in complex areas like the dome. Such detail enhances the precision of burst pressure and failure predictions.
An important enabler for accuracy is compaction simulation, which models how fiber tows deform and consolidate during winding. In composite pressure vessels, especially filament-wound COPVs, compaction during manufacturing is far from uniform. As each layer is wound onto a curved geometry — particularly in the dome area — the contact pressure, fiber path and layer conformity vary significantly. This leads to nonhomogeneous fiber volume content (FVC)/FVF throughout the laminate, which in turn affects stiffness, strength and failure behavior.
Instead of assuming a constant value, layer-by-layer compaction simulation helps to derive realistic local FVF across the vessel — capturing the effects of tow accumulation, inter-tow voids and local thickening. Incorporating these FVF distributions into the structural simulation yields a more representative stiffness and strength profile of the actual laminate, enabling more accurate predictions of mechanical performance and failure behavior, including burst pressure, fatigue life and post-impact behavior for more trustworthy safety margins. Ultimately, this enables smarter design optimization, removing unnecessary material, reducing cost and enhancing safety.
In-process resin content control
For tank manufacturers, an optimized design is only as good as its ability to be produced in actual scaled production. Thus, design for manufacturing (DfM) is a critical aspect of optimized tank design. This requires considering winding process constraints and variables early in the design and potential adaptations to fit production methods. It also means collecting accurate data during winding to feed back into simulations.
Using towpreg (pre-impregnated fiber tow) instead of wet winding can reduce variability in FVF and resin content and also increases winding speed by eliminating the resin bath. However, towpreg is currently more expensive, so that wet winding still makes up the majority of composite tank and COPV production. Thus, it is important to reduce wet winding variability as much as possible. For example, excess resin uptake in the resin bath can add unnecessary weight (and cost) without strengthening the structure. Also, having more resin than what’s needed for fiber bonding can prolong curing times. Conversely, insufficient resin uptake can lead to dry spots, poor fiber wet-out and internal voids, which degrade the mechanical performance and reliability of the laminate.
CIKONI’s patented system monitors resin uptake in wet filament winding of pressure vessels and dynamically adjusts resin bath parameters to maintain optimal impregnation.
The goal is to achieve the target FVF (typically around 60%) consistently throughout the vessel, ensuring optimal structural integrity with minimal waste. Traditionally, manufacturers control how much resin the fiber tow carries out of the bath by adjusting the resin viscosity, bath temperature, the resin gap resulting from doctor blade position and pulling speed. In addition, higher fiber tension during winding compresses fibers together, which can squeeze out excess resin and result in a more compact laminate with higher FVF. Conversely, if tension is too low, fibers may carry extra resin into the laminate. Thus, proper control of tension and speed are also key to achieving optimized laminate quality.
In order to help monitor these variables and provide data into simulations that are as accurate as possible, CIKONI has developed a patent-pending in-process quality control system that continuously measures resin content during wet winding. This sensor-based system enables real-time detection of resin uptake fluctuations and dynamically adjusts resin bath parameters — such as doctor blade position and fiber tension and pull speed — to maintain optimal impregnation. The result is a stable and well-impregnated laminate, with FVF controlled to the design target across the entire structure. By closing the loop between process monitoring and control, CIKONI’s system ensures predictable laminate quality, avoids over- or under-impregnation and helps manufacturers meet both performance and cost targets more reliably.
In-process fiber alignment and quality monitoring
Composite Winding Process Watch (CWPWatch) uses sensors and optical inspection to monitor fiber alignment, gaps and overlaps in real time during composite pressure vessel production.
Even with the best design and process controls, quality variation can still occur during manufacturing — a misaligned fiber, a wrinkle or a gap can weaken a pressure vessel and lead to rework or scrap. That’s why in-process quality monitoring is crucial, especially for automated filament winding and towpreg winding. CIKONI addresses this with a technology suite — originally called DrapeWatch for monitoring fabric draping during preforming — now adapted for winding as Composite Winding Process Watch (CWPWatch). This system uses sensors and optical inspection to watch the fiber placement in real time during production.
CWPWatch monitors the fiber winding on the fly, checking for deviations in fiber angle, width, overlaps and/or gaps between roving passes. If an error is detected, the system can alert operators or even automatically adjust the process. By catching issues during winding, CWPWatch prevents defective layers from being buried under subsequent layers. This can reduce scrap and rework significantly, as defects can be corrected on the spot rather than discovered in final inspection.
The benefits of such real-time monitoring are manifold:
- Ensures each tank meets the design intent, which maintains safety and avoids hidden flaws.
- Reduces cost by minimizing defects and rejects — fewer scrapped tanks means lower overall cost per good part.
- Aids process optimization, feeding data back into the design and simulation loop — recorded fiber orientations from production, for example, can be fed directly back into simulation.
Integrating “as-built” data into the simulation can help define robust manufacturing tolerances without overconstraining production.
This closed loop between manufacturing and design means simulation models can be updated with “as-built” fiber paths, improving their accuracy for future design iterations. Over time, this learning loop makes both the product and process more robust. Further, integrating as-manufactured geometries and deviations into the simulation is also valuable in assessing structural sensitivity to process variations, which helps define robust manufacturing tolerances without overconstraining production.
Quality monitoring systems like CWPWatch are part of a broader trend of Industry 4.0 in composites manufacturing where sensors, vision systems and AI-assisted data analysis are being used to achieve zero-defect production. For COPV manufacturers, investing in such technology pays off by ensuring consistent product performance (essential for certifications) and by driving down the cost of non-quality. By catching a fiber placement error that might have caused a composite pressure vessel to fail during burst testing, this 4.0 system saves not just that tank but also the downtime and investigation that would follow a test failure.
In summary, composite pressure vessels have become crucial in high-value industries such as aerospace, defense, energy and ground-based transportation. The level of precision required for these applications is increasing as industry demands lighter, more efficient and less costly systems that are safe and more sustainable. High-fidelity multidisciplinary, multiscale simulation using a variety of tools enables this level of prediction accuracy. But even further value is possible by coupling this approach with sensors and real-time monitoring that not only safeguards quality but also feeds “as-manufactured” data back into simulations and ensures that optimized tanks can be manufactured and perform as designed. The goal is to help meet current industry demands and produce safe and lightweight pressurized composite storage tanks that meet targeted cost and scale with confidence.
About the Authors
Dr. Farbod Nosrat Nezami
Dr. Farbod Nezami holds degrees in mechanical engineering from TU Dresden and the University of Stuttgart and has completed a Ph.D. in composite engineering. His professional experience includes international projects in the automotive and aerospace industries, and he is a frequent speaker and seminar leader on forming technologies for carbon fiber composites, contributing to several industry associations and training institutions. Nezami is the author of more than 30 patent applications in the field of composite technologies and has received multiple innovation awards.
Dr. Jan-Philipp Fuhr
Dr. Jan-Philipp Fuhr studied aerospace engineering at the University of Stuttgart and worked as a research associate at the Institute of Aircraft Design and at Audi AG as a composite materials R&D engineer. He has extensive experience in the development of digital process chains, simulation methodologies and quality control systems for composites. Fuhr has contributed to numerous international projects including American, Japanese and Korean partners.
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