PSI - Issue 77

Niels Grigat et al. / Procedia Structural Integrity 77 (2026) 365–375 N. Grigat, B. Vollbrecht et. al. / Structural Integrity Procedia 00 (2026) 000 – 000

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The preliminary phase encompasses the delineation of material systems and structural configurations. A range of fibre – matrix combinations are under investigation, incorporating glass, carbon, and aramid fibres within thermoset or thermoplastic resin systems. The laminate architecture, fibre orientation, and wall structure are meticulously engineered to withstand operating pressures of up to 100 bar and beyond. Subsequent to the conceptual phase, material models are established in order to describe the mechanical and diffusion behaviour of the composites under hydrogen exposure. Finite element (FE) simulations are utilised to predict the stress distribution, strain development, and potential failure modes under internal pressure loading. These simulations form the basis for design optimisation, allowing the identification of critical parameters such as winding angles and layer configurations.The process of experimental validation is initiated with material-level testing. In this instance, rather than utilising full pipes, wound plate specimens are produced from pre-impregnated (towpreg) fibre systems, in accordance with the procedure [7]. These plates provide a controllable geometry for mechanical and hydrogen permeation testing. The experimental results are utilised to calibrate and refine the simulation models, thereby ensuring an accurate representation of the material behaviour. In the final stage, the validated material and process data are applied to the production of full-scale FRP pipeline prototypes using advanced filament winding or braiding technologies. Subsequently, the prototypes are exposed to internal pressure and permeation testing under hydrogen conditions. The results of these tests provide critical feedback for process optimisation and confirm the transferability of material-level results to the system level. This iterative approach ensures a reliable, scalable, and scientifically validated pathway from material concept to functioning hydrogen pipeline. 3.2. Material Testing Comprehensive material testing is conducted to characterise the mechanical and diffusion properties of the developed FRP composites. The testing protocol encompasses evaluations of tensile and burst strength, in addition to hydrogen permeation measurements conducted under controlled conditions. The objective of this study is to ascertain the correlation between microstructural composition, fibre orientation, and gas barrier performance. Furthermore, environmental conditioning tests evaluate the long-term stability under temperature and pressure cycling. In order to systematically evaluate the influence of different fibre systems, three types of towpregs — based on glass, carbon, and aramid fibres — are produced using a controlled impregnation process with a thermosetting epoxy resin matrix. The epoxy system has been selected on the basis of its high interfacial adhesion, low gas permeability, and proven processability in filament winding. All towpregs are manufactured under identical process parameters with the objective of ensuring reproducibility and comparability of results across different material systems. Material testing is conducted on flat, filament-wound plate specimens, which serve as a representative section of the final pipeline laminate. Mechanical testing encompasses the measurement of tensile and flexural strength in accordance with DIN EN ISO 527 The experiment is conducted under strictly defined conditions of pressure and temperature in order to accurately quantify the diffusion behaviour of the epoxy-based composites. The amalgamation of these tests engenders a comprehensive comprehension of the structure-property relationship, thereby supporting the calibration of numerical simulation models.

Table 3.1:

Experimental setup for material testing of FRP towpreg systems

Parameter Fibre Types Matrix System

Description / Specification

E-glass, Carbon (HT), Aramid (Kevlar®-type)

Thermosetting epoxy resin

Towpreg Manufacturing Fibre Orientation Specimen Geometry Mechanical Tests

Kümpers GmbH

Unidirectional (89°) – filament-wound plates Flat plates (300 × 300 × 2 mm³), cut into test specimen

Tensile (DIN EN ISO 527)

Purpose

Input data for models and simulation