5.3 Polymere Verbundwerkstoffe
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Current recycling methods for polymer matrix composites produce short, unoriented carbon fibres, limiting their use to intermediate-strength applications. A method is therefore needed to recycle fibres while preserving their original length and orientation, enabling a circular economy for carbon fibre composites. This study proposes a novel hierarchical composite, designed to retain fibre length and orientation during recycling. Virgin carbon fibres are encased in an insoluble epoxy matrix to form tapes that act as the primary units of the structure. These tapes are protected by the primary matrix from chemical degradation and maintain the fibre orientation. The tapes are then embedded in a secondary recyclable matrix, Elium®, a thermoplastic polymer soluble in acetone with mechanical properties comparable to epoxy. The composite is recycled by dissolving the secondary Elium matrix in acetone and recovering the primary tape units with intact fibre length and orientation. The primary units can then be used to assemble new composites. In this study, hierarchical composite laminates underwent recycling up to three times. Their mechanical properties were assessed after each cycle. Laminates with an Elium secondary matrix retained 60–90% of the mechanical performance of epoxy-based laminates. Minimal degradation was observed between cycles, and fibre length, orientation, and volume fraction were fully preserved. Pushout tests confirmed that fibres in the primary tapes were sufficiently shielded during the recycling process. These results validate the feasibility of a hierarchical recyclable composite that combines recyclability with high mechanical performance, serving as a proof of concept and providing opportunities for future development.
A significant step towards achieving climate neutrality in the European Union (EU) by 2050 is the conversion of the energy supply to renewable energy sources. The availability of hydrogen (H₂) as a flexible energy source in sufficient quantities is currently a central challenge. At present, hydrogen is mainly produced from fossil fuels such as natural gas, while water electrolysis only contributes 4 % of total production. Less than 0.1 % of global production comes from renewable energy sources. Compared to the production of grey hydrogen, the production of green hydrogen with PEM electrolyzers is still associated with high costs. Reducing the procurement and production costs of PEM electrolyzers is therefore a key factor in realizing the goals of the EU's hydrogen strategy.
Around 50 % of the system costs are attributable to the system peripherals, meaning that savings can be achieved through the standardization of system components and the use of more cost-efficient materials. Currently, cost-intensive steel materials are used to guide media systems and cooling circuits in the plant periphery. Substitution by polymer materials offers a high cost-saving potential due to automated production processes and simple joining techniques.
In the collaborative project ‘PolyH2Pipe’, which is funded by the German Federal Ministry for Economic Affairs and Energy continuous fiber-reinforced thermoplastic (TP-FR) pipe systems are being designed, joining techniques developed and the requirements for the media piping validated. The objective of the research project is to conduct preparatory measures to initiate market launch activities for large-scale production of TP-FR media pipes for H2 electrolyzer and fuel cell systems. In the context of the presentation, methods and test results for validating the requirements of the pipes will be presented.
Understanding and controlling structure–property relationships remains central to the design of high-performance polymer composites. Among the diverse strategies to tune composite behavior, surface modification—whether at the level of fillers, interfaces, or polymer matrices plays a particularly decisive role in governing chemistry, morphology, and ultimately macroscopic functionality. Yet the complex interplay between modification routes, processing conditions, and multiscale material structure often obscures clear predictive relationships. This talk presents an integrated experimental and data-driven approach to elucidate these relationships and accelerate composite design. By combining targeted surface-modification experiments with machine-learning models trained on both curated laboratory datasets and heterogeneous literature-derived data, we map how chemical functionality, interfacial treatments, and processing parameters influence key composite properties. Interpretable models reveal nonlinear eects and parameter sensitivities that are often inaccessible through intuition or single-variable studies, oering mechanistic insight into how modified interfaces influence transport, mechanical performance, and stability. In parallel, data-driven predictions are validated through experiments on newly designed modified composite systems, demonstrating the ability of ML-guided strategies to forecast performance with high accuracy and to guide the selection of promising chemistries before synthesis. Taken together, these methods show how surface modification—supported by explainable machine learning and FAIR data practices—enables a more systematic and accelerated route toward engineering polymer composites with tailored properties.
The ongoing digitalization trend has fostered a significant shift in polymer science and engineering towards increased utilization of digital methods. The integration and reuse of data across materials synthesis, production, characterization, and modeling leads to enhanced innovation. Recognizing the importance of FAIR data principles, OntoFNCT is introduced as an ontology specifically tailored to represent data from full notch creep tests (FNCT) in the interoperable RDF format. FNCT is a method for assessing polymer material behavior under defined stress and environmental conditions. OntoFNCT is aligned with the corresponding ISO 16770 standard and enriches FNCT data with Semantic technologies (ST). Using OntoFNCT, data exchange among stakeholders is facilitated while enhancing speed, precision, and reliability in material evaluation and quality control processes. The integration with higher-level ontologies promotes interoperability and reusability of FNCT data across diverse sources. Additionally, an automated Python-based analysis workflow tailored to FAIR RDF graph data obtained through SPARQL queries was developed to determine FNCT characteristic values. Its usability was successfully demonstrated through its application to real FNCT datasets with correct automated RDF conversion for all test records without data loss and reduced manual analysis time by approximately 60% compared to traditional spreadsheet-based evaluation.
Current recycling methods for polymer matrix composites produce short, unoriented carbon fibers, limiting their use to intermediate‐strength applications. A method is therefore needed to recycle fibers while preserving their original length and orientation, enabling a circular economy for carbon fiber composites. This study proposes a novel hierarchical composite designed to retain fiber length and orientation during recycling. Virgin carbon fibers are encased in an insoluble epoxy matrix to form tapes that act as the primary units of the structure. The primary tape matrix shields the fibers from chemical degradation while preserving their alignment throughout recycling. The tapes are then embedded in a secondary recyclable matrix, Elium, a thermoplastic polymer soluble in acetone with mechanical properties comparable to epoxy. The composite is recycled by dissolving the secondary Elium matrix in acetone and recovering the primary tape units with intact fiber length and orientation. The primary units can then be used to assemble new composites. In this study, hierarchical composite laminates underwent recycling up to three times. Their mechanical properties were assessed after each cycle. Laminates with an Elium secondary matrix retained 60%–90% of the mechanical performance of epoxy‐based laminates. Minimal degradation was observed between cycles, and fiber length, orientation, and volume fraction were fully preserved. Pushout tests confirmed that fibers in the primary tapes were sufficiently shielded during the recycling process. These results validate the feasibility of a hierarchical recyclable composite that combines recyclability with high mechanical performance, serving as a proof of concept and providing opportunities for future development.
Given the high experimental effort required to verify fiber‑reinforced polymer composites (FRP) in aviation, the PROVING project (Production, Optimization, and Virtual Verification for Generative Manufacturing Processes) aims to establish a streamlined and robust verification methodology based on analytical and numerical approaches. As a foundation for this virtual verification process, BAM contributed extensive material testing for parameter identification, feeding directly into the material models and probabilistic methods.
Beyond the experiments, an analytical‑numerical model was developed to more accurately determine the in‑situ stress state within the composite matrix. Since damage initiation in FRP is largely driven by inter-fiber failure, the three‑dimensional matrix stress state is essential for structural verification. In addition to external loading, thermomechanical residual stresses arising from the mismatched thermal expansion of fibers and matrix contribute to the stress state.
Within PROVING, a calculation method was developed that incorporates the thermomechanical behavior of carbon‑fiber‑reinforced polymers (CFRP) into the verification process with minimal experimental effort. The method determines matrix thermal residual stresses using micromechanical modeling combined with finite element analysis.
Im Rahmen des Forschungsvorhabens PROVING wurde eine Methode zur rechnerischen Bestimmung thermomechanischer Eigenspannungen in CFK entwickelt. Ziel ist die Berücksichtigung des thermischen Ausdehnungsverhaltens bei der Bestimmung des dreidimensionalen in-situ-Spannungszustands der Matrix für den strukturellen Nachweis. Die Eigenspannungen werden über mikromechanische Modellierung und FEM berechnet; die zugrunde liegenden Ausdehnungsfunktionen wurden experimentell validiert.
Im Rahmen des Forschungsvorhabens PROVING wurde eine Methode zur rechnerischen Bestimmung thermomechanischer Eigenspannungen in CFK entwickelt. Ziel ist die Berücksichtigung des thermischen Ausdehnungsverhaltens bei der Bestimmung des dreidimensionalen in-situ-Spannungszustands der Matrix für den strukturellen Nachweis. Die Eigenspannungen werden über mikromechanische Modellierung und FEM berechnet; die zugrunde liegenden Ausdehnungsfunktionen wurden experimentell validiert.
The behavior of high‐density polyethylene with respect to resistance against environmental stress cracking (ESC) is usually regarded as an inherent material property being specific for respective types of PE‐HD and tested using standardized methods, conditions, and also standard testing liquids (usually aqueous surfactant solutions). On the other hand, for practical applications the ESC behavior of those polymeric materials, commonly used for pipes or containers, in contact with other liquids (e.g., fuels) is often of relevant interest, but for a reasonable assessment, where consistent benchmark data for a direct comparison are often missing, it is essential to determine the actually prevailing failure mode and classify it related to crack propagation or other mechanisms. Using the well‐established Full Notch Creep Test, which favorably allows for a detailed microscopic fracture surface analysis after failure, the behavior of two typical PE‐HD types for container applications is investigated in biodiesel and diesel and compared to a standard surfactant solution. This enables a clear identification of characteristic features of the interaction of biodiesel and diesel as sorptive fuels in contact with the polymer, revealing the complex interplay of sorption and plasticization as well as ESC inducing effects on PE‐HD, which could be clearly shown for both fuels.
Glass Fiber Reinforced Polymers (GFRPs) are widely used in structural applications but degrade over time due to internal damage. Structural Health Monitoring (SHM) enables early damage detection, improving reliability and reducing maintenance costs. Traditional SHM methods are often invasive and expensive. An emerging solution involves the embedding of carbon‐based filler like carbon nanotubes and reduced graphene oxide into GFRPs, forming conductive networks that detect damage through resistance changes. However, poor adhesion among GF, filler, and matrix can reduce mechanical performance. Therefore, tailoring GF and filler surface chemistry is essential to enhance durability and enable effective self‐sensing properties. This review summarizes the most recent efforts in modifying GF with carbon‐based filler to design GFRP with improved sensing ability and mechanical performance. After a brief introduction on the role of SHM solutions in early damage detection, an overview of the common GF and filler used in GFRPs will be provided. Then, the most relevant GF modification strategies exploited to incorporate carbon‐based filler in GFRPs will be described, focusing on the chemical grafting approach, which allows a careful optimization of the fiber/matrix interface. Last, a concise summary of the key mechanical and electrical tests to evaluate interfacial adhesion and self‐sensing will be supplied.
