Formation of thermally-induced crack patterns in anisotropic, fiber- reinforced composites with a brittle matrix

• Applicants: Privatdozent Dr. Michael Fleck; Professor Dr.-Ing. Walter Krenkel
• Subject Area: Glass, Ceramics and Derived Composites ; Materials in Sintering Processes and Generative Manufacturing Processes ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 431968427

• Final Report Year: 2024

Final Report Abstract

In the course of the project, the curing and pyrolysis behavior as well as fracture mechanical and thermal properties of various phenolic resin systems and composites were characterized. Crosslinking kinetics, carbon residue and pyrolysis reactions are linked to the curing agent content via the resulting polymer structure. The fracture toughness of the composites decreases due to the increasing ceramization of the matrix during pyrolysis, which favors crack initiation when pyrolysis of the matrix begins. Shrinkage of the materials is almost completely hindered by the fiber reinforcement in the respective reinforcement directions. The resulting stresses, together with the decreasing fracture toughness, lead to characteristic interlaminar matrix cracks. The morphology of the crack pattern is characterized by the fiber reinforcement and fiber-matrix bond strength. All resulting crack patterns were characterized with respect to the interlaminar crack spacing and the corresponding crack width with a very high number of measuring points. By in-situ heating cell experiments, the crack initiation in the fiber bundle and the crack propagation into the matrix could be shown directly. The thermal and (fracture) mechanical parameters could be integrated as direct input parameters into newly developed phase field simulation models. The crack morphologies, crack growth and stress fields predicted by simulation models could be directly verified by experiments and represent a valuable tool for future research in the field of thermally induced cracking for different material classes.

Publications

• Phase-Field Modeling of Precipitation Microstructure Evolution in Multicomponent Alloys During Industrial Heat Treatments. Lecture Notes in Mechanical Engineering, 70-78. Springer International Publishing.
  Fleck, Michael; Schleifer, Felix; Holzinger, Markus; Lin, Yueh-Yu & Glatzel, Uwe
  
• Quantitative Shape-Classification of Misfitting Precipitates during Cubic to Tetragonal Transformations: Phase-Field Simulations and Experiments. Materials, 14(6), 1373.
  Lin, Yueh-Yu; Schleifer, Felix; Holzinger, Markus; Ta, Na; Skrotzki, Birgit; Darvishi, Kamachali Reza; Glatzel, Uwe & Fleck, Michael
  
• Simulation of the θ′ Precipitation Process with Interfacial Anisotropy Effects in Al-Cu Alloys. Materials, 14(5), 1280.
  Ta, Na; Bilal, Muhammad Umer; Häusler, Ines; Saxena, Alaukik; Lin, Yueh-Yu; Schleifer, Felix; Fleck, Michael; Glatzel, Uwe; Skrotzki, Birgit & Darvishi, Kamachali Reza
  
• Consistent Quantification of Precipitate Shapes and Sizes in Two and Three Dimensions Using Central Moments. Integrating Materials and Manufacturing Innovation, 11(2), 159-171.
  Schleifer, Felix; Müller, Moritz; Lin, Yueh-Yu; Holzinger, Markus; Glatzel, Uwe & Fleck, Michael
  
• Frictionless Motion of Diffuse Interfaces by Sharp Phase-Field Modeling. Crystals, 12(10), 1496.
  Fleck, Michael; Schleifer, Felix & Zimbrod, Patrick
  
• On diffuse interface modeling with super efficient spatial resolutions. European Mechanics of Materials Conference 18, Oxford, UK, 04.04.2022 (2022)
  M. Fleck & F. Schleifer
  
• Reactivity, pyrolysis, mass-loss kinetics and carbon residue of phenol-formaldehyde resins with different hexa-contents. Ceramics in Europe, 10. – 14.07.2022, Krakau, Polen (European Ceramic Society, ECerS) (2022)
  F. Wich, N. Langhof, W. Krenkel & S. Schafföner
  
• Sharp phase-field modeling of isotropic solidification with a super efficient spatial resolution. Engineering with Computers, 39(3), 1699-1709.
  Fleck, Michael & Schleifer, Felix
  
• Sharp phase-field modeling of isotropic solidification with a super efficient spatial resolution. Multiscale Materials Modeling 10, 02.-07.10.2022 Baltimore, MD, USA (2022)
  M. Fleck & F. Schleifer
  
• The Elastic Effect of Evolving Precipitate Shapes on the Ripening Kinetics of Tetragonal Phases. Metallurgical and Materials Transactions A, 54(5), 1843-1856.
  Schleifer, Felix; Lin, Yueh-Yu; Glatzel, Uwe & Fleck, Michael
  
• Crack pattern evolution during the pyrolysis of unidirectional fiber reinforced ceramic matrix composites. XVIII ECers, 02. – 06.07.2023, Lyon, Frankreich (European Ceramic Society, ECerS) (2023)
  F. Wich, M. Moos, N. Langhof, W. Krenkel & S. Schafföner
  
• Influence of fibre volume content, reinforcement architecture and fibre orientation on the thermally induced crack pattern of C/C-composites - An experimental and statistical investigation. 11th International Conference on High Temperature Ceramic Matrix Composites (HT-CMC), 27. – 31.08.2023, Jeju, Südkorea (2023)
  F. Wich, M. Moos, N. Langhof, W. Krenkel & S. Schafföner
  
• Influence of hexa on crosslinking and pyrolysis of novolak resins applied as carbon precursors for cmc. Indo-German workshop on recent advances in polymer/precursor derived ceramics: Bridging the boundaries and catalysing translational research (PDC-IT), 6. – 10.03.2023, Chennai, Indien (IGSTC) (2023)
  F. Wich, C. Sitzmann, N. Langhof, W. Krenkel & S. Schafföner
  
• Processing properties and pyrolysis behavior of novolak-hexamethylenetetramine mixtures. Advanced Manufacturing: Polymer & Composites Science, 9(1).
  Wich, Felix; Flauder, Stefan; Schneider, Natalie; Fleck, Michael; Langhof, Nico; Krenkel, Walter & Schafföner, Stefan