Intelligent Design of LSI-processed C/SiC Composites with improved nonlinear elastic-damageable behaviour

• Applicant: Professor Dr.-Ing. Dietmar Koch
• Subject Area: Glass, Ceramics and Derived Composites
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545506280

Ceramic fiber composites made of carbon fiber-reinforced silicon carbide (C/SiC) are high-performance materials that can withstand extreme thermal and mechanical conditions and are used in the automotive, aerospace and industrial sectors. The LSI process (Liquid Silicon Infiltration) can be used for their production, which is more recent and less well researched than the better-known CVI process (Chemical Vapor Infiltration). Compared to CVI, the LSI process leads to shorter production times and an almost complete densification of the material, which results in better oxidation resistance and thermal conductivity but lower mechanical performance. The aim is to improve the proportional limit and strength of these composites through a more extended non-linear behavior (i.e. a measurable strain energy before failure). The properties should be preserved at high temperatures (HT). The process-property relationships are also being investigated. The targeted production should make it possible to generate C/SiC composites with improved mechanical behavior. First, the processing is carried out with different parameters: different fiber-preform architectures, fiber/matrix and bundle/matrix bonds, use of LSI or a mixture of CVI and LSI, matrix content between the bundles (i.e. residual silicon and carbon content). Mechanical tests are then performed at RT and HT. The materials are characterized in-situ and at the micro, meso and macro level with fracture mechanics tests. This results in a good understanding of the mechanical material behavior regarding the development of microcrack formation/debonding and the localization of damage. In addition, the crack development resulting from the manufacturing process and the residual stresses are investigated. This project is supported by modeling activities. A first task, which is crucial for increasing the proportionality limit, is the calculation of the thermal residual stresses from the processing step. This requires an appropriate model and precise characteristic values of the components. The second task is to establish a quantitative criterion for the onset of damage, including the influence of the various microstructural and physical parameters investigated. This research subject attracts the attention of several German and French industries. This is the case both for Safran (SiC/BN/SiC composite) and CEA (C/SiC and C/C/SiC composites), which are partners of LCTS. Other companies are also interested, e.g., MBDA for hypersonic applications, Ariane for aerospace applications, SGL/Brembo for braking systems or Schunk for heavy industry.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Cooperation Partner: Professor Gérard Louis Vignoles, Ph.D.