On the influence of matrix and reinforcement nature on the quasi-static mechanical properties of composite materials in cryogenic environments – An experimental study
Topic(s) : Special Sessions
Co-authors :
Suzanne LAIK (FRANCE), Louis MAKSOUD (FRANCE), Vivien ANDREAbstract :
Composite materials are increasingly used in cryogenic applications due to their properties such as low thermal conductivity and high specific strength as compared to metals. A right selection of fibers and matrix materials can achieve optimal combinations of lightweight design, durability, mechanical strength, low thermal conductivity and low thermal contraction. However, they may experience internal damage due to complex internal stress states induced by large thermal gradients between processing temperature and operation cryogenic temperatures (CT), enhanced by the material strong anisotropy.
Due to the wide offer of matrix/reinforcement combinations and the discrepancy of cryogenic testing means and methods, the evolution of mechanical properties at CT is not fully covered, especially for thermoplastic composites. While there is a general debate on whether design based on room-temperature (RT) mechanical properties could be applied at CT as a conservative approach, the influence of material constituent nature and shape on the highly-anisotropic and complex composite properties at these cryogenic temperatures still requires investigation.
The present study aims at i) evaluating the influence of matrix type and reinforcement nature and shape, on cryogenic behaviour based on defined discriminatory properties ; ii) performing quasi-static characterization of a down-selected material over the temperature range (RT, -162°C and -253°C), requiring specific testing features and tools development. Toughened epoxy and PEI-based materials were supplied and tested, either UD or fabric with carbon (CF) or glass fibre (GF) references. A first screening phase was performed based on interlaminar shear testing (ILSS) and 0°-compression at RT, -162°C and after thermal cycling. Post-mortem fractographic study was conducted on the specimens.
PEI-based materials, whatever the reinforcement type, show an increase or a conservation of their performances from RT to CT. For both matrix types, CF UD laminates show the greatest increase, both in matrix- and fiber-governed properties. Fabric materials show mitigated results; they retain or increase their properties at CT for PEI references but lose up to 17% in ILSS for epoxy references. The applied thermal cycling does not appear to influence significantly the evaluated properties.
Therefore, the PEI/CF UD is selected for characterization. Tensile, compression, in-plane shear and ILSS is conducted over the temperature range. While the fiber-governed stiffnesses do not evolve between RT and -162°C, all the other properties (matrix-dominated stiffnesses, and failure properties) increase at CT. Nevertheless, further investigations of the damage-sensitivity of the material in thermal and/or mechanical fatigue on multi-directional lay-ups shall be conducted for the sake of design safety over the service life of targeted applications.
Due to the wide offer of matrix/reinforcement combinations and the discrepancy of cryogenic testing means and methods, the evolution of mechanical properties at CT is not fully covered, especially for thermoplastic composites. While there is a general debate on whether design based on room-temperature (RT) mechanical properties could be applied at CT as a conservative approach, the influence of material constituent nature and shape on the highly-anisotropic and complex composite properties at these cryogenic temperatures still requires investigation.
The present study aims at i) evaluating the influence of matrix type and reinforcement nature and shape, on cryogenic behaviour based on defined discriminatory properties ; ii) performing quasi-static characterization of a down-selected material over the temperature range (RT, -162°C and -253°C), requiring specific testing features and tools development. Toughened epoxy and PEI-based materials were supplied and tested, either UD or fabric with carbon (CF) or glass fibre (GF) references. A first screening phase was performed based on interlaminar shear testing (ILSS) and 0°-compression at RT, -162°C and after thermal cycling. Post-mortem fractographic study was conducted on the specimens.
PEI-based materials, whatever the reinforcement type, show an increase or a conservation of their performances from RT to CT. For both matrix types, CF UD laminates show the greatest increase, both in matrix- and fiber-governed properties. Fabric materials show mitigated results; they retain or increase their properties at CT for PEI references but lose up to 17% in ILSS for epoxy references. The applied thermal cycling does not appear to influence significantly the evaluated properties.
Therefore, the PEI/CF UD is selected for characterization. Tensile, compression, in-plane shear and ILSS is conducted over the temperature range. While the fiber-governed stiffnesses do not evolve between RT and -162°C, all the other properties (matrix-dominated stiffnesses, and failure properties) increase at CT. Nevertheless, further investigations of the damage-sensitivity of the material in thermal and/or mechanical fatigue on multi-directional lay-ups shall be conducted for the sake of design safety over the service life of targeted applications.