About the tensile mechanical behaviour of carbon fibers fabrics reinforced thermoplastic composites under very high temperature conditions

International audienc

Mechanical behavior of carbon fibers polyphenylene sulfide composites exposed to radiant heat flux and constant compressive force

International audienceThe thermo-mechanical behavior of carbon/PPS laminates under a constant compressive stress and radiant heat flux has been studied in the case of a quasi-isotropic layup. Though lots of studies focus on the time-to-failure, the present work is aimed at investigating the influence of thermal and mechanisms phenomena on the fire behavior of composite structures. The mechanical response is studied at different scales. From the total macroscopic strain standpoint, the response is divided into three stages, referred to as transient, stationary and failure stages. During these stages, different thermal and mechanical mechanisms compete and prevail depending on the applied compressive stress: thermal and thermo-chemical expansion, decomposition, changes in the mechanical properties, etc. With the measurement of macroscopic thermal strains, the mechanical strain is calculated, enabling the calculation of a macroscopic damage factor describing only the mechanical phenomena. Other quantitative indicators are also used to study the competition between thermally-and mechanically-induced mechanisms: maximal expansion, strain rate, etc. It is shown that under a low compressive force, the thermal expansion is a strain-driven mechanism. Failure is studied at the meso scale. The formation and development of porosities associated with the transition liquid-gas (due to the PPS matrix decomposition) leads to micro-buckling in matrix-rich areas and ultimately , to the formation and propagation in the transverse direction of plastic kink bands. Post-failure observations show that this macroscopic kinking propagates specifically according to the decomposition state of the material

Influence of matrix nature on the post-fire mechanical behaviour of notched polymer-based composite structures for high temperature applications

WOS:000381324200011International audienceThis study aims to investigate the influence of matrix nature (thermosetting - epoxy 914; and thermoplastic - Polyphenylene Sulfide PPS) on the tensile thermo-mechanical behaviour of both notched and unnotched laminates. Depending on variable prior fire-exposures, the purpose was to compare the changes on the residual tensile mechanical properties of carbon fibre reinforced epoxy 914- and PPS based laminates subjected to stress concentration for aeronautical purposes (e.g., at service temperatures higher than glass transition temperature, T-g). With respect to the unnotched laminates, the area of the hole is an open access through the thickness for the heat flux causing more or less thermal degradation (depending on matrix nature) and resulting in variably decreasing the laminate tensile properties. Surprisingly, a low heat flux leads to virtually no decrease in the residual tensile strength of PPS-based laminates; however, in epoxy 914-based composites, the exposure to a low heat flux is more detrimental as exposure time is long. Fractography analyses were performed to investigate damage mechanisms in perforated laminates. The influence of fire-induced damages, the subsequent degradation of the mechanical properties due to fire exposure, combined with the overstresses near the hole all contribute to significantly decrease both stiffness and strength of C/epoxy notched laminates. In notched C/PPS laminates, the fire-induced degradation, resulting from the redistribution of melted PPS matrix within the fibre network, may compete with a relaxation effect in the overstressed 0 degrees carbon fibres in the vicinity of the hole. These competing mechanisms are expected to reduce the influence of fire-exposure on the residual tensile strength of notched CiPPS laminates. (C) 2016 Elsevier Ltd. All rights reserved

Mechanical behavior of carbon fibers polyphenylene sulfide composites exposed to radiant heat flux and constant compressive force

International audienceThe thermo-mechanical behavior of carbon/PPS laminates under a constant compressive stress and radiant heat flux has been studied in the case of a quasi-isotropic layup. Though lots of studies focus on the time-to-failure, the present work is aimed at investigating the influence of thermal and mechanisms phenomena on the fire behavior of composite structures. The mechanical response is studied at different scales. From the total macroscopic strain standpoint, the response is divided into three stages, referred to as transient, stationary and failure stages. During these stages, different thermal and mechanical mechanisms compete and prevail depending on the applied compressive stress: thermal and thermo-chemical expansion, decomposition, changes in the mechanical properties, etc. With the measurement of macroscopic thermal strains, the mechanical strain is calculated, enabling the calculation of a macroscopic damage factor describing only the mechanical phenomena. Other quantitative indicators are also used to study the competition between thermally-and mechanically-induced mechanisms: maximal expansion, strain rate, etc. It is shown that under a low compressive force, the thermal expansion is a strain-driven mechanism. Failure is studied at the meso scale. The formation and development of porosities associated with the transition liquid-gas (due to the PPS matrix decomposition) leads to micro-buckling in matrix-rich areas and ultimately , to the formation and propagation in the transverse direction of plastic kink bands. Post-failure observations show that this macroscopic kinking propagates specifically according to the decomposition state of the material

Influence of matrix nature on the post-fire mechanical behaviour of notched polymer-based composite structures for high temperature applications

WOS:000381324200011International audienceThis study aims to investigate the influence of matrix nature (thermosetting - epoxy 914; and thermoplastic - Polyphenylene Sulfide PPS) on the tensile thermo-mechanical behaviour of both notched and unnotched laminates. Depending on variable prior fire-exposures, the purpose was to compare the changes on the residual tensile mechanical properties of carbon fibre reinforced epoxy 914- and PPS based laminates subjected to stress concentration for aeronautical purposes (e.g., at service temperatures higher than glass transition temperature, T-g). With respect to the unnotched laminates, the area of the hole is an open access through the thickness for the heat flux causing more or less thermal degradation (depending on matrix nature) and resulting in variably decreasing the laminate tensile properties. Surprisingly, a low heat flux leads to virtually no decrease in the residual tensile strength of PPS-based laminates; however, in epoxy 914-based composites, the exposure to a low heat flux is more detrimental as exposure time is long. Fractography analyses were performed to investigate damage mechanisms in perforated laminates. The influence of fire-induced damages, the subsequent degradation of the mechanical properties due to fire exposure, combined with the overstresses near the hole all contribute to significantly decrease both stiffness and strength of C/epoxy notched laminates. In notched C/PPS laminates, the fire-induced degradation, resulting from the redistribution of melted PPS matrix within the fibre network, may compete with a relaxation effect in the overstressed 0 degrees carbon fibres in the vicinity of the hole. These competing mechanisms are expected to reduce the influence of fire-exposure on the residual tensile strength of notched CiPPS laminates. (C) 2016 Elsevier Ltd. All rights reserved

Biallelic CRELD1 variants cause a multisystem syndrome including neurodevelopmental phenotypes, cardiac dysrhythmias, and frequent infections

PURPOSE: We sought to delineate a multisystem disorder caused by recessive CRELD1 variants. METHODS: The impact of CRELD1 variants was characterized through an international collaboration utilizing next generation DNA sequencing, gene knockdown and protein overexpression in Xenopus tropicalis, and in vitro analysis of patient immune cells. RESULTS: Biallelic variants in CRELD1 were found in 18 participants from 14 families. Affected individuals displayed an array of phenotypes involving developmental delay, early-onset epilepsy, and hypotonia, with about half demonstrating cardiac arrhythmias and some experiencing recurrent infections. Most harbored a frameshift in trans with a missense allele, with one recurrent variant, p.(Cys192Tyr), identified in 10 families. X. tropicalis tadpoles with creld1 knockdown displayed developmental defects along with increased susceptibility to induced seizures compared to controls. Additionally, human CRELD1 harboring missense variants from affected individuals had reduced protein function, indicated by a diminished ability to induce craniofacial defects when overexpressed in X. tropicalis. Finally, baseline analyses of peripheral blood mononuclear cells showed similar proportions of immune cell subtypes in patients as compared to healthy donors. CONCLUSION: This patient cohort combined with experimental data provide evidence of a multisystem clinical syndrome mediated by recessive variants in CRELD1.Accepted version (6 month embargo), submitted versionRD&E staff can access the full-text of this article by clicking on the 'Additional Link' above and logging in with NHS OpenAthens if prompted