Resposta à flexão e análise de tenacidade de argamassas reforçadas com fibra de Curauá

O desenvolvimento e comercialização de materiais compósitos produzidos a partir de fibras naturais são considerados extremamente importante, uma vez que essas fibras reduzirão a dependência dos materiais produzidos com recursos não renováveis. Dentre essas fibras naturais destaca-se a fibra do curauá, sua utilização na produção de compósitos melhora de forma notável as propriedades do conjunto fibra matriz, logo o presente artigo objetiva estudar as propriedades mecânicas de compósitos reforçados com fibra de curauá, em especial sua resistência à flexão e tenacidade. Para isso foram confeccionadas cinco famílias de argamassas, uma de referência sem utilização da fibra e as outras quatro reforçada com fibra variando o comprimento da fibra e sua fração volumétrica. Verificou-se que a fibra do curauá ao ser adicionada em matriz cimentícia melhora suas propriedades mecânicas comparada a um compósito não reforçado com fibra, sua deformação, resistência à flexão e tenacidade são melhoradas

Improved high gain observer design for a class of disturbed nonlinear systems

International audienceAbstract This paper provides a redesigned version of the Standard High Gain Observer (SHGO) to cope with the peaking phenomenon occurring during the transient periods as well as the sensitivity to high frequency measurement noise. The observer design is performed for a class of uniformly observable systems with noise free as well as noisy output measurements and the resulting observer is referred to as Non Peaking Filtered High Gain Observer (NPFHGO). The NPFHGO shares the same structure as its underlying SHGO and differs only by its corrective term which is still parameterized by a unique positive scalar up to an appropriate expression involving nested saturations. Of a fundamental interest, the power of the scalar parameter does not exceed one unlike in the case of the SHGO where this power grows from 1 to the system dimension. Moreover, it is shown that the equations of the NPFHGO become identical to those of the SHGO after a transient time horizon that can made arbitrarily small for sufficiently high values of the design parameter. A particular emphasis is put on the case of systems with noisy output measurements. It is shown how a multiple integrator of the corrupted outputs can be cascaded with the original system leading to an augmented system included in the class of systems for which the NPFHGO has been designed. The performance and main properties of the NPFHGO are highlighted and compared to those of its underlying SHGO through simulation results involving a single link robot arm system

Physicochemical and Mechanical Performances of Technical Flax Fibers and Biobased Composite Material: Effects of Flax Transformation Process

International audienceIn France, the use of flax fibers as reinforcement in composite materials is growing exponentially in the automotive sector, thanks to their good physicochemical properties, environmental reasons, health neutrality and due to the European Council Directives on the reuse, recycling and valorization of car components and materials. The aim of our study is to investigate biochemical, physicochemical, and mechanical properties of technical flax fibers to evaluate the impact of transformation processes (scutching, hackling, and homogenization) on final properties of associated composite materials. Different chemical analysis such as Van Soest (biochemical fraction measurement), FTIR (Fourier Transform InfraRed spectroscopy), and XRD (X-ray diffraction) were carried out on different process modalities and show that there is no significant difference in terms of biochemical fraction and crystallinity index. By the same token, mechanical behavior shows that Young's modulus is not affected by the transformation process. This result is also observed for thermal behavior. The results highlight the fact that the transformation processes of technical fibers do not really affect their physicochemical and mechanical performances

Design of doum palm fibers biocomposites by Reactor/elongational flow MiXer: Evaluation of morphological, mechanical, and microstructural performances

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