This paper focuses on the morphology evolution in the forming process of unidirectional flax reinforced polypropylene composite laminates. The link between the morphology evolution and thermal conductivity during consolidation stages is investigated. Hot press forming allows to manufacture several composite laminates at different consolidation stages as a function of the compaction thickness. Microscopic evolution of the laminates in terms of morphology and porosity fractions are evaluated by scanning electron microscopy and X-ray microtomography (µ-CT). Hot disk technique is applied to measure the thermal conductivity of the laminates in in-plane and transverse directions. It is found that the in-plane thermal conductivity almost linearly increases with the reduction of porosity fraction. However, the transverse thermal conductivity remained constant. Beside the proposed relations, a theoretical model, based on a two-level Mori-Tanaka homogenization method is proposed. Considering the three-phases material (i.e., porosity, fiber, and polymer matrix), there is a good agreement between the experiment data and model predictions, but limited predictivity for porosity level above 15% certainly due to simplifying assumptions used in the predictive model.
Following the third part of the IPCC report (GIEC, 2022), carbon capture and utilisation of CO2 emitted by fossil fuel represents one of many ways to curb an increasingly alarming global warming. Reaching this goal implies the transition from a fossil fuel dependant and energy-intensive society to a sober and carbon-free one. According to the (ADEME et al., 2020), steam methane reforming, main production path for syngas, still generates 11 kg CO2/kg H2. Countless scientists have already studied different solutions aiming to lower these emissions, including through the design of innovative CO2 recovering processes. Among these solutions, the integration of CO2 within natural gas based methanol (MeOH) production processes appears to be promising (Nami et al., 2019 ; Wang et al., 2021). Contributing to the development of these more sober and sustainable production sectors involves the implementation of innovative conceptual approaches, along with the design of processes with excellent energetic performances. To this end, there has been a growing interest in exergy analysis in the last few years. This technique is able to identify and characterise a process’ thermodynamic inefficiencies, thus assisting the engineer in the development of innovative processes (Dincer and Rosen, 2015; Gourmelon et al., 2017). The COOPERE method (COmbiner Optimisation des ProcédEs, Récupération et analyse Exergétique), developed in the Laboratoire de Génie Chimique de Toulouse (Gourmelon, 2015), lies on the combined use of exergy analysis, a case based reasoning approach (Roldan Reyes, 2012) and pinch analysis. This method enables to design processes as energetically sober as economically viable. In this paper, the latter is applied to a MeOH production process based on natural gas and recovered CO2, described by (Yang et al., 2018).
Infrared welding technology is currently used in the automotive industry to assemble very complex composite shapes made of short glass fiber reinforced polymers. Such applications are targeted more towards short joining times than towards the optimization of adhesive properties. Through this work, the authors joined their efforts on the experimental investigation of driving mechanisms and their optimization, enabling the welding of high-performance materials typically selected for aeronautics applications. The thermal field through the thickness and on the surface was investigated. The best configuration of the LM-PAEK/C laminate presented a single lap shear (SLS) strength of 43.5 MPa with a standard deviation of 0.7 MPa compared to a strength of 24.9 MPa with a standard deviation of 2.3 MPa obtained with the welding configuration without insulation. These results highlight the major effect of a thermal gradient during infrared welding. It is specific to infrared welding to observe that the major resulting defects are located not at the interface area but inside the composite substrate, where voids, generated during the heating step, are unable to be reconsolidated during pressure application. The impact of the decompaction behavior on the thermal gradient was studied through a MATLAB© implemented 1D numerical model, developed internally and called “LysIR”.
Fusion assembly is a highly promising technique for joining thermoplastic composite to thermoset composites, enabling the use of both the most affordable composite material and process for each substructure. However, some major challenges need to be addressed such as functionalizing the thermoset composite surface through co-curing with an appropriate thermoplastic interlayer or realizing a fast and robust welding process that meets all quality and mechanical requirements. In this paper, we investigated the potential of polyetheretherketone (PEEK) and its amorphous (PEEK A) and semicristalline (PEEK SC) states as interlayer materials, co-cured onto thermoset composites. A surface preparation involving the atmospheric plasma process demonstrated that both PEEK state materials can be used as interlayer with favorable adhesion properties. The influence of the plasma treatment on surface properties and morphology was also experimentally characterized.
Fusion assembly is a highly promising technique to join thermoplas- tic to thermoset composites, enabling the use of both the most affordable com- posite material and process for each sub structure.Yet, some major challenges need to be pull through such as the functionalizing of the thermoset compos- ite surface by co-curing an appropriate thermoplastic interlayer or realizing a fast and robust welding process that fulfils all quality and mechanical require- ments. In the present paper, we investigated the potential of Polyetherether- ketone (PEEK) and its amorphous (PEEK A) and semi-cristalline (PEEK SC) states as interlayer materials, co-cured onto the thermoset composite. A surface preparation by atmospheric plasma process demonstrated that both PEEK state materials can be used as interlayer with auspicious resulting ad- hesion properties. The influence of the plasma treatment on surface properties and morphology is also experimentally characterized. An infrared (IR) welding process, barely studied in the literature, is studied to assemble hybrid struc- tural composite. In order to avoid the expected thermal degradation of the thermoset matrix, a dissimilar infrared heating input power is proposed. More- over, to decrease the possible thermal degradation of the thermoset composites during the fusion bonding, a dissimilar infrared welding process have been ex- plored. Single lap shear test and failure mode analysis have been performed to highlight the promising performance of PEI as well as PEEK interlayer based hybrid joint.
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