CETIM CERMAT and the LPMT have been developing a new kind of active structure
over the past few years: CBCM (controlled behavior composite material). The
CBCM process consists in generating an internal source of heating within the
composite structure and then in using the thermomechanical properties of the
various components in order to deform the material. Carbon yarns are used as the
internal heating source: being connected to a power supply, they are conductive and
provide heating by the Joule effect. In this work, various aspects of the CBCM are
studied by means of model plates. First, the plates and their constitutive layers are
described. Second, the bending properties of the CBCM are presented. Third,
it is shown how the structure can become active. Finally, in order to illustrate
the capacities of this new active composite, a prototype of an aerodynamic flap
integrating CBCM is developed. Experimental and numerical results are compared.
As is well known, the structure of nonwoven fabrics is very complex. They can be considered to be anisotropic porous media [5] that contain two phases: a solid phase (filaments or fibers) and a void phase (the pores). Three scales of this complex structure can be considered: a microscale at the level of the filament diameter (up to 1 mm), a midscale at the level of the yarn (made of several filaments) (a few centimeters), and a macroscale at the level of the planar web (larger than a few tens of centimeters). The nonwoven fibrous network is considered to be a pseudo-random network [11] and as far as this complex structure is considered, its macroscopic properties are always influenced to a greater or lesser degree by the way the fibers are tangled up [11,12]. This indicates that the tensile behavior of nonwovens is complex. 1 Many authors have carried out experiments involving uniaxial tensile tests in order to get one aspect of this behavior [1,2,9,18,16]. Tension versus strain curves classically show an important nonlinear zone and demonstrate significant extensions that nonwoven textiles support before failure.Made of fibers, these textiles are probably subject to numerous phenomena occurring at the scale of fibrous tanAbstract The complex behavior of nonwoven structures can be studied by tensile tests. To understand the influence of mesoscopic phenomena on macroscopic behavior, the whole thermomechanical behavior was considered. During uniaxial tensile tests three parameters were measured: the load, the strain, and the temperature on the surface of the specimen. Mesoscopic phenomena corresponding to a rise of temperature are said to be dissipative. Two nonwoven structures were considered: a needlepunched and a thermo-bonded fabric. The needlepunched structure was quite anisotropic in terms of the strain field as well as the temperature. The dissipative phenomena involved were the anelastic extension of filaments and their failure. The thermo-bonded structure was more isotropic but was also a locked structure. The mechanical behavior was similar in the two directions and a rise of temperature was noticed during the whole test as a consequence of the failure of the bonded points, the anelastic extension, and the failure of filaments.
Glass–fiber‐reinforced polymers were manufactured either through a room temperature thermal curing or under ultraviolet (UV) light from a LED. The thermal system yields high performances when a post‐curing process at 65°C is applied. The photochemical curing leads to a composite in a faster timescale, albeit at the extent of the mechanical properties. It is found that in this case, impregnation and vacuum steps are too fast to allow a good wetting of the fibers, thereby leading to mechanical weaknesses and larger void volume. However, when applying longer vacuum and impregnation steps, the mechanical properties of the photochemically cured sample match the best thermally cured one. As a conclusion, it is shown that photochemical curing of glass–fiber‐reinforced polymer can lead to high performance composite provided that the preparation steps are well controlled.
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