Micro-CT characterization of variability in 3D textile architecture

In the present work, we explore the potential of X-ray micro-computed tomography (X-ray micro CT) to characterize the microstructural variation of four different 3D warp-interlaced fabrics. The accuracy of the technique was determined quantitatively by comparing measured values of yarn thickness, width and spacing between the yarns from X-ray micro CT images with measurements obtained from optical micrographs of the same textile. This comparison indicates that the difference between the two techniques is not statistically significant, lending credence to X-ray micro CT as a means to acquire input for models of textiles and textile composites. Micro-structural variation in a given fabric was found to be quite large (standard deviation of the geometrical parameters up to 16%). A comparison of similar yarns in different directions and fabrics also resulted in large variations. Variability of the fabric parameters is implemented in a "virtual textile" model of 3D fabrics. The influence of the variability of the fabric internal geometry on the mechanical properties of the composite is estimated using a micro-mechanical model.status: publishe

Designing new materials from wheat protein

We recently discovered that wheat gluten could be formed into a tough, plasticlike substance when thiol-terminated, star-branched molecules are incorporated directly into the protein structure. This discovery offers the exciting possibility of developing biodegradable high-performance engineering plastics and composites from renewable resources that are competitive with their synthetic counterparts. Wheat gluten powder is available at a cost of less than $0.5/lb, so if processing costs can be controlled, an inexpensive alternative to synthetic polymers may be possible. In the present work, we demonstrate the ability to toughen an otherwise brittle protein-based material by increasing the yield stress and strain-to-failure, without compromising stiffness. Water absorption results suggest that the cross-link density of the polymer is increased by the presence of the thiol-terminated, star-branched additive in the protein. Size-exclusion high performance liquid chromatography data of molded tri-thiol-modified gluten are consistent with that of a polymer that has been further cross-linked when compared directly with unmodified gluten, handled under identical conditions. Remarkably, the mechanical properties of our gluten formulations stored in ambient conditions were found to improve with time.status: publishe

Carbon fibres reinforced composites. Electrical impedance analysis: a gateway to smartness

International audienceFor more than 7 years, our research work is focussed upon the electrical behavior of carbon fiber reinforced composites. Effectively carbon/polymeric matrix laminates can be considered as an electrically conductive network (i.e. carbon fibers) embedded in an insulating medium (i.e. the polymeric matrix). Consequently, from an electrical point of view laminated composites have been modelled owing to combinations of electrical resistances (i.e. fibers themselves and the contact points between the fibers) and capacitances (i.e. polymeric matrix). During their manufacturing, composite material such as thermoset matrix composites for instance, undergo various changes in their physical (including electrical and mechanical) properties and in their geometrical characteristics. In fact, in the case of manufacturing processes such as oven curing (vacuum bag), autoclave curing or heating plate press, beside the chemo-rheological changes, the laminated parts are the place of a compaction phenomenon inducing changes in fiber volume fraction and thicknesses. The idea developed in this paper is that since the carbon/polymeric matrix laminate can be considered as an electrical network, it can then be view and used as a sensor for following the material state during the manufacturing process enabling thus defects to be detected and this without any additional sensing material or device