Coupled thermo-mechanics of single-wall carbon nanotubes

The temperature-dependent transverse mechanical properties of single-walled nanotubes are studied using a molecular mechanics approach. The stretching and bond angle force constants describing the mechanical behaviour of the sp^{2} bonds are resolved in the temperature range between 0 K and 1600 K, allowing to identify a temperature dependence of the nanotubes wall thickness. We observe a decrease of the stiffness properties (axial and shear Young's modulus) with increasing temperatures, and an augmentation of the transverse Poisson's ratio, with magnitudes depending on the chirality of the nanotube. Our closed-form predictions compare well with existing Molecular Dynamics simulations.Comment: 15 pages, 4 figures. Accepted for Applied Physics Letter

Two-dimensional graded metamaterials with auxetic rectangular perforations

This work describes the in-plane uniaxial tensile mechanical properties of two-dimensional graded rectangular perforations metamaterials using numerical homogenization finite element approaches benchmarked by experimental results. The metamaterial configuration is based on graded patterns of centre-symmetric perforated cells that can exhibit an auxetic (negative Poisson's ratio) behavior. Global and local equivalent mechanical properties of the metamaterial are measured using digital image correlation techniques mapped over Finite Element models to identify strain patterns and related stress distributions at different scales. The samples and their numerical counterpart are parametrized against the spacing and aspect ratios of the cells. The overall stiffness behavior of the graded perforated metamaterial plates features a higher degree of compliance that depends both on the geometries of the cells of the graded areas, but also on the graded pattern used. Local Poisson's ratio effects show a general constraint of the auxetic behavior compared to the case of uniform plates, but also interesting and controllable shape changes due to the uniaxial tensile loading applied

Ageing of autoclaved epoxy/flax composites:effects on water absorption, porosity and flexural behaviour

International audienceThis work investigates the effects of ageing on autoclaved composites made with unidirectional prepreg epoxy and flax tape in environments with 50% and 100% of relative humidity. A Design of Experiment (DoE) has been used first to determine the effect of the ageing time (0,2, 4, 6, 8 and 16 days), type of bending (3-point and 4-point bending) and fibre orientation (longitudinal and transverse) on the water absorption and flexural properties of 50% saturated composites. A second experiment at 100% humidity has been also performed to further characterise the composites and to identify the equivalent ageing time that provides the mechanical behaviour of the 50% humidity samples after sixteen days. The water absorption and apparent porosity levels increase progressively with the ageing time, in particular for the case of transverse laminates; these features compromise the flexural properties of the composites. The laminates subjected to 4-point bending showed increased water absorption levels and improved flexural properties compared to the samples under 3-point bending. The flexural properties of flax composites at 50% humidity after 16 days are equivalent to those shown by composites immersed in water for less than one day

Static, fatigue and impact behaviour of an autoclaved flax fibre reinforced composite for aerospace engineering

International audienceThis work describes the physical and mechanical characterization of unidirectional [0]12 and crossply [(0/90)3/]S flax fibre reinforced composites fabricated in autoclave using a prepreg flax tape impregnated with fire retardant epoxy polymer. Tensile, bending and impact properties are evaluated along the longitudinal and transverse fibre directions. The tensile-tensile fatigue behaviour is characterised along the fibre direction. Physical and specific properties are also assessed to identify the potential characteristics of these bio-based composites for lightweight and secondary loadbearing applications. The robust manufacturing process described in this work, coupled with precision laser cutting, makes this type of composite a promising sustainable material for aircraft, transport and lightweight construction designs