International audienceThis paper investigates experimentally the quasi-static and dynamic torsional behaviour of shape memory alloys wires under cyclic loading. A specifically designed torsional pendulum made of a Ni–Ti wire is described. Results on the quasi-static behaviour of the wire obtained using this setup are presented, giving an overall view of the damping capacity of the material as function of the amplitude of the loading (imposed torsional angle), the frequency and the temperature. The dynamical behaviour is then presented through measured frequency response function between forcing angle at the top of the pendulum and the difference between top and bottom rotation angles in the vicinity of the first eigenfrequency of the wire, i.e. in the range [0.3 Hz, 1 Hz]. The softening-type non-linearity and its subsequent jump phenomenon, predicted theorically by the decrease of the effective stiffness when martensite transformation starts is clearly evidenced and analysed

International audienceThe non-linear dynamic thermomechanical behaviour of superelastic shape memory alloys is investigated. To this end, the Zaki-Moumni model, initially developed for quasi-static loading cases, is extended to simulate the uniaxial forced oscillations of a shape memory alloy device. First, the influence of loading rate is accounted for by considering the thermomechanical coupling in the behaviour of NiTi shape memory alloy. Comparisons between simulations and experimental results show good agreement. Then, the forced response of a shape memory alloy device is investigated at resonance. Both isothermal and non-isothermal conditions are studied, as well as non-symmetric tensile-compressive restoring force. In the case of large values of forcing amplitudes, simulation results show that the dynamic response is prone to jumps, bifurcations and chaotic solutions

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To meet the growing demand for the use of environmentally and friendly materials in various applications, many efforts have been done in order to provide lighweighting, biodegradable, and renewable composites leading to a diminution of greenhouse gas emissions. However, they are confronting some challenges that may limit their utilization in industries such as poor interfacial adherence, high moisture absorption, low processing temperature, and impact strength. Several research works have been carried out regarding the mechanical, thermal, and hydric properties of natural fibers reinforced composites to deal with above underlined drawbacks. Actually, based on our analysis, there are two relevant concerns that prevent their integration in other industries such as marine and renewable energy sectors. In this context, the current critical review offers an up to date overview of the factors influencing the properties of the different components of natural fibers composites (fiber, matrix, fiber/matrix interface) as well as their physicochemical, mechanical, thermal and hydric behaviors. Recent works on the mechanical properties of nanobiocomposites based on cellulosic fibers, crystals, and nano-clay fillers are reviewed. The future directions are also discussed to overcome the challenges confronted by these materials, that is, fire resistance and moisture absorption, in order to widespread their utilization especially for wet and fire retardant purposes.