Escaping the Ashby limit for mechanical damping/stiffness trade-off using a constrained high internal friction interfacial layer.

The development of new materials with reduced noise and vibration levels is an active area of research due to concerns in various aspects of environmental noise pollution and its effects on health. Excessive vibrations also reduce the service live of the structures and limit the fields of their utilization. In oscillations, the viscoelastic moduli of a material are complex and it is their loss part - the product of the stiffness part and loss tangent - that is commonly viewed as a figure of merit in noise and vibration damping applications. The stiffness modulus and loss tangent are usually mutually exclusive properties so it is a technological challenge to develop materials that simultaneously combine high stiffness and high loss. Here we achieve this rare balance of properties by filling a solid polymer matrix with rigid inorganic spheres coated by a sub-micron layer of a viscoelastic material with a high level of internal friction. We demonstrate that this combination can be experimentally realised and that the analytically predicted behaviour is closely reproduced, thereby escaping the often termed 'Ashby' limit for mechanical stiffness/damping trade-off and offering a new route for manufacturing advanced composite structures with markedly reduced noise and vibration levels

P2X7 receptor: Death or life?

The P2X7 plasma membrane receptor is an intriguing molecule that is endowed with the ability to kill cells, as well as to activate many responses and even stimulate proliferation. Here, the authors give an overview on the multiplicity and complexity of P2X7-mediated responses, discussing recent information on this receptor. Particular attention has been paid to early and late signs of apoptosis and necrosis linked to activation of the receptor and to the emerging field of P2X7 function in carcinogenesis

In-situ, microscale characterization of heterogeneous deformation around notch in martensitic Shape Memory Alloy

Deformation characterization of low-symmetry phases such as martensite in SMAs is challenging due to a fine-scale hierarchical microstructure. Using X-ray microLaue diffraction, in-situ deformation of martensite is examined in a notched NiTi specimen. The local deformation is influenced by the notch stress field, initial martensite microstructure, and interaction between notch stress field and the external load. The microstructure evolves heterogeneously and inelastically, with detwinning and twin nucleation occurring simultaneously through loading. These results contrast with the traditional view of martensite deformation that is partitioned in three distinct regimes: elasticity, reorientation and de-twinning

Study of Different Modelling Techniques of SMA Actuator and Their Validation Through Simulation

With the increased emphasis on both reliability and functionality, shape memory alloys (SMAs) are fast becoming an enabling technology capturing the attention of engineers and scientists worldwide. The thermal-electrical-mechanical dynamics of SMA are nonlinear and hysteretic in nature, possessing a problem for the researchers to model the actuator. The increased range of applications and better realisation of SMA actuators have led to the research on modelling of SMA’s thermo-mechanical response. The paper discusses various SMA actuator modelling approaches such as Preisach model, Fermi–Dirac statistics, Duhem hysteresis model and Brinson model and attempts to elucidate their advantages and limitations through Simulink-based models and simulation results

Nonlinear dynamic model and simulation of morphing wing profile actuated by shape memory alloys

Morphing aircraft have the ability to actively adapt and change their shape to achieve different missions efficiently. The development of morphing structures is deeply related with the ability to model precisely different designs in order to evaluate its characteristics. This paper addresses the dynamic modeling of a sectioned wing profile (morphing airfoil) connected by rotational joints (hinges). In this proposal, a pair of shape memory alloy (SMA) wires are connected to subsequent sections providing torque by reducing its length (changing airfoil camber). The dynamic model of the structure is presented for one pair of sections considering the system with one degree of freedom. The motion equations are solved using numerical techniques due the nonlinearities of the model. The numerical results are compared with experimental data and a discussion of how good this approach captures the physical phenomena associated with this problem. © The Society for Experimental Mechanics, Inc. 2012