No abstract

Piezoelectric vibration-based energy harvesting systems have been used as an interesting alternative power source for actuators and portable devices. These systems have an inherent disadvantage when operating in linear conditions, presenting a maximum power output by matching their resonance frequencies with the ambient source frequencies. Based on that, there is a significant reduction of the output power due to small frequency deviations, resulting in a narrowband harvester system. Nonlinearities have been shown to play an important role in enhancing the harvesting capacity. This work deals with the use of nonsmooth nonlinearities to obtain a broadband harvesting system. A numerical investigation is undertaken considering a single-degree-of-freedom model with a mechanical end-stop. The results show that impacts can strongly modify the system dynamics, resulting in an increased broadband output power harvesting performance and introducing nonlinear effects as dynamical jumps. Nonsmoothness can increase the bandwidth of the harvesting system but, on the other hand, limits the energy capacity due to displacement constraints. A parametric analysis is carried out monitoring the energy capacity, and two main end-stop characteristics are explored: end-stop stiffness and gap. Dynamical analysis using proper nonlinear tools such as Poincaré maps, bifurcation diagrams, and phase spaces is performed together with the analysis of the device output power and efficiency. This offers a deep comprehension of the energy harvesting system, evaluating different possibilities related to complex behaviors such as dynamical jumps, bifurcations, and chaos.

No abstract

Magnetic shape memory alloy is an interesting class of material that offers fast and contactless actuation associated with large deformation. This article deals with a novel constitutive model based on internal variables that describes the phenomenological behavior of magnetic shape memory alloys. Model formulation is developed within the framework of continuum mechanics and thermodynamics defining a mixture free energy potential based on four macroscopic phases. Zeeman effect is considered to incorporate the magnetic behavior. A numerical procedure is proposed to deal with the model nonlinearities. Model predictions are presented for different thermo-magneto-mechanical loadings treating reorientation and phase transformations. Numerical simulations are carried out showing the model capabilities and comparisons with experimental data available in the literature attesting its ability to capture the general thermo-magneto-mechanical behavior of magnetic shape memory alloys.