Compact autonomous power sources are one of the prerequisites for the development of wireless sensor networks. In this work vibration energy harvesting via piezoelectric resonant bimorph beams is studied. The available analytical approaches for the modeling of the coupled electromechanical behavior are critically evaluated and compared with a finite element (FEM) numerical model. The latter is applied to analyze thoroughly the stress and strain states, as well as to evaluate the resulting voltage and charge distributions in the piezoelectric layers. The aim of increasing the specific power generated per unit of scavenger volume is pursued by optimizing the shape of the scavengers. Two optimized trapezoidal configurations are hence identified and analyzed. An experimental set-up for the validation of the proposed numerical model and of the obtained optimized structures is developed. Results of a preliminary experimental assessment, confirming the improved performances of optimized scavengers, are finally given

This paper presents a preliminary investigation on energy harvesting from human walking via piezoelectric vibrating cantilevers. Heel accelerations during human gait are established by correlating data gathered from the literature with direct experimental measurements. All the observed relevant features are synthesized in a typical (standard) acceleration signal, used in subsequent numerical simulations. The transient electromechanical response and the harvested power of a shoe-mounted bimorph cantilever excited by the standard acceleration signal is computed by numerical simulations and compared with measurements on a real prototype. A sensitivity analysis is finally developed to estimate the mean harvested power for a wide range of scavenger configurations. Acceptability criteria based on imposed geometrical constraints and resistance strength limits (e.g. fatigue limit) are also established. This analysis allows a quick preliminary screening of harvesting performance of different scavenger configurations.

In this work, the thermo-mechanical response of fire doors for naval application is considered. In order to evaluate their behaviour, fire doors must undergo a standardized fire test. A realistic simulation of the heating process can be useful during the design phase in order to reduce the number of prototypes to be constructed and tested. In this work, a finite element model is developed with the aim of capturing the qualitative behaviour of the fire door and its supporting frame. Two different types of thermal analysis are considered: (1) transient analysis and (2) steady-state analysis. A non-linear mechanical analysis predicts the displacement field that occurs at the end of the heating phase. The adopted model is validated through a comparison with experimental measurements obtained during standard fire tests, confirming that the proposed approach can be a valid tool for the prediction of the thermo-mechanical performance of a naval fire door. © The Author(s) 2015

The behavior of thermo-mechanical stresses in functionally graded axisymmetric rotating hollow disks with variable thickness is analyzed. The material is assumed to be functionally graded in the radial direction. First, a two-dimensional axisymmetric model of the functionally graded rotating disk is developed using the finite element method. Exact solutions for stresses are then obtained assuming that the plane theory of elasticity holds. These solutions are in accordance with finite element ones, thus showing the validity of the assumption. Finally, in order to reduce the maximum equivalent stress along the radius, the optimization of the material distribution is addressed. To avoid subsequent finite element simulations in the optimization process, which can be computationally demanding, a nonlinear constrained optimization problem is proposed, for which the solution is obtained numerically by the sequential quadratic programming method, showing prominent results in terms of equivalent stress uniformity.

Usually the design of fire doors is carried out to fulfil thermal requirements only, whereas also thermal distortion could significantly affect the safety behavior of the door. Indeed, the door tends to bend away from its supporting frame due to a non-uniform temperature distribution, which could lead to flame and smoke propagation. In this work an innovative design scheme is proposed, where the mechanical response of the door is enhanced without affecting its insulating properties. This improvement is achieved by changing the disposition of the constitutive elements (insulating material and structural plates). The behavior of a conventional and of an innovative door during a fire test was simulated with three-dimensional (3D) finite element models. A non-linear thermo-mechanical transient analysis was performed as well. The numerical results were validated with an experimental campaign made on true scale specimens, where the doors were heated by a furnace reaching a maximum temperature of 950°C. The temperature distribution was measured with several thermocouples and an infrared camera, whereas displacements were monitored with a laser sensor. It was observed that, while temperatures on the unexposed surface were around 120°C in both cases, the maximum out-of-plane displacement measured in the innovative door was 3 times smaller than that of the conventional configuration. © 2017 Springer Science+Business Media New Yor