Paolo Ermanni

Broadband vibration energy harvesting based on cantilevered piezoelectric bi-stable composites

Bi-stable composites are considered for vibration based energy harvesting, thanks to the broadband nature of their dynamic response. In this letter, a cantilevered piezoelectric bi-stable composite concept is introduced for broadband energy harvesting. The proposed configuration allows for exploiting the large strains developed close to the clamped root, significantly enhancing the harvesting effectiveness in comparison to previous settings. A simple model is used for designing the dynamic response aiming to maximise broadband oscillations. Experimental results reveal wide bands of high power conversion. Additionally, a shunting circuit suitable for broadband conversion is employed, further increasing the effectiveness of the proposed concept.

Aero-Structural Optimization of Morphing Airfoils for Adaptive Wings

The design of an airfoil structure involves the disciplines of aerodynamics and structural mechanics, both of which are considered in the design methodology presented in this article. The approach described in this article starts from a requirement formulation based on a time-series of spanwise lift distributions on a morphing wing, representing the mission profile of the aircraft as a whole. This allows to specify goals based directly on aerodynamic performances instead of prescribing fixed geometrical shapes. Using the aero-structural analysis tool presented here, together with a parametrization representing the airfoil outer shape as well as its mechanical properties, allows the formulation of a combined aero-structural optimization problem. Promising aerodynamic and structural morphing performances have been obtained by applying the method to a morphing concept using Dielectric Elastomers (DEs) as actuators. Although the coupled physics are considered and a detailed material model has been used, results can be obtained within reasonable computational time by parallel evaluation of the candidate solutions. Improved aerodynamic performances have been obtained using this concurrent coupled method, in comparison to a sequential aerodynamic and structural optimization.

Measurement of insulating and dielectric properties of acrylic elastomer membranes at high electric fields

This work reports on the investigation of VHB 4910 acrylic elastomer insulating and dielectric properties. This material is widely exploited for the realization of actuators with large deformations, dielectric elastomer actuators (DEA), and belongs to the group of so-called electroactive polymers (EAP). Extensive investigations concerning its mechanical properties are available in literature while its electric behavior at working conditions has not received the same level of attention. In this work, the relative permittivity and the volume resistivity have been measured on VHB 4910 membranes under different fixed stretch conditions (λ1, λ2 = 3, 3.6, 4, 5) using circular gold electrodes sputtered onto both sides of the specimens. The measured values of relative permittivity are in fairly good agreement with the results previously published by other groups. The volume resistivity, at field values close to the operational ones, has shown a field-dependent behavior revealing dissipative properties that should...

Structural Vibration Control via R-L Shunted Active Fiber Composites

This article presents a successful extension of passive R-L shunt damping to piezoelectric ceramic elements working in direct 3-3 mode and a performance comparison to elements working in indirect 3-1 mode. A new circuit topology is implemented to synthesize the very large inductances required by the low inherent piezoelectric device capacitance at relatively low frequencies. This allows for efficient tuning of the R-L circuit to the structure resonance frequency to be damped. The vibration suppression performance of monolithic piezoelectric ceramic actuators and active fiber composites is compared in this study. For this purpose, different actuators are bonded on aluminum cantilever plates. An integrated FE model is implemented for the prediction of structure resonance frequencies, optimum values for electric components, and the resulting vibration suppression performance. The passive structure, bonded active patch, and shunted electrical network are analyzed within the same FE model. Active fiber composite patches working in the direct 3-3 mode show equivalent specific damping performance compared to conventional monolithic 3-1 actuated patches. Issues related to the sensitivity of R-L shunts to variations in environmental and operational conditions are discussed in this study. In short, monolithic actuators operating on the 3-1 piezoelectric effect seem to be the best for use in R-L shunting.

Thermal Phenomena in Fiber-reinforced Thermoplastic Tape Winding Process: Computational Simulations and Experimental Validations

This paper presents experimentally validated three-dimensional transient simulations of the thermal phenomena of the tape winding process, as well as a method to determine separately the heat transfer between the hot gas originating from a torch and the composite material. The computational model predicts the temperature of the incoming tape and the substrate during the winding process. Each numerical simulation is based on an explicit time integration scheme and covers the duration of the process. The simulation within each time step employs a steady-state model. This method takes into account the cyclic nonuniform heating of the material and the effect of the growing mass. The comparison of the simulation results with the experimental data shows good agreements. The experiments were performed with preconsolidated glass fiber-reinforced polypropylene tapes. The measurements were performed with infrared pyrometry. This technique can handle moving points during the entire process, and is nonintrusive.

Controlling Phase Distributions in Macroporous Composite Materials through Particle-Stabilized Foams

Aqueous foams stabilized by ceramic and thermoplastic polymeric particles provide a general method for producing novel porous materials because their extraordinary stability against disproportionation and drainage allows them to be dried and sintered into solid materials. Here, we report the different microstructures that can be obtained from liquid foams stabilized by binary mixtures of particles when the interfacial energies between the particles and the air-liquid interfaces are manipulated to promote either preferential or competitive self-assembly of the particles at the foam interface. Modification of the interfacial energies was accomplished through surface modification of the particles or by decreasing the surface tension of the aqueous phase. Materials derived from liquid foams stabilized by poly(vinylidene fluoride) (PVDF) and alumina (Al(2)O(3)) particles are investigated. However, as is shown, the method can be extended to other polymeric and ceramic particles and provides the possibility to manufacture a wide range of porous composite materials.

Aero-Structural Optimization of Three-Dimensional Adaptive Wings with Embedded Smart Actuators

The design of morphing wings involves the disciplines of aerodynamics and structural mechanics; the aero-structural coupling is of chief importance in case smart materials are used as distributed actuators. Considering these specific requirements, this paper presents an approach to optimize concurrently the variables describing the wing external shape, the internal compliant structure, and the embedded actuators. An aeroelastic analysis tool is developed to simulate the response of distributed compliance three-dimensional wings, considering the activation of the smart materials. A method to formulate the optimization requirements based on the aircraft mission is presented, using the aerodynamic performance from the aeroelastic study in the optimization goal. To prove the validity and the computational feasibility of this methodology, a morphing wing for a 3-m-wingspan radio-controlled plane is optimized. A structural concept actuated by single crystal Macro Fiber Composites and dielectric elastomers is in...

Designing macroporous polymers from particle-stabilized foams

Particle-stabilized liquid foams provide a general route for producing low-density macroporous materials from melt-processable and intractable thermoplastic polymers. In this paper, we demonstrate how these liquid foams can be used to design macroporous polymers with tailored microstructures and properties by adjusting the various processing parameters. By varying the size, concentration, and wettability of the particles in the colloidal suspensions and controlling the frothing, drying, and sintering conditions, macroporous materials with porosities between 33 and 95% and median pore sizes (D50) between 13 and 634 μm were obtained. This foaming process is applicable to a wide range of hydrophobic materials and is demonstrated here on commercially available polymeric powders of poly(tetrafluoroethylene) (PTFE), poly(vinylidene fluoride) (PVDF), poly(ether imide) (PEI), and poly(ether ether ketone) (PEEK).

Passive damping of composite blades using embedded piezoelectric modules or shape memory alloy wires: a comparative study

Emission reduction from civil aviation has been intensively addressed in the scientific community in recent years. The combined use of novel aircraft engine architectures such as open rotor engines and lightweight materials offer the potential for fuel savings, which could contribute significantly in reaching gas emissions targets, but suffer from vibration and noise issues. We investigated the potential improvement of mechanical damping of open rotor composite fan blades by comparing two integrated passive damping systems: shape memory alloy wires and piezoelectric shunt circuits. Passive damping concepts were first validated on carbon fibre reinforced epoxy composite plates and then implemented in a 1:5 model of an open rotor blade manufactured by resin transfer moulding (RTM). A two-step process was proposed for the structural integration of the damping devices into a full composite fan blade. Forced vibration measurements of the plates and blade prototypes quantified the efficiency of both approaches, and their related weight penalty.

Linear direct current sensing system for flow monitoring in Liquid Composite Moulding

Direct Current (DC) resistance measurement is a well-established technique for monitoring Liquid Composite Moulding (LCM) processes. Through on-line resistance measurement of the sensing gap between two crossing wires (i.e. at a node), it is possible to determine the presence of resin and the degree of curing at the node location. Linear Direct Current (LDC) measurement as presented in this paper is based on the same physical principle. The main advantage of the LDC method is that the flow front position can be tracked along the entire length of two contiguous wires and not only at discrete node locations. Preliminary measurements were conducted in a 1D flow channel to quantify the sensitivity of the LDC sensing technique and to optimise the experimental set-up. Evaluation criteria include the qualitative comparison of results of visual and LDC monitoring systems with regard to position and shape of the flow front and permeability characterisation. Permeability of the fibre lay-up in the flow channel was determined using output data from the LDC measurement and with conventional methods based on video capture of the flow front position. Comparison of the results shows a difference of between KLDC and Kvisual which corresponds to a relative difference of 0.45%. The second part of the paper deals with the improvement of measurement accuracy and data handling. A software was developed to display the 2D flow front position based on the information provided by the LDC system. This study has shown the potential of the technique for monitoring LCM injection processes. Next step will include the application of LDC technology in an industrial environment to support the fabrication of complex-shaped 3D structures.