Loading...
31 results
Search Results
Now showing 1 - 10 of 31
- High deformation multifunctional composites: materials, processes, and applicationsPublication . Costa, Pedro; Nunes-Pereira, João; Rial Tubio, Carmen; Dios, Jose Ramón; Lanceros-Mendez, SenentxuStructural health monitoring (SHM) is a nondestructive process of collecting and analyzing data from structures to evaluate their conditions and predict the remaining lifetime. Multifunctional sensors are increasingly used in smart structures to self-sense and monitor the damages through the measurements of electrical resistivity of composite materials. Polymer-based sensors possess exceptional properties for SHM applications, such as low cost and simple processing, durability, flexibility, and excellent piezoresistive sensitivity. Thermoplastics, thermoplastic elastomers, and elastomer matrices can be combined with conductive nanofillers to develop piezoresistive sensors. Polymer, reinforcement fillers, processing and design have critical influences in the overall properties of the composite sensors. Together with the properties of the functional composites, environmental concerns are being increasingly relevant for applications, involving advances in materials selection and manufacturing technologies. In this scenario, additive manufacturing is playing an increasing role in modern technological solutions. Stretchable multifunctional composites applications include piezoresistive, dielectric elastomers (mainly for actuators), thermoelectric or magnetorheological materials. In the following sections, piezoresistive materials and applications will be mainly addressed based on their increasing implementation into applications.
- Effect of Polymer Dissolution Temperature and Conditioning Time on the Morphological and Physicochemical Characteristics of Poly(Vinylidene Fluoride) Membranes Prepared by Non-Solvent Induced Phase SeparationPublication . Cardoso, V. F.; Botelho, Gabriela; Morão, António; Nunes-Pereira, João; Lanceros-Mendez, SenentxuThis work reports on the production of poly(vinylidene fluoride) (PVDF) membranes by non-solvent induced phase separation (NIPS) using N,N-dimethylformamide (DMF) as solvent and water as non-solvent. The influence of the processing conditions in the morphology, surface characteristics, structure, thermal and mechanical properties were evaluated for polymer dissolution temperatures between 25 and 150 C and conditioning time between 0 and 10 min. Finger-like pore morphology was obtained for all membranes and increasing the polymer dissolution temperature led to an increase in the average pore size ( 0.9 and 2.1 m), porosity ( 50 to 90%) and water contact angle (up to 80 ), in turn decreasing the PVDF content ( 67 to 20%) with the degree of crystallinity remaining approximately constant ( 56%). The conditioning time did not significantly affect the polymer properties studied. Thus, the control of NIPS parameters proved to be suitable for tailoring PVDF membrane properties.
- Mesoporous poly(vinylidene fluoride-co-trifluoroethylene) membranes for lithium-ion battery separatorsPublication . Costa, C. M.; Kundu, Manab; Dias, J. C.; Nunes-Pereira, João; Botelho, Gabriela; Silva, M. M.; Lanceros-Mendez, SenentxuMesoporous separator membranes based on poly(vinylidene fluoride-co-trifluoroethylene), PVDF-TrFE, were prepared through the removal of ZnO nanoparticles from the polymer matrix composite. Different filler concentrations were used, and the evaluation of the morphology, mechanical properties, uptake and ionic conductivity of the membranes were demonstrated that they depend on initial ZnO content in the composite. On the other hand, the vibration peaks characteristics of PVDF-TrFE and the thermal properties are independent on initial filler content. The membrane with the best ionic conductivity, 1.6 mS/cm, is the one prepared after 70 wt.% ZnO removal. The separator membranes were assembled in Li/C-LiFePO4 half-cells exhibiting good rate capability and cycling performance, the best battery performance being obtained for the PVDF-TrFE after 70 wt.% ZnO removal. The good performance of the developed separators was also demonstrated in full battery cells. Thus, a way to tailor membrane mesoporosity is presented and it is shown that the obtained membranes represent suitable separators for lithium-ion battery applications.
- Manufacturing and characterisation of a piezoresistive strain sensor based on the rGO@PDMS composite for skin and prosthetic support systemsPublication . Gonçalves Ferreira, Rodrigo; Pereira Silva, A; Nunes-Pereira, JoãoDue to an ever-increasing amount of population focusing more on their personal health, thanks to rising living standards, there is a pressing need to improve personal healthcare devices. These devices presently require laborious, time-consuming, and convoluted procedures that heavily rely on cumbersome equipment, causing discomfort and pain for the patients during invasive methods such as sample-gathering, blood sampling, and other traditional bench-top techniques [1]. The solution lies in the development of new flexible sensors with temperature, humidity, strain, pressure, and sweat detection and monitoring capabilities, mimicking some of the sensory capabilities of the skin [2]. Along these lines, carbon-based composite materials, which include graphene and other allotropes, have also garnered significant interest due to their electromechanical stability, extraordinary electrical conductivity, high specific surface area, variety, and relatively low cost [3].Thus, in this work, a piezoresistive strain sensor based on a polydimethylsiloxane (PDMS) composite nano reinforced with reduced graphene oxide (rGO) was manufactured, characterised, and tested for possible applications which include joint movement and breathing pattern monitoring, exhibiting the physical and electromechanical characteristics required for the effective detection of physiological signals. The samples were prepared via solution casting, followed by characterisation of the piezoresistive effect of the material, mechanical (3-point bending and tensile), morphological (SEM), structural (FTIR), and thermal (TGA) properties, along with performance testing in live-human’s body parts. Regarding results, it was observed the influence of the used PDMS elastomer-crosslinker ratio, cure temperature and time, dispersant and rGO content in the final performance of the sensor, with the possibility to tune certain characteristics to be better adjusted to specific applications. For this kind of application, the indicated elastomer-crosslinker is 15:1 cured at 120 °C for 20 minutes, with isopropyl alcohol as the dispersant and a rGO content between 3-5 wt.%. The obtained average gauge factors ranged from 7.49-14.85 for 3 wt.%, 9.84-30.8 for 4 wt.%, and 0.56-9.16 for 5 wt.% rGO, establishing these samples as effective piezoresistive sensors for bioengineering applications. It was also concluded that the manufactured composites exhibited good linearity and piezoresistive performance in the 1.54-2.87% strain range, some stability in the 100 cycle 3-point bending tests, the tensile strength varied from 1.05 MPa to 3.084 MPa, the degradation temperature ranged from 380 °C to 410 °C, as well as composites reversibly losing their electrical component before the structure integrity was lost, when tensile tested. Lastly, two proofs of concept were developed, where real-time acquisition and monitoring of data related to joint movements and breathing patterns was successfully performed in volunteers.
- Dielectric barrier discharge plasma actuators based on thermosetting composites for flow control in wind turbines bladesPublication . Nunes-Pereira, João; Rodrigues, Frederico; Abdollahzadehsangroudi, Mohammadmahdi; Pina dos Santos, Paulo Sérgio; Silva, Marco; Pereira Silva, A; Pascoa, Jose; Lanceros-Mendez, SenentxuThe massive use of fibre reinforced plastics (FRP) in several industrial sectors such as aeronautics, aerospace, or wind turbines, raises serious environmental concerns with respect to the end-of-life of these structures, based on their poor recyclability. The low density of FRP gives it outstanding specific properties, such as strength and stiffness, when compared to materials with high recyclability rates, such as metals1. FRP find several applications in structures in which the aerodynamic performance is of extreme importance to guarantee a proper operation. In this sense, to endow these structures with the ability to control or modulate the flow around their surface could be an extraordinary feature to improve the performance of the structure, thus saving considerable amounts of energy and increasing its useful life cycle, contributing in this sense also to reduce the environmental impact of the materials. This work is focused on the development of dielectric barrier discharge (DBD) plasma actuators supported on fibre reinforced thermosetting composites, which can be used in manufacturing of wind turbine blades: epoxy resin and glass, aramid (Fig. 1) and natural flax fibres. DBD plasma actuators are electrohydrodynamic devices capable of generating induced flows of a few m/s through nonthermal plasma, that can be successfully leveraged for flow control applications2, 3. The characterization of the system was carried out in terms of mechanical (flexural strength, strain and stiffness), electrical (power consumption, capacitance, charge-discharge cycles) and electromechanical (induced flow velocity, electromechanical power and efficiency) properties. The results showed the multifunctionality of the composites, demonstrating their suitability for the application, in particular, the epoxy/glass composite with a bending stress of ≈600 MPa, which obtained an induced flow velocity of ≈2.1 m/s with a power consumption of ≈15.1 W, when powered by an AC signal of 11 kVpp and 24 kHz.
- Multifunctional Ceramics for Aeronautical and Aerospace ApplicationsPublication . Shvydyuk, Kateryna; Nunes-Pereira, João; Rodrigues, Frederico; Pascoa, Jose; Lanceros-Mendez, Senentxu; Pereira Silva, AIn the areas of aeronautics and aerospace, ceramic composites play an essential and increasing role due to their superior performance and tailorable properties, exhibiting highly specialized mechanical, thermal, and electric features1. Their main applications include thermal protection systems (TPS), thermal barrier coatings (TBC), and dielectric barrier discharge (DBD) plasma actuators, both for instrumentation and control purposes2. This work reports the manufacture and characterization of three ceramic composites capable of fulfilling the multifunctional ceramic condition according to the aforementioned applications. Accordingly, MgO-Al2O3 (MA), MgOCaZrO3 (MCZ), and Y2O3 stabilized ZrO2 (YSZ) are introduced for TPS, TBC, and DBD dielectric elements. To this aim, MA, MCZ, and YSZ ceramic composites were fabricated via a sequential process, encompassing the selection of raw powders and milling, die pressing, and sintering. Further, the samples were polished for surface optimization. Overall, the results obtained, including mechanical (Young’s and shear moduli, flexural strength, hardness, and fracture toughness), thermal (thermal conductivity and thermal expansion (CTE)), and electrical (dielectric constant) properties, report evidence that the developed ceramics show suitable multifunctional characteristics and therefore fulfil the aeronautical and aerospace demands for increased materials performances. The combined analysis of the Young’s and shear moduli (Fig.1a) with the CTE – the latter over a wide range of temperatures (Fig. 1b) – allows concluding that the cost-effective and widely used alumina appears suitable for bulk monolithic (TPS) and joint applications (TPS, TBC, and DBD).
- Piezoelectric Energy ProductionPublication . Nunes-Pereira, João; Costa, Pedro; Lanceros-Mendez, SenentxuThe concept of piezoelectric energy production is based on energy-harvesting devices using generation materials such as single crystals, ceramics, polymers, and composites. These production systems can harvest wasted environmental energy and convert it essentially into electrical energy. There are different nano- and microscale power harvesters which are increasingly useful for powering mobile electronics and low-power devices, even in hardly accessible areas. Despite many efforts in the development of new materials, the most widely used materials in device applications remain the ceramics of the lead zirconate titanate family, since they still present the higher output performances in the range of milliwatts of generated power.
- Plasma Actuators Based on Alumina Ceramics for Active Flow Control ApplicationsPublication . Rodrigues, Frederico; Shvydyuk, Kateryna; Nunes-Pereira, João; Pascoa, Jose; Silva, AbilioPlasma actuators have demonstrated great potential for active flow control applications, including boundary layer control, flow separation delay, turbulence control, and aircraft noise reduction. In particular, the material used as a dielectric barrier is crucial for the proper operation of the device. Currently, the variety of dielectrics reported in the literature is still quite restricted to polymers including Kapton, Teflon, poly(methyl methacrylate) (PMMA), Cirlex, polyisobutylene (PIB) rubber, or polystyrene. Nevertheless, several studies have highlighted the fragilities of polymeric dielectric layers when actuators operate at significantly high-voltage and -frequency levels or for long periods. In the current study, we propose the use of alumina-based ceramic composites as alternative materials for plasma actuator dielectric layers. The alumina composite samples were fabricated and characterized in terms of microstructure, electrical parameters, and plasma-induced flow velocity and compared with a conventional Kapton-based actuator. It was concluded that alumina-based dielectrics are suitable materials for plasma actuator applications, being able to generate plasma-induced flow velocities of approximately 4.5 m/s. In addition, it was verified that alumina-based ceramic actuators can provide similar fluid mechanical efficiencies to Kapton actuators. Furthermore, the ceramic dielectrics present additional characteristics, such as high-temperature resistance, which are not encompassed by conventional Kapton actuators, which makes them suitable for high-temperature applications such as turbine blade film cooling enhancement and plasma-assisted combustion. The high porosity of the ceramic results in lower plasma-induced flow velocity and lower fluid mechanical efficiency, but by minimizing the porosity, the fluid mechanical efficiency is increased.
- Property characterization and numerical modelling of the thermal conductivity of CaZrO3-MgO ceramic compositesPublication . Carneiro, Pedro; Maceiras, Alberto; Nunes-Pereira, João; Silva, Pedro Dinho da; Silva, Abilio; Baudin, CarmenThree composite materials with different CaZrO3/MgO fractions (2/3, 1/2, 1/3) and two single-phase materials (CaZrO3 and MgO) were fabricated and their thermal conductivity was investigated. Complete thermal and mechanical characterizations (thermal expansion coefficient, thermal diffusivity, specific heat, hardness and toughness) of the materials were performed. Values of the thermal conductivity up to 480 ◦C of the composites were compared with those calculated with the main analytical models. From the real microstructures of the three composites, representative volume elements (RVE) were built and used for finite element modelling (FEM) of thermal conductivity using conductivities of the single-phase materials as inputs. The FEM results showed no differences for the 3 spatial directions of the RVE, nor for the different edge lengths (11, 14 and 17 μm). Results of all analytical models are statistically different from the experimental ones, being those from the Bruggeman model the closest. Results of the proposed FEM are statistically coincident with the experimental ones, showing sensitivity to temperature variation.
- Characterization of a Functionally Gradient Ceramic Based on CaZrO3 – MgOPublication . Babo, Débora Rafaela Telha de; Nunes-Pereira, João; Silva, Pedro D.; Pena, Pilar; Baudin, Carmen; Pereira Silva, AIn the case, where the structure is exposed to severe conditions of operation, such as high strength, wear and high-temperature gradients (e.g. engine components, insulation system, thermal barrier and thermal shield) must be applied. In this work, it was developed and characterized a functional gradient ceramic coating. A ceramic composite based in CaZrO3 – MgO was used in order to design a material with successive layers of molar composition 2:3, 1:1 and 1:3 of CaZrO3:MgO, respectively. A dense material was obtained by sintering assisted reaction (Figure 1). Thermal conductivity at room temperature, hardness, fracture toughness, surface energy, and microstructure were characterized.The results show for monolithic specimens of 2:3 CZ, 1:1 CZ and 1:3 CZ a H of 9,9 GPa, 9,8 GPa and 10,1GPa; a Kc of 1,6 MPa.m1/2, 1,7 MPa.m1/ and 2,1 MPa.m1/2; a k of 0,59 W/mK; 0,76 W/mK and 0,79 W/mK; and a surface energy (SE) of 43,27 mN/m, 51,39 mN/m and 46,55 mN/m, respectively. The functional gradient ceramic shows a H of 10,7 GPa, a Kc of 1,97 MPa.m1/2; a k of 0,82 W/mK and SE of 53,98 mN/m. The individual composition and the functional gradient ceramic show a similar relative density of 4,3 g/cm3 and a porosity of 0,2%. This design methodology has the advantage of allowing the properties of the same material to suit different substrates.