Centre for Mechanical and Aerospace Science and Technologies

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Publications

Dureza e módulo de elasticidade em cerâmicas multifásicas

Publication . Silva, Abilio

O problema proposto consiste em elucidar se a contribuição de cada fase para propriedades como a dureza e o módulo de elasticidade em compósitos cerâmicos multifásicos CaZrO3-MgO-ZrO2 podem ser estimados com base em modelos simples como a “regra das misturas” ou se existem outros fatores para levar em consideração tais como o tamanho, a forma e os limites de grão. Assim, as propriedades de dois materiais previamente desenvolvidos [10-12], com as mesmas fases principais (CaZrO3, MgO e c-ZrO2), mas em diferentes frações volumétricas e tamanho de grão foram analisadas de modo a cumprir as seguintes tarefas: i) Determinar a dureza de cada material usando macro indentação; ii) Determinar a dureza e o módulo de elasticidade de cada uma das fases principais por nano indentação; iii) Verificar a independência das fases constituintes face aos dois materiais e comparar os resultados obtidos com os descritos na literatura; iv) Determinar a contribuição esperada de cada uma das fases para as propriedades da cerâmica multifásica (compósito).

2018-07-03Report

Open access

Fabrication Of Adhesively-Bonded CFRP T-Joints For Stiffener Pull-Off Tests

Publication . Cardoso, João; Nunes-Pereira, João; Silva, Abilio

Adhesively bonded joints have been increasingly applied in primary aerostructures, mainly due to their numerous advantages over riveted or fastened joints. More specifically, bonded T-joints made from carbon fibre reinforced plastics (CFRP) are commonly found as stiffening members (stiffeners, or stringers) on wing panels and fuselage sections. However, aluminium stiffeners can yet be considered a safer and more conservative solution, since composite T-joints face delamination problems that typically initiate at the central noodle of the stiffener - the part where the three arms of the stiffener come together. In order to better comprehend the failure mechanisms and sequence of these joints, Stiffener-Pull- Off Tests (SPOT) were experimentally conducted on a two CFRP adherends (SEAL® Texipreg HS 160 REM) - skin and stiffener - adhesively bonded with a structural film adhesive (EA451 U150). These specimens were fabricated following a novel fabrication plan, which left open the possibility of re-engineering the noodle region with the scope of increasing the through-thickness strength of the bonded joint. This can be achieved by eliminating the problem of the twisted fibres at the noodle that occur during the cure stage when no filler material is used.

2018-04Conference object

Open access

Recent Progress on Piezoelectric, Pyroelectric, and Magnetoelectric Polymer‐Based Energy‐Harvesting Devices

Publication . Costa, Pedro; Nunes-Pereira, João; Pereira, Nelson; Castro, Nélson; Gonçalves, Sérgio; Lanceros-Mendez, Senentxu

Energy harvesting from the environment based on electroactive polymers has been increasing in recent years. Ferroelectric polymers are used as mechanical-to-electrical energy transducers in a wide range of applications, scavenging the surrounding energy to power low-power devices. These energy-harvesting systems operate by taking advantage of the piezoelectric, pyroelectric, and magnetoelectric properties of the polymers, harvesting wasted environmental energy and converting it mainly into electrical energy. There have been developed different nano- and micro-scale power harvesters with an increasing interest for powering mobile electronics and low-power devices, including applications in remote access areas. Novel electronic devices are developed based on low-power solutions, and therefore, polymer-based materials represent a suitable solution to power these devices. Among the different polymers, the most widely used in the device application is the poly(vinylidene fluoride) (PVDF) family, due to its higher output performance.

2019Journal article

Restricted access

Advanced CaZrO3-MgO Ceramic Compositions for High Responsability Applications

Publication . Nunes-Pereira, João; Pereira Silva, A; Pena, Pilar; Baudin, Carmen

The development of new advanced materials for harsh environment operation conditions, such as high temperature, wear and severe erosion and corrosion, is of growing interest, namely for transport and energy industries, due to the ecological and energetic current concerns on a global scale. Particularly, in aerospace industry the increase of working temperature of engines and turbines combined with weight reduction will give rise to higher thrust and lower fuel consumption and consequently less emissions. [...]

2018-04Conference object

Open access

Design and Thermal Conductivity Characterization of a Functionally Gradient Ceramic Based on CaZrO3 – MgO Composition

Publication . Babo, Débora Rafaela Telha de; Nunes-Pereira, João; Pereira Silva, A; Pena, Pilar; Baudin, Carmen

Space exploration involves the use of state-of-the-art technologies such as satellite production, propulsion systems, avionics, aerodynamics, research and development of materials, etc. In the particular case of human spaceflight, the insulation system of the spacecraft is also required in order to ensure crew safety in re-entry of the atmosphere and, if possible, the spacecraft re-use. In the case, where the structure is exposed to high temperature gradients, among other systems a thermal barrier must be used for the structure in order to protect it from critical damage. Based on this concept, in this work it was developed and characterized a design of a functional gradient ceramic coating. Recently, several studies have proposed the stoichiometric composition of calcium zirconate (CaZrO3) as a viable alternative for harsh environments subjected to high temperatures, corrosion and wear, and the mechanical properties of this compound can be improved through a solid solution ion order to obtain a CaZrO3-MgO multiphase ceramic composites. In this work, a functional gradient material was produced with successive layers with variation in its molar composition (1:3, 1:1 and 2:3 of CaZrO3:MgO) and its thermal conductivity characterized.

2018-04Conference object

Open access