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Composites are used in a wide range of engineering applications, as a result, exposure to hostile environments is rather common and its mechanical properties degradation is unavoidable. It is necessary to have a complete understanding of the impact of hostile environments on mechanical performance, namely critical solicitations as low velocity impacts. Therefore, this work intends to analyse the low velocity impact response of a carbon fibre/epoxy composite, and a similar architecture with an epoxy matrix filled with cork, after immersion into different solutions: diesel, H2SO4, HCl, NaOH, distilled water, seawater, and seawater at 60 °C. These solutions significantly affected the impact properties. In this context, the maximum load, maximum displacement, and restored energy behaviour were studied to understand the influence of exposure time. It was possible to conclude that such impact parameters were significantly affected by the solutions, where the exposure time proved to be determinant. The benefits of cork on the perforation threshold were investigated, and this parameter increased when the epoxy matrix was filled with cork. Finally, cork filled epoxy laminates also show less variation in maximum load and recovered energy than carbon/epoxy laminates.
Marco P. Silva; Paulo Santos; João Parente; Sara Valvez; Paulo N. B. Reis. Effect of Harsh Environmental Conditions on the Impact Response of Carbon Composites with Filled Matrix by Cork Powder. Applied Sciences 2021, 11, 7436 .
AMA StyleMarco P. Silva, Paulo Santos, João Parente, Sara Valvez, Paulo N. B. Reis. Effect of Harsh Environmental Conditions on the Impact Response of Carbon Composites with Filled Matrix by Cork Powder. Applied Sciences. 2021; 11 (16):7436.
Chicago/Turabian StyleMarco P. Silva; Paulo Santos; João Parente; Sara Valvez; Paulo N. B. Reis. 2021. "Effect of Harsh Environmental Conditions on the Impact Response of Carbon Composites with Filled Matrix by Cork Powder." Applied Sciences 11, no. 16: 7436.
Additive manufacturing (AM) is the process through which components/structures are produced layer-by-layer. In this context, 4D printing combines 3D printing with time so that this combination results in additively manufactured components that respond to external stimuli and, consequently, change their shape/volume or modify their mechanical properties. Therefore, 4D printing uses shape-memory materials that react to external stimuli such as pH, humidity, and temperature. Among the possible materials with shape memory effect (SME), the most suitable for additive manufacturing are shape memory polymers (SMPs). However, due to their weaknesses, shape memory polymer compounds (SMPCs) prove to be an effective alternative. On the other hand, out of all the additive manufacturing techniques, the most widely used is fused filament fabrication (FFF). In this context, the present paper aims to critically review all studies related to the mechanical properties of 4D-FFF materials. The paper provides an update state of the art showing the potential of 4D-FFF printing for different engineering applications, maintaining the focus on the structural integrity of the final structure/component.
Sara Valvez; Paulo Reis; Luca Susmel; Filippo Berto. Fused Filament Fabrication-4D-Printed Shape Memory Polymers: A Review. Polymers 2021, 13, 701 .
AMA StyleSara Valvez, Paulo Reis, Luca Susmel, Filippo Berto. Fused Filament Fabrication-4D-Printed Shape Memory Polymers: A Review. Polymers. 2021; 13 (5):701.
Chicago/Turabian StyleSara Valvez; Paulo Reis; Luca Susmel; Filippo Berto. 2021. "Fused Filament Fabrication-4D-Printed Shape Memory Polymers: A Review." Polymers 13, no. 5: 701.
Olives’ consumption produces copious agricultural byproducts that have accompanied humanity for millennia, but the increasing worldwide production complicates its management. Most wastes are generated during olive oil production in form of olive stones and other lignocellulosic derivatives. Industrial processes of chemical or physical nature to recover economically compounds from biomass residues are costly, difficult, and non-environmentally friendly. Cellulose, hemicellulose, and lignin biopolymers are the principal components of olive stones, which present interesting qualities as lignocellulosic fillers in polymeric composites. This review will summarize examples of composites based on thermoplastic polymers, such as polystyrene (PS), polylactide (PLA), polyvinyl chloride (PVC), polypropylene (PP), and polycaprolactone (PCL); thermosetting resins (phenol-formaldehyde, unsaturated polyesters, and epoxy) and acrylonitrile butadiene rubber/devulcanized waste rubber (NBR/DWR) blends focusing on the fabrication procedures, characterization, and possible applications. Finally, thanks to the wide disparity in polymer matrix types, the variability in applications is important, from adsorption to mechanical enhancement, showing the easiness and benefit of olive stone integration in many materials.
Sara Valvez; Alberto Maceiras; Paulo Santos; Paulo Reis. Olive Stones as Filler for Polymer-Based Composites: A Review. Materials 2021, 14, 845 .
AMA StyleSara Valvez, Alberto Maceiras, Paulo Santos, Paulo Reis. Olive Stones as Filler for Polymer-Based Composites: A Review. Materials. 2021; 14 (4):845.
Chicago/Turabian StyleSara Valvez; Alberto Maceiras; Paulo Santos; Paulo Reis. 2021. "Olive Stones as Filler for Polymer-Based Composites: A Review." Materials 14, no. 4: 845.
This work intends to study the effect of the curing parameters on the mechanical properties of a polyester resin without a complete curing reaction process. For this purpose, cures at room temperature, 40 °C, and 60 °C, and post-cures at 40 °C and 60 °C, with different exposure times, were considered. Three-point bending tests were performed to assess the bending properties and both stress relaxation and creep behavior. The degree of crosslinking was estimated by evaluating the C = C ester bond, by Fourier infrared spectroscopy and complemented with the thermal characterization made by differential scanning calorimetry. The results showed that higher curing temperatures are preferable to methods involving curing and post-curing, which can be confirmed by the higher degree of conversion of unsaturated ester bonds at 60 °C. Compared to the resin cured at room temperature, the bending strength increased by 36.5% at 40 °C and 88.6% at 60 °C. A similar effect was observed for bending stiffness. In terms of stress relaxation and creep strain, the lowest values were obtained for samples cured at 60 °C.
Marco P. Silva; Paulo Santos; João M. Parente; Sara Valvez; Paulo N. B. Reis; Ana P. Piedade. Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin. Polymers 2020, 12, 1927 .
AMA StyleMarco P. Silva, Paulo Santos, João M. Parente, Sara Valvez, Paulo N. B. Reis, Ana P. Piedade. Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin. Polymers. 2020; 12 (9):1927.
Chicago/Turabian StyleMarco P. Silva; Paulo Santos; João M. Parente; Sara Valvez; Paulo N. B. Reis; Ana P. Piedade. 2020. "Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin." Polymers 12, no. 9: 1927.
In recent years, there has been a rapid growth in the use of composite materials in engineering applications, and this evidence should continue. However, the desire and necessity to improve the efficiency of these materials for engineering applications more ambitious have led to use of several nano-sized fillers. In fact, nanoparticles with typical dimensions in the range between 1 and 100 nm have been widely studied due to their unique surface effect, increased chemical activity and physical properties. From all nanofillers studied to improve the mechanical performance of composite materials, graphene is the latest and promising nano-reinforcement due to its unique mechanical properties combined with its good electrical performance. Therefore, this work intends to develop a short review about the benefits of the graphene fillers on the fatigue strength, especially in terms of polymeric resins, elastomers and composites. This subject is very important, because fatigue failures can lead to tragic consequences. It was possible to conclude that the presence of this filler improves the fatigue strength, but the knowledge is not yet enough to establish a complete understanding of this subject.
J.M. Parente; Paulo Sérgio Pina dos Santos; S. Valvez; M.P. Silva; P.N.B. Reis. Fatigue behaviour of graphene composites: An overview. Procedia Structural Integrity 2020, 25, 282 -293.
AMA StyleJ.M. Parente, Paulo Sérgio Pina dos Santos, S. Valvez, M.P. Silva, P.N.B. Reis. Fatigue behaviour of graphene composites: An overview. Procedia Structural Integrity. 2020; 25 ():282-293.
Chicago/Turabian StyleJ.M. Parente; Paulo Sérgio Pina dos Santos; S. Valvez; M.P. Silva; P.N.B. Reis. 2020. "Fatigue behaviour of graphene composites: An overview." Procedia Structural Integrity 25, no. : 282-293.
Additive manufacturing is a flexible processing technique that can be applied to polymers, metals, ceramics and other materials. Fused Deposition Modelling (FDM) is one of the available additive manufacturing techniques that use thermoplastic polymers to print components/structures. Although there are many materials that can be used as filaments in this technique, PLA is one of the most widely used, not only for its characteristics, but also for society’s environmental awareness. Depending on the desired characteristics of 3D printed models, PLA can be reinforced with fillers. Therefore, this short review paper aims to summarize all studies involving continuous carbon fibre reinforced PLA composites.
S. Valvez; Paulo Sérgio Pina dos Santos; João Parente; Marco Silva; P.N.B. Reis. 3D printed continuous carbon fiber reinforced PLA composites: A short review. Procedia Structural Integrity 2020, 25, 394 -399.
AMA StyleS. Valvez, Paulo Sérgio Pina dos Santos, João Parente, Marco Silva, P.N.B. Reis. 3D printed continuous carbon fiber reinforced PLA composites: A short review. Procedia Structural Integrity. 2020; 25 ():394-399.
Chicago/Turabian StyleS. Valvez; Paulo Sérgio Pina dos Santos; João Parente; Marco Silva; P.N.B. Reis. 2020. "3D printed continuous carbon fiber reinforced PLA composites: A short review." Procedia Structural Integrity 25, no. : 394-399.
Eco-friendly and biodegradable composites are desirable due to the enormous pressure on industry as a result of the air pollution, global warming and the scarcity of fossil fuels. On the other hand, due to inherent viscoelasticity of the matrix phase, polymer composites are prone to creep and stress relaxation. Therefore, the main goal of this work is to study the hybridization effect on the viscoelastic properties of composites reinforced natural fibres. For this purpose, composites with the same lay-up, but with different fibres (flax and glass fibres), were manufactured with a green epoxy resin. These viscoelastic properties were evaluated in bending mode. It was concluded that, contrary to creep deformation, stress decreases with time, but this tendency is strongly attenuated with the addition of glass fibres. Therefore, the hybridization is an efficient way to decrease the viscoelastic behaviour of natural fibre reinforced composites. Finally, due to the good accuracy obtained between the experimental and theoretical results, the Kohlrausch-Williams-Watts (KWW) equation and the Findley model can be used to predict stress relaxation time and creep displacement.
P. Santos; João Parente; Sara Valvez; Marco Silva; P.N.B. Reis. Hybridization effect on the bending properties of flax composites. Procedia Structural Integrity 2020, 25, 370 -377.
AMA StyleP. Santos, João Parente, Sara Valvez, Marco Silva, P.N.B. Reis. Hybridization effect on the bending properties of flax composites. Procedia Structural Integrity. 2020; 25 ():370-377.
Chicago/Turabian StyleP. Santos; João Parente; Sara Valvez; Marco Silva; P.N.B. Reis. 2020. "Hybridization effect on the bending properties of flax composites." Procedia Structural Integrity 25, no. : 370-377.
The experiments performed were oriented to produce and characterize a sandwich panel with an optimized composition of cork granules, obtained from industrial by-products, and a green epoxy resin. Static bending tests were performed to characterize the mechanical strength and its viscoelastic response. Stress relaxation tests evidence a decrease of the stress over the time and the experimental data can be fitted by Kohlrausch-Williams-Watts (KWW) model successfully. In terms of creep, the displacement increases and while the KWW model is preferable to the Findley model for short-term predictions, the opposite trend occurs for long-term predictions. Fatigue life was also investigated, where the damage mechanisms that govern the fatigue strength, as well as the residual mechanical properties, were characterized. Small cracks were observed under the pin load contact region, between skin and core, which grow around the cork grains and follow the direction of middle plane toward the tips of the specimen.
P.N.B. Reis; Marco Silva; Paulo Sérgio Pina dos Santos; João Parente; Sara Valvez; A. Bezazi. Mechanical performance of an optimized cork agglomerate core-glass fibre sandwich panel. Composite Structures 2020, 245, 112375 .
AMA StyleP.N.B. Reis, Marco Silva, Paulo Sérgio Pina dos Santos, João Parente, Sara Valvez, A. Bezazi. Mechanical performance of an optimized cork agglomerate core-glass fibre sandwich panel. Composite Structures. 2020; 245 ():112375.
Chicago/Turabian StyleP.N.B. Reis; Marco Silva; Paulo Sérgio Pina dos Santos; João Parente; Sara Valvez; A. Bezazi. 2020. "Mechanical performance of an optimized cork agglomerate core-glass fibre sandwich panel." Composite Structures 245, no. : 112375.