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P.N.B. Reis
CEMMPRE, Department of Mechanical Engineering, University of Coimbra, 3030-788 Coimbra, Portugal

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Journal article
Published: 12 August 2021 in Applied Sciences
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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.

ACS Style

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 Style

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 (16):7436.

Chicago/Turabian Style

Marco 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.

Journal article
Published: 29 June 2021 in Construction and Building Materials
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As part of local agricultural date palm waste valorization, this work describes bio-composites made with a cement matrix reinforced with short Mesh date palm fibers for non-structural civil engineering applications. The study focuses in particular on investigating the influence of four parameters on the bending and compression properties of the bio-fiber reinforced mortar: the fiber content, length, NaOH concentration and immersion times of those fibers in the chemical solution. For this purpose, flexural and compression tests have been carried out. An experimental design representing 27 combinations of the above four parameters has been established to minimize the number of experimental trials and build a surface response methodology (SRM) using the design expert software 12 code. The results obtained show that the incorporation of mesh date palm fibers into the mortar improve the mechanical properties of the bio-fiber reinforced mortar. The bending stress of beams with the bio-based reinforcement increases 27.5% compared to the reference configuration; the bending modulus conversely improves by 18.9%. Compression stress and modulus showed increases around 46.6% and 36.3%, respectively. The objective function used to optimize the mechanical properties provides however an increase in bending stress and modulus around 50.0% and 20.0%, respectively, compared to the reference mortar case. The parametric design of the bio-composites that provided the best compression performance was very close to the one identified by the minimum of the objective function. Confirmatory experimental tests results compared to those from the objective function model developed show good agreement, with 3.3% and 3.8% differences for the bending stress and modulus, respectively.

ACS Style

Hocine Khelifa; Abderrezak Bezazi; Haithem Boumediri; Gilberto Garcia del Pino; Paulo N.B. Reis; Fabrizio Scarpa; Alain Dufresne. Mechanical characterization of mortar reinforced by date palm mesh fibers: Experimental and statistical analysis. Construction and Building Materials 2021, 300, 124067 .

AMA Style

Hocine Khelifa, Abderrezak Bezazi, Haithem Boumediri, Gilberto Garcia del Pino, Paulo N.B. Reis, Fabrizio Scarpa, Alain Dufresne. Mechanical characterization of mortar reinforced by date palm mesh fibers: Experimental and statistical analysis. Construction and Building Materials. 2021; 300 ():124067.

Chicago/Turabian Style

Hocine Khelifa; Abderrezak Bezazi; Haithem Boumediri; Gilberto Garcia del Pino; Paulo N.B. Reis; Fabrizio Scarpa; Alain Dufresne. 2021. "Mechanical characterization of mortar reinforced by date palm mesh fibers: Experimental and statistical analysis." Construction and Building Materials 300, no. : 124067.

Review
Published: 23 June 2021 in Polymers
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The objective of current work is to analyse the influence of different welding techniques and welding parameters on the morphology and mechanical strength of friction stir welds (FSW) in polymers, based on data collected in the literature. In the current work, only articles that provide data on the joint efficiency, or sufficient information to estimate it are considered. The process using conventional tool is presented and compared with new procedures developed for FSW of polymers, such as those using tools with heated stationary shoulder, preheating of the polymer or double-side passage of the tool. The influence of tool rotational speed (w), welding speed (v), tilt angle and geometry of the pin are discussed. This work focuses on the polymers most studied in the literature, polyethylene (PE) and polypropylene (PP). The use of external heating and tools with stationary shoulder proved to be of great importance in improving the surface finish, reducing defects, and increasing the mechanical strength of the welds. The increase in the w/v ratio increased the joint efficiency, especially when using conventional tools on PE. A trend was obtained for conventional FSW, but it was difficult to establish mathematical relationships, because of the variability of welding conditions.

ACS Style

Miguel Pereira; Ana Amaro; Paulo Reis; Altino Loureiro. Effect of Friction Stir Welding Techniques and Parameters on Polymers Joint Efficiency—A Critical Review. Polymers 2021, 13, 2056 .

AMA Style

Miguel Pereira, Ana Amaro, Paulo Reis, Altino Loureiro. Effect of Friction Stir Welding Techniques and Parameters on Polymers Joint Efficiency—A Critical Review. Polymers. 2021; 13 (13):2056.

Chicago/Turabian Style

Miguel Pereira; Ana Amaro; Paulo Reis; Altino Loureiro. 2021. "Effect of Friction Stir Welding Techniques and Parameters on Polymers Joint Efficiency—A Critical Review." Polymers 13, no. 13: 2056.

Review
Published: 26 February 2021 in Polymers
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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.

ACS Style

Sara Valvez; Paulo Reis; Luca Susmel; Filippo Berto. Fused Filament Fabrication-4D-Printed Shape Memory Polymers: A Review. Polymers 2021, 13, 701 .

AMA Style

Sara Valvez, Paulo Reis, Luca Susmel, Filippo Berto. Fused Filament Fabrication-4D-Printed Shape Memory Polymers: A Review. Polymers. 2021; 13 (5):701.

Chicago/Turabian Style

Sara Valvez; Paulo Reis; Luca Susmel; Filippo Berto. 2021. "Fused Filament Fabrication-4D-Printed Shape Memory Polymers: A Review." Polymers 13, no. 5: 701.

Review
Published: 10 February 2021 in Materials
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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.

ACS Style

Sara Valvez; Alberto Maceiras; Paulo Santos; Paulo Reis. Olive Stones as Filler for Polymer-Based Composites: A Review. Materials 2021, 14, 845 .

AMA Style

Sara Valvez, Alberto Maceiras, Paulo Santos, Paulo Reis. Olive Stones as Filler for Polymer-Based Composites: A Review. Materials. 2021; 14 (4):845.

Chicago/Turabian Style

Sara Valvez; Alberto Maceiras; Paulo Santos; Paulo Reis. 2021. "Olive Stones as Filler for Polymer-Based Composites: A Review." Materials 14, no. 4: 845.

Journal article
Published: 03 September 2020 in Applied Sciences
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The literature reports benefits when the cork powder obtained from industrial by-products is used as the filler of composite laminates. For example, while the fatigue life is insensitive to the presence of cork in the resin, significant improvements are achieved in terms of to low-velocity impact strength. However, in terms of ballistic domain, the literature does not yet report any study about the effect of incorporating powdered cork into resins. Therefore, this study intended to analyse the ballistic behaviour and damage tolerance of Kevlar/epoxy reinforced composites with matrix filled by cork powder. For this purpose, high-velocity impacts were studied on plates of Kevlar bi-directional woven laminates with surfaces of 100 × 100 mm2. It was possible to conclude that the minimum velocity of perforation is 1.6% higher when the cork powder is added to the resin, but considering the dispersion, this small difference can be neglected. In terms of damage areas, they are slightly lower when cork dust is added, especially for velocities below the minimum perforation velocity. Finally, the residual bending strength shows that these composites are less sensitive to impact velocity than the samples with neat resin. In addition to these benefits, cork powder reduces the amount of resin in the composite, making it more environmentally friendly.

ACS Style

Ana Martins Amaro; Paulo Nobre Balbis Reis; Ines Ivañez; Sonia Sánchez-Saez; Shirley Kalamis Garcia-Castillo; Enrique Barbero. The High-Velocity Impact Behaviour of Kevlar Composite Laminates Filled with Cork Powder. Applied Sciences 2020, 10, 6108 .

AMA Style

Ana Martins Amaro, Paulo Nobre Balbis Reis, Ines Ivañez, Sonia Sánchez-Saez, Shirley Kalamis Garcia-Castillo, Enrique Barbero. The High-Velocity Impact Behaviour of Kevlar Composite Laminates Filled with Cork Powder. Applied Sciences. 2020; 10 (17):6108.

Chicago/Turabian Style

Ana Martins Amaro; Paulo Nobre Balbis Reis; Ines Ivañez; Sonia Sánchez-Saez; Shirley Kalamis Garcia-Castillo; Enrique Barbero. 2020. "The High-Velocity Impact Behaviour of Kevlar Composite Laminates Filled with Cork Powder." Applied Sciences 10, no. 17: 6108.

Journal article
Published: 26 August 2020 in Polymers
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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.

ACS Style

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 Style

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 (9):1927.

Chicago/Turabian Style

Marco 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.

Journal article
Published: 09 May 2020 in Frattura ed Integrità Strutturale
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ACS Style

Paulo Nb Reis; Ana Amaro; Altino Loureiro. Comparison of mechanical performance between friction-stir spot welded and adhesive bonded joints. Frattura ed Integrità Strutturale 2020, 14, 124 -133.

AMA Style

Paulo Nb Reis, Ana Amaro, Altino Loureiro. Comparison of mechanical performance between friction-stir spot welded and adhesive bonded joints. Frattura ed Integrità Strutturale. 2020; 14 (53):124-133.

Chicago/Turabian Style

Paulo Nb Reis; Ana Amaro; Altino Loureiro. 2020. "Comparison of mechanical performance between friction-stir spot welded and adhesive bonded joints." Frattura ed Integrità Strutturale 14, no. 53: 124-133.

Journal article
Published: 18 April 2020 in Composite Structures
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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.

ACS Style

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 Style

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.

Chicago/Turabian Style

P.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.

Review
Published: 10 April 2020 in Applied Sciences
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Structural sandwich composites have been widely used in many engineering applications, and this trend continues due to their superior mechanical properties, thermal insulation and acoustic damping. However, to further improve their mechanical properties, literature reports significant benefits obtained with nano-reinforcements. In this context, nanoclays are the most popular nano-reinforcements for polymeric nanocomposites, due to their relatively high ion exchange capacity, high aspect ratio and economic advantages. In order to stablish a systematic understanding for design criteria, this work intends to summarize all studies present in the open literature about this topic. It was possible to conclude that using nanoclays improves the mechanical properties of structural sandwich composites, especially in terms of impact strength. Nevertheless, the benefits obtained regarding fatigue performance are not adequately reported in the literature, revealing the need to develop these studies.

ACS Style

João Parente; Paulo N. B. Reis; M. Neto; A. M. Amaro. Mechanical Properties of Sandwich Composites Reinforced by Nanoclays: An Overview. Applied Sciences 2020, 10, 2637 .

AMA Style

João Parente, Paulo N. B. Reis, M. Neto, A. M. Amaro. Mechanical Properties of Sandwich Composites Reinforced by Nanoclays: An Overview. Applied Sciences. 2020; 10 (7):2637.

Chicago/Turabian Style

João Parente; Paulo N. B. Reis; M. Neto; A. M. Amaro. 2020. "Mechanical Properties of Sandwich Composites Reinforced by Nanoclays: An Overview." Applied Sciences 10, no. 7: 2637.

Journal article
Published: 01 February 2020 in Composite Structures
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The main goal of this work is to study the effect of solid particle erosion on the impact fatigue life. For this purpose, impingement angles of 10°, 45° and 90°, stand-off distances of 75 mm, 100 mm and 125 mm and particles size of 20 mesh, 24 mesh and 54 mesh were considered. After exposure to corundum particles flow, during 20 seg and constant pressure of 2 bar, the glass/epoxy laminates were evaluated in terms of weight loss and depth of eroded area. Finally, all samples were submitted to multi-impacts until full perforation. From the experimental tests, it can be concluded that weight loss and depth of eroded area increase with the increasing of impingement angle, reaching maximum values for 90°. In terms of distance between nozzle and target, higher values promote larger and shallower damaged areas, while smaller particles are responsible by lower weight loss and depth. Finally, the fatigue life is very sensitive to the erodent size, but the opposite tendency occurs for impingement angle and stand-off distance, alternating according to their values.

ACS Style

A.M. Amaro; A.J.R. Loureiro; M.A. Neto; P.N.B. Reis. Residual impact strength of glass/epoxy composite laminates after solid particle erosion. Composite Structures 2020, 238, 112026 .

AMA Style

A.M. Amaro, A.J.R. Loureiro, M.A. Neto, P.N.B. Reis. Residual impact strength of glass/epoxy composite laminates after solid particle erosion. Composite Structures. 2020; 238 ():112026.

Chicago/Turabian Style

A.M. Amaro; A.J.R. Loureiro; M.A. Neto; P.N.B. Reis. 2020. "Residual impact strength of glass/epoxy composite laminates after solid particle erosion." Composite Structures 238, no. : 112026.

Journal article
Published: 20 December 2019 in Polymers
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Polyamide creates high-performance composite materials, which are replacing the traditional epoxy composites in several applications. In this context, exposure to hostile environments is expected. On the other hand, due to the viscoelastic nature of the matrix, these composite materials are prone to stress relaxation. Therefore, the stress relaxation behaviour of glass/polyamide 6 composites was studied considering different fibre directions, as well as exposure to NaOH and HCl solutions. Stress relaxation tests on the bending mode were carried out, and the stress recorded during the loading time (7200 s). All tests were characterized by a stress decrease over time, but laminates with higher fibre angles were more prone to stress relaxation. However, exposure to hostile solutions promoted more significant decreases, where the highest stress relaxation was achieved for alkaline environments with values that were three times higher for laminates with fibres at 0° and around one and half times higher for 45° fibre alignments when compared with the control samples. Finally, the Kohlrausch–Williams–Watts (KWW) model showed that it can be used to predict stress relaxation time, due to the accuracy that was obtained between the experimental and theoretical results.

ACS Style

Paulo Nobre Balbis Dos Reis; Ana Martins Amaro; Maria Augusta Neto. Effect of Fibre Orientation and Hostile Solutions on Stress Relaxation of Glass/Polyamide Composites. Polymers 2019, 12, 20 .

AMA Style

Paulo Nobre Balbis Dos Reis, Ana Martins Amaro, Maria Augusta Neto. Effect of Fibre Orientation and Hostile Solutions on Stress Relaxation of Glass/Polyamide Composites. Polymers. 2019; 12 (1):20.

Chicago/Turabian Style

Paulo Nobre Balbis Dos Reis; Ana Martins Amaro; Maria Augusta Neto. 2019. "Effect of Fibre Orientation and Hostile Solutions on Stress Relaxation of Glass/Polyamide Composites." Polymers 12, no. 1: 20.

Journal article
Published: 11 December 2019 in Applied Sciences
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In this paper an experimental investigation on fire retardancy of a new polymer nanocomposite derived from organic montmorillonite and exolit fire retardant in an acrylonitrile- butadiene-styrene copolymer by analyzing the flammability and fire behavior is described. The samples were prepared by melting and mixing nanocomposites and fire retardant in different concentrations in an acrylonitrile-butadiene-styrene base polymer. It was found that using only one component (organic montmorillonite or fire retardant) the burning stops in 10 s on the sample. Confirmation of synergy in flammability by combining both montmorillonite and flame retardants was noticed and is discussed regarding the flame-retardant mechanisms assessed by means of the Limiting oxygen index (LOI), UL 94, and cone-calorimeter methods. The acrylonitrile- butadiene-styrene preparation with 15–20 wt% fire retardant and 1–2 wt% organic montmorillonite reached a UL-94 V-0 classification, contrasting with the pure acrylonitrile- butadiene-styrene and the acrylonitrile-butadiene-styrene with 15 wt% fire retardant and acrylonitrile-butadiene-styrene with 1–2 wt% organic montmorillonite formulations, which completely burned. Finally, the samples showed a very good synergy going to a higher reduction of the peak heat release rate and to a minimum mass reduction, as obtained from cone calorimeter tests.

ACS Style

Tudor Mihai Simionescu; Alina Adriana Minea; Paulo Nobre Balbis Dos Reis. Fire Properties of Acrylonitrile Butadiene Styrene Enhanced with Organic Montmorillonite and Exolit Fire Retardant. Applied Sciences 2019, 9, 5433 .

AMA Style

Tudor Mihai Simionescu, Alina Adriana Minea, Paulo Nobre Balbis Dos Reis. Fire Properties of Acrylonitrile Butadiene Styrene Enhanced with Organic Montmorillonite and Exolit Fire Retardant. Applied Sciences. 2019; 9 (24):5433.

Chicago/Turabian Style

Tudor Mihai Simionescu; Alina Adriana Minea; Paulo Nobre Balbis Dos Reis. 2019. "Fire Properties of Acrylonitrile Butadiene Styrene Enhanced with Organic Montmorillonite and Exolit Fire Retardant." Applied Sciences 9, no. 24: 5433.

Journal article
Published: 05 November 2019 in Composite Structures
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Due to the viscoelastic properties of cork and polymeric matrices, stress relaxation and creep behaviour of multiphase composites incorporating cork are important properties that should be considered at the design stage. For this purpose, composites with the same lay-up but with different fibres were manufactured with neat epoxy resin and epoxy resin filled with cork powder. It was concluded that higher values of relaxation and creep displacement occur when Kevlar fibres are used in place of carbon fibres and, for both, when cork powder was introduced into the resin. Considering the strain correspondent to 150 MPa for Kevlar composites, the difference observed between the initial and final bending stress is around 19.1 MPa for laminates with neat resin and 13.5% higher for laminates with matrix filled by cork powder. In terms of creep and comparatively to the neat resin, the displacement increases 24.6% when the resin incorporates cork powder. Regardless of whether the resin was pure or filled with cork powder, the same trend was observed for carbon composites, but with less expressive values for the same comparisons previously established. Finally, the maximum error obtained between the theoretical and experimental results of 0.6% for all conditions tested shows that the Kohlrausch-Williams-Watts (KWW) function can be used to accurately predict the relaxation stress response. In terms of creep response, this function was compared with the Findley model and, regardless of the success obtained with both, the best predictions are reached with the KWW model.

ACS Style

P.N.B. Reis; Marco Silva; Paulo Sérgio Pina dos Santos; João Parente; Abderrezak Bezazi. Viscoelastic behaviour of composites with epoxy matrix filled by cork powder. Composite Structures 2019, 234, 111669 .

AMA Style

P.N.B. Reis, Marco Silva, Paulo Sérgio Pina dos Santos, João Parente, Abderrezak Bezazi. Viscoelastic behaviour of composites with epoxy matrix filled by cork powder. Composite Structures. 2019; 234 ():111669.

Chicago/Turabian Style

P.N.B. Reis; Marco Silva; Paulo Sérgio Pina dos Santos; João Parente; Abderrezak Bezazi. 2019. "Viscoelastic behaviour of composites with epoxy matrix filled by cork powder." Composite Structures 234, no. : 111669.

Journal article
Published: 26 August 2019 in Material Design & Processing Communications
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ACS Style

João M. Parente; Marco P. Silva; Paulo Santos; Paulo N.B. Reis. Viscoelastic behaviour of nanocomposites enhanced by graphene: An overview. Material Design & Processing Communications 2019, 1, 1 .

AMA Style

João M. Parente, Marco P. Silva, Paulo Santos, Paulo N.B. Reis. Viscoelastic behaviour of nanocomposites enhanced by graphene: An overview. Material Design & Processing Communications. 2019; 1 (6):1.

Chicago/Turabian Style

João M. Parente; Marco P. Silva; Paulo Santos; Paulo N.B. Reis. 2019. "Viscoelastic behaviour of nanocomposites enhanced by graphene: An overview." Material Design & Processing Communications 1, no. 6: 1.

Article
Published: 25 June 2019 in Fibers and Polymers
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For the different loading modes, literature reports conveniently the delaminations’ effect on the mechanical properties. However, as consequence of the inherent viscoelasticity of the matrix phase, polymer composites are prone to stress relaxation, making it a great challenge when they are used in long-term applications. Therefore, stress relaxation tests were carried out on the bending mode, and the stress was recorded during the time. It is possible to conclude that the stress decreases with the time, however, this tend becomes more pronounced with the increasing of the delamination’s length. The results were fitted following the Kohlrausch-Williams-Watts model, evidencing good accuracy of the model for the stress relaxation time.

ACS Style

P. N. B. Reis; Marco Silva; Paulo Sérgio Pina dos Santos. Stress Relaxation in Delaminated Carbon/Epoxy Composites. Fibers and Polymers 2019, 20, 1284 -1289.

AMA Style

P. N. B. Reis, Marco Silva, Paulo Sérgio Pina dos Santos. Stress Relaxation in Delaminated Carbon/Epoxy Composites. Fibers and Polymers. 2019; 20 (6):1284-1289.

Chicago/Turabian Style

P. N. B. Reis; Marco Silva; Paulo Sérgio Pina dos Santos. 2019. "Stress Relaxation in Delaminated Carbon/Epoxy Composites." Fibers and Polymers 20, no. 6: 1284-1289.

Journal article
Published: 01 May 2019 in Materials
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Samples having nominal compositions of AlSi12 and Al6082-T4 were prepared using a lost wax casting process, with nominal relative densities of 20%, 40%, and 60%, as well as arrangements of a uniform cell structure (US) or a dual-size cell (DS). For comparison, samples of aluminium foam-filled tubes having the same nominal composition were also prepared with the same technique, with nominal relative densities of 20% and similar arrangements (US and DS). Impact tests at different velocities were performed using a split Hopkinson pressure bar (SHPB). It is possible to conclude that Al6082-T4 foams have better performance, in both configurations, than the AlSi12 ones. Considering a uniform cell structure and a density of 20%, the absorbed energy by the Al6082-T4 foams was around 25% higher than the value observed for the AlSi12 ones. In terms of arrangement, the US structure presents absorbed energy around 57% lower than the DS ones, while the AlSi12 foams with a relative density of 20% were compared. Finally, the absorbed energy growths from 2.8 × 105 to 5.2 × 105 J/m3, when the density increased from 20% to 60%. However, when these foams were involved with a tube, the performances increased substantially.

ACS Style

Ana M. Amaro; Maria A. Neto; José S. Cirne; Paulo N.B. Reis. Mechanical Characterization of Different Aluminium Foams at High Strain Rates. Materials 2019, 12, 1428 .

AMA Style

Ana M. Amaro, Maria A. Neto, José S. Cirne, Paulo N.B. Reis. Mechanical Characterization of Different Aluminium Foams at High Strain Rates. Materials. 2019; 12 (9):1428.

Chicago/Turabian Style

Ana M. Amaro; Maria A. Neto; José S. Cirne; Paulo N.B. Reis. 2019. "Mechanical Characterization of Different Aluminium Foams at High Strain Rates." Materials 12, no. 9: 1428.

Journal article
Published: 02 March 2019 in Frattura ed Integrità Strutturale
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ACS Style

Carlos Alexandre Campos Pais Coelho; Fábio V.P. Navalho; P.N.B. Reis. Impact response of laminated cylindrical shells. Frattura ed Integrità Strutturale 2019, 13, 411 -418.

AMA Style

Carlos Alexandre Campos Pais Coelho, Fábio V.P. Navalho, P.N.B. Reis. Impact response of laminated cylindrical shells. Frattura ed Integrità Strutturale. 2019; 13 (48):411-418.

Chicago/Turabian Style

Carlos Alexandre Campos Pais Coelho; Fábio V.P. Navalho; P.N.B. Reis. 2019. "Impact response of laminated cylindrical shells." Frattura ed Integrità Strutturale 13, no. 48: 411-418.

Conference paper
Published: 14 January 2019 in MATEC Web of Conferences
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Delaminations are the most typical damage in composite laminates, and the industrial community is continually searching new techniques to combine efficiency with cost benefits. Therefore, this work intends to analyse the application of screws on repair of composite laminates containing delaminations. It was found that this technique is beneficial for delaminations with lengths higher than 15 mm. For example, considering delaminations with 20 mm, the compressive load increases around 46.4% relatively to the delaminated samples. However, for small lengths, this technique is not viable due to the stress concentration induced by the hole.

ACS Style

Ana Amaro; Maria Augusta Neto; A.J.R. Loureiro; M.P. Silva; P.N.B. Reis. Repair Delaminations in Carbon/epoxy Laminates. MATEC Web of Conferences 2019, 253, 02001 .

AMA Style

Ana Amaro, Maria Augusta Neto, A.J.R. Loureiro, M.P. Silva, P.N.B. Reis. Repair Delaminations in Carbon/epoxy Laminates. MATEC Web of Conferences. 2019; 253 ():02001.

Chicago/Turabian Style

Ana Amaro; Maria Augusta Neto; A.J.R. Loureiro; M.P. Silva; P.N.B. Reis. 2019. "Repair Delaminations in Carbon/epoxy Laminates." MATEC Web of Conferences 253, no. : 02001.

Conference paper
Published: 01 January 2019 in 2019 International Congress on Ultrasonics
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In this work, different approaches for damage evaluation in composite laminates using ultrasonic C-scan imaging were used: (1) amplitude and (2) time-of-flight (TOF) immersion pulse-echo and (3) air-coupled through-transmission. Five carbon/epoxy laminates with different stacking sequences and thicknesses were impacted. The immersion C-scan images were produced using different frequencies and were compared with the ones obtained by the air-coupled system. The images show that the different methodologies are all able to detect the defects and give reasonable information about their size. The TOF images provide better information about the defects, whenever the delaminations behavior over the sample thickness is of interest, for instance their location and evolution. Better image resolution with sharp defects contour were obtained for high frequencies, as expected. The main advantage of ultrasonic air-coupled system is the absence of water in the inspection procedure, which makes it simpler and less expensive. It is also important when the materials to inspect cannot be wetted for integrity or contamination reasons. As disadvantage, the air C-scan requires transmitted waves of higher power and a great amplification of the received signals in order to face the problem of acoustic losses associated with air.

ACS Style

Mário J. Santos; Jaime B. Santos; Paulo Reis; Ana Amaro. Ultrasonic C-scan techniques for damage evaluation of Carbon Fiber Reinforced Polymers submitted to low energy impacts. 2019 International Congress on Ultrasonics 2019, 38, 030002 .

AMA Style

Mário J. Santos, Jaime B. Santos, Paulo Reis, Ana Amaro. Ultrasonic C-scan techniques for damage evaluation of Carbon Fiber Reinforced Polymers submitted to low energy impacts. 2019 International Congress on Ultrasonics. 2019; 38 (1):030002.

Chicago/Turabian Style

Mário J. Santos; Jaime B. Santos; Paulo Reis; Ana Amaro. 2019. "Ultrasonic C-scan techniques for damage evaluation of Carbon Fiber Reinforced Polymers submitted to low energy impacts." 2019 International Congress on Ultrasonics 38, no. 1: 030002.