Viscoelastic behaviour of composites with epoxy matrix filled by cork powder

Reis, P.N.B.; Silva, Marco Aurélio Pinto; Santos, P.; Parente, J.M.; Bezazi, Abderrezak

doi:10.1016/j.compstruct.2019.111669

Cited by 27 publications

(24 citation statements)

References 60 publications

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“…In both cases, the data were analyzed according to the respective ASTM standards. On the other hand, and as reported in the open literature [ 26 , 27 , 28 ], these short-term tests reveal to be an easy, fast, and reliable method to predict long-term behavior. In fact, due to the main costs incurred with long-term test programs, in addition to the fact that long periods between the development of new or improved materials and their applications are not allowed, it is highly desirable that the design data could be obtained by extrapolating the results obtained by short-term tests.…”

Section: Methodssupporting

confidence: 64%

“…In general, the stress decreased over time to one value expected to be constant, but in the present work, this constant bending stress was not achieved because it focuses on short-term tests. These tests represent an easy, fast, and reliable method to predict long-term behavior [ 26 , 27 , 28 ]. Another similarity with the open literature is the existence of an initial stage, in which the stress decreases considerably with the remaining time [ 38 , 39 , 40 ].…”

Section: Resultsmentioning

confidence: 99%

“…In terms of stress relaxation, for example, literature reports complex models to the detriment of those based on spring-dashpot systems, because the data are not fitted by a linear function. Therefore, the Kohlrausch–Williams–Watts (KWW) function, an empirical “stretched exponential” function, is suggested by the open literature as an appropriate methodology to model the stress relaxation [ 27 , 28 , 39 , 40 , 48 , 49 ]. According with this model, the relaxation function ∅ as a function of time is given by Equation (4):

where σ ( t ) and σ 0 are the stress at time t and at t = 0, respectively, β a fractional power exponent (known as non-exponential factor), and τ the KWW relaxation time.…”

Section: Resultsmentioning

confidence: 99%

“…The Findley’s power law is given by Equation (5):

where ε ( t ) is the creep displacement at time t , ε 0 is the instantaneous elastic displacement or time-independent, A is the amplitude of transient creep (time-dependent), and n is a constant independent of the stress and generally less than one [ 51 ]. Several studies can be found in the open literature, where the Findley’s power law was also applied to short-term creep data [ 27 , 28 , 51 , 52 , 53 ].…”

Section: Resultsmentioning

confidence: 99%

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Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin

et al. 2020

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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.

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Section: Methodssupporting

confidence: 64%

Section: Resultsmentioning

confidence: 99%

where σ ( t ) and σ 0 are the stress at time t and at t = 0, respectively, β a fractional power exponent (known as non-exponential factor), and τ the KWW relaxation time.…”

Section: Resultsmentioning

confidence: 99%

“…The Findley’s power law is given by Equation (5):

Section: Resultsmentioning

confidence: 99%

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Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin

et al. 2020

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“…In fact, Amaro et al [13,14] and Reis et al [45] observed a significant decrease on the flexural strength and higher stress relaxation due to fibre/matrix interface degradation that was promoted by the immersion of the composite into acid and alkaline solutions. Hence, it is clear that the Polymers 2020, 12, 20 3 of 12 interface properties play a relevant role on stresses, because relaxation occurs due to the breaking of bonds and their propagation [46]. However, to the best of our knowledge, in the literature, there is a lack of studies about the effect of hostile solutions combined with different fibre directions on viscoelastic behaviour.…”

mentioning

confidence: 99%

Effect of Fibre Orientation and Hostile Solutions on Stress Relaxation of Glass/Polyamide Composites

2019

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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. Polymers 2020, 12, 20 2 of 12On the other hand, in terms of corrosive environments (alkaline and acidic solutions), the literature is much more abundant with respect to thermoset composites than thermoplastics. For instance, studies developed by Stamenovic et al. [11] in glass-polyester composites demonstrated that alkaline solutions are responsible for the decrease of tensile strength and elastic modulus, because they are highly corrosive, whereas the opposite tendency occurs when these composites are exposed to acid solutions. However, for both solutions, the changes observed are very dependent on the pH value and exposure time. Feng et al. [12] studied the effect of different solutions (H 2 SO 4 , NaCl and NaOH) on glass fibre-reinforced polymer (GFRP)/epoxy composites and observed a decrease in hardness, flexural strength and elastic modulus, and this trend is even higher for higher concentrations. Moreover, Amaro et al. [13] analysed the effect of alkaline (NaOH) and acid (HCl) solutions on the flexural properties of these composites, and the worst bending properties were obtained when the glass/epoxy composites were exposed to NaOH solutions. The effect of hydrochloric acid (HCl) and sulphuric acid (H 2 SO 4 ) was also compared by these authors, and the HCl solution was responsible for the poorest results [14]. Similar conclusions were also obtained by Kamal and Kadhim [15] on nano-silica-reinforced (glass/Kevlar) fabric polyester hybrid composites, due to the higher corrosive effect of alkaline solutions. Finally, the effects of strong acids (HCl, H 2 SO 4 , HNO 3 and H 3 PO 4 ) on mechanical properties of glass/polyester glass-reinforced pipes (GRP) at normal and high temperatures were evaluated by Mahmoud and Tantawi [16]. They observed significan...

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Creep properties and damage mechanism of molded glass fiber reinforced plastic

Liu

et al. 2023

Polymer Composites

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Glass fiber reinforced plastic (GFRP) has become one of the most commonly used materials in the structure of aero engines in the last decades. In this study, GFRP was fabricated by molding with phenolic resin as the matrix. Specimens were prepared along horizontal and vertical directions. Fiber distribution, tensile properties, long‐term creep performance, and damage mechanism were systematically investigated. Experimental results shows that horizontal specimens have better tensile properties, lower viscoelasticity, and excellent creep resistance. The fibers inside the cylindrical material exhibit a 3D core‐shell morphology with transverse isotropy in the core region. Load is carried by the fibers and the damage is in the form of fiber fracture and pull‐out in horizontal specimens. Random distribution and interweaving leads to double fracture sections of fibers. Load is carried by the interface and resin, and the damage is in the form of fiber pull‐out laterally and interfacial debonding in vertical specimens. High viscoelasticity of the resin and the weak interfacial bonding ability lead to large creep deformation of vertical specimens. In addition, the creep strain under different loads can be accurately predicted by Modified Time Hardening model.

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Viscoelastic behaviour of composites with epoxy matrix filled by cork powder

Cited by 27 publications

References 60 publications

Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin

Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin

Effect of Fibre Orientation and Hostile Solutions on Stress Relaxation of Glass/Polyamide Composites

Creep properties and damage mechanism of molded glass fiber reinforced plastic

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