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Mechanical Properties and Durability of Epoxy Resins and Epoxy-Based Composites

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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Analysis and Characterization".

Deadline for manuscript submissions: closed (31 August 2022) | Viewed by 26399

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Dr. Tatjana Glaskova-Kuzmina

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Institute for Mechanics of Materials, University of Latvia, Riga LV-1004, Latvia
Interests: mechanical engineering; materials engineering; polymers; composites; nanomaterials; environmental effects
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Dear Colleagues,

The range and amount of applications of polymers and polymer-based composites including fiber-reinforced plastics are growing continuously, mostly due to their intrinsic characteristics such as high specific strength and rigidity, good resistance to fatigue and corrosion, and the possibility to integrate additional functions. The main drawback of epoxy resins and epoxy-based composites is their relatively high sensitivity to environmental factors (e.g., moisture, temperature, UV radiation, etc.). Therefore, the analysis of the durability of such materials is particularly important for long-term applications. The use of sustainable and recyclable epoxy resins and fibers/fillers (including nanofillers) may lead to prolonged durability of such materials and also contribute to the circular economy as a whole.

This Special Issue aims to present current scientific results on the effects of the environment on the mechanical properties and durability of epoxy resins and epoxy-based composites, including experimental characterization and modelling.

The topics of interest regard the following aspects of epoxy resins and epoxy-based composites:

mechanical properties
environmental degradation and stability
structure–properties relationship
analysis and prediction of durability
long-term deformability

Dr. Tatjana Glaskova-Kuzmina
Guest Editor

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Published Papers (9 papers)

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Research

12 pages, 1436 KiB

Open AccessArticle

Comparison of Two-Component Silyl-Terminated Polyether/Epoxy Resin Model and Complete Systems and Evaluation of Their Mechanical, Rheological and Adhesive Properties

by Ritvars Berzins, Remo Merijs-Meri and Janis Zicans

Polymers 2022, 14(12), 2421; https://doi.org/10.3390/polym14122421 - 15 Jun 2022

Cited by 4 | Viewed by 2395

Abstract

The current research is devoted to the investigation of the influence of a secondary amine compatibilizer and customized additive package on the tensile, rheological and adhesive properties of a Silyl-terminated polyether (SIL)/Epoxy resin (EP) model and completed two-component systems. A SIL/EP model and completed two-component systems were developed over a broad range of the both pre-polymer ratios (90/10–30/70 wt.-to-wt%). Additive packages of the components A and B were designed to prevent premature polycondensation of the respective pre-polymers (including suitable catalysts for each of the pre-polymers, as well as vinyltrimetoxysilane as a drying agent for moisture control), to ensure easy processing and stable performance of the system. Results of the investigation testify that the values of the tensile strength and Shore-A hardness of the compatibilized systems are higher in comparison to unmodified ones. In the presence of the additive package, a further improvement of tensile strength and tensile strain values is observed for SIL-rich compositions (SIL content above 70 wt%), whereas at lower SIL concentrations, the reinforcing effect is considerably reduced. In respects to adhesion properties, the highest values to a broad range of substrates with different surface polarities are observed at the SIL/EP range from 80/20 to 50/50 wt.-to-wt%. Full article

(This article belongs to the Special Issue Mechanical Properties and Durability of Epoxy Resins and Epoxy-Based Composites)

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24 pages, 8968 KiB

Open AccessArticle

Heat-Affected Zone and Mechanical Analysis of GFRP Composites with Different Thicknesses in Drilling Processes

by Usama A. Khashaba, Mohamed S. Abd-Elwahed, Ismai Najjar, Ammar Melaibari, Khaled I. Ahmed, Redouane Zitoune and Mohamed A. Eltaher

Polymers 2021, 13(14), 2246; https://doi.org/10.3390/polym13142246 - 8 Jul 2021

Cited by 22 | Viewed by 2862

Abstract

This article presents a comprehensive thermomechanical analysis and failure assessment in the drilling of glass fiber-reinforced polymer (GFRP) composites with different thicknesses using a CNC machine and cemented carbide drill with a diameter of 6 mm and point angles of ϕ = 118°. The temperature distribution through drilling was measured using two techniques. The first technique was based on contactless measurements using an IR Fluke camera. The second was based on contact measurements using two thermocouples inserted inside the drill bit. A Kistler dynamometer was used to measure the cutting forces. The delamination factors at the hole exit and hole entry were quantified by using the image processing technique. Multi-variable regression analysis and surface plots were performed to illustrate the significant coefficients and contribution of the machining variables (i.e., feed, speed, and laminate thickness) on machinability parameters (i.e., the thrust force, torque, temperatures, and delamination). It is concluded that the cutting time, as a function of machining variables, has significant control over the induced temperature and, thus, the force, torque, and delamination factor in drilling GFRP composites. The maximum temperature recorded by the IR camera is lower than that of the instrumented drill because the IR camera cannot directly measure the tool–work interaction zone during the drilling process. At the same cutting condition, it is observed that by increasing the thickness of the specimen, the temperature increased. Increasing the thickness from 2.6 to 7.7 had a significant effect on the heat distribution of the HAZ. At a smaller thickness, increasing the cutting speed from 400 to 1600 rpm decreased the maximum thrust force by 15%. The push-out delaminations of the GFRP laminate were accompanied by edge chipping, spalling, and uncut fibers, which were higher than those of the peel-up delaminations. Full article

(This article belongs to the Special Issue Mechanical Properties and Durability of Epoxy Resins and Epoxy-Based Composites)

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19 pages, 7065 KiB

Open AccessArticle

Hygrothermal Aging Characteristics of Silicone-Modified Aging-Resistant Epoxy Resin Insulating Material

by Yongqiang Wang, Zhuo Zeng, Meng Gao and Ziye Huang

Polymers 2021, 13(13), 2145; https://doi.org/10.3390/polym13132145 - 29 Jun 2021

Cited by 14 | Viewed by 2949

Abstract

To study the improvement effect of silicone materials on the hygrothermal resistance of epoxy resin and the aging mechanism of silicone-modified insulation materials under hygrothermal conditions, diphenylsilanediol was added to epoxy resin as a modifier in various quantities to synthesize silicone-modified epoxy resin, and a hygrothermal aging test was carried out. Water sorption, surface contact angles and dielectric properties of the insulation material were measured, and scanning electron microscope (SEM), Fourier-transform infrared spectrometry (FT-IR) and frequency domain spectroscopy (FDS) were used to analyze the results. The results showed that under 10 wt%, the silicone-modified insulation materials exhibited lower absorption rate and better dielectric properties, including lower dissipation factors and lower dielectric constant during the hygrothermal aging process, while epoxy resin modified with excessive silicone material tend to show worse dielectric performance. Closer analysis found that diphenylsilanediol decreases the size of the cracks within the material during hygrothermal aging, indicating that cracks generated during the hygrothermal aging process may be the reason for the worse dielectric performance, and diphenylsilanediol improves the hygrothermal aging resistance mainly by slowing down the generation and growth rate of cracks. FT-IR results confirmed the existence of hydrolysis and found that the rate of hydrolysis does not change with the content of diphenylsilanediol. FDS results also indicated that modified materials contain less dipoles after hygrothermal aging. Full article

(This article belongs to the Special Issue Mechanical Properties and Durability of Epoxy Resins and Epoxy-Based Composites)

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13 pages, 4771 KiB

Open AccessArticle

Hygrothermal Ageing Influence on BVI-Damaged Carbon/Epoxy Coupons under Compression Load

by Maria Pia Falaschetti, Matteo Scafé, Nicola Zavatta and Enrico Troiani

Polymers 2021, 13(13), 2038; https://doi.org/10.3390/polym13132038 - 22 Jun 2021

Cited by 9 | Viewed by 2069

Abstract

Composite materials usage in several industrial fields is now widespread, and this leads to the necessity of overcoming issues that are still currently open. In the aeronautic industry, this is especially true for Barely Visible Impact Damage (BVID) and humidity uptake issues. BVID is the most insidious kind of impact damage, being rather common and not easily detectable. These, along with the ageing that a composite structure could face during its operative life, could be a cause of fatal failures. In this paper, the influence of water absorption on impacted specimens compressive residual strength was studied. Specimens were impacted using a modified Charpy pendulum. Two different locations were chosen for comparison: Near-Edge (NE) and Central (CI). Accelerated hygrothermal ageing was conducted on impacted and reference nonimpacted coupons, placing them in a water-filled jar at 70 °C. Compressive tests were performed in accordance with the Combined Loading Compression (CLC) test method. A Dynamic Mechanical Analysis (DMA) was performed as well. The results showed the influence of hygrothermal ageing, as expected. Nevertheless, the influence of impact location on compressive residual strength is not clearly noticeable in aged specimens, leading to the conclusion that hygrothermal ageing may have a greater effect on composite compressive strength than the analysed BVI damage. Full article

(This article belongs to the Special Issue Mechanical Properties and Durability of Epoxy Resins and Epoxy-Based Composites)

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10 pages, 1381 KiB

Open AccessArticle

Effect of Thermal Ageing on the Mechanical Strength of Carbon Fibre Reinforced Epoxy Composites

by Nicola Zavatta, Francesco Rondina, Maria Pia Falaschetti and Lorenzo Donati

Polymers 2021, 13(12), 2006; https://doi.org/10.3390/polym13122006 - 19 Jun 2021

Cited by 32 | Viewed by 3327

Abstract

Applications of Carbon Fibre Reinforced Polymers (CFRP) at temperatures over 150–200 °C are becoming common in aerospace and automotive applications. Exposure of CFRP to these temperatures can lead to permanent changes in their mechanical properties. In this work, we investigated the effect of thermal ageing in air on the strength of carbon fabric/epoxy composites. To this end, accelerated artificial ageing at different temperatures was performed on carbon fabric/epoxy specimens. The flexural and interlaminar shear strengths of the aged specimens were assessed by three-point bending and short beam shear tests, respectively, and compared to those of unaged samples. For ageing at temperatures below the glass transition temperature of the resin,

T_{g}

, a moderate reduction of strength was found, with a maximum decrease of 25% for 2160 h at 75%

T_{g}

. On the other hand, a rapid strength decrease was observed for ageing temperatures above

T_{g}

. This was attributed to degradation of the epoxy matrix and of the fibre/epoxy interface. In particular, a 30% strength decrease was found for less than 6 h at 145%

T_{g}

. Therefore, it was concluded that even a short exposure to operating temperatures above

T_{g}

could substantially impair the load-carrying capability of CFRP components. Full article

(This article belongs to the Special Issue Mechanical Properties and Durability of Epoxy Resins and Epoxy-Based Composites)

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13 pages, 6073 KiB

Open AccessArticle

MXene (Ti₃C₂T_x) Functionalized Short Carbon Fibers as a Cross-Scale Mechanical Reinforcement for Epoxy Composites

by Lu Liu, Guobing Ying, Cheng Sun, Huihua Min, Jianxin Zhang, Yinlong Zhao, Dong Wen, Ziying Ji, Xing Liu, Chen Zhang and Cheng Wang

Polymers 2021, 13(11), 1825; https://doi.org/10.3390/polym13111825 - 31 May 2021

Cited by 20 | Viewed by 3569

Abstract

The surface modification technology of carbon fibers (CFs) have achieved considerable development, and it has achieved great success in improving the interfacial shear strength (IFSS) of the polymer matrix. Among them, MXene (Ti₃C₂T_x) functionalized CFs have been proven to improve the interface performance significantly. Unfortunately, the results on the microscopic scale are rarely applied to the preparation of macroscopic composite materials. Herein, the process of MXene functionalized CFs were attempted to be extended to short carbon fibers (SCFs) and used to strengthen epoxy materials. The results show that the cross-scale reinforcement of MXene functionalized SCFs can be firmly bonded to the epoxy matrix, which significantly improves the mechanical properties. Compared to neat epoxy, the tensile strength (141.2 ± 2.3 MPa), flexural strength (199.3 ± 8.9 MPa) and critical stress intensity factor (K_IC, 2.34 ± 0.04 MPa·m^1/2) are increased by 100%, 67%, and 216%, respectively. Full article

(This article belongs to the Special Issue Mechanical Properties and Durability of Epoxy Resins and Epoxy-Based Composites)

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17 pages, 7079 KiB

Open AccessArticle

Interfacial Binding Energy between Calcium-Silicate-Hydrates and Epoxy Resin: A Molecular Dynamics Study

by Xianfeng Wang, Wei Xie, Jun Ren, Jihua Zhu, Long-Yuan Li and Feng Xing

Polymers 2021, 13(11), 1683; https://doi.org/10.3390/polym13111683 - 21 May 2021

Cited by 21 | Viewed by 2991

Abstract

Microcapsules encapsulated within epoxy as a curing agent have been successfully applied in self-healing materials, in which the healing performance significantly depends on the binding behaviour of the epoxy curing agent with the cement matrix. In this paper, the binding energy was investigated by molecular dynamics simulation, which could overcome the shortcomings of traditional microscopic experimental methods. In addition to the construction of different molecular models of epoxy, curing agents, and dilutants, seven models were established to investigate the effects of chain length, curing agent, and epoxy resin chain direction on the interfacial binding energy. The results showed that an increase of chain length exhibited had limited effect on the binding energy, while the curing agent and the direction of the epoxy significantly affected the interfacial binding energy. Among different factors, the curing agent tetrethylenepentamine exhibited the highest value of interfacial binding energy by an increment of 31.03 kcal/mol, indicating a better binding ability of the microcapsule core and the cement matrix. This study provides a microscopic insight into the interface behaviour between the microcapsule core and the cement matrix. Full article

(This article belongs to the Special Issue Mechanical Properties and Durability of Epoxy Resins and Epoxy-Based Composites)

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16 pages, 5015 KiB

Open AccessArticle

Interrelation between Fiber–Matrix Interphasial Phenomena and Flexural Stress Relaxation Behavior of a Glass Fiber–Polymer Composite

by George C. Papanicolaou, Diana V. Portan and Lykourgos C. Kontaxis

Polymers 2021, 13(6), 978; https://doi.org/10.3390/polym13060978 - 23 Mar 2021

Cited by 7 | Viewed by 2126

Abstract

The response of fiber-reinforced polymer composites to an externally applied mechanical excitation is closely related to the microscopic stress transfer mechanisms taking place in the fiber–matrix interphasial region. In particular, in the case of viscoelastic responses, these mechanisms are time dependent. Defining the interphase thickness as the maximum radial distance from the fiber surface where a specific matrix property is affected by the fiber presence, it is important to study its variation with time. In the present investigation, the stress relaxation behavior of a glass fiber-reinforced polymer (GFRP) under flexural conditions was studied. Next, applying the hybrid viscoelastic interphase model (HVIM), developed by the first author, the interphase modulus and interphase thickness were both evaluated, and their variation with time during the stress relaxation test was plotted. It was found that the interphase modulus decreases with the radial distance, being always higher than the bulk matrix modulus. In addition, the interphase thickness increases with time, showing that during stress relaxation, fiber–matrix debonding takes place. Finally, the effect of fiber interaction on the interphase modulus was found. It is observed that fiber interaction depends on both the fiber–matrix degree of adhesion as well as the fiber volume fraction and the time-dependent interphase modulus. Full article

(This article belongs to the Special Issue Mechanical Properties and Durability of Epoxy Resins and Epoxy-Based Composites)

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14 pages, 2574 KiB

Open AccessArticle

Basalt Fibre Composite with Carbon Nanomodified Epoxy Matrix under Hydrothermal Ageing

by Tatjana Glaskova-Kuzmina, Aldobenedetto Zotti, Anna Borriello, Mauro Zarrelli and Andrey Aniskevich

Polymers 2021, 13(4), 532; https://doi.org/10.3390/polym13040532 - 11 Feb 2021

Cited by 15 | Viewed by 2237

Abstract

This work aimed to investigate the effect of hybrid carbon nanofillers (e.g., carbon nanotubes/carbon nanofibers in the ratio 1:1 by mass) over the electrical and flexural properties for an epoxy matrix and corresponding basalt fibre reinforcing composite (BFRC) subjected to full-year seasonal water absorption. Hydrothermal ageing was performed by full immersion of the tested materials into distilled water according to the following model conditions (seasons). The mechanical properties were measured in three-point bending mode before environmental ageing and after each season. Upon environmental ageing, the relative change of flexural strength and elastic modulus of the epoxy and NC was within 10–15%. For nanomodified BFRCs, the slightly higher effect (approx. by 10%) of absorbed moisture on flexural characteristics was found and likely attributed to higher defectiveness (e.g., porosity, the formation of agglomerates etc.). During flexural tests, electrical resistance of the nanocomposites (NC) and BFRC/NC samples was evaluated. The electrical conductivity for UD BFRC/NC, before and after hydrothermal ageing, was by 2 and 3 times higher than for the NC, accordingly, revealing the orientation of electrically conductive nanoparticles and/or their agglomerates during lay-up manufacturing which was evaluated by the rules of the mixture. Based on all results obtained it can be concluded that the most potentially applicable for damage indication was UD BFRC/NC along fibres since full-year hydrothermal ageing improved its electrical conductivity by approx. 98% and, consequently, the ability to monitor damages was also enhanced. Full article

(This article belongs to the Special Issue Mechanical Properties and Durability of Epoxy Resins and Epoxy-Based Composites)

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