Effect of Long-Term Thermal Relaxation of Epoxy Binder on Thermoelasticity of Fiberglass Plastics: Multiscale Modeling and Experiments
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials
- Epoxy resin KER 828, with the following main characteristics: Epoxy Group Content (EGC) 5308 mmol/kg, Epoxide Equivalent Weight (EEW) 188.5 g/eq, viscosity at 25 °C 12.7 Pa·s, HCl 116 mg/kg, and total chlorine 1011 mg/kg. Manufacturer: KUMHO P&B Chemicals, Gwangju, South Korea.
- Hardener for epoxy resin methyl tetrahydrophthalic anhydride with the following main characteristics: viscosity at 25 °C 63 Pa·s, anhydride content 42.4%, volatile fraction content 0.55%, and free acid 0.1%. Manufacturer: ASAMBLY Chemicals company Ltd., Nanjing, China.
- Alkophen (epoxy resin curing accelerator) with the following main characteristics: viscosity at 25 °C 150 Pa·s, molecular formula C15H27N3O, molecular weight 265, and amine value 600 mg KOH/g. Manufacturer: Epital JSC, Moscow, Russian Federation.
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- Thickness 0.190 + 0.01/−0.02 mm;
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- Surface density 200 + 16/−10 g/m2;
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- Number of yarns per 1 cm of fabric on the basis 12 +/− 1;
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- Number of yarns per 1 cm of fabric on the weft 8 +/− 1;
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- Weave—plain;
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- Oiling agent—paraffin emulsion.
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- Thickness, 0.27 + 0.01/−0.02 mm;
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- Surface density, 260 + 25/−25 g/m2;
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- Number of yarns per 1 cm of fabric on the basis 12 +/− 1;
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- Number of yarns per 1 cm of fabric on the weft 8 +/− 1;
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- Weave—plain;
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- Oiling agent—aminosilane.
2.2. Methods
2.2.1. Long Heat Treatment
2.2.2. Investigation of Elasticity Modulus under Heating
2.2.3. Prediction of the Deformation Characteristics of FRP
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- The fiber composite being modeled consists of isotropic linear-elastic matrix material and isotropic or transversally isotropic linear-elastic filament material;
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- The volume fraction of fibers in the filaments is constant;
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- The representative volume of the material is strictly periodic.
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- The following parameters are set as the initial data for the woven composite model:
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- Weaving type—a type of fabric weaving (plain or twill);
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- Fiber volume fraction—share of fiber volume in the volume of the whole RVE;
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- Yarn fiber volume fraction is the fraction of volume in a separate thread, which is taken up by the fiber material (glass in our case), the volume of the yarn “net”;
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- Shear angle—the angle in degrees of warping the fibers due to drape properties of the fabric;
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- Yarn spacing—the distance between the centers of cross-sections of neighboring yarns;
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- Fabric thickness—thickness of the modeled RVE;
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- Repeat count—number of elementary cells considered in the model in the direction of each coordinate;
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- Align with x-direction—the fibers are oriented along the x-axis (if not, they are oriented at a 45° angle to the x-axis).
3. Results
3.1. Experimental Results
3.2. Prediction of the Thermomechanical Characteristics of Fiberglass Plastics Using the Finite Element Method
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- Stage 2—the refinement of the elastic modulus of the multilayer composite using three-point bend modeling (for example, in the ANSYS APDL module), considering the polymer matrix interlayers between the reinforced monolayers.
3.3. Predicting Properties Using the Entropy Approach
4. Discussion
5. Conclusions
- After a prolonged exposure of the fiberglass samples (504 h in total) at temperatures higher than the initial glass transition temperature of the polymer–binder matrix, the flexural modulus at temperatures above 100 to 110 °C significantly increased (up to 1.6 times for samples on the EZ-200 fabric, up to 1.9 times for samples on the T-23 fabric), at lower temperatures the flexural modulus either did not change or decreased slightly.
- The bending strength after curing decreased by about 16% in the samples on the EZ-200 fabric and by 8% in the samples on the T-23 fabric.
- The entropy value of fiberglass plastic was up to two times lower than that of unreinforced polymer, indicating that the composite structure was much more ordered. After thermal relaxation, the entropy level decreased by another 20% and leveled out for both types of FRP (on different types of glass fabrics). Therefore, the difference between the elastic properties of fiberglass composites on different fabrics may be related to their somewhat different fiber–matrix bonding properties.
- The calculated values of the modulus of elasticity at room temperature showed the best coincidence with the experiment (almost complete coincidence), while at elevated temperatures, the experimental values of the modulus of elasticity were higher than the predicted ones, which, on the one hand, requires additional research to clarify the reason for the difference, and on the other hand, from the standpoint of reliability for solving practical problems, it is better than overestimation, since it goes into the reliability reserve.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
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Description of FRP | Type No | Specimen No | b, mm | h, mm | E, MPa | σ, MPa | Eav, MPa | σav, MPa | Eunexp/Eexp * | σunexp/σexp * |
Epoxy FRP on EZ-200 unexposed | 1 | 10 | 17.35 | 2.3 | 13.827 | 286 | 13,307/381 (2.86%) | 325/54 (16.7%) | 1.18 | 1.24 |
1 | 11 | 18.8 | 2.4 | 13.281 | 374 | |||||
1 | 12 | 16.55 | 2.35 | 13.380 | 270 | |||||
1 | 13 | 16.85 | 2.55 | 12.650 | 374 | |||||
1 | 14 | 18.1 | 2.35 | 13.270 | 272 | |||||
1 | 15 | 17.15 | 2.5 | 13.435 | 376 | |||||
Epoxy FRP on EZ-200 exposed | 1 | 4 | 17.75 | 2.45 | 12.100 | 304 | 11,323/781 (6.90%) | 263/40.4 (15.35%) | ||
1 | 5 | 18.5 | 2.9 | 10.150 | 254 | |||||
1 | 6 | 17.6 | 2.6 | 10.700 | 278 | |||||
1 | 7 | 18 | 2.45 | 12.100 | 216 | |||||
1 | 8 | 16.85 | 2.55 | 11.610 | 308 | |||||
1 | 9 | 17.65 | 2.7 | 11.280 | 219 | |||||
Epoxy FRP on T-23 unexposed | 3 | 9 | 17.6 | 2.45 | 13.540 | 205 | 13,348/622 (4.66%) | 201/11.9 (5.92%) | 1.06 | 1.26 |
3 | 10 | 17.7 | 2.25 | 13.160 | 186 | |||||
3 | 11 | 17.55 | 2.2 | 13.590 | 196 | |||||
3 | 12 | 16.9 | 2.45 | 12.240 | 193 | |||||
3 | 13 | 17.7 | 2.2 | 14.100 | 220 | |||||
3 | 14 | 18.65 | 2.35 | 13.460 | 205 | |||||
Epoxy FRP on T-23 exposed | 3 | 2 | 16.35 | 2.5 | 11.600 | 146.4 | 12,612/831 (6.59%) | 159/12.4 (7.77%) | ||
3 | 4 | 18.6 | 2.45 | 11.790 | 147 | |||||
3 | 5 | 18.6 | 2.45 | 12.480 | 150 | |||||
3 | 6 | 17.5 | 2.3 | 13.720 | 170 | |||||
3 | 7 | 17.75 | 2.35 | 13.310 | 172.3 | |||||
3 | 8 | 18.45 | 2.45 | 12.770 | 168 |
Description of FRP | Type No | Average Density Unexposed, kg/m3 | Average Density Exposed, kg/m3 | Average Density Change | Average Mass Change |
---|---|---|---|---|---|
Epoxy FRP on EZ-200 | 1 | 1607.7 | 1672.2 | 4.01% | −0.983% |
Epoxy FRP on T-23 | 3 | 1803.7 | 1841.0 | 2.07% | −1.175% |
Composition | Temperature, °C | Efact, MPa | S, J/J | Ecalc, MPa | % Deviation | |
---|---|---|---|---|---|---|
EP + EZ-200 before thermal relaxation | 25 | 11.405 | 2.4 | 1.000 | - | - |
65 | 11.340 | 0.698 | 10.131 | −10.7 | ||
110 | 10.460 | 0.398 | 7925 | −24.2 | ||
140 | 4265 | 0.217 | 5568 | 30.6 | ||
160 | 3780 | 0.103 | 3241 | −14.3 | ||
EP + EZ-200 after thermal relaxation | 25 | 11.295 | 2.0 | 1.000 | - | |
110 | 9575 | 0.498 | 8741 | −8.7 | ||
140 | 6465 | 0.347 | 7311 | 13.1 | ||
160 | 5485 | 0.253 | 6081 | 10.9 | ||
180 | 5080 | 0.162 | 4526 | 10.9 | ||
200 | n/a | 0.076 | 2496 | - |
Composition | Temperature, °C | Efact, MPa | S, J/J | Ecalc, MPa | % Deviation | |
---|---|---|---|---|---|---|
EP + T-23 before thermal relaxation | 25 | 11.680 | 2.42 | 1 | - | - |
65 | 11.600 | 0.695 | 10.362 | −10.7 | ||
110 | 10.000 | 0.393 | 8063 | −19.4 | ||
140 | 3955 | 0.210 | 5589 | 41.3 | ||
160 | 3640 | 0.096 | 3124 | −14.2 | ||
EP + T-23 after thermal relaxation | 25 | 11.555 | 2.0 | 1 | - | - |
110 | 10.155 | 0.498 | 8942 | −11.9 | ||
140 | 7115 | 0.347 | 7479 | 5.1 | ||
160 | 5780 | 0.253 | 6221 | 7.6 | ||
180 | 5115 | 0.162 | 4630 | −9.5 | ||
200 | n/a | 0.076 | 2553 | - |
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Mishnev, M.; Korolev, A.; Ekaterina, B.; Dmitrii, U. Effect of Long-Term Thermal Relaxation of Epoxy Binder on Thermoelasticity of Fiberglass Plastics: Multiscale Modeling and Experiments. Polymers 2022, 14, 1712. https://doi.org/10.3390/polym14091712
Mishnev M, Korolev A, Ekaterina B, Dmitrii U. Effect of Long-Term Thermal Relaxation of Epoxy Binder on Thermoelasticity of Fiberglass Plastics: Multiscale Modeling and Experiments. Polymers. 2022; 14(9):1712. https://doi.org/10.3390/polym14091712
Chicago/Turabian StyleMishnev, Maxim, Alexander Korolev, Bartashevich Ekaterina, and Ulrikh Dmitrii. 2022. "Effect of Long-Term Thermal Relaxation of Epoxy Binder on Thermoelasticity of Fiberglass Plastics: Multiscale Modeling and Experiments" Polymers 14, no. 9: 1712. https://doi.org/10.3390/polym14091712