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17 pages, 4596 KiB

Open AccessArticle

Understanding the Dynamic Loss Modulus of NR/SBR Blends in the Glassy–Rubbery Transition Zone

by Angel J. Marzocca, Marcela A. Mansilla, María Pía Beccar Varela and María Cristina Mariani

Polymers 2025, 17(10), 1312; https://doi.org/10.3390/polym17101312 - 11 May 2025

Viewed by 213

Abstract

The motivation of this research was to analyze the dynamic properties, mainly the loss modulus, of vulcanized immiscible blends of natural rubber (NR) and styrene-butadiene rubber (SBR) in the glass transition zone, where the SBR phase is in a glassy state and the [...] Read more.

The motivation of this research was to analyze the dynamic properties, mainly the loss modulus, of vulcanized immiscible blends of natural rubber (NR) and styrene-butadiene rubber (SBR) in the glass transition zone, where the SBR phase is in a glassy state and the NR phase is in a rubbery state. The blends were cured at 433 and 443 K and studied around the glass transition using a dynamic mechanical analyzer. The dependence of the loss modulus on temperature was described by considering the phase separation, and the frequency dependence was also included to provide a deeper insight into the dynamic properties. This was achieved by integrating the mechanical model proposed by Zener, which considers a single relaxation time related to temperature using both the Arrhenius and Vogel–Fulcher–Tammann (VFT) relations. The best correlation with the data was obtained using the Arrhenius relationship. The activation energy of the NR phase increases with the NR content in the blend, while in the SBR phase, it varies slightly. The trends obtained are related to curative migration from the SBR to the NR phase, increasing the crosslink density at NR domain boundaries. These insights are valuable for optimizing the performance of these elastomeric blends in practical applications. Full article

(This article belongs to the Special Issue Mechanical and Dynamic Characteristics of Polymers and Polymer Composites)

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14 pages, 9154 KiB

Open AccessArticle

Evaluation of the Mechanical Properties of Highly Oriented Recycled Carbon Fiber Composites Using the Vacuum-Assisted Resin Transfer Molding, Wet-Layup, and Resin Transfer Molding Methods

by Mio Sato, Yuki Kataoka, Masumi Higashide, Yuichi Ishida and Sunao Sugimoto

Polymers 2025, 17(10), 1293; https://doi.org/10.3390/polym17101293 - 8 May 2025

Viewed by 332

Abstract

Recycling carbon-fiber-reinforced plastics (CFRPs) is crucial for sustainable material utilization, particularly in aerospace applications, where large quantities of prepreg waste are generated. This study investigated the mechanical properties of highly oriented recycled CFRP (rCFRP) molded using vacuum-assisted resin transfer molding (VaRTM), wet-layup, and [...] Read more.

Recycling carbon-fiber-reinforced plastics (CFRPs) is crucial for sustainable material utilization, particularly in aerospace applications, where large quantities of prepreg waste are generated. This study investigated the mechanical properties of highly oriented recycled CFRP (rCFRP) molded using vacuum-assisted resin transfer molding (VaRTM), wet-layup, and traditional RTM methods. Recycled carbon fibers (rCFs) obtained via solvolysis and pyrolysis were processed into nonwoven preforms to ensure fiber alignment through carding. The influence of molding methods, fiber recycling techniques, and fiber orientation on mechanical performance was examined through tensile tests, fiber volume fraction (Vf) analysis, and scanning electron microscopy observations. The results indicated that the solvolysis-recycled rCF exhibited superior interfacial adhesion with the resin, leading to a higher tensile strength and stiffness, particularly in the RTM process, where a high Vf was achieved. Wet-layup molding effectively reduced the void content owing to autoclave curing, maintaining stable properties even with pyrolyzed rCF. VaRTM, while enabling vacuum-assisted resin infusion, exhibited a higher void content, limiting improvements in mechanical performance. This study highlights that tailoring the molding method according to the desired performance, such as increasing stiffness potential by enhancing Vf in RTM or improving tensile strength by improving fiber–matrix adhesion in wet-layup molding, is critical for optimizing rCFRP properties, providing important insights into sustainable CFRP recycling and high-performance material design. Full article

(This article belongs to the Special Issue Mechanical and Dynamic Characteristics of Polymers and Polymer Composites)

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17 pages, 5072 KiB

Open AccessArticle

Numerical Simulations for Damage and Failure of a Polymer Material Subjected to Thermal Fatigue Loading

by Jun Koyanagi, Takumu Sugiyama, M. J. Mohammad Fikry, Yutong Li and Takuhei Tsukada

Polymers 2025, 17(9), 1153; https://doi.org/10.3390/polym17091153 - 23 Apr 2025

Viewed by 243

Abstract

This study proposes a novel numerical approach to simulate damage accumulation and failure in polymer materials under thermal fatigue, using an entropy-based damage criterion. Unlike the many experimental studies in this area, few numerical simulations exist due to the complexity of modeling thermal [...] Read more.

This study proposes a novel numerical approach to simulate damage accumulation and failure in polymer materials under thermal fatigue, using an entropy-based damage criterion. Unlike the many experimental studies in this area, few numerical simulations exist due to the complexity of modeling thermal fatigue. In our method, thermal and mechanical stresses arising from thermal expansion mismatches and temperature gradients are modeled through a coupled simulation approach. A viscoelastic constitutive equation is implemented in ABAQUS via a user-defined subroutine to capture damage progression. The method includes surface and internal thermal conduction, thermal deformation, and time–temperature superposition using reduced viscosity, enabling accurate simulation under varying thermal conditions. The results show that localized thermal stresses induced by temperature gradients lead to progressive damage and failure. This study demonstrates the first successful numerical simulation of thermal fatigue-induced damage in polymer materials. The proposed framework reduces the need for extensive experiments and offers insights into residual stress prediction and durability evaluation, contributing to polymer design and application in high-performance environments. Full article

(This article belongs to the Special Issue Mechanical and Dynamic Characteristics of Polymers and Polymer Composites)

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16 pages, 4499 KiB

Open AccessArticle

Change in Thermodynamic Entropy and Free Volume of Epoxy Resin During Tensile Deformation

by Takuma Inoue, Yutaka Oya, Jun Koyanagi and Takenobu Sakai

Polymers 2025, 17(4), 477; https://doi.org/10.3390/polym17040477 - 12 Feb 2025

Viewed by 697

Abstract

The relationship between thermodynamic entropy generation and free volume changes during the tensile deformation of epoxy resin was investigated. Thermodynamic entropy generation was evaluated using differential scanning calorimetry (DSC) for samples at various strain levels, while free volume changes were measured with positron [...] Read more.

The relationship between thermodynamic entropy generation and free volume changes during the tensile deformation of epoxy resin was investigated. Thermodynamic entropy generation was evaluated using differential scanning calorimetry (DSC) for samples at various strain levels, while free volume changes were measured with positron annihilation lifetime spectroscopy (PALS). Volumetric strain was assessed through the digital image correlation (DIC) method. The results showed that both thermodynamic entropy and free volume increase during tensile deformation, and the average free volume radius becomes more uniform. It was observed that thermodynamic entropy generation and free volume each exhibit a linear relationship with volumetric strain. Additionally, thermodynamic entropy generation increased linearly with free volume. These findings suggest that the increase in thermodynamic entropy during tensile deformation is attributed to irreversible changes, such as the expansion of free volume within the material. Full article

(This article belongs to the Special Issue Mechanical and Dynamic Characteristics of Polymers and Polymer Composites)

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18 pages, 4043 KiB

Open AccessArticle

Numerical Simulation of Fatigue Damage in Cross-Ply CFRP Laminates: Exploring Frequency Dependence and Internal Heat Generation Effects

by Natsuko Kudo, M. J. Mohammad Fikry, Shinji Ogihara and Jun Koyanagi

Polymers 2025, 17(3), 432; https://doi.org/10.3390/polym17030432 - 6 Feb 2025

Viewed by 880

Abstract

A numerical simulation investigating the frequency dependence of fatigue damage progression in carbon fiber-reinforced plastics (CFRPs) is conducted in this study. The initiation and propagation of transverse cracks under varying fatigue test frequencies are successfully simulated, consistent with experiments, using an enhanced degradable [...] Read more.

A numerical simulation investigating the frequency dependence of fatigue damage progression in carbon fiber-reinforced plastics (CFRPs) is conducted in this study. The initiation and propagation of transverse cracks under varying fatigue test frequencies are successfully simulated, consistent with experiments, using an enhanced degradable Hashin failure model that was originally developed by the authors in 2022. The results obtained from the numerical simulation in the present study, which employs adjusted numerical values for the purpose of damage acceleration, indicate that the number of cycles required for the formation of three transverse cracks was 174 cycles at 0.1 Hz, 209 cycles at 1 Hz, and 165 cycles at 10 Hz. Based on these results, it is demonstrated that under high-frequency cyclic loading, internal heat generation caused by dissipated energy from mechanical deformation, attributed to the viscoelastic and/or plastic behavior of the material, exceeds thermal dissipation to the environment, leading to an increase in specimen temperature. Consequently, damage progression accelerates under high-frequency fatigue. In contrast, under low-frequency fatigue, viscoelastic dissipation becomes more pronounced, reducing the number of cycles required to reach a similar damage state. The rate of damage accumulation initially increases with test frequency but subsequently decreases. This observation underscores the importance of incorporating these findings into discussions on the fatigue damage of real structural components. Full article

(This article belongs to the Special Issue Mechanical and Dynamic Characteristics of Polymers and Polymer Composites)

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12 pages, 1202 KiB

Open AccessArticle

Influence of Monomer Size on CO₂ Adsorption and Mechanical Properties in Microporous Cyanate Ester Resins

by Yukun Bai, Gota Kikugawa and Naoki Kishimoto

Polymers 2025, 17(2), 148; https://doi.org/10.3390/polym17020148 - 9 Jan 2025

Viewed by 726

Abstract

Molecular simulations offer valuable insights into thermosetting polymers’ microstructures and interactions with small molecules, aiding in the development of advanced materials. In this study, we design two cyanate resin models featuring monomers of different sizes and employ a previously developed method to generate [...] Read more.

Molecular simulations offer valuable insights into thermosetting polymers’ microstructures and interactions with small molecules, aiding in the development of advanced materials. In this study, we design two cyanate resin models featuring monomers of different sizes and employ a previously developed method to generate crosslinked structures. We then analyze their crosslinking processes and physicochemical properties. Using quantum chemistry calculations and a GCMC/MD approach, we investigate CO₂ adsorption. Our results show that monomer size does not significantly affect the crosslinking process and provides a degree of polymerization as 83.8 ± 0.3% vs. 76.7 ± 1.4%, but it does influence key properties, such as the glass transition temperature (520 K vs. 420 K) and Young’s modulus (2.32 GPa vs. 1.77 GPa). Moreover, CO₂ adsorption differs between the two models: the introduction of propyl ether moieties lowers by around 70% CO₂ uptake, indicating that specific adsorption sites impact gas adsorption. This study demonstrates a promising strategy for designing and optimizing thermosetting polymers with controllable gas separation and storage capabilities. Full article

(This article belongs to the Special Issue Mechanical and Dynamic Characteristics of Polymers and Polymer Composites)

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12 pages, 2894 KiB

Open AccessArticle

Efficient Prediction of Fatigue Damage Analysis of Carbon Fiber Composites Using Multi-Timescale Analysis and Machine Learning

by Satoru Yoshimori, Jun Koyanagi and Ryosuke Matsuzaki

Polymers 2024, 16(23), 3448; https://doi.org/10.3390/polym16233448 - 9 Dec 2024

Cited by 1 | Viewed by 1036

Abstract

Carbon fiber reinforced plastic (CFRP) possesses numerous advantages, such as a light weight and high strength; however, its complex damage mechanisms make the evaluation of fatigue damage particularly challenging. Therefore, this study proposed and demonstrated an entropy-based damage evaluation model for CFRP that [...] Read more.

Carbon fiber reinforced plastic (CFRP) possesses numerous advantages, such as a light weight and high strength; however, its complex damage mechanisms make the evaluation of fatigue damage particularly challenging. Therefore, this study proposed and demonstrated an entropy-based damage evaluation model for CFRP that leverages the entropy derived from heat capacity measurements and does not require knowledge of the loading history. This entropy-based fatigue degradation model, though accurate, is computationally intensive and impractical for high-cycle analysis. To address this, we reduce computational cost through multi-timescale analysis, replacing cyclic loading with constant displacement loading. Characteristic variables are optimized using the machine learning model LightGBM and the response surface method (RSM), with LightGBM achieving a 75% lower root mean squared error than RSM by increasing features from 3 to 21. This approach cuts analysis time by over 90% while retaining predictive accuracy, showing that LightGBM outperforms RSM and that multi-timescale analysis effectively reduces computational demands. Full article

(This article belongs to the Special Issue Mechanical and Dynamic Characteristics of Polymers and Polymer Composites)

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14 pages, 3219 KiB

Open AccessArticle

Numerical Simulation for Durability of a Viscoelastic Polymer Material Subjected to Variable Loadings Fatigue Based on Entropy Damage Criterion

by Yutong Li, M. J. Mohammad Fikry and Jun Koyanagi

Polymers 2024, 16(20), 2857; https://doi.org/10.3390/polym16202857 - 10 Oct 2024

Cited by 5 | Viewed by 1304

Abstract

This study aims to explore the impact of load history on the premature failure of the viscoelastic polymer matrix in carbon-fiber-reinforced plastics (CFRPs) using a method based on the concept of fracture fatigue entropy (FFE). A user-defined subroutine (UMAT) developed by the authors [...] Read more.

This study aims to explore the impact of load history on the premature failure of the viscoelastic polymer matrix in carbon-fiber-reinforced plastics (CFRPs) using a method based on the concept of fracture fatigue entropy (FFE). A user-defined subroutine (UMAT) developed by the authors in previous studies was incorporated to apply the FFE damage criterion using ABAQUS software. Several variable-amplitude load modes, including frequent load amplitude changes and intermittent interruptions, were designed based on the conventional linear damage accumulation method (Palmgren–Miner rule), and the fatigue life under these loadings was obtained via numerical simulations. The results show that both frequent amplitude changes and even brief pauses in loading can accelerate damage accumulation, leading to premature failure of the polymer matrix. In these scenarios, the fatigue life ranged from 33.6% to 91.9% of the predictions made using the Palmgren–Miner rule, which shows significant variation and highlights cases in which the predicted fatigue life falls far short of expectations. This study offers a more practical and reliable approach for predicting fatigue life under complex loading conditions. Since the accuracy of the FFE criterion has been comprehensively validated in previous studies, this research focuses on its application to predict failure under variable loading conditions. Full article

(This article belongs to the Special Issue Mechanical and Dynamic Characteristics of Polymers and Polymer Composites)

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Review

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21 pages, 3082 KiB

Open AccessReview

Review on Damage and Failure in Adhesively Bonded Composite Joints: A Microscopic Aspect

by Sota Oshima and Jun Koyanagi

Polymers 2025, 17(3), 377; https://doi.org/10.3390/polym17030377 - 30 Jan 2025

Viewed by 1018

Abstract

Adhesively bonded joints offer numerous advantages for industrial applications. However, because damage and failure in adhesively bonded joints occur within thin adhesive layers between stiff adherends, experimental characterization and numerical simulation that account for microscopic phenomena are particularly challenging. For adhesively bonded composite [...] Read more.

Adhesively bonded joints offer numerous advantages for industrial applications. However, because damage and failure in adhesively bonded joints occur within thin adhesive layers between stiff adherends, experimental characterization and numerical simulation that account for microscopic phenomena are particularly challenging. For adhesively bonded composite joints, in particular, the interaction between adhesive and adherend damage must also be carefully considered. This review article mainly discusses and reviews the microscopic aspects of damage and failure in adhesively bonded composite joints for aerospace applications. Three main topics are addressed in this article. First, the peculiar deformation and damage behaviors of polymeric materials, including their dependence on stress triaxiality, are discussed. Second, the experimental characterization of deformation and damage in adhesive layers using advanced microscale inspection techniques is reviewed. Lastly, the modeling and numerical simulation of damage and failure processes, incorporating microscopic phenomena, are explored. The article concludes with a discussion of future perspectives. Full article

(This article belongs to the Special Issue Mechanical and Dynamic Characteristics of Polymers and Polymer Composites)

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