Search Results (75)

Polyurethane (PU) mixtures exhibit superior mechanical performance compared to traditional asphalt mixtures, owing to the excellent engineering properties of the PU binder. This study investigates the dynamic rheological properties of an open-graded polyurethane mixture (PUM–OGFC) in comparison with a dense-graded polyurethane mixture (PUM–AC). The time–temperature superposition principle and three rheological models (Standard Logistic Sigmoid (SLS), Generalized Logistic Sigmoid (GLS), and Havriliak–Negami (HN)) were employed to construct and analyze master curves. The results show that while PUM–AC possesses a higher dynamic modulus, PUM–OGFC exhibits a lower phase angle, indicating a more elastic response. Critically, PUM–OGFC demonstrated superior rutting resistance, as evidenced by its higher rutting parameter (|E*|/sin δ). Aggregate gradation significantly influenced all rheological properties. The master curve analysis further revealed that PUM–OGFC exhibits greater temperature sensitivity than PUM–AC. The SLS and GLS models provided excellent fits for both dynamic modulus and phase angle data, whereas the HN model was suitable only for dynamic modulus. In summary, the open-graded structure, when combined with a PU binder, creates a high-performance composite with an exceptional balance of elasticity and rutting resistance, showcasing its potential for demanding pavement applications. Full article

To limit reflective cracking in asphalt pavements with cold-recycled base courses, cold recycling mixtures (CRMs) are designed to provide predominantly bituminous bonding, making their viscoelastic behaviour of paramount importance. This study presents an experimental evaluation of the viscoelasticity of CRMs containing 0–90% RAP, 5.5–7.4% bitumen emulsion, and 1% cement. The dynamic modulus and phase angle were determined according to AASHTO T 378-22 across temperatures of 5–40 °C and loading frequencies of 0.1–25 Hz. To assess the applicability of the time–temperature superposition principle (TTSP) for describing the CRMs’ mechanical behaviour, master curves were constructed and the statistical analysis of the model fit quality was performed. The research findings demonstrate that CRMs’ mechanical behaviour can be effectively modelled using TTSP, with their viscoelastic response being influenced by RAP and bitumen emulsion content. CRMs showed lower temperature sensitivity than HMA, yet changes in dynamic modulus and phase angle remained statistically significant. This study advances the performance-based design of CRMs and points to the potential of rheological modelling for their constitutive characterization. Full article

This review systematically examined the transformative role of machine learning in predicting polymer aging lifetime, addressing critical limitations of conventional methods such as the Arrhenius model, time–temperature superposition principle, and numerical fitting approaches. The primary objective was to establish a comprehensive framework that integrates multi-mechanism coupling with dynamic data-driven modeling to enhance prediction accuracy across complex aging scenarios. Four key machine learning categories demonstrate distinct advantages: support vector machines effectively capture nonlinear interactions in multi-stress environments; neural networks enable cross-scale modeling from molecular dynamics to macroscopic failure; decision tree models provide interpretable feature importance quantification; and hybrid approaches synergistically combine complementary strengths. These methodologies have shown significant success in critical industrial applications, including building trades, photovoltaic systems, and aerospace composites, creating an integrated predictive system that bridges molecular-level dynamics with service-life performance. By transforming life prediction from empirical extrapolation to mechanism-based simulation, this machine-learning-driven paradigm offers robust methodological support for engineering safety design in diverse polymer applications through its capacity to model complex environmental interactions, adapt to real-time monitoring data, and elucidate underlying degradation mechanisms. Full article

Acrylic is increasingly being used in structural engineering applications due to its characteristics of light weight, capability of bulk polymerization, and absence of self-destruction risk, compared to tempered glass. However, structural acrylic exhibits creep behavior when subjected to prolonged loading. In order to study the creep performance of structural acrylic base material and coupons connected using the bulk polymerization technique, short-term tensile tests and long-term creep tests were conducted, and the effect of annealing temperature controlled in the bulk polymerization process was considered. The results show that annealing temperature significantly affects the quality of bulk polymerization. The Burgers model accurately describes the viscoelastic behavior of acrylic, and the Prony series converted from the parameters in the Burgers model can be directly implemented in Abaqus and accurately simulates the creep behavior of acrylic. The equation proposed in this study, on the basis of the Findley model, is precise enough to predict the creep curves of acrylic base material and connecting coupons. The Time–Stress Superposition Principle is valid when the time is greater than the threshold value. Full article

The complex condition of an adjacent tunnel in urban city includes high water content, limited construction space, and the presence of an adjacent tunnel. To address these challenges, the artificial ground freezing method is employed to ensure construction safety and stability. Considering the complex problem of temperature field interaction in the freezing construction process of adjacent tunnels, for the first time, this paper proposes a generalized analytical solution for two-dimensional steady-state temperature fields suitable for the annular double-loop freezing system of adjacent tunnels. Based on the polar coordinate heat conduction control equation and the conformal transformation method, the complex geometric arrangement is mapped into a linear system that can be solved, and the analytical solution expression is constructed by combining the heat source superposition principle. In this paper, a numerical model of the adjacent tunnel annular double-loop freezing pipe is established through COMSOL Multiphysics 6.2 software. At the same time, the formula of the analytical method is programmed and solved using Python 3.12, and finally the temperature fields obtained by the two methods are compared. The results show that the analytical solution has good consistency in isotherm distribution, temperature field trend and characterization of frozen core area, which verifies the theoretical rationality and practicability of the constructed model. Full article

This study investigates the constitutive model and relaxation modulus master curve of composite modified double-base (CMDB) propellants through uniaxial constant-rate tensile tests and stress relaxation tests. The experimental observations demonstrate that CMDB propellants exhibit pronounced strain-rate dependence and temperature dependence. Specifically, the yield stress and fracture strength of the propellant increase with increasing strain rate and decrease with increasing temperature. Conversely, the fracture strain increases with increasing temperature. The stress–strain curves of CMDB propellants display marked nonlinearity, attributed to progressive damage accumulation. The relaxation modulus increases significantly with decreasing temperature. Utilizing the time-temperature superposition principle, we constructed a master curve model for the relaxation modulus of CMDB propellants across varying temperatures. Furthermore, based on the observed stress relaxation behavior, a nonlinear constitutive model for CMDB propellants was developed. Theoretical predictions derived from this model show good agreement with experimental data. This model effectively captures the characteristic stress softening and damage evolution in CMDB propellants, thereby providing a theoretical foundation for assessing its mechanical performance and predicting its service life. Full article

Accurately modelling and simulating the stiffness modulus of asphalt mixtures is essential for reliable pavement design and performance prediction under varying environmental and loading conditions. The preceding is commonly achieved through master curves, which relate stiffness to loading frequency at a reference temperature. However, conventional master curves face two primary limitations. Firstly, temperature is not treated as a state variable; instead, its effect is indirectly considered through shift factors, which can introduce inaccuracies due to their lack of thermodynamic consistency across the entire range of possible temperatures. Secondly, conventional master curves often encounter convergence difficulties when calibrated with experimental data constrained to a narrow frequency spectrum. In order to address these shortcomings, this investigation proposes a novel formulation known as the Thermo-Stiffness Integration (TSI) model, which explicitly incorporates both temperature and frequency as state variables to predict the stiffness modulus directly, without relying on supplementary expressions such as shift factors. The TSI model is built on thermodynamics-based principles (such as Eyring’s rate theory and activation free energy) and leverages the time–temperature superposition principle to create a physically consistent representation of the mechanical behaviour of asphalt mixtures. This manuscript presents the development of the TSI model along with its application in a case study involving eight asphalt mixtures, including four hot-mix asphalts and four warm-mix asphalts. Each type of mixture contains recycled concrete aggregates at replacement levels of 0%, 15%, 30%, and 45% as partial substitutes for coarse natural aggregates. This diverse set of materials enables a robust evaluation of the model’s performance, even under non-traditional mixture designs. For this case study, the TSI model enhances computational stability by approximately 4 to 45 times compared to conventional master curves. Thus, the main contribution of this research lies in establishing a valuable mathematical tool for both scientists and practitioners aiming to improve the design and performance assessment of asphalt mixtures in a more physically realistic and computationally stable approach. Full article

The topical application of curcumin can act directly on the tissue, but there are problems related to solubility and permeation. Bigels combine hydrogels and organogels to enhance the release and transport of bioactives through the skin. The aim of this study was to develop bigels for the topical delivery of curcumin. Employing a rheology test, it was found that all bigels showed a solid-like behavior structure (G′ > G″) with stiffness increasing with higher organogel content. The principle of time–temperature superposition (TTS) was used to generate master curves. Microscopy revealed a morphological structure that depended on the organogel/hydrogel ratio. The bigels exhibited a pH compatible with that of human skin, and the curcumin content met the standards for uniform dosage. Thermal characterization showed the presence of three peaks in coconut oil bigels and two peaks in castor oil bigels. Bigels with a 45% castor oil organogel/55% hydrogel ratio exhibited a longer controlled release of curcumin, while bigels with coconut oil showed a faster release. The release data were fitted to mathematical models indicating non-Fickian release. The permeability of curcumin through Strat-M membranes was investigated, and greater permeation was observed with increasing organogel content. The developed bigels could be a promising option for the topical delivery of curcumin. Full article

Carbon black (CB)-filled rubber has been widely used in engineering. However, its time-dependent behavior, such as creep, is undesirable during the service process. In addition, the long-term creep test is time- and cost-consuming. To this end, the objective of this paper aims to predict the creep behavior from the short-term storage modulus by use of the collocation method. First, the master curve of storage modulus was constructed based on the time–temperature superposition principle (TTSP), and the validation of shift factors was verified by use of the Williams–Landel–Ferry (WLF) equation. Second, the generalized Kelvin model was used to describe the master curve of storage modulus by use of the collocation method, and the corresponding parameters were obtained. Compared with the existing works, the collocation method had the advantages of avoiding the occurrence of waviness of the fitting curve. Lastly, the creep compliance of CB-filled rubber was calculated by substituting the fitting parameters into the creep compliance expression. In order to verify the reliability of the calculation result, the creep tests were carried out. It was obvious that the calculation result is in good agreement with the experimental one with a RMSE value of 0.0055, which means that the calculation result is reliable. Full article

To investigate the dynamic mechanical properties of warm-mix steel slag-crumb rubber modified asphalt mixtures across wide- and narrow-frequency domains and evaluate the applicability of warm-mix technology, four distinct mixtures were prepared. The dynamic modulus characteristics under measured temperatures and frequencies were initially analyzed through complex modulus testing to elucidate narrow-frequency-domain mechanical behavior. Subsequently, leveraging the linear viscoelastic (LVE) theory and time–temperature superposition principle (TTSP), both the 2 Springs, 2 Parabolic Elements and 1 Dashpot (2S2P1D) mechanical element model and Modified Havriliak–Negami (MHN) mathematical model were established based on experimental data to characterize wide-frequency-domain dynamic responses. The results demonstrate substantial consistency in mechanical interpretation between narrow- and wide-frequency domain datasets, with enhanced information resolution achieved in wide-frequency analysis. Both models demonstrate comparable accuracy in characterizing the thermomechanical behavior of warm-mix steel slag-crumb rubber modified asphalt mixture across extended frequency and temperature ranges, while showing negligible performance discrepancies between the 2S2P1D and MHN formulations. Furthermore, both Cole–Cole and Black diagrams convincingly demonstrate the reliability of model predictions. This systematic investigation confirms the technical viability of warm-mix steel slag-crumb rubber modified asphalt mixture while establishing a dual-validated modeling framework for comprehensive performance prediction. Full article

In the field of nondestructive evaluation (NDE) using ultrasonic guided waves, accurately assessing the aging failure of insulation coatings remains a challenging and prominent research topic. While the application of ultrasonic guided waves in material testing has been extensively explored in the existing literature, there is still a significant gap in quantitatively evaluating the aging failure of insulation coatings. This study innovatively proposes an NDE method for assessing insulation coating aging failure by integrating signal processing and machine learning technologies, thereby effectively addressing both theoretical and practical gaps in this domain. The proposed method not only enhances the accuracy of detecting insulation coating aging failure but also introduces new approaches to non-destructive testing technology in related fields. To achieve this, an accelerated aging experiment was conducted to construct a cable database encompassing various degrees of damage. The effects of aging time, temperature, mechanical stress, and preset defects on coating degradation were systematically investigated. Experimental results indicate that aging time exhibits a three-stage nonlinear evolution pattern, with 50 days marking the critical inflection point for damage accumulation. Temperature significantly influences coating damage, with 130 °C identified as the critical threshold for performance mutation. Aging at 160 °C for 100 days conforms to the time-temperature superposition principle. Additionally, mechanical stress concentration accelerates coating failure when the bending angle is ≥90°. Among preset defects, cut defects were most destructive, increasing crack density by 5.8 times compared to defect-free samples and reducing cable life to 40% of its original value. This study employs Hilbert–Huang Transform (HHT) for noise reduction in ultrasonic guided wave signals. Compared to Fast Fourier Transform (FFT), HHT demonstrates superior performance in feature extraction from ultrasonic guided wave signals. By combining HHT with machine learning techniques, we developed a hybrid prediction model—HHT-LightGBM-PSO-SVM. The model achieved prediction accuracies of 94.05% on the training set and 88.36% on the test set, significantly outperforming models constructed with unclassified data. The LightGBM classification model exhibited the highest classification accuracy and AUC value (0.94), highlighting its effectiveness in predicting coating aging damage. This research not only improves the accuracy of detecting insulation coating aging failure but also provides a novel technical means for aviation cable health monitoring. Furthermore, it offers theoretical support and practical references for nondestructive testing and life prediction of complex systems. Future studies will focus on optimizing model parameters, incorporating additional environmental factors such as humidity and vibration to enhance prediction accuracy, and exploring lightweight algorithms for real-time monitoring. Full article

To ensure ammunition safety, a protective structure and pressure detection system are essential; however, there is a lack of an accurate constitutive model to describe the mechanical response characteristics of protective structures composed of various polymer materials. In this work, a constitutive model for the composite structure based on the superposition principle is successfully constructed derived from the quasi-static compression behavior of rigid polyurethane foam (RPUF), silicone rubber foam (SRF), and flexible pressure sensors (FPSs) through experimental investigations. The constitutive model accurately reflects the influence of each type of polymer foam on the mechanical performance of composite structures, underscoring the significance of thickness ratios. Test results within the temperature range of 25 °C to 55 °C validate the model’s accuracy, with an average fitting error of 8.6%. Furthermore, a multi-channel pressure detection system has been integrated into the composite structure. Under conditions of out-of-plane loads ranging from 0 to 10 kilonewtons, the accuracy of the pressure monitoring system, adjusted using the constructed model, has improved by 16%. The constitutive model and the pressure sensing system effectively predict the mechanical properties of the protective structure and enable real-time force state monitoring, which is crucial for ammunition safety and has broader applications for safeguarding other objects. Full article

Carbon fiber-reinforced polymers (CFRPs) are widely used in aerospace for their lightweight and high-performance characteristics. This study examines the long-term viscoelastic behavior of CFRP after UV-C exposure, simulating low Earth orbit conditions. The viscoelastic properties of the polymer were evaluated using dynamic mechanical analysis and the time-temperature superposition principle on both unexposed and UV-C-exposed samples. After UV-C exposure, the polymer’s instantaneous modulus decreased by about $15\%$. Over a 32-year period, the modulus of the unexposed resin is expected to degrade to approximately $25\%$ of its initial value, while the exposed resin drops to around $15\%$. These experimental results were incorporated into finite element method models of a unidirectional CFRP representative volume element. The simulations showed that UV-C exposure caused only a slight reduction in the CFRP’s axial relaxation coefficient along the fiber’s axis, with no significant time-dependent degradation, as the fiber dominates this behavior. In contrast, the axial relaxation coefficient perpendicular to the fiber’s axis, as well as the off-diagonal and shear relaxation coefficients, showed more notable changes, with an approximate $10\%$ reduction in their initial values after UV-C exposure. Over 32 years, degradation became much more severe, with differences between the pre- and post-exposure coefficient values reaching up to nearly $60\%$. Full article

Reclaimed asphalt pavement (RAP) reduces energy consumption and enhances economic benefits by recycling road materials, making it an effective approach for the sustainable use of solid waste resources. The performance of reclaimed asphalt pavement is significantly affected not only by the degradation of asphalt binders due to aging but also by the dosage of the rejuvenator used. The master curve of the complex shear modulus is widely recognized as a valuable tool for characterizing the rheological properties of asphalt binders. First, a virgin asphalt binder with a grade of SK70 was subjected to varying degrees of aging, followed by the rejuvenation of the aged asphalt using different dosages of the rejuvenator. Second, frequency sweeps were conducted on the aged and rejuvenated asphalt binders at various temperatures. Complex modulus master curves were constructed, and the CAM model was applied to fit these curves. The viscoelastic properties of asphalt at different aging levels and rejuvenator dosages were then analyzed based on the CAM parameters. Next, by applying a curve-shifting technique based on the least squares method to a reference state, both the time–temperature–aging (TTA) and time–temperature–regenerator (TTR) master curves of the complex modulus were constructed. The relationships between aging shift factors and aging times, as well as between regenerator shift factors and dosages, were established to predict the complex moduli of both aged and rejuvenated asphalt. Finally, the shear stress–strain relationships and material integrity of aged and rejuvenated asphalt were evaluated to assess their fatigue performance. The results indicated that aging significantly increases the complex modulus of asphalt, with TFOT (Thin Film Oven Test) aging having a more pronounced impact than PAV (Pressurized Aging Vessel) aging, resulting in reduced viscous deformation and an increased risk of cracking. Rejuvenator dosage reduces the complex modulus, with a 6% dosage effectively restoring mechanical properties and enhancing low-temperature performance. The TTA master curve demonstrates a strong linear correlation between aging shift factors and time, allowing for accurate predictions of the complex modulus of aged asphalt. Similarly, the TTR master curve reveals a linear relationship between regenerator dosage and shift factor, offering high predictive accuracy for optimizing regenerator dosages in engineering applications. The study further explores how varying levels of aging and rejuvenator dosage affect fatigue life under different strain conditions, uncovering complex behaviors influenced by these aging and regeneration processes. Full article

The rheological properties of a polyamide (PA) resin with low crystallinity were modified by melt-mixing it with a small amount of an alternative α-olefin–maleic anhydride copolymer as a reactive compound. Because PA has a low melting point, rheological characterization was performed over a wide temperature range. Owing to the reaction between PA and the alternative α-olefin–maleic anhydride copolymer, the blend sample behaved as a long-chain branched polymer in the molten state. The thermo-rheological complexity was obvious owing to large flow activation energy values in the low modulus region, i.e., the rheological time–temperature superposition principle was not applicable. The primary normal stress difference under steady shear was greatly increased in the wide shear rate range, leading to a large swell ratio at the capillary extrusion. Furthermore, strain hardening in the transient elongational viscosity, which is responsible for favorable processability, was clear. Because this is a simple modification method, it will be widely employed to modify the rheological properties of various polyamide resins. Full article