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The paper provides new experimental evidence for vulnerable artifacts on the dependence of failure strain on the loading rate corresponding to typical environmental loads lasting between hours and months. Animal glue-based ground was chosen for this study as an easily available, hygroscopic and brittle material as well as due to its abundance in collections and its relevance when discussing the risk of mechanical damage to objects. Gesso specimens were tested using dynamic mechanical analysis and tensile testing at different frequencies, under a variety of loading rates and temperatures. The time-temperature superposition principle was used to predict the material response to slow deformations (lasting hours to months) that are otherwise inaccessible on laboratory timescales. The results demonstrate that brittle materials such as animal glue-based grounds do not benefit from longer cycles of applied loads as failure strain is not time-dependent within the investigated timescale. [ABSTRACT FROM AUTHOR]

Background: Restorative solutions designed for edentulous patients such as dentures and their accompanying denture adhesives operate in the complex and dynamic environment represented by human oral physiology. Developing material models accounting for the viscoelastic behavior of denture adhesives can facilitate their further optimization within that unique physiological environment. This study aims to statistically quantify the degree of significance of three physiological variables - namely: temperature, adhesive swelling, and pH - on denture adhesive mechanical behavior. Further, based on these statistical significance estimations, a previously-developed viscoelastic material modelling approach for such denture adhesives is further expanded and developed to capture these variables' effects on mechanical behavior. Methods: In this study a comparable version of Denture adhesive Corega Comfort was analysed rheologically using the steady state frequency sweep tests. The experimentally derived rheological storage and loss modulus values for the selected physiological variables were statistically analyzed using multi parameter linear regression analysis and the Pearson's coefficient technique to understand the significance of each individual parameter on the relaxation spectrum of the denture adhesive. Subsequently, the parameters are incorporated into a viscoelastic material model based on Prony series discretization and time-temperature superposition, and the mathematical relationship for the loss modulus is deduced. Results: The results of this study clearly indicated that the variation in both the storage and loss modulus values can be accurately predicted using the oral cavity physiological parameters of temperature, swelling ratio, and pH with an adjusted R2 value of 0.85. The R2 value from the multi-parameter regression analysis indicated that the predictor variables can estimate the loss and storage modulus with a reasonable accuracy for at least 85% of the rheologically determined continuous relaxation spectrum with a confidence level of 98%. The Pearson's coefficient for the independent variables indicated that temperature and swelling have a strong influence on the loss modulus, whereas pH had a weak influence. Based on statistical analysis, these mathematical relationships were further developed in this study. Conclusions: This multi-parameter viscoelastic material model is intended to facilitate future detailed numerical investigations performed with implementation of denture adhesives using the finite element method. [ABSTRACT FROM AUTHOR]

Polyamide 6 (PA6) film as a typical viscoelastic material, satisfies the time–temperature superposition (TTS), and demonstrates obvious dynamic strain amplitude and frequency correlation under dynamic load. The investigation of the dynamic mechanical behavior of PA6 film is essential to ensure the safety of these materials in practical applications. In addition, dynamic mechanical property testing under conventional experimental conditions generally focuses on the short-term mechanical performance of materials. Therefore, the dynamic viscoelasticity of PA6 film was tested using a dynamic thermo-mechanical analyzer (DMA) in this study, and the complex modulus master curve was constructed based on time–temperature superposition (TTS) to realize the accelerated characterization of long-term mechanical properties. Furthermore, according to experimentally obtained asymmetric characteristics of the Cole–Cole diagram and the loss modulus master curve of the PA6 film, the parameter distribution of the fractional Zener model and the modified fractional Zener model were compared, and the asymmetric dynamic viscoelastic response of PA6 film under different conditions was systematically investigated using these models. The results indicate that the modified fractional Zener model can truly describe the dynamic asymmetric characteristics of PA6 film, verify the feasibility and advantages of the modified fractional rheological model, and provide some theoretical guidance for exploring the tensile rheological mechanism of PA6 film. [ABSTRACT FROM AUTHOR]

In this letter, we present interfacial fracture toughness data for a polymer-metal interface where tests were conducted at various test temperatures T and loading rates δ ˙ . An adhesively bonded asymmetric double cantilever beam (ADCB) specimen was utilized to measure toughness. ADCB specimens were created by bonding a thinner, upper adherend to a thicker, lower adherend (both 6061 T6 aluminum) using a thin layer of epoxy adhesive, such that the crack propagated along the interface between the thinner adherend and the epoxy layer. The specimens were tested at T from 25 to 65 °C and δ ˙ from 0.002 to 0.2 mm/s. The measured interfacial toughness Γ increased as both T and δ ˙ increased. For an ADCB specimen loaded at a constant δ ˙ , the energy release rate G increases as the crack length a increases. For this reason, we defined rate effects in terms of the rate of change in the energy release rate G ˙ . Although not rigorously correct, a formal application of time–temperature superposition (TTS) analysis to the Γ data provided useful insights on the observed dependencies. In the TTS-shifted data, Γ decreased and then increased for monotonically increasing G ˙ . Thus, the TTS analysis suggests that there is a minimum value of Γ. This minimum value could be used to define a lower bound in Γ when designing critical engineering applications that are subjected to T and δ ˙ excursions. [ABSTRACT FROM AUTHOR]

Polyurethane (PU) is a versatile material that can be customized to meet specific commercial requirements in different industries because of its favorable mechanical properties. However, it is not resistant to high temperatures, and it requires structural modifications before it can be used in high‐temperature structural materials. In this study, isocyanates and anhydrides are copolymerized at high temperatures to obtain a solvent‐free oligomer, thus eliminating the risks associated with highly polar aprotic solvents. A casting technique is used to synthesize a solid poly(urethane‐imide) (PUI) elastomer. According to the results, casting PUI (CPUI) exhibits optimal physical properties at a hard segment content of 30.5%. Incorporating an ether, symmetric, or imide structure into CPUI may reduce its hysteresis and improve its thermal creep performance. Compared with PU, CPUI exhibits considerably higher creep aging resistance. In dynamic load application tests, CPUI wheels take a substantially longer time to reach failure compared with PU wheels. Overall, CPUI is an environmentally friendly material with high elasticity, low creep, and high heat aging resistance and is suitable for static and dynamic manufacturing applications. [ABSTRACT FROM AUTHOR]

The fabrication of pressure sensitive adhesives (PSAs) using liquid crystal elastomers (LCEs), which are known for their excellent dissipation properties, is explored in this work. The adhesive properties of the PSAs are evaluated using the 180° peeling test at various conditions. The performance of the LCE adhesives is found to show significant rate and temperature dependence. When the adhesion energy is plotted against the rate, LCE shows an anomalously large power law exponent (n ≈ 1.17) compared to existing PSAs (n ≈ 0.1–0.6). The unusual rate sensitivity is hypothesized to originate from the synergy of soft elasticity and non‐linear viscoelasticity. The adhesive properties at various rates and temperatures are correlated to the results from dynamic mechanical analysis. Moreover, the large strain stiffening behavior of LCE under uniaxial tension reveals the distinctive advantages offered by LCE as adhesives. Time‐temperature superposition is used to obtain a master curve of adhesion energy that spans rates beyond typical experimental limits. The extreme rate dependence and the large strain stiffening of LCE yield a new category of adhesives that possess special properties, such as reversible adhesion and impact resistance, unlike traditional adhesives. [ABSTRACT FROM AUTHOR]

The dissolution of wool yarns in the ionic liquid 1-ethyl-3-methyl-imidazolium acetate [C2mim][OAc] has been investigated. Wool yarns were submerged into [C2mim][OAc] and dissolved for various times and temperatures before coagulating with water. Optical microscopy was used to track the yarn's cross-sectional area. We propose that there are two competing dissolution processes, one rate-limited by disulfide bonds at low temperatures (LTs), and a second by hydrogen bonds at high temperatures (HTs), with a crossover point between the two regimes at 70 ℃. The corresponding activation energies were ELT = 127 ± 9 kJ/mol and EHT = 34 ± 1 kJ/mol. The remaining area of the dissolved wool yarn could be shifted via time–temperature superposition to plot a single master curve of area against time for both regions. Finally, the dissolution could be modelled by a diffusion process, giving self-diffusion coefficients for the [C2mim][OAc] ions (0.64–15.31 × 10−13 m2/s). [ABSTRACT FROM AUTHOR]

Asphalt binders have been studied extensively with respect to their linear viscoelastic properties. From these properties, performance metrics have been derived and used for specification purposes. However, these materials are used in asphalt concrete pavements where they may experience time-dependent loads in the nonlinear regime. In the past, the vast majority of asphalt binders exhibited strong correlations between their linear and nonlinear properties and so despite this mismatch in characterization and the actual use phase domains, a system based on linear properties could be reliably deployed. More recently though, novel binders and additives have been introduced with differing relationships between linear and nonlinear behaviors. As such there is a need to characterize the asphalt binder response under large strains and use specifications that more explicitly account for the binder nonlinearity. Here, an attempt has been made to characterize the nonlinear rheological properties of asphalt binder using large amplitude oscillatory shear. The response of a single terminal blend, crumb rubber modified binder under large strains is analyzed using Lissajous-Bowditch plots while the contribution of higher harmonics is evaluated using Fourier-transform rheology. Finally, the elastic and viscous contributions are obtained using stress decomposition to an orthogonal set of Chebyshev polynomials. It is found that the relative nonlinearity increases with increasing strain and frequency under the tested conditions. The asphalt binder evaluated in this study predominantly exhibits shear thinning and either strain stiffening or softening behavior depending upon the test conditions. The applicability of time-temperature superposition in the nonlinear regime for asphalt binders is also evaluated. [ABSTRACT FROM AUTHOR]

Temperature and physical aging effects on the three-dimensional behaviors, such as shear and bulk properties, of viscoelastic solids are critical for developing polymer composite systems but are rarely addressed. Furthermore, accurate identification of time-temperature-dependent viscoelastic constitutive theories remains a challenging problem. In this work, we propose a robust and automated method to simultaneously identify the viscoelastic, temperature, and physical aging related three-dimensional model parameters based on the Bayesian framework. The proposed method was applied to three-dimensional experimental data from nonisothermal physical aging tests on polycarbonate at different temperatures. The posterior distribution of the model parameters was obtained through Markov chain Monte Carlo (MCMC) simulations, which allowed us to determine the minimum number of material parameters yielding an optimized accuracy. The experimental results are in excellent agreement with the predictions of the identified parameters. Moreover, we have found through the experimental results that the shear properties of polycarbonate are affected by temperature and physical aging, whereas its bulk properties are affected only by temperature and are relatively insignificant in comparison to the shear properties. The proposed method can be applied to polymers or composites to predict their long-term three-dimensional mechanical properties under complex working conditions. [ABSTRACT FROM AUTHOR]

Polyamide 6 (PA6) film as a typical viscoelastic material, satisfies the time–temperature superposition (TTS), and demonstrates obvious dynamic strain amplitude and frequency correlation under dynamic load. The investigation of the dynamic mechanical behavior of PA6 film is essential to ensure the safety of these materials in practical applications. In addition, dynamic mechanical property testing under conventional experimental conditions generally focuses on the short-term mechanical performance of materials. Therefore, the dynamic viscoelasticity of PA6 film was tested using a dynamic thermo-mechanical analyzer (DMA) in this study, and the complex modulus master curve was constructed based on time–temperature superposition (TTS) to realize the accelerated characterization of long-term mechanical properties. Furthermore, according to experimentally obtained asymmetric characteristics of the Cole–Cole diagram and the loss modulus master curve of the PA6 film, the parameter distribution of the fractional Zener model and the modified fractional Zener model were compared, and the asymmetric dynamic viscoelastic response of PA6 film under different conditions was systematically investigated using these models. The results indicate that the modified fractional Zener model can truly describe the dynamic asymmetric characteristics of PA6 film, verify the feasibility and advantages of the modified fractional rheological model, and provide some theoretical guidance for exploring the tensile rheological mechanism of PA6 film.

Polymers find widespread applications in various industries, such as civil engineering, aerospace, and industrial machinery, contributing to vibration control, dampening, and insulation. To accurately design products that are able to predict their dynamic behavior in the virtual environment, it is essential to understand and reproduce their viscoelastic properties via material physical modeling. While Dynamic Mechanical Analysis (DMA) has traditionally been used, innovative non-destructive techniques are emerging for characterizing components and monitoring their performance without deconstructing them. In this context, the Time–Temperature Superposition Principle (TTSP) represents a powerful empirical procedure to extend a polymer's viscoelastic behavior across a wider frequency range. This study focuses on replicating an indentation test on viscoelastic materials using the non-destructive Viscoelasticity Evaluation System evolved (VESevo) tool. The primary objective is to derive a unique temperature–frequency relationship, referred to as a "shift law", using characteristic curves from this non-invasive approach. Encouragingly, modifying the device setup enabled us to replicate, virtually, three tests under identical initial conditions but with varying indentation frequencies. This highlights the tool's ability to conduct material testing across a range of frequencies. These findings set the stage for our upcoming experiment campaign, aiming to create an innovative shift algorithm from at least three distinct master curves at specific frequencies, offering a significant breakthrough in non-destructive polymer characterization with broad industrial potential. [ABSTRACT FROM AUTHOR]

Physiological parameters of the oral cavity have a profound impact on any restorative solutions designed for edentulous patients including denture adhesives. This study aims to mathematically quantify the influence of three such variables, namely: the temperature, pH, and the swelling of such adhesives under the influence of saliva on its mechanical behavior. The mathematical quantification is further aimed to implement a material model for such adhesives which considers the impact of such physiological factors. The denture adhesive is experimentally investigated by means of rheological steady state frequency sweep tests to obtain the relaxation spectrum of the material. The relaxation behavior is measured for a wide range of oral cavity temperatures and pH. Also, the adhesive is hydrated and upon swelling to different levels again tested to understand the impact of swelling on the mechanical behavior. The experimentally measured continuous relaxation spectrum is modeled as a viscoelastic material using a discrete set of points based on the Prony series discretization technique. The relaxation spectrums for various temperatures are compared and the possibility of a time-temperature superposition is explored for the model. Similarly, the measured values of Storage and loss modulus are investigated to understand the role of pH and swelling. The results in this study clearly indicated a horizontal shift in the relaxation behavior with increase in temperature. And hence, the time-temperature shift factor was calculated for the adhesive. The relaxation spectrum also showed a strong correlation with swelling of the adhesive and the pH. The influence of these two parameters were captured into the model based on the relaxation time parameter in the Prony series approach. Based on this study the impact of these parameters could be appreciated on the performance and mechanical behavior of denture adhesives and implemented into a Prony series based viscoelastic material model which can be used with numerical simulations. [ABSTRACT FROM AUTHOR]

Polyamides serve as matrix material for fiber reinforced composites and are widely applied in many different engineering applications. In this context, they are exposed to various environmental influences ranging from temperature to humidity. Thus, the influence of these environmental conditions on the mechanical behavior and the associated implications on the performance of the material is of utmost importance. In this work, the thermoviscoelastic behavior of polyamide 6 (PA 6) for two equilibrium moisture contents is investigated. To this end, dynamic mechanical analysis tests with and without humidity control of the environmental chamber were performed. In terms of relaxation tests, the experimental results reveal drying effects and increased diffusion activities when the sample's equilibrium moisture content differs from the ambient humidity level within the testing chamber. Temperature-frequency tests quantify the humidity-induced shift of the glass transition temperature. The linear generalized Maxwell model (GMM) and time-temperature superposition are used to analyze the hydrothermal effects on the linear viscoelastic material properties and the onset of mechanical nonlinearity. Based on these investigations and findings, insight is gained on the humidity influence on the material properties and the limitations of linear thermoviscoelastic modeling. Furthermore, the computational construction of master curves and the parameter identification for a generalized Maxwell model are described in detail. [ABSTRACT FROM AUTHOR]

This work investigated the dissolution rate of flax fibers in the ionic liquid 1-ethyl-3-methylimidazolium acetate [C2mim] [OAc] with the addition of a cellulose anti-solvent, water. The dissolution process was studied as a function of time, temperature and water concentration. Optical microscopy is used to analyse the resultant partially dissolved fibers. Distilled water was added to the solvent bath at the concentrations of 1%, 2% and 4% by weight in order to understand its influence on the dissolution process. The effect of the addition of even small amounts of water was found to significantly decrease the speed of dissolution, decreasing exponentially as a function of water concentration. The resulting data of both pure (as received from the manufacturers) ionic liquid and ionic liquid/anti-solvent mixtures showed the growth of the coagulated fraction as a function of both dissolution time and temperature followed time temperature superposition. An Arrhenius behavior was found, enabling the measurement of the activation energy for the dissolution of flax fiber. The activation energy of the IL as received (0.2% water) was found to be 64 ± 5 kJ/mol. For 1%, 2% and 4% water systems, the activation energies were found to be 74 ± 7 kJ/mol, 97 ± 3 kJ/mol and 116 ± 0.6 kJ/mol respectively. Extrapolating these results to zero water concentration gave a value for the hypothetical dry IL (0% water) of 58 ± 4 kJ/mol. The hypothetical dry ionic liquid is predicted to dissolve cellulose 23% faster than the IL as received (0.2% water). [ABSTRACT FROM AUTHOR]

A theoretical framework that underlies an accelerated testing method for unidirectional (UD) composites is proposed in this article, based on the continuum damage mechanics and time–temperature superposition. By the way of demonstration, it has been applied to problems involving constant strain rates and fatigue loading conditions. The damage evolution law for the matrix of composites was constructed using the Weibull distribution of defects, which will develop into cracks as a result of deformation. In conjunction with the Wiechert model, the theoretical framework formulated here is capable of capturing the mechanical behaviour of UD composites. Demonstration and initial verification of this acceleration method were carried out through experiments. This work can provide theoretical and technical support for the durability verification and the evaluation of the high cycle fatigue performance of composite structures.

Extensive studies have been conducted on utilising natural fibres as reinforcement in composite production. All-polymer composites have attracted much attention because of their high strength, enhanced interfacial bonding and recyclability. Silks, as a group of natural animal fibres, possess superior properties, including biocompatibility, tunability and biodegradability. However, few review articles are found on all-silk composites, and they often lack comments on the tailoring of properties through controlling the volume fraction of the matrix. To better understand the fundamental basis of the formation of silk-based composites, this review will discuss the structure and properties of silk-based composites with a focus on employing the time–temperature superposition principle to reveal the corresponding kinetic requirements of the formation process. Additionally, a variety of applications derived from silk-based composites will be explored. The benefits and constraints of each application will be presented and discussed. This review paper will provide a useful overview of research on silk-based biomaterials. [ABSTRACT FROM AUTHOR]

In this paper the viscoelastic continuum damage theory was used to investigate the damage and self-healing potential of bituminous binders, considering the effects of rest temperature, thixotropy, and non-linearity. Experimental testing was carried out by using a procedure in which continuous oscillatory shear loading was imparted to the specimens with the inclusion of a single rest period under multiple temperature conditions. Quantification of self-healing included the determination of material integrity gained and damage parameter recovered after the rest period. Such parameters were calculated by excluding time-dependent and non-linear biasing effects, which were directly evaluated by means of a distinct set of experiments. Results were modelled by using the so-called self-healing master curves, constructed by applying the linear viscoelastic time-temperature shift factors. These self-healing master curves are intended to be used as straightforward tools for the prediction of the self-healing response of neat and polymer modified binders in various time-temperature combinations. [ABSTRACT FROM AUTHOR]

The dependences of the elongation speed and temperature on the ultimate tensile properties in polyethylene solids was investigated, in which a double-edge-notched specimen was used to avoid necking. The data on ultimate properties such as the tensile strength and elongation at break for different temperatures were superimposed, by shifts along the elongation speed axis, to give a master curve as a function of the time to rupture. The shift factors obtained from the super-positioning of both the tensile strength and ultimate strain followed the form of the Williams–Landel–Ferry (WLF) equation. On the other hand, the strain rate and temperature dependences of yield behavior followed a kinetic process proposed by Eyring. [ABSTRACT FROM AUTHOR]

In this work, the long-term creep response of high-performance carbon fiber PEKK (CF/PEKK) composites was evaluated by performing extrapolated short-term flexural creep tests at various temperatures. The time-temperature superposition principle (TTSP) with vertical as well as horizontal shifting was used to generate master curves at reference temperatures of 120°C. Satin weave-based CF/PEKK prepregs were used to manufacture eight-layer composites via compression molding, with three different stacking sequences: (a) zero-direction [0]8 (b) cross-ply [0, 90]4 and (c) quasi-isotropic [90, −45, 45, 0]2 s. The flexural properties under three-point bending arrangement in a universal testing machine were also evaluated. A dynamic mechanical thermal analyzer (DMTA) in three-point bending mode was used to evaluate the temperature-dependent viscoelastic properties of the three types of composites. The creep and creep-recovery behavior was evaluated at 40°C, 80°C, 120°C, 160°C and 200°C. To construct a master curve, extrapolated short-term isothermal creep tests were performed from 120°C to 180°C at the intervals of 10°C. The predicted master curve represents the creep behavior of composites over more than 10 years. It was shown that the quasi-isotropic CF/PEKK composites exhibited 27% and 12% higher creep resistance at 120°C as compared to zero-direction and cross-ply laminates, respectively. Higher flexural modulus (23%) and flexural strengths (33%) were also exhibited by the quasi-isotropic CF/PEKK composites. The final thickness of quasi-isotropic laminates was 8% lower than the 0o laminates. After analyzing the cross-sections of the composites, it was proposed that the superior mechanical properties of the quasi-isotropic laminates could be due to enhanced nesting between neighboring prepreg layers during the compression molding process, which resulted in closer packing of the fibers. It has been shown that the prepreg stacking sequence could affect the creep behavior and flexural properties of the compression-molded CF/PEKK composites. [ABSTRACT FROM AUTHOR]

Plain woven carbon fabric reinforced polyamide (CF/PA) composite laminate was developed using hot-pressed processing with a vacuum-assisted system. Temperature-dependent mechanical properties of the CF/PA composite laminate under longitudinal compressive loading were examined. The compressive mechanical properties of the composite laminate decreased considerably with increasing the temperature to 120°C. The compressive strength and strain at maximal stress reduced rapidly below 80°C, while the compressive modulus declined slightly underneath 50°C. The glass transition temperature of the CF/PA composite was found to be about 50°C by the differential scanning calorimetry, which almost corresponded to the slight reduction of the elastic modulus at temperatures below 50°C. The time-dependent creep behavior of the CF/PA laminate under compressive loading at isotherms between 25°C and 50°C was studied. Creep strains of the CF/PA composite samples increased with rising temperature. The smooth creep compliance master curve of the CF/PA composite was obtained by shifting short-term creep compliance curves using the time–temperature superposition principle. The master curve provided a creep prediction to 961.6 days with the measured data in only 12.5 days. [ABSTRACT FROM AUTHOR]

Shear stiffening gels (SSGs) exhibit the unique behavior of a rapid increase of modulus or viscosity with increasing strain rate. Because of this rate-dependent behavior, SSGs are used in shock-absorbing applications such as helmets and body armor. In this study, the constitutive relationship of SSGs was investigated by preparing an SSG and then performing various experiments for rheological characterization using a rheometer for low and medium shear rates, and a split Hopkinson pressure bar test for high shear rates. Then, using a stress and corresponding strain invariant, the stress and strain rate were plotted in a graph, from which a non-Newtonian relationship was established for the SSG. Finally, the impact behaviors of multi-layer structures made from the SSG were simulated, and the results were compared with experimental results, validating the constitutive relationship. [ABSTRACT FROM AUTHOR]

The dissolution of wool yarns in the ionic liquid 1-ethyl-3-methyl-imidazolium acetate [C2mim][OAc] has been investigated. Wool yarns were submerged into [C2mim][OAc] and dissolved for various times and temperatures before coagulating with water. Optical microscopy was used to track the yarn’s cross-sectional area. We propose that there are two competing dissolution processes, one rate-limited by disulfide bonds at low temperatures (LTs), and a second by hydrogen bonds at high temperatures (HTs), with a crossover point between the two regimes at 70 ℃. The corresponding activation energies were ELT = 127 ± 9 kJ/mol and EHT = 34 ± 1 kJ/mol. The remaining area of the dissolved wool yarn could be shifted via time–temperature superposition to plot a single master curve of area against time for both regions. Finally, the dissolution could be modelled by a diffusion process, giving self-diffusion coefficients for the [C2mim][OAc] ions (0.64–15.31 × 10−13 m2/s).

The dynamic modulus is a key property determining the short- and long-term performance of asphalt pavement, and its strong dependence on confining pressure and material density (mixture compactness) has been clearly indicated in the literature. It is always challenging to reproduce three-dimensional in situ stress conditions in the laboratory. To alleviate this difficulty, in this study, a convenient experimental setup was developed, in which the lateral confinement was made present and variable as a concomitant reaction of the surrounding materials to the vertical loading. Three dense-graded mixtures were prepared to a set of four different densities and then subjected to the confined dynamic modulus test. The results indicated a significant dependence of the confined modulus on the three factors of temperature, frequency, and compactness and that the mixture with coarser gradation demonstrated a less sensitivity to these parameters. A mathematical model was developed for the dynamic modulus master curve unifying these factors by means of horizontal shifting due to the time–temperature superposition principle (validated against the variable confinement at different compactness) and the vertical shift factor as a function of reduced frequency and compactness. The adequacy of the model was demonstrated using the experimental data, and its potential application in field pavement compaction was discussed. [ABSTRACT FROM AUTHOR]

We herein report the influences of glass fibers (GFs) on the thermal stability and long-term mechanical performance at elevated temperatures of thermotropic liquid crystal polyester (TLCP) composites for advanced applications in the industrial sectors of automotive, electric/electronics, aerospace, and construction. For this purpose, TLCP-based composites with 10–40 wt% GF loadings are fabricated by facile melt-mixing and injection-molding. The scanning electron microscopy (SEM) images and X-ray diffraction patterns demonstrate that the GFs are dispersed in the TLCP matrix with a microfibrillar structure. The specific interactions between TLCP and GFs in the composites are identified by ATR FT-IR spectroscopic analyses. The thermal degradation temperatures of the composites increase slightly with the increment of GFs with high thermal stability and heat capacity. The long-term mechanical durability of TLCP/GF composites at 150 °C is analyzed by obtaining time-dependent storage modulus master curves based on the stepped isothermal method and time–temperature superposition principle. The dynamic mechanical moduli, activation energy, and long-term mechanical durability are found to be highly enhanced for TLCP composites with higher GF loadings, which is owing to the efficient stress transfer from the TLCP matrix to reinforcing GF fillers via specific interactions at the composite interface. [ABSTRACT FROM AUTHOR]

The present study investigated how the applications of the time-moisture superposition principle (TMSP) under a moisture content (MC) range of 0–14.2% and the time-temperature superposition principle (TTSP) under a temperature range of 30–150 °C would affect to Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) creep behaviors across grain orientations via a dynamic mechanical analysis instrument. The results showed that both TMSP and TTSP could describe the evolution of creep in the radial and tangential directions. Master curves constructed by TMSP and TTSP overlapped at a reference condition (30 °C, 0% MC), regardless of the grain orientation. In addition, an equivalent relation between the effects of moisture and temperature on the creep behavior was assumed based on TMSP and TTSP. Under the tested temperature, the effect of the per unit MC was equivalent to that at ca. 33 and 44 °C for the radial and tangential specimens, respectively. These findings elucidate the effects of moisture and temperature on the rheological properties of wood cell walls and are helpful for better utilizing wood in civil engineering applications. [ABSTRACT FROM AUTHOR]

Abstract Vibration characteristics of wood-based materials are essential parameters in considering the indoor environment of a building. This study investigates the effect of the physical properties of water-based adhesives on vibration characteristics of wood-based materials. Adhesive films and particle boards (PB) were prepared from acrylic emulsion adhesives (AE) with differential glass transition (T g), and loss tangent of dynamic viscoelasticity (tanδ D) and flexural vibration property (tanδ F) were compared. The tanδ D master curve and tanδ F showed a similar tendency regarding frequency dependence. The apparent activation energy (ΔH) calculated from the shift factor of the master curve tends to be different depending on the T g of AE and was especially high for AE with T g = 13 °C along with blended AE. The dynamic Young’s modulus (E F) calculated from the flexural vibration tests showed higher values for AE at T g = 13 °C, 41 °C, and 90 °C than that of urea–formaldehyde adhesive (UF).

The linear amplitude sweep (LAS) test is esteemed as an effective tool for assessing bitumen fatigue performance. Utilizing a pseudo-strain energy (PSE) based failure analysis, this research investigated the impact of temperature on the failure mechanism of rejuvenated RAP bitumen's fatigue resistance using the LAS test. Based on a PSE simplified viscoelastic continuum damage (S-VECD) approach, the analysis results revealed that the flow failure mechanism rather than cohesive failure would be dominant, once the dynamic shear moduli (| G* |) were selected above a certain critical temperature. Similarly, at intermediate and enough low temperatures, adhesive and cohesive failures, respectively, between the bitumen samples and DSR palates is found to confound results. Considering that the actual test procedure does not specify the testing temperature, it is necessary to assess the failure mechanism to verify test results and prevent inconsistent outcomes. Accordingly, the temperature should be selected carefully once the | G* | falls within the range of 9–55 MPa to avoid confounding impacts of adhesion loss and flow. Based on this finding, time-temperature superposition was utilized to PSE S-VECD results and fatigue life trends with temperature variations illustrated to be bitumen dependent. Observations from the simplified approach revealed a very strong correlation with the measured fatigue life of rejuvenated RAP bitumen. • Explored the impact of temperature on the fatigue life (Nf) of rejuvenated RAP bitumen mixes. • Introduced failure mechanism types to guide the selection of testing temperature. • Investigated the utilization of pseudo-strain within the S-VECD model to analyze LAS results. • Introduced a simplified method for predicting bitumen Nf at cohesive temperatures. • Explored two failure criteria for determining bitumen Nf in the new prediction approach. [ABSTRACT FROM AUTHOR]

In this paper, a composite cold-mixed epoxy asphalt binder (CCEAB) is made using diluted epoxy resin (DER) and cold-mixed solvent (CMS). The rheological behavior of CCEAB is analyzed by rotary viscosimeter at different temperatures, curing times, shear rates, DER and CMS contents. The fluid type of the CCEAB is identified, and its flow curve is modeled. The parallel phenomenon of apparent viscosity curves is revealed, and the shift factor is analyzed. The results showed that temperature, CMS content and shear rate are negatively correlated with viscosity, while time and DER content are positively correlated with it. CCEAB has typical shear thinning behavior and is a pseudoplastic fluid without yield stress. When the shear rate is greater than 18.6 s−1, the viscosity curves trend stable, and the final viscosity is about 60 % of the initial viscosity. The 5 variables have been added to the power law model to establish the flow curve of CCEAB, whose parameters are identified by the generalized inverse matrix. The parallel of viscosity curves follows the time-temperature superposition, and the shift factor function with 4 variables describes the conversion of viscosity curves. The flow curve of CCEAB has the same form and essence as the shift factor function, meaning the flow curve also describes the parallel. If the shift factor is regarded as a viscosity prediction method, it is not as accurate as the flow curve. • Composite cold-mixed epoxy asphalt binder is pseudoplastic without yield stress. • The flow curve with 5 variables is derived based on the power law model. • Time-temperature superimposition reveals the parallel of viscosity curves. • Shift factor doesn't predict viscosity curves as accurately as the flow curve. [ABSTRACT FROM AUTHOR]

Polymers find widespread applications in various industries, such as civil engineering, aerospace, and industrial machinery, contributing to vibration control, dampening, and insulation. To accurately design products that are able to predict their dynamic behavior in the virtual environment, it is essential to understand and reproduce their viscoelastic properties via material physical modeling. While Dynamic Mechanical Analysis (DMA) has traditionally been used, innovative non-destructive techniques are emerging for characterizing components and monitoring their performance without deconstructing them. In this context, the Time–Temperature Superposition Principle (TTSP) represents a powerful empirical procedure to extend a polymer’s viscoelastic behavior across a wider frequency range. This study focuses on replicating an indentation test on viscoelastic materials using the non-destructive Viscoelasticity Evaluation System evolved (VESevo) tool. The primary objective is to derive a unique temperature–frequency relationship, referred to as a “shift law”, using characteristic curves from this non-invasive approach. Encouragingly, modifying the device setup enabled us to replicate, virtually, three tests under identical initial conditions but with varying indentation frequencies. This highlights the tool’s ability to conduct material testing across a range of frequencies. These findings set the stage for our upcoming experiment campaign, aiming to create an innovative shift algorithm from at least three distinct master curves at specific frequencies, offering a significant breakthrough in non-destructive polymer characterization with broad industrial potential.

Polymers are widely used in applications where they may be subjected to impact loading leading to high strain rate deformation. Plastic work on deformation generates heat in the material. At high strain rates, there is insufficient time for this heat to diffuse out of the material, leading to adiabatic conditions. This leads to post-yield thermal softening in the mechanical response, which modifies the material response and must be considered in Engineering design. In this paper, a novel technique is presented in which this adiabatic self-heating can be simulated experimentally at low strain rates using programmed temperature profiles. We show that, in some cases, these simulations can very accurately capture the mechanical response at higher rates, but in others, the replication is less accurate. This may give further insights into the thermodynamics of high strain rate polymer mechanics. This technique therefore enables a number of avenues of research: the work to heat conversion can be investigated systematically; diagnostic tools that are limited to low strain rates can be applied; and we can better understand material behaviour and thereby improve predictive models.

The time–temperature superposition (TTS) is a data processing method of viscoelastic mechanics, which is realized by translating and superposing the responses at different temperatures to get master curves beyond the test time or frequency. In this study, an automatic shift method is developed to obtain master surfaces of the carbon fiber reinforced plastics and epoxy resin. First step, an interpolation is used to process the dynamic mechanical analysis test data measured by frequency sweep/temperature step or continuous heating‐up method. Second step, the Prony series of the generalized Maxwell model are used to fit the storage and loss modulus at each temperature, which makes the fitting curves have physical meaning and causality. Third step, the automatic shift is achieved by minimizing the sum of squares of the vertical distances between two fitting curves. Last step, master surfaces are created by Prony series fitting and interpolation, and the storage modulus, loss modulus, loss factors, and relaxation modulus at any temperature, frequency or time can be found on the master surfaces. Both storage modulus and loss modulus are considered at same time according to the weight. The effects of different weights are studied. [ABSTRACT FROM AUTHOR]

The rheological behavior of recycled asphalt binders is important in the design of the optimum content of reclaimed asphalt pavement (RAP) material to be used in highway recycling projects. In this study, oscillatory tests were performed on recycled binders of varying RAP concentrations. The complex modulus master curves were constructed using the time–temperature superposition principle. The zero shear viscosities (ZSVs) were estimated using the Carreau–Yasuda model on the complex viscosity master curves for all the recycled binder combinations. It was found that the activation energy of flow changed linearly from 115.1 to 185.8 kJ/mol with an increase in the RAP content, whereas ZSV varied exponentially with an increase in the RAP content. A good correlation was found between the ZSV and the Superpave rutting parameter (G*/sinδ). An equation was derived to predict the G*/sinδ at any RAP concentration and temperature. For practical use, a G*/sinδ contour plot approach is introduced to calculate directly the maximum and minimum RAP content for any target binder grade suitable for the construction site. cA noticeable change in rheological behavior of recycled binders was observed on either side of the 40% RAP incorporation level. [ABSTRACT FROM AUTHOR]

In order to further study the blast mitigation performance of polyurea and to investigate the protection mechanism and damage characteristics of polyurea-protected structures under contact explosion loads, based on earlier work, this paper investigated the response and energy absorption performance of polyurea under various frequency loads. Qtech T26 blast mitigation polyurea (T26 polyurea) was adopted to protect the reinforced concrete (RC) slab and damage analysis of the post-explosion specimens was carried out at micro and macro levels. The response and energy absorption capacity of the material towards different frequency loads were investigated by dynamic mechanical analysis (DMA). Protective performance of T26 polyurea on RC slab was examined with a 10 kg TNT contact explosion test. Scanning electron microscopy (SEM) was employed to analyze the microscopic fracture morphology of the typical areas of the coating after the explosion. The chemical structure changes of the blast-face coating before and after the explosion were compared by Fourier transform infrared spectroscopy (FTIR). The results show that the glass transition region of T26 polyurea is −40 °C to 10 °C, which is a large temperature range, and the microphase separation of T26 polyurea is low. It is significantly influenced by the ambient temperature and loading frequency. The energy absorption of T26 polyurea is realized through the interaction between the hard and soft segments. When the frequency is between 102 Hz and 106 Hz, the loss factor of T26 polyurea is between 0.20 and 0.31, which exhibits a good energy dissipation performance. In the contact explosion of 10 kg TNT, the fragmentation rate of the coated specimen decreased significantly compared with that of the unprotected specimen, realizing the zero fragmentation protection effect on the back-blast face. The maximum deformation area and the main energy absorption area of T26 polyurea under contact explosion is the ring area outside the longitudinal deformation area. The chemical structure of T26 polyurea changed significantly after the explosion; typically the N-H bonds, etc., were broken and the percentage of hydrogen bonding was reduced. T26 polyurea has realized the protection effect of zero fragmentation of large-equivalent contact explosion, which has a high application value for blast mitigation and blast-fragmentation prevention in actual engineering. [ABSTRACT FROM AUTHOR]

Polyvinyl butyral (PVB), used in safety glass and photovoltaic panels, is commonly described as a complex viscoelastic solid. However, this description is questionable: a viscoelastic solid rheology does not account well for the data obtained at high temperature and the value of the long-time elastic modulus is poorly defined. In this article, an extended rheological study of this polymer in shear geometry has been performed for temperatures ranging between 25 and 140 °C thanks to relaxation and oscillatory experiments. We provide the time–temperature superposition master curve for PVB as well as its time–temperature state diagram. Last, by interconverting the frequency measurements in the time scale and shifting the relaxation modulus through temperature–time superposition, we obtain the evolution of the relaxation modulus as a function of time over 13 orders of magnitude. This curve reveals the predominance of the viscous character of PVB at long times with a vanishing long-time elastic modulus. [ABSTRACT FROM AUTHOR]

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Highly oriented electrospun conductive nanofibrous biocomposites (CNBs) of polylactic acid (PLA) and polyaniline (PANi) are fabricated using electrospinning. At the percolation threshold (φc), the growth of continuous paths between PANi particles leads to a steep increase in the electrical conductivity of fibers, and the McLachlan equation is fitted to identify φc. Annealing generates additional conductive channels, which lead to higher conductivity for dynamic percolation. For the first time, dynamic percolation is investigated for revealing time-temperature superposition in oriented conductive nanofibrous biocomposites. The crystallinity (χc) displays a linear dependence on annealing temperature within the confined fiber of CNBs. The increase in crystallinity due to annealing also increases the Young's modulus E of CNBs. The present study outlines a reliable approach to determining the conductivity and elasticity of nanofibers that are highly desirable for a wide range of biological tissue applications. [ABSTRACT FROM AUTHOR]

For suspensions with electromagnetic particles exposed to an external field, we examine the effect of the solidification of the suspending medium on the formation of particle structures, representative of the curing of a photo-reactive resin during stereolithography. To that end, Brownian Dynamics (BD) simulations are examined in which the solidification of the suspending medium can be incorporated by increasing its viscosity in the course of time. For illustrative purposes, it is assumed that the viscosity function is known apriori in explicit and parametrized form, however, experimental data can be used as well. It is demonstrated that one can study the effects of the viscosity increase by a transformation of time, akin to the time–temperature superposition principle, but here also in the presence of thermal noise on the suspended particles. Therefore, instead of performing BD simulations with a continuously increasing viscosity (computationally inefficient), we advocate performing simulations at a constant (low) viscosity and subsequently transform time (nonlinearly) for re-interpretation of the simulation results. So doing, one can predict the formation of particle structures during on-going solidification of the suspending medium. In practice, the viscosity increase is so drastic that further evolution of the particle structure can be considered as arrested after the characteristic transition-time of the viscosity is reached. Semi-quantitative rules of thumb are formulated for the 3D-printing practitioner. [ABSTRACT FROM AUTHOR]

Creep is a long-term deformation that can cause redistribution of stresses, large deformations, and prestress or post-tensioning losses in prestressed or post-tensioned structures, respectively. A major challenge in quantifying the effect of creep in such structures is that creep of concrete is known to continue for decades. In this paper, we examine the time-temperature superposition principle as a method to predict long-term basic creep of mature portland cement mortar from short-term creep experiments conducted at multiple elevated temperatures. For this purpose, we design a unique, miniature version of the standardized concrete creep frame to be amenable to placing in climatic chambers. We use Bažant's B4 model to verify that the drying creep component of the measured creep behavior is negligible in comparison to the basic creep component. We develop a basic creep compliance master curve for nearly 60 years of deformation at 20 °C using experimental creep data obtained at higher temperatures for test durations of 600 days. [ABSTRACT FROM AUTHOR]

• Analysis of the glass transition temperature of oligomeric epoxy resins. • Determination of the fragility of epoxy oligomers using rheometry and differential scanning calorimetry (DSC). • Estimation of the molecular weight characteristics based on the frequency dependence of loss modulus. Bis-phenol A based oligomeric epoxy resins with known molecular characteristics were selected as model liquids for the study of glass transition processes, rheological properties and tack. The effect of cooling and heating rates on the glass transition dynamics of epoxy resins has been studied. Rheology and differential scanning calorimetry methods were used to determine the fragility indices of oligomeric epoxy resins. The tack of oligomers was determined as a function of the reduced temperature T/Tg, and it is shown that the tack parameters for all studied oligomers correlate well with their fragility indices. Rheological measurements of epoxy oligomers were performed in the oscillation mode in a wide frequency range. Applying the principle of time-temperature superposition, generalized dependencies of the storage and loss modulus on the weight average molecular weight and molecular-mass distribution was determined. The parameters of generalized frequency dependences of the complex modulus components and the molecular weight characteristics of oligomers were correlated. [Display omitted] [ABSTRACT FROM AUTHOR]

The steady-state shear viscosity η(γ̇)\eta (\dot{\gamma }) is required in controlling processing parameters for the extrusion processing of polymer melts. A new method, the so-called ramp test, is investigated in this study to obtain the steady-state shear viscosity with a closed cavity rheometer (CCR). To verify the method and the accuracy of the CCR data, three commercial polyolefin polymers, a low-density polyethylene (LDPE), a linear low-density polyethylene (LLDPE), and a polybutadiene (PBD), were used as model systems. Measurements of the magnitude of the complex viscosity ∣η⁎(ω)∣| {\eta }^{\ast }(\omega )| were compared with the steady-state shear viscosity data obtained by capillary rheometer and CCR. Further, time–temperature superposition master curves of the magnitude of the complex viscosity and steady-state shear viscosity obtained by CCR were developed for LLDPE and PBD. The influence of the cavity sealing on the instrument’s accuracy to obtain the steady-state shear viscosity was investigated using the finite element method simulations. Thus, it was shown that the ramp test performed by CCR is a practical method to determine reliable and reproducible data of the steady-state shear viscosity within a wide range of temperatures (T = 50–180°C) for low and high viscous materials (∣η⁎(ω)∣| {\eta }^{\ast }(\omega )| = 1.6–480 kPa s, M w = 144–375 kg mol−1).