Time-temperature Equivalence Principle Research Articles

Microstructure Evolution of Reactive Polyurethane Films During In Situ Polyaddition and Film-Formation Processes.

Due to the advantages of low energy consumption, no air and water pollutions, the reactive polyurethane films (RPUFs) are replacing the solvated and waterborne PUFs nowadays, which significantly promotes the green and low-carbon production of PU films. However, the microstructure evolution and in situ film-formation mechanism of RPUFs in solvent-free media are still unclear. Herein, according to time-temperature equivalence principle, the in situ polyaddition and film-formation processes of RPUFs generated by the typical polyaddition of diisocyanate terminated prepolymer (component B) and polyether glycol (component A) are thoroughly investigated at 25 °C. According to the temporal change of viscosity, the RPUFs gradually transfer from liquid to gel and finally to solid state. Further characterizing the molecular weight, hydrogen bonds, crystallinity, gel content, and phase images, the polyaddition and film-formation processes can be divided into three stages as 1) chain extension and microcrystallization; 2) gelation and demicrocrystallization; 3) microphase separation and film-formation. This work promotes the understanding of the microstructure evolution and film-formation mechanism of RPUFs, which can be used as the theoretical guidance for the controllable preparation of high-performance products based on RPUFs.

Prediction of storage lifetime of rubber materials for flexible joint elastomers

To investigate the aging performance and storage lifetime of rubber materials used in flexible joint elastomers for solid rocket engines, a compression permanent deformation was used as the performance evaluation index to conduct aging tests on the elastic specimens of joint rubber materials at different temperatures. The results showed that the compression permanent deformation increased with the aging time and temperature, and the value of compression permanent deformation was greater in the initial stage of aging than in the later stage. Based on the regularity of material aging performance, the storage lifetime of rubber materials at room temperature of 25°C is extrapolated to be approximately 17.35 years through the linear equation of aging kinetics. Given that the aging mechanism remains unchanged, the calculation based on the principle of time-temperature equivalence reveals that as the aging temperature of the rubber material increases, the accelerated aging time to reach the regular storage lifetime becomes faster. Aging for 11.25 days at 140°C is equivalent to storing for this rubber material 15 years at 25°C. This research provides references for the future design, manufacturing, maintenance, and storage reliability of flexible joints.

Study on Viscoelastic Properties of Various Fiber-Reinforced Asphalt Binders.

This study analyzed the viscoelastic properties of asphalt binders reinforced with various fibers, such as modified asphalt binder, modified asphalt binder reinforced with lignin fibers (LFs), polyester fibers (PFs), and polypropylene fibers (PPFs), using dynamic shear rheological (DSR) testing. Then, the experiment generated data on the dynamic modulus and phase angle, which described the dynamic rheological characteristics at varying temperatures. The generalized Maxwell model was employed to select the appropriate element, and the test curve was fitted into a discrete time spectrum based on the time-temperature equivalence principle (TTSP). The master curves of the relaxation modulus and creep compliance were established to predict the relaxation and creep properties of various asphalt binders. The analysis indicated that fiber-reinforced binders offer superior resistance to high temperatures and long-term deformation, while being less sensitive to temperature and having a more significant elastic characterization. The binders reinforced with PPFs and LFs exhibited superior performance in high-temperature settings and long-term durability, respectively. On the other hand, the binder reinforced with PFs displayed exceptional high-temperature elastic properties. Additionally, based on the experimental data and corresponding discussion, it appears that the 13-element GM model is more appropriate for fitting the data.

Research and prediction of creep behavior of triaxial warp‐knitted composites by time–temperature equivalent principle

AbstractIn this paper, the creep behavior of triaxial warp‐knitted composites (TWKC) was investigated. The TWKC specimens were prepared by applying vacuum‐assisted resin infusion (VARI), and the three‐point bending creep experiments at different temperatures were carried out. The shift factor was calculated based on the activation energy method, and the creep curve at 25°C within 105s was obtained according to the time–temperature equivalence principle, the time–temperature equivalent model was established, and the model was verified by measuring the long‐term creep data with self‐made instrument. There is approximately agreement between the prediction result and experimental one, which is less than 10% within 105s. The results show that the model could be used to predict the creep behavior of TWKC. The viscoelastic properties of the specimen were analyzed based on dynamic mechanical analysis (DMA), and the creep behavior of TWKC was further analyzed by acoustic emission and digital image correlation damage analysis.Highlights The viscoelasticity of TWKC was analyzed based on dynamic mechanical analysis (DMA), and the activation energy was calculated. Based on the activation energy method, the time–temperature equivalent model was established to predict the creep behavior of TWKC. The creep behavior of TWKC were further analyzed by acoustic emission (AE) and digital image correlation (DIC) damage analysis.

Evaluation of the microscale structure and performance of asphalt mixtures under different design methods

Asphalt mixture design methods have an important influence on both the microscale structure formed and the corresponding properties. This research compared the performance of asphalt mixtures with the Balanced design method, Marshall design method, and Superpave design method. CT scans were performed on the mixture specimens under different design methods to analyze the mixtures' void distribution law and skeleton structure stability. Then, the water stability of asphalt mixtures with different skeleton structures was evaluated by the water immersion Marshall test and freeze–thaw splitting test, and the effects of temperature and loading frequency on the dynamic modulus of asphalt mixtures under different skeleton structures were assessed by uniaxial compression dynamic modulus test. Finally, based on the time–temperature equivalence principle and Sigmoid model, the master curves of the dynamic modulus of asphalt mixtures under different design methods were constructed. The results showed that the number of coarse aggregate contact points and the average coordination number of asphalt mixtures were relatively larger under the Balanced design method, and the residual strength ratio of asphalt mixture under the Marshall design method was 1.4% larger than that of the Balanced design method, and the residual strength ratio of specimens under Superpave design method was 6.1% larger than that of the Balanced design method. At the same time, based on the differences in the air void of the specimens under different design methods and the different skeleton structures, the dynamic modulus laws under the action of different frequencies were obtained, and the mechanism of the influence of the skeleton structure on the dynamic modulus of the mixture was revealed. This research has important implications for the durability improvement of asphalt mixtures.

Investigation of Asphalt Self-Healing Capability Using Microvasculars Containing Rejuvenator: Effects of Microvascular Content, Self-Healing Time and Temperature

The oily rejuvenator acted as the healing agent in microvasculars. A tensile test was designed to evaluate the self-healing efficiency of asphalt affected by microvascular number, self-healing time and temperature. It was found that the healing agent was slowly released through the microporous channels on the inner shell of the microvascular. The release modes of the agent can work together to improve the self-healing efficiency. The self-healing values of the three samples (asphalt, asphalt/microvasculars without rejuvenator and asphalt/microvasculars with rejuvenator) are 51%, 53%, and 71%. The self-healing capability of the asphalt samples with a healing agent is much greater than that of the other two without a healing agent at the same time. More microvascular rupture at the asphalt sample interface led to a higher self-healing efficiency. The self-healing efficiency values of the three samples (asphalt samples with one, two, and three microvasculars) are 52%, 67%, and 73%, respectively. The self-healing efficiency of the same sample increased during 1–3 days from 26% to 88% in one self-healing cycle. The self-healing efficiency value indicated that increasing the temperature improved each sample’s self-healing efficiency. The above trend of change also applies to the second self-healing process. A higher temperature reduces the resistance to molecular motion and accelerates the molecular action of bitumen and the healing agent. The time–temperature equivalence principle can be fully applied to comprehend asphalt self-healing.

Assessment of Durability and Aging Resilience in a Novel Structural Building Adhesive: An Examination of the Time-Temperature Equivalence Principle

Assessment of Durability and Aging Resilience in a Novel Structural Building Adhesive: An Examination of the Time-Temperature Equivalence Principle

Study on master curve of tensile strength of thermal aging composite modified double base propellant

In order to study the mechanical properties of thermal aging composite modified double-base propellant (CMDB), the tensile properties of CMDB propellant were investigated at four temperatures (323, 293, 273, 253 K) and different strain rates (3.3 × 10-5- 3.3 × 10-2 s−1). Uniaxial tensile tests were carried out on CMDB propellant samples with different aging time (0,10,20,35,50,65,80,100 d). The mechanical properties of CMDB propellant after aging were studied. The results show that the maximum tensile strength decreases with the aging time, and the strength value fluctuates within a certain range (Δσ<30 %). The master curve of the maximum tensile strength of CMDB propellant was obtained by using the time-temperature equivalence principle (TTSP), and the master curve equation of the aging strength was established. The equation can be used to predict the maximum tensile strength of CMDB propellant with different aging time in the range of quasi-static strain rate.

Research on improved gas‐assisted extrusion of plastic sheets based on time–temperature equivalence principle

AbstractBased on the time–temperature equivalence principle, the relationship between the melt relaxation time (MRT) and melt heating temperature (MHT) in an improved gas‐assisted extrusion (GAE) of a polypropylene (PP) sheet was investigated by numerical simulations. In the simulations, the MRT was varied and the inherent properties of the MHT were controlled using experimental methods. With an increase in MRT, the velocity in all directions, pressure drop, and shear rate of the melt increased; however, increasing the MRT does not always yield a positive effect on the GAE process of the melt. For instance, the melt velocity increased vertically at the die exit with MRT, resulting in an outward extrudate swell. In addition, the extruded product was intact when the melt was heated to 220°C, which verified the principle of time–temperature equivalence.

Preparation and tribological behavior of high‐temperature oil‐containing porous polyimides

AbstractThis paper aimed to attempt the fabrication of high‐temperature oil‐containing porous polyimides (OCPPIs) using as‐polymerized powder with a no processing melting point, as well as investigate its tribological behavior. The OCPPIs were fabricated using a cold‐press sintering technique containing multiple gradient processing steps. Coalescence tightly among polymer powders was successfully achieved under a high‐elastic state by extending holding time vastly based on the time–temperature equivalence principle. The results indicate that OCPPIs possessed a high performance of oil retention after centrifuging in rotation 6000 r/min within 120 min whether low or high porosity. The tribological behaviors were evaluated by reciprocating friction tests under point‐contact conditions. Surprisingly, the tribological properties showed counterintuitive performance, wherein the best performance on the anti‐friction and wear resistance is encountered for the PPIs with the lowest porosity due to the excellent mechanical performance. The corresponding tribological mechanism with respect to multi‐phase wear and liquid–solid lubrication was also discussed comprehensively. This work fills the gap with respect to the fabrication of high‐temperature oil reservoirs and contributes to further understanding the forming mechanisms of porous materials under a high‐elastic state.

Contact stress analysis of a packer based on shape memory polymers using finite element method

Shape memory polymers (SMPs) possess multiple advantages as a sealing element for a packer. The contact stress between the SMP rubber and a casing (or the formation) is an essential indicator in evaluating the sealability of packers. This work conducts a finite element simulation based on the generalized Maxwell viscoelastic model and the time-temperature equivalence (TTE) principle to analyze the contact stress during the setting. The proposed model simulates the mechanical response of the polymer, including the stretch at a high temperature, cooling with a fixed shape, unloading at a low temperature, the shape recovery with reheating, and the stress relaxation. The results show that the contact stress distribution in the middle section of the packer is relatively uniform. The average contact stress is over 7.5 MPa and meets sealing needs. More significant stresses occur at the shoulders of the packer due to stress concentration. Both the shape recovery and the stress relaxation finish fast that it needs about 228.7 s to obtain stable contact stress after shape recovery. This study provides a method to evaluate the performance of the packer based on SMPs.

Eco-friendly, disposable bamboo fiber dishware: Static and dynamic mechanical properties and creep behavior

The global ban on plastics and the COVID-2019 epidemic have accelerated the demand for eco-friendly disposable dishware. As an alternative to plastic, the characterization of low-cost, widely-sourced, and sustainable plant fibers for degradable, eco-friendly dishware is urgently needed. In this study, bamboo fiber dishware (BFD) and poly lactic acid (PLA) dishware were investigated by exploring how the properties of their microstructures affect their mechanical properties. Thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) were used to characterize the thermal decomposition behavior and dynamic viscoelasticity of both dishware types. Their modulus reductions were predicted using the accelerating creep mode, according to the time-temperature equivalence principle. The results showed that (1) the eco-friendly BFD was light weight and strong. Its specific strength, specific modulus were 4.50 and 3.09 times higher than those of PLA dishware, respectively. The efficient three-dimensional structure formed by the bamboo fibers and held together by hydrogen bonding played an important role in maintaining the excellent physical and mechanical properties. (2) The BFD and PLA dishware exhibited glass transition temperatures of 63.2 °C and 54.7 °C, respectively, according to the loss modulus curves, and their activation energies were 70.76 kJ/mol and 132.53 kJ/mol, respectively. Compared to the PLA dishware, the thermal decomposition behavior and storage modulus of the BFD were showed a lower sensitivity to temperature. (3) The time-temperature principle could be applied to the long-term creep prediction of BFD and PLA dishware. It showed that BFD exhibited a greater creep resistance in protecting food. • BFD’s specific strength and modulus were 4.50 and 3.09 times higher than PLA. • BFD could maintain high storage modulus at high temperature than PLA. • BFD had better creep resistance than PLA after a long time.

A visco-elastoplastic constitutive model of aircraft polymethylmethacrylate related to strain rate and temperature

The visco-elastoplastic mechanical behavior related to the applied strain rate and temperature around the glass transition temperature of Polymethylmethacrylate (PMMA) has been systematically investigated. The uniaxial tensile test was performed at strain rate and temperature rangs 1.0 × 10−4–1.0 × 10−2 s−1 and 363–393 K, respectively, and the Dynamic Mechanical Analysis (DMA) test was carried out between 363 K and 413 K at various frequencies. Moreover, the robust complex constitutive model considering the temperature and strain rate effect is proposed. A nonlinear viscoelastic model is established to describe the viscoelastic response on the basis of the Zhu-Wang-Tang (ZWT) model and the time temperature equivalence principle, including the dependence of strain rate and temperature. Considering the yield stress, the cooperative model is adopted. The viscoplastic mechanical response is manifested as the competition performance of the softening deformation and hardening behavior. The predicted mechanical responses maintain good consistency with the experimental results, indicating that the visco-elastoplastic constitutive model proposed can accurately predict the mechanical behavior of PMMA materials within the imposed strain rate and near the glass transition temperature range.

Thermo-mechanical analysis of laminated cylindrical shell with viscoelastic bonding interlayers

This work proposes analytical solutions to present coupling thermo-mechanical analysis of laminated cylindrical shells bonded by viscoelastic interlayers, considering the temperature effects on both thermal expansion difference of adjacent layers and temperature-dependent viscoelastic property of bonding interlayer. In the analytical model, according to the heat transport theory, the solutions of non-uniform temperature fields in the laminated cylindrical shells are solved by means of the transfer matrix method. Then, based on the thermo-elasticity theory as well as the viscoelasticity theory, the governing equations for the laminated cylindrical shell are established. The standard linear solid model is employed to simulate the temperature-dependent viscoelastic property of the interlayer, in which the viscoelastic constants are determined according to the time–temperature equivalence principle. At last, the analytical solutions of time-dependent stresses and displacements are determined by the Laplace transform and the Fourier series expansion. The results indicate the present solutions are consistent with the finite element solutions. The influences of temperature, material and geometric parameters on the long-term bending behavior of the laminated cylindrical shell are studied.

Research on creep modeling and simulation of cotton fiber assembly based on the three-dimensional discrete element

In order to analyze the mesoscopic contact characteristics of cotton fiber creep, this paper uses the meso-particle discrete element method to establish a cotton fiber assembly creep microscopic model based on the existing cotton fiber creep experiment. The microscopic parameters of the Particle Flow Code contact constitutive model are calibrated according to the macroscopic mechanical indexes of cotton fiber creep obtained from experiments, and the creep strain of the cotton fiber in the instantaneous creep stage under different compressive stresses and the contact force between particles are analyzed. According to the time–temperature equivalence principle, the calculation efficiency of the viscoelastic discrete element model is optimized, which improves the time scale of the simulation test. The results show that the numerical simulation results accord with the variation characteristics of the experimental creep variables, which verifies the feasibility of the method in this paper. The research results can provide a certain reference for the deeper study of cotton fiber creep characteristics and its mechanism.

Characterization and modelling of bisphenol-a type epoxy polymer over a wide range of rates and temperatures

Epoxy resins are employed in many engineering applications in which mechanical properties at different strain rates and temperatures must be quantified for effective use. It is known that these properties are related through the principle of time-temperature equivalence. In this paper, the application of this equivalence is explored in detail, at both small and large strains, and used as part of a strategy for calibrating a constitutive model that can reproduce the stress-strain behaviour in different mechanical conditions. In order to achieve this, quasi-static compression experiments were performed at temperatures from −40 to +40 °C in a screw-driven load frame; room temperature rate dependent experiments were performed from 0.0005 to 6300 s−1 using a screw-driven load frame, hydraulic compression system and Split Hopkinson Pressure Bar apparatus. Dynamic mechanical analysis and differential scanning calorimetry were also performed. A three-network (TN) polymer model was fit to the mechanical behaviour up to a strain of 0.5. This model, combined with time-temperature based mappings gave a good understanding of the thermomechanical behaviour of the material, and also demonstrates an approach that can be used for a wide range of polymers.

Analysis of the trend in evolution of multilevel mechanical properties of solvent-based cold mixed liquid asphalt and mixture

This paper primarily analyzes the change in performance of liquid asphalt and its mixture in each stage and proposes suggestions for fabricating liquid asphalt mixtures in cold weather. The results of GPC and SEM can explain the reasons for the increase in viscosity and strength of liquid asphalt after curing. In addition, the generalized time–temperature equivalence principle is used to predict the performance changes of liquid asphalt, asphalt mortar, asphalt mastic and asphalt mixtures under different curing conditions. The results show that increasing the filler content improves the deformation resistance of liquid asphalt mixtures. The low-temperature performance of liquid asphalt mixtures is outstanding. During construction in cold weather, liquid asphalt or its mixtures can be used after curing at 60 ∼ 110 °C for 1 ∼ 10 h. These parameters can ensure the strength of cold mixed liquid asphalt mixtures in low-temperature environments, and roads repaired with this asphalt can be rapidly opened to traffic.

Rubber aging life prediction based on interpolation and improved time-temperature superposition principle

With focus on quickly and accurately predicting and evaluating the aging performance degradation of rubber at room temperature, the pseudo-failure life at each different acceleration temperature is proposed to be calculated by interpolation method based on indoor high temperature accelerated aging data, and on the basis of the obtained pseudo-failure life. By introducing the time-temperature equivalence principle, a shift factor obeying to an Arrhenius law is derived, and master curves are built as well for the compression set as for the ultimate mechanical properties. The concept of the sum of squares of dispersion coefficient errors is proposed to evaluate the prediction accuracy. Meanwhile a quantitative calculation method that considers the effect of temperature on the performance degradation curve and the shift factor is innovatively proposes. The results show that the proposed optimization method based on the traditional time-temperature superposition principle can quickly process the aging life at room temperature, and the prediction results are distributed within the 3-fold dispersion line, which can well meet the engineering requirements. The reduction of the DSC value from 1.4164 to 1.0828 further demonstrates the effectiveness of the proposed method above. This method can provide some reference for other related polymer materials accelerated aging data processing and life prediction.

Comparative analysis on rheological characteristics of different modified asphalt based on DSR and BBR evaluation

PurposeIn order to evaluate the rheological properties of asphalt more comprehensively and effectively, and to explore and discuss the practicability of relevant models in the evaluation of the rheological properties of asphalt.Design/methodology/approachBased on the rheological and viscoelastic theories, temperature scanning, frequency scanning and multiple stress creep recovery (MSCR) tests of different modified asphalt were carried out by dynamic shear rheometer (DSR) to obtain relevant viscoelastic parameters and evaluate the high temperature properties of different modified asphalt. Based on the time-temperature equivalence principle, the main curve was constructed to study the viscoelastic properties of asphalt in a wider frequency domain. The main curve was fitted with the CAM model, and the rheological properties of different modified asphalt were evaluated through the analysis of model parameters. The creep stiffness and creep velocity of different modified asphalt were obtained through the rheological test of bending beam (BBR), and the low-temperature performance of different modified asphalt was analyzed by using Burgers model to fit the creep compliance.FindingsThe results show that the high temperature rheological properties of several modified asphalt studied in the test are ranked from best to worst as follows: PE modified asphalt > SBS modified asphalt > SBR modified asphalt. Short-term aging can improve the high temperature performance of asphalt, and different types of modifiers can promote or inhibit this improvement effect. Based on BBR test and Burgers model fitting analysis, SBR modified asphalt has the best low temperature performance, followed by SBS modified asphalt, while PE modified asphalt has poor low temperature performance, so it is not suitable to be used as road material in low temperature area.Originality/valueCombined with effective evaluation methods, the rheological properties of asphalt at different temperatures and angles were systematically evaluated, and the evolution of rheological properties of asphalt characterized by model parameters was further analyzed by advanced model simulation.

Study of Allowable Interlaminar Normal Stress Based on the Time-Temperature Equivalence Principle in Automated Fiber Placement Process.

Automatic fiber placement (AFP) is a type of labor-saving automatic technology for forming composite materials that are widely used in aviation and other fields. In this process, concave surface delamination is a common defect, as existing research on the conditions for this defect to occur is insufficient. To predict the occurrence of this defect, the concept of allowable interlaminar normal stress is proposed to define its occurrence conditions, and based on this concept, probe tests are carried out using the principle of time–temperature equivalence. Through the laying speed/allowable normal stress curve measured in the probe experiment, the physical meaning of allowable normal stress is discussed. At the same time, the measured curve is quantitatively analyzed, combined with viscoelastic theory and the molecular diffusion reptation model, and the dominating effect in the formation of a metal/prepreg layer and prepreg/prepreg layer is determined. Finally, the experimental data are used to guide the parameter selection in an automatic placement engineering case and prove its correctness.