Time-temperature Superposition Method Research Articles

Application of the non-linear three-component model for simulating accelerated creep behavior of polymer-alloy geocell sheets

The polymer-alloy geocell sheets (PAGS) represent a novel geocell material developed to replace conventional geocell materials. Accelerated creep testing, a convenient and precise performance evaluation method, presents a viable alternative to traditional creep testing for obtaining long-term creep strains. Nonetheless, there is a lack of prediction and in-depth exploration of accelerated creep testing. This paper aims to assess the efficacy of using the non-linear three-component (NLTC) model to simulate the accelerated creep behavior of PAGS. The predictive accuracy of the NLTC model has undergone evaluation through a comparison between stepped isothermal method (SIM) accelerated creep experimental tests and numerical simulations. Subsequently, the validated NLTC model was employed to simulate the time-temperature superposition method (TTSM), time-stress superposition method (TSSM), and stepped isostress method (SSM) accelerated creep tests, thereby verifying its effectiveness in predicting all accelerated creep tests. The results indicate that the NLTC model can effectively simulate creep deformation induced by temperature increases, particularly the temperatures below 41 °C. Although some errors are observed at elevated temperatures, it is within the acceptable range of 17.4%. Numerical simulation results of TTSM, TSSM, and SSM tests also suggest the model's proficiency in simulating the accelerated creep behavior by temperature and creep load increasing.

Modeling the thermo-oxidative aging effects on fatigue life of natural rubber using a continuum damage mechanics approach

Thermo-oxidative aging (TOA) significantly impacts the fatigue life of rubbers by reducing the fatigue strength and modifying the slope of the Wöhler curve, rendering traditional time-temperature superposition methods inadequate. In this work, we aim to develop a model capable of predicting the effect of TOA on the fatigue properties of rubbers. For this purpose, dumbbell specimens of natural rubber (NR) were subjected to aging in an air-vented oven at different temperatures prior to mechanical testing. Tensile tests were conducted to quantify the aging effects on a microscale network parameter known as elastically active chains (EAC) density, along with determining ultimate properties such as the stress and strain at break. By using a time-temperature equivalence and the Arrhenius shift factor, master curves were constructed for both EAC density and ultimate properties. Subsequently, the fracture properties of the aged material were predicted using an energy limiter approach whose evolution follows that of EAC density. Furthermore, a relationship between the parameters of the continuum damage mechanics (CDM) approach (specifically, the power law parameters of the Wöhler curve) and the fracture properties was proposed, resulting in accurate estimates of the fatigue life regardless of the aging conditions. Satisfactory agreement was observed between the model predictions and the data for nine aging conditions encompassing four different temperatures. The CDM approach also allows assessing the evolution of mechanical damage within the material influenced by TOA. The novelty of this approach lies in establishing a direct relationship between fatigue and fracture properties. Moreover, this is the first time to the best of our knowledge that TOA has been explicitly incorporated into a fatigue life prediction model via the evolution of the EAC density.

Solvent-induced phase separation and Hofmeister effect enhanced strong, tough, and adhesive polyion complex hydrogels

Polyion complex (PIC) hydrogels possess excellent strength and toughness due to the dynamic and synergetic energy dissipation mechanism associated with the co-existence of both strong and weak bonds, ionic and hydrogen, in their networks. On the other hand, PIC hydrogels usually exhibit poor wet adhesion properties. Furthermore, the role such dynamic energy dissipation mechanism plays in determining interfacial binding is unknown. To address these challenges, here, we report the fabrication of an adhesive PIC hydrogel, poly(sodium p-styrenesulfonate) (NaSS)/poly(acryloyloxyethyltrimethyl ammonium chloride (DAC)–co-2-vinyl-4,6-diamino-1,3,5-triazine (VDT), i.e. PNaSS/P(DAC-co-VDT), by introducing a multi-hydrogen bonding capacity functional co-monomer, VDT, and solvent-induced gel phase separation into the fabrication process. The resulting hydrogel exhibited as high as 174 kPa adhesion strength, with retained high mechanical properties, typically 1.2 MPa tensile strength, 2.12 MPa Young’s modulus, and 452% strain. The mechanical properties of PNaSS/P(DAC-co-VDT) were tunable by adjusting the content of VDT and of the total monomer concentration in hydrogel precursor solutions (Cm), as well as by taking advantage of the Hofmeister effect. The dynamic modulus spectra of PNaSS/P(DAC-co-VDT) hydrogels at different Cm’s in extended frequency windows with time–temperature superposition method (TTS) were acquired and analyzed to explore the influence of polymer entanglement on the hydrogel network structure. The microscopic structure-macroscopic mechanical property relationship of PNaSS/P(DAC-co-VDT) hydrogels at different Cm’s and immersed in different salt solutions was further studied using the Mooney-Rivlin equation and by fitting the tensile data to Creton’s viscoelastic model. This study may provide new insights into designing and constructing strong and tough PIC hydrogel-based adhesives.

Cross-scale analysis of asphalt binder tensile fracture using molecular dynamics simulation

The tensile failure behavior of asphalt binder is crucial for longevity and durability of asphalt concrete, which is one of most common infrastructure materials. This study provides a cross-scale approach to investigate tensile fracture of asphalt binder using MD simulations. First, two asphalt models for asphaltene-doped and saturate-doped binders were constructed at nanoscale. Tensile simulations were then conducted to observe the evolution of nanovoids and changes in voids surface area. Using tensile strength values at various temperatures and strain rates, the master curve of tensile strength was established based on time-temperature superposition. Results show that cohesive cracking in asphalt binders begins with nanovoids, which rapidly evolve into larger cavities and form thinning filamentation structures, eventually resulting in a complete crack. Locations with lower concentrations of polar components are more likely to initiate nanovoids. After complete fracture, voids surface area of asphaltene-doped binder is larger than that of saturate-doped binder. Increasing the proportion of asphaltene enhances tensile strength of asphalt binders. As expected, tensile strength increases with strain rate but decreases with temperature The time-temperature superposition method is shown to be effective in obtaining macroscale tensile strengths from MD simulations that are comparable to experimental measurements. This study presents an effective simulation method to obtain cross-scale parameters, providing new insights into crack initiation and propagation in asphalt binders.

Use of Time–Temperature Superposition and Stepped Isothermal Method for Estimating Long-Term Properties of Recycled Aggregate Roller-Compacted Concrete

Abstract Although the use of recycled materials in civil engineering construction is a desirable option from a sustainability standpoint, the questionable long-term performance of these materials often hinders their widespread use in practice. The primary focus of this study was to perform accelerated aging and testing for estimating long-term properties of a roller-compacted concrete composed of crushed recycled aggregate, Type-I portland cement, and ASTM Class-F fly ash replacing up to 50 % of cement by weight. Accelerated aging was accomplished by curing cylindrical specimens at three different elevated temperature regimes for specific time durations. At the end of each time–temperature regime, the residual stiffness of the specimen was measured in a nondestructive fashion. Series of stiffness–time master curves were then constructed for each mix using the time–temperature superposition (TTS) technique and the stepped isothermal method (SIM). While the TTS method uses different sets of specimens for each elevated time–temperature regime, SIM uses a single set of specimens that are stepped up in temperature and held at each regime for a specified duration. Results indicated that for all mixes, the material stiffness degraded with time. Based on the Arrhenius equation, stiffness–equivalent age master curves were developed. Stiffness prediction was accomplished up to an equivalent age of almost 600 days, although the actual short-term test lasted only up to 6 days. It was also found that SIM and TTS provided comparable results, thus implying that the testing time and the number of specimens can be significantly reduced by using the SIM.

The relationship between color and mechanical properties of heat-treated wood predicted based on support vector machines model

Abstract Thermal modification or heat treatment can cause the loss of mechanical property of wood. In this study, Poplar (Populus tomentosa Carr.) and spruce (Picea obies Mast.) were heat treated at 180, 200, and 220 °C for 2–10 h. Changes of color (L*, a* and b*) and mechanical strength including modulus of elasticity (MOE), modulus of rupture (MOR) and shear strength after heat treatment were analyzed. Time-temperature superposition methods were used to quantify color and mechanical strength. The prediction models of MOR, MOE and shear strength were assessed with support vector regression model (SVR) based on color parameters. The trends of color change and mechanical strength after heat treatment were highly consistent. The values of apparent activation energy (E a ) calculated from color parameters (110.6–187.2 kJ/mol) were identical to those from mechanical strengths (103.2–219.2 kJ/mol). Color parameters were used as input variables, and the MOE, MOR, and shear strength were output parameters in the established SVR model. Gaussian radial basis function (RBF) was found to be a kernel function for SRV model. Optimal hyperparameters in SVR model were obtained using cross-validation and grid search. The determination coefficients for MOE, MOR, and shear strength were 0.903, 0.835, and 0.865, respectively for poplar. The high correlation suggested that wood mechanical strength can be predicted non-destructively through measuring color parameters after heat treatment.

Study on Regenerative Processing Performance of Chlorinated Polyethylene Based on Wireless Network and Artificial Intelligence Technology.

The development of Information Technology has intruded the chemical industry. In the conventional chemical industry, humans are involved in monitoring the chemical evaporation processes. If there is any damage, then humans suffer enormously. These drawbacks are overcome in the chemical industry by implanting the sensors to the required blocks for monitoring the levels of chemical substances. An alert system can be introduced with an artificial intelligence algorithm to regenerate the process using details updated in the database. In this research, the machine-based Time-Temperature Superposition (TTS) method is implemented to monitor the chemical reactions in the chemical component manufacturing company.

Lifespan Model of the Relationships between Ethanol Indicator and Degree of Polymerization of Transformer Paper Insulation

A growing body of evidence suggests that the ethanol dissolved in the oil can be used as an indicator to effectively monitor the aging behavior of insulating paper. In this study, thermal aging experiments are performed on oil-paper systems with different initial moisture contents and aging temperatures, and then a gas chromatography-mass spectrometer equipped with an automatic headspace sampler is used to test the ethanol contents of the oil samples. The variations and correlations of ethanol contents with temperature, moisture and aging degree are analyzed. The experimental results show that the ethanol contents in oil had a strong correlation with temperature, and is also affected by the cellulose hydrolysis. In addition, a preliminary lifespan assessment of the oil-paper systems under laboratory conditions is conducted by establishing the relationship between ethanol and the degree of polymerization. Then, the time-temperature superposition method is applied to the relationship, and a lifespan model with any temperature is determined according to the ethanol kinetic equation. Based on the model, further observation of the fitting parameters in the case of the two moisture contents (0.8%, 2.3%), the goodness of fit reached higher values of 0.961 and 0.973, respectively. The results of this promising model can help us to a better understanding of ethanol indicator to condition assessment for the transformer paper insulation.

Thermal modification kinetics and chemistry of poplar wood in dry and saturated steam media

AbstractThis research work presents a modelling strategy to analyse thermal conversion rates of two thermal wood modification processes based on time-temperature superposition method. It gathers in a single study different original and bibliographic experimental works analysing the dry mass variation that occurs during thermal and hydro-thermal wood modification processes. The mass loss kinetic was successfully modelled using a modified Arrhenius approach. The time-temperature superposition method allowed to define for each wood modification process a master curve and its time shift depending on the treatment temperature. The analysis of ventilated oven and saturated steam treatments pointed out the existence of a continuous single kinetic for the ventilated oven which became more complex for saturated steam since a second kinetic stage appeared. This kinetic difference was sustained by infrared spectra chemical analysis which showed that hemicelluloses degraded much faster in presence of steam while lignin degradation occurred in both conditions.

Stress relaxation behavior and life prediction of gasket materials used in proton exchange membrane fuel cells

Silicone rubber gaskets are employed to keep fuel gases and oxidation in their own zones. Due to the viscosity and elasticity, the assembly force could relax when the silicone rubber is compressed in a proton exchange membrane fuel cell. In this work, the stress relaxation behavior of silicone rubber samples is studied under different temperatures and simulated operating conditions. The results show that the stress relaxes exponentially with time at 25% strain level, especially at higher temperature or with higher acid concentration solution. The three-term Prony series can simulate the viscoelastic behavior well, and the Master curves are established by applying a time-temperature superposition method to estimate the life of the samples. It can save approximately 50% and 78% of the test time when an operating temperature and acid solution are chosen appropriately.

Effect of the comonomer content on the solid‐state mechanical and viscoelastic properties of poly(propylene‐co‐1‐butene) films

ABSTRACTIn this study, we quantified the thermal and solid‐state mechanical and viscoelastic properties of isotactic polypropylene (i‐PP) homopolymer and poly(propylene‐1‐butene) copolymer films having a 1‐butene ratio of 8, 12, and 14 wt %, depending on the comonomer content. The uniaxial tensile creep and stress‐relaxation behaviors of the samples were studied in a dynamic mechanical analyzer at different temperatures. The creep behaviors of the samples were modeled with the four‐element Burger equation, and the long‐term creep strains were predicted with the time–temperature superposition method. The short‐term mechanical properties of the samples were also determined with tensile and impact testing at room temperature. We found that the Young's modulus and ultimate strength values of the samples decreased with increasing amount of 1‐butene in the copolymer structure. On the other hand, the strain at break and impact strength values of the samples improved with increasing amount of 1‐butene. Creep analysis showed that i‐PP exhibited a relatively lower creep strain than the poly(propylene‐co‐1‐butene)s at 30 °C. However, interestingly, we discovered that the temperature increase resulted in different effects on the creep behaviors. We also found that short‐chain branching improved the creep resistance of polypropylene at relatively high temperatures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46350.

Inefficiency predictions in a hypoid gear pair through tribodynamics analysis

A tribo-dynamics model, predicting the conjunctional inefficiency and dynamic response of automotive hypoid gear pairs is presented. A dynamics model is coupled with an analytical friction model (viscous and boundary). The temperature rise at the centre of the conjunction is accounted for through use of thermal network model and Time Temperature Superposition (TTS) method, as well as the time varying geometry of the meshing gear teeth. Newtonian and non-Newtonian lubricant shear behaviour are both considered Surface topography measurements of a run-in pinions are obtained. Inefficiency calculations are performed for typical automotive drive cycle snapshots. Precisely measured lubricant shear characterstics for lubricants different blended viscosity modifiers and evolving surface topography are used in the study of transmission inefficiency. The integrated thermal-tribodynamic analysis is shown to distinguish between different viscosity modifier types, an approach not hitherto reported in literature.

Physical and Viscoelastic Properties of Different Moisture Content Highland Barley Kernels

Abstract: The study is conducted to investigate the physical and viscoelastic properties of the highland barley kernels in different moisture content range from 10.1 %% to 20.5 %% (w.b.). Highland barley kernel samples were selected with physical properties in terms of length, width, thickness, 1000-kernel weight, volume, geometric and arithmetic mean diameter changing in linear trends. By using a dynamic mechanical analyzer, the 4-element Burgers model was found to adequately represent the creep behavior of the highland barley kernels (R 2 > 0.977). The creep behavior of the ventral groove and dorsal side was also matched perfectly with Burgers model (R 2 > 0.946). The creep behavior of these kernels at long-time frame was studied applying time-temperature superposition (TTS). TTS method was successfully used to predict the creep behavior of these kernels at longer frame of time. The Tg values for the kernels decreased with increasing moisture content. The Tg values for the kernels at the moisture contents of 10.1 %%and 20.5 %% were 114.33 °C and 67.95 °C, respectively. The magnitude of the storage modulus, loss tangent and their change rates with frequency were maximum at 10.1 %% and minimum at 20.5 %% moisture contents.

Determination of the nonlinearity and activation energy parameters in the TNM model of structural recovery

The structural recovery of amorphous glassy materials is nonlinear and nonexponential, and the relaxation process can be described by the phenomenological Tool–Narayanaswamy–Moynihan and Kovacs–Aklonis–Hutchinson–Ramos models. The nonlinearity parameter x in these models can be determined by several methods, including inflectional analysis, time–temperature superposition, and a new modified temperature-jump method, the latter a modification of the two-step Lagasse et al.’s method. The activation energy ∆h/R can also be determined by the first two methods. In this paper, the applicability of these methods for determining x and ∆h/R is analyzed using simulated structural recovery data as a function of aging time, after cooling at high rates such as those obtainable experimentally using Flash DSC. The results indicate that the activation energy obtained by the time–temperature superposition method is slightly better than that estimated by the inflectional analysis method. The results also indicate that the nonlinearity parameter x can be obtained by the inflectional analysis method for β = 1.0 and for low x and high β. On the other hand, the new modified temperature-jump method works for a broader range of x and β.

NIR spectral–kinetic analysis for thermally degraded Sugi (Cryptomeria japonica) wood

Kinetic analysis was conducted on principal component scores calculated from second-derivative near-infrared (NIR) spectra of thermally treated Sugi (Cryptomeria japonica) wood samples. NIR reflectance spectra were measured for wood samples thermally treated at 90, 120, 150 and 180 °C in an air-circulating oven for periods ranging from 5 min to approximately 1.4 years. The Arrhenius approach, which involves the time–temperature superposition method, is used to understand the change in the principal component score. The master curve corresponded well with the change in principal component scores at each temperature and yielded a determination coefficient between the measured and estimated data of 0.99 for second principal component score. This report shows that kinetic analysis is useful to understand changes in the principal component score calculated from NIR spectra of wood subjected to thermal treatment.

Validity of predictive models of stress relaxation in selected dental polymers

ObjectiveThe goal of this investigation was to assess validity of predictive models of stress relaxation in dental polymers when applied to extended master curves generated from short time experimental data by WLF time temperature superposition method. MethodsThe stress relaxation modulus changes with time at three different temperatures near the ambient body temperature were determined for selected mono-methacrylate (PEMA and PMMA) and dimethacrylate (bis-acryl) dental polymers. WLF time–temperature superposition procedure of logarithmic shift of the data from other temperatures to those at 37°C was used to generate extended master curves of relaxation modulus changes with time. The extended data were analyzed for conformity to three different predictive models of stress relaxation including Maxwell, KWW stretched exponential function and Nutting's power law equation. ResultsMaxwell model was found to be a poor fit for the extended data in all polymers tested, but the data showed a much better fit for KWW (0.870<R2<0.901) and Nutting's (0.980<R2<0.986) models. The non-exponential factor β in the KWW function and the fractional power exponent n in Nutting's equation were both significantly different for PEMA based system when compared to that of PMMA and bis-acryl systems. SignificanceThe mean values of β in KWW function and power exponent n in Nutting's equation for PEMA resin is consistent with significant viscoplastic contribution to its deformation under stress unlike in PMMA and bis-acryl resin systems. This may have significant bearing for PEMA use in medium to longer term stress-bearing applications even as a temporization material.

Long-Term Hydrothermal Aging Behavior and Life-Time Prediction of Polyamide 6

The long-term hydrothermal aging behavior of polyamide 6 (PA6), with and without stabilizers at 100% relative humidity/90ºC was studied. It was found that the first stage of aging was the Fickian process and corresponded to the physical absorption of water until equilibrium, resulting in slight change of reduced viscosity and chemical structure of the sample of PA6. The second stage of aging was the initiation process of hydrolytic degradation of PA6, which resulted in a decrease of reduced viscosity and increase of end group content. In the final stage of aging, the relative weight gain (Wr) dropped, the reduced viscosity decreased monotonically, and end groups increased continuously, resulting from the hydrolysis of amido links and molecular degradation of PA6. The presence of four types of stabilizers effectively weakened the oxidation reaction and resulting molecular degradation of PA6 during aging. The lifetime of PA6 in a hydrothermal environment was predicted through a method based on the Arrhenius model by considering both temperature and humidity as environmental factors, and, furthermore, was predicted through the time–temperature superposition method.

A Study on Accelerated Thermal Aging of High Modulus Carbon/Epoxy Composite Material

Composite materials have been used increasingly for various space applications due to the favorable characteristic of high modulus to density ratio and potential for near-zero coefficient of thermal expansion. In composite system, depending on the orientation of fibers, strength and stiffness can be changed so that the optimum structure can be accomplished. This is because the coefficient of thermal expansion (CTE) of carbon fibers is negative. For spacecraft and orbiting space structure, which are thermally cycled by moving through the earth' shadow for at least 5 years, it is necessary to investigate the change of properties of the material over time. In this study, thermal aging of epoxy matrix/high modulus carbon fiber composite materials are accelerated to predict the long term creep property. Specimens are tested at various temperatures of 100~140�� with dynamic mechanical analysis to obtain creep compliances that are functions of time and temperature. Using Time Temperature Superposition method, creep compliance curves at each temperature are shifted to the reference temperature by shift factor and a master curve is generated at the reference temperature. This information is useful to predict the long term thermal aging of high modulus composite material for spacecraft application.

Creep behavior of starch-based nanocomposite films with cellulose nanofibrils.

Nanocomposite films were successfully prepared by incorporating cellulose nanofibrils (CNFs) from sugar beet pulp into plasticized starch (PS) at CNFs concentration of 5-20%. The storage (G') and loss (G″) moduli, creep and creep-recovery behavior of these films were studied. The creep behavior of these films at long time frame was studied using time-temperature superposition (TTS). The CNFs were uniformly distributed within these films up to 15% of CNFs. The PS-only and the PS/CNFs nanocomposite films exhibited dominant elastic behavior. The incorporation of CNFs increased both the G' and G″. The CNFs improved the creep resistance and reduced the creep recovery rate of the PS/CNFs nanocomposite films. TTS method was successfully used to predict the creep behavior of these films at longer time frame. Power law and Burgers model were capable (R(2)>0.98) of fitting experimental G' versus angular frequency and creep strain versus time data, respectively.

Kinetic analysis of color changes in keyaki (Zelkova serrata) and sugi (Cryptomeria japonica) wood during heat treatment

The kinetics of color changes in keyaki (Zelkova serrata Makino) and sugi (Cryptomeria japonica D. Don) wood during heat treatment were examined. The color of wood specimens treated at 90, 120, 150, and 180 °C was measured by an imaging spectrophotometer and expressed using CIELAB color parameters. At any treatment temperature, values for L* and $$ \Updelta E_{ab}^{*} $$ decreased and increased in both wood species, respectively, with increased treatment time. Changes in a* and b* varied depending on wood species and treatment temperature. The color changes were successfully analyzed using the kinetic approach applying time–temperature superposition method. This approach elucidated and accurately predicted color changes during heat treatment.