Creep Compliance Master Curves Research Articles

An efficient and robust method for evaluating the low-temperature performance of asphalt binder based on DSR testing

The BBR test has received growing concerns regarding its applicability to field studies and special materials due to the large amount of long-term aged asphalt binder used in preparing asphalt binder beams and the time-consuming beam preparation and testing process. In recent years, the application of a dynamic shear rheometer (DSR) to investigate the low-temperature performance of asphalt binder has attracted widespread attention because it uses significantly less asphalt binder for testing and allows for easy specimen preparation. The objective of this study was to develop an efficient and robust method to evaluate the low-temperature performance of asphalt binder based on DSR testing. Frequency sweep tests were performed on twelve asphalt binders at temperatures ranging from 0 to 25 °C using the 8-mm parallel plate geometry. Two conversions were applied to frequency sweep test data in order to predict the flexural creep stiffness and m-value of asphalt binder, namely the conversion from frequency domain to time domain and the conversion from shear loading to bending loading. The 1S2P1D model was employed to construct the master curves of storage modulus and loss modulus. Afterwards, the flexural creep stiffness was predicted using the shear creep compliance master curve model, which was derived from the 1S2P1D model using the inverse Laplace transform, and the Poisson’s ratio, which was assumed to be constant. It was found that the predicted values of S(60) and m(60) were comparable to the counterparts measured by the BBR, which well demonstrated the feasibility of the proposed DSR-BBR conversion method. In comparison to existing analysis methods, the proposed conversion method strictly complied with the linear viscoelastic theory, and it enabled efficient and robust predictions because the prediction model of flexural creep stiffness had the same parameters as those of the 1S2P1D model, thus avoiding multiple data fittings.

Thermomechanical characterisation and plane stress linear viscoelastic modelling of ethylene-tetra-fluoroethylene foils

AbstractEthylene-tetra-fluoroethylene (ETFE) is a polymer employed in tension membrane structures with mechanical properties that strongly depend on time and temperature effects. A comprehensive understanding of the mutual influence of these variables and a unified viscoelastic constitutive model design can enable wider exploitation of ETFE in sustainable lightweight construction. This study presents a thermomechanical characterisation of ETFE foils through quasi-static tensile experiments spanning two orders of magnitude of strain rates, creep, relaxation, shear and dynamic cyclic tests in a wide range of temperatures suitable for building applications, from $-20^{\circ }\text{ C}$ − 20 ∘ C to $60^{\circ }\text{ C}$ 60 ∘ C . The experimental results in different material orientations are used to identify the limits of the linear viscoelastic domain, define the direction-dependent creep compliance master curves and calibrate the parameters of a plane stress orthotropic linear viscoelastic model, employing the Boltzmann superposition and the time-temperature superposition principles. The model has been numerically implemented using a recursive integration algorithm and its code is provided open source. A validation on independently acquired data shows the accuracy of the constitutive model in predicting ETFE behaviour within the linear viscoelastic regime usually adopted during structural design, with excellent extrapolation capabilities outside the range of the calibration data.

Accurate and efficient determination of glass thermo-viscoelastic properties using creep compliance master curve construction approach

An accurate and efficient method for determining the thermo-viscoelastic properties of glass was proposed using a creep compliance master curve construction approach based on the time-temperature superposition principle. This method mainly involved obtaining creep compliance at multiple temperatures, constructing the master curve, and converting into relaxation modulus. By applying this method, the shear relaxation modulus and Williams-Landel-Ferry constants were successfully obtained for K9 glass. A smooth creep compliance master curve at 590 °C was constructed covering a vast timescale up to 2.6×105 seconds, despite a single curve's duration being only 619 seconds. Consequently, the derived relaxation modulus encompassed a broad range of relaxation times spanning six orders of magnitude. The high accuracy of the determined thermo-viscoelastic properties was firmly validated across all tested temperatures. Furthermore, the detrimental impact of friction on the method's accuracy can be effectively minimized by selecting a suitably large height-to-diameter ratio for the cylindrical glass specimen.

Time-and temperature-dependent compressive behavior of woven carbon fabric reinforced polyamide composite laminate

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.

Mechanical properties evaluation of crumb rubber asphalt mixture for elastic trackbed

As a new type of railway structure, the elastic trackbed can avoid the inherent limitations of railway ballast tracks and slab tracks. Therefore, it is of great significance to provide excellent materials for the elastic trackbed. In this paper, the feasibility of applying crumb rubber asphalt mixture (CRM) to the railway trackbed is preliminarily investigated by evaluating the mechanical properties of CRM. The static modulus, vertical deformation and lateral stability of CRM for the elastic trackbed are characterized via the uniaxial compression test as well as the interfacial shear test. In addition, via the dynamic creep test, the temperature susceptibility, the viscoelastic behaviours as well as the creep compliance master curve of CRM are studied. The uniaxial compression results show that the stiffness of CRM with 3 wt% and 6 wt% crumb rubber particles decreases compared with the ordinary asphalt mixture. And the vertical deformation can also meet the requirements of the elastic trackbed. Furthermore, it is shown from the shear test that the interfacial strength, which presents a linear relationship with temperature, can provide satisfactory lateral stability of the elastic trackbed. Additionally, the dynamic creep test results reveal that the addition of 3 wt% crumb rubber will not lead to excessive accumulation and the increased temperature susceptibility of permanent deformation at high temperature. The viscoelastic parameters gained from the dynamic creep test also show that asphalt mixture with 6 wt% crumb rubber particles shows the worst resistance to deformation despite having the best recovery performance. Finally, the creep compliance master curve of CRM between 10-2 to 109 domain can be obtained by horizontally shifting the creep curves at high temperature. And the horizontal shift factors can be gained. Then, the long-term deformation of the elastic trackbed under the dynamic train load can be predicted by using the equivalent conversion loading time from the short-term dynamic creep test results at 25 ℃ and 0.25 MPa.

Evaluation on the influence of dynamic water pressure environment on viscoelastic mechanical performance of asphalt mixture using the bending beam rheometer method

With the degraded service performance induced by the erosion of dynamic water pressure environment in summer, asphalt pavement has to subsequently overcome the challenge of low-temperature environment in winter. Considering the unique phenomenon of the gradual disintegration of asphalt mixtures’ components, it is still a lack of systematic research on moisture damage induced by dynamic water pressure environment from the perspective of viscoelastic properties. This study adopted the bending beam rheometer (BBR) method to evaluate the influence of dynamic water pressure environment on viscoelastic mechanical performance for asphalt mixture. The results indicated that both creep stiffness modulus and relaxation modulus of asphalt mixture showed similar downward trends with the increase in severities of different water environments, while values of relaxation modulus were slightly smaller than that of creep stiffness modulus. Master curves of creep compliance gradually moved upward with the increase in severities of dynamic water pressure environments, while master curves of relaxation modulus inversely moved downward. Specially, master curves of both creep compliance and relaxation modulus exhibited irregular trends for the dynamic water pressure environment of 60 ℃ − 0.414 MPa, which implied that significant erosion had been brought into asphalt mixture. A relative larger size of coarse aggregate skeleton could improve the resistance of asphalt mixture to moisture damage. The positive effect on improving resistance of asphalt mixture to moisture damage induced by SBS modified asphalt binder was stronger than the negative effect induced by the gradation with a relatively small nominal maximum aggregate size (NMAS). Differences existed in the reaction mechanisms of different types of asphalt binder subjected to the erosion of different water environments.

Characterization of viscoelastic bending stiffness of uncured carbon-epoxy prepreg slit tape

In support of computational modeling of tow placement at elevated temperature, the creep response of IM7/8552 uncured prepreg slit tape material during 3-point bend loading at different temperatures is measured using an RSA III dynamic mechanical analyzer. Short term creep experiments were conducted for a duration of 1000 s at ten different temperatures ranging from −5°C (below Tg of 0 °C) to 40 °C, with the latter being the nominal processing temperature for the tow. Results show that the tow material obeys the time-temperature superposition principle (TTSP) in the temperature range selected for the creep experiments. Using the TTSP, creep compliance master curve spanning more than eight logarithmic decades is obtained for the nominal processing temperature of 40 °C. The time–temperature shift factor is observed to follow closely the William-Landel-Ferry (WLF) model, with the WLF parameters obtained by least square fitting of the experimentally determined shift factors utilizing closed form shifting algorithm (CFS). The WLF model for the material is used to extend the master curve to a range of temperatures above glass transition temperature (Tg) of the material. The creep compliance data is further employed to obtain the retardation spectra of the material using an algorithm based on the work of a co-author and applied recently to a different material system by the authors. Details for extraction of the retardation spectra from the creep compliance results are provided. Results from these studies demonstrate that the creep compliance reconstructed from the retardation spectra accurately represent the experimental results while providing baseline data to quantify the importance of viscoelastic behavior in wrinkle formation during advanced manufacturing of aerospace components.

Thermorheological approach to predict long-term creep of cement mortar from short-term tests

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.

Long-term creep behaviour of E-glass/epoxy composite: time-temperature superposition principle

ABSTRACT Creep behaviour of an epoxy matrix composite with a similar arrangement of composites used in a root joint of a wind turbine blade is investigated in this research. The vacuum infusion process was used to manufacture the composite. Due to the linearity of the viscoelastic behaviour of the composite, the time-temperature superposition principle (TTSP) is applied by using an activation energy shifting method to predict long-term creep behaviour. The activation energy (ΔH) is determined to be 281 kJ mol−1. The calculated shift factor in generating the master curve at the reference temperature of 20°C is 4.75 for a 50°C-creep curve and 7.3 for a 70°C-creep curve. Under operating conditions of the root joint, namely at 20°C/40 MPa, the creep compliance is determined to be 0.63 × 10−12 Pa−1 within 27.8 h (105 s) and increases to 8.6 × 10−12 Pa−1 within 10 years (108.5 s). The creep compliance master curves at 20°C/40, 100 and 300 MPa within 1157 days (108 s) are determined to be 7.1 × 10−12, 12.5 × 10−12 and 18.3 × 10−12 Pa−1, respectively. Scanning electron microscopy examination shows cusps, scarps and pull-out of fibres.

Application of time-temperature-stress equivalence to nonlinear creep in poly(methyl methacrylate)

The uniaxial tensile creep of a commercial grade poly(methyl methacrylate)(PMMA) was measured for 4000 s at 26 ℃ and at stress levels ranging from 14 MPa to 32 MPa. Considering the influence of physical aging and rheological damage factors on the long-term creep properties of polymers, another time-temperature-stress superposition principle expression was derived. This expression as used to predict the long-term creep mechanical behaviour of PMMA. It was found that a long-term creep compliance master curve considering physical aging and damage agrees well with actual long-term creep test results.

Nonlinear Creep Deformation of Polycarbonate at High Stress Level: Experimental Investigation and Finite Element Modeling

It is well known that polycarbonate (PC) undergoes time-dependent deformation (i.e., creep deformation), and nonlinear creep deformation is often experienced at high stress level. Using the time–temperature–stress superposition principle (TTSSP), we obtain a new master curve, which covers higher stress level, and successfully establish a new modeling method of creep deformation of PC. First, to investigate the effect of applied stress level on the creep compliance (i.e., stress-dependent nonlinear creep deformation), this study conducted various creep tests with eight different stress levels. We found that the creep compliance curve strongly depended on the applied stress level; in particular, a higher stress level induced a larger difference in creep compliance. According to the TTSSP, the creep compliance curve at each stress level shifts with the creep time (i.e., stress reduced time). When we appropriately selected the stress reduced time, we obtained the master curve of creep compliance, which is unified with respect to various applied stresses. However, we found that the stress-shifted factor is not compliant with the previous TTSSP, especially in the higher stress regime. Therefore, this regime was also considered to obtain a new master curve that can cover a wide range of stress levels. Finally, our established creep model (master curve and stress shift factor) was introduced into FEM, and then this numerical model was verified by comparison with experimental data. Our model may be useful for predicting the creep deformation of PC subjected to a wide range of applied stresses.

Experimental analysis and prediction of viscoelastic creep properties of PP/EVA/LDH nanocomposites using master curves based on time–temperature superposition

ABSTRACTPrediction of viscoelastic behavior of polymers over a long‐term period is of vital importance for engineering applications. An attempt was made to uncover the interplay between the morphology and viscoelastic behavior of compatibilized polypropylene/ethylene vinyl acetate (EVA) copolymer blends in the presence of layered double hydroxide (LDH) nanoplatelets. The time–temperature superposition (TTS) principle and WLF equations were merged to obtain master curves of storage modulus at defined reference temperatures enabling prediction of storage modulus at high frequency ranges which are not experimentally measureable. Moreover, the creep compliance master curves were acquired for different reference temperatures to predict the creep compliance of nanocomposites over long period of times. It was found that the presence of LDH decreases the creep compliance at long period of times while it decreases the unrecoverable deformation of EVA domains. A simple mechanism was proposed to explain the creep and recovery behavior of samples blend at different temperatures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46725.

Modelling creep and recovery response of asphalt binders using generalized burgers model

Appropriate modeling creep and response of asphalt binders can save time, and resources and efforts required for multiple experimentations. Creep compliance master-curves were obtained from short duration creep experiments on 10 different asphalt binders each at 0.1 and 3.2 kPa stress levels. It was shown that, a four Kelvin-element generalized Burger’s model could closely approximate creep and recovery response at any combination of loading and unloading cycle. A single run of dynamic shear rheometer used for conducting short time creep experiments at different temperatures, can be adequate for modeling creep and recovery response of asphalt binders.

Prediction of mechanical properties of PP/EVA polymer blends governed by EVA phase change in the presence of environmentally‐friendly inorganic tungsten disulfide nanotubes (INT‐WS2)

Anticipating dynamic mechanical behavior of polymeric materials over long period of time and under different frequencies is the first step to be taken to afford load‐bearing applications. Nevertheless, what we know about dynamic mechanical behavior of polymers is only limited to experiments, which necessitates large pools of data spending too much money, time, and energy. Environmentally‐friendly inorganic tungsten disulfide nanotube (INT‐WS2), was introduced to polypropylene/ethylene vinyl acetate copolymer (PP/EVA, 75/25 wt/wt) blends through melt mixing, and dynamic mechanical analysis (DMA) frequency sweep tests were performed to obtain master curves based on time‐temperature superposition (TTS) theorem. The influence of EVA phase change (solid, semi solid, and melt domains) on the creep and recovery behavior of nanocomposites in linear region was then studied. It was found that using INT‐WS2 along with PP‐g‐MA results in distinctive improvement in creep‐recovery response of nanocomposites. Burger and Weibull models were used to mimic viscoelastic behavior of the nanocomposites. Creep compliance master curves predicted creep compliance, while analysis of cyclic creep‐recovery at 30 °C revealed almost constant permanent strain parameters for sample having 5 wt% INT‐WS2 and PP‐g‐MA after three times repeating test cycles. Influence of phase change phenomenon of EVA domains on creep‐recovery behavior of nanocomposites was mechanistically demonstrated. POLYM. COMPOS., 40:1964–1978, 2019. © 2018 Society of Plastics Engineers

Temperature and frequency‐dependent creep and recovery studies on PVDF‐HFP/organo‐modified layered double hydroxides nanocomposites

ABSTRACTA series of poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) loaded with various contents of layered double hydroxides (LDHs) nanoparticles were prepared via a melt mixing method. Detailed investigations on LDH dispersion state in the polymeric matrix conducted by TEM revealed intercalated/exfoliated, and agglomerated structures at low (1 wt %) and high (>3 wt %) loadings of LDH contents, respectively. Wide angle X‐ray scattering and DSC results showed that incorporation of LDH into PVDF‐HFP matrix reduced its overall crystallinity and helped to form polar crystallites, while the crystal size at 020 crystallographic directions was found to be most affected by presence and dispersion state of LDH in the matrix. TGA results showed LDH improved thermal stability of matrix however, unlike many other nanomaterials it significantly reduced the residual mass which highlights catalytic role of LDH in degradation of residual carbon char. Detailed analysis on creep and recovery data over wide range of selected temperatures revealed that the creep compliance of nanocomposites are basically controlled by crystallinity and presence of LDH at low and high temperatures, respectively. Based on obtained storage modulus and creep compliance master curves it was also found that the influence of LDH on decreasing the creep compliance and improving viscoelastic properties of PVDF‐HFP over long time period and over high frequency ranges becomes more pronounced. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46352.

Linear viscoelastic creep compliance and retardation spectra of bitumen impregnated fiberglass mat and polymer modified bitumen

Temperature-controlled experiments are performed to characterize the viscoelastic response of materials commonly used in asphalt roofing shingles, including both creep compliance master curves and shear retardation spectra. Material systems characterized in this study include polymer modified bitumen (PMB) and bitumen impregnated fiberglass mat (BIFM). BIFM experiments are conducted using 3-point bend specimens in a TA instruments RSA III DMA, whereas PMB results are obtained from torsional loading of two cylindrical specimens in a MARS II controlled stress rheometer. Short term (duration of 1000s) isothermal creep experiments are conducted at temperatures above the bitumen glass transition (Tg=−42°C) (a) on BIFM specimens in the range −30°C≤T≤30°C and (b) on PMB specimens in the temperature range −30°C≤T≤20°C. Using the time-temperature superposition principle (TTSP), creep compliance master curves for both materials are obtained at a reference temperature of 0°C. The results are then used to obtain the shift factors and develop both Williams-Landel-Ferry (WLF) and Arrhenius models. Results show that BIFM has≈2.2X lower creep compliance than PMB at T=0°C, with the difference increasing at higher temperatures. Furthermore, beyond the early, short-term creep times, significant deviations between the retardation spectra of BIFM and PMB are observed.

Hot mix asphalt time-temperature shifting and fitting techniques: A comparative study

In this study hot mix asphalt (HMA) creep compliance master curves were constructed using different temperature shifting techniques and fitting functions. The study aimed to compare the capability of using five different shifting techniques (numerical, log-linear, William-Landel-Ferry (WLF), Modified Kaelble (MK) and Arrhenius) and two different fitting functions (the Sigmoidal fitting function, and Prony series) to construct creep compliance master curves. To achieve this aim, one hundred and twenty (120) HMA specimens were prepared at three air voids levels (3.4, 4.9 and 6.4%). Half of the prepared HMA specimens were modified using Elvaloy Reactive Elastomeric Terpolymer (Elvaloy® RET at 2% by weight) while the other half remain unmodified. Also, half of the prepared HMA specimens were exposed to short-term aging (STA), while the other half exposed to both short term aging and level 2 long-term aging (LTA2). All the prepared HMA specimens were exposed to a dynamic creep test using a pulse load of 107kPa at five different testing temperatures (5, 15, 25, 45 and 60°C). Both graphical and statistical comparisons were made among different shifting techniques and different fitting functions. Generally, The Sigmoidal fitting function was found to be the most accurate fitting function. Comparing with the numerical shifting technique, the best fit between measured and predicted shift factors was found for WLF followed by log-linear, MK and Arrhenius techniques, respectively.

Effect of HDPEH polymer on viscoelastic properties of SBS modified asphalt

Styrene-Butadiene-Styrene (SBS) is one of the polymer that has been used for enhancing asphalt binder properties. The present work discusses the combined effect of High Density Polyethylene Homo Polymer (HDPEHP) and SBS on conventional and rheological properties of viscosity grade 30 asphalt commonly used in India. Six blends of binders were prepared using varying percentages of SBS and HDPEHP. Various rheological tests were performed on unaged, short-term aged and long-term aged binders to evaluate the effect of both polymers. Use of both polymers increased the viscosity of polymer modified blends marginally when compared to unmodified binder. Comparison of complex modulus mastercurves indicated that at lower reduced frequencies, complex modulus values were higher for polymer modified blends in relation to unmodified binder. Higher elasticity was provided by addition of HDPEHP when compared to other blends. Analysis of relaxation modulus and creep compliance mastercurves indicated combination of SBS and HDPEHP offered higher resistance under creep load and strain under long term conditions. Thus, it can be concluded that addition of HDPEHP enhances viscoelastic properties of SBS modified binder.

Investigations on tensile creep of CNT-epoxy shape memory polymer nanocomposites

In this work, epoxy-based shape memory polymer nanocomposites (SMPnCs) were prepared using 0.5 wt% and 1 wt% multi walled carbon nanotubes (MWCNTs) pre-dispersed in epoxy resin. This was cured with triethylene tetraamine (TETA) curing agent. The glass transition temperatures (Tg) were determined using Advanced Rheometric Expansion System (ARES). The creep behaviour of the 0 wt% CNT SMPnC as well as the 0.5 wt% and 1 wt% MWCNT SMPnCs were studied through short term tensile creep test at different temperatures. Master curves of creep compliance were derived using a time-temperature superposition principle (TTSP) based on Williams-Landel-Ferry (WLF) equation. A Findley power-law model was used to predict the creep deformation behaviour of 0, 0.5 and 1 wt% CNT SMPnCs. Good correlations between experimental data and the predictive model were obtained for both SMPs particularly at lower temperature and above Tg.

Creep behavior and lifetime prediction of PMMA immersed in liquid scintillator

The creep behavior of PMMA immersed in liquid scintillator at room temperature was experimentally studied with a new type of creep test machine. Both short-term and creep-rupture tensile tests at eight stress levels were performed. A master curve of creep compliance at a reference stress was obtained according to the Time-Stress Superposition Principle. The master curve was compared with the actual long-term creep curve. It demonstrates that the two curves coincide well at short times. However, the actual creep data shows a higher creep rate as time goes on. The actual lifetime is much shorter than that predicted by the master curve. Furthermore, the relationship between long-term creep limited strength and service life was determined. The results can be used to guide the safety design of PMMA vessels for application in a neutrino observatory.