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Different types of models are used to study the stress-strain behavior of asphalt concrete mixture during compaction. For modeling it is necessary to know the values of model parameters in the whole range of changes in the characteristics of the compacted material. The aim of the paper is to develop a methodology for determining model parameters based on the results of laboratory creep-recovery testing of asphalt-concrete mixture. In the paper, a model reflecting elastic, visco-elastic and visco-fluid properties of the compacted material is adopted. A differential equation representing the law of behavior of the asphalt-concrete mixture layer under load is obtained. The stages of creep-recovery testing are analytically described, namely: rapid loading with a constant load and deformation under this load; load removal and recovery. Initial conditions for the mentioned stages are determined. Taking into account the initial conditions, analytical expressions of the laws of deformation of the model under the action of a constant load and in the process of recovery are obtained. The methodology of laboratory experiments on creep-recovery is described, according to the results of which the required values of the model parameters with minimum absolute error are obtained. The developed methodology allows to determine the parameters of the model describing the stress-strain behavior of asphalt-concrete mixture of different density and temperature. Consequently, it is possible to simulate the behavior of the asphalt concrete mixture layer at the preliminary, main and final stages of compaction in order to determine the effective operating modes of compaction equipment.

Resistant starch (RS) promotes health benefits; however, when added to foods, it could change the rheological properties. The effect of adding different concentrations (2.5, 5, 7.5, and 10%) of retrograded corn starch with 27% (RNS) or 70% (RHS) amylose content on the properties of yogurt was evaluated through measurements of flow behavior and gel structure. Syneresis and resistant starch content were also assessed. Results were analyzed using multiple regression to describe the effect of starch concentration and storage time on the properties of yogurt added with RNS or RHS. Syneresis was reduced, RNS reinforced the structure increasing the water absorption capacity and the consistency index; meanwhile, RHS provided a yogurt containing up to 10 g of RS in 100 g of sample, allowing obtaining a functional dairy product. Creep-recovery test showed that adding RNS or RHS favored the matrix conformation, and the yogurt samples were able to recover. The final product behaved like a solid material with a firmer and more stable gel structure, resulting in a strengthened gel without weakening the yogurt structure, showing a characteristic like Greek-style or stirred yogurt depending on the type and concentration of retrograded starch. [ABSTRACT FROM AUTHOR]

This work studies the influence of aging and modification on the properties of oil oxidized bitumen grade BND 70/100 and the asphalt mastic based on it. Active powder of discretely devulcanized rubber produced by high-temperature shear grinding is used as a modifier. The results of tensile tests conducted using a ductilometer are compared with the results of a single-cycle creep–recovery test conducted using a dynamic shear rheometer. [ABSTRACT FROM AUTHOR]

In this paper, the effect of temperature on the creep-recovery behavior of a polypropylene matrix syntactic foam material under low stresses is analyzed. Previous dynamic mechanical analyses have shown that the mechanical response of the composite material is strongly time dependent with the polymeric nature of its matrix despite a high volume fraction of hollow glass microspheres. The permanent deformations are more pronounced at the higher temperatures. With the low level of the applied stress, the results lead to the assumption that the microcracks can be generated in the matrix of the composite material. Under the effect of temperature gradients in the offshore environment, the response of the material could evolve from a linear viscoelastic behavior to a behavior of which one part could be associated with the viscoelasticity of the matrix and a second with its viscoplasticity. We propose to use hooke, spectral triangular, and Zapas-Crissmann models to predict the overall creep response of a polypropylene matrix syntactic foam at the different temperatures. The results showed that the creep deformation at the higher temperatures conforms well to the global model including a power law that takes into account the permanent deformations of the polypropylene matrix composite of syntactic foam material type. [ABSTRACT FROM AUTHOR]

Under the service conditions, steel pipelines coated with the thermal protection system are subjected to cyclic loadings of axial tension and hydrostatic pressure. The finite element method generally used to simulate the behavior of composite structures under these loadings allows us to estimate the stresses generated in the system and to conclude on several origins of damage. However, for the framework of displacement or deformation analyses in such multilayer systems, these calculations do not allow a better prediction of their behavior. The methods used do not take sufficiently into account the characteristics of the different coating materials to predict their response in service conditions under cyclic loading. In this paper, we consider the viscosity of the thermoplastic materials used for the five layers coating system. Finite element calculations allow us to observe the areas of highest stress concentration at the interface with the steel pipe. Simulations allowed us to observe that the applied loads lead to increases in residual deformation in the thermoplastic matrix composite material. Cyclic tensile loading causes cracks in the matrix of the syntactic foam material. The study carried out here makes it possible to justify the origin of the failure mechanism in the composite material at the time of the installation of the pipelines which could limit the duration of their use in an offshore environment. The tensile failure of the syntactic foam considered as the polypropylene matrix composite material on which cyclic loads have been applied, is due to the stress level at a given temperature. [ABSTRACT FROM AUTHOR]

One environmental problem in most countries is the huge quantities of plastic waste, which has different types of polymers such as polyethylene terephthalate (PET), polypropylene (PP)., These plastics become a problem because of their non-biodegradability, toxicity, etc. The recovery of plastic waste in pavements has become an ecological technique that contributes to the preservation of natural resources. In this study, PET waste was used as an additive for hot mix asphalt at two sizes (2.50 to 1.25 mm, and 0.315 to 0.160 mm) and three contents (3%, 5%, and 7% by weight of binder), PET modified mixes creep-recovery behavior was tested by four points bending test and compared with control mix (without PET waste) at three different temperatures (0�, 25� and 50�C), were added directly to the mixture as the method of dry process. The results showed that the addition of PET waste yields better results that which could increase the asphalt bituminous resistance against permanent deformation and a clear rigidity improvement in the various temperature because it's more thermally stable and can limit the degradation risks of the bituminous mixtures compared to the control mixture. Further, can be prepared an eco-friendly road construction with less material cost.

Bread staling is a complex phenomenon in which multiple interconnected mechanisms involving water operate, including the formation of amylopectin crystallites sequestering water, crumb-to-crust moisture migration, and the escalating immobilization of water reducing gluten plasticization. Considering the pivotal role of water-gluten-starch interactions, the integration of the highly-soluble, water-avid, arabinoxylan-rich psyllium husk (PSY) into a wheat dough/bread system was explored, to understand the impact of PSY on the water and biopolymer dynamics that could lead to lower staling. With the addition of PSY, optimal dough development required more water (from 68.0 to 119.5 % in control and 10 % wheat flour replacement with PSY, respectively). LF-NMR showed a parallel increase in the proton population attributed to free water entrapped by the continuous network of biopolymers surrounding granular starch (A 23), and its relaxation time (T 23). PSY resulted in freshly baked bread with similar specific volume, porosity and starch gelatinization than the control, but with a much higher proportion of intergranular free water (A 23). Importantly, PSY did not affect amylopectin retrogradation nor shortened the relaxation time of water protons in exchange with gluten, suggesting that PSY did not withdraw plasticizing water from starch or gluten, respectively. During storage, PSY resulted in a dose-dependent delay of both crumb hardening (correlated to T 23 , r = −0.76, p < 0.05) and loss of cohesiveness (correlated to T 23 , r = 0.71, p < 0.05 and A 23 , r = 0.74, p < 0.05). PSY also resulted in greater crumb resilience, which was related to the self-assembly of PSY molecules and its impact on dough elasticity (with up to two-fold increase in recovery strain). [Display omitted] • With the addition of psyllium husk (PSY), dough development required more water. • PSY enabled greater dough and bread hydration in the form of intergranular water. • PSY did not withdraw plasticizing water from starch or gluten during storage. • The antistaling effect of PSY was related to intergranular water and gluten plasticization. • PSY doubled dough elasticity and enhanced the resilience of fresh and stored bread. [ABSTRACT FROM AUTHOR]

Creep deformation in cartilage can be observed under physiological loads in daily activities such as standing, single-leg lunge, the stance phase of gait. If not fully recovered in time, it may induce irreversible damage in cartilage and further lead to early osteoarthritis. In this study, 36 cruciform-shape samples in total from 18 bulls were employed to conduct the uniaxial and biaxial creep-recovery tests by using a biaxial cyclic testing system. Effects of stress level (σ = .5, 1.0, 1.5 MPa) and biaxial stress ratio (B = 0, .3, .5, 1.0) on creep-recovery behaviors of cartilage were characterized. And then, a viscoelastic constitutive model was employed to predict its creep-recovery behaviors. The results showed that the creep strain and its three components, namely instantaneous elastic strain, delayed elastic strain and viscous flow strain, increase with the increasing stress level or with the decreasing biaxial stress ratio. Compared with uniaxial creep-recovery, biaxial creep-recovery exhibits a smaller creep strain, a faster recovery rate of creep strain and a smaller residual strain. Besides, the built viscoelastic model can be used to describe the uniaxial creep-recovery behaviors of cartilage as a good correlation between the fitted results and test results is achieved. The findings are expected to provide new insights into understanding normal joint function and cartilage pathology.

This study aimed to apply H2O2 at different concentrations in combination with mince:water (M:W) ratios and different washing cycles (WCs) to produce surimi gel from silver carp without compromising its quality characteristics. Color, texture, microstructure, and rheological properties of surimi gels were investigated. Water holding capacity, texture profile, and gel strength showed a greater dependency on number of WCs than the M:W ratios and percentage of H2O2 (p <.05), that is, higher WCs, firmer surimi gel. Accordingly, T2 (one WC, 2% H2O2, 1:3), T10 (two WC, 1% H2O2, 1:2), and T16 (three WC, 1% H2O2, 1:2) treatments resulted the most cohesive and resilient surimi compared with the rest (p <.05), confirmed by scanning electron microscopy images. However, all treated fish mince samples with H2O2, resulted in a surimi gel with lower texture quality compared with the control surimi prepared by conventional washing process without H2O2 (p <.05). A temperature sweep test was conducted based on the linear viscoelastic region stress and frequency values and the aforementioned surimi gels exhibited an obvious valley shape pattern at temperature range of 48–62°C. In the creep–recovery test, the Burgers model satisfactorily described the internal structure of the surimi gel samples as the lowest deformation belonged to the control samples followed by T2. However, after 300 s strain, neither of surimi gels were fully recovered their original shape. Altogether, further studies are needed to clarify the effects of H2O2 in reduction of WCs, without significantly affecting the textural and rheological properties of resultant surimi gel. [ABSTRACT FROM AUTHOR]

One environmental problem in most countries is the huge quantities of plastic waste, which has different types of polymers such as polyethylene terephthalate (PET), polypropylene (PP)., These plastics become a problem because of their non-biodegradability, toxicity, etc. The recovery of plastic waste in pavements has become an ecological technique that contributes to the preservation of natural resources. In this study, PET waste was used as an additive for hot mix asphalt at two sizes (2.50 to 1.25 mm, and 0.315 to 0.160 mm) and three contents (3%, 5%, and 7% by weight of binder), PET modified mixes creep-recovery behavior was tested by four points bending test and compared with control mix (without PET waste) at three different temperatures (0°, 25° and 50°C), were added directly to the mixture as the method of dry process. The results showed that the addition of PET waste yields better results that which could increase the asphalt bituminous resistance against permanent deformation and a clear rigidity improvement in the various temperature because it's more thermally stable and can limit the degradation risks of the bituminous mixtures compared to the control mixture. Further, can be prepared an eco-friendly road construction with less material cost. [ABSTRACT FROM AUTHOR]

The application of polysaccharides in the food industry mainly depends on their rheological properties and the polysaccharides in different concentration regions exhibit different rheological properties due to the interactions between polymer chains. Hence, this work investigated the concentration-dependent rheological behavior of Lignosus rhinocerotis polysaccharide (LRP) in water and determined the critical concentrations. The intrinsic viscosity of LRP was 378 ± 32 mL/g and the LRP exhibited more apparent shear-thinning behavior with increasing concentration. The LRP critical overlap and aggregation concentration in water was ~ 2.5 mg/mL, implicating the formation of hydrophobic regions may result from the aggregation and overlap between hyperbranched LRP molecules. The LRP/water system showed higher storage modulus than loss modulus with slight frequency dependence at the concentration of 15 mg/mL, exhibiting the structured liquid behavior. When the concentration increased from 10 mg/mL to 30 mg/mL, the compliance recovery percentage value increased from 58.51% to 92.30%, indicating the formation of a strong gel network in the LRP/water system. Furthermore, the micro-rheological test revealed that the LRP/water system exhibited a concentration-dependent increase in elasticity and viscosity and deterioration in fluidity. • LRP showed more apparent shear-thinning behavior at higher concentrations. • Critical overlap and aggregation concentration of LRP in water was ~2.5 mg/mL. • LRP molecules aggregated to form hydrophobic regions with increasing concentration. • The viscoelasticity of LRP/water system increased with increasing concentration. • LRP/water system was inclined to be elastic solids at concentrations ≥15 mg/mL. [ABSTRACT FROM AUTHOR]

The present paper is aimed at studying the in-plane shear response of a flax fiber - epoxy resin composite laminate. Rectangular specimens, with ±45° laminate orientation with respect to loading direction were used for the experimental procedure. Tensile testing up to failure allowed to extract the shear strain-shear stress curve, which have shown a linear domain, up to approximately 25 MPa, where a shear modulus was calculated, of 1.67 GPa and a Poisson ratio of 0.7, value which is typical for off axis laminates. Strain measurement during these tests, using Digital Image Correlation, have shown that, at high stress levels, concentrators occur in the specimen in the region of failure. Repeated loading tests have shown that the material stiffens approximately 9% when increasing loading speed, leading to conclude that a viscoelastic component of the deformation is present during loading. Repeated creeprecovery tests showed that, for longer periods of time, viscoplastic deformations appear as well, with an exponential evolution with respect to the creep duration. [ABSTRACT FROM AUTHOR]

The creep-recovery test was used to analyze the rheological properties of black bean-wheat flour blends in linear and nonlinear viscoelastic regions. After adding black bean powder to wheat flour, the water absorption rate and development time of the dough were both increased, and the stable time of the dough showed a trend of increasing first and then decreasing. Creep and recovery data fitted well with the 4-element Burgers model (R2>0.94). During the creep time of 3、5、10 and 15 min, the λc、μc、Jcm、and Jmax of the dough gradually increased, the Jro and the recovery rate gradually decreased. Jco、Jro、Jcm generally showed a decreasing trend. After the deformation, the recovery rate of the dough in the recovery time of 3、5、10 and 15 min was 63.51%～73.6%. Under the shear stress of 150、250、500 and 1 000 Pa, the Jco、Jcm and Jmax of the dough gradually increased, μc、Jro、λr and recovery rate dropped from 89.99% to 32.36%. When the amount of black bean flour added in wheat flour was 10%, the weakening of the dough was the smallest and the stable time was relatively longer. The Linear creep-response analysis results showed that the dough had reached steady shear during the creep time of 3 min, prolonging of the creep time affected the elastic recovery and recovery speed of the dough, and the elastic network of the dough was broken partially; the recovery rate of the dough was 73.6% at the recovery time of 10 min. The nonlinear creep-analysis results showed that the dough was sensitive to shear stress outside the linear viscoelastic region, but it still had typical viscoelastic properties,improved the shear stress, reduced the steady shear viscosity of the dough, and accelerated the delayed elastic recovery.

Hydrogels with thixotropic and pH-sensitive properties exhibit injectablity and response to external stimulation. Thixotropic and pH-responsive hydrogels were fabricated from xanthan gum (XG) and a hyperbranched β-D-glucan (TM3a) crosslinked with sodium trimetaphosphate (STMP) for injectable and release-controlled application. Thixotropy and creep-recovery tests were carried out to determine injectable and viscoelastic properties of the XG-TM3a-STMP hydrogels. Introduction of TM3a and formation of chemically crosslinking structures resulted in higher yield stress (43.6–168.9 Pa) and elastic modulus (146.9–1245.7 Pa), lower retardation time (32.6–44.4 s), and higher recovery percentage (49.5–66.7%) for XG-TM3a-STMP compared to XG-STMP and XG-TM3a-water. FTIR spectra and SEM observation demonstrated that TM3a disassembled XG aggregates by partially breaking hydrogen bonds, resulting in a relatively thin wall of the grids for XG-TM3a-STMP. The XG-TM3a-STMP hydrogels exhibited pH dependant swelling property and controlled release behavior. The hybrid hydrogels have potential applications in 3D printing or injectable tissue engineering and drug release fields.

The production of gluten-free (GF) laminated dough pieces is still a challenge in food industry. This work aims to evaluate changes in GF bulk dough characteristics as affected by the addition of hydrocolloids and the process of production of laminated products. Xanthan gum (XG), hydroxypropyl methylcellulose (HPMC) and psyllium (P) were added at 2.5 and 5% in GF dough made with rice and soy flour and cassava starch. Protein fractions were extracted, quantified and analyzed by electrophoresis. Rheology was evaluated by a creep and recovery test and proton mobility was explored by nuclear magnetic resonance. Tests were done on samples before and after the refrigerated rest time to assess the impact of that production step. Extractability of native proteins increased with lower doses of additives, while higher doses reduced it. The opposite behavior was observed on extractability of noncovalent proteins. Under stress, XG (J0: 7.7·10–6 and 4.9·10–6 Pa−1; J1: 7.3·10–6 and 4.9·10–6 Pa−1) and HPMC samples (J0: 7.0·10–6 and 6.5 10–6 Pa−1; J1: 8.2·10–6 and 8.6·10–6 Pa−1) showed lower instantaneous and viscoelastic compliance than control sample (J0: 9.8·10–6 Pa−1; J1: 10.5 10–6 Pa−1), while P had higher values (J0: 10.4·10–6 and 9.8·10–6 Pa−1; J1: 12.5·10–6 and 12.5·10–6 Pa−1). Additives promoted more viscous dough relaxation. After the refrigerated rest time, XG-2.5% elastic recover enhanced, while HPMC showed the opposite. XG decreased water proton mobility and P increased it. The refrigerated rest time enhanced water structuration. [ABSTRACT FROM AUTHOR]

Dynamic rheology, phase morphology and mechanical properties of isotactic polypropylene/poly(acrylonitrile-butadiene-styrene) (iPP/ABS) blends containing various amounts of ABS were investigated. The results of small-amplitude oscillatory shear studies show that the complex viscosity and storage modulus of the blends display significant negative deviation from the linear mixing rule, which is related to the poor interfacial interaction between two components. This was justified by mechanical property measurements. All the blends have a two-phase morphology, indicating the immiscibility of the ABS and iPP. Clear co-continuous morphology for P60A40, P50A50, and P40A60 blends could be observed, with creep recoverable compliances showing maximum values. Dynamic rheological measurements (including small-amplitude oscillatory shear and creep-recovery) are sensitive tools to get insights into the compatibility and phase morphology in the polymer blends, as well as interfacial interaction in such systems. [ABSTRACT FROM AUTHOR]

β-Glucans are known for their beneficial physiological roles but can be used as potential food hydrocolloid. The present study was performed to assess the potential of barley β-glucan concentrates (native and partially hydrolyzed) in altering the functional properties of water chestnut flour dough. The β-glucan concentrate was subjected to partial hydrolysis to prepare a low molecular weight polymer. The WAC, swelling behavior, and pasting properties were significantly modified after the addition of β-glucan concentrates. The water chestnut dough incorporated with β-glucan concentrates displayed enhanced viscoelastic and creep characteristics and the efficacy of β-glucans in providing strength to water chestnut dough depended on its molecular weight. Hydrolyzed β-glucan concentrates increased the elasticity of dough to the greater magnitude in comparison to its native counterpart. Unlabelled Image • Water chestnut flour was supplemented with native and partially hydrolyzed β-glucan. • Hydration properties of water chestnut flour were significantly modified. • M w of β-glucan had a prominent role in modifying flour pasting viscosities. • Hydrolyzed β-glucan imparted higher viscoelasticity to the water chestnut dough. [ABSTRACT FROM AUTHOR]

This study was aimed at evaluating the potential of barley β‐glucan concentrates (native and partially hydrolyzed) in modifying the techno‐functionality of rice flour dough. β‐Glucan concentrate was partially hydrolyzed to obtain a low molecular weight polymer and their influence on the pasting, rheological, and thermal properties of rice dough were assessed. Hydration, thermal, and pasting properties were significantly modified with the added β‐glucans. The rice dough supplemented with β‐glucan concentrates showed improved viscoelastic and creep behavior and the effectiveness of β‐glucans in imparting strength to rice dough depended on its molecular weight. Hydrolyzed β‐glucan concentrates having low molecular weight increased dough elasticity to the greater extent in comparison to native β‐glucan concentrates. The micrographs of supplemented dough showed a strong and dense network indicating improved structure and strength. [ABSTRACT FROM AUTHOR]

Concrete creep results in the strain increment of concrete-filled steel tube. In this article, a new method was established for creep prediction of concrete-filled steel tube considering the creep-recovery effect of the concrete core with creep model and separate creep-recovery model, named two-function method. Five creep models including the recent proposed B4 model and two separate creep-recovery models were used in the method. First, the creep models were compared with 197 test curves of creep of sealed concrete. The results show that the B4 model offers the highest prediction accuracy for load duration time longer than 200 days. Then, the two-function method was used for creep prediction of normal strength concrete-filled steel tube and high-strength concrete-filled steel tube. For comparison, the creep prediction method for concrete-filled steel tube based on the principle of superposition was also adopted. The principle of superposition did not predict the creep of concrete-filled steel tube accurately. The calculation results based on the two-function method are closer to the test data, especially for normal strength concrete-filled steel tube. Finally, the uncertainty of creep in concrete-filled steel tube was analyzed considering the variability of the concrete strength. The results indicate that the variances calculated by the methods with the MC 2010 creep model are smaller than that of the B4 model. The creep strains of concrete-filled steel tube calculated by the two-function method are subject to normal distribution. [ABSTRACT FROM AUTHOR]

Burgos-type cheese is an ultrafiltered soft fresh cheese widely commercialized in Spain. Its structural behavior against external forces is of great importance for the dairy industry, since consumer acceptance depends mainly on texture. In the present study, dynamic and static oscillatory shear rheological analyses of 15 commercial Burgos-type fresh cheeses of different composition, brand and species were carried out to determine the relationship between cheese characteristics and rheological properties. Cheeses were differentiated mainly based on their fat:protein (F:P) ratio into 3 groups: low (L, F:P ≤ 0.1), medium (M, 0.1 < F:P < 0.9) and high (H, F:P ≥ 0.9). H cheeses showed higher complex modulus (G* 0 , 4131 ± 1238 Pa) when compared to L (2366 ± 1825 Pa), mainly related to cheese protein levels. L cheeses presented higher compliance (13.0 ± 4.5 × 10−4 Pa-1) than H (6.5 ± 3.3 × 10−4 Pa-1), indicating differences in the cohesiveness of the cheese matrix. The present research shows that low amplitude shear analysis together with creep-recovery assays would be complementary tools suitable for the rheological characterization of Burgos-type fresh cheeses and that their F:P ratio has a strong impact on cheese final structure. [Display omitted] • Manufacture of Burgos-type fresh cheeses affects their rheological parameters. • Firmness and cohesion mainly depend on the cheese fat:protein ratio (F:P). • Cheeses with high F:P showed the greatest resistance to external forces. • Creep-Recovery assay reveals less cohesive matrix structure in low F:P cheeses. [ABSTRACT FROM AUTHOR]

The creep and recovery and the stress relaxation behaviors of poly(butylene adipate‐co‐terephthalate) (PBAT) and polyhydroxyalkanoates (PHA) binary blends incorporating 30 wt % of a mixture of trisilanolisobutyl polyhedral oligomeric silsesquioxanes (POSS) and calcium phosphate glass (CaP‐g) were investigated under simulated physiological and human body temperature conditions. The synergistic effect of PHA and CaP‐g/POSS filler remarkably improved the creep behavior of the PBAT matrix and decreased its residual strain, consequently enhancing its elastic recovery. A considerable increase of the relaxation modulus of the hybrid materials was also observed upon incorporation of PHA and CaP‐g/POSS. The relaxation modulus of the neat PBAT sample increased from ~60 MPa to ~1600 MPa after addition of 30 wt % CaP‐g/POSS and 70 wt % PHA. However, after exposure of the composites to the simulated human body conditions for 14 days, a drop of dynamic mechanical properties of the studied material systems was observed along with formation of a desirable calcium phosphate phase on the material surface. The long‐term (i.e., up to 7 × 105 s) viscoelastic behavior of the studied materials was successfully predicted using the time–temperature superposition principle and the obtained creep strain and the relaxation modulus master curves were satisfactorily fitted to the Findley power law equation and the generalized Maxwell model, respectively. This study demonstrates a facile method for tailoring CaP‐g/POSS bioactive glasses composition for bone‐like apatite formation on biopolymer surfaces. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2419–2432, 2019. [ABSTRACT FROM AUTHOR]

Starch from pearl millet varieties viz. ProAgro 9444 and HHB 67, selected on the basis of amylose content was studied for steady, dynamic and creep recovery characteristics as affected by concentration (3–15%). ProAgro 9444 and HHB 67 possess amylose content of 20.21% and 15.05%, respectively. Starch gel exhibited shear thinning behavior with flow behavior index <1, well described by Herschel Bulkley model (R2 > 0.969) at all the concentrations. The starch pastes were thixotropic and the extent increased with increasing concentration and amylose content. Dynamic shear properties obtained within the linear viscoelastic region suggested weak gel like behavior at all concentrations, except 3% starch from HHB 67 which was categorized as dilute solution. Weak gel like behavior at other concentrations was supported by tan δ < 1, and the gel from ProAgro 9444 was more elastic. Power law analysis of data from mechanical spectra also r eflected weak gel behavior except for 3% HHB 67. High amylose and increasing concentration favored gel formation as magnitude of temperature at peak G′ and G″ were lower. Creep compliance followed Burger model at higher concentrations whereas 3% HHB 67 exhibited Newtonian behavior. The strain recovery increased with increase in starch concentration and amylose content. [ABSTRACT FROM AUTHOR]

• CNT addition improve the rutting performance of asphalt binder. • CNT addition may increase the stress sensitivity of asphalt binder. • It is desirable to have a higher value of η m for improved rutting performance. • Modified power law can model nonlinear strain response in the recovery period. • CNT addition also improve the performance of asphalt binder under sustained loading. The present study aimed at evaluating the rutting performance of Carbon Nano Tube (CNT) modified asphalt binder under different loading conditions. CNT content was varied as 0%, 0.4%, 0.75%, 1.5% and 2.25% by the weight of control binder. Superpave rutting parameter (G*/Sinδ) and Shenoy parameter (G*/(1-(1/TanδSinδ))) were initially evaluated using temperature sweep test. Though both parameters showed a similar trend, the later one found to have more sensitivity towards evaluating unrecoverable strain value. Creep-recovery test was further conducted at four different stress levels (100 Pa, 3200 Pa, 5000 Pa, and 10000 Pa) to understand the effect of CNT under cyclic loading-unloading condition. Improvement in recovery value and a corresponding decrease in non-recoverable creep compliance value was observed with the addition of CNT. Further attempt was made to model the strain response from creep-recovery test using the Burgers model and Power model. Based upon the variation of viscous component of steady flow obtained from the Burgers model, CNT addition found to improve the rutting performance. Further, the power model also showed an excellent prediction of strain response under creep period, however, deviation from the experimentally observed response was observed in the recovery period. Modification to the power law model was done which significantly improved the strain prediction in the recovery period. Likewise, the effects of CNT under sustained loading condition was evaluated using a creep test at two different stress levels (100 Pa and 3200 Pa). Incremental dosages of CNT shifted the binder response from linear to nonlinear viscoelastic region at comparatively lower creep period. Significant decrease in deformation rate was also observed with CNT addition. [ABSTRACT FROM AUTHOR]

Clinical cartilage repair strategies can be tested using the sheep model as suggest by the European Medicines Agency. To characterize variation within the joint a full biomechanical mapping is necessary. The aim of this study is to establish a loading model, to map regional differences within the knee and determine reference areas for area specific replacement techniques. A porous indenter was selected to evaluate 22 defined test locations (femoral condyles, tibia plateau, patella, femoral groove) on ovine knees (n = 7). A high-dynamic force-controlled micro creep and creep-recovery indentation test system applied five loading (0.11 MPa) and unloading (5.6 kPa) cycles for 60 s each and recorded creep-recovery. Needle indentation was used to measure cartilage thickness and calculate total strain. Steady state behaviour was observed from the third cycle and further evaluated. Little variation of stiffness in N/mm was found within the patella (4.3SD0.5) and femoral groove (8.1SD0.7) compared to larger variations in the femur (7.9SD2.0) and tibia (7.5SD3.2). Creep indentation showed values of 14.5%(SD2.7%) for the patella and 17.4%(SD3%) for the femoral grove opposed to 13.4%(SD4.3%) for the femoral condyles and 21.8%(SD6.6%) for the tibia plateau. Similar trends were observed analysing creep-recovery. Values were normalized to cartilage thickness which ranged between 0.36 mm and 1.14 mm. Our setup allows a reliable evaluation of zonal differences. Homogenous biomechanical behaviour is found within the patella and femoral groove whereas significant biomechanical variation within the femoral condyles and tibia plateau indicates the need for site-specific cartilage repair products. • Clinical cartilage repair strategies need be developed site-specific. • Creep and creep-recovery indentation mimics physiological loading and unloading. • Mapping shows zonal variation of stiffness, creep, creep-recovery and thickness. • Cartilage replacement materials need to be designed according to joint region. [ABSTRACT FROM AUTHOR]

Abstract Since the accumulations of ratcheting strain combined with creep deformation, which are produced in normal activities, can accelerate the fatigue damage of cartilage in joint, the creep-ratcheting and creep-recovery-ratcheting behaviors of articular cartilage are experimentally investigated under creep-fatigue loads. The effect of pre-creep on ratcheting behavior of cartilage was probed firstly and it is found that the initial ratcheting strain of cartilage presents the larger value (30% and 35%) due to its pre-creep deformation in spite of the short pre-creep time applied. With the increasing pre-creep time the ratcheting strain of sample increases while the ratcheting strain rate decreases. The effects of pre-creep and recovery on ratcheting behavior of cartilage were also investigated and it is noted that the strain of cartilage increases fast at first, decreases partly and then changes periodically with cyclic stress. The ratcheting strain evolutions of different layers are not coincident for cartilage sample after the pre-creep or pre-creep-recovery and the ratcheting strains of different layers with pre-creep are larger than them with pre-creep-recovery. Finally the creep-ratcheting strain of cartilage with different peak-holding time during cyclic compression was studied and it is found that the creep-ratcheting strain with peak-holding time is significantly greater than that without peak-holding time. The creep-ratcheting strain increases with increase of peak-holding time or stress amplitude, while it reduces with rising of stress rate. The creep-ratcheting behavior of cartilage is dependent on its depth. These findings point out that the accumulated deformations, including creep deformation and ratcheting deformation, can accelerate the cartilage's damage. Highlights • Due to pre-creep, ratcheting strain of cartilage increases, while its rate reduces. • Larger ratcheting strain occurs due to residual strain after creep-recovery. • Creep-ratcheting strain is greater in spite of short peak holding time. • Creep-ratcheting strain of cartilage is dependent on its depth. • Accumulated creep-ratcheting strains can accelerate cartilage's damage. [ABSTRACT FROM AUTHOR]

Abstract The objective of this study is to examine the fundamental rheological properties of gluten extracted from six commercial wheat flours and four gluten products (GA, GB, GC and GD) at two substitution levels (3 and 6 g/100 g). Experimental data from creep-recovery (shear deformation, 100 Pa) and compression-recovery (biaxial compression, 8 N) tests were fitted into a Burgers model. GA and GC were associated with variation in elastic recovery (strength) and zero-shear viscosity (related to molecular weight) while CB and GD with variation in softening effect that would result in improved extensibility. Differences in composition based on mass-to-charge ratio suggested that GA and GC can form longer polymer chains and have higher LMW-GS and LMW-GS/HMW-GS ratio compared to GB and GD, which form shorter polymer chains. Redundancy analysis clearly separated the effect of gluten substitutions and levels across the six flours in terms of strength and deformability of the structure. Highlights • Gluten viscoelasticity related to its composition, acidity and secondary structure. • Substitution of gluten GB (pH 4.2) and GD produced softening effect. • Substitution of gluten GA and GC increased gluten rigidity. • Elastic recovery was useful in discriminated the effect of gluten substitution. [ABSTRACT FROM AUTHOR]

Highlights • Creep behaviour of Raffia vinifera fibre can be described by the Eight-element model (Kelvin-voigt-Burger's model). • Creep-recovery of Raffia vinifera fibre can be observed by the Schapery model and their parameters were defined as a 3rd-order polynomial in function of stress. • The dissipated energy of Raffia vinifera fibre decreases exponentially during the first fifth cycles and becomes zero above. Abstract In this paper, the study was focused on the viscoelastic behaviour of Raffia vinifera fibres in the optimization of bio-composites. We designed and constructed a device that was used to carry out the uniaxial tensile creep-recovery test which was validated by the comparative tests carried out on the tensile machine MTS 20/M. Among several models tested, the 8-elements Burger model described better the experimental points and the obtained parameters vary according to the stress. In addition, the creep-recovery behaviour was studied through the Schapery model and its parameters were evaluated. Generally, it appears that these parameters can be modelled by a 3-order polynomial. Then the multiple step loading behaviour was carried out and allowed the 8-elements Burger model to be consolidated with the duration of a load being taken into account to describe it. Finally, from the study of cyclic loading, it showed that the energy dissipated during the first cycle is very important compared to that of the other cycles and it becomes negligible from the 10th cycle. This shows that the Raffia vinifera fibre loses less energy during cyclic stresses. [ABSTRACT FROM AUTHOR]

The creep-recovery (CR) test starts out with a period of shearing at constant stress (creep) and is followed by a period of zero-shear stress where some of the accumulated shear strain gets reversed. Linear viscoelasticity (LVE) allows one to predict the strain response to repeated creep-recovery (RCR) loading from measured small-amplitude oscillatory shear (SAOS) data. Only the relaxation and retardation time spectra of a material need to be known and these can be determined from SAOS data. In an application of the Boltzmann superposition principle (BSP), the strain response to RCR loading can be obtained as a linear superposition of the strain response to many single creep-recovery tests. SAOS and RCR data were collected for several unmodified and modified bituminous binders, and the measured and predicted RCR responses were compared. Generally good agreement was found between the measured and predicted strain accumulation under RCR loading. However, in the case of modified binders, the strain accumulation was slightly overestimated (≤20% relative error) due to the insufficient SAOS information at long relaxation times. Our analysis also demonstrates that the evolution in the strain response under RCR loading, caused by incomplete recovery, can be reasonably well predicted by the presented methodology. It was also shown that the outlined modeling framework can be used, as a first approximation, to estimate the rutting resistance of bituminous binders by predicting the values of the Multiple Stress Creep Recovery (MSCR) test parameters. [ABSTRACT FROM AUTHOR]

This work presents different rheological methods to determine the effect of fiber surface treatment on their interaction with a polymer matrix. In particular, surface-initiated catalytic polymerization was investigated on hemp fibers to improve their adhesion with linear medium-density polyethylene (LMDPE). The selected rheological tests (creep-recovery (solid state), small and large amplitude oscillation shear, and transient rheology (melt state)) were used to compare the treated and untreated fiber composites with the neat matrix. The results showed a significant improvement of the treated hemp composite (LPHC) creep modulus with respect to its untreated counterpart (LNHC) leading to a reduction of the creep strain, especially as temperature increases. The transient viscosity was modeled using a modified Kohlrausch-Williams-Watt (KWW) equation showing an increase in the transient viscosity (η0+) and relaxation time (τ) with fiber addition and surface treatment. These results were confirmed by large amplitude oscillatory shear (LAOS) through the reduction of the relative third harmonic (I3/1), intrinsic nonlinearity parameter (Q0), and nonlinear viscoelastic ratio (NRL). The results clearly show that catalytic polymerization is a good surface modification technique to increase the compatibility between natural fibers and polymer matrices as to improve all their final properties.ᅟ [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: The present study aimed to investigate changes in the fundamental rheological properties of dough prepared from wheat grains stored for 6 months at 20 °C, at ambient temperature (temperature varied with time) and at 4 °C. Stress/shear rate ramp, oscillation and creep‐recovery tests were performed to assess the changes in rheological properties as a result of storage. RESULTS: Samples were observed to be non‐Newtonian; thus, the Bingham model estimated the yield stress, which was maximum for the wheat stored under ambient conditions and minimum for wheat stored at 20 °C. The stress required to break the bonds was maximum for wheat‐dough stored under ambient conditions and minimum for wheat stored at 20 °C. Wheat stored at 20 °C also had the highest maximum creep and recovery strain. The viscoelastic properties of the three wheat‐dough samples were compared. CONCLUSION: The results obtained in the present study show that the wheat‐dough prepared under ambient conditions behaves as a rigid and stiff material. The dough prepared from wheat stored at 20 °C had the maximum elasticity. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The creep-recovery behavior of both normal and high strength concrete (HSC) under various load conditions has not been studied thoroughly. Although the use of HSC is long-established, rational creep-recovery prediction of HSC is still unavailable since current study just regards recovery deformation as a secondary result of creep experiments. In this paper, a new prediction model for creep-recovery of normal strength concrete (NSC) with considering the influence of stress level and load history was proposed at first. Then, a model for HSC creep-recovery was established according to creep-recovery data of NSC and HSC in literatures and the influence of compressive strength of concrete. To validate the HSC model, an experimental study of the creep behavior of C80 concrete was conducted. Creep and residual strain after unloading of specimens at various compression stress levels (30% and 50% of the compression strength) were compared with the HSC creep-recovery model. Although the HSC model tends to underestimate the first 7 days’ creep-recovery value, the results show high overall prediction accuracy. Moreover, parametric analysis results indicate that the recoverable creep of HSC reduces significantly than that of NSC. The effect becomes stronger with the increase of loading age and weaker with a prolongation of load duration. [ABSTRACT FROM AUTHOR]

The enzymes glucose oxidase and transglutaminase are frequently used to improve the breadmaking performance of wheat flours, as they have the ability to considerably alter the viscoelastic nature of the gluten network. To evaluate a flour's breadmaking performance, rheological tests offer an attractive framework. In this study, the rheological impact of adding glucose oxidase or transglutaminase to wheat flour dough is investigated by means of linear oscillatory shear tests, creep-recovery shear tests and startup extensional tests. The former tests reveal that the enzymes render the dough stiffer and enhance its elastic character, until saturation is reached. In the breadmaking process, the use of excessive amounts of enzyme is known to be counterproductive. The strain-hardening index clearly reveals this overcross-linking effect. Besides enzymes, the gluten network can also be reinforced by adding supplementary gluten, which was indeed found to enhance the extent of strain-hardening. [ABSTRACT FROM AUTHOR]

The durability of the adhesion between coating and substrate is of utmost importance in organic coatings. In the present study, we endeavor to find a correlation between adhesion durability (loss of adhesion and adhesion recovery) after wet conditions and viscoelastic properties of coatings. To that end, an epoxy resin was cured with four types of hardeners. Furthermore, Polyamine-based hardener, Polyamido amine-based hardener, Polyether polyamine-based hardener, and Cycloaliphatic Polyamine-based hardener, were employed in order to prepare the coatings with different viscoelastic properties. The storage modulus increased as H active of hardeners and crosslink density decreased. After applying these coatings to mild steel, the samples were placed in humidity chamber for 2000 h. Adhesion loss and recovery of adhesion were measured in wet and dry conditions during the time by pull-off test. We found that the higher the elastic module, the more the adhesion loss. Recovery of adhesion after wet and dry cycles correlated with glass transition temperature and elastic element of creep and recovery data. Polyether polyamine based sample and polyamine based samples indicated good adhesion durability through cycles. Moreover, creep recovery of these samples (response of polymer to constant load and its effect on removal of that load) demonstrated a more reversible behavior compared to polyamido amine and cycloaliphatic polyamine based sample. The microscopic delaminated areas of coatings were analyzed by breakpoint frequency method (another useful parameter to describe the extent of coating detachment from the substrate when exposed to humidity) using electrochemical impedance spectroscopy measurement. Finally, EIS measurements approved the adhesion data. [ABSTRACT FROM AUTHOR]

The viscoelastic properties of wheat flour dough are known to be very sensitive to small changes in water content and mixing time. In this study the simple scaling law originally proposed by Hibberd (1970) [Rheol. Acta 9, 497-500] to capture the water dependency of the dynamic moduli in small amplitude oscillatory shear, was also applied to creep-recovery shear tests and extensional tests. The scaling law turns out to be valid not only in the linear region, but to a certain extent also in the non-linear region. At sufficiently high water levels, a 'free' water phase exists in dough, which attenuates the starch-starch and gluten-starch interactions. Dough characterisation after different mixing times shows that overmixing may cause a disaggregation or even depolymerisation of the gluten network. The network breakdown, as well as the subsequent (partial) recovery, are clearly reflected in the value of the strain-hardening index, for which a maximum is reached at a mixing time close to the optimum as determined with the Mixograph. Finally, the gluten proteins turn out to be much less susceptible to overmixing in an oxygen-lean environment, which demonstrates the significant role of oxygen in the degradation process. [ABSTRACT FROM AUTHOR]

The deformation of bone when subjected to loads is not instantaneous but varies with time. To investigate this time-dependent behaviour sixteen bovine trabecular bone specimens were subjected to compressive loading, creep, unloading and recovery at multiple load levels corresponding to apparent strains of 2000-25,000 με. We found that: the time-dependent response of trabecular bone comprises of both recoverable and irrecoverable strains; the strain response is nonlinearly related to applied load levels; and the response is linked to bone volume fraction. Although majority of strain is recovered after the load-creep-unload-recovery cycle some residual strain always exists. The analysis of results indicates that trabecular bone becomes stiffer initially and then experiences stiffness degradation with the increasing load levels. Steady state creep rate was found to be dependent on applied stress level and bone volume fraction with a power law relationship. [ABSTRACT FROM AUTHOR]

In this letter, both the viscoelastic and electrical properties of poly(methyl methacrylate)/carbon black (PMMA/CB) nanocomposites with different CB concentrations prior to and after annealing were investigated. The linear steady-state recoverable compliance of pure PMMA is independent of annealing as it reflects only polymer-polymer interactions. While the conductivity of PMMA/CB nanocomposites increases gradually with annealing, and the viscoelastic properties show different regions of response depending on the CB concentration. At CB contents below the percolation threshold the recoverable compliances increase after annealing, whereas the reverse trend is found at CB contents above the percolation threshold. This behavior is related to the interplay between network formation and particle-particle interactions. [ABSTRACT FROM AUTHOR]

Thermo-rheological behaviour of chestnut flour doughs supplemented with kappa/iota-hybrid carrageenan (HC) (up to 2.0%, flour basis (f.b.)) and sodium chloride (1.8%, f.b.) was determined at both target (C1) and final (C5) mixing peaks. For this purpose, small amplitude oscillatory shear (0.01 to 100 Hz), creep-recovery (loading of 50 Pa for 60 s, 30 °C), temperature sweeps (from 30 up to 180 °C) and heating/cooling cycles (between 30 and 60 °C) were conducted on a controlled stress rheometer. Previously, the thermal-mixing behaviour at proposed mixing temperature (50 °C) was conducted on Mixolab® apparatus. Results showed that the dough stability (from 2.2 to 5.8 min) in mixing stage and starch heat resistance to dough processing were significantly improved at proposed mixing temperature, even in the absence of HC. No statistical differences in rheological properties were observed for doughs evaluated in C1; however, those analysed in C5 were significantly modified in the presence of HC, mainly in terms of viscous behaviour (from 52.1 × 10 to 39.1 × 10 Pa s). Creep-recovery data sets, successfully fitted using Burgers model, revealed that the elasticity ( J / J from 73.3 to 87.6%) of doughs analysed in C5 improved with HC addition. Thermal tests showed that the starch transitions were significantly promoted and stabilized with HC addition. [ABSTRACT FROM AUTHOR]

There is still considerable debate in the literature about the respective roles of starch and gluten in both the linear and non-linear rheology of wheat flour dough. Hence, to elucidate the individual contributions of gluten and starch to the overall dough behaviour, the rheological properties of dough and mixtures of different gluten-starch ratios were studied systematically in shear and extension, by means of an adequate rheological toolbox consisting of linear small amplitude oscillatory shear tests and non-linear tests such as creep-recovery in shear and uniaxial extension. The starch component plays a pivotal role in linear dough rheology. With increasing starch content, the linearity limit observed in oscillatory shear tests decreases as a power-law function. Starch also clearly affects the extensional viscosity at small strains. Consequently, in the linear region differences between different gluten systems may become obscured by the presence of starch. As breadmaking qualities are known to be intrinsically linked to the gluten network, it is imperative to probe the non-linear behaviour of dough in order to expose differences in flour quality. The quality differences between a strong and a weak flour type were revealed most clearly in the value of the strain-hardening index in uniaxial extension and the total recovery compliance in non-linear creep-recovery tests. Notwithstanding its earlier successful application to pure gluten gels, the accuracy of the critical gel model in predicting the linear rheological properties of dough was found to be limited, due to dough having a small linearity limit and a finite longest relaxation time. [ABSTRACT FROM AUTHOR]

Electrokinetic properties of Polythiophene- graft -Chitosan (PT- g -CS) copolymer were investigated by means of zeta (ζ)-potential measurements as a function of pH, electrolytes, surfactants, and temperature in aqueous medium. The ζ-Potential of pure PT was observed to enhance from +25 mV to +36 mV after grating with polycationic CS. Concomitantly, the isoelectric point of the pure PT shifted from 6.4 to 8.3. The ζ-Potential of PT- g -CS dispersion also shifted to more positive regions with increasing valency of the electrolytes and concentrations of cationic surfactant (cetyltrimethylammonium bromide). The ζ-Potential of PT- g -CS was determined to be +38 mV which indicated colloidal stability in silicone oil (SO) medium. Electrorheological (ER) and viscoelastic measurements revealed that the PT- g -CS/SO system has elasto-viscous behavior under applied electric field strengths. The yield stress of the ER fluid was determined to be a function of the electric field strength in a power law form as τ y = E 1.55 which obey to the conduction model. Creep and creep-recovery tests revealed reversible non-linear viscoelastic deformations of %31 < %40 < %43 under E = 1; 2 and 3 kV/mm conditions. [ABSTRACT FROM AUTHOR]

This study investigated the solution behaviors and sol–gel transition of myofibrillar protein (MP) from grass carp muscle by rheological methods. In steady shear measurements, shear-thinning behavior was observed in the MP solutions and became more apparent with increasing concentration ( c ), though Newtonian plateaus appeared at c ≤ 0.025 mg/mL. Based on the Cross model, zero shear viscosity ( η 0 ) and structural relaxation time ( K ) increased with increasing c , indicating the reinforcement of chain interaction and entanglement. From the dependence of η 0 on c , the MP showed the rod-like polymer features due to its α -helical tail, and the coil overlap concentration ( c* ) was estimated to be 4.5 mg/mL, at which the MP coils begin to overlap and interpenetrate undergoing the transition from a dilute to concentrated solution. In frequency sweep, the MP system was classified to two regions: an entanglement network or concentrated solution (5 and 10 mg/mL), and a weak gel (15 and 20 mg/mL). Furthermore, the sol–gel transition concentration ( c gel ) was further identified as 13 mg/mL by the Winter–Chambon criterion. According to the creep-recovery data fitted by the Burger model, the elastic coefficients ( G 1 and G 2 ) and viscous coefficients ( η 1 and η 2 ) increased with increasing temperature (5–40 °C), while the maximum deformation ( J MAX ) and residual deformation ( J ∞ ) decreased, leading to an increase in the final percentage recovery ( R %). This result indicated that the chain rigidity of MP increased with elevated temperature, the MP gel network formed and became stronger, confirming the denaturation, aggregation and pre-gelation of MP at ∼40 °C. [ABSTRACT FROM AUTHOR]

Two types of graphene nanoplatelets (GNP-M and GNP-C) were incorporated in PLA by melt-blending at 0.25 wt.% loading, and the resulting composites subject to hydrolytic degradation for 6 months in phosphate-buffered saline (PBS) at 37 °C. The materials were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), size exclusion chromatography (GPC-SEC), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), tensile testing, creep-recovery testing, and biocompatibility assays. After two months degradation, all materials presented a low decrease in molecular weight (about 10%), while after six months the decrease was higher than 85%. For this degradation time, temperatures of onset of intense thermal degradation decreased by about 10 °C for all samples. Both fillers were able to improve the mechanical properties of PLA, and to reduce the decay of its mechanical performance after 6 months biodegradation. Unfilled PLA showed a 10-fold decrease in toughness (AUC) after 6 months degradation, while toughness was only reduced by 3.3 and 1.7-fold, respectively, for the GNP-M and GNP-C composites. In addition, the composites had stable behaviour under cyclic creep-relaxation testing, while PLA exhibited significant cumulative permanent stain and ruptured after only 4 cycles. Comparing with PLA, the GNP-based composites presented similar human foreskin fibroblasts (HFF-1) adhesion and growth at the surface until 72 h, and did not release toxic products after the degradation period. [ABSTRACT FROM AUTHOR]

Epoxy-based shape memory polymers (SMEPs) are gaining importance in the area of aerospace structures due to their high strength and stiffness which is a primary requirement for an SMEP in structural applications. The understanding of viscoelastic behavior of SMEPs is very essential to assess their shape memory effect. In the present work, three types of SMEPs with varying cross-linking densities were developed by curing an aromatic epoxy resin with aliphatic amines. Glass transition temperature ( T ) was measured for these SMEPs using advanced rheometric expansion system, and from the T measurements, a range of temperatures from glassy to rubbery regimes were chosen. At selected temperatures, creep-recovery tests were performed in order to evaluate the viscoelastic behavior of SMEPs and also to investigate the effect of temperature on creep-recovery. Further, a three-parameter viscoelastic model (Zener) was used to fit the data obtained from experiments. Model parameters like moduli of the springs and viscosity of the dashpot were evaluated by curve fitting. Results revealed that Zener model was well suited to describe the viscoelastic behavior of SMEPs as a function of test temperatures. [ABSTRACT FROM AUTHOR]