Strain Sweep Tests Research Articles

Enchancment in viscoelastic properties of flake-shaped iron based magnetorheological fluid using ferrofluid

We have investigated the effect of ferrofluid incorporated (5–20% v/v) flake-shaped iron particles in silicion oil based magnetorheological fluid (MR fluid). The fluids physical properties like crystalline phase, shape size distribution and magnetization of both the fluids were studied individually. Thereafter, magnetic stimuli-response of ferrofluid doped MR fluid on rheological properties was determined in static and dynamic modes. The observed enhancement in yield stress due to addition of magnetic nanoparticles is correlated using universal yield stress scaling equation with magnetic field strength. Subsequently, cylindrical measurement technique is used to investigate fluid stability over time. Further, the relative viscosity (η/η∞) −vs- Mason number (Mn) shows scaling (Mn≤10−2), at higher magnetic field confirming negligible thermal and colloidal forces. The oscillatory strain sweep tests reveals a cross-over from viscoelastic-to-viscous behavior of suspension at critical strain value y=0.1. The increase in dynamic efficiency at is due to the reduction in sliding friction.

Modelling self-heating and thixotropy phenomena under the cyclic loading of asphalt

Asphalt concrete is a heterogeneous material containing a viscoelastic bituminous matrix and elastic aggregates. When testing asphalt materials under cyclic loading, various phenomena (so-called biasing effects) can decrease the modulus. This effect has been explained by an increase in the temperature of materials due to energy dissipation (self-heating), thixotropy and damage. The aim of this study is to analyse a uniaxial cyclic tension-compression test performed on bitumen and asphalt mixes, in modelling self-heating as one of the biasing effects. To quantify the self-heating and dissipated energy (as a heat source), a heterogeneous thermomechanical approach is introduced by separating the viscoelastic bituminous matrix from the elastic aggregates. According to this approach, various processes such as energy dissipation in the matrix due to viscoelastic properties, the thermal sensitivity of the matrix as well as its capacity to develop a heat source and diffuse heat through aggregates can all be studied. Local temperature variations are calculated by considering the heterogeneous dissipated energy field as a heat source. The complex modulus variation can then be calculated by taking into account both the temperature field and thermal sensitivity of the material. Simulation results show that as opposed to bitumen, in which 100% of complex modulus variations observed during a strain sweep test are due to self-heating, the results on asphalt mixes indicate that thixotropy varies with mechanical properties to a greater extent than self-heating. This fact is probably correlated with a higher strain level in thin bituminous matrix films, a higher load velocity in thin matrix films, material heterogeneity, and the 3D characteristic of matrix loading during the tension-compression test on asphalt mixes.

Obtaining the fatigue laws of bituminous mixtures from a strain sweep test: Effect of temperature and aging

Fatigue is associated with the deterioration caused by applying repeated loads, and is affected by temperature or aging. Generally, time sweep tests are used to simulate fatigue, in order to obtain the fatigue laws. However, this requires too much time, often preventing its use. A method to estimate the fatigue laws from a strain sweep test is presented. The test was performed on a semi-dense mixture with different types of binder (unconditioned or aged) tested at different temperatures. This test is able to estimate fatigue laws more quickly, allowing the effect of different factors on the mixtures' fatigue life to be studied.

Non-linear Rheological Properties of Soy Protein Isolate Dispersions and Acid-Induced Gels

Abstract This study presents the non-linear viscoelastic properties of soy protein isolate (SPI) dispersions and acid-induced gels to considerable detail. The storage (G′) and loss (G′′) moduli of SPI dispersions showed Type III (week strain overshoot) and Type IV (strong strain overshoot) networks when the strain amplitudes varied between 0.01 and 1.00 and 1.00 to 100.00, respectively. In the case of acid-induced SPI gels the rheological parameters showed the characteristics of Type I (strain thinning) network. Fourier transform rheological experiments showed that the higher harmonic curves obtained u strain sweep test showed quite different shapes for SPI dispersions and gels. In the case of dispersions, the highest I 3/1 (0.101) occurred at the strain amplitude of 0.40 and then decreased to below 0.02. In the case of acid-induced SPI gels, the I 3/1 value began to be appreciable at the strain amplitude of 0.1 increased rapidly to its highest value (I 3/1=0.05).

Evaluating fatigue performance of fine aggregate matrix of asphalt mix containing recycled asphalt shingles

The use of recycled asphalt shingles (RAS) has been increasing rapidly due to potential environmental and cost-saving benefits. RAS contains 20–30% aged asphalt binder that can replace a considerable portion of binder required in a mix. However, shingle binders are different than typical paving grade binders due to their advanced aging condition taking place during production and after years of service as roofing. This can influence mix properties upon interaction and blending with virgin binder. Asphalt mix fatigue performance is highly dominated by the properties of its fine aggregate matrix (FAM). The properties of FAM containing blends of RAS, virgin asphalt binders, from different sources and with different grades, and rejuvenating agent were evaluated in this study using the conventional time sweep test and a proposed strain sweep test. The tests were performed on small FAM cylindrical bars using a torsion bar fixture in a dynamic shear rheometer (DSR). Based on the results of the preliminary tests, it was observed that the strain sweep test and the time sweep test can similarly predict the fatigue life of the mix. The strain sweep has therefore been recommended due to its time-saving benefits. The fatigue performance of FAM mixes was found to be adversely affected by adding RAS. However, rejuvenating agent could improve the fatigue performance to some extent. The fatigue performance of FAM mixes evaluated was found to be the similar for mixes containing binders with similar grades, but from different sources.

Complexity of the behaviour of asphalt materials in cyclic testing

This paper compares the results obtained in two types of cyclic tension-compression tests, a time sweep test, constant strain amplitude, and a strain sweep test, increasing strain amplitude every 5000 cycles, called EBADE (standing for the Spanish words for strain sweep test). This comparison has shown that the rapid loss of stiffness during the initial part of cyclic testing is recoverable in bituminous materials. It has been found that reversible phenomena dominate in asphalt binders, while in mixtures are as important as damage. A damage equation has been proposed to describe the evolution of the material distress during the phase II in time sweep tests. In addition, a new methodology to estimate the fatigue law of bituminous mixtures is proposed.

Rheological Characterization of Alginate Based Hydrogels for Tissue Engineering

ABSTRACTHydrogels have been widely used in many applications from tissue engineering to drug delivery systems. For both tissue engineering and drug delivery, the mechanical properties are important because they would affect cell-materials interactions and injectability of drugs encapsulated in hydrogel carriers. Therefore, it is important to study the mechanical properties of these hydrogels, particularly at physiological temperature (37°C). This study adopted strain sweep and frequency sweep rotational rheological tests to investigate the rheological characteristics of various tissue engineering relevant hydrogels with different concentrations at 37°C. These hydrogels include alginate, RGD-alginate, and copolymerized collagen/alginate/fibrin. It has revealed that the addition of RGD has negligible effect on the elastic modulus and viscosity of alginate. Alginate gels have demonstrated shear thinning behavior which indicates that they are suitable candidates as carriers for cells or drug delivery. The addition of collagen and fibrin would reinforce the mechanical properties of alginate which makes it a strong scaffold material.

New methodology to estimate the fatigue behavior of bituminous mixtures using a strain sweep test

Fatigue cracking of bituminous mixtures is closely related to the loss of ductility produced by the stiffening of the bituminous binder. The main two factors that cause the asphalt binder to lose its ductility are aging and exposure to low temperatures. However, most of the tests designed to evaluate the fatigue behavior of bituminous mixtures are very time consuming, and make unpractical those studies that try to evaluate the influence of many variables. In this research project a strain sweep test was used to analyze the influence of aging, test temperature and bituminous binder type on the fatigue behavior of a continuously graded mixture. As expected, the mixture with SBS polymer modified binder retained more ductility at low temperatures, while the mixture with crumb rubber modified binder had the highest stiffness modulus. All mixtures exhibited the worst fatigue behavior at low temperatures and aging was equivalent to testing an unaged mixture at a lower temperature. The main result of this paper was the implementation of a new methodology to estimate the fatigue law of the material using a strain sweep test, which allowed this fatigue analysis to be carried out in nearly 10 times less testing time than that required by the procedure described in the EN 12697-24 standard.

Effects of salt ions on rheological properties of SPI-GG hybrid system

The rheological characteristic of soy protein isolate (SPI), is one of the most important properties in its application in food industry. The effects of different concentrations of guar gum (GG, polysaccharide) and sodium chloride (salt ion) on the rheological properties of SPI were studied in this research. Steady-state shear, strain sweep and frequency sweep tests (static and dynamic rheological tests) were performed, and the following phenomenon and conclusions were drawn: (1) The viscosity of the hybrid system increases with the GG addition. This trend could also be seen with the appropriate adding of salt ion; (2) As the applied frequency increases, the storage modulus G′ and the loss modulus G″ of the hybrid system increase at a similar rate. And the frequency sweep parameters of the hybrid system rise significantly with the increase of both GG and ionic concentration; The frequency dependence of the system varies significantly with the addition of salt ion; (3) With the concentration of the salt ion increase, the storage module G′ of the hybrid system decrease indicating that salt ion destroyed the network structure of hybrid dispersion to a certain extent. Keywords: guar gum, salt ions, soy protein isolate, rheological property, frequency dependence, food additive DOI: 10.25165/j.ijabe.20171005.3245 Citation: Bi C H, Zhang Y L, Wu M, Ni Z J, Li G, Liu Y, et al. Effects of salt ions on rheological properties of SPI-GG hybrid system. Int J Agric & Biol Eng, 2017; 10(5): 234–241.

Effect of filler nature and content on the bituminous mastic behaviour under cyclic loads

The role of the filler in asphalt mixtures is particularly important because of its influence on mastic behaviour. The filler improves the resistance properties of bitumen against the action of traffic loads and temperature. However, the filler can also adversely affect bitumen in mastics excessively brittle and stiff due to inappropriate design. For these reasons, it is interesting to investigate the effect of filler type and content on mastic composition. This paper presents results from a strain sweep test applied to bituminous mastics prepared with different filler types and contents at several temperatures. The obtained stiffness modulus and failure strain results provide information to assess the fatigue behaviour of the analysed mastics.

Effect of shade and thermo-mechanical viscosity stimulation methods on the rheological properties of nanohybrid resin composite

The aim of the present study is to measure the rheological properties of nanohybrid resin composite of three shades in pre-polymerized phase using different thermomechanical stimulations. Nanohybrid composite (Kerr Herculite XRV Ultra) in enamel, dentin, and incisal shades was included. Rheological measurements were made with a rotational rheometer in dynamic oscillation mode using three methods: (a) Strain Sweep test explored a range of deformation γ0 from 0.025 to 3% with a frequency ω = 1 Hz (temperature set at 25 and 65 °C), (b) Frequency Sweep test explored frequencies between 1 and 100 rad/s applying a deformation γ0 = 0.5% (temperature set at 25; 45; 65 °C), and (c) Ramp Temperature test explored a heating phase from 25 to 75 °C then a cooling phase back to 25 °C applying a γ0 = 0.5% and a ω = 10 rad/s. Data were analyzed using a three-way ANOVA and Tukey’s test (α = 0.05). Viscosity measurement (p < 0.05) and shade of the composites (p < 0.05) significantly affected the results. Viscosity turned out to be subordinate to strain amplitude, frequency, temperature, and axial force applied during each test. Enamel shade was the most viscous whereas dentin shade was 8% less viscous (p < 0.05). The incisal shade was significantly less viscous (70%) than enamel (p < 0.05). Pre-heating decreased viscosity of incisal shade (30%) above 50 °C but this value was 90 and 98%, respectively, for strain and frequency sweep test. Preheating had a side effect as in the cooling phase, viscosity increased from 66 to 450% exceeding the value recorded at the beginning of the test. Preheating was not effective to reduce viscosity, and may reveal some side effects. The composite tested might not be pre-heated above 45 °C.

Rheological and Physicochemical Modification of trans‐Free Blends of Palm Stearin and Soybean Oil by Chemical Interesterification

AbstractIn this study, binary blends of palm stearin and soybean oil were interesterified using sodium methoxide. The changes in free fatty acids (FFA), slip melting point (SMP), solid fat content (SFC), plastic range, induction period of oxidation at 120 °C (IP120) and rheological properties of fat blends, before and after interesterification, were investigated. All blends were trans‐free and contained high essential fatty acids content. Interesterification modified the melting properties of fat blends by reducing SMP and SFC. FFA increased and IP120 decreased after interesterification. Strain sweep, frequency sweep and temperature sweep tests were used to evaluate the rheology of fats. Briefly, the 10:90 and 30:70 (palm stearin : soybean oil) interesterified blends displayed increased storage (G′) and loss (G″) moduli, as compared with the initial blends. However, G′ and G″ moduli of interesterified 50:50 blend were lower than those of initial blends. The elastic character of interesterified 10:90, 30:70 and 50:50 blends was predominant up to 28.8, 37.9, and 41.8 °C, respectively. The interesterified blends of palm stearin and soybean oil showed desirable characteristics suited for production of trans‐free soft tub, stick and Baker's margarine, all‐purpose shortening and Iranian vanaspati.Practical ApplicationsIntake of high amounts of trans fatty acid (TFA) has been correlated with increased risk of heart diseases. In this context, chemical interesterification is an important technological option for production of trans‐free fats with different food applications. The results obtained here provide information about the scientific aspects of the effect of interesterification on rheological and physicochemical properties of palm stearin and soybean oil blends. Practically, this study can find its application in development of formulations for production of trans‐free fat products such as liquid, soft tub, stick and baker's margarine, all‐purpose shortenings and Iranian vanaspati.

Vegetable organogels incorporation in cream cheese products

Edible oleogels made from rice bran wax (RBW) or ethylcellulose (EC) organogelators in combination with vegetable oils and other non-fat ingredients were used to produce oleogel cream cheese products. Four oleogel cream cheese products, two containing RBW and two with EC, were prepared and compared to control samples including full-fat and fat-free commercial cream cheese samples. Upon compositional analysis, all the oleogel cream cheese (OCC) samples showed approximately a 25% reduction in total fat content in comparison to the full-fat commercial control. More specifically by the replacement of saturated fat with healthier unsaturated fat alternatives, an improved fatty acid profile of cream cheese products was documented. Similar compositional analysis was also performed on a cream cheese sample made with non-gelled vegetable oil. Using a single penetration test and a strain sweep test, oleogel cream cheese samples prepared with RBW displayed comparable hardness, spreadability, and stickiness values to the full-fat commercial control sample. EC OCC samples also showed comparable hardness, spreadability and stickiness values but exhibited reduced adhesiveness values compared to the full-fat control. The successful microstructural incorporation of oleogels into a cream cheese, along with similarities in fat globule size, between OCC samples and commercial controls was confirmed with Confocal Laser Scanning Microscopy. The similarity in microstructure can be accounted for the similarities in textural properties between the OCC samples and the full-fat control. These results provide a thorough characterization of the use of RBW and EC in oleogels and their potential as a healthy alternative to saturated fat in cream cheese applications.

Rheological behaviour of oil-filled polymer nanoparticles in aqueous dispersion

Hybrid organic nanoparticles of poly(styrene-co-maleimide) with 70 wt.-% incorporated palm oil (SMI/oil) were provided in aqueous dispersion for use in industrial coating processes. The rheological characteristics of dispersions with 65 wt.-% and 35 wt.-% solid content have been determined by creep, oscillatory and rotational testing under different shear stresses, shear rates, frequencies and temperatures. The effects of oil on viscoelastic properties have been demonstrated by comparative tests on a 35 wt.-% pure SMI nanoparticle dispersion. The creep and strain recovery data show viscoelastic responses only for 65 wt.-% SMI/oil dispersions at low stresses, as further detailed by the calculated Burger model parameters. The 65 wt.-% SMI/oil dispersion at higher stresses and 35 wt.-% SMI/oil dispersion over the full stress range become viscous. From strain sweep tests, the cross-over of G’ and G” demonstrates linear features at low strain and a transition into viscoelastic properties at high strain. The frequency sweep test indicates a linear solid-like behaviour with storage and loss modulus independent of frequencies at temperatures up to 70 °C. From rotational tests, the sensitivity of shear-viscosity properties to concentration and temperature has been demonstrated. The oscillatory and rotational data can be fitted by the Cox-Merz rule using dynamic viscosity and shear viscosity as a function of frequency or shear stress, while a yield point has been detected as a function of shear stress for both 65 and 35 wt.-% SMI/oil dispersions.

Preparation and Characterization of JP‐10 Gel Propellants with Tris‐Urea Low‐Molecular Mass Gelators

AbstractThe preparation and characterization of high‐energy density hydrocarbon fuel JP‐10 supramolecular gel propellants are reported. The low‐molecular mass gelator 1,1′,1′′‐((2,4,6‐trioxo‐1,3,5‐triazinane‐1,3,5‐triyl)tris(hexane‐6,1‐diyl))tris(3‐octadecylurea) (HDIT‐18) shows powerful gelation ability for JP‐10, the critical gelator concentration for JP‐10 is as low as 0.0638 wt‐%. The JP‐10 supramolecular gel propellants exhibit high thermal stability. Scanning electron microscopy (SEM) studies reveal that the gelator molecules self‐assemble into 1–3 μm fibers in JP‐10. Rheological studies show the JP‐10 supramolecular gels are thixotropic and shear‐thinning (for a shear rate range from 0.3 to 30 s−1), the dynamic strain sweep test shows that the critical strain percentage of the gel materials is 1 %. The studies reported herein provide a potential fuel material for gel propellants.

Analysis of the thixotropic behavior and the deterioration process of bitumen in fatigue tests

The characterization of fatigue damage on bituminous materials under cyclic loading has been classically studied using tests and procedures previously developed for the characterization of metallic materials. However, these materials present important differences in their behavior in cyclic testing. For instance, the significant loss of modulus the bitumen exhibits at early stages of the test or its total recovery when loading is removed.Comparison between two types of cyclic testing applied to bitumens, time and strain sweep tests has proven that this phenomenon is related with the nonlinear behavior of the bitumen, thixotropy and viscoelasticity, and that the amount of modulus loss during the initial part of cyclic testing is directly related to the strain applied.Using the framework of the work potential theory, a new expression has been found for the damage law that describes the loss of modulus of bitumens during the linear phase of the fatigue tests. Additionally, a procedure is proposed to estimate the fatigue relation between the strain applied and the number of cycles to failure using only the data obtained in strain sweep tests. These relations fit reasonably well the experimental data obtained in more time consuming time sweep tests.Applying this estimation procedure implies a great time savings in the characterization of the fatigue behavior of asphalt binders and the determination of their fatigue laws.

Effect of ageing and temperature on the fatigue behaviour of bitumens

Bitumen ageing plays a significant role in determining the resistance of asphalt mixes to fatigue cracking. Regardless of the type of ageing (oxidation during manufacture or during the service life), hardening effects increase the risk of cracking. The objective of this work is to examine the combined effect of the loss of volatiles and oxidation produced during ageing on the fatigue behaviour of the bitumen. To this end, different types of bitumen were subjected to accelerated ageing in the laboratory, simulating long-term ageing (RTFOT + PAV). They were then subjected to traditional tests (penetration, softening point, Fraass fragility point, dynamic viscosity, etc.), Dynamic Shear Rheometer tests (frequency and temperature sweep), and the EBADE test (a fatigue strain sweep test at different temperatures). Different temperatures have been used to evaluate the effect of visco-elastic phenomena on aged binder fatigue. The results showed that, in terms of their response to ageing, modified binders show a higher rate of variation in their general properties than conventional binders. In addition, it was shown that temperature plays an important role in the impact of ageing on the fatigue response of bituminous binders, and in the same way, in the mechanical response of these materials.

Matrix dependence of the linear viscoelastic region in magnetorheological elastomers

The aim of this work is to study the linear viscoelastic region limit of isotropic magnetorheological elastomers at different compositions and working conditions. Regarding the synthesis process, the matrix and the particle content are analysed. The analysed matrixes are a natural rubber, a silicone rubber and ELASTOSIL® silicone, and three particle contents are synthesised. The influence of the characterisation variables on the linear viscoelastic limit, that is, frequency, external magnetic field and temperature, is also analysed. Strain sweep tests are used to determine the dynamic complex modulus. The loss factor and the storage modulus are analysed to define the linear viscoelastic limit of each isotropic magnetorheological elastomer sample in all the working conditions. The results show that the linear viscoelastic region of the magnetorheological elastomers is defined by the loss factor. Moreover, the volumetric particle content reduces and frequency increases the linear viscoelastic region of all the matrixes, whereas the external magnetic field and the temperature influences are matrix dependent.

Viscoelastic shear properties of porcine temporomandibular joint disc.

To investigate the intrinsic viscoelastic shear properties in porcine TMJ discs. Twelve fresh porcine TMJ discs from young adult pigs (6-8months) were used. Cylindrical samples (5mm diameter) with uniform thickness (~1.2mm) were prepared from five regions of the TMJ disc. Torsional shear tests were performed under 10% compressive strain. Dynamic shear was applied in two methods: 1) a frequency sweep test over the frequency range of 0.1-10rad/s with a constant shear strain amplitude of 0.05rad and 2) a strain sweep test over the range of 0.005-0.15rad at a constant frequency of 10rad/s. Transient stress relaxation tests were also performed to determine the equilibrium shear properties. As the frequency increased in the frequency sweep test, the dynamic shear complex modulus increased, with values ranging from 7 to 17kPa. The phase angle, ranging from 11 to 15 degrees, displayed no pattern of regional variation as the frequency increased. The dynamic shear modulus decreased as the shear strain increased. The equilibrium shear modulus had values ranging from 2.6 to 4kPa. The posterior region had significantly higher values for dynamic shear modulus than those in the anterior region, while no significant regional difference was found for equilibrium shear modulus. Our results suggest that the intrinsic region-dependent viscoelastic shear characteristics of TMJ disc may play a crucial role in determining the local strain of the TMJ disc under mechanical loading.

Laboratory scale study on rheological behavior, morphological and structural properties of crosslinked polyacrylamide composite hydrogels embedded with date seed powder

ABSTRACTIncorporation of biofillers in polymeric hydrogels has continued to receive great attention in recent times because of their excellent properties. In this study, polyacrylamide (PAM) and polyethyleneimine (PEI) were used to develop novel composite hydrogels filled with date seed powder (DSP) via chemical crosslinking technique. Pristine PAM/PEI hydrogel and PAM/PEI‐DSP hydrogels at various DSP loadings were fabricated and subjected to gelation at 40°C for 24 h. The impact of various DSP loadings on the hydrogel samples developed was investigated using hybrid rheometer, SEM, XRD, and FTIR instruments, respectively. Rheological measurements confirmed the viscoelastic responses of the neat PAM/PEI hydrogel and the PAM/PEI‐DSP hydrogels reinforced with various DSP contents (0.8, 2.4, and 4 wt %). The dynamic strain, dynamic frequency and time sweep tests demonstrated that PAM/PEI‐DSP hydrogels were slightly more elastic than the virgin PAM/PEI hydrogel. The SEM characterization revealed the surface micrographs of the neat PAM/PEI hydrogel and the PAM/PEI‐DSP hydrogels at different DSP loadings to be smooth, homogeneous, and dense. Besides, the SEM micrographs supported the incorporation of DSP in the PAM/PEI‐DSP hydrogel samples. XRD analysis showed that the structures of neat PAM/PEI hydrogel and PAM/PEI‐DSP hydrogels filled with various DSP contents were predominantly amorphous while FTIR results confirmed the functional groups and evidence of crosslinking in the neat PAM/PEI hydrogel and the PAM/PEI‐DSP hydrogels embedded with different DSP contents. It is believed that these new hydrogels have huge development potentials and promising future in wastewater treatment and removal of heavy metal ions in aqueous solutions. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42110.