Complex Dynamic Modulus Research Articles

Retrogradation of Maize Starch after High Hydrostatic Pressure Gelation: Effect of Amylose Content and Depressurization Rate.

High hydrostatic pressure (HHP) has been employed to gelatinize or physically modify starch dispersions. In this study, waxy maize starch, normal maize starch, and two high amylose content starch were processed by a HHP of the order of 600 MPa, at 25°C for 15min. The effect of HHP processing on the crystallization of maize starches with various amylose content during storage at 4°C was investigated. Crystallization kinetics of HHP treated starch gels were investigated using rheology and FTIR. The effect of crystallization on the mechanical properties of starch gel network were evaluated in terms of dynamic complex modulus (G*). The crystallization induced increase of short-range helices structures were investigated using FTIR. The pressure releasing rate does not affect the starch retrogradation behaviour. The rate and extent of retrogradation depends on the amylose content of amylose starch. The least retrogradation was observed in HHP treated waxy maize starch. The rate of retrogradation is higher for HHP treated high amylose maize starch than that of normal maize starch. A linear relationship between the extent of retrogradation (phase distribution) measured by FTIR and G* is proposed.

Preparation and properties of luffa fiber- and kenaf fiber-filled poly(butylene succinate-co-lactate)/starch blend-based biocomposites

Biodegradable poly(butylene succinate-co-lactate) (PBSL)/starch blends that contain various amounts of starch were prepared. In addition, luffa fiber (LF) and kenaf fiber (KF) were incorporated, individually, into PBSL/starch (70/30) blend to achieve biocomposites. The LF and KF were treated with NaOH(aq) prior to their addition to the blend. The Young's modulus and flexural modulus of PBSL increased with the addition of starch and increased further after the formation of the biocomposites. The highest Young's modulus increment, which was found in the KF-added system, was up to a 2.2-fold increase compared with neat PBSL. The tensile/flexural/impact strength of PBSL declined after the formation of the blends. With the further addition of LF/KF, the said properties leveled off. The blends exhibited higher complex viscosity and dynamic storage modulus in the melt state than the neat PBSL, and the values further increased in the biocomposites. The crystallization temperature of PBSL slightly decreased in the blends. By contrast, the biocomposites showed an increment in PBSL crystallization temperature, from 73.0 °C (PBSL) to 75.3 °C (KF-added composite), thereby confirming the surface nucleation effect of LF/KF. The blends showed a higher degree of water absorption than PBSL. The formation of biocomposites led to an even higher degree of water absorption. The current approach of including LF/KF in the PBSL/starch blend to enhance the rigidity and biodegradability was advantageous in expanding the applications of PBSL.

Dynamic and static tensile mechanical properties of myocardial tissue.

Event Abstract Back to Event Dynamic and static tensile mechanical properties of myocardial tissue. Sherif Ramadan1, 2, 3, Hani Naguib1, 2, 3 and Narinder Paul3, 4 1 University of Toronto, Mechanical and Industrial Engineering, Canada 2 University of Toronto, Smart and Adaptive Polymers Lab, Canada 3 University of Toronto, Institute of Biomaterials and Biomedical Engineering, Canada 4 Toronto General Hospital, Joint Department of Medical Imaging, Canada Introduction: Heart disease is a significant cause of morbidity and mortality that affects 1.3 million Canadians annually[1]. Coronary artery disease (CAD) is a leading cause of heart disease and is due to progressive accumulation of arterial plaque resulting in occlusion of the arterial lumen and abnormal myocardial contractility[2]. Computed Tomography Coronary Angiography (CTCA) is used to exclude significant CAD in patients with low-intermediate pre-test probability[3],[4]. However, dynamic anthropomorphic CT phantom devices that realistically mimic normal and diseased cardiac tissues are required to test new imaging techniques and algorithms that target ultralow radiation dose and high resolution CTCA. This study aims to quantify the mechanical properties of myocardial tissue to allow for the fabrication of phantoms that mimic the behaviour of heart tissue under varying hemodynamic conditions. Materials and Methods: The elasticity of myocardial tissue was tested under static and dynamic conditions. Tensile testing was performed to obtain the Young’s modulus and a dynamic mechanical analyzer (DMA) induced a frequency sweep to determine the complex (dynamic) modulus. A frequency range of 0.5Hz to 3.5Hz was analyzed as these frequencies correspond to human heart rates of 30 to 210bpm. Multiple tissue samples were taken from each pig and lamb heart, these animal models were chosen as they are close human analogues and are commonly used as replacements for human tissue[5],[6].The heart tissue was tested while freshly sacrificed without any intervening freeze-thaw cycles to ensure the integrity of the muscle tissue. The tissue was placed in a balanced salt solution and tested at 37°C to simulate in vitro conditions[7]. Results and Discussion: Preliminary data (mean ± SD): The tensile and complex moduli were tested on 6 pig and lamb hearts; tensile modulus of lamb = 0.06 ±0.03 (n=15 samples) and for pig =0.04 ± 0.03 (n=11 samples); the complex modulus for lamb = 0.03Mpa at 0.5Hz to 0.06 Mpa at 3.5Hz ± 0.02 (n=15 samples) and for pig = 0.03Mpa at 0.5Hz to 0.06 Mpa at 3.5Hz ± .01 (n=15 samples) and both exhibited a linear trend. These values indicate that myocardial tissue behaves similarly to soft rubbers and stiffens under higher frequency loads. Moreover, for tensile testing there was no statistical difference between individual hearts or animals (P values of 0.235, 0.483, and 0.73 between the animals, pig hearts, and lamb hearts respectively). Conclusions: The static and dynamic moduli of myocardial tissue in pig and lamb hearts is between 0.02 and 0.1Mpa which is similar to soft, rubber-like materials. This quantitative data will inform selection and fabrication of customized biomaterials for construction of the myocardium in a dynamic anthropomorphic tissue realistic heart phantom.

Experimental characterisation of base asphalt binder used for shingles production under static and dynamic loading

Significant fluctuations in asphalt binder cost and limited budget for road construction, as well as growing needs for saving natural resources, have contributed to the increased use of recyclable materials in asphalt pavement industries. During the past decades, many transportation agencies in the USA have investigated the effect of adding different types of recycled asphalt shingle (RAS) on the asphalt mixtures performance, while limits were proposed on the maximum amount of RAS that can be recycled. However, not many studies in the USA and Europe have addressed the possibility of directly using base roofing shingles binders for preparing asphalt mixture despite this binder is relatively less expensive than conventional asphalt binders. In this paper, the mechanical performance of base asphalt binder used for roofing flux and shingle production was evaluated with two experimental test methods: bending beam rheometer creep test and dynamic shear rheometer complex modulus test. Based on experimental data, creep stiffness, m-value, thermal stress, critical cracking temperature and complex modulus were calculated and then compared graphically and statistically with the same parameters obtained from two conventional binders commonly used for asphalt pavements. The comparison between the three binders indicates that the shingle binder presents reasonable low and high temperature performance even though the base binder may have different consistency and performance grade compared to the conventional ones. The statistical analysis suggests that the base binder for shingle production can be successfully incorporated into asphalt mixture and that any current specification limiting the content of shingles binder in asphalt mixture should be more asphalt binder type and mix design specific.

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.

Development of new tissue conditioner using acetyl tributyl citrate and novel hyperbranched polyester to improve viscoelastic stability

ObjectiveThe objective was to develop a new tissue conditioner using acetyl tributyl citrate (ATBC), tributyl citrate (TBC), and a novel hyperbranched polyester (TAH) with long-term stable viscoelasticity. MethodsPlasticizers, i.e., ATBC, TBC, TAH (number-average molecular weight, 1306g/mol; weight-average molecular weight, 4245g/mol), butyl phthalyl butyl glycolate (BPBG), dibutyl phthalate (DBP), benzyl benzoate (BB), Shofu Tissue Conditioner II (Shofu), and GC Soft-Liner (GC), in nine combinations (ATBC+TAH, TBC+TAH, ATBC, TBC, BPBG, DBP, BB, Shofu, and GC), with gelation times between 120 and 180s were used; Shofu and GC were used for comparison. The dynamic viscoelasticity properties, i.e., shear storage modulus (G′), shear loss modulus (G″), loss tangent (tanδ), and complex dynamic shear modulus (G*) were determined at 37°C, using a rheometer, after immersion in water for 0, 1, 3, 7, 14, and 28 d. The surface hydrophobicity was examined using a static contact angle analyzer, and the biocompatibility was evaluated using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. Weight changes, solubility, and water absorption were measured using an analytical balance. ResultsTAH addition increased the viscoelastic stability; ATBC+TAH was the most stable among the tested groups. TAH decreased the contact angle and increased the water absorption, but decreased the ATBC solubility. The ATBC+TAH group biocompatibility was similar to those of the control group. SignificanceThe developed ATBC+TAH plasticizer has potential applications as a new tissue conditioner. Its clinical efficacy needs to be evaluated in clinical trials.

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.

Performance of reclaimed asphalt pavement mixtures under static and oscillatory loading

The use of recycled materials in asphalt pavement is common practice as it yields economic benefits and reduced exploitation of natural resources. Over recent decades, many agencies in the USA have investigated the effect of adding reclaimed asphalt pavement on the field performance of asphalt mixtures used for pavement applications. In this work, the effect of reclaimed asphalt pavement on the low-temperature properties of hot mix asphalt was investigated using two tests: bending beam rheometer mixture creep, which is based on static loading, and dynamic shear rheometer mixture complex modulus, which uses oscillatory loading. Based on the experimental data, creep stiffness, m-value, thermal stress, critical cracking temperature and complex modulus were calculated, and then statistically and graphically evaluated. The results revealed that, at low temperature, most of the mixtures prepared with reclaimed asphalt pavement had poorer performance than a mixture prepared from virgin materials. However, no significant differences in creep and complex modulus properties were observed beyond a specific reclaimed asphalt pavement content, which is in the range of 25–40% depending on the stiffness of the binder used.

Dynamic Modulus of Asphalt Mixtures

Mix properties that deviate appreciably from the design properties during the production and construction of asphalt mixtures can lead to premature pavement distress or even failure. The objective of this study was to quantify the differences in the dynamic modulus of specimens prepared during design, production, and construction of dense-graded asphalt pavements and their effects on pavement performance prediction. For the achievement of this objective, Superpave® mixtures were collected from Iowa, Florida, Virginia, Michigan, South Dakota, Louisiana, Minnesota, and Wisconsin during design [laboratory-mixed and laboratory-compacted (LL)], production [plant-produced and laboratory-compacted (PL)], and construction [plant-produced and field-compacted (PF) specimens]. The nominal maximum aggregate size was kept constant at 12.5 mm. An indirect tension dynamic complex modulus (IDT | E*|) was measured for the three specimen types (i.e., LL, PL, and PF). Results showed that laboratory-compacted and field-compacted specimens exhibited large and significant differences. This finding was attributed to differences in the compaction effort and procedure between the field and the laboratory. Results of the AASHTOWare Pavement ME Design showed that the use of dynamic moduli obtained from different specimen types would result in significant differences in pavement performance prediction. This research was part of NCHRP Project 9-48, Field Versus Laboratory Volumetrics and Mechanical Properties.

Rheology of multiphase polymer blends with and without reactive compatibiliser: evaluation of interfacial tension using theoretical predictions

The phase morphology and rheology of polyamide 12/polypropylene (PA12/PP) blends have been studied. Effects of blend ratio and reactive compatibilisation on the rheological properties of compatibilised and uncompatibilised blends were analysed. The viscosity ratio between the polymers was found to be sensitive to frequency. The complex viscosity and dynamic modulus increased with increase in the amount of compatibiliser, up to critical micelle concentration. The interfacial tension between the polymers was calculated from the storage modulus of the blends using Palierne and Choi-Schowalter models. It was found that the rheological properties of both compatibilised and uncompatibilised blends are intimately related to their phase morphology.

Comparison of conventional, polymer, and rubber asphalt mixtures using viscoelastic continuum damage model

In this study, a laboratory experimental programme was conducted to compare the material properties and fatigue performance characteristics for reference, polymer-modified and rubber-modified gap-graded mixtures. These mixtures were placed on E18 highway between the interchanges Järva Krog and Bergshamra in the Stockholm area of Sweden. The advanced material characterisation tests included dynamic (complex) modulus for stiffness evaluation and the uniaxial tension–compression for fatigue assessment. The data were used to compare the performance of the rubber-modified gap-graded mixture to the reference and polymer-modified gap mixtures using the viscoelastic continuum damage (VECD) approach. Different researchers have successfully applied the VECD model to describe the fatigue behaviour of asphalt concrete mixtures. The damage characteristic (C–S) curves were established for each of the three mixtures. The fatigue behaviour for the three mixtures was ranked based on the C–S curve results and the rubber-modified mixture showed the best fatigue damage resistance followed by the polymer-modified and reference mixtures. The VECD approach provides a more comprehensive analysis to evaluate fatigue resistance compared with the traditional fatigue evaluation using a number of cycles at a given stiffness reduction.

Loaded rubber-like materials subjected to small-amplitude vibrations

This paper proposes a constitutive law and a method for characterizing highly preloaded viscoelastic materials subjected to linear (small-amplitude) vibrations. A multiplicative non-separable variables law has been suggested to model the behavior that depends on both stretch and time/frequency. This approach allows splitting the intricate combined test performed simultaneously on both stretch and frequency, generally in a limited experimental domain up to 100 Hz, into two independent tests. Thus, on one hand, the dynamic complex modulus dependent on frequency alone is evaluated on the basis of vibration tests in a large experimental domain up to 100 kHz. On the other hand, energetic parameters are determined from a quasi-static hyperelastic tensile test. The complex modulus, dependent on both stretch and frequency, is then deduced from the results acquired from uncoupled investigations. This work shows that, in extension, the elastic modulus increases with increasing stretch, and the loss factor decreases with increasing stretch; while, in compression, around the material undeformed state, the modulus increases as the stretch increases till a certain value of compression stretch (upturn point depending on material characteristics), and then the modulus decreases as the stretch increases. Globally, preload rigidifies materials but reduces their damping property. These results closely match a well-known observation in solid mechanics.

Rheological Properties of High Grade Asphalt and its Mixture

Viscosity test, dynamic shear test, dynamic modulus test and creep test were conducted to investigate the rheological properties of high modulus asphalt and its mixture. Test results indicated that the viscosity of hard grade asphalt could be increased when compared with the ordinary asphalt, especially at high temperatures. The complex shear modulus and dynamic modulus of hard-grade asphalt binder and its mixture were increased, which implied that the stiffness of them was enhanced. Furthermore, the elastically portions for viscoelastic property of asphalt binders were increased, which resulted in the reduction of phase angle for hard grade asphalt binders and mixtures. The rutting parameter for hard-grade asphalt mixture was increased remarkably, which revealed that the resistance to permanent deformation could be significantly improved for hard grade asphalt mixture.

NATURAL RUBBER/CARBON BLACK NANOCOMPOSITES PREPARED BY ULTRASONICALLY AIDED EXTRUSION

ABSTRACTSignificant efforts have been made in rubber research to improve the dispersion of carbon black (CB) in rubbers to achieve better processibility and performance of tires and rubber products. In addressing these issues, the present study is an attempt to further improve the processibility and dispersion by means of application of ultrasonic waves. Natural rubber (NR)/CB nanocomposites at loadings from 15 to 60 phr were prepared by ultrasonically aided extrusion at ultrasonic amplitudes up to 7.5 μm. A die pressure significantly decreased with an increase of amplitude, especially at higher loadings, indicating an improvement in processibility. Ultrasonic power consumption was almost insensitive to loadings. The complex dynamic viscosity, storage, and loss moduli of compounds and vulcanizates at loadings of 15, 25, 35, and 60 phr were reduced by the ultrasonic treatment at an amplitude of 7.5 μm, indicating NR chain scission. Bound rubber in compounds decreased by the ultrasonic treatment. The maximum torque in curing curves, cross-link density, gel fraction, hardness, M100, M300, tensile strength, and abrasion resistance of vulcanizates at loadings of 15, 25, 35, and 60 phr decreased at an amplitude of 7.5 μm, due to the NR chain scission, whereas the elongation at break increased. Atomic force microscope (AFM) studies of vulcanizates showed a penetration of rubber chains into agglomerates at an amplitude of 7.5 μm, indicating an improvement of dispersion of CB. Based on AFM images, a dispersion index was introduced, showing that the ultrasonic treatment at an amplitude of 7.5 μm led to a better dispersion of CB in vulcanizates. Comparison of NR/CB compounds and vulcanizates with those of NR/carbon nanotube (CNT) of an earlier study was carried out. In general, the CB-containing NR showed significantly lower modulus and abrasion resistance but higher tensile strength and bound rubber than CNT-containing NR.

Heterogeneous Finite-Element Modeling of the Dynamic Complex Modulus Test of Asphalt Mixture Using X-ray Computed Tomography

Asphalt mixture is a heterogeneous, composite material consisting of aggregate, mastic, and air voids. Analysis of laboratory tests such as the dynamic complex modulus assumes that this material can be dealt with as a homogeneous material while overlooking the particulate nature of this composite. Because of the limitations of the elastic continuum theory, pavement engineers have recently paid considerable attention to the use of advanced modeling techniques for simulating the realistic behavior of asphalt mixtures. The objective of this study is to develop a three-dimensional (3D), heterogeneous model to describe the response of asphalt mixtures in the dynamic complex modulus test using an X-ray computed tomography image-based finite-element (FE)-modeling approach. Experimental testing results for two superpave mixtures, including one conventional hot-mix asphalt and one warm-mix asphalt, were used to validate and calibrate the developed FE models. Acceptable agreement between laboratory-measured and model-predicted dynamic modulus test results was achieved. Results of the developed FE models at different temperatures indicated that most of the deformations during the dynamic modulus test are derived from the mastic. In addition, the asphalt mastic had more influence than the aggregates on the results of the dynamic complex modulus test.

Determining the impact of degree of blending and quality of reclaimed asphalt pavement on predicted pavement performance using pavement ME design

Past studies indicated binder from reclaimed asphalt pavement (RAP) aggregates only partial degree of blending (DOB) within hot mix asphalt (HMA). Most state agencies assume full blending, which may lead to under asphalting. This study focuses on determining the impact of it on predicted performance using ME level I analysis of six 25% RAP mixes. Dynamic complex modulus (DCM) tests were conducted with full and “actual” blending, all greater than 85%, using varying conditions comparing rutting and fatigue performance. The results indicate high DOB RAP mixes with uniform gradations have negligible effect on predicted performance and would not compromise performance.

Study on Transforming Dynamic Modulus Master Curve into Static Relaxation Modulus Master Curve Basing on the Relaxation Time Spectrum of Asphalt Mixture

In order to transform dynamic complex modulus into static relaxation modulus, an advanced Shear Rheometer is used to get complex modulus master curve of asphalt mixture. Dynamic modulus master curve is transformed into static modulus master curve basing on the relaxation time spectrum. Results show it is feasible that the dynamic modulus master curve can be transformed into relaxation modulus master curve in wide frequency domain basing on the relaxation time spectrum.

Performance Evaluation of High Modulus Asphalt Mixture with Button Rock Asphalt

In this paper, Button rock asphalt particle was directly added into hot asphalt mixture (HMA) to produced high modulus asphalt mixture (HMAM). In order to evaluate the performance properties of HMAM with BRA, dynamic compressive complex modulus (E*) test, rutting test and moisture resistance test were used to investigate HMAM with BRA and HMA with SBS modifier. Test results indicate BRA can greatly improve dynamic E*and rutting resistance of HMA compared with SBS modified asphalt mixture. Moisture resistance ability of HMAM with BRA has the same level with SBS modified asphalt mixture. Therefore, BRA particle can be used to produce HMAM, which have more superior performance properties than SBS asphalt modifier.

An application of the Peano series expansion to predict sound propagation in materials with continuous pore stratification

This work reports on an application of the state vector (Stroh) formalism and Peano series expansion to solve the problem of sound propagation in a material with continuous pore stratification. An alternative Biot formulation is used to link the equivalent velocity in the oscillatory flow in the material pores with the acoustic pressure gradient. In this formulation, the complex dynamic density and bulk modulus are predicted using the equivalent fluid flow model developed by Horoshenkov and Swift [J. Acoust. Soc. Am. 110(5), 2371-2378 (2001)] under the rigid frame approximation. This model is validated against experimental data obtained for a 140 mm thick material specimen with continuous pore size stratification and relatively constant porosity. This material has been produced from polyurethane binder solution placed in a container with a vented top and sealed bottom to achieve a gradient in the reaction time which caused a pore size stratification to develop as a function of depth [Mahasaranon et al., J. Appl. Phys. 111, 084901 (2012)]. It is shown that the acoustical properties of this class of materials can be accurately predicted with the adopted theoretical model.

Rheology of silica-filled polystyrene: From microcomposites to nanocomposites

Rheology and viscoelastic behavior of polystyrene (PS)/silica microcomposites and nanocomposites were studied. The apparent viscosity, transient shear stress growth after startup shear flow and stress relaxation after cessation of flow at various shear rates, the complex dynamic viscosity, the storage and loss moduli at small and large strain amplitudes and various frequencies were performed. The effect of size, shape and volume concentration of silica was discussed. The maximum volume concentration, corresponding to the concentration at which the relative viscosity of mixtures goes to infinity, with respect to the hydrodynamic contribution of the particles and to polymer-filler interactions was obtained. The difference between the yield stress and residual stress is shown. The domain of equivalence between the apparent viscosity as a function of the shear rate in steady state flow and the complex dynamic viscosity as a function of the strain rate amplitude in highly nonlinear region of oscillatory flow was established. The viscoelastic behavior was interpreted based on the morphology of microcomposites and nanocomposites observed by SEM.