Search

For bonded Fibre Reinforced Polymer (FRP) strengthening systems in civil engineering projects, the adhesive joint performance is a key factor in the effectiveness of the strengthening; however, it is known that the material properties of structural epoxy adhesives change with temperature. This present paper examines the implied relationship between the curing regimes and the storage modulus response of the adhesive using a Machine Learning (ML) approach. A dataset containing 157 experimental data collected from the scientific papers and academic theses was used for training and testing an Artificial Neural Network (ANN) model. The sensitivity analysis reveals that the curing conditions have a significant effect on the glass transition temperatures (T g) of the adhesive, and consequently on the storage modulus response at elevated temperatures. Curing at an extremely high temperature for a long time does not, however, guarantee a better thermal performance. For the studied adhesive, curing in a warm (≥ 45°C) and dry (near 0 % RH) environment for 21 days is recommended for practical applications. A software with a Graphical User Interface (GUI) was established, which can predict the storage modulus response of the adhesive, plot the corresponding response curve, and estimate the optimum curing condition.

Engineered unfired clay bricks are an ecological alternative to overcome conventional construction materials’ inconvenience. This work investigates the rheological behavior of organo-silica suspensions, made from almond husk waste and illite clay, in relation to the compressive strength of unfired clay bricks incorporating the same waste. Selected proportions by weight of almond husk are 2, 5, 10, and 20 wt.%. Results from the compressive strength test show an improvement, of 8.98% in bricks with 2 wt.% waste content compared to the control sample, thanks to an increase in friction and the fiber bridging mechanism. Then, a progressively decrease in strength is recorded with the addition of waste. The decrease in strength is reported to be the creation of pores in the matrix, and loss of cohesion. It is found that the storage modulus, on a logarithmic scale, follows inversely the same trend of the compressive strength in previously prepared bricks. The results from the strength test and rheological test are linearly correlated. Strong coefficients of determination are found; R2=0.9809 (with 40 wt.% water content) and R2=0.9206 (with 50 wt.% water content). The findings from this study demonstrate the possibility of assessment and prediction of unfired bricks’ strength using rheometry.

The aim of this research was to define the compression strength of polylactic acid bolts produced using the fused deposition modelling method. In accomplishing this, static and cyclic compression tests for different metric thread sizes were carried out in accordance with ISO 4014. Tests were conducted on M42, M48, M56, M60, and M64 threads, while samples with three different types of pitch—one nominal and two fine threads—were prepared for each diameter. Standard ISO 604 for defining the compression modulus Ec was implemented as the test basis. Accordingly, the mean compression modulus value Ec for all measurements was 917.79 ± 184.99 MPa. Cyclic compression tests were then carried out on samples with the M64 × 4 thread. Fifty thread loading cycles were carried out for each variant to obtained different strain amplitude values and strain frequencies. Our work indicated that the values of the storage modulus defined in cyclic tests E′ increased, while the values of the loss modulus E″ decreased when the value of the strain frequency increased. We found it not possible to determine the nature of the changes in the value of the storage modulus E′ in the function of the strain amplitude. We did, however, observe an increase in the value of the loss modulus E″, together with the increase in the tested range of the strain amplitude. The determined mechanical values can be therefore be used for designing threaded connections made of polylactic acid using the fused deposition modelling method.

This paper focuses on the rheological properties of 3D printed magnesium potassium phosphate cements (MKPCs) with different magnesium-to-phosphate (M/P) mass ratio, MgO fineness and supplementary cementitious materials (SCMs) types. The variable shear rate tests were used to monitor the extrudability. The highest slope of the evolution of storage modulus (G') and the maximum static yield stress (Mτs) value were used as an indication of the rigidification rate. The increased M/P mass ratio, MgO fineness and SCMs addition resulted in the promoted structural build-up of 3D printed MKPCs. The consistency between the evolution of G' and Mτs with elapsed time were observed and the comparable time values of tg and tMτs were obtained. XRD results indicate the reversible agglomeration at the very early minutes can be ascribed to the solely physical flocculation changes other than the new hydration product.

This paper develops two equations for relaxation time and storage modulus of biopolymer nanocomposites at unlike frequency ranges. The relaxation time is correlated to zero complex viscosity, yield stress, K constant and power-law index. In addition, the blends and nanocomposites of biopolymers and carbon nanotubes (CNT) are fabricated and their complex viscosity and storage modulus are characterized. The experimental results of relaxation time for the organized specimens are linked to the calculations. Also, a model is suggested for storage modulus by yield stress, relaxation time, zero complex viscosity and power-law index. The significances of various parameters on the relaxation time and storage modulus are determined and vindicated to authorize the established equations. The model’s guesstimates acceptably follow the investigational results of relaxation time representing the predictability of the advanced model. Both yield stress and K directly manipulate the relaxation time. Moreover, a low zero complex viscosity and a big power-law index increase the relaxation time. The yield stress, relaxation time and zero complex viscosity directly govern the storage modulus, but the power-law index plays an adverse role.

From commercial pellets of recycled polyethylene terephthalate glycol (R-PETG), 1.75 mm diameter filaments for 3D printing were produced. By varying the filament’s deposition direction between 10° and 40° to the transversal axis, parallelepiped specimens were fabricated by additive manufacturing. When bent at room temperature (RT), both the filaments and the 3D-printed specimens recovered their shape during heating, either without any constraint or while lifting a load over a certain distance. In this way, free-recovery and work-generating shape memory effects (SMEs) were developed. The former could be repeated without any visible fatigue marks for as much as 20 heating (to 90 °C)-RT cooling–bending cycles, while the latter enabled the lifting of loads over 50 times heavier than the active specimens. Tensile static failure tests revealed the superiority of the specimens printed at larger angles over those printed at 10°, since the specimens printed at 40° had tensile failure stresses and strains over 35 MPa and 8.5%, respectively. Scanning electron microscopy (SEM) fractographs displayed the structure of the successively deposited layers and a shredding tendency enhanced by the increase in the deposition angle. Differential scanning calorimetry (DSC) analysis enabled the identification of the glass transition between 67.5 and 77.3 °C, which might explain the occurrence of SMEs in both the filament and 3D-printed specimens. Dynamic mechanical analysis (DMA) emphasized a local increase in storage modulus of 0.87–1.66 GPa that occurred during heating, which might explain the development of work-generating SME in both filament and 3D-printed specimens. These properties recommend 3D-printed parts made of R-PETG as active elements in low-price lightweight actuators operating between RT and 63 °C.

Polyethylene terephthalate (PET) is used worldwide for packing, and for this reason, it is the main material in plastic waste. The paper uses granules of recycled PET (R-PET) as raw material for producing filaments for 3D printing, subsequently used for printing the test specimens in different ways: longitudinally and at angles between 10° and 40° in this direction. Both the filaments and the printed specimens experience thermally driven shape memory effect (SME) since they have been able to recover their straight shape during heating, after being bent to a certain angle, at room temperature (RT). SME could be reproduced three times, in the case of printed specimens, and was investigated by cinematographic analysis. Then, differential scanning calorimetry (DSC) was used, in R-PET granules, filaments and 3D printed specimens, to emphasize the existence of glass transition, which represents the governing mechanism of SME occurrence in thermoplastic polymers, as well as a recrystallization reaction. Subsequently, the paper investigated the 3D printed specimens by dynamic mechanical analysis (DMA) using a dual cantilever specimen holder. Temperature (DMA-TS) and isothermal scans (DMA-Izo) were performed, with the aim to discuss the variations of storage modulus and loss modulus with temperature and time, respectively.

The effect of ultrasonic frequency mode (mono, dual and tri-frequency) and ultrasonic power (0–300 W) on structural properties (intrinsic fluorescence and sulfhydryl content) of whey protein was studied. Emulsions prepared with modified whey protein were used to form the heat-set gels, and the properties of whey protein emulsion gels (WPEG) and their digestion were investigated. The textural and rheological properties of WPEG prepared using whey protein pretreated by mono and dual-frequency ultrasound at the power between 180–240 W were enhanced, while those of WPEG prepared with whey protein pretreated by triple-frequency above the power of 180 W were declined. WPEG prepared using whey protein pretreated by dual-frequency ultrasound (DFU) with the power of 240 W had the highest hardness and storage modulus which were 3.07 and 1.41 times higher than the control. The microstructure of WPEG prepared using DFU pretreated whey protein showed homogeneous and denser networks than those of the control according to the results of confocal laser scanning microscope (CLSM). The modification in the microstructure and properties of the WPEG prepared using DFU pretreated whey protein delayed the protein disintegration during the first 30 min of gastric digestion when compared with control. Whereas the release rate of free amino group of the WPEG prepared using whey protein modified by ultrasonic pretreatment increased during the intestinal phase when compared with that of control. The results indicated that using dual-frequency ultrasound to modify whey protein is more efficient in improving the properties of WPEG, and ultrasonic power should be considered during the application of ultrasound pretreatment in producing protein gels. The fine network of WPEG prepared with whey protein pretreated by ultrasound resulted in better hardness and storage modulus. Partially unfolding of the protein induced by ultrasound pretreatment might make the whey protein more susceptible to the digestive enzyme. Our results could provide new insights for using ultrasound as the potential processing tool on designing specific protein emulsion gels as the delivery system for nutrients.

This article explores the potential of vibro-acoustics to detect physical ageing of plastic pipes. For this purpose, two different topics are combined: the ability of vibro-acoustics to estimate the storage modulus of a plastic pipe, and the sensitivity of the estimated storage modulus to changes due to ageing. Concerning the first topic, a vibro-acoustic method was applied to two water-filled HDPE pipes, one surrounded by air and another by sand. The excitation was achieved via an impact hammer and the propagating signal was recorded with the aid of hydrophones. Signal analysis led to the estimation of the axial wavenumber of the propagating axisymmetric fluid-borne wave. This value was used in the dispersion equation for the propagating mode to evaluate the storage modulus of the pipe material for a given experimental setup. Results revealed that the vibro-acoustic method gives consistent and reliable estimations of the storage modulus. Concerning the second topic, samples from two PVC pipes with an age difference of 41 years were subjected to dynamic mechanical analysis to study the behaviour of the storage modulus as a function of frequency. Results showed that it is feasible to distinguish discrepancies in the magnitude of the storage modulus due to ageing, provided that the measurement uncertainty is small. The uncertainty analysis highlighted the parameters that need to be more accurately known in order to lower the overall uncertainty of the estimated storage modulus when the proposed vibro-acoustic method is used. Irrespectively of the medium surrounding the pipe (air or soil), the distance between the points of the recording signals should be sufficiently long to measure the signal phase accurately. It was found that the accurate knowledge of the pipe's geometry, i.e. the wall thickness and internal radius, was more or equally important for controlling the overall uncertainty than that of the parameters of surrounding soil.

This experimental assessment was carried out to study the viscoelastic performance of crude oil-xanthan emulsions employing a RheoStress RS100 rheometer. Crude oil with a concentration range of 0–75% by volume was used to prepare the oil-gum emulsions. Two xanthan gums of Sigma and Kelzan were added in the emulsions with concentration ranges of 0–104 ppm. The linear viscoelastic ranges of all the tested oil-gum emulsions were found in the range of 0.1–10 Pa. Thus, the experimental tests were completed within the linear viscoelastic range of 1 Pa. The complex modulus increased gradually and steadily with frequency and gum concentration for all the examined emulsions. The addition of crude oil into the lighter xanthan concentration of

Physiological loading of knee cartilage is highly dynamic and may contribute to the progression of osteoarthritis. Thus, an understanding of cartilage's dynamic mechanical properties is crucial in cartilage research. In this study, vibrometry was used as a fast (2 h), noncontact and novel alternative to the slower (30 h), traditional mechanical and biochemical assays for characterization of cartilage from the condyle, patella, trochlear groove and meniscus. Finite-element models predicted tissue resonant frequencies and bending modes, which strongly correlated with experiments (R2= 0.93). Vibrometry-based viscoelastic properties significantly correlated with moduli from stress relaxation and creep tests, with correlation strengths reaching up to 0.78. Loss modulus also strongly correlated with glycosoaminoglycan (GAG) content. Dynamic properties measured by vibrometry significantly differed among various knee cartilages, ranging between 6.1 and 56.4 MPa. Interestingly, meniscus viscoelastic properties suggest that contrary to common belief, it may lack shock absorption abilities; instead, condylar hyaline cartilage may be a better shock absorber. These data demonstrate for the first time that vibrometry is a noncontact approach to dynamic mechanical characterization of hyaline and fibrocartilage cartilage with concrete relationships to standard quasi-static mechanical testing and biochemical composition. Thus, with a single tool, vibrometry greatly facilitates meeting multiple regulatory recommendations for mechanical characterization of cartilage replacements.

International audience; In this paper, the viscoelastic behavior of a polyethylenimine (PEI) crosslinked polymer gel prepared with a low hydrolysis/high molecular weight hydrolyzed polyacrylamide (PHPA), is investigated through dynamic shear measurements. The gel samples were cured at 80 °C while the rheological measurements were operated in a parallel-plate geometry at 25 °C. The effect of various parameters namely the reactants concentrations, the polymer’s molecular weight, the curing temperature, the presence of inorganic salts and the solution’s initial pH, on the storage (G’) and loss (G”) moduli were systematically investigated through frequency sweep tests. As a result, the final gel strength (G’ = 69.5 Pa) of a typical PHPA/PEI formulation was lower than those of the PAtBA/PEI and PAM/PEI systems reported in literature. Both storage (G’) and loss (G”) moduli varied proportionally and following exponential relationships with polymer concentration, crosslinker concentration, polymer’s molecular weight and temperature but unproportionally with the presence of inorganic salts (NaCl and CaCl2). On the other side, the effect of the gelant solution’s initial pH on the final gel strength was variable, with stronger gels formed around pH≈10, which was related to the asymmetrical effect of the pH on the two reactants (PHPA and PEI).

In the present study, the effects of magnesia particles on thermal, dynamic mechanical, morphological, and surface properties of polystyrene resin are investigated. In general, the addition of magnesia particles in polystyrene matrix increases the thermal stability, storage modulus, and wettability, on other hand does not affect the molecular mobility. SEM results showed a limited distribution of magnesia particles in the polystyrene matrix at 15 wt.%.

This study focuses on the variations in the brain tissue dynamic behaviour pointing out new insight into the material nonlinear viscoelasticity. Shear dynamic response curves are obtained in different working conditions in terms of strain sweep and superimposed static compression offsets (SCO) applied in orthogonal direction to the shear. The strain sweep mode is used to study the storage and loss moduli dependence on the amplitude of the applied strain. It is found that the material exhibits linear viscoelastic behaviour up to about 0.1% strain amplitude. Above this critical threshold, the storage modulus G' decreases rapidly with increasing dynamic strain amplitude and this effect is gradually intensified as the SCO are increased. In addition, it is observed that the loss factor (G''/G') increases by increasing the SCO applied to the specimens. The dynamic strain amplitude results of the storage modulus reveal that the elastic component of the brain tissue's stiffness (G') evaluated at low strain strongly increases with increasing static superimposed compression strain while the loss factor in the same strain range appears to be SCO independent. Finally, dynamic stiffness recovery after a large strain deformation is considered. The reduction in low amplitude dynamic modulus and subsequent recovery kinetics due to a perturbation is found to be independent of the level of the SCO. The same assessments were carried out on 5 consecutive strain sweep cycle loading. It has been noticed that at the last cycle, the dissipation peak is reduced, and the non-linearity of the curve begins earlier. This could be explained by the effects of cerebral edema on cells and their surrounding environment.

In this article, a magnetorheological shear thickening fluid (MRSTF) was fabricated based on magnetorheological (MR) material and shear thickening fluid (STF). The STF was firstly fabricated as the liquid phase, and carbonyl iron particles were then mixed with the prefabricated STF to synthesise a series of MRSTFs with various iron concentrations. Then, a rheometer was used to measure their viscosities by varying the shear rate under various magnetic fields. Both static and dynamic tests were conducted to study the rheology of MRSTFs under different magnetic fields. The tested results revealed that the MRSTF showed shear thickening under zero magnetic field and MR effect with increasing applied magnetic field. It was also noted that the viscosity of the MRSTFs can be controlled by both shear rate and the applied magnetic field. The concentration of iron particles played an important role in the MRSTFs’ rheological properties. The MRSTFs with higher iron particle concentrations revealed lower shear thickening effects but higher MR effects, which means the MRSTF with higher iron concentration can be treated as an effective MR fluid. Meanwhile, the MRSTF with low iron concentration displays good shear thickening effect under weak magnetic field. To summarise the behavior of MRSTFs with various iron concentrations and under different magnetic fields, three regions were proposed to provide guidelines to design MRSTFs and assist in their applications.

Collagen and elastin proteins are major components of the extracellular matrix of many organs. The presence of collagen and elastin networks, and their associated properties, in different tissues have led scientists to study collagen and elastin composites for use in tissue engineering. In this study, we characterized physical, biochemical, and optical properties of gels composed of collagen and elastin blends. We demonstrated that the addition of varying amounts of elastin to the constructs alters collagen fibrillogenesis, D-banding pattern length, and storage modulus. However, the addition of elastin does not affect collagen fibril diameter. We also evaluated the autofluorescence properties of the different collagen and elastin blends with fluorescence lifetime imaging (FLIm). Autofluorescence emission showed a red shift with the addition of elastin to the hydrogels. The fluorescence lifetime valuesof the gels increased with the addition of elastin and were strongly correlated with the storage moduli measurements. These results suggest that FLIm can be used to monitor the gels' mechanical properties nondestructively. These collagen and elastin constructs, along with the FLIm capabilities, can be used to develop and study collagen and elastin composites for tissue engineering and regenerative medicine.

Atomic force microscopy (AFM) is a widely use technique to acquire topographical, mechanical, or electromagnetic properties of surfaces, as well as to induce surface modifications at the micrometer and nanometer scale. Viscoelastic materials, examples of which include many polymers and biological materials, are an important class of systems, the mechanical response of which depends on the rate of application of the stresses imparted by the AFM tip. The mechanical response of these materials thus depends strongly on the frequency at which the characterization is performed, so much so that important aspects of behavior may be missed if one chooses an arbitrary characterization frequency regardless of the materials properties. In this paper we present a linear viscoelastic analysis of intermittent-contact, nearly resonant dynamic AFM characterization of such materials, considering the possibility of multiple characteristic times. We describe some of the intricacies observed in their mechanical response and alert the reader about situations where mischaracterization may occur as a result of probing the material at frequency ranges or with probes that preclude observation of its viscoelastic behavior. While we do not offer a solution to the formidable problem of inverting the frequency-dependent viscoelastic behavior of a material from dynamic AFM observables, we suggest that a partial solution is offered by recently developed quasi-static force–distance characterization techniques, which incorporate viscoelastic models with multiple characteristic times and can help inform dynamic AFM characterization.

This article provides comprehensive experimental data of two water-swelling materials, water swelling rubber (WSR) and water-swelling polyurethane (WSP). Swelling tests, Dynamic Mechanical Analyzer (DMA) and Scanning Electron Microscope (SEM) were performed. Sealing properties of WSR and WSP were characterized by the data of swelling ratios (Sw and Sa), storage moduli (E') and images of micro-damage morphologies. These data can be useful for the prediction of the long-term waterproof performance of water-swelling materials and provide reference for material selection. The data presented herein was used for the article, titled “Laboratory evaluation of long-term sealing behaviors of two water-swelling materials for shield tunnel gasket” [1] .

Heat treatment is commonly applied as a primary method for ensuring the microbial safety of poultry meat and to enhance its palatability. Although texture and color of cooked chicken breast meat are important quality parameters for the consumers that need to be controlled during thermal processing, studies assessing the temperature-time-dependent quality changes during thermal treatment are lacking. This work aims to investigate the texture and color changes of chicken breast meat during thermal processing and to develop kinetic models that describe these changes. We studied the storage modulus changes of chicken breast meat as function of temperature. The storage modulus increases from 55 °C until leveling off in an equilibrium value above 80 °C, which was attributed to microstructure changes and described with a sigmoidal function. The changes in the texture (TPA) and color (CIE L * a * b * ) of chicken breast meat were measured as function of temperature and time. The texture and color parameters show a rise with heating time until reaching an equilibrium value, while the rate of change increased with temperature. Kinetic models that take the non-zero equilibrium into account were developed to describe the color (lightness) and texture (hardness, gumminess, and chewiness) changes with heating time and temperature. The kinetic models provide a deeper insight into the mechanisms of texture and color changes during thermal treatment. They can be used to predict the texture and color development of chicken breast meat during thermal processing and, thus, help to optimize the process.

Polymers of intrinsic microporosity (PIMs) are currently attracting interest due to their unusual combination of high surface areas and capability to be processed into free-standing films. However, there has been little published work with regards to their physical and mechanical properties. In this paper, detailed characterisation of PIM-1 was performed by considering its chemical, gas adsorption and mechanical properties. The polymer was cast into films, and characterised in terms of their hydrogen adsorption at −196 °C up to much higher pressures (17 MPa) than previously reported (2 MPa), demonstrating the maximum excess adsorbed capacity of the material and its uptake behaviour in higher pressure regimes. The measured tensile strength of the polymer film was 31 MPa with a Young’s modulus of 1.26 GPa, whereas the average storage modulus exceeded 960 MPa. The failure strain of the material was 4.4%. It was found that the film is thermally stable at low temperatures, down to −150 °C, and decomposition of the material occurs at 350 °C. These results suggest that PIM-1 has sufficient elasticity to withstand the elastic deformations occurring within state-of-the-art high-pressure hydrogen storage tanks and sufficient thermal stability to be applied at the range of temperatures necessary for gas storage applications.

The influence of microstructure evolution on the dynamic mechanical properties, including storage modulus and internal friction, of the 2.5D SiCf/SiCm composites after high-temperature treatment (800 &deg, C and 1400 &deg, C) in the air was investigated by three-point bending vibration test. The effects of test frequency and amplitude on storage modulus and internal friction were also evaluated. The results show that as-prepared samples have maximum storage modulus and internal friction. However, the composites treated at 800 &deg, C in the air have the minimum storage modulus due to a large number of defects produced within the composite structure, and the composites treated at 1400 &deg, C have the minimum internal friction due to the formation of &alpha, cristobalite in the interface between the matrix and fibers, resulting in stronger interface bonding. With regard to test conditions, the storage modulus is sensitive to amplitude but not frequency, however, the internal friction is sensitive to both frequency because of anelasticity and amplitude due to the static hysteresis.

With the advancement of composite technology, the selection of proper reinforcement in the matrix becomes vital, especially to enhance the damping capacity in metal matrix composites. The overall damping capacity of the composites greatly depends on the reinforcement used and is proportional to the individual damping capacities of the reinforcement. This paper is concerned with the measurement of damping behavior in elemental rice husk ash (RHA), fly ash (FA), silicon carbide (SiC) and graphite (Gr) powders. The damping measurements were carried on dynamic mechanical analyzer (DMA) at different frequencies of 0.1, 1 and 10 Hz over a continuous heating temperature from room temperature to 150 °C. The storage modulus and damping capacity were analyzed. The related mechanisms were discussed and presented.

Understanding and controlling the morphology of thermoplastic polyurethane (TPU) is crucial, as it is closely linked with its thermal and mechanical properties. The morphology of a TPU with a high hard segment content was investigated. When hard segment crystallisation was avoided by fast cooling, a crystallisation-induced phase separation occurred upon reheating. At higher temperatures, a second polymorph was additionally created. Cooling slowly from the melt directly induced the formation of both polymorphic forms. The complex thermal behaviour could hence be explained by the (cold) crystallization and melting of two polymorphs. The disordered two-phase nanomorphology, revealed by AFM at room temperature after cooling slowly, was validated for both fast and slowly cooled samples at higher temperatures by fitting model SAXS patterns to time resolved synchrotron SAXS data. Annealing fast cooled samples at high temperature induced some ordered, lamellar stacks in addition. Finally, the morphology was linked to the evolution of storage modulus with increasing temperature. publisher: Elsevier articletitle: Linking the morphology of a high hard segment content polyurethane to its thermal behaviour and mechanical properties journaltitle: Polymer articlelink: http://dx.doi.org/10.1016/j.polymer.2015.11.007 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved. ispartof: Polymer vol:81 pages:1-11 status: published

Complexity in the behaviour of an asphalt binder is further escalated with geopolymer (fly ash and alkali liquid) modification, thus making it difficult to accurately predict the performance of the binder. This study employs artificial neural network modelling to predict the complex shear modulus, storage modulus, loss modulus and phase angle outcomes of experimental results from dynamic shear rheometer (DSR) oscillation tests under four separate scenarios. The proposed artificial neural network models received test conditions (temperature and frequency) and three different geopolymer concentrations (3%, 5% and 7% by the weight of bitumen) as the predictor parameters. The variants of the optimal algorithms were Levenberg-Marquardt (LM), Scaled conjugate gradient and Polak-Ribiere conjugate gradient (CPG) training algorithms with different combinations of network structures and tan-sig and log-sig as activation functions. The coefficient of determination, covariance and root mean square error (RMSE) were used as statistical measures of model prediction performance. Based on the statistical performance indicators, the LM algorithm with a 3-5-1 network architecture and tan-sig as the activation function was the best performing model for predicting the complex modulus with R2 values of 0.996 for the training dataset and 0.971 for the testing dataset and RMSE values of 0.118 and 0.139 for the training and testing datasets, respectively. Furthermore, it was observed that the least efficient model was the phase angle prediction model developed with the CPG training algorithm, which had a 3-8-1 network architecture and log-sig as the activation function. The model yielded R2 values of 0.909 and 0.829 for the training and testing datasets, respectively. Poor prediction performance for the testing dataset indicated that the model was unable to learn complexity in the data and would perform below a significance level of 0.90 in predicting using untrained data.

Magnetorheological elastomers are an important area of study in non-classical engineering materials. These are smart materials, in which some of the physical properties are dependent on the applied magnetic field. This unique property allows to suggest new, innovative practical applications. It is therefore relevant to carry out studies in the possible application of magnetorheological elastomers in machine construction. The present article presents the results of study regarding the properties of the discussed materials subject to compressive stresses. Particular attention is given to the observed growth of surface area of mechanical hysteresis loops, which is evidence of the possibility to change the damping properties of magnetorheological elastomers. This property can be utilized in the construction of different types of machines and devices. These mostly applies to energy absorbers such as active vibration absorbers.

The dynamic viscoelasticity of full-size wood composite panels (WCPs) under the free-free vibrational state were determined by a vibration testing method. Vibration detection tests were performed on 194 pieces of three types of full-size WCPs (particleboard, medium density fiberboard, and plywood (PW)). The dynamic viscoelasticity from smaller specimens cut from the panels was measured using a cantilever beam vibration test apparatus, and the two data sets were compared. A strong linear relationship was discovered between the dynamic viscoelasticity values measured by the vibration detection test and the cantilever beam vibration test. The storage modulus values of the panels were far higher than their loss modulus values, and PW panels had the smallest value of loss modulus. For the panels tested, density had a good linear impact on storage modulus. In comparison with density, logarithmic decrement had a greater linear impact on loss modulus. This study demonstrated that the vibration test method is a valid approach for determining the dynamic viscoelasticity of full-size WCPs.

Wheat flour dough was mixed in a spiral mixer for different operating conditions, at a speed ranging from 80 to 320 rpm, for a period of 7-15 min. The specific mechanical energy E, delivered and the dough temperature T-d were continuously recorded and varied from 7 to 82 kJ/kg and T-d of 13.5 to 36 degrees C, respectively. E-s and T-d were strongly correlated because of viscous dissipation but variations of ingredients initial temperature allowed to uncouple them. The energy balance during mixing process was set through a simple model assuming constant heat transfer (h = 75 W/(m(2) degrees C)) which took into account thermal losses. Shear viscosity curves of the dough were determined by correlating volumic power to angular speed; by comparison to typical dough shear flow curve, a constant characteristic of the mixer geometry (K-s = 1.55) was determined like for models of mixer power consumption. The impact of mixing on small deformation rheological properties was assessed by DMA and the variations of the ratio, of maximum (75 degrees C) to minimum (50 degrees C) elastic modulus, was interpreted in relation with gluten network development. (C) 2011 Elsevier Ltd. All rights reserved.

The polymer-modified cementitious materials are widely used as functional building materials since the expanding of the application of polymer in construction industry. The dynamic mechanical properties of EVA polymer-modified cement pastes at early age were investigated by dynamic mechanical analysis at 0.49Hz-100 Hz (loading frequency). Experimental results show that the dynamic flexural properties, as expressed by the storage modulus and loss tangent, ascended linearly with a logarithmic frequency. The storage modulus increased with the increase of the hydration time. On the contrary, the loss tangent of 3% and 5%P/C decreased according to increase of the hydration time at 7dyas.

Fading memory is a distinguishing characteristic of viscoelastic solids. Its assessment is often achieved by measuring the stress due to harmonic strain histories at different frequencies: from the experimental point of view, the storage and loss moduli are, hence, introduced. On the other side, the mathematical modeling of viscoelastic materials is usually based on the consideration of a kernel function whose decay rate is sufficiently fast. For several different solid materials, we have collated experimental evidence showing an high sensitivity to frequency variations of both the storage and loss moduli. By contrast, we prove that the commonly employed viscoelastic kernels (Prony series, continuous kernel, etc.) cannot reproduce this experimental behavior, as the resulting frequency sensitivity of the storage modulus is always zero when assessed at low frequency. This leads to identification problems of the material parameters which are strongly ill conditioned. However, we identify the specific kernel property which is responsible for this misbehavior: the long-term material memory must not decrease too fast. Some viscoelastic kernels, showing the correct memory’s rate of decay, are introduced and their improved ability to match the experimental data analyzed.

Drilling in high-pressure high-temperature (HPHT) conditions is a challenging task. The drilling fluid should be designed to provide high density and stable rheological properties. Barite is the most common weighting material used to adjust the required fluid density. Barite settling, or sag, is a common issue in drilling HPHT wells. Barite sagging may cause many problems such as density variations, well-control problems, stuck pipe, downhole drilling fluid losses, or induced wellbore instability. This study assesses the effect of using a new copolymer (based on styrene and acrylic monomers) on the rheological properties and the stability of an invert emulsion drilling fluid, which can be used to drill HPHT wells. The main goal is to prevent the barite sagging issue, which is common in drilling HPHT wells. A sag test was performed under static (vertical and 45&deg, incline) and dynamic conditions in order to evaluate the copolymer&rsquo, s ability to enhance the suspension properties of the drilling fluid. In addition, the effect of this copolymer on the filtration properties was performed. The obtained results showed that adding the new copolymer with 1 lb/bbl concentration has no effect on the density and electrical stability. The sag issue was eliminated by adding 1 lb/bbl of the copolymer to the invert emulsion drilling fluid at a temperature &gt, 300 &deg, F under static and dynamic conditions. Adding the copolymer enhanced the storage modulus by 290% and the gel strength by 50%, which demonstrated the power of the new copolymer to prevent the settling of the barite particles at a higher temperature. The 1 lb/bbl copolymer&rsquo, s concentration reduced the filter cake thickness by 40% at 400 &deg, F, which indicates the prevention of barite settling at high temperature.

Dynamic Mechanical Analysis (DMA) is one of the most powerful tools to study the behavior of plastic and polymer composite materials and it is potentially very useful tool to simulate behavior of plastic optic fibers (POF) in real applications. Possibility of simultaneous measurements of some optical properties during DMA would significantly upgrade investigations of POF alone or embedded in some materials. In this work, single cantilever DMA of the POFs that was done simultaneously with measuring the transmitted optical signal intensity is described and discussed. In order to compare mechanical results of the same material for cylindrical and rectangular specimens, rectangular plates were prepared by melting POFs and the same kind of tests were performed. It is shown that changing the optical signal intensity corresponds to the changes of storage modulus of the POF during DMA, and the maximums in optical signals intensity indicate the beginning of glass transition processes in the POF material.

Purpose Magnetic resonance elastography (MRE) is a rapidly growing noninvasive imaging technique for measuring tissue mechanical properties in vivo. Previous studies have compared two‐dimensional MRE measurements with material properties from dynamic mechanical analysis (DMA) devices that were limited in frequency range. Advanced DMA technology now allows broad frequency range testing, and three‐dimensional (3D) MRE is increasingly common. The purpose of this study was to compare 3D MRE stiffness measurements with those of DMA over a wide range of frequencies and shear stiffnesses. Methods 3D MRE and DMA were performed on eight different polyvinyl chloride samples over 20–205 Hz with stiffness between 3 and 23 kPa. Driving frequencies were chosen to create 1.1, 2.2, 3.3, 4.4, 5.5, and 6.6 effective wavelengths across the diameter of the cylindrical phantoms. Wave images were analyzed using direct inversion and local frequency estimation algorithm with the curl operator and compared with DMA measurements at each corresponding frequency. Samples with sufficient spatial resolution and with an octahedral shear strain signal‐to‐noise ratio > 3 were compared. Results Consistency between the two techniques was measured with the intraclass correlation coefficient (ICC) and was excellent with an overall ICC of 0.99. Conclusions 3D MRE and DMA showed excellent consistency over a wide range of frequencies and stiffnesses. Magn Reson Med 77:1184–1192, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.

The aim of the study was to characterize four unique varieties of honey (saffron, apple, cherry and Plectranthus rugosus) from Kashmir valley of India on the basis of physico-chemical parameters (moisture content, pH, hydroxymethylfurfural, water activity, proline content, invertase and diastase activity) and carbohydrate profile. Also the effect of temperature (0, 5, 10, 20 and 30 °C) on rheological properties of all unique honey varieties was studied. All the physicochemical parameters studied were significantly different (P

Cement is a material that has been in use since the ancient times and is the most widely manufactured material in industry today. During the production of cement, limestone undergoes a process called calcination which releases CO2. In order to reduce the environmental impact and cost of cement production it has become standard practice to replace a portion of the cement mixture with ground limestone, but this causes a change in the rheological profile of the mixture. This change in rheology affects both the short and long term workability of the material. In this study, small amplitude oscillatory shear (SAOS) was used to characterize the rheology of cement mixtures with a water to cement ratio (w/c) of .42. The tested samples were unaltered cement, cement blended with coarse limestone (10.8 µm), and cement blended with fine limestone (1.3 µm). The evolution of G’ and G” was tracked during the early stages of cement setting. Results of the study show that the storage (G’) and loss (G”) moduli increase as the limestone particle size is made smaller than the cement particle size. Tests also show that cement pastes exhibit greater shrinkage with the finer particles.

The rheological behaviour of ethylene glycol-based nanofluids containing hexagonal scalenohedral-shaped α-Fe2O3 (hematite) nanoparticles at 303.15 K and particle weight concentrations up to 25% has been carried out using a cone-plate Physica MCR rheometer. The tests performed show that the studied nanofluids present non-Newtonian shear-thinning behaviour. In addition, the viscosity at a given shear rate is time dependent, i.e. the fluid is thixotropic. Finally, using strain sweep and frequency sweep tests, the storage modulus G', loss modulus G″ and damping factor were determined as a function of the frequency showing viscoelastic behaviour for all samples.

Objectives: Glass-ceramic veneered zirconia is used for the application as fixed partial dentures. The aim of this investigation was to evaluate whether the heat treatment during veneering, the application of glass-ceramic for veneering or long term storage has an influence on the storage modulus of zirconia. Methods: Zirconia bars (Cercon, DeguDent, G; 0.5x2x20 mm) were fabricated and treated according to veneering conditions. Besides heating regimes between 680°C and 1000°C (liner bake and annealing), sandblasting (Al2O3) or steam cleaning were used. The bars were investigated after 90 days storage in water and acid. For investigating the influence of veneering, the bars were veneered in press- or layer technique. Dynamic mechanical analysis (DMA) in a three-point-bending design was performed to determine the storage modulus between 25°C and 200°C at a frequency of 1.66 Hz. All specimens were loaded on top and bottom (treatment on pressure or tensile stress side). Scanning electron microscopy (SEM) was used for evaluating the superficial changes of the zirconia surface due to treatment. Statistical analysis was performed using Mann Whitney U-test (α=0.05). Results: Sintered zirconia provided a storage modulus E’ of 215 (203/219) GPa and tan δ of 0.04 at 110°C. A 10%-decrease of E’ was found up to 180°C. The superficial appearance changed due to heating regime. Sandblasting reduced E’ to 213 GPa, heating influenced E’ between 205 GPa (liner bake 1) and 222 GPa (dentin bake 1). Steam cleaning, annealing and storage changed E’ between 4 GPa and 22 GPa, depending on the side of loading. After veneering, strong E’-reduction was found down to 84 GPa and 125 GPa. Conclusions: Veneering of zirconia with glass-ceramic in contrast to heat treating during veneering procedure had a strong influence on the modulus. The application of the glass-ceramic caused a stronger decrease of the storage modulus.

Ethylene-co-(5,7-dimethylocta-1,6-diene) copolymers with various 5,7-dimethylocta-1,6-diene contents incorporate double bonds in the lateral chains that facilitate the development of crosslinkings in the resulting polymeric material after electron beam irradiation. As an effect of such irradiation, crystallization is delayed but crystallinity remains practically constant after melting and further cooling of irradiated specimens. Crystallinity, crystallite thickness and gel content are key parameters in the mechanical performance of these copolymers. Consequently, the controlled incorporation of non-conjugated dienes into the polyethylene structure appears as an alternative strategy for tuning the mechanical response in crosslinked polyolefins. Moreover, the resulting materials exhibit good thermal stability. © 2011 Society of Chemical Industry., The authors are grateful for the financial support of Ministerio de Ciencia e Innovación (project MAT2010-19883), Exchange Collaboration Program CSIC/FCT (projects 2005PT0033/Proc. 4-1-1 Espanha 2006/2007 and 2009PT0026/Proc. 441.00 CSIC) and Fundaçâo para a Ciência e a Tecnologia, Programa Operacional Ciência Tecnologia e Inovaçâo (POCTI) do Quadro Comunitário de Apoio III e comparticipado pelo Fundo Comunitário Europeu FEDER (project PDCT/CTM/66408/2006). The synchrotron work, performed at DESY, received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 226716.

Dynamic mechanical analysis (DMA) is one of the most powerful tools to study the behavior of plastic and polymer composite materials and it is a potentially very useful tool to simulate behavior of plastic optic fibers (POF) in real applications. The possibility of simultaneous measurements of some optical properties during DMA would significantly upgrade investigations of POF alone or embedded in some materials. In this work, single cantilever DMA of the POFs that was done simultaneously with measuring the transmitted optical signal intensity is described and discussed. In order to compare mechanical results of the same material for cylindrical and rectangular specimens, rectangular plates were prepared by melting POFs and the same kind of tests were performed. It is shown that changes of the optical signal intensity correspond to the changes of storage modulus of the POF during DMA, and the maximums in optical signals intensity indicate the beginning of glass transition processes in the POF material. Dinamičko-mehanička analiza (DMA) je jedna od najefikasnijih metoda za proučavanje ponašanja plastičnih i polimernih kompozitnih materijala i potencijalno može biti veoma korisna za simulaciju ponašanja plastičnih optičkih vlakana (POV) u realnim primenama. Mogućnost istovremenog merenja nekih optičkih svojstava za vreme DMA može značajno da unapredi proučavanje POV, samih ili ugrađenih u neki materijal. U ovom radu je opisano i diskutovano merenje mehaničkih svojstava POV pomoću 'single cantilever' DMA koje je izvršeno istovremeno sa merenjem intenziteta propuštene svetlosti kroz POV. Kako bi se uporedili rezultati DMA koji su dobijeni za pravougaone i cilindrične uzorke od istog materijala, ista vrsta ispitivanja vršena je i na pravougaonim pločicama dobijenim topljenjem POV. U radu je pokazano da promene intenziteta optičkih signala odgovaraju promenama modula sačuvane energije POV za vreme DMA, a da dobijene maksimalne vrednosti optičkih signala označavaju početak procesa prelaza u staklasto stanje u materijalu od koga je napravljeno optičko vlakno.

Rheology of UF concentrated milk coagulation, in relation to milk heat treatment, was researched by the dynamic measurements with the low amplitude oscillation method. Milk was heat treated using four different treatments: A – 72°C, 15 s; B – 77°C, 120 s; C – 85°C, 120 s; D – 100°C, 120 s. Using ultrafiltration, heat treated milk was concentrated to CF 1; CF 2; CF 5 and CF 6. High heat milk treatment completely inhibits coagulation process of samples with standard protein level. By the increase of protein concentration the negative effect of milk heat treatment is reduced and partly, compensated yielding in moderate increase of storage modulus. In the case of extreme heat treatment, casein concentration has light effect on coagulation process resulting in significant reduction of storage modules of samples with highest protein concentration. U radu je, pomoću dinamičkih merenja, metodom kontinuelnih oscilacija proučavan tok koagulacije mleka koncentrovanog ultrafiltracijom, u zavisnosti od stepena koncentrovanja mleka i režima njegove termičke obrade. Uticaj termičke obrade mleka obuhvatio je praćenje četiri režima termičke obrade mleka (A – 72°C, 15 s; B – 77°C, 120 s; C – 85°C, 120 s; i D – 100°C 120 s). Termički obrađeno mleko je koncentrovano ultrafiltracijom do CF 1 CF 2, CF 5 i CF 6. Praćenjem toka koagulacije pojedinih uzoraka ustanovljeno je da se povećanjem koncentracije kazeina može donekle kompenzovati delovanje umereno visokih temperatura, ali da se pri korišćenju ekstremno visokih temperatura termičke obrade ne mogu porastom koncentracije kazeina značajnije kompenzovati nepovoljni efekti delovanja visokih temperatura.

The aim of the present work was the study of mechani- cal properties of MWCNT/PU. Four types of coatings were compared. Two different concentrations of MWCNTs com- mercially functionalized with COOH group were prepared and studied. These composites showed improved mechanical properties compared to PU, and the modified nanotubes proved to be much better fillers than the unmodified MWCNTs due to stronger filler-to-matrix attachment. Be- cause the modified nanotubes seem to be much more conven- ient composite filler, the first experiments with nanotube modification have been carried out. Modification using induc- tively coupled discharge in argon and oxygen mixture was successful and the mechanical properties of the composite were increased at the same level as in case of the commer- cially COOH functionalized MWCNT fillers. V práci byly studovány mechanické vlastnosti vrstev MWCNT/PU a porovnávány čtyry různé typy jejich nanášení. Práce byla zaměřená zejména na studium vlivu funkcionalizace uhlíkových nanotrubek v plazmatu na mechanické vlastnosti výsledného kompozitu. Rovněž se zabývalo modelováním viskoelastických a viskoplastických vlastností kompozitů MWCNT/PU.

The effect of blend ratio and compatibilization on dynamic mechanical properties of PP/NBR blends was investigated at different temperatures. The storage modulus of the blend decreased with increase in rubber content and shows two T g's indicating the incompatibility of the system. Various composite models have been used to predict the experimental viscoelastic data. The Takayanagi model fit well with the experimental values. The addition of phenolic modified polypropylene (Ph-PP) and maleic modified polypropylene (MA-PP) improved the storage modulus of the blend at lower temperatures. The enhancement in storage modulus was correlated with the change in domain size of dispersed NBR particles. The effect of dynamic vulcanization using sulfur, peroxide, and mixed system on viscoelastic behavior was also studied. Among these peroxide system shows the highest modulus. ? 1997 John Wiley & Sons, Inc.