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1
Lakie, Martin, e Kenneth S. Campbell. "Muscle thixotropy—where are we now?" Journal of Applied Physiology 126, n. 6 (1 giugno 2019): 1790–99. http://dx.doi.org/10.1152/japplphysiol.00788.2018.
Testo completoAbstract (sommario):
Relaxed skeletal muscle has an inbuilt resistance to movement. In particular, the resistance manifests itself as a substantial stiffness for small movements. The stiffness is impermanent, because it forms only when the muscle is stationary for some time and is reduced upon active or passive movement. Because the resistance to movement increases with time at rest and is reduced by movement, this behavior has become known as muscle thixotropy. In this short review, we describe the phenomenon of thixotropy and illustrate its significance in postural control with particular emphasis on human standing. We show how thixotropy came to be unambiguously associated with muscle mechanics and we review present knowledge of the molecular basis of thixotropic behavior. Specifically, we examine how recent knowledge about titin, and about the control of cross-bridge cycling, has impacted on the role of non-cross-bridge mechanisms and cross-bridge mechanisms in explaining thixotropy. We describe how thixotropic changes in muscle stiffness that occur during transitions from posture to movement can be tracked by analyzing physiological tremor. Finally, because skeletal muscle contains sensory receptors, and because some of these receptors are themselves thixotropic, we outline some of the consequences of muscle thixotropy for proprioception.
2
De Schryver, Robin, e Geert De Schutter. "Insights in thixotropic concrete pumping by a Poiseuille flow extension". Applied Rheology 30, n. 1 (9 novembre 2020): 77–101. http://dx.doi.org/10.1515/arh-2020-0103.
Testo completoAbstract (sommario):
AbstractThixotropy is a reversible time-dependent phenomenon in fluids, in which an internal structure grows due to flocculation and breaks down under shear action. Numerous fluids are thixotropic, e.g. concretes and cementitious suspensions. Pumping of concrete is an important application. Since current approaches omit thixotropic effects, we aim to develop a simple theoretical model to evaluate or understand the significance of thixotropy on the concrete pumping behaviour. We therefore extended Poiseuille flow for thixotropic concretes and reformulated it in a dimensionless form to gain insights. After a validation, the results and significance are elaborated and concluded.Results showed that for increasing thixotropy and decreasing flow rates, the plug radius, wall shear rate and pumping pressure loss increase. Even though all thixotropy mechanisms may not be covered, a simple model is delivered to interpret or predict the effect of thixotropy on the pumping behaviour of cementitious suspensions. The dimensionless formulations via the Bingham number Bn and related discharge diagrams are sufficiently elegant for computational implementation and very insightful to distinguish a thixotropic flow regime. The model could be extended for more complicated thixotropies, irreversible time-dependent effects or even other pumping related phenomena.
3
Tang, Bin, Tianli Liu e Biaohe Zhou. "Duncan–Chang E-υ Model Considering the Thixotropy of Clay in the Zhanjiang Formation". Sustainability 14, n. 19 (27 settembre 2022): 12258. http://dx.doi.org/10.3390/su141912258.
Testo completoAbstract (sommario):
The clays of the Zhanjiang Formation in the coastal area of Beibu Gulf of China are thixotropic, and the existing constitutive relationship models relevant for clay are incapable of accurately simulating their stress–strain relationships. It is vital to study the changes of mechanical properties of Zhanjiang Formation clay that occur during thixotropy, and to establish a constitutive model considering thixotropy. The varying measures of its shear strength, cohesion, internal friction angle, and initial tangential modulus during thixotropy were investigated by means of triaxial consolidation and drainage tests. Furthermore, the quantitative relationships between the clay’s cohesion, internal friction angle, and initial tangential modulus of the clay and time were examined. This relationship was introduced into the Duncan–Chang model, and a Duncan–Chang model considering the thixotropy of clay was developed. The established model was used to make predictions to assume the validation of the experimental data, and numerical simulations were then carried out. All of the results from the model’s prediction, numerical simulation and experimental measurements were compared against each other in order to verify the reasonableness of the model we had utilized. The results positively demonstrated that: (1) the shear strength, cohesion, angle of internal friction, and initial tangent modulus of the clay gradually increases with longer curing times, and eventually it will stabilize; and (2) compared with the Duncan–Chang model not considering thixotropy, the established thixotropic model is better able to reflect the influence of clay thixotropy on the clay stress–strain relationship, as its mean relative error is smaller. The results of this study provide references for calculating strength and deformation of the clay thixotropy. Further, it also provides references for bearing load calculations of pile foundations in thixotropic clay strata when subjected to long-term loading conditions.
4
Shao, Peng, Yu Yang Liu, Li Fen Zhou e Yu Qi Wu. "Progress in Research on Explosion Induced Thixotropy of Concrete". Materials Science Forum 675-677 (febbraio 2011): 643–46. http://dx.doi.org/10.4028/www.scientific.net/msf.675-677.643.
Testo completoAbstract (sommario):
Thixotropy is an important property possessed by fresh concrete of changing from gel to liquid under shearing stress and returning to the original state when at rest. The thixotropic process is usually described to be an isothermal and static (or quasi-static) gel-sol-gel transformation. Now the thixotropy of concrete subjected to explosive loads became a new subject in research of synchronous explosive lining technology, which offers an advanced trechless method for underground space construction in soil. Because the detonation of explosives is a short-duration process accompanying with high temperature and high pressure, thixotropic behavior of concrete is no longer as same as that of in general meaning. This review summarizes the recent progress in research on explosion induced thixotropy of concrete, including the thixotropic behavior, thixoforming, influence of thixotropic process on microstructure, macrostructure and mechanical performances of concrete and steel fibre reinforced concrete. Additional, some arguments and suggestions for the future research are presented.
5
Gu, Ling Ya, Kai Yuan Luo, Bei Qing Huang e Yin Di Song. "Effects of Fillers on the Transfer Properties of UV Waterless Offset Ink". Applied Mechanics and Materials 262 (dicembre 2012): 510–13. http://dx.doi.org/10.4028/www.scientific.net/amm.262.510.
Testo completoAbstract (sommario):
In order to investigate the effects of fillers on the transfer properties of UV waterless offset ink, four ink samples compound with different fillers(SiO2 , CaCO3 and Talc) were prepared, the flow curve, thixotropy and ink transferred ratio were tested, and the effects of rheological properties on ink-transfer were discussed. The results show that: all of four ink samples show a typical shear thinning characteristics. Sample use SiO2 and CaCO3 as fillers has a higher viscosity, and with the increase of shearing rate, the viscosity decreased sharply. Sample use SiO2 and CaCO3 as fillers has the minimum thixotropic area, and the minimum thixotropy. Sample use SiO2 and Talc as fillers has the largest thixotropic area, and the largest thixotropy. Sample use SiO2 and CaCO3 as fillers has the highest ink transfer ratio.
6
Sen, Samya, e Randy H. Ewoldt. "Thixotropic spectra and Ashby-style charts for thixotropy". Journal of Rheology 66, n. 5 (settembre 2022): 1041–53. http://dx.doi.org/10.1122/8.0000446.
Testo completoAbstract (sommario):
There is no universal model for thixotropy, and comparing thixotropic effects between different fluids is a subtle yet challenging problem. We introduce a generalized (model-insensitive) framework for comparing thixotropic properties based on thixotropic spectra. A superposition of exponential stress modes distributed over thixotropic time scales is used to quantify buildup and breakdown times and mode strengths in response to step-change input. This mathematical framework is tested with several experimental step-shear rate data on colloidal suspensions. Low-dimensional metrics based on moments of the distribution reveal characteristic average thixotropic properties, which are visualized on Ashby-style diagrams. This method outlines a framework for describing thixotropy across a diverse range of microstructures, supporting scientific studies as well as material selection for engineering design applications.
7
Tang, Bin, Biaohe Zhou, Liang Xie, Jianfeng Yin, Shengnan Zhao e Zhibing Wang. "Strength Recovery Model of Clay during Thixotropy". Advances in Civil Engineering 2021 (2 febbraio 2021): 1–11. http://dx.doi.org/10.1155/2021/8825107.
Testo completoAbstract (sommario):
Thixotropy is a hot topic in the field of rheology of dispersed systems. Many researchers have proposed different models and hypotheses to explain the thixotropy of clay. In this paper, the strength recovery model of Zhanjiang Formation clay in the process of thixotropy is studied. Firstly, through unconfined compressive strength test, the influence of soil sensitivity, moisture content, and density on the strength growth of remolded soil was studied. The results show great influence of sensitivity, moisture content, and density on the thixotropic strength of the Zhanjiang Formation clay: the higher the sensitivity and the density, the stronger the thixotropy of soil; the higher the moisture content, the weaker the thixotropy of soil. Based on the test results, a strength recovery model of Zhanjiang Formation clay in the process of thixotropy was established. The model was verified by the validation test data and the data obtained from the existing literature. The results suggest that the model prediction is in good agreement with the verification test data and data from existing literature, which proves the confidence of the model in predicting the degree of strength recovery in the process of thixotropy of Zhanjiang Formation clay. The model provides basis for stability calculation of surrounding soil after construction disturbance of underground structures in this stratum.
8
Yang, Xu, Wen Chen, Rui Xiao e Leevan Ling. "A fractional model for time-variant non-Newtonian flow". Thermal Science 21, n. 1 Part A (2017): 61–68. http://dx.doi.org/10.2298/tsci160426245y.
Testo completoAbstract (sommario):
This work applies a fractional flow model to describe a time-variant behavior of non-Newtonian substances. Specifically, we model the physical mechanism underlying the thixotropic and anti-thixotropic phenomena of non-Newtonian flow. This study investigates the behaviors of cellulose suspensions and SMS pastes under constant shear rate. The results imply that the presented model with only two parameters is adequate to fit experimental data. Moreover, the parameter of fractional order is an appropriate index to characterize the state of given substances. Its value indicates the extent of thixotropy and anti-thixotropy with positive and negative order respectively.
9
Nicia, David, Nicholas Fobbe, Daniel Jansen e Dirk Lowke. "Rheology of low‐clinker suspensions: Multiscale comparison of the effect of PCE on thixotropy". ce/papers 6, n. 6 (dicembre 2023): 705–14. http://dx.doi.org/10.1002/cepa.2811.
Testo completoAbstract (sommario):
AbstractAddressing climate change requires reducing the carbon footprint of cement‐based building materials on a global scale. One promosing approach involves decreasing the clinker content by incorporating fine supplementary cementitious materials (SCM), which, however, can increase the stickiness of fresh concrete. Along with viscosity, thixotropic structural build‐up is a critical rheological parameter that impacts the stickiness of the SCM‐rich suspensions. Thus, it is essential to gain a precise understanding of how the molecular structure and mode of addition of polycarboxylate ethers (PCE) affect the thixotropic structural build‐up in low‐clinker suspensions. To address this issue, we investigate key parameters affecting thixotropy, specifically PCE adsorption and early hydration kinetics at the cement paste and mortar level, using a multiscale approach. In an application‐oriented concept, we maintain a constant yield stress by varying the PCE dosage to achieve constant workability. Our results demonstrate that higher thixotropy correlates with increased PCE charge density and direct addition in cement pastes and mortars. Moreover, it is indicated that increasing specific surface area and ettringite contents promote additional thixotropy‐enhancing mechanisms.
10
Ma, Xiaoyan, Yubo Wang, Junpeng Hou, Yanping Sheng, Wanpeng Zheng e Shujuan Wu. "Study on Thixotropic Properties of Asphalt Mastics Based on Energy Viewpoint". Coatings 13, n. 3 (20 marzo 2023): 650. http://dx.doi.org/10.3390/coatings13030650.
Testo completoAbstract (sommario):
An asphalt mastic has thixotropic characteristics that significantly influence its fatigue and healing performance. Therefore, understanding the thixotropy of an asphalt mastic is clearly of great importance. However, research in this area is still in the early stages. This study focuses on self-heating as one of the biasing performances of asphalt material by analyzing the viscosity, stress, and hysteresis loops the of asphalt mastics under cyclic shear loading. Twelve types of asphalt mastics fabricated with asphalt, as well as different types of mineral filler, were selected to examine thixotropy. In addition, the filler/asphalt ratio was examined via the hysteresis technique to analyze the hysteresis loop and the viscosity–shear rate. The thixotropic potential function was also studied from the energy viewpoint. The results show that asphalt mastics with different asphalt binders, mineral fillers, and filler volume fractions showed hysteresis loops for shear stress versus shear rate diagrams. With an increase in the loading times of the cyclic load, the area of the hysteresis loop gradually decreases, and the hysteresis area most likely features a relatively stable value. The thixotropy of the asphalt can be significantly reduced by adding filler, and different types of mineral filler can slightly influence the thixotropy. The viscosity decreases with an increase in the shear rate, and it gradually recovers with a decrease in the shear rate. The greater the filler/asphalt ratio, the greater the viscosity, and the faster the viscosity’s descent is with the prolongation of time. Due to the existence of a higher amount of filler content, the recovery of a viscosity crack is more difficult. For asphalt mastics with high filler/asphalt ratios, the thixotropic mechanism can be explained via particle agglomeration and the depolymerization theory. For asphalt mastics with low and medium filler/asphalt ratios, the thixotropic mechanism can be explained via the particle chain theory. The damage and recovery of the internal structure of an asphalt mastic can be characterized by the structural failure potential function and the structural recovery potential function, respectively.
11
Guo, Li Ping, Lei Wang e Yi Min Zhang. "Evaluation of Thixotropic Models of Waxy Crude". Advanced Materials Research 581-582 (ottobre 2012): 85–88. http://dx.doi.org/10.4028/www.scientific.net/amr.581-582.85.
Testo completoAbstract (sommario):
Thixotropy, which is an important rheological behavior of waxy crudes, is very important to the hydraulic characteristics and safety of the restart process of crude oil pipelines. Thixotropic behaviors of four waxy crudes were studied experimentally under three kinds of loading conditions, which were constant shear rate, stepwise increase of shear rate and cyclic change of shear rate, namely hysteresis loop. Eight thixotropic models were evaluated by least-square regressions based on experimental data. The average absolute deviation was taken as the measurement of fitness of a model. It is concluded that the model, which was established on the basis of Houska model and Cheng’s idea that wax crude oil contains both complete and partial reversibility structures, is the most suitable model to describe the thixotropy of wax crude oil
12
Lakevičs, Vitālijs, Valentīna Stepanova, Santa Niedra, Inga Dušenkova e Augusts Ruplis. "Thixotropic Properties of Latvian Illite Containing Clays". Environment. Technology. Resources. Proceedings of the International Scientific and Practical Conference 1 (6 agosto 2015): 133. http://dx.doi.org/10.17770/etr2013vol1.813.
Testo completoAbstract (sommario):
Thixotropic properties of Latvian Devonian and Quaternary clays were studied. Dynamic viscosity of the water clay suspensions were measured with a rotating viscometer. Influence of concentration, pH and modifiers on the thixotropic clay properties was analyzed. It was found that Latvian clays have thixotropic properties. Stability of clay suspensions is described with the thixotropy hysteresis loop. Increasing the speed of the viscometer rotation, dynamic viscosity of the clay suspension decreases. It was found that the solid phase concentration and mineralogical composition make an impact on the thixotropy of clays. Decreasing the solid phase concentration in the clay suspensions from 50% to 25%, dynamic viscosity decreases proportionally to the solid phase concentration. It was found that modifying clay suspensions with carboxymethyl cellulose (0,1g) increases concentration of structure forming. In the same time, modifying of clay suspensions with calcified soda (0,1g) decreases the structure forming concentration. Dependence of pH value from the solid phase concentration slightly decreases with the clay phase concentration increasing in the suspension.
13
Skadsem, Hans Joakim, Amare Leulseged e Eric Cayeux. "Measurement of Drilling Fluid Rheology and Modeling of Thixotropic Behavior". Applied Rheology 29, n. 1 (1 marzo 2019): 1–11. http://dx.doi.org/10.1515/arh-2019-0001.
Testo completoAbstract (sommario):
Abstract Drilling fluids perform a number of important functions during a drilling operation, including that of lifting drilled cuttings to the surface and balancing formation pressures. Drilling fluids are usually designed to be structured fluids exhibiting shear thinning and yield stress behavior, and most drilling fluids also exhibit thixotropy. Accurate modeling of drilling fluid rheology is necessary for predicting friction pressure losses in the wellbore while circulating, the pump pressure needed to resume circulation after a static period, and how the fluid rheology evolves with time while in static or near-static conditions. Although modeling the flow of thixotropic fluids in realistic geometries is still a formidable future challenge to be solved, considerable insights can still be gained by studying the viscometric flows of such fluids. We report a detailed rheological characterization of a water-based drilling fluid and an invert emulsion oilbased drilling fluid. The micro structure responsible for thixotropy is different in these fluids which results in different thixotropic responses. Measurements are primarily focused at transient responses to step changes in shear rate, but cover also steady state flow curves and stress overshoots during start-up of flow. We analyze the shear rate step change measurements using a structural kinetics thixotropy model.
14
Zhang, Shunxian, Chuanxi Luo, Zhiyong Huang e Jian Li. "Study on Thixotropy of Mastic Asphalt Binder and Asphalt Mastic". Buildings 13, n. 9 (19 settembre 2023): 2380. http://dx.doi.org/10.3390/buildings13092380.
Testo completoAbstract (sommario):
In order to analyze the thixotropy of mastic asphalt concrete during the mixing process, the factors affecting the thixotropy of mastic asphalt binder and asphalt mastic are studied, and the measures to shorten the mixing time of mastic asphalt mixture are given. The dynamic viscosity of mastic asphalt binder and asphalt mastic with time and shear rate is obtained via the step frequency method, and the thixotropic constitutive models of mastic asphalt binder and asphalt mastic are constructed by structural dynamics model, exponential equation, and extended exponential equation respectvely. The improved time thixotropy index is used to analyze the effects of asphalt type, asphalt–aggregate ratio, filler type, heating temperature, and shear rate, and the laws of various factors affecting the thixotropy of mastic asphalt binder and asphalt mastic are obtained. The research shows that the extended exponential model can better characterize the thixotropy of mastic asphalt binder and asphalt mastic under different shear rates. When the amount of lake asphalt or cement is increased, the viscosity of the system and the mixing time to reach a steady viscosity increases; that is, the mixing time needs to be increased. Increasing shear temperature does not change the time parameter to reach steady viscosity; that is, it cannot shorten mixing time. When the shear rate is increased, the time for the system to reach the steady viscosity will be shortened; that is, the time for mixing the mixture can be shortened.
15
Wang, Yilin, e Randy H. Ewoldt. "Thixotropy, antithixotropy, and viscoelasticity in hysteresis". Journal of Rheology 67, n. 6 (31 ottobre 2023): 1199–219. http://dx.doi.org/10.1122/8.0000620.
Testo completoAbstract (sommario):
Thixotropy, antithixotropy, and viscoelasticity are three types of time-dependent dynamics that involve fundamentally different underlying physical processes. Here, we show that the three dynamics exhibit different signatures in hysteresis by examining the fingerprints of the simplest thixotropic kinetic model, a new antithixotropic model that we introduce here, and the Giesekus model. We start by showing that a consistent protocol to generate hysteresis loops is a discrete shear-rate controlled ramp that begins and ends at high shear rates, rather than at low shear rates. Using this protocol, we identify two distinguishing features in the resulting stress versus shear rate loops. The first is the direction of the hysteresis loops: clockwise for thixotropy, but counterclockwise for viscoelasticity and antithixotropy. A second feature is achieved at high ramping rates where all responses lose hysteresis: the viscoelastic response shows a stress plateau at low shear rates due to lack of stress relaxation, whereas the thixotropic and antithixotropic responses are purely viscous with minimal shear thinning or thickening. We establish further evidence for these signatures by experimentally measuring the hysteresis of Laponite suspensions, carbon black suspensions, and poly(ethylene oxide) solutions, each representing a historically accepted example of each class of material behavior. The signatures measured in experiments are consistent with those predicted by the three models. This study reveals different fingerprints in hysteresis loops associated with thixotropy, antithixotropy, and viscoelasticity, which may be helpful in distinguishing the three time-dependent responses.
16
Cheng, D. C. H. "Thixotropy". International Journal of Cosmetic Science 9, n. 4 (agosto 1987): 151–91. http://dx.doi.org/10.1111/j.1467-2494.1987.tb00472.x.
Testo completo
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Mewis, Jan, e Norman J. Wagner. "Thixotropy". Advances in Colloid and Interface Science 147-148 (marzo 2009): 214–27. http://dx.doi.org/10.1016/j.cis.2008.09.005.
Testo completo
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Alexandrou, Andreas N., Georgios C. Florides e Georgios C. Georgiou. "Squeeze Flow of Semi-Solid Slurries". Solid State Phenomena 192-193 (ottobre 2012): 263–68. http://dx.doi.org/10.4028/www.scientific.net/ssp.192-193.263.
Testo completoAbstract (sommario):
A standard method used to determine material properties of semi-solid slurries is the squeeze flow experiment in which a fixed amount of material is squeezed under constant force or velocity. The relation between the force and the displacement provides information about the rheology of the slurry. The thixotropy and the time response of the sample however is rarely, if ever, taken into consideration. In this work we study how thixotropy affects the flow characteristics and consequently the predicted material properties. We show that depending on the method of compression and the thixotropic constants the flow can be significantly different. Therefore the predicted material constants can vary and hence cannot be unique.
19
Sun, Zhiwen, Gangqiang Kong, Yang Zhou, Yang Shen e Hanyu Xiao. "Thixotropy of a Transparent Clay Manufactured Using Carbopol to Simulate Marine Soil". Journal of Marine Science and Engineering 9, n. 7 (4 luglio 2021): 738. http://dx.doi.org/10.3390/jmse9070738.
Testo completoAbstract (sommario):
A transparent clay manufactured using Carbopol® UltrezTM 10 (simplified as U10) was introduced, and its manufacturing processes were briefly described. Both relative transparency (RT) and modulation transfer function (MTF) methods were used to quantify the optical character variation via soil thickness. The transparency of this new transparent clay was analyzed and compared with four traditional transparent materials. The thixotropic properties of this synthetic transparent clay were measured in detail through the laboratory vane test. An exponential function was used to describe the thixotropy and sensitivity of the clay. The results showed that the new transparent clay has a relatively higher optical transparency than the majority of previous materials. Good-fitting results showed a similar development trend in thixotropy for the synthetic transparent clay and the natural ones. Furthermore, the sensitivity of the transparent clay was low to medium, which can simulate marine soil. With higher optical transparency than and similar thixotropy and sensitivity as natural clays, Carbopol® UltrezTM 10 shows great potential as a substitute for natural clay and is expected to be widely used in model tests.
20
Poluektova, V. A., e N. A. Shapovalov. "Thixotropic polymercement concrete: modeling, research, application". Perspektivnye Materialy 2 (2022): 5–16. http://dx.doi.org/10.30791/1028-978x-2022-2-5-16.
Testo completoAbstract (sommario):
The article describes methods currently used to measure the thixotropic properties of concrete. It represents the theoretical substantiation of the thixotropy process from the point of view of colloidal chemistry with the usage of the potential energy curve of interaction between particles. The choice of the mathematical model for the approximation of experimental results has been justified. The works deals with the simplest and most adequate thixotropy model of polymercement concrete (PC-concrete) for construction printing and self-compacting cast concrete (SCC). The Russel’s model is consistent with the results of other researchers of cement concrete mixtures, which can be found in the literature, and with the proposed classification of concrete by the flocculation rate Athix. The rheological regularities for highly concentrated polymercement dispersions experimentally received on the laboratory rheometer “Reotest 2.1” are matched with the predictions of the thixotropic model. The author of the article describes the possibility of this model usage for layer-by-layer concrete application when using additive technologies. It is shown that non-thixotropic concrete can be used for cast self-compacting concrete elements (low flocculation rate), but construction printing requires only thixotropic or highly thixotropic concrete (high flocculation speed). Polymercement concrete P/C = 0.1 is demonstrated as the most adapted material for using in construction additive technologies. The achievement of the required properties is due to the increase in thixotropic properties with simultaneous increase in adhesion between layers.
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Spanjaards, Michelle, Gerrit Peters, Martien Hulsen e Patrick Anderson. "Numerical Study of the Effect of Thixotropy on Extrudate Swell". Polymers 13, n. 24 (14 dicembre 2021): 4383. http://dx.doi.org/10.3390/polym13244383.
Testo completoAbstract (sommario):
The extrusion of highly filled elastomers is widely used in the automotive industry. In this paper, we numerically study the effect of thixotropy on 2D planar extrudate swell for constant and fluctuating flow rates, as well as the effect of thixotropy on the swell behavior of a 3D rectangular extrudate for a constant flowrate. To this end, we used the Finite Element Method. The state of the network structure in the material is described using a kinetic equation for a structure parameter. Rate and stress-controlled models for this kinetic equation are compared. The effect of thixotropy on extrudate swell is studied by varying the damage and recovery parameters in these models. It was found that thixotropy in general decreases extrudate swell. The stress-controlled approach always predicts a larger swell ratio compared to the rate-controlled approach for the Weissenberg numbers studied in this work. When the damage parameter in the models is increased, a less viscous fluid layer appears near the die wall, which decreases the swell ratio to a value lower than the Newtonian swell ratio. Upon further increasing the damage parameter, the high viscosity core layer becomes very small, leading to an increase in the swell ratio compared to smaller damage parameters, approaching the Newtonian value. The existence of a low-viscosity outer layer and a high-viscosity core in the die have a pronounced effect on the swell ratio for thixotropic fluids.
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Zhou, Hao, Cai Chen, Feng Feng, Changsheng Zhou, Wenling Zhang e Wei-Tao Wu. "Study of Thixotropic Characteristics of a Kerosene Gel Propellant by Bayesian Optimization". Gels 9, n. 1 (26 dicembre 2022): 15. http://dx.doi.org/10.3390/gels9010015.
Testo completoAbstract (sommario):
The rheological behavior of gel propellants is crucial for their practical applications, especially in the rocket engine and ramjet fields. The thixotropic characteristics of gel propellants are an important component of their rheological properties and have a notable impact on their flow and injection process. However, most gel propellants contain rich, dynamic cross-linked network structures, which impart complex non-Newtonian fluid properties, and it is difficult to establish a unified mathematical model. In view of this, this study addresses the thixotropy of a prepared RP-3 kerosene gel and determines the mathematical model and model parameters describing its thixotropy. Experiments show that the kerosene gel exhibits shear-thinning properties as well as thixotropy. To describe the microstructural changes in the gel, three thixotropic constitutive models are introduced to analyze the rheological data, and the constitutive equation parameters are optimized. The three models are all structural dynamic models, which can be used to describe microstructural changes within the material. In addition, the fitting of the constitutive equation is a multiparameter optimization problem, and an appropriate optimization method must be used for parameter fitting. Therefore, the Bayesian optimization method combined with Gaussian process regression and the upper confidence bound (UCB) acquisition function is used in the multiparameter fitting of the constitutive models. Both experiments and numerical results show that the thixotropic model, which introduces a pre-factor with shear strain and assumes that the breakdown of the gel structure is related to energy dissipation rather than the shear rate, has a better fitting effect and prediction ability with regard to the gel. Combined with transient experiments at different shear rates, the model parameters of the constitutive law can be determined quickly by applying the Bayesian optimization method.
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Gibala, D., K. Laohapisitpanich, D. Thomas e G. R. Hamed. "Cure and Mechanical Behavior of Rubber Compounds Containing Ground Vulcanizates. Part II—Mooney Viscosity". Rubber Chemistry and Technology 69, n. 1 (1 marzo 1996): 115–19. http://dx.doi.org/10.5254/1.3538351.
Testo completoAbstract (sommario):
Abstract Mooney viscosities and thixotropic behavior have been determined for SBR melts containing carbon black and/or ground vulcanizate particles. A composition containing ambiently ground rubber has a higher viscosity than one with cryogenically ground rubber. This is attributed to occlusion of continuum rubber within the sponge-like, ambiently ground rubber; occlusion is not possible with the smooth, cryo-ground particles. Viscosity was independent of particle size. On an equal phr (weight) basis, the addition of N330 carbon black and cryo-ground rubber augment Mooney viscosity to a similar extent. While the Guth-Gold Equation is approximately applicable to black-filled melts, samples containing ground rubber are a much better fit by the simple Einstein Equation. Ground rubber addition has only a minor influence of thixotropy, in contrast to carbon black, which greatly increases thixotropy.
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Žitný, Rudolf, Aleš Landfeld, Jan Skočilas, Jaromír Štancl, Vlastimil Flegl e Milan Houška. "UNSTEADY FLOW OF THIXOTROPIC COLLAGEN SUBSTANCE IN PIPES". Acta Polytechnica 55, n. 5 (31 ottobre 2015): 352. http://dx.doi.org/10.14311/ap.2015.55.0352.
Testo completoAbstract (sommario):
Unsteady flow of thixotropic liquid in pipes is solved by 1D and 2D numerical methods using the same constitutive equation — the only difference is in the radial diffusion of the structural parameter. Comparison shows that the neglected diffusion of structural parameter implicates a much stronger effect of thixotropy. The models are applied for analysis of the observed hysteresis of hydraulic characteristic of collagen.
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Jamali, Safa, e Gareth H. McKinley. "The Mnemosyne number and the rheology of remembrance". Journal of Rheology 66, n. 5 (settembre 2022): 1027–39. http://dx.doi.org/10.1122/8.0000432.
Testo completoAbstract (sommario):
The concept of a Deborah number is widely used in the study of viscoelastic materials to represent the ratio of a material relaxation time to the time scale of observation and to demarcate transitions between predominantly viscous or elastic material responses. However, this construct does not help quantify the importance of long transients and nonmonotonic stress jumps that are often observed in more complex time-varying systems. Many of these nonintuitive effects are lumped collectively under the term thixotropy; however, no proper nouns are associated with the key phenomena observed in such materials. Thixotropy arises from the ability of a complex structured fluid to remember its prior deformation history, so it is natural to name the dimensionless group representing such behavior with respect to the ability to remember. In Greek mythology, Mnemosyne was the mother of the nine Muses and the goddess of memory. We, thus, propose the definition of a Mnemosyne number as the dimensionless product of the thixotropic time scale and the imposed rate of deformation. The Mnemosyne number is, thus, a measure of the flow strength compared to the thixotropic time scale. Since long transient responses are endemic to thixotropic materials, one also needs to consider the duration of flow. The relevant dimensionless measure of this duration can be represented in terms of a mutation number, which compares the time scale of experiment/observation to the thixotropic time scale. Collating the mutation number and the Mnemosyne number, we can construct a general two-dimensional map that helps understand thixotropic behavior. We quantify these ideas using several of the simplest canonical thixotropic models available in the literature.
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Bhattacharyya, Tulika, Alan R. Jacob, George Petekidis e Yogesh M. Joshi. "On the nature of flow curve and categorization of thixotropic yield stress materials". Journal of Rheology 67, n. 2 (marzo 2023): 461–77. http://dx.doi.org/10.1122/8.0000558.
Testo completoAbstract (sommario):
Thixotropy is a phenomenon related to time dependent change in viscosity in the presence or absence of flow. The yield stress, on the other hand, represents the minimum value of stress above which steady flow can be sustained. In addition, the yield stress of a material may also change as a function of time. Both these characteristic features in a material strongly influence the steady state flow curve of the same. This study aims to understand the interrelation between thixotropy, yield stress, and their relation with the flow curve. In this regard, we study five thixotropic materials that show yield stress. The relaxation time of all the five systems shows power-law dependence on aging time with behaviors ranging from weaker than linear, linear to stronger than linear. Furthermore, the elastic modulus and yield stress have been observed to be constant for some systems while time dependent for the others. We also analyze the experimental behavior through a viscoelastic thixotropic structural kinetic model that predicts the observed experimental behavior of constant as well as time-dependent yield stress quite well. These findings indicate that a nonmonotonic steady-state flow curve in a structural kinetic formalism necessarily leads to time-dependent yield stress, while constant yield stress is predicted by a monotonic steady-state flow curve with stress plateau in the limit of low shear rates. The present work, therefore, shows that thixotropic materials may exhibit either monotonic or nonmonotonic flow curves. Consequently, thixotropic materials may show no yield stress, constant yield stress, or time-dependent yield stress.
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Silva, I. A., I. D. S. Pereira, F. K. A. Sousa, R. R. Menezes, G. A. Neves e H. C. Ferreira. "Thixotropic evaluation of bentonitic clay dispersions modified with nonionic surfactants for organic drilling fluids". Cerâmica 64, n. 371 (settembre 2018): 425–30. http://dx.doi.org/10.1590/0366-69132018643712392.
Testo completoAbstract (sommario):
Abstract The use of nonionic surfactants to modify the surface of bentonite is still quite restricted, although many advantages of that method can be found in the literature, like superior stability and low toxicity. On the other hand, problems involving the fluidity and viscosity of dispersions used in organic drilling fluids have become more and more challenging to colloid science. Therefore, the present study had the purpose of assessing the thixotropic behavior of dispersions of Brazilian bentonite organophilizated with nonionic surfactants for use in organic drilling fluids. Bentonite samples were organophilizated by a combination of two nonionic surfactants, being the process evaluated by X-ray diffraction and thermogravimetric analysis, in which the amount of nonionic surfactants incorporated was quantified. Fluid evaluation followed current standards. The flow curves of the organophilic clays revealed pseudoplastic behavior and the presence of hysteresis, which suggested thixotropy, with a relation between the thixotropy and the apparent viscosity of the final dispersions. Most of the process parameters evaluated showed significant effects on the value of d001 and the overall performance. Factors like clay type and organophilization method also directly affect the thixotropic behavior of dispersions. One of the samples can be considered promising for use in organic drilling fluids.
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Tan, Ye Fa, Sheng Qiang Hao, Hong Wei Li, Hua Tan, Chun Hua Zhou e Li Gao. "Effects of Thixotropic Agent and Storage Time on the Rheological Properties of Epoxy Resin". Applied Mechanics and Materials 217-219 (novembre 2012): 582–85. http://dx.doi.org/10.4028/www.scientific.net/amm.217-219.582.
Testo completoAbstract (sommario):
In order to modify the rheological properties of epoxy resin adhesive in casting moulding technology and improve its bonding quality, the effects of thixotropic agents of hydrophilic nano-silica, organic bentonite and the composite agent of the two thixotropic ones on the rheological properties of epoxy resin (E-44) were studied by the evaluation parameters of viscosity and thixotropic index in this paper. The variation regulation of rheological properties of epoxy resin (E-44) with different thixotropic agents as the storage time was also investigated. The results show that the two thixotropic agents play a significant role in thickening the density and modifying the thixotropy of the epoxy resin (E-44). Especially, the thickening and thixotropic effects of the composite agent of 3phr hydrophilic nano-silica with 6phr organic bentonite are the most remarkable and the storage stability is also excellent.
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Fatahian, Esmaeel, Naser Kordani e Hossein Fatahian. "A REVIEW ON RHEOLOGY OF NON-NEWTONIAN PROPERTIES OF BLOOD". IIUM Engineering Journal 19, n. 1 (14 marzo 2018): 237–50. http://dx.doi.org/10.31436/iiumej.v19i1.826.
Testo completoAbstract (sommario):
Human blood is composed of red cells, white blood cells, and platelets in a fluid called plasma that contains organic and mineral salts and protein. The rheological characteristics of blood are determined by the properties of these combinations and their interaction with each other. The plasma is essentially a Newtonian fluid, but the blood as a whole behaves as a non-Newtonian fluid showing all signs of non-Newtonian rheology including deformation rate dependency, viscoelasticity, yield stress, and thixotropy. The purpose of this study is mainly a review based on past work on blood rheology, determinants of blood viscosity, yield stress, thixotropy, blood viscosity measurement, and heat transfer in blood flow to better understand the non-Newtonian effect in the blood circulation system. ABSTRAK: Darah manusia terdiri daripada sel-sel merah, sel darah putih dan platlet dalam cecair yang dipanggil plasma, mengandungi garam organik dan mineral dan protein. Ciri-ciri sifat reologi darah ditentukan oleh sifat-sifat kombinasi ini dan interaksi antara satu sama lain. Plasma adalah pada dasarnya Newtonian cecair tetapi secara keseluruhannya darah bersifat sebagai bukan suatu cecair Newtonian yang menunjukkan tanda-tanda bukan Newtonian reologi, mengandungi pergantungan kadar ubah bentuk, kelikatkenyalan, tegasan alah dan thixotropi. Tujuan kajian ini adalah berkenaan ulasan kajian-kajian lepas berkaitan rheology darah, penentu viskositi darah, tegasan alah dan thixotropi, ukuran kelikatan darah dan pemindahan haba dalam aliran darah bagi memahami kesan bukan Newtonian dalam sistem peredaran darah.
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Woodcock, Leslie V. "Origins of Thixotropy". Physical Review Letters 54, n. 14 (8 aprile 1985): 1513–16. http://dx.doi.org/10.1103/physrevlett.54.1513.
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Barnes, Howard A. "Thixotropy—a review". Journal of Non-Newtonian Fluid Mechanics 70, n. 1-2 (maggio 1997): 1–33. http://dx.doi.org/10.1016/s0377-0257(97)00004-9.
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Shan, Wei Wei, Ju Fu Jiang e Shou Jing Luo. "Microstructure and Stress Variation of Semi-Solid Magnesium Alloy during Isothermal Compression and Its Relationship to Thixotropy". Solid State Phenomena 116-117 (ottobre 2006): 643–47. http://dx.doi.org/10.4028/www.scientific.net/ssp.116-117.643.
Testo completoAbstract (sommario):
Thixotropy is the most important characteristic of semi-solid materials, and it is decided by the variation of microstructure during action of handling. In this paper, for the sake of the industrial thixoforming and numerical simulation, microstructure and stress variation of semisolid magnesium alloys during isothermal compression is researched. Here, samples are heated to the desired temperature in the empty space with various holding times and compressed horizontally. Stress–strain curves during compression can be given directly by the experimental computer, and each of curves show a peak stress in a small strain and then decrease rapidly, which originally because of the thixotropy of semisolid materials. Moreover, thixotropy of semisolid magnesium alloys is clearer with the evolution of microstructures including agglomeration and deagglomeration of solid particles and the moving way of liquid at different places and strain under different conditions. Microstructures during isothermal compression show that the deagglomeration of solid particles increase with increasing the strain rate, therefore, the thixotropy of semisolid magnesium alloys increases. However, when solid volume fractions are lower, the agglomeration of solid particles doesn’t change obviously with increase or decrease factors, meaning that the thixotropy is smaller. Relationships between thixotropy and microstructure at other different conditions are also given according to the experiments and analysis.
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Luo, Kai Yuan, Xian Fu Wei, Bei Qing Huang e Mu Qun Yu. "Influence of Filler on the Rheological Properties of UV Curable Offset Ink". Applied Mechanics and Materials 200 (ottobre 2012): 666–69. http://dx.doi.org/10.4028/www.scientific.net/amm.200.666.
Testo completoAbstract (sommario):
In order to investigate the influence of filler on the rheological properties of UV curable offset ink, ink samples with various varieties and contents of fillers were prepared, the flow curve, thixotropy, dynamic and viscoelastic properties have been tested, and the rheological properties UV offset ink samples with various varieties and contents of fillers have been discussed. The results indicated that: variety and content have great influence on the rheological properties of ink samples. Sample use SiO2 as filler has the highest viscosity, the largest thixotropy and G’; Sample use SiO2as filler has the lowest viscosity, the largest thixotropy, while it’s G’ has no big difference from the sample use CaCO3. Along with the increase of filler content, the viscosity, thixotropy and G’ will increase.
34
Ma, Yuan, Mingming Liu, Tao Guo e Tengwei Wu. "Experimental Study on Thixotropy of Temporarily Stored Sludge". Journal of Physics: Conference Series 2610, n. 1 (1 ottobre 2023): 012013. http://dx.doi.org/10.1088/1742-6596/2610/1/012013.
Testo completoAbstract (sommario):
Abstract Aiming at the problems of strong viscosity and low transportation efficiency of temporary stored sludge in Laogang Shanghai, an experimental study on sludge thixotropy was carried out to study the changes of sludge viscosity with shear rate and standing time, the changes of shear stress with shear rate at different solid content, and the changes of sludge shear stress with time at constant shear rate at different solid content. On this basis, dynamic equilibrium rheological curves for different solid content were established, and numerical simulation techniques were used to form a mathematical expression of the dynamic equilibrium rheological curve for temporary storage sludge. The thixotropic index for different solid content was obtained, providing theoretical support for efficient transportation of temporary storage sludge.
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Keung, W. C., Y. F. Lee, Wei Wei Shan e Shou Jing Luo. "Thixotropic Strength and Thixotropic Criteria in Semi-Solid Processing". Solid State Phenomena 141-143 (luglio 2008): 319–23. http://dx.doi.org/10.4028/www.scientific.net/ssp.141-143.319.
Testo completoAbstract (sommario):
Thixotropy is essential to semi-solid processing, and because of it the semi-solid material is characterized by ‘shear shinning’. Here, thixotropic strength and thixotropic criteria in semi-solid processing are put forward based on related theories and experiments, and thixotropic mechanism and its influencing factors are also investigated. The results are as follows: 1) the term of thixotropic strength means that with constant shear rate at semi-solid temperature, the semi-solid body begins to flow when the shear stress reach a certain value. This value of shear stress is defined as the thixotropic strength; 2) Thixotropic behavior happens with ‘shear thinning’ because of the deagglomeration of solid particles, while ‘shear thickening’ happens because of the agglomeration at the same time. With increasing shear time, the shear stress increases first and then decreases rapidly to reach a stable value. 3) There are three important factors that influence ‘thixotropic strength’: temperature (hence solid content), initial microstructure (including size, shape factor and uniformity of solid particles) and shear rate.
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Panda, Biranchi, Nisar Ahamed Noor Mohamed, Suvash Chandra Paul, GVP Bhagath Singh, Ming Jen Tan e Branko Šavija. "The Effect of Material Fresh Properties and Process Parameters on Buildability and Interlayer Adhesion of 3D Printed Concrete". Materials 12, n. 13 (4 luglio 2019): 2149. http://dx.doi.org/10.3390/ma12132149.
Testo completoAbstract (sommario):
The advent of digital concrete fabrication calls for advancing our understanding of the interaction of 3D printing with material rheology and print parameters, in addition to developing new measurement and control techniques. Thixotropy is the main challenge associated with printable material, which offers high yield strength and low viscosity. The higher the thixotropy, the better the shape stability and the higher buildability. However, exceeding a minimum value of thixotropy can cause high extrusion pressure and poor interface bond strength if the printing parameters are not optimized to the part design. This paper aims to investigate the effects of both material and process parameters on the buildability and inter-layer adhesion properties of 3D printed cementitious materials, produced with different thixotropy and print head standoff distances. Nano particles are used to increase the thixotropy and, in this context, a lower standoff distance is found to be useful for improving the bond strength. The low viscosity “control” sample is unaffected by the variation in standoff distances, which is attributed to its flowability and low yield stress characteristics that lead to strong interfacial bonding. This is supported by our microscopic observations.
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OLEKSY, MARIUSZ, e HENRYK GALINA. "Characterization of thixotropic compositions of unsaturated polyester resins. The absolute thixotropy index". Polimery 44, n. 06 (giugno 1999): 430–32. http://dx.doi.org/10.14314/polimery.1999.430.
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Su, Zhenhua, Chunxiao Li, Guilin Jiang, Jiajie Li, Hao Lu e Fenghui Guo. "Rheology and Thixotropy of Cement Pastes Containing Polyacrylamide". Geofluids 2022 (15 luglio 2022): 1–10. http://dx.doi.org/10.1155/2022/1029984.
Testo completoAbstract (sommario):
In this article, the rheological and thixotropic properties of fresh cement pastes (fcps) with nonionic polyacrylamide (PAM) are investigated through the coaxial rotary method. The B-HB model is resorted to fit the shear stress versus shear rate diagram, from which the slurry plastic viscosity is particularly discussed. The results show that with the development of PAM, the plastic viscosity increases first, then decreases, and then increases again, exhibiting the “up-down-up” trend, which is consistent with the fcps fluidity. The adsorption, lubrication, and entanglement mechanisms of PAM are successfully used to interpret this phenomenon. Combined with the suspension density, the relationship among plastic viscosity, flowability, and density is successfully established follower via a multivariate linear regression method. The Durbin-Watson coefficient, variance inflation factor, μ significance, ρ significance, and R 2 are 2.122, 1.024, 0.014, 0.004, and 0.776, respectively, demonstrating the feasibility of fitting formula. Besides that, the PAM containing slurry which exhibits the explicit thixotropy is also found according to the appeared hysteresis curve during one shearing cycle. With the increase of PAM dosage, the thixotropic indexes including Th1 and Th2 decreased, until the PAM exceeded 0.5%-0.6% dosage, both of them yielded negative values. The phenomenon that the fcps final shear stress exceeds its initial value occurs.
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Cayeux, Eric, e Amare Leulseged. "The Effect of Thixotropy on Pressure Losses in a Pipe". Energies 13, n. 23 (24 novembre 2020): 6165. http://dx.doi.org/10.3390/en13236165.
Testo completoAbstract (sommario):
Drilling fluids are designed to be shear-thinning for limiting pressure losses when subjected to high bulk velocities and yet be sufficiently viscous to transport solid material under low bulk velocity conditions. They also form a gel when left at rest, to keep weighting materials and drill-cuttings in suspension. Because of this design, they also have a thixotropic behavior. As the shear history influences the shear properties of thixotropic fluids, the pressure losses experienced in a tube, after a change in diameter, are influenced over a much longer distance than just what would be expected from solely entrance effects. In this paper, we consider several rheological behaviors that are relevant for characterizing drilling fluids: Collins–Graves, Herschel–Bulkley, Robertson–Stiff, Heinz–Casson, Carreau and Quemada. We develop a generic solution for modelling the viscous pressure gradient in a circular pipe under the influence of thixotropic effects and we apply this model to configurations with change in diameters. It is found that the choice of a rheological behavior should be guided by the actual response of the fluid, especially in a turbulent flow regime, and not chosen a priori. Furthermore, thixotropy may influence pressure gradients over long distances when there are changes of diameter in a hydraulic circuit. This fact is important to consider when designing pipe rheometers.
40
Huang, Ching-Rong, e Shiey-Shiun Horng. "Viscoelastic-thixotropy of blood". Clinical Hemorheology and Microcirculation 15, n. 1 (1995): 25–36. http://dx.doi.org/10.3233/ch-1995-15104.
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Agarwal, Mayank, Shweta Sharma, V. Shankar e Yogesh M. Joshi. "Distinguishing thixotropy from viscoelasticity". Journal of Rheology 65, n. 4 (luglio 2021): 663–80. http://dx.doi.org/10.1122/8.0000262.
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Yang, Shaoli, e Knut H. Andersen. "Thixotropy of Marine Clays". Geotechnical Testing Journal 39, n. 2 (8 dicembre 2015): 20150020. http://dx.doi.org/10.1520/gtj20150020.
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Cheng, D. C. H. "Characterisation of thixotropy revisited". Rheologica Acta 42, n. 4 (1 luglio 2003): 372–82. http://dx.doi.org/10.1007/s00397-002-0286-3.
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Abu-Farsakh, Murad, Firouz Rosti e Ahmad Souri. "Evaluating pile installation and subsequent thixotropic and consolidation effects on setup by numerical simulation for full-scale pile load tests". Canadian Geotechnical Journal 52, n. 11 (novembre 2015): 1734–46. http://dx.doi.org/10.1139/cgj-2014-0470.
Testo completoAbstract (sommario):
During pile installation, stresses and void ratios in the surrounding soils change significantly, creating large displacements, large strains, soil disturbance, and development of excess pore-water pressures. The surrounding disturbed soil tends to regain its strength with time due to both consolidation and thixotropic effects. In this paper, the pile installation process and subsequent consolidation, thixotropy, and load tests conducted at different times after end of driving (EOD) were modeled for test piles at the Bayou Laccassine Bridge site, Louisiana. In the finite element (FE) model, the pile was considered as an elastic material and the anisotropic modified Cam-clay model (AMCCM) was used to describe the behavior of the surrounding clayey soils. Pile installation was modeled by applying prescribed radial and vertical displacements on the nodes at the soil–pile interface (volumetric cavity expansion), followed by vertical deformation to activate the soil–pile interface friction and simulate static load tests. The thixotropic effect was incorporated by applying a time-dependent reduction parameter, β, which affects both interface friction and material properties. Results from the FE numerical simulation include the development of excess pore-water pressure during pile installation and its dissipation with time, the increase in effective lateral stress at the pile–soil interface, changes in stress state of the surrounding soil, and setup attributed to both the soil consolidation and thixotropy at different times. FE results are compared with measured values obtained from full-scale instrumented pile load tests, which show good agreement between measured and FE-predicted results.
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Pramanik, Bapan. "Short Peptide-Based Smart Thixotropic Hydrogels †". Gels 8, n. 9 (7 settembre 2022): 569. http://dx.doi.org/10.3390/gels8090569.
Testo completoAbstract (sommario):
Thixotropy is a fascinating feature present in many gel systems that has garnered a lot of attention in the medical field in recent decades. When shear stress is applied, the gel transforms into sol and immediately returns to its original state when resting. The thixotropic nature of the hydrogel has inspired scientists to entrap and release enzymes, therapeutics, and other substances inside the human body, where the gel acts as a drug reservoir and can sustainably release therapeutics. Furthermore, thixotropic hydrogels have been widely used in various therapeutic applications, including drug delivery, cornea regeneration and osteogenesis, to name a few. Because of their inherent biocompatibility and structural diversity, peptides are at the forefront of cutting-edge research in this context. This review will discuss the rational design and self-assembly of peptide-based thixotropic hydrogels with some representative examples, followed by their biomedical applications.
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Pérez-Jiménez, Félix, Ramon Botella e Rodrigo Miró. "Damage and Thixotropy in Asphalt Mixture and Binder Fatigue Tests". Transportation Research Record: Journal of the Transportation Research Board 2293, n. 1 (gennaio 2012): 8–17. http://dx.doi.org/10.3141/2293-02.
Testo completoAbstract (sommario):
Fatigue cracking is considered one of the main damage mechanisms in asphalt pavement design. Design methods use fatigue laws obtained by laboratory testing of the materials involved. Typically, these tests consist of subjecting the asphalt mixture to cyclic loading until failure occurs. However, failure is associated not with specimen fracture (which is unusual), but with a slight decrease in the mechanical properties of the material, usually in the complex modulus. As a consequence, it is important to differentiate between real damage to the material and changes in its viscoelastic behavior and thixotropy. It is also crucial to account for the healing that occurs in asphalt material after rest periods. The above considerations are important in the fatigue testing of asphalt binders because these materials show pronounced viscoelastic behavior and thixotropy, especially when subjected to cyclic loading. This paper demonstrates that in many cases what is taken for fatigue failure during testing (i.e., a decrease in the complex modulus below half of its initial value) is actually thixotropy. Thus, the complex modulus can be recovered by reducing the loading or, as in this study, the strain applied. In contrast, asphalt mixtures experience irreversible damage, and depending on the asphalt binder, the thixotropic effects are more or less pronounced. This paper analyzes the failure criteria currently used in the fatigue testing of asphalt mixtures and binders and evaluates the parameters chosen, namely, complex modulus (G*) and phase angle (δ) to characterize asphalt binders (G*sin δ). A cyclic uniaxial tension–compression test under strain-controlled conditions was performed. Three test modalities were used: time sweeps (constant strain amplitude until total failure), increasing strain sweeps (increase in strain amplitude every 5,000 cycles), and up-and-down strain sweeps (alternating increases and decreases in strain amplitude).
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Homma, Ikuo, e Karl-Erik Hagbarth. "Thixotropy of rib cage respiratory muscles in normal subjects". Journal of Applied Physiology 89, n. 5 (1 novembre 2000): 1753–58. http://dx.doi.org/10.1152/jappl.2000.89.5.1753.
Testo completoAbstract (sommario):
In this study, we searched for signs of thixotropic behavior in human rib cage respiratory muscles. If rib cage respiratory muscles possess thixotropic properties similar to those seen in other skeletal muscles in animals and humans, we expect resting rib cage circumference would be temporarily changed after deep rib cage inflations or deflations and that these aftereffects would be particularly pronounced in trials that combine conditioning deep inflations or deflations with forceful isometric contractions of the respiratory muscles. We used induction plethysmography to obtain a continuous relative measure of rib cage circumference changes during quiet breathing in 12 healthy subjects. Rib cage position at the end of the expiratory phase (EEP) was used as an index of resting rib cage circumference. Comparisons were made between EEP values of five spontaneous breaths immediately before and after six types of conditioning maneuvers: deep inspiration (DI); deep expiration (DE); DI combined with forceful effort to inspire (FII) or expire (FEI); and DE combined with forceful effort to inspire (FIE) or expire (FEE), both with temporary airway occlusion. The aftereffects of the conditioning maneuvers on EEP values were consistent with the supposition that human respiratory muscles possess thixotropic properties. EEP values were significantly enhanced after all conditioning maneuvers involving DI, and the aftereffects were particularly pronounced in the FII and FEI trials. In contrast, EEP values were reduced after DE maneuvers. The aftereffects were statistically significant for the FEE and FIE, but not DE, trials. It is suggested that respiratory muscle thixotropy may contribute to the pulmonary hyperinflation seen in patients with chronic obstructive pulmonary disease.
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Alatalo, Diana, e Fatemeh Hassanipour. "An Experimental Study on Human Milk Rheology: Behavior Changes from External Factors". Fluids 5, n. 2 (27 marzo 2020): 42. http://dx.doi.org/10.3390/fluids5020042.
Testo completoAbstract (sommario):
The influence of external factors, including temperature, storage, aging, time, and shear rate, on the general rheological behavior of raw human milk is investigated. Rotational and oscillatory experiments were performed. Human milk showed non-Newtonian, shear-thinning, thixotropic behavior with both yield and flow stresses. Storage and aging increased milk density and decreased viscosity. In general, increases in temperature lowered density and viscosity with periods of inconsistent behavior noted between 6–16 ∘ C and over 40 ∘ C. Non-homogeneous breakdown between the yield and flow stresses was found which, when coupled with thixotropy, helps identify the source of nutrient losses during tube feeding.
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Voznesensky, Eugene A., Vladimir Y. Kalachev, Victor T. Trofimov e Victoria V. Kostomarova. "Dynamic instability of seasonally thawing silty soils". Canadian Geotechnical Journal 31, n. 3 (1 giugno 1994): 454–62. http://dx.doi.org/10.1139/t94-053.
Testo completoAbstract (sommario):
The peculiarities of the dynamic behaviour of silty soils in laboratory experiments that simulate their interaction with gas mining equipment are analyzed. These seasonally thawing soils appear to be very sensitive to dynamic loading and sometimes even liquefaction. Several peculiarities of their dynamic behaviour include: (i) their special sensitivity to very definite and narrow vibration frequency ranges, which vary with grain size and moisture content, and result from the resonant effects in the soil; (ii) the redistribution of pore water during the vibration and subsequent regain; (iii) the thixotropic recovery of the soil after vibration, resulting in the regain of its strength over initial levels, water content and density being constant. Both dilatant and thixotropic effects take place in such soils during dynamic loading, distinguishing them from both clean sands and clayey soils. On the basis of the peculiarities of dynamic behaviour discussed, the authors consider such soils as dilatantly thixotropic dispersed systems. Key words : dynamic properties, soils, thixotropy, liquefaction, resonance, silts.
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Krasinskyi, Volodymyr, Emil Spišák, Ivan Gajdoš e Tomasz Garbacz. "Heat-Resistant Coatings on the Basis of Phenol-Formaldehyde Compositions". Materials Science Forum 818 (maggio 2015): 105–8. http://dx.doi.org/10.4028/www.scientific.net/msf.818.105.
Testo completoAbstract (sommario):
The determination of the effect of composition formula and hardening conditions on technological characteristics of developed thermostable enamels on the basis of phenol-formaldehyde resins modified by epoxy resin and polyvinylpyrrolidone (PVP) was the task of this work. The mechanism of resins modification and hardening has been determined. The developed modified composition is characterized by high index of thixotropy in contrast to phenol-formaldehyde resin (PFR) containing urotropine. It was determined that novolac phenol-formaldehyde resin modification by PVP and ED-20 results in a significant improvement of thixotropic characteristics and enamel technological effectiveness and in physico-mechanical properties and thermostability improvement as well.