Viscous Materials Research Articles

A parallel GPU-based computational framework for the micromechanical analysis of geotechnical and erosion problems

Abstract This article deals with the relevance and practical feasibility of micromechanical simulations for their application to general geomechanical problems involving fluid-saturated granular assemblies, whether frictional or cohesive. A set of conceptual and numerical tools is here presented, advocating for a parallel computation using graphical processing units (GPUs) to treat large numbers of degrees of freedom with conventional desktop computers. The fluid phase is here simulated with a particle-resolved approach in the frame of the Lattice Botzmann Method (LBM) while the granular solid phase is modelled as a collection of discrete particles from a Molecular Dynamics DEM perspective. The range of possible material behaviours for the solid granular phase is intended here to cover a broad spectrum from purely frictional to viscous cohesive materials with either brittle or transient debonding features. Specific details of the implementation and some validation cases are put forward. Finally, some exemplary applications in the fields of soil erosion and geotechnical profile installation are provided along with a discussion on the parallel performance of the presented models. The results show that a micromechanical approach can be feasible and useful in practice, providing meaningful insights into complex engineering problems like the erosion kinetics of a soil under an impinging jet or the penetration resistance of a deep foundation in a layered soil profile.

Dynamic load modelling for tank containers with the frame of circle pipes and structurally improved fittings

Higher efficiency of bulked cargo transportation along international transport corridors can be achieved with a resource-saving tank container described in the study. A characteristic feature of a tank container is the use of circle pipes as the carrying elements of the frame. In order to decrease impact loads between fittings of the tank container and fitting stops of the flat wagon at shunting impacts, the authors suggest filling fittings with viscous or viscoelastic materials of dumping or anticorrosive properties. The study also deals with modelling dynamic loading for the suggested tank container. The accelerations obtained were considered in strength calculations for a tank container as components of the dynamic loading. It was determined that the maximum equivalent loads did not exceed the admissible loads. The research will promote designing new-generation tank containers of improved technical, economical and ecological properties, and improve the working efficiency of combined transportation.

Energy estimation of the interaction of a roller vibratory classifier’s blade with crushed rock mass for solving design problems

The roller vibratory classifier is equipped with an impact device for implementing vibro-shock mode, which improves the classification efficiency, especially of viscous and wet materials. The new device is a disk nozzle with blades, which are made like petals of wearresistant polymer. The immersion of a petal at a given depth in a crushed rock mass is investigated experimentally. Theoretical studies includes pair correlation and regression analysis methods. It is obtained that an increase in humidity promotes penetration and leads to a decrease in the energy necessary for impact, whereas an increase in particle size and layer thickness leads to its increase. Analysis of regression equations makes it possible to establish the percentage ratio of influencing factors. The article presents mathematical models of impact energy from variable factors for the initial moisture content of the material, including separately for small classes (-2.5 + 1) mm and further, with variation of all three parameters in the range: layer thickness – 20-40 mm, particle size 1-10 mm, humidity – up to 9 %. The obtained correlation dependencies and regression models are necessary for improving the existing and designing new blade-type roller vibratory classifiers.

SITE-SPECIFIC PROTEST: LIBERATE TATE’S PERFORMANCES AT TATE MODERN

This paper analyzes the site-specific performances of Liberate Tate, an artist collective that staged protest works at Tate institutions to protest the sponsorship deal with the multinational corporation BP. Arguing that the aesthetic, spatial, political, social, and ecological components of Liberate Tate’s works at Tate Modern are intricately enmeshed, the paper offers a close visual analysis of the performances in relation to one of their sites, Turbine Hall at Tate Modern. Doing so, the paper demonstrates how the artist collective reacted to the socio-political structuring of the physical space in their own political mode of aesthetics. The site-specific works of the group attend to and confront the museum space to such an extent that the intervened space presiding over the performative acts, bodies, and props becomes Liberate Tate’s principal medium in their performances. Through their horizontal arrangement mode, choice of messy, dirty, and viscous materials, and approach to nature, culture, and history as inseparable concepts, Liberate Tate’s site-specific performances challenge the hegemonic neoliberal rhetoric of Tate Modern. The contrasts and conflicts Liberate Tate introduces against the visual discourse of Turbine Hall not only reveals the dominant political, financial, and social order of the space but also transforms the museum albeit temporarily into a truly public space of democracy. Key words: site-specific art, activist art, institutional critique, museum space, Liberate Tate

The Plot Thickens: The Emerging Role of Matrix Viscosity in Cell Mechanotransduction.

Cell mechanotransduction is an area of intense research focus. Until now, very limited tools have existed to study how cells respond to changes in the extracellular matrix beyond, for example, mechanical deformation studies and twisting cytometry. However, emerging are a range of elastic, viscoelastic and even purely viscous materials that deform and dissipate on cellular length and timescales. This article reviews developments in these materials, typically translating from 2D model surfaces to 3D microenvironments and explores how cells interact with them. Specifically, it focuses on emerging concepts such as the molecular clutch model, how different extracellular matrix proteins engage the clutch under viscoelastic-stress relaxation conditions, and how mechanotransduction can drive transcriptional control through regulators such as YAP/TAZ.

Effect on the Emulsification Stability and Quality of Emulsified Sausages Added with Wanggasi-Chunnyuncho (Opuntia humifusa f. jeollaensis) Fruit Powders.

In this study, the Opuntia humifusa f. jeollaensis (Wanggasi-Chunnyuncho) fruit (WCF) was used as a source of viscous dietary fiber and color pigmentation in sausage production to improve quality characteristics, including cooking loss and emulsion stability. Control and treatment sausages were formulated with 0%, 1%, 5%, and 10% WCF powder, respectively, and the following quality measures were investigated: general composition, fiber content, cooking loss, emulsion stability, chromaticity, pH, texture, and sensory properties. The moisture, dietary fiber, and ash contents showed increasing trends (all p<0.05) with increasing concentrations of fruit powder. Conversely, crude protein and crude fat contents exhibited decreasing trends with increasing fruit powder concentrations (p<0.05). Moreover, both the moisture and dietary fiber contents affected cooking loss, water retention capacity, and the sausage texture, causing the cooking loss to decrease, while the water and oil retention capacity increased (p<0.05) with increasing concentrations of WCF powder. Furthermore, hardness exhibited a significant decreasing trend as the concentration of WCF powder increased (p<0.05). This finding suggested that both dietary fiber and viscous materials, along with the protein and moisture content, affected the product hardness. In addition, sensory evaluation of the WCF powder groups showed better results than did the control group, and the strongest results obtained for the group containing 5% fruit powder (p<0.05). Therefore, this study suggests that WCF powder improves the quality of emulsified sausages and can potentially be applied as a naturally-derived additive.

Synchronous circuits with self-adaptive mechanical switches of viscous material: a parameter study

Dedicated units are generally needed for operating the switches in synchronous extraction circuits which are considered to be effective in enhancing the power of piezoelectric generators. This paper presents a novel design of self-adaptive mechanical switch using viscous materials. It can trace the displacement peaks and perform the switching operations synchronously with higher performance, less electronic components and lower voltage threshold. A parameter study shows that the relaxing time of the viscous material has different effects in the case of harmonic and noise excitations with varied optimization goals.

Midsole Properties Affect the Amplitude of Soft Tissue Vibrations in Heel-Toe Runners.

Soft tissue vibrations can generate discomfort and may necessitate a greater energy demand to preserve an efficient motion in running. Vibration damping is thus of interest from a comfort and performance standpoint. Our purpose was to assess whether changes in midsole material affect the properties of (a) soft tissue vibrations and (b) myoelectric activity. Two midsole conditions were compared. The control condition corresponded to a full ethylene-vinyl acetate foam midsole. The experimental condition was a bimaterial midsole with a material combination of viscous and viscoelastic materials. Twelve participants ran on an indoor track in both conditions while recording the longitudinal acceleration and the EMG activity of vastus medialis (VM) and gastrocnemius medialis (GM). Wavelet transforms were performed for EMG and acceleration signals to assess the intensity of the muscle activity at low and high frequencies (37-128 and 170-395 Hz, respectively) and to calculate the damping coefficient (D) for soft tissue vibrations. The soft tissue vibrations were also characterized by the peak of acceleration (apeak), the frequency of the power peak (fpeak), and the power of the soft tissue vibrations (PSD[8-55]). The variables apeak and PSD[8-55] decreased for VM and GM in the viscous condition. Before heel strike, low-frequency EMG activity decreased for VM, and high-frequency EMG activity tended to decrease for GM in the viscous condition. The damping D was reduced only for VM, and fpeak was unchanged. A more viscous midsole substantially reduced the amplitude of soft tissue vibrations, but not their frequency. Looking at individual results, it was noted that muscle activity was tuned in response to the acceleration input, and that the damping of soft tissue vibrations was affected by the intensity of muscle activity.

Rheology of mixed deformation mechanisms and mineral phase assemblages

This paper examines the rheological behaviour of power law viscous materials arising from mixtures of deformation mechanisms and/or different mineral assemblages. The mixing relation is based on classical thermodynamics mixing relations where the enthalpy of the mixture is the sum of the molar volume proportions of the individual molar enthalpies; this is equivalent to the 1887 Arrhenius mixing relation for Newtonian viscosities. We compare this mixing relation to viscosities obtained from finite element simulations of deforming mixed mineral phases and from experimental results. The mixing relation helps understanding of apparent anomalies in experimental results for calcite and quartz. This then enables the construction of flow laws and of deformation mechanism maps for mixtures of deformation mechanisms and of mineral assemblages over a range of grain size distributions. The rheological implications for changes in the topology (such as anisotropy) of mineral arrangements, for mixtures of grain sizes, for the interpretation of experimental results and for geodynamic modelling are discussed.

Spectral shape simplicity of viscous materials.

A broad survey of viscoelastic data demonstrates that van der Waals, hydrogen-bonded, and ionic liquids, as well as polymeric, inorganic, and metallic melts share a structural relaxation pattern virtually insensitive to their morphological details. This mechanical simplicity is connected with that characterizing the fast reorientation dynamics prevailing in liquids devoid of a distinguishable secondary susceptibility peak. By these means one is able to uncover a generic spectral pattern which rationalizes the recently reported "universality" of relaxation strength vs stretching of the dielectric response of viscous liquids, significantly broadening the framework in which their relaxation behavior is assessed.

Development of a sensor for monitoring mechanically stressed adhesive joints

A strengthening system with adhesively bonded CFRP reinforcement was developed in the Infravation project FASSTbridge to extend the remaining fatigue lifetime of existing steel bridge constructions. The premature debonding of CFRP and steel is seen as a major risk to lose the contribution of the retrofitting system. Consequently, an ultrathin debonding sensor to be integrated in the adhesive layer between steel and CFRP was developed as part of the strengthening system. It is suited for continuous monitoring of the integrity of the adhesive joint.The paper explains the underlying physical principles of the sensor and gives insight into the performed tests for the calibration and verification of its functionality. The sensor conception takes the change of a capacitor’s electrical impedance as a basis, which occurs when a change in distance between the adjacent conductive faces takes place. It is well assumed that debonding yields separation, which leads to an increase of the monitored impedance. The relationship is explored through single lap sheer experiments and vertical tension bond tests. The sensitivity and the accuracy of the impedance with respect to deformations are revealed by comparing several groups of prototypes with different dielectric layers and viscous materials. The influences of different temperature effects and fatigue loadings are also presented.

Dynamic analysis of vibrating flip-flow screens equipped with support and shear rubber springs

Vibrating flip-flow screens provide an effective means of screening highly viscous or fine materials, and the dynamic characteristics of the main and the floating screen frames are largely responsible for a flip-flow screen’s screen performance and its processing capacity. An accurate dynamic model of the rubber shear springs used within the frame of the screen is critical for its dynamic analysis – to understand deficiencies and improve its performance. In this paper, the Sjöberg model is used to predict the frequency-and amplitude-dependent behaviour of the rubber shear springs. A friction model represents the amplitude dependency of the rubber shear springs. The fractional derivative model is used to describe its frequency dependency with its elasticity being represented by a linear spring. This model is further validated by cyclic tests of the rubber shear springs. Furthermore, dynamic response of the VFFS have been analysed using the Sjöberg model and the Kelvin-Voigt model, respectively. Experimental results indicate that dynamic response of VFFS can be better predict using the Sjöberg model than Kelvin-Voigt model in time region as well as in the frequency domain.

Visuo-Haptic Discrimination of Viscoelastic Materials.

In our daily lives, we interact with different types of deformable materials. Regarding their mechanical behavior, some of those materials lie in a range that is between purely elastic and purely viscous. This range of mechanical behavior is described as viscoelasticity. In certain types of haptic interactions, such as assessment of ripeness of fruit, firmness of cheese, and consistency of organ tissue, we rely heavily on our haptic perception of viscoelastic materials. The relationship between the mechanical behavior of viscoelastic materials and our perception of them has been investigated in the field of psychorheology. However, our knowledge on how we perceive viscoelastic materials is still quite limited though some research work has already been done on purely elastic and purely viscous materials. History- and frequency-dependent behavior of viscoelastic materials result in a complex time-dependent response, which requires relatively more sophisticated models to investigate their behavior than those of purely elastic and viscous materials. In this study, we model viscoelasticity using a "springpot" (i.e., fractional-order derivative element) and express its behavior in the frequency domain using two physical parameters-"magnitude" and "phase" of complex stiffness. In the frequency domain, we are able to devise signal detection experiments where we can investigate the perception of viscoelastic materials using the perceptual terms of "firmness" and "bounciness," corresponding to the physical parameters of "magnitude" and "phase." The results of our experiments show that the just-noticeable difference (JND) for bounciness increases linearly with increasing "phase," following Weber's law, while the JND for firmness is surprisingly independent of the level of "phase."

Thermo-Mechanical Properties of Injection Molded Components Manufactured by Engineered Biodegradable Blends

Engineering of ductile, tough and thermal resistant PLA-based materials requires blending of PLA with other constituents by reactive twin-screw co-rotating extrusion to achieve compounds with adequate thermo-mechanical properties. Then, the compound of the polymeric blends must be melt processed to the final shape with an additional technology, namely the injection molding. The two-stage process the polymeric blends must undergo and the different rheological properties the blends must feature to be suitable to the different processing steps make extremely difficult to engineer the material. Extrusion compounding requires high viscous materials low melt flow index (MFI), while injection molding requires materials with low viscosity (high MFI). To overcome these shortcomings, this manuscript deals with the design of novel biodegradable PLA-based blends that rely on mixing PLA grades with different MFI (i.e. very low for extrusion and high for injection molding), each chosen to feature the rheological characteristics needed for each step of the two-stage transformation process. The ratio of the two PLA-grades inside the blends was the matter of the present investigation. The blends were subsequently tested for the manufacturing of single-use biodegradable and thermal resistant injection molded small cups, specifically designed for brewing of hot beverages. Lastly, the thermo-mechanical performance of the as-is and annealed cups were studied. Experimental evidences show blending of two-different grades of PLA is a promising route to formulate low impact polymeric materials suitable for demanding packaging solutions.

Numerical modelling of boudinage under pure shear: Implications for estimating viscosity ratios and finite strain from natural examples

Numerical experiments of torn boudinage reworking under layer-parallel stretching are reported. In our simulations, we have reproduced the whole spectrum of previously reported boudin shapes due to reworking, and we also report some new structures, including field examples. The results show that boudin shape depends on both the boudin to matrix viscosity ratio and the initial gap width normalized upon the layer thickness. Central bulges develop within the interior boudin faces for intermediate gap widths, in the range of between 0.05 and 0.15 of the initial layer thickness. Convex interiors are reported for initially very narrow separations of about 0.01 the initial layer thickness. The initial normalized gap width together with the viscosity ratio control the internal deformation and separation of the boudins. Lowering the viscosity of the gap infill strongly influences boudin shape evolution and it suppresses the bulging of the interior faces. Boudin aspect ratio has only minor influence on the developing boudin shape. The non-linear viscous reworking of boudins is not significantly different to the one observed in linear viscous materials. We show a natural example of how the geometry of the developing bow-tie vein combined with boudin shape and separation can be used to infer strain and rheological properties. Rhomboidal boudins under layer-parallel stretching exhibit rotation and they tend to produce monoclinic structures, which are similar to structures forming due to layer-parallel shear. We caution the use of asymmetric boudins as shear sense indicators.

Mechanical Characterization by Mesoscale Indentation: Advantages and Pitfalls for Tissue and Scaffolds.

Regenerative medicine and tissue engineering are hindered by the lack of consistent measurements and standards for the mechanical characterization of tissue and scaffolds. Indentation methods for soft matter are favored because of their compatibility with small, arbitrarily shaped samples, but contact mechanics models required to interpret data are often inappropriate for soft, viscous materials. In this study, we demonstrate indentation experiments on a variety of human biopsies, animal tissue, and engineered scaffolds, and we explore the complexities of fitting analytical models to these data. Although objections exist to using Hertz contact models for soft, viscoelastic biological materials since soft matter violates their original assumptions, we demonstrate the experimental conditions that enable consistency and comparability (regardless of arguable misappropriation). Appropriate experimental conditions involving sample hydration, the indentation depth, and the ratio of the probe size to sample thickness enable repeatable metrics that are valuable when comparing synthetic scaffolds and host tissue, and bounds on these parameters are carefully described and discussed. We have also identified a reliable quasistatic parameter that can be derived from indentation data to help researchers compare results across materials and experiments. Although Hertz contact mechanics and linear viscoelastic models may constitute oversimplification for biological materials, the reporting of such simple metrics alongside more complex models is expected to support researchers in tissue engineering and regenerative medicine by providing consistency across efforts to characterize soft matter. Impact Statement To engineer replacement tissue requires a deep understanding of its biomechanical properties. Mesoscale indentation (between micron and millimeter length scales) is well-suited to characterize tissue and engineered replacements as it accommodates small, oddly shaped samples. However, it is easy to run afoul of the assumptions for common contact models when working with biological materials. In this study, we describe experimental procedures and modeling approaches that allow researchers to take advantage of indentation for biomechanical characterization while minimizing its weaknesses.

A Geometrically Consistent Viscous Fluid Solver with Two‐Way Fluid‐Solid Coupling

AbstractWe present a grid‐based fluid solver for simulating viscous materials and their interactions with solid objects. Our method formulates the implicit viscosity integration as a minimization problem with consistently estimated volume fractions to account for the sub‐grid details of free surfaces and solid boundaries. To handle the interplay between fluids and solid objects with viscosity forces, we also formulate the two‐way fluid‐solid coupling as a unified minimization problem based on the variational principle, which naturally enforces the boundary conditions. Our formulation leads to a symmetric positive definite linear system with a sparse matrix regardless of the monolithically coupled solid objects. Additionally, we present a position‐correction method using density constraints to enforce the uniform distributions of fluid particles and thus prevent the loss of fluid volumes. We demonstrate the effectiveness of our method in a wide range of viscous fluid scenarios.

Surface Tension Measurements of Viscous Materials by Pendant Drop Method: Time Needed to Establish Equilibrium Shape

The pendant drop method of surface tension measurements published in 1938 has been frequently used since late 1960s. The time to reach equilibrium drop shape for viscous materials was mentioned in few papers only. The aim of this paper is to estimate time needed to reach a shape sufficiently close to equilibrium as a function of required precision and material viscosity. The procedure is based on Roe's error analysis of the pendant drop method and on a prerequisite of similarity in relaxation times of pendant drop and that of ellipsoid droplet published by Luciani and Utracki. An equation for time needed to reach equilibrium shape of pendant drop has been derived. Estimates have been verified through measurements of a test liquid; strong correction using empirical coefficients is needed to predict equilibration times correctly. The formula found is useful to assess whether the measurement can be accomplished before the material starts to degrade or otherwise change significantly. Since approximation using formula for ellipsoid relaxation is a weak point of the estimate, the challenge remaining for future is to describe the relaxation of pendant drop.

Why do wet-particles adhere to a high-speed roll in a three-roll mill?

A three-roll mill is used in various engineering fields to manufacture high-value-added products. This mill has three horizontally positioned rolls with different rotational velocities. In the mill, viscous materials (or pastes) pass through the narrow gap between the rolls to be mixed, refined, dispersed, and/or homogenized. The viscous materials tend to consist of wet-particles connected by liquid bridges. Although viscous materials always adhere to a faster roll in the three-roll mill, the mechanism has not yet been clarified. Herein, the adhesion mechanism is clarified scientifically by numerical simulation. In the calculations, a Lagrangian method, such as the discrete element method, is used to analyze the specific phenomena in the particle–particle and the particle–wall interaction. A latest liquid bridge force model is used in this study to examine the effect of a wide range of liquid volumes on the adhesion phenomena. In the calculation, a lump of wet-particles is fed into the gap between the two rolls and the roll speed is changed to investigate its influence on the adhesion phenomena. Through numerical examples, it is proven that wet-particles always adhere to a fast roll because the liquid bridge force that acts on the faster roll is larger than that on the slower roll after the compression force is released. This is because the extension of the wet-particles is larger on the faster roll because of the speed difference between the two rolls. Consequently, the adhesion mechanism of the wet-particles in the three-roll mill is proven scientifically to be the force balance due to the liquid bridge force.

Mass Production of Nanocomposites Using Electrospinning

Many conventional polymer processing technologies for compounding micro-/nanocomposites are known in the field. These methods include the direct use of high shear mixers, roll mixers, Banbury mixers, and extruders. With recent interest in advanced composites with nanoscale fillers, efforts have been made to enhance conventional processing technologies as the imposed input energy is often ineffective at breaching the energy barrier to breakup agglomerated nanofiller structures. Electrospinning is a simple, inexpensive process that can be used to produce continuous fibers from submicron to nanometer diameter scale through an electrically charged polymer jet. In this paper, authors present a rotary electrospinning method developed to produce nanocomposites at mass scale by using simultaneously mechanical and electrical forces with a proprietary apparatus. A case study using silica nanoparticles and silicone rubber matrix is presented to demonstrate the capability of the above method of dispersing nanoparticles in highly viscous polymer matrix materials.