Showing papers on "Viscoplasticity published in 2022"

Norton-Hoff model for deformation of growing solid shell of thin slab casting in funnel-shape mold

Abstract: Abstract A funnel-type mold is commonly used to provide necessary clearance for the submerged entry nozzle in the thin slab casting (TSC). The partially solidified shell is subjected to the mechanical deformations, which can lead to the defects formation and, as a results, to a breakout. Traditionally, the results of the flow simulation, performed by the finite volume method (FVM), are fed to the external package for the finite element analysis of stress and strain. A coupled model was assembled using “creeping solid” approach by blending the Norton-Hoff viscoplastic stress for the solidifying shell with the Newtonian viscous stress of the liquid melt. The FVM was used to combine both liquid and solid stress models within a single solver. The iterative procedure based on the improved both side diffusion method was introduced to treat the nonlinear relation between the viscoplastic stress and the strain rate. The modeled shell thickness was verified by previously published breakout measurements and the simulation results. Temperature distribution, obtained during the TSC simulation, dominantly corresponds to the viscoplastic range. Developed numerical approach is robust and has direct industrial application.

The Role of Structure in Polymer Rheology: Review

Abstract: The review is devoted to the analysis of the current state of understanding relationships among the deformation-induced structure transformations, observed rheological properties, and the occurrence of non-linear effects for polymer liquids (melts, solutions, and composites). Three levels of non-linearity are the base for consideration. The first one concerns changes in the relaxation spectra of viscoelastic liquids, which are responsible for weak non-linear phenomena. The second one refers to the strong non-linearity corresponding to such changes in the structure of a medium that leads to the emergence of a new relaxation state of a matter. Finally, the third one describes the deformation-induced changes in the phase state and/or the occurring of bifurcations and instability in flow and reflects the thermodynamic non-linear behavior. From a structure point of view, a common cause of the non-linear effects is the orientation of macromolecules and changes in intermolecular interaction, while a dominant factor in describing fluid dynamics of polymer liquids is their elasticity. The modern understanding of thixotropic effects, yielding viscoplastic materials, deformation-induced phase transition, and the experimental observations, demonstrating direct correlations between the structure and rheology of polymer liquids, are the main objects for discussion. All these topics are reviewed and discussed mainly on the basis of the latest five-year publications.

Jeffery–Hamel flow of a shear-thinning fluid that mimics the reponse of viscoplastic materials

Abstract: The flow between two divergent plane walls with a source at the vertex (Jeffery–Hamel flow) of a shear-thinning fluid, that mimics the response of a class of seemingly viscoplastic materials, is studied. The semi-inverse approach is used to obtain the governing equations for the velocity profile. The third-order non-linear ordinary differential equation governing the flow is solved numerically, and the effects of the material moduli that characterize the fluid, the angle between plane walls, and the inertial term, on the velocity are reported and discussed. Results show that there is a critical angle beyond which flow reversal occurs, and the number and angular extent of inflow regions varies based on the material moduli and the inertial term. • The Jeffery–Hamel flow of a shear-thinning fluid that mimics viscoplastic materials is studied. • Governing equations for the velocity profile are obtained using the semi-inverse approach and solved numerically. • Effects of the material moduli, the angle between the plane walls, and the inertial term on the velocity are analyzed. • Variation of material moduli led to the appearance of flow reversal regions whose number and angular extent changed. • Variation of angle showed a critical angle at which flow reversal takes place.

Coupling of phase field and viscoplasticity for modelling cyclic softening and crack growth under fatigue

Abstract: A coupled phase field-viscoplasticity approach was developed to model the deformation and crack growth in a nickel-based superalloy under fatigue. The coupled model has an advantage in predicting the cyclic softening behavior of the alloy caused by fatigue damage, overcoming a major limitation of the original cyclic viscoplasticity model. The coupled approach is also highly effective in predicting fatigue crack propagation under varied dwell times at peak load, an important behavior for crack growth under dwell fatigue. By incorporating the stress state factor, the coupled model is further utilized to investigate the growth behavior of 3D cracks under fatigue. Both the geometrical feature of the 3D crack front and the overall crack growth rate are well captured, confirming the predicative capability of the coupled model.

Coupling of phase field and viscoplasticity for modelling cyclic softening and crack growth under fatigue

Abstract: A coupled phase field-viscoplasticity approach was developed to model the deformation and crack growth in a nickel-based superalloy under fatigue. The coupled model has an advantage in predicting the cyclic softening behavior of the alloy caused by fatigue damage, overcoming a major limitation of the original cyclic viscoplasticity model. The coupled approach is also highly effective in predicting fatigue crack propagation under varied dwell times at peak load, an important behavior for crack growth under dwell fatigue. By incorporating the stress state factor, the coupled model is further utilized to investigate the growth behavior of 3D cracks under fatigue. Both the geometrical feature of the 3D crack front and the overall crack growth rate are well captured, confirming the predicative capability of the coupled model.

Propagation and rupture of elastoviscoplastic liquid plugs in airway reopening model

Abstract: The propagation and rupture of mucus plugs in human lungs is investigated experimentally by injecting synthetic mucus in a pre-wetted capillary tube. The rheology of our test liquid is thoroughly characterized, and four samples of synthetic mucus are considered in order to reproduce elastoviscoplastic regimes of physiological interest for airway reopening. Our experiments demonstrate the significant impact of the viscoplasticity and viscoelasticity of mucus. In support to our experiments, we propose a one-dimensional reduced-order model that takes into account capillarity, and elastoviscoplasticity. Our model manages to capture the cross-section averaged dynamics of the liquid plug and is used to elucidate and interpret the experimental evidence. Relying on it, we show that the liquid film thickening due to non-Newtonian effects favors plug rupture, whereas the increase of the effective viscosity due to higher yield stresses hinders plug rupture. As a result of such two effects, increasing the polymeric concentration in the mucus phase leads to a net increase of the rupture time and traveling length. Hence, non-Newtonian effects hinder airway reopening.

Rate-dependent deformation of amorphous sulfide glass electrolytes for solid-state batteries

Abstract: Sulfide glasses are emerging as potential electrolytes for solid-state batteries. The mechanical behavior of these materials can significantly impact cell performance, and it is thus imperative to understand their deformation and fracture mechanisms. Previous work mainly reports properties obtained under quasi-static loading conditions, but very little is known about deformation under dynamic conditions. The current investigation shows that the sulfide glass mechanical behavior is dominated by viscoplasticity, differing substantially from polycrystalline oxide and sulfide solid electrolytes. Finite element modeling indicates that the sulfide glass stiffness is high enough to maintain good contact with softer lithium metal electrodes under moderate stack pressures. The observed viscoplasticity also implies that battery operating conditions will play an important role in electro-chemo-mechanical processes that are associated with dendritic lithium penetration. In general, the rate-dependent mechanical behavior of the sulfide glass electrolytes documented here offers a new dimension for designing next-generation all-solid-state batteries.

Bearing Capacity Factors for Rough Conical Footing by Viscoplasticity Finite-Element Analysis

Abstract: Many researchers have computed the bearing capacity of the strip and circular footings resting on the soil with the low and medium friction angle (ϕ ≤ 35°) by employing the finite-element method (FEM). It is reported that the numerical instability occurs with the high value of ϕ. Thus, based on the suggested values of soil dilation angle (ψ) in this study, the numerical computation can be achieved for all ϕ. Therefore, this paper presents the computation of the vertical bearing capacity factors Nc, Nq, and Nγ of a rough conical footing placed on the soil with friction angle ranging from ϕ = 5° to 45° by using the FE-based viscoplastic strain method under the Mohr–Coulomb (MC) yield criterion. The numerical simulations are solved using in-house MATLAB codes. The effects of the cone apex angle (β) and ϕ on the bearing capacity are examined thoroughly by the computation of factors individually and compared with the available solutions. The current solutions are found to be in good agreement for Nc, Nq, Nγ values; however, the discrepancies are also observed and presented. Therefore, the bearing capacity factor charts are established, and, consequently, the ultimate load of the footing can be determined by using the superposition assumption in Terzaghi’s equation.

Bearing Capacity Factors for Rough Conical Footing by Viscoplasticity Finite-Element Analysis

Abstract: Many researchers have computed the bearing capacity of the strip and circular footings resting on the soil with the low and medium friction angle (ϕ ≤ 35°) by employing the finite-element ...

Advances in Permanent Deformation Modeling of Asphalt Concrete—A Review

Abstract: Permanent deformation is one of the dominant asphalt concrete damages. Significant progress has been made to realistically predict the damage. In the last decade, the mechanistic approach has been the focus of research, and the fundamental theories of viscoelasticity, viscoplasticity, continuum mechanics, and micromechanics are applied to develop the material laws (constitutive equations). This paper reviews the advancement of permanent deformation models including analogical, microstructural, and continuum-based methods. Pavement analysis using the nonlinear damage approach (PANDA) is the most comprehensive and theoretically sound approach that is available in the literature. The model coupled different damages and other phenomena (such as cracking, moisture, and phenomena such as healing, aging, etc.). The anisotropic microstructure approach can be incorporated into the PANDA approach for a more realistic prediction. Moreover, the interaction of fatigue and permanent deformation is the gap that is lacking in the literature. The mechanistic approaches have the capacity to couple these damages for unified asphalt concrete damage prediction.

Viscoplastic sessile drop coalescence

Abstract: The evolution of the liquid bridge formed between two coalescing sessile yield-stress drops is studied experimentally. We find that the height of the bridge evolves similar to a viscous Newtonian fluid, h 0 ∼ t , before arresting at long time prior to minimizing its liquid/gas interfacial energy. We numerically solve for the final arrested profile shape and find it depends on the fluid’s yield stress τ y and coalescence angle α , represented by the Bingham number τ y h drop /σ modified by the drop’s height-width aspect ratio. We present a scaling argument for the bridge’s temporal evolution using the length scale found from an analysis of the arrested shape as well as from the similarity solution derived for the bridge’s evolution.