Elastic Response Research Articles

Polytopal discontinuous Galerkin discretization of brain multiphysics flow dynamics

A comprehensive mathematical model of the multiphysics flow of blood and Cerebrospinal Fluid (CSF) in the brain can be expressed as the coupling of a poromechanics system and Stokes' equations: the first describes fluids filtration through the cerebral tissue and the tissue's elastic response, while the latter models the flow of the CSF in the brain ventricles. This model describes the functioning of the brain's waste clearance mechanism, which has been recently discovered to play an essential role in the progress of neurodegenerative diseases. To model the interactions between different scales in the porous medium, we propose a physically consistent coupling between Multi-compartment Poroelasticity (MPE) equations and Stokes' equations. In this work, we introduce a numerical scheme for the discretization of such coupled MPE-Stokes system, employing a high-order discontinuous Galerkin method on polytopal grids to efficiently account for the geometric complexity of the domain. We analyze the stability and convergence of the space semidiscretized formulation, we prove a-priori error estimates, and we present a temporal discretization based on a combination of Newmark's β-method for the elastic wave equation and the θ-method for the other equations of the model. Numerical simulations carried out on test cases with manufactured solutions validate the theoretical error estimates. We also present numerical results on a two-dimensional slice of a patient-specific brain geometry reconstructed from diagnostic images, to test in practice the advantages of the proposed approach.

Elastic response reveals the pairing symmetry

Elastic response reveals the pairing symmetry

Laser speckle rheological microscopy reveals wideband viscoelastic spectra of biological tissues.

Viscoelastic transformation of tissue drives aberrant cellular functions and is an early biomarker of disease pathogenesis. Tissues scale a range of viscoelastic moduli, from biofluids to bone. Moreover, viscoelastic behavior is governed by the frequency at which tissue is probed, yielding distinct viscous and elastic responses modulated over a wide frequency band. Existing tools do not quantify wideband viscoelastic spectra in tissues, leaving a vast knowledge gap. We present wideband laser speckle rheological microscopy (WB-SHEAR) that reveals elastic and viscous response over sub-megahertz frequencies previously not investigated in tissue. WB-SHEAR uses an optical, noncontact approach to quantify wideband viscoelastic spectra in specimens spanning a range of moduli from low-viscosity fibrin to highly elastic bone. Via laser scanning, micromechanical imaging is enabled to access wideband viscoelastic spectra in heterogeneous tumor specimens with high spatial resolution (25 micrometers). The ability to interrogate the viscoelastic landscape of diverse biospecimens could transform our understanding of mechanobiological processes in various diseases.

Uncovering the impacts of depleting aquifers: A remote sensing analysis of land subsidence in Iran.

Intensive groundwater pumping, previously unrecognized in its full extent, is blamed for aquifer degradation and widespread land subsidence in Iran. We use a 100-meter resolution satellite survey from 2014 to 2020 to assess the recent implications of groundwater usage across the country. Results indicate that approximately 56,000 km2 (3.5%) of the country's area is subject to land subsidence, primarily linked to irrigation; 3000 km2 of this area experiences subsidence rates greater than 10 cm/year. The central plateau catchment hosts two-thirds of the country's depleting aquifers, with locations sinking at rates higher than 35 cm/year. The results suggest an annual groundwater depletion of 1.7 billion cubic meters (BCM) from confined and semiconfined aquifers, with the long-term inelastic compaction for most aquifers being approximately one order of magnitude larger than their seasonal elastic response. This underscores the permanent loss of aquifers that jeopardizes the sustainability of water resources across Iran.

Finite Element Analysis of Manufacturing Deformation in Polymer Matrix Composites.

This paper introduces a unique finite element analysis (FEA) technique designed to predict elastic response in polymer matrix composites (PMCs). Extensive research has been conducted to model the manufacturing process of multiple 'L'-shaped components, fabricated from SPRINTTM materials (GLP 43 and GLP 96) at two thicknesses (15 mm and 25 mm). Three distinct FEA methodologies were utilised to determine the impact of thermal loads and rigid fixtures. An error deviation of 3.23% was recorded when comparing simulation results to experimental data, thereby validating the effectiveness of the FEA methodology.

From creep to flow: Granular materials under cyclic shear

When unperturbed, granular materials form stable structures that resemble the ones of other amorphous solids like metallic or colloidal glasses. Whether or not granular materials under shear have an elastic response is not known, and also the influence of particle surface roughness on the yielding transition has so far remained elusive. Here we use X-ray tomography to determine the three-dimensional microscopic dynamics of two granular systems that have different roughness and that are driven by cyclic shear. Both systems, and for all shear amplitudes Γ considered, show a cross-over from creep to diffusive dynamics, indicating that rough granular materials have no elastic response and always yield, in stark contrast to simple glasses. For the system with small roughness, we observe a clear dynamic change at Γ ≈ 0.1, accompanied by a pronounced slowing down and dynamical heterogeneity. For the large roughness system, the dynamics evolves instead continuously as a function of Γ. We rationalize this roughness dependence using the potential energy landscape of the systems: The roughness induces to this landscape a micro-corrugation with a new length scale, whose ratio over the particle size is the relevant parameter. Our results reveal the unexpected richness in relaxation mechanisms for real granular materials.

Improvement of a hypoplastic model for sand under undrained loading conditions

An important drawback of the hypoplastic model is the inaccurate prediction of the sand behavior under undrained monotonic loading conditions. The model is not able to reproduce the limited liquefaction type response widely observed in undrained tests on loose sand, and it often underestimates the initial stiffness and hardening rate of sand during the shearing. To address these issues, three novel modifications are introduced into a basic hypoplastic model to enhance its undrained predictive capability. Firstly, a new factor is added to the nonlinear term of the model, allowing the simulation of a purely elastic response at the beginning of loading. By doing so, the model can accurately capture the initial stiffness and undrained effective stress path of sand. Secondly, the characterized void ratios are related to an evolving state variable, enabling the model to reasonably reproduce the limited flow response and quasi-steady state. Furthermore, a new term is incorporated into the deviatoric part of the strain rate to adjust the hardening rate of the model. The model performance for undrained loading is significantly improved through the above modifications, as evidenced by the good agreement between simulation results and experimental data for tests with varying densities and confining pressures.

Phase transition and polar cluster behavior above Curie temperature in ferroelectric BaTi0.8Zr0.2O3

We study the phase transition behavior of the ferroelectric BaTi0.8Zr0.2O3 in the paraelectric region. The temperature dependencies of thermal, polar, elastic, and dielectric properties indicate the presence of local structures above the paraelectric–ferroelectric transition temperature Tc = 292 K. The non-zero remnant polarization is measured up to a characteristic temperature T* ∼ 350 K, which coincides with the temperature where the dielectric constant deviates from the Curie–Weiss law. Resonant piezoelectric spectroscopy shows that DC field cooling above Tc using fields smaller than the coercive field leads to an elastic response and remnant piezoelectricity below T*, which likely corresponds to the coherence temperature associated with polar nanostructures in ferroelectrics. The observed remnant effect is attributed to the reorientation of polar nanostructures above Tc.

An exploration into surface wrinkling in 3D printing inspired orthotropic bilayer systems

Surface instability, termed wrinkling, might occur in compressed bilayer systems constituted by an external rigid skin resting on an internal soft substrate, where wrinkling is favored by the rigidity contrast between the two layers. In this paper, the same instability mechanism is explored by considering a substrate characterized by an orthotropic elastic response. By varying the orientation of the principal axes of the substrate’s material, the critical strain of wrinkling and the wrinkles’ wavelength can be tuned during compression. Theoretical formulations for wrinkling are discussed along with the results obtained by linear bifurcation and geometrically nonlinear analyses carried out with two-dimensional finite element models. To experimentally validate the results, the intrinsic properties of Fused Deposition Modeling (FDM) 3D printing technology are leveraged: bilayer objects are manufactured by printing continuous outer shells (corresponding to the rigid skin) along the borders, while the inner raster is shaped with a porous infill pattern, forming a substrate with an orthotropic elastic response.

An anisotropic hyperelastic strain energy function based on 21 icosahedron fiber distributions

The microscopic Cauchy strain energy for linear elasticity based on the sum of quadratic strain energies due to pair potentials has only 15 material rari-constants. It is shown that the six vectors connecting opposing vertices of a regular icosahedron can be used to develop a strain energy function for general linear elastic anisotropic response with 21 material constants. Specifically, the six strains of material fibers characterized by these vectors are enhanced by 15 fiber distribution strains due to all combinations of distinct pairs of these vectors. These two-vector fiber distributions introduce coupling that is essential to obtaining general anisotropy. The model is generalized for large deformations by replacing the strains with stretches and by using a Fung-type exponential strain energy which couples the responses of the 21 stretches. The resulting nonlinear hyperelastic strain energy function can be used to model the anisotropic hyperelastic response of fibrous tissues.

Effect of fluid elasticity on the emergence of oscillations in an active elastic filament.

Many microorganisms propel themselves through complex media by deforming their flagella. The beat is thought to emerge from interactions between forces of the surrounding fluid, the passive elastic response from deformations of the flagellum and active forces from internal molecular motors. The beat varies in response to changes in the fluid rheology, including elasticity, but there are limited data on how systematic changes in elasticity alter the beat. This work analyses a related problem with fixed-strength driving force: the emergence of beating of an elastic planar filament driven by a follower force at the tip of a viscoelastic fluid. This analysis examines how the onset of oscillations depends on the strength of the force and viscoelastic parameters. Compared to a Newtonian fluid, it takes more force to induce the instability in viscoelastic fluids, and the frequency of the oscillation is higher. The linear analysis predicts that the frequency increases with the fluid relaxation time. Using numerical simulations, the model predictions are compared with experimental data on frequency changes in the bi-flagellated alga Chlamydomonas reinhardtii. The model shows the same trends in response to changes in both fluid viscosity and Deborah number and thus provides a possible mechanistic understanding of the experimental observations.

Seismic hazard zonation map and definition of seismic actions for Greece in the context of the ongoing revision of EC8

The Greek National Annex for current Eurocode 8 has adopted the seismic hazard zonation map published in 2003 as part of the modifications to the Greek Seismic Code EAK 2000 (EAK 2003). This map, which followed the catastrophic earthquakes that hit the country between 1978 and 2001, includes three seismic hazard zones with peak ground acceleration (PGA) ranging between 0.16 and 0.36 g. In this paper, following the significant progress that has been made worldwide in the last two decades towards the improvement of the definition of seismic actions and the seismic hazard maps using fully probabilistic models, we make a complete proposal for the Greek National Annex of the ongoing revision of Eurocode 8, which includes a new seismic hazard zonation map for Greece, as well as a novel site categorization scheme and related site amplification factors. To this end, we use the results of the European Seismic Hazard Model, ESHM20, as reported by Danciu et al. (The 2020 update of the European Seismic Hazard Model: Model Overview, 2021) which will be adopted as informative reference for the seismic hazard at European level in the forthcoming revision of Eurocode 8 (CEN/EC8). The herein proposed ground shaking zonation for rock conditions includes five zones with PGA values ranging between 0.13 and 0.37 g. For each zone, two newly proposed ground motion parameters, i.e., Sα,475 and Sβ,475, are provided, which are the two parameters used for anchoring the elastic response spectrum as defined in CEN/EC8, along with all the other necessary parameters for the definition of the elastic response spectrum, including site amplification. The proposal for the new seismic zonation is supported by a preliminary investigation of the impact of its adoption on the seismic design of new structures and on the seismic risk of the current building stock in Greece, to help gain a better insight on how important the differences imposed by the new zonation might be for the end-users and the administration.

New insights into MHD squeezing flows of reacting-radiating Maxwell nanofluids via Wakif's–Buongiorno point of view

AbstractThis work presents a computational investigation of a squeezing nanofluid flow under the influence of thermal radiation, magnetohydrodynamics (MHD), and chemical process in a constrained parallel-wall geometry. In this study, the non-Newtonian behavior of a rate-type (Maxwell) nanofluid is captured by rheological expressions that serve as the foundation for the flow formulation. This kind of thinking makes it possible to simulate the intricate nanofluid behavior that incorporates the elastic and viscous responses, which are useful in a variety of situations related to nanofluid dynamics, rheology, and materials science. Additionally, the transport equations are modeled properly using Wakif's–Buongiorno nanofluid model. The equations reflecting the dynamics of the nanofluid and heat-mass transport are developed based on admissible physical assumptions, such as the negligible viscous dissipation as well as the lower magnetic Reynolds number. After that, several similarity variables are introduced in these equations to get the dimensionless formulation form. Akbari–Ganji's method is used to carry out extensive computational simulations. Our results show that the increased squeezing parameters lead to larger horizontal and vertical velocities. On the other hand, the temperature showed a reverse relationship with the increasing squeezing parameters and exhibiting a cooling impact.

Effect of Corrosion-Induced Structural Degradation on the Ultimate Strength of a High-Tensile-Steel Ship Hull

Standard structural assessments of ship hulls include the evaluation of the elastic structural response. Elastic analysis neglects extreme and unpredicted loadings, which can produce catastrophic outcomes, such as the loss of the ship’s ultimate strength. Moreover, hull elements are considered unaffected by age-related degradation. Therefore, this study models and quantifies the effect of corrosion-induced structural degradation on the ultimate strength of a high-tensile-steel (HTS) cargo ship using progressive collapse and nonlinear finite element methods. Uniform and pitting corrosion are modeled through selected scenarios, which hull elements might encounter during exploitation, producing a total of 148 calculation models. The findings show that corrosion-induced degradation can significantly decrease the ultimate strength of the hull (up to 30% for the most severe scenarios assessed). Furthermore, ultimate strength decreases almost proportionally to the amount of wastage considered. It was found that stiffener corrosion has a significant effect on the total ultimate strength. This study’s aim is to emphasize the vast importance of including ultimate strength along with ageing effects in industry-standard structural assessments of large HTS ship structures, designed to last for several decades whilst exposed to excessive and unpredicted bending moments.

Stability and Elasticity of Ultrathin Sphere-Patterned Block Copolymer Films.

Sphere-patterned ultrathin block copolymer films are potentially interesting for a variety of applications in nanotechnology. We use self-consistent field theory to investigate the elastic response of sphere monolayer films with respect to in-plane shear, in-plane extension, compression deformations, and bending. The relations between the in-plane elastic moduli are roughly compatible with the expectations for two-dimensional elastic systems with hexagonal symmetry, with one notable exception: The pure shear and the simple shear moduli differ from each other by roughly 20%. Even more importantly, the bending constants are found to be negative, indicating that free-standing block copolymer membranes made of only a sphere monolayer are inherently unstable above the glass transition. Our results are discussed in view of the experimental findings.

Anisotropic Liesegang pattern for the nonlinear elastic biomineral-hydrogel complex.

The Liesegang pattern is a beautiful natural anisotropic patterning phenomenon observed in rocks and sandstones. This study reveals that the Liesegang pattern can induce nonlinear elasticity. Here, a Liesegang-patterned complex with biomineral-hydrogel repetitive layers is prepared. This Liesegang-patterned complex is obtained only when the biomineralization is performed under the supersaturated conditions. The Liesegang-patterned complex features a nonlinear elastic response, whereas a complex with a single biomineral shell shows a linear behavior, thus demonstrating that the Liesegang pattern is essential in achieving nonlinear elasticity. The stiff biomineral layers have buffered the concentrated energy on behalf of soft hydrogels, thereby exposing the hydrogel components to reduced stress and, in turn, enabling them to perform the elasticity continuously. Moreover, the nonlinear elastic Liesegang-patterned complex exhibits excellent stress relaxation to the external loading, which is the biomechanical characteristic of cartilage. This stress relaxation allows the bundle of fiber-type Liesegang-patterned complex to endure greater deformation.

Giant electrostriction in bulk RE (III) substituted CeO2: Effect of RE-[formula omitted] interaction and RE concentration

Recent discovery of giant electrostriction in bulk polycrystalline ceramics and thin films of rare earth (RE (III)) substituted ceria (CeO2) driven by electroactive defect complexes and their coordinated elastic response, expands the material spectrum for electrostrain applications beyond the conventional piezoelectric materials. Bulk ceramics provide an ideal platform to systematically study electrostriction as a function of parameters such as RE3+-defect (VO••) interaction and RE concentration. In this work, we perform structure-property correlation studies in bulk ceramics of RE3+ substituted ceria (RECO) with RE=Y, La and Gd, all of them having weak dopant-defect interaction, with Y- VO•• being attractive, La-VO•• being repulsive, and Gd-VO•• being neutral. We employ large signal measurements to measure the electrostrictive coefficients of all the RECO ceramics, with varying concentration of RE3+, and show that an attractive defect-dopant interaction with atleast 20% of substituent ion concentration yields both giant M and Q electrostrictive response.

Multilayer heterostructure inhomogeneous model for the functionally graded spherical shell with rotation effect for arbitrarily varying material properties

With the development of functionally graded materials (FGMs) composite technology, structural safety analysis related to FGMs has been widely concerned. An innovative multilayer heterostructure power-law inhomogeneous (MHPI) model is taken to solve the rotating FGMs hollow spherical shell with arbitrarily varying material properties (elastic modulus and density) along the radial direction. The basic idea of MHPI model is that the rotating FGMs spherical shell is divided into multiple sublayers, and two power functions approximate the elastic modulus and density of each sublayer respectively. For each single sublayer, the analytical solutions include two undetermined constants, which can be obtained from the boundary and continuity conditions. Many numerical examples of the rotating FGMs spherical shell are discussed, involving seven property profiles gradient laws assumptions, three boundary conditions, and nine volume fraction gradient models. Finally, this study further discusses the rotating FGMs spherical shell optimization design. The greatest advantage of this study is that the elastic response of the rotating FGMs spherical shell under various gradient assumptions is completely discussed. The numerical results show that the MHPI model can solve the problem of circumferential stress oscillation well and have good convergence and high accuracy. For many numerical examples, the error of the MHPI model results is about 5‰ when sublayer number reaches 15.

On the boundary conditions for a thin circular plate conjugated to a massive body

The problem of deformation under the action of uniform pressure of a circular plate coupled with a massive base is considered, while the condition for the coupling of the plate with the base is modeled using boundary conditions of the generalized elastic embedding type, i.e. the relationship between the bending moment and forces at the edge of the plate with displacements and rotation angles through the compliance matrix. The main goal of the work is to study the influence of the elasticity of the embedding on the elastic response of the plate. The solution to the problem was obtained in the formulation of the linear theory of plates, the theory of membranes in the approximation of homogeneity of longitudinal forces, and the Foppl — von Karman theory, also in the approximation of the assumption of homogeneity of longitudinal forces. The values of the coefficients of the compliance matrix were obtained using the finite element method for the auxiliary problem and compared with the values of the coefficients obtained for related problems by analytical methods. Numerical results were obtained for an aluminum wafer on a silicon base. The obtained solution was compared with the solution obtained for the rigid embedment condition for all three models used. It is shown that in the case of large deflections (several plate thicknesses), taking into account the compliance of the embedment becomes essential.

Evaluation of the response of historical structures fitted with seismic-isolation

The paper highlights the performance of the seismic isolation devices installed on retrofitted buildings in reducing the seismic response when subjected to earthquakes. Two buildings from the beginning of the XXth century in Bucharest are chosen from many more, monitored over the city area. We discuss the response of these base-seismic isolated structures, relying on good quality data acquired from the recent strong earthquake (3 November 2022, MW = 5.0). Elastic response spectra computed from recordings at two levels of each structure are used, placed under and right above the isolating layer. At one building, the existence of previous recordings and the particularity of the sensors allow a comparison with the other two relatively recent medium-intensity earthquakes. The assessment is carried out in terms of maximum acceleration amax, measured at certain levels in each structure, spectral acceleration amplitude SAmax, and spectral-peak corresponding period. We find that the base-isolation methodology is effective in reducing the response of the building right above the isolating layer, an observation valid for both structures, all components of the recordings, and spectral acceleration values. Moreover, the outcomes from the modal evaluation performed prior to rehabilitation and the seismic isolation process are presented by pointing out a higher newly acquired fundamental period of the isolated structures.