Rubberlike materials exhibit strong rate-dependent mechanical response which manifests itself in creep and relaxation tests as well as in the hysteresis curves under cyclic loading. Unlike linear ...viscoelasticity, creep and relaxation response of rubber is nonlinear and amplitude-dependent. Within this context, the contribution of this work is three fold. (i) On the experimental side, the characterization of equilibrium and non-equilibrium responses are carried out by means of uniaxial and equibiaxial extension tests. Also performed are the creep and relaxation experiments at various stress and strain levels. (ii) On the theoretical side, we extend the well-known eight-chain model via incorporating a simple yet instrumental tube-constraint term composed of the second invariant into the non-affine network contribution reflecting the ground state equilibrium response. For the non-equilibrium response, we propose a new evolution equation for the creep/relaxation behavior of rubberlike materials based on a relaxation kinetics of a single polymer chain. The geometric non-linearity is incorporated via the finite deformation kinematics based on the multiplicative split of the deformation gradient into elastic and viscous parts, whereas the volumetric and isochoric split of the deformation gradient is entirely discarded. The rheology uses a nonlinear spring responsible for equilibrium elastic response in parallel to n number of Maxwell elements, leading to a generalized Maxwell-Wiechert viscoelastic solid. (iii) The algorithmic implementation of the model features the spectral decomposition of the respective terms and is demonstrated within the context of the finite element method. The developed model is validated by fitting both the elastic and viscoelastic model responses with respect to the experimental data in the sense of uniaxial, (equi)biaxial extensions, and pure shear tests. Relaxation and creep behavior of the model are thoroughly assessed. Also presented in the manuscript is the capability and the performance of the model in the face of a relevant non-homogeneous boundary value problem. The quality of the findings earns the model vast utilization areas from an engineering perspective.
The linear stability analysis of Rivlin-Ericksen uids of second order is investigated for boundary layer ows, where a semi-infinite wedge is placed symmetrically with respect to the ow direction. ...Second order uids belong to a larger family of uids called Order uids, which is one of the first classes proposed to model departures from Newtonian behaviour. Second order uids can represent non-zero normal stress differences, which is an essential feature of viscoelastic uids. The linear stability properties are studied for both signs of the elasticity number K, which characterises the non-Newtonian response of the uid. Stabilisation is observed for the temporal and spatial evolution of two-dimensional disturbances when K > 0, in terms of increase of critical Reynolds numbers and reduction of growth rates, whereas the ow is less stable when K < 0. By extending the analysis to three-dimensional disturbances, we show that a positive elasticity number K destabilises streamwise independent waves, while the opposite happens for K < 0. We show that, as for Newtonian uids, the nonmodal amplification of streamwise independent disturbances is the most dangerous mechanism for transient energy growth which is enhanced when K > 0 and reduced when K < 0. A preliminary study of boundary layer ows of UCM, Oldroyd B, Phan-Thien Tanner and Giesekus uids is performed. Asymptotic Suction Boundary Layer theory allows us to simplify the governing equations and obtain analytical solutions for the UCM and Oldroyd B models. The mean ow obtained can be used as a starting point for a modal and nonmodal linear stability analysis, following the analysis performed for second order models.
A theory of finite deformation magneto-viscoelasticity Saxena, Prashant; Hossain, Mokarram; Steinmann, Paul
International journal of solids and structures,
November 2013, 2013-11-00, 20131101, Letnik:
50, Številka:
24
Journal Article
Recenzirano
Odprti dostop
This paper deals with the mathematical modelling of large strain magneto-viscoelastic deformations. Energy dissipation is assumed to occur both due to the mechanical viscoelastic effects as well as ...the resistance offered by the material to magnetisation. Existence of internal damping mechanisms in the body is considered by decomposing the deformation gradient and the magnetic induction into ‘elastic’ and ‘viscous’ parts. Constitutive laws for material behaviour and evolution equations for the non-equilibrium fields are derived that agree with the laws of thermodynamics. To illustrate the theory the problems of stress relaxation, magnetic field relaxation, time dependent magnetic induction and strain are formulated and solved for a specific form of the constitutive law. The results, that show the effect of several modelling parameters on the deformation and magnetisation process, are illustrated graphically.
Introduction Sleep deprivation has a strong impact on facial appearance with visible associated signs of fatigue but the impacts on skin biophysical features still remains unknown. Methods The ...present study investigates the impact of two consecutive nights with sleep restriction to 3 hours per night on facial skin, by using noninvasive instrumental methods for sebum (sebumeter), hydration (corneometer CM 825/Courage & Khazaka), trans-epidermal water loss (tewameter TM 210), biomechanical properties (cutometer MPA 580), pH (PH 900), desquamation (D-squameter and image analysis) quantification and image analysis (ColorFace/Newtone Technologies). Twenty-four healthy Caucasian women aged 30-55 were selected for their well-sleeping with Epworth scale, Pittsburg quality index and homogeneity of their circadian typology with Horne and Ostberg questionnaire. Sleep deprivation was controlled by actimetry, and a sleep diary. Biophysical measurements and image of the face were taken in the morning and the evening the day before and the day after the sleep deprivation. Results We observed that sebum and PIE were more intense in the afternoon than in the morning without any impact of sleep deprivation on these parameters. On the contrary, hydration of the skin surface, pH and viscoelastic properties of the skin e.g. extensibility (Uf), elasticity (Ue), and delayed extensibility (Uv) as well as well single desquamating corneocytes (invisible desquamation) and radiance were significantly reduced after sleep deprivation. Conclusion This study identifies several important skin facial parameters significantly affected by acute sleep deprivation e.g. hydration, acidity, desquamation homogeneity, viscoelastic properties and complexion luminosity and highlights the importance of the sleep quality (or length) in physiological skin homeostasis, aesthetic and comfort. Support (If Any) LVMH Research, France
As counterfeit techniques continue to evolve, ensuring the security of conventional “static” encryption methods becomes increasingly challenging. Here, the viscoelasticity‐controlled relaxation is ...introduced for the first time in a bilayer wrinkling system by regulating the density of hydrogen bond networks in polymer to construct a “dynamic” encryption material. The wrinkling surface can manipulate light during the dynamic relaxation process, exhibiting three stages with frosted glass, structural color, and mirror reflection. By regulating the viscoelasticity of skin layer through UV irradiation, the wavelength and the relaxation rate of the wrinkles can be controlled. As a result, dynamic wrinkling anti‐counterfeiting patterns and time‐resolved multistage information encryption are achieved. Crucially, the encryption material is developed as an anti‐counterfeiting label for packing boxes in daily applications, allowing the encrypted information to be activated manually and identified by naked eyes, surpassing the existing time‐resolved encryption materials in utilization potential. Besides, the dynamic hydrogen bond networks are extended to various dynamic interaction networks, demonstrating the versatility of the dynamic encryption strategy. This work not only provides an additional dimension for dynamic information encryption in daily practical use, but also offers theoretical guidance for the development of advanced optical anti‐counterfeiting and smart display materials in the future.
This study reports a “dynamic” wrinkling system with controllable polymer interaction networks. By regulating the viscoelasticity of polymer interaction networks, the wavelength and the relaxation rate of the wrinkles can be controlled. Consequently, dynamic wrinkling anti‐counterfeiting patterns and time‐resolved multistage information encryption are achieved, which can be further utilized to develop a practical encryption label.
To capture specific characteristics of non-Newtonian fluids, during the past years fractional constitutive models have become increasingly popular. These models are able to capture, in a simple and ...compact way, the complex behaviour of viscoelastic materials, such as the change in power-law relaxation pattern during the relaxation process of some materials. Using the Lagrangian Smoothed-Particle Hydrodynamics (SPH) method we can easily track particle history; this allows us to solve integral constitutive models in a novel way, without relying on complex tasks.
Hence, we develop here a SPH integral viscoelastic method which is first validated for simple Maxwell or Oldroyd-B models under Small Amplitude Oscillatory Shear (SAOS) and start-up channel flows. By exploiting the structure of the integral method, a multi-mode Maxwell model is then implemented. Finally, the method is extended to include fractional constitutive models, validating the approach by comparing results with theory.
•SPH is used to efficiently discretize integral methods for viscoelasticity.•The primary focus is on power-law materials under SAOS.•The proposed scheme works for multi-mode Maxwell model and fractional constitutive equations.•The model can be directly expanded to include non-linear behaviour, allowing for more complex flows.
ObjectiveThe superior frontal cortex (SFC) supports executive functioning, which may be impaired from exposure to repetitive head impacts (RHI); therefore, SFC damage caused by RHI may contribute to ...impaired functioning. This study assessed morphological and viscoelastic changes in the SFC over an ice hockey season, and examined how those changes relate to head impact exposure.DesignProspective-cohort.SettingCollegiate club sports.Participants7 male defensemen/forwards; goaltenders were not included.Interventions (or Assessment of Risk Factors)T1-weighted anatomical and high-resolution magnetic resonance elastography (MRE, 60 Hz vibration) images were collected from participants at two timepoints: pre-season (prior to first game) and post-season (±2 weeks after final game). Participants wore triaxial accelerometers at practices and home games to quantify head impact exposure.SFC volume and thickness were segmented from MPRAGE images using FreeSurfer. A nonlinear inversion algorithm calculated viscoelastic shear stiffness from MRE displacement fields. SFC masks were generated by registering MPRAGE images to the corresponding MRE data. Wilcoxon signed-ranks tests were performed to examine pre-to-post-season differences in SFC volume, thickness, and stiffness. Pearson correlations examined the relationship between the significantly different measures and number of impacts sustained.Outcome MeasuresSFC volume, thickness, stiffness; # head impacts.Main ResultsSFC stiffness decreased from pre-to-post-season (p=0.02); this change was related to # head impacts sustained (p=0.04, r=0.77).ConclusionsRHI may be damaging to the SFC, as decreased stiffness reflects degradation of microstructural tissue components (axons, extracellular matrix, myelination). Furthermore, these results suggest that MRE is more sensitive to RHI-related structural changes than morphometry.
The physical and architectural cues of the extracellular matrix (ECM) play a critical role in regulating important cellular functions such as spreading, migration, proliferation, and differentiation. ...Natural ECM is a complex viscoelastic scaffold composed of various distinct components that are often organized into a fibrillar microstructure. Hydrogels are frequently used as synthetic ECMs for 3D cell culture, but are typically elastic, due to covalent crosslinking, and non-fibrillar. Recent work has revealed the importance of stress relaxation in viscoelastic hydrogels in regulating biological processes such as spreading and differentiation, but these studies all utilize synthetic ECM hydrogels that are non-fibrillar. Key mechanotransduction events, such as focal adhesion formation, have only been observed in fibrillar networks in 3D culture to date. Here we present an interpenetrating network (IPN) hydrogel system based on HA crosslinked with dynamic covalent bonds and collagen I that captures the viscoelasticity and fibrillarity of ECM in tissues. The IPN hydrogels exhibit two distinct processes in stress relaxation, one from collagen and the other from HA crosslinking dynamics. Stress relaxation in the IPN hydrogels can be tuned by modulating HA crosslinker affinity, molecular weight of the HA, or HA concentration. Faster relaxation in the IPN hydrogels promotes cell spreading, fiber remodeling, and focal adhesion (FA) formation – behaviors often inhibited in other hydrogel-based materials in 3D culture. This study presents a new, broadly adaptable materials platform for mimicking key ECM features of viscoelasticity and fibrillarity in hydrogels for 3D cell culture and sheds light on how these mechanical and structural cues regulate cell behavior.
The Maxwellian relaxation and internal friction of a mixture of amorphous polymers: polyvinyl butyral (PVB) - polyvinyl chloride (PVC) are studied. It has been found that by changing the temperature ...(T) and content (j ) of the ingredients, it is possible to control the value of viscoelastic moduli, viscosity, damping force, and energy dissipation due to Maxwellian relaxation caused by the action of ultrasonic vibrations with a frequency (w ) of 0.4 MHz on the composite. The use of computational methods, models, and a phenomenological approach made it possible to differentiate the effects of relaxation and indicate the ways to optimally combine the desired properties of the components in the system.
Досліджено максвеллівську релаксацію та внутрішнє тертя суміші аморфних полімерів: полівінілбутираль (ПВБ) – полівінілхлорид (ПВХ). Встановлено, що змінюючи температуру (Т) та вміст (j) інгредієнтів можна регулювати величину в’язкопружних модулів, в’язкості, демпфруючої сили, дисипації енергії за рахунок максвеллівської релаксації, обумовленої дією на композит ультразвукових коливань частотою (w) 0,4 МГц. Використання обчислювальних методів, моделей та феноменологічний підхід дозволив диференціювати ефекти релаксації і вказати шляхи оптимального поєднання в системі бажаних властивостей компонентів.
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