This paper presents a comprehensive review on different theoretical elastic and viscoelastic foundation models in oscillatory systems. The review covers the simplest foundation models to the most ...complicated one and fully tracks the recent theories on the topic of mechanical foundations. It is fully discussed why each theory has been developed, what limitations each one contains, and which approaches have been applied to remove these limitations. Moreover, corresponding theories about structures supported by such foundations are briefly reviewed. Subsequently, an introduction to popular solution methods is presented. Finally, several important practical applications related to the linear and nonlinear foundations are reviewed. This paper provides a detailed theoretical background and also physical understanding from different types of foundations with applications in structural mechanics, nanosystems, bio-devices, composite structures, and aerospace-based mechanical systems. The presented information of this review article can be used by researchers to select an appropriate kind of foundation/structure for their dynamical systems. The paper ends with a new idea of intelligent foundations based on nanogenerators, which can be exploited in future smart cities for both energy harvesting and self-powered sensing applications.
We present a model to study the non-steady V-shaped peeling of a viscoelastic thin tape adhering to a rigid flat substrate. Geometry evolution and viscoelastic creep in the tape are the main features ...involved in the process, which allows to derive specific governing equations in the framework of energy balance. Finally, these are numerically integrated following an iterative scheme to calculate the process evolution assuming different controlling conditions (peeling front velocity, peeling force, tape tip velocity). Results show that the peeling behavior is strongly affected by viscoelasticity. Specifically, for a given applied force, the peeling can either be prevented, start and stop after some while, or endlessly propagate, depending on the original undeformed tape geometry. Viscoelasticity also entails that the interface toughness strongly increases when the tape tip is fast pulled, which agrees to recent experimental observations on tougher adhesion of natural systems under impact loads, such as see waves and wind gusts.
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•Viscoelastic V-peeling of thin tapes leads to non-stationary propagation.•Both the peeling force and angle may present non-monotonic time-history.•Peeling propagation may start and stop after some while due to load and geometry.•Impact loads induce enhanced toughness, as reported for mussels and spiders anchors.•Tape viscoelasticity leads to delayed peeling start after force application.
This study aims to facilitate intracranial simulation of traumatic events by determining the mechanical properties of different anatomical structures of the brain. Our experimental indentation ...paradigm used fresh, post-operative human tissue, which is highly advantageous in determining mechanical properties without being affected by postmortem time. This study employed an inverse finite element approach coupled with experimental indentation data to characterize mechanical properties of the human hippocampus (CA1, CA3, dentate gyrus), cortex white matter, and cortex grey matter. We determined that an uncoupled viscoelastic Ogden constitutive formulation was most appropriate to represent the mechanical behavior of these different regions of brain. Anatomical regions were significantly different in their mechanical properties. The cortex white matter was stiffer than cortex grey matter, and the CA1 and dentate gyrus were both stiffer than cortex grey matter. Although no sex dependency was observed, there were trends indicating that male brain regions were generally stiffer than corresponding female regions. In addition, there were no statistically significant age dependent differences. This study provides a structure-specific description of fresh human brain tissue mechanical properties, which will be an important step toward explicitly modeling the heterogeneity of brain tissue deformation during TBI through finite element modeling.
Discriminating bacterial adhesion profiles at strain‐specific level is crucial for simulating and predicting infections and persistence, as well as developing more efficient antibacterial therapies. ...Herein, it is proposed that label‐ and receptor‐free bacterial discrimination can be achieved by dynamic viscoelastic and adhesion monitoring over specified timescales using the quartz crystal microbalance with dissipation monitoring (QCM‐D). Using two closely related E. coli strains, ATCC 8739 and JM109(DE3), it is shown that their viscoelastic and adhesion properties evolve in time through strain‐specific profiles that are clearly distinguishable over a period of 3–4 h. In addition, the viscoelasticity of both E. coli strains shows a strong strain‐specific dependence on the medium ionic strength, allowing to further amplify the differences in the bacterial adhesion signatures. Furthermore, the viscoelastic and adhesion behaviors of the two E. coli strains with two additional bacteria, Citrobacter freundii and Serratia marcescens, are compared. For all four bacteria, distinct viscoelastic profiles and adhesion fingerprints emerge over similar timescales that allow to reliably discriminate the various bacteria. These results and similar studies on other bacteria might have pharmacological benefits, for instance, by highlighting the role of bacterial–substrate adhesion and viscoelastic properties on disease pathogenesis and persistence, toward developing more effective therapies.
Dynamic viscoelastic and adhesion monitoring with quartz‐crystal microbalance enables label‐free bacterial discrimination. The time‐evolution of the dissipation and mass‐loading signals displays strain‐specific profiles with clear differences that become pronounced over time scales of 3 h. Unique adhesion fingerprints, obtained from the dissipation versus frequency plots, provide further insight into pharmacologically relevant, bacterial‐specific adhesion mechanisms.
Abstract The strategy using water as a medium for dynamic modulation of competitive plasticity and viscoelasticity provides a unique perspective to attain adaptive materials. We reveal sustainable ...polymers, herein cellulose phenoxyacetate as a typical example, with unusual water-responsive dual-mechanic functionalities addressed via a chronological water training strategy. The temporal significance of such water-responsive mechanical behaviors becomes apparent considering that a mere 3-minute exposure or a prolonged 3-hour exposure to water induced different types of mechano-responsiveness. This endows the materials with multiple recoverable shape-changes during water and air training, and consequently even underlines the switchability between the pre-loaded stable water shapes (> 20 months) and the sequentially fixed air shapes. Our discovery exploits the competitive mechanics initiated by water training, enabling polymers with spatially regulated microstructures via their inherently distinct mechanical properties. Insights into the molecular changes represents a considerable fundamental innovation, can be broadly applicable to a diverse array of hydroadaptive polymers.
•By analyzing the viscoelastic heat production principle of various materials, the thermal effect principle of focused ultrasound is applied for defect detection in viscoelastic materials.•The ...thermal defect detection method of focused ultrasound overcomes the limitation of the half-wavelength sensitivity of traditional ultrasonic nondestructive testing technology.•The variation rule of surface temperature of different size and depth defect specimens is analyzed to provide the theoretical basis for the subsequent quantitative detection of viscoelastic material defects.
Viscoelastic materials will absorb and dissipate energy under stress, resulting in energy loss and heat generation. The conventional non-destructive testing methods have certain limitations when it comes to detecting near-surface defects in viscoelastic materials. In this paper, a detection method of near-surface defects based on focused ultrasonic thermal effect is proposed. Firstly, the difference in thermal effects caused by defective and non-defective regions of the material under ultrasound is analyzed according to the stress response equation of viscoelastic materials, and the detection principle is elucidated. Secondly, the feasibility of this method is verified through finite element simulation with an example of plexiglass material Subsequently, the variations in the surface temperature distribution of defective specimens with varying diameters and depths are analyzed. Finally, experimental validation reveals that ultrasonic waves operating at 1.12 MHz successfully detect artificial defects with a diameter of 1 mm. With the increase of the equivalent diameter of the defect, the width of the low-temperature depression area in the surface temperature field exhibits a linear increase relationship. With the increase of the defect depth, the surface temperature difference between the corresponding position of the defective and the surrounding non-defective area gradually decreases. This method effectively overcomes the half-wavelength limitation and introduces a novel detection approach for near-surface defect identification in viscoelastic materials such as plexiglass.
This work aims to examine modal damping behavior in a delaminated viscoelastic structure. A numerical assessment of a viscoelastic delaminated structure using one-dimensional theories based on the ...Carrera Unified Formulation (CUF) was conducted to achieve this goal. The CUF-based models were formulated with Lagrange polynomials and a layer-wise approach, which made it possible to simulate inter-layer defects with relative ease, computational efficiency, and accuracy similar to 3D models. The current framework is based on time-domain method verification and exploits the frequency-based structural damping model to estimate the modal loss factor and natural damped frequency. The numerical outcomes confirm the approximation of the viscoelastic damping by the structural damping model and validate the adopted numerical method for solving the complex frequency-dependent eigenvalue problem with a comparison of the literature. In conclusion, by evaluating the modal parameters, this research provides an innovative, comprehensive understanding of the viscoelastic damping mechanism in a delaminated structure. The proposed numerical method based on the CUF can be used to simulate inter-layer defects and determine the damping behavior of viscoelastic structures, which can have significant implications for structural health monitoring and maintenance.
The rapidly decreasing dimensions of many technological devices have spurred interest in confinement effects. Long before, living organisms invented ingenious ways to cope with the requirement of ...space-saving designs down to the cellular level. Typical length scales in cells range from nanometres to micrometres so that the polymeric constituents of the cytoskeleton are often geometrically confined. Hence, the mechanical response of polymers to external confinement has potential implications both for technology and for our understanding of biological systems alike. Here we report a study of in vitro polymerized filamentous actin confined to emulsion droplets. We correlate observations of the microstructure, local rheological properties and single-filament fluctuations. Enforcing progressively narrower confinement is found to induce a reduction of polymer fluctuations, network stiffening, structural heterogeneities and eventually cortex formation. We argue that the structural and mechanical effects can be consistently explained by a gradual suppression of single-polymer eigenmodes.
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