Stress Stiffening Research Articles

Abstract P443: Role of miRNA-99a, endothelial mineralocorticoid receptor and CD36 in arterial stiffening

The surge in overweight and obesity rates has triggered a rise in metabolic syndrome cases and related cardiovascular diseases, including vascular stiffness and hypertension. We recently found that consumption of a high-fat/high-fructose Western diet (WD) increases the expression and activation of endothelial cell (EC) mineralocorticoid receptor (ECMR), which is associated with arterial oxidative stress, inflammation, remodeling, and vascular stiffening. However, the precise mechanisms by which enhanced activation of ECMR induces vascular stiffening remain to be elucidated. We hypothesize that miR-99a regulates the activated ECMR-induced upregulation of ECCD36 expression, which promotes vascular endothelial dysfunction and aortic stiffness. First, 16 weeks of WD inhibited miR-99a in the aorta which was prevented by additional spironolactone treatment. With bioinformatics, we predicted that miR-99a would target CD36 expression. To test our hypothesis that miR-99a, regulated by ECMR activation, may also directly affect CD36 mRNA expression in cultured ECs, we used miR-99a mimic or inhibitor to transfect ECs with or without palmitic acid treatment. miR-99a mimic also prevented palmitic acid-induced EC CD36 expression and lipid droplet formation. In vivo gene deletion of ECCD36 blunted WD-induced increases in pulse pressure and reduced vascular activity as well as aortic remodeling. These data indicate that the interaction of endothelial-specific ECMR/miRNA/ECCD36 mediates vascular endothelium dysfunction and prompts arterial stiffness.

Stress stiffening effects in flexible Earth observation satellites with spinning appendage

Modern satellites often adopt innovative configurations to meet the escalating requirements of space operations. This study specifically focuses on one such configuration, exemplified by an Earth observation spacecraft equipped with a large rotating payload connected to the main bus through a flexible boom. The rotational motion of the payload is designed to extend the scanned area, resulting in a substantial reduction in the time required to complete a set of measurements, thus enhancing the overall performance. However, this configuration introduces greater complexity both in the analysis of the dynamical behavior and in the design of the control architecture. When dealing with flexible structures subject to rotational motion, as in this scenario, the stiffening effect resulting from inertial loads—particularly the centrifugal action—becomes crucial. In this study, we derive the dynamic equations of the multibody flexible spacecraft using Kane's formulation, which provides a streamlined set of ordinary differential equations by simplifying their derivation. Treating the link as an elastic beam, flexibility is incorporated through a modal decomposition approach that considers nonlinear elastic dynamics, ensuring the inclusion of stress stiffening in the dynamical model. Stress stiffening emerges as a fundamental effect in spinning space structures, where the contribution of the centrifugal force is significant. Incorrect predictions and structural instability for high spinning rates are observed when this effect is neglected. Furthermore, the error associated with overlooking this physical phenomenon is found to be dependent on the spinning rate. We identify kinematical conditions that render this effect negligible in relation to the fundamental deformation frequencies of the space system. Several numerical results are presented and discussed.

A Comprehensive Seismic Monitoring of the Pillar Threatening the World Cultural Heritage Site Chauvet‐Pont d'Arc Cave, Toward Rock Damage Assessment

AbstractFragile geological features must undergo frequent structural health assessments to prevent catastrophic failure events. The mechanical behavior of natural sites is largely guided by vibrations of the earth and environmental exposure, but damage is rarely assessed, except empirically. The Chauvet‐Pont d’Arc cave, a UNESCO World Heritage Site, represents a shining example of fragility that would benefit from monitoring. It is overhung by a rock column known as Abraham's pillar that extends out from the cliff like a natural tuning fork. For this study, we monitored dancing movements of this pillar for over 2 years to analyze its elastic response to weather conditions. Using ambient‐seismic‐noise‐based methods, we identified the pillar's first two natural resonance modes. Through extensive monitoring of the site, we observed the striking temporal evolution of these two resonance frequencies on hourly, daily, seasonal, and pluriannual scales in response to changes in air temperature and insolation. Based on thermo‐acousto‐elastic modeling with a simplified 3D geometric structure, we determined how thermally‐induced stress stiffening affects the rock material, by applying convective and radiative heat fluxes to the model. From the results obtained, we suggest a novel quantitative method based on daily observations that can estimate the level of damage within the rock material. Our work provides a foundation for distinguishing between reversible processes and damage for hazard studies in the frame of climate change. Such knowledge is crucial not only for the preservation of heritage sites but also for enhancing risk assessment protocols and informing conservation efforts worldwide.

Effect of GGBFS and fly ash proportions on fresh, tensile and cracking features of alkali activated concrete with low NaOH concentrations

This study mainly investigated the tensile and cracking features of ash alkali activated concrete with different slag-fly ash proportions and low NaOH concentrations cured at ambient temperature. High-molarity NaOH leads to risk and is costly, whereas, in field conditions, heat curing is difficult. Therefore, in this study three mixes (mix-A, B and C) were developed using 0/100, 20/80, 40/60, 60/40, 80/20, and 100/0 slag-fly ash proportions in this study. Sodium hydroxide (SH) and sodium silicate (SS) were used as activators and concentrations of sodium hydroxide were used as 1M, 2M and 4M in mixes A, B and C respectively, but alkaline ratio (SS/SH) was fixed as 1.5 in all the mixes. Slump, and strength aspects (compressive, split tensile, and flexural) were evaluated. The tensile (tensile strength, tension stiffening) and cracking characteristics (crack spacing, crack width) were evaluated under uniaxial tensile loading on reinforced prismatic members. From test outcomes, workability in terms of slump of the composites decreased with increased percentage of slag or granulated blast furnace slag (GGBFS) in the total binder, but the tensile (tensile stress and tension stiffening effect) and compressive strengths increased with increasing percentage of GGBFS. Better cracking properties (i.e., minimum crack widths and reduced crack spacings) were observed when the mixes contained higher percentages of GGBFS. The obtained crack spacings were correlated with CEB-FIP model code, and existing research studies. The crack spacings obtained in this study are consistent with CEB-FIP model code. Finally, this study demonstrated that when slag-fly ash alkali activated concretes were prepared with solutions containing low NaOH concentrations and cured at room temperature (ambient), there was an increase in the strength and cracking properties with higher percentages GGBFS.

A unified buckling formulation for linear and nonlinear analysis of laminated plates using penalty based [formula omitted] FEM-HSDT model

In this paper, the effect of pre-buckling boundary conditions and the type of nonlinearity for stress stiffening used in different linear and nonlinear buckling approaches is studied for laminated composite plates. The study is conducted using a C0 finite element (FE) plate model, employing a unified C1 higher-order shear deformation theory (HSDT). The set of governing equations is derived using the principle of virtual displacement and solved using the tangent-based arc-length method in conjunction with a simple branch switching technique. The performance of the present C0 FE model is assessed through a validation exercise and comparison with results obtained via the use of ANSYS and, for linear analysis, Navier solution, as well as solutions available in the literature. The influence of the different in-plane loads, boundary conditions, side-to-thickness ratio, fiber orientation, types of imperfection and penalty stiffness matrix are also examined. The results show that the same boundary conditions must be utilized in both pre-buckling and linear eigenvalue analyses for accurate and realistic predictions of critical buckling loads, as confirmed from the nonlinear buckling analyses. Furthermore, the critical buckling loads obtained using Green–Lagrange nonlinearity are observed to be more conservative than those obtained using von Kármán nonlinearity. The nonlinear buckling approach is a generalized approach while the nonlinear eigenvalue approach has a limited range of application.

Effects of rotation on the rolling noise radiated by wheelsets in high-speed railways

Railway rolling noise is produced by the vibration of both the wheelsets and the track; the wheelsets dominate the high frequency noise and become increasingly important at high speed. The effect of rotation on the wheelset vibration and noise radiation is investigated using different wheelset models in a rolling noise prediction model for a wide range of speeds. Each wheelset model takes account of the rotation to a different extent. An axisymmetric finite element model of a flexible rotating wheelset is implemented based on a complex exponential formulation and expressed in either an inertial or a non-inertial frame of reference. The model can include the inertial Coriolis and centrifugal forces and is also extended to include stress stiffening. Modes of the rotating wheel with non-zero number of nodal diameters are split into co- and counter-rotating waves with separated natural frequencies. The extent of the frequency separation depends on the shape of the mode and its dominant component of vibration. At common train speeds the frequency shifts due to stress-stiffening and spin-softening effects are found to be small compared with the gyroscopic effects due to the Coriolis forces. The effect of including the inertial Coriolis and centrifugal forces on the overall A-weighted sound power level is less than 0.3 dB below 400 km/h, while for higher train speeds, differences may exceed 1 dB in some one-third octave bands. Overall, these differences are small compared with other sources of uncertainty in rolling noise modelling, confirming that representing the wheel rotation with a moving load approach provides a suitable approximation for use in rolling noise predictions.

Centrifugal forces enable band gaps that self-adapt to synchronous vibrations in rotating elastic metamaterial

The rotation of mechanical systems can greatly change their modal and wave propagation response. In the classic example of the Foucault pendulum, the Coriolis force from the Earth’s rotation causes the pendulum path to appear deflected to an observer on Earth. More recently, Coriolis forces and gyroscopic effects from rotation have been shown to break time-reversal symmetry, induce non-reciprocity, and change the band structure of phononic crystals. However, rotation also introduces centrifugal forces that can considerably affect the vibration response through stress stiffening and spin softening effects. Although this is well studied in the field of rotor dynamics, the effects of centrifugal forces on the dynamic behavior of acoustic metamaterials (AMs) are still unexplored. In this paper, we study the dependence of torsional band gaps on rotational speed in a rotating shaft with attached local resonances. Different from previous studies, we explicitly consider the effects of stress stiffening in local resonances by introducing a stress stiffening function in a reduced order model of the rotating AM. We then calculate the stress stiffening function for beam-tip-mass resonators and show that these resonators have a resonant frequency that scales linearly with the rotational speed in the asymptotic limit, which in turn causes the band gaps of the AM to depend linearly on the rotational speed. Motivated by the presence of synchronous vibrations in rotating machinery, in which frequency is also linearly dependent on rotational speed, we show that this rotating AM supports band gaps that self-adjust to the synchronous vibration frequency, resulting in attenuation over a wide range of frequencies and thus rotational speeds. Finally, we validate the reduced order model of the rotating AM using 3D finite element analysis. This work contributes a foundational understanding of the effects of rotation in AMs and builds a connection between the AM and rotor dynamics communities, with the potential to introduce novel vibration control in rotor dynamics problems.

Why Are Perivascular Spaces Important?

Perivascular spaces (PVS) and their enlargement (EPVS) have been gaining interest as EPVS can be visualized non-invasively by magnetic resonance imaging (MRI) when viewing T-2-weighted images. EPVS are most commonly observed in the regions of the basal ganglia and the centrum semiovale; however, they have also been identified in the frontal cortex and hippocampal regions. EPVS are known to be increased in aging and hypertension, and are considered to be a biomarker of cerebral small vessel disease (SVD). Interest in EPVS has been significantly increased because these PVS are now considered to be an essential conduit necessary for the glymphatic pathway to provide the necessary efflux of metabolic waste. Metabolic waste includes misfolded proteins of amyloid beta and tau that are known to accumulate in late-onset Alzheimer's disease (LOAD) within the interstitial fluid that is delivered to the subarachnoid space and eventually the cerebral spinal fluid (CSF). The CSF acts as a sink for accumulating neurotoxicities and allows clinical screening to potentially detect if LOAD may be developing early on in its clinical progression via spinal fluid examination. EPVS are thought to occur by obstruction of the PVS that associates with excessive neuroinflammation, oxidative stress, and vascular stiffening that impairs flow due to a dampening of the arterial and arteriolar pulsatility that aids in the convective flow of the metabolic debris within the glymphatic effluxing system. Additionally, increased EPVS has also been associated with Parkinson's disease and non-age-related multiple sclerosis (MS).

Large-amplitude vibration of rotating functionally graded blades including geometrical nonlinearity and stress stiffening effects

The nonlinear frequency responses of functionally graded (ceramic/metal/ceramic) straight/curved blade-type structures are examined under rotation and thermal environment. Here, the geometrical nonlinearity is introduced using Green-Lagrange’s strain via the higher-order shear deformation theory. The constituent materials, i.e. ceramic and metal-alloy, are considered to be temperature-dependent, whereas, the overall blade material properties are evaluated using Voigt’s homogenization scheme via a modified power-law function. The equations of motion are obtained using Hamilton’s principle by including the geometrical nonlinearity and stress stiffening effects. The linear and the nonlinear frequency responses are computed through the developed nonlinear finite element method and Picard’s successive iteration scheme. An exhaustive computation is carried out to report the linear and the nonlinear vibrational behavior of the proposed composite straight/curved blade model at small-to-large amplitudes for various sets of combinations of geometric and material parameters, such as blade span, blade thickness, volume fractions, rotational speed, and temperature.

Photoinduced Dithiolane Crosslinking for Multiresponsive Dynamic Hydrogels.

While many hydrogels are elastic networks crosslinked by covalent bonds, viscoelastic hydrogels with adaptable crosslinks are increasingly being developed to better recapitulate time and position-dependent processes found in many tissues. In this work, 1,2-dithiolanes are presented as dynamic covalent photocrosslinkers of hydrogels, resulting in disulfide bonds throughout the hydrogel that respond to multiple stimuli. Using lipoic acid as a model dithiolane, disulfide crosslinks are formed under physiological conditions, enabling cell encapsulation via an initiator-free light-induced dithiolane ring-opening photopolymerization. The resulting hydrogels allow for multiple photoinduced dynamic responses including stress relaxation, stiffening, softening, and network functionalization using a single chemistry, which can be supplemented by permanent reaction with alkenes to further control network properties and connectivity using irreversible thioether crosslinks. Moreover, complementary photochemical approaches are used to achieve rapid and complete sample degradation via radical scission and post-gelation network stiffening when irradiated in the presence of reactive gel precursor. The results herein demonstrate the versatility of this material chemistry to study and direct 2D and 3D cell-material interactions. This work highlights dithiolane-based hydrogel photocrosslinking as a robust method for generating adaptable hydrogels with a range of biologically relevant mechanical and chemical properties that are varied on demand.

Size-Dependent Rigid–Flexible Coupling Dynamics of Functionally Graded Rotating Moderately Thick Microplates

Micro air vehicles, which are typical small-sized rotating-motion systems, have seen major advancements in recent years. To provide some theoretical basis for developing and producing micro air vehicles, this study establishes a novel rigid–flexible coupling dynamic model for functionally graded (FG) moderately thick rectangular microplates attached to a central rotating rigid hub based on the modified couple stress theory and first-order shear deformation theory. The proposed model incorporates nonlinear coupling term of in-plane deformation to reflect the dynamic stiffening effect caused by rotational motion. Material characteristics of the FG microplate have a linear power-law distribution along the thickness axis. Further, the discrete form dimensionless coupling dynamic equations and their numerical solutions are obtained by combining the Euler–Lagrange equation and the Chebyshev–Ritz method. Convergence and comparative studies are carried out to demonstrate the accuracy and validity of the proposed model. Thereafter, the influence of material length scale parameter, rotational speed, gradient index, and aspect ratio on the frequency of the microplates is investigated. Numerical results reveal that couple stress and dynamic stiffening effects both enhance the rigidity of the microplates, whereas the gradient index decreases the rigidity. Nonlinear coupling term which leads to significant differences in frequency value and trace line can’t be ignored for rotative structure. In-plane motion and its coupling terms play a significant function for the moderately thick or thick microplates. The increase of rotational speed and gradient index will reduce the size dependency of the microplate. Furthermore, the frequency trajectory steering and corresponding mode transition phenomenon are graphically represented.

Self-adapting band gaps in rotating elastic metamaterials

Rotation in mechanical systems can drastically change their vibrational response. For example, it can enable new properties, such as break time-reversal symmetry and induce non-reciprocity in acoustic metamaterials, due to Coriolis forces and gyroscopic effects. Rotation can also be highly detrimental: for example, synchronous vibrations occur in rotating mechanical components and can be extremely damaging when they coincide with system resonances. In addition, centrifugal forces from rotation significantly affect the dynamics of rotating systems, through stress stiffening and spin softening, however their effects on acoustic and elastic metamaterials have rarely been explored. Here, we demonstrate that centrifugal forces in rotating elastic metamaterials enable band gaps that “self-adapt” to synchronous vibrations, attenuating these vibrations over a broadband frequency range. Specifically, this talk presents a reduced order model that captures stress stiffening effects on the band gaps of a rotating elastic metamaterial. The resonators are beams with tip masses oriented perpendicular to the rotational axis, such that stress stiffening causes their resonant frequency to be linearly proportional to the rotational speed. The reduced order models are validated by full finite element simulations of a 3D elastic metamaterial whose band gap self-adapts to synchronous vibrations that are linearly proportional to rotational speed.

Research on 3D Modeling and Dynamic characteristics of wind turbine blade

In order to prevent blade resonance, reduce blade deflection, improve wind turbine power generation efficiency and wind energy utilization rate, the blade model of 3 kW wind turbine is established, and the natural frequency of wind turbine blade is analyzed. Based on the vibration theory, the effects of dynamic stiffening and rotational softening on the natural frequencies of blades are analyzed. Study the change rule of blade vibration mode under rotating speed of 0~300rpm, and analyze the influence of two effects on blade frequency. The results show that at low speed, the rotating softening effect of the blade is obvious, and the vibration frequency decreases; At high speed, the stress stiffening effect is more obvious, the vibration frequency increases, and the coupling vibration has greater destructiveness.

Nonlinear Microscale Mechanics of Actin Networks Governed by Coupling of Filament Crosslinking and Stabilization.

Actin plays a vital role in maintaining the stability and rigidity of biological cells while allowing for cell motility and shape change. The semiflexible nature of actin filaments-along with the myriad actin-binding proteins (ABPs) that serve to crosslink, bundle, and stabilize filaments-are central to this multifunctionality. The effect of ABPs on the structural and mechanical properties of actin networks has been the topic of fervent investigation over the past few decades. Yet, the combined impact of filament stabilization, stiffening and crosslinking via ABPs on the mechanical response of actin networks has yet to be explored. Here, we perform optical tweezers microrheology measurements to characterize the nonlinear force response and relaxation dynamics of actin networks in the presence of varying concentrations of α-actinin, which transiently crosslinks actin filaments, and phalloidin, which stabilizes filamentous actin and increases its persistence length. We show that crosslinking and stabilization can act both synergistically and antagonistically to tune the network resistance to nonlinear straining. For example, phalloidin stabilization leads to enhanced elastic response and reduced dissipation at large strains and timescales, while the initial microscale force response is reduced compared to networks without phalloidin. Moreover, we find that stabilization switches this initial response from that of stress stiffening to softening despite the increased filament stiffness that phalloidin confers. Finally, we show that both crosslinking and stabilization are necessary to elicit these emergent features, while the effect of stabilization on networks without crosslinkers is much more subdued. We suggest that these intriguing mechanical properties arise from the competition and cooperation between filament connectivity, bundling, and rigidification, shedding light on how ABPs with distinct roles can act in concert to mediate diverse mechanical properties of the cytoskeleton and bio-inspired polymeric materials.

Similarity design method for dynamic characteristics of rotating composite blades in thermal environment

A similarity method for rotating composite blades in thermal environment is developed for the problems of difficulty, time consumption, high cost, and risk in the dynamic test under a high-temperature environment. Within this study, a set of scaling laws are derived for thin-walled composite plates based on their dynamic models and the applicability of the scaling laws is demonstrated in the similitude design of composite blades. The present dynamic model takes into account thermal stress and centrifugal stiffening effect. Analytical calculations show that the scaled models at relatively low temperatures can well reproduce the dynamic characteristics of their corresponding prototypes at high temperatures when taking into account the scaling of temperature change and rotational speed.

Meteorological Controls on Reversible Resonance Changes in Natural Rock Arches

AbstractContinuous ambient seismic monitoring is becoming common for structural health assessment of geologic features. However, the ability to detect or predict permanent mechanical change associated with damage requires detailed understanding of reversible drifts in resonance attributes associated with changing meteorological conditions. Here, we analyze the response of 17 sandstone rock arches to changing meteorological conditions during extended vibration‐based monitoring, with a focus on 1 arch in Utah which was continuously monitored for 15 months. Our results show that variations in resonance are correlated with temperature on daily and yearly time scales, but that the temperature sensitivity of frequency changes are variable at different sites and resonance modes, generally ranging from 0.5% to 6% per 10°C. Numerical modeling suggests the primary mechanism governing these frequency drifts is stress stiffening, where confined thermal dilation induces bulk stress changes in the low‐stress, nonlinear elastic regime via fracture closure. Secondary mechanisms affecting resonance attributes are driven by moisture, including formation of shallow pore ice, which can generate sharp frequency changes of up to 17% per −10°C, and moisture‐induced softening. Daily lag times of several hours between temperature and frequency extrema provide constraints on the rock volumes affected by these mechanisms, indicating modal attributes are sensitive to thermally driven changes occurring in the outermost centimeters of the structure. Through improved understanding of the reversible variations of rock mass resonance, our results aid future assessment of irreversible frequency changes associated with damage, and thus structural health monitoring of fragile geologic features.

Under pressure: testing the compressional stress stiffening of synthetic detergents

Studying synthetic detergent deformation properties to improve the production of solid shampoo, conditioner, and facial soap bars.

Detecting Changes in Boundary Conditions based on Sensitivity-based Statistical Tests

Structural health monitoring is a promising technology to automatically detect structural changes based on permanently installed sensors. Vibration-based methods that evaluate the global system response to ambient excitation are suited to diagnose changes in boundary conditions, i.e. changes in member prestress or imposed displacements. In this paper, these changes are evaluated based on sensitivity-based statistical tests, which are capable of detecting and localizing parametric structural changes. The main contribution is the analytical calculation of sensitivity vectors for changes in boundary conditions (i.e., changes in prestress or support conditions) based on stress stiffening, and the combination with a numerically efficient algorithm, i.e. Nelson’s method. One of the main advantages of the employed damage diagnosis algorithm is that, although it uses physical models for damage detection, it considers the uncertainty in the data-driven features, which enables a reliability-based approach to determine the probability of detection. Moreover, the algorithm can be trained and the probability of detecting future damages can be predicted based on data from the undamaged structure—in an unsupervised learning mode—making it particularly relevant for unique structures, where no data from the damaged state is available. For proof of concept, a numerical case study is presented. The study assesses the loss of prestress in a two-span reinforced concrete beam and showcases suitable validation approaches for the sensitivity calculation.

Ratcheting and strain ranges in the shakedown state with stress stiffening using the Simplified Theory of Plastic Zones

The behavior of elastic-plastic structures under cyclic loading can be determined by incremental elastic-plastic analyses where a given load histogram is analysed cycle-by-cycle until shakedown is achieved. Many cycles may be required for this, if a ratchet mechanism is causing plastic strains to accumulate in each cycle until either elastic or plastic shakedown is achieved. The complexity of the elastic-plastic response of a structure is further increased if geometric effects are present. It may be very costly to get the accumulated strains and strain ranges in the state of shakedown by incremental analyses so that simplified or direct methods have been developed as an alternative. The Simplified Theory of Plastic Zones (STPZ) has proven itself for estimating the required quantities in the state of elastic and plastic shakedown within the framework of the 1st order theory, i.e., if the equilibrium conditions are satisfied for the undeformed structure. It is shown in this paper, how the STPZ can be expanded to capture 2nd order effects introduced by the equilibrium of the deformed structure. Some examples are used to demonstrate its applicability and the quality of the results, but also its limitations with respect to determining the accumulated strains and elastic-plastic strain ranges.

Simplified Theory of Plastic Zones in the state of elastic shakedown with stress stiffening

Cyclic loading may cause elastic-plastic strains to accumulate if a ratcheting mechanism is present. After a number of cycles, strain accumulation may cease so that a state of either elastic or plastic shakedown is reached. Determination of strains and other quantities in the state of shakedown (post-shakedown quantities) by means of incremental analyses is costly. Direct methods such as the Simplified Theory of Plastic Zones (STPZ) aim at providing estimates of the post-shakedown quantities, bypassing cycle-by-cycle analyses. If geometric effects such as stress stiffening play a role, determination of accumulated strains even becomes more complicated. The STPZ has been further developed in order to account for the combination of plasticity and stress stiffening with respect to elastic shakedown. The theory is described and illustrated using examples such as a pipe bend subjected to cyclic in-plane bending. The implications of cyclic as opposed to constant stress stiffness are discussed. The effect of stress stiffening on ratcheting interaction diagrams (RID), separating regions of elastic and plastic shakedown in the space of loading parameters, is discussed.