Hysteresis Stiffness Research Articles

Aortic Stiffness Hysteresis in Isolated Mouse Aortic Segments Is Intensified by Contractile Stimuli, Attenuated by Age, and Reversed by Elastin Degradation

Aim: Cyclic stretch of vascular tissue at any given pressure reveals greater dimensions during unloading than during loading, which determines the cardiac beat-by-beat hysteresis loop on the pressure-diameter/volume relationship. The present study did not focus on hysteresis during a single stretch cycle but investigated whether aortic stiffness determined during continuous stretch at different pressures also displayed hysteresis phenomena.Methods: Aortic segments from C57Bl6 mice were mounted in the Rodent Oscillatory Set-up for Arterial Compliance (ROTSAC), where they were subjected to high frequency (10 Hz) cyclic stretch at alternating loads equivalent to a constant theoretical pulse pressure of 40 mm Hg. Diastolic and systolic diameter, compliance, and the Peterson elastic modulus (Ep), as a measure of aortic stiffness, was determined starting at cyclic stretch between alternating loads corresponding to 40 and 80 mm Hg, at each gradual load increase equivalent to 20 mm Hg, up to loads equivalent to pressures of 220 and 260 mm Hg (loading direction) and then repeated in the downward direction (unloading direction). This was performed in baseline conditions and following contraction by α1 adrenergic stimulation with phenylephrine or by depolarization with high extracellular K+ in aortas of young (5 months), aged (26 months) mice, and in segments treated with elastase.Results: In baseline conditions, diastolic/systolic diameters and compliance for a pulse pressure of 40 mm Hg were larger at any given pressure upon unloading (decreasing pressure) than loading (increasing pressure) of the aortic segments. The pressure-aortic stiffness (Ep) relationship was similar in the loading and unloading directions, and aortic hysteresis was absent. On the other hand, hysteresis was evident after activation of the VSMCs with the α1 adrenergic agonist phenylephrine and with depolarization by high extracellular K+, especially after inhibition of basal NO release with L-NAME. Aortic stiffness was significantly smaller in the unloading than in the loading direction. In comparison with young mice, old-mouse aortic segments also displayed contraction-dependent aortic hysteresis, but hysteresis was shifted to a lower pressure range. Elastase-treated segments showed higher stiffness upon unloading over nearly the whole pressure range.Conclusions: Mouse aortic segments display pressure- and contraction-dependent diameter, compliance, and stiffness hysteresis phenomena, which are modulated by age and VSMC-extracellular matrix interactions. This may have implications for aortic biomechanics in pathophysiological conditions and aging.

Structural responses of large-sized floating wind turbine with consideration of mooring-line dynamics based on coupled FEM simulations

ABSTRACT The dynamic response of a 5 MW floating wind turbine is examined using the coupled finite element simulations, and the dynamic effects of the catenary is considered, while the coupling between flexible components are included. The restoring performance of the mooring-line is analysed based on the vector equations and numerical simulations. The stiffness hysteresis and the influence of the catenary dynamics on the restoring performance are studied. Then the structural responses undergoing wind and wave loads, are examined. Our results show that the mooring-line tension significantly rise due to catenary dynamics, and the snap tension gets around three times larger. The mooring-line stiffness presents a hysteresis character, owing to the fluid/structural damping, which becomes more obvious with the increase of motion frequency/amplitude. Moreover, the structural response gets smaller principally because of the hysteresis effect. The spar displacement and the tower root stress become respectively 18.4% and 32.7% smaller.

On the stiffness hysteresis of profiled rail guides

Profiled rail guides are standard components extensively used in machine tools. While produced and developed further for decades, this paper shows for the first time nonlinear hysteretic behavior in the deflection response to mechanical loading after preload liftoff. We investigate characteristics of the hysteresis by measuring overall deflection as well as strain directly on the raceways and at the flanks. The obtained results are reproducible for different linear guides and on different test benches. Findings are merged into a parametric model, which assumes friction in the rolling element contact as the origin of the phenomenon. The model predicts the measured hysteresis curve well. In addition, an effective compensation method is proposed and successfully employed to reduce hysteresis errors.

Prediction of higher-order harmonics generation due to contact stiffness hysteresis using Harmonic Balance: theory and experimental validation

In the presented paper, an analytical approach based on the Harmonic Balance method is used to evaluate amplitudes of higher-order harmonics generated due to the interaction of a propagating shear wave with surfaces in frictional contact. The motion between surfaces is initially assumed to be of symmetric hysteretic stick-and-slip type. Experimental investigation is performed on steel samples with prepared contact surfaces, in order to validate the introduced solution approach. It shows that the hysteretic behavior obtained from the experiment exhibits asymmetric characteristic features. Consequently, a new asymmetric description of the hysteretic stress–strain relation is developed and used to confirm these findings. As a result, both qualitative and quantitative agreement between considered investigation methods are achieved. Finally, the identification study shows the impact of higher-order harmonics on particular features of the stiffness hysteresis.

Experimental assessment of the static stiffness of machine parts and structures by changing the magnitude of the hysteresis as a function of loading

Abstract Static stiffness is determined by one-sided loading and unloading of machine parts relative to the selected base. For each structure, there will be some loss of potential energy due to the dissipative forces that occur during the loading inside the structure. This loss is manifested in hysteresis in the stiffness diagram. A new approach to the assessment of static stiffness consists in gradual, bilateral loading and unloading of the structure through the effect of static forces of different magnitude. In this process, the stiffness hysteresis varies, depending on the intrinsic nature of the dissipative forces, a specific property suitable for assessing the condition of machines.

Deformation dependencies of sand stiffness

Convention does not provide a solution combining drained and undrained response, loss and recovery of sand stiffness, all in one irregular loading sequence. Alas, such solution is necessary for designing offshore wind turbine foundations and predicting soil behavior during (and after) seismic events. To gain deeper understanding of the fundamental phenomenon governing disturbed sand behavior, unconventional testing procedures were attempted using a frictionless triaxial apparatus. The resulting observations revealed a new physical phenomenon (deformation dependent stiffness hysteresis loops). The new observations were then used to derive an unconventional model (BSM), which uses a strain (deformation) envelope.

Validation of a dynamic joint contracture measuring device in a live rabbit model of arthrofibrosis.

The current method of measuring arthrofibrosis in live rabbits is critically limited. Specifically, this method involves radioactive fluoroscopy, error-prone goniometric measurements, and static joint angle outcomes that fail to approximate the compliance of tissues surrounding the joint. This study aims to validate a novel method of capturing the compliance of contracted tissues surrounding the joint without the use of fluoroscopy or animal sacrifice. Surgically induced contractures of one-hundred and eight rabbits were measured using the current standard of contracture measurement (a pulley system) as well as a newly designed dynamic load cell (DLC) device. The DLC device was highly reliable when compared to the pulley system (r = 0.907, p < 0.001). Finally, the DLC device produced joint stiffness hysteresis curves capable of approximating the compliance of stiff joint tissues, ultimately calculating a mean joint stiffness of 1.57 ± 1.31 N · m · rad-1 (range, 0.33-6.37 N · m · rad-1 ). In conclusion, the DLC device represents a valid method for measuring joint contractures. Further, the DLC device notably improves current techniques by introducing the capacity to approximate the compliance of contracted tissues in living rabbits. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Tracking control of variable stiffness hysteretic-systems using linear-parameter-varying gain-scheduled controller

Tracking control of systems with variable stiffness hysteresis using a gain-scheduled (GS) controller is developed in this paper. Variable stiffness hysteretic system is represented as quasi linear parameter dependent system with known bounds on parameters. Assuming that the parameters can be measured or estimated in real-time, a GS controller that ensures the performance and the stability of the closed-loop system over the entire range of parameter variation is designed. The proposed method is implemented on a spring-mass system which consists of a semi-active independently variable stiffness (SAIVS) device that exhibits hysteresis and precisely controllable stiffness change in real-time. The SAIVS system with variable stiffness hysteresis is represented as quasi linear parameter varying (LPV) system with two parameters: linear time-varying stiffness (parameter with slow variation rate) and stiffness of the friction-hysteresis (parameter with high variation rate). The proposed LPV-GS controller can accommodate both slow and fast varying parameter, which was not possible with the controllers proposed in the prior studies. Effectiveness of the proposed controller is demonstrated by comparing the results with a fixed robust <TEX>$\mathcal{H}_{\infty}$</TEX> controller that assumes the parameter variation as an uncertainty. Superior performance of the LPV-GS over the robust <TEX>$\mathcal{H}_{\infty}$</TEX> controller is demonstrated for varying stiffness hysteresis of SAIVS device and for different ranges of tracking displacements. The LPV-GS controller is capable of adapting to any parameter changes whereas the <TEX>$\mathcal{H}_{\infty}$</TEX> controller is effective only when the system parameters are in the vicinity of the nominal plant parameters for which the controller is designed. The robust <TEX>$\mathcal{H}_{\infty}$</TEX> controller becomes unstable under large parameter variations but the LPV-GS will ensure stability and guarantee the desired closed-loop performance.

CARBON BLACK FOR RACING AND MOTORCYCLE TIRE TREADS. PERFORMANCE MODEL DEVELOPMENT

Abstract Racing tires and motorcycle tires present individual segments of the tire market. For instance, while the average life of car and truck tires is 50 000 miles, the average life of race tires is 100 miles. Because tires play a critical role in a race, technical demands to assure safety and performance are growing. Similarly, tires have a large influence on safety, handling/grip, and performance of the rapidly growing world fleet of motorcycles, due to the fact of only two wheels being in contact with the ground. Thus, the common feature of both market segments is that the typical tire compromise of wear, rolling resistance, and traction is strongly weighted toward traction. Most of the recent efforts of rubber scientists have been directed toward lowering rolling resistance of the tread compounds, which left a certain void in the science of compounding for racing and motorcycle treads. Particularly, the industrial assortment of polymers and fillers used for motorcycle treads is commonly different from that used for car or truck treads, but it is not known how the filler properties affect the hysteresis–stiffness compromise. The objective of this study is to evaluate the effects of the carbon black characteristics on the important properties of a typical racing and motorcycle tire tread compound. More than 50 individual carbon blacks were mixed in a SBR formulation. The acquired data were statistically analyzed, and a linear multiple regression model was developed to relate rubber properties (responses), such as static modulus, complex dynamic modulus, hysteresis, and viscosity to the key carbon black characteristics (variables) of surface area, structure, aggregate size distribution, and surface activity. Prediction profiles created from the model demonstrate rubber performance limits for the range of carbon blacks tested, and indicate the niches to provide required combinations of the rubber properties.

Linear Parameter-varying Control for Active Vibration Isolation Systems with Stiffness Hysteresis

We consider the use of linear parameter-varying methods for the control of stiffness hysteresis in vibration isolation systems. We assume that the hysteresis model is known, and we describe it using a stiffness parameter that takes values in a compact convex set. The proposed parameter-dependent controller is continuously scheduled based on real-time measurements or estimates of the stiffness, and provides guaranteed stability and performance for the full range of stiffness variability. The method is applied to a simplified model of a microgravity vibration isolation system with an umbilical stiffness hysteresis non-linearity. Simulations show that the parameter-varying design is stable in the presence of hysteresis and that the desired isolation performance is achieved over the full range of displacements considered. The results are compared with those obtained with a fixed robust H∞ controller that considers the stiffness variability as uncertainty. We discuss robustness issues and demonstrate the effect of hysteresis model uncertainty in the implementation of the proposed control scheme.

Hysteresis loop behavior of the aorta and other extensible tissues.

Hysteresis loop behavior of the aorta and other extensible tissues.