Mechanical Viscoelastic Model Research Articles

Megathrust Locking and Viscous Mantle Flow Induce Continental Shortening in Central Andes

Crustal faults at subduction zones show evidence of activity over geological time, but at the scale of earthquake cycle the mechanical behavior of these faults is not fully understood. Here we construct 2-D viscoelastic models constrained by both horizontal and vertical GPS-derived interseismic velocities to investigate the contribution and interrelation between subduction zone locking, viscous mantle flow, and upper plate faulting on surface deformation in Central Andes. Main pattern of horizontal velocities can be explained by a combination of locking degree and viscous flow, whereas vertical signal is found essential for estimating the locking depth. A sharp deformation gradient near the major back-arc fault suggests an active interseismic shorting across this structure. We further conduct mechanical viscoelastic models with a frictional back-arc fault to analyze its displacement and activation conditions. Our results suggest that the back-arc fault is creeping at ~ 3 mm/year and its motion is mainly driven by the interseismic viscous mantle flow, which spreads plate tectonic stresses broadly across the continent. Moreover, the frictional strength of the back-arc fault must be remarkably weak and its mechanics re-distributes the interseismic deformation and shortens the continental plate in Central Andes. Geological estimates suggest that the long-term shortening rate at the back-arc fault is ~ 10 mm/year, suggesting that this structure can accumulate ~ 7 mm/year of slip deficit, confirming the seismic potential of this structure.

Fault-Tolerant Control for Linear Time-Variant Impulsive Singular Systems Subject to Actuator Saturation and L∞ Disturbances

This paper explores the fault-tolerant control problem for uncertain impulsive singular linear time-variant (LTV) systems in the presence of bounded-power or L∞ disturbances. Here, a saturation avoidance mechanism is employed to prevent faulty actuators from overloading. Also, the conflict between attenuating the effect of L∞ disturbances and enlarging the domain of attraction is tackled by proposing a nonconstant state feedback controller. In addition, the proposed method is capable of tolerating time-varying faults. The suggested method is implemented on a mechanical viscoelastic model of cortical bone with impulsive and time-varying nature to evaluate its competency.

Mathematical modeling of uniaxial mechanical properties of collagen gel scaffolds for vascular tissue engineering.

Small diameter tissue-engineered arteries improve their mechanical and functional properties when they are mechanically stimulated. Applying a suitable stress and/or strain with or without a cycle to the scaffolds and cells during the culturing process resides in our ability to generate a suitable mechanical model. Collagen gel is one of the most used scaffolds in vascular tissue engineering, mainly because it is the principal constituent of the extracellular matrix for vascular cells in human. The mechanical modeling of such a material is not a trivial task, mainly for its viscoelastic nature. Computational and experimental methods for developing a suitable model for collagen gels are of primary importance for the field. In this research, we focused on mechanical properties of collagen gels under unconfined compression. First, mechanical viscoelastic models are discussed and framed in the control system theory. Second, models are fitted using system identification. Several models are evaluated and two nonlinear models are proposed: Mooney-Rivlin inspired and Hammerstein models. The results suggest that Mooney-Rivlin and Hammerstein models succeed in describing the mechanical behavior of collagen gels for cyclic tests on scaffolds (with best fitting parameters 58.3% and 75.8%, resp.). When Akaike criterion is used, the best is the Mooney-Rivlin inspired model.

902 ガス絶縁開閉装置用ニトリルゴムOリングの劣化予測に関する研究(OS9-(1),OS9 オーガナイズドセッション《発電機器の材料・構造解析と評価》)

In this paper, the purpose of this study is lifetime evaluation of seal performance of the O ring made in NBR (Nitrile- Butadiene Rubber) used for sealing up of the GIS (Gas Insulated Switchgear). We developed thermo -mechanical viscoelastic model using finite element analysis to predict aging of EP (Ethylene-Propylene)-rubber O-rings. To expand this life prediction method to NBR O-rings, material property of NBR was investigated experimentally. Stress relaxation tests and biaxial tension tests were performed to identify material property. As a result, experimental and calculated elastic potential showed good coincident and some values related temperature dependency indicate necessity of reexamination.

Time Dependent Viscoelastic Behaviour of EPS Geofoam

A series of laboratory tests was carried out to assess the time-dependent creep behaviour of EPS geofoam at room temperature (23°C) and at 40°C. The experimental data were then used to calibrate and to validate mechanical viscoelastic models along with an empirical Power Law model, at these two temperatures. The viscoelastic models examined were the 3-element (Maxwell-Kelvin), the 4-element (Burgers) and the Modified 4-element models. The modified 4-element model and the base case, the empirical power law model, were found to give the best predictions. As anticipated, the experimental results show that creep rate is higher at elevated temperatures. The results, at 23°C and 40°C, offer a means to assess and model creep behavior in geotechnical applications at normal, and at a practical elevated, temperature where use of EPS geofoam in warmer climate may be a concern.

Viscoelasticity of coagulated alumina suspensions

The solid-to-liquid transition of a model coagulated alumina suspension at concentrations above the gel point was investigated to explore the critical parameter for describing network failure under shear forces. Static (creep and creep-recovery) and dynamic (small and large amplitude oscillatory) shear experiments were combined to examine shear softening in these systems and time-based dependence in the yielding dynamics. The particulate network structure exhibits failure and viscous dissipation under creep and oscillatory shear tests at stress values well below the conventionally defined yield stress. Results from strain recovery tests highlight a time-dependence for failure, where only partial recovery of strain energy was possible once a specific duration of creep was surpassed. The system was observed to fail at a common strain value across all methods of rheology testing. These results are self-consistent, showing a clear transition from the linear to non-linear viscoelastic region for a coagulated material under shear stress. It provides the starting point to incorporate mechanical viscoelastic models to extract time constants for yielding behaviour. This work also presents one of the first reported LAOS and creep results for particulate suspensions using a vane geometry.

Shape memory properties of polyurethane/poly(oxyethylene) blends

Shape memory behavior of polymer blends consisting of thermoplastic polyurethane (PU) and crystalline poly(oxyethylene) (POE) have been investigated. PU is in a rubbery state at room temperature and has an ability to recover from a deformed temporary shape to a permanent shape by entropic elasticity, and POE has a role to fix the temporary shape by crystallization and solidification of the system. As a result, excellent shape memory properties can be obtained by blending elastic PU and crystalline POE. With increasing POE content in the blend, the shape fixity ratio below crystallization temperature was increased to almost 100%, but shape recovery above melting temperature occurred more slowly. These experimental results were reasonably described by viscoelasticity and the phase separated morphology of the PU/POE blend. The effect of changing molecular weight of POE on the shape memory behavior was not remarkable. The shape recovery behavior was found to be expressed by using a simple mechanical viscoelastic model.

210 MR流体コンポジットのレオロジー特性とその動的機械モデル(1)(OS2-3 機能性流体工学の先端融合化,OS2 機能性流体工学の先端融合化,オーガナイズドセッション)

210 MR流体コンポジットのレオロジー特性とその動的機械モデル(1)(OS2-3 機能性流体工学の先端融合化,OS2 機能性流体工学の先端融合化,オーガナイズドセッション)

Shape-memorized crosslinked ester-type polyurethane and its mechanical viscoelastic model

A series of shape-memorized crosslinked ester-type polyurethanes (PUs), based on different compositions of 4,4′-diphenyl methane diisocyanate (MDI), poly(butylene adipate) glycol (PBAG) with different molecular weight (MW) and trimethylol propane (TMP), were synthesized. The morphology of samples was investigated by using DSC, WAXD, and dynamic mechanical analysis (DMA). It was found that the morphology of the soft segment, which was PBAG with a different MW, was in an amorphous state and no crystalline domain was found. By increasing the crosslinked density (varying the content of TMP) or decreasing the length of the soft segment (MW of PBAG), the glass transition temperature of studied samples increased. But the range of transition broadened and the modulus ratio E′−20°C)/E′+20°C) also decreased. The shape-memory behavior was studied by the bending test method adopted from the shape-memory alloy. The sample with high Tg showed not only a high recovered temperature (Tr) but also a high recovered rate (Vr) with a high modulus ratio. By introducing the chemical crosslinked structure, the deformed samples completely recovered their original shape and rendered shape-memory behavior under the complex deformation. The shape-memorized crosslinked ester-type PUs can be applied at different operating temperatures. A mechanical viscoelastic model is discussed for the shape-memory behavior of PUs, and the modified Bonart's viscoelastic model properly describes the mechanism of the shape memory of PUs. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1305–1319, 1999

Wave splitting in linear viscoelasticity

The problem of transient propagation in a homogeneous linear viscoelastic solid is investigated by means of the wave splitting technique. Two mechanical viscoelastic models are considered in particular, corresponding respectively to a single Maxwell element and to the series of a Maxwell element plus a Kelvin element. Analytical solutions for the split field are evaluated in terms of the wave propagator via the Laplace transforms. The reflectivity of a viscoelastic half-space is explicitly for the two mechanical models and the corresponding inverse problem is approached. Finally, the reflection and transmission problem for a transient wave is solved for a viscoelastic layer.

Theoretical Foundation on a Noninvasive Estimation for Viscoelastic Mechanical Property of Blood Vessels by Ultrasonic Doppler Effect

The method used in this paper is developed to estimate the degree of viscoelasticity of the blood vessel wall in a noninvasive mechanical method. In this proposed method, we can obtain an output waveform connected with mechanical behavior of blood vessels by using Ultrasonic Doppler Effect Sensory (UDES). Characterizing parameters on this waveform are established to estimate the mechanical properties of blood vessels. By analyzing the characteristics of these parameters, we attempt to estimate the viscoelastic property of blood vessels. Previously, it was found that these parameters are related to viscoelastic mechanical properties of materials. In this paper, we carried out computer analysis on the mechanical viscoelastic model and compared the theoretical behavior of blood vessels with the experimental output waveform by UDES. From these results, it was proved that values of these parameters connect with the change of the viscoelastic mechanical property of blood vessels. Therefore, the characterizing parameters of experimental output waveforms can be used to estimate the viscoelastic property of blood vessels in a noninvasive method.

Visco-elastic properties of the bladder wall.

Stepwise cystometry is a new method proposed to analyse the visco-elastic properties of the bladder. It is based on a mathematical analysis of the pressure decay after a stepwise filling. By assumption of a mechanical visco-elastic model of bladder tissue and a model of the geometry, the derived parameters are interpreted as elasticity and viscosity moduli. Static cystometry is involved in this new procedure. From analysis by stepwise cystometry it is concluded that static cystometry attained by following a slow-filling procedure is unacceptable in studying elastic behaviour.