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Contact mechanics theories are commonly developed using the half-space approximation, which may raise concerns when dealing with contact region sizes comparable to or even larger than the size of the contacting bodies. In this study, we examine the normal adhesive contact between a rigid, wavy indenter and a viscoelastic substrate with a finite thickness. To achieve this, we utilize a recently developed finite element model that incorporates adhesive interactions based on the Lennard–Jones potential law. The results demonstrate that adhesive behavior is influenced by a combination of rate and size effects. Additionally, when considering non-negligible viscous effects, an optimal thickness can be determined to maximize the pull-off stress. [ABSTRACT FROM AUTHOR]

Low-temperature cracking is one of the most common failures in asphalt pavements, especially in cold regions. Accordingly, considerable amount of research has been performed in order to understand the low-temperature cracking mechanisms and to propose test methods for characterizing and determining cracking performance of bitumen and asphalt mixtures under freezing conditions. The existing test methods, however, require expensive equipment and skilled technicians; they are thus not well suited for routine tests. As a contribution to mitigate this situation, this study intends to investigate experimentally and characterize numerically the low-temperature cracking behavior of bitumen and mastic materials using a refined thermal cracking test method. The proposed method, the annular restrained cold temperature induced cracking (ARCTIC) test, allows to determine the low-temperature cracking properties of the mastic and bitumen with a relatively simple setup. In this paper, finite element (FE) modeling is used for evaluating the effect of test parameters on the temperature, stress and strain gradients induced in the specimen during the test. The ARCTIC test is employed to measure cracking temperatures of two bitumen and two mastic materials. The measurements repeatability is examined and the effect of bitumen type on the thermal cracking potential of bitumen and mastic is evaluated. FE modeling is employed to examine the effect of thermomechanical parameters on thermal cracking performance of the materials and to back-calculate fracture stress and strain from measurements. The results highlight the potential of the proposed test and analysis method for evaluation of low-temperature cracking in bitumen and asphalt mastic. [ABSTRACT FROM AUTHOR]

Using the diaphragm-type air spring as the research object. The ratio of the vertical stiffness change caused by compressed air to the total vertical stiffness change was calculated, and it was determined that the nonlinearity of air spring vertical stiffness was mainly caused by the deformation stiffness of the rubber airbag. The variation law of vertical dynamic stiffness of air spring was predicted by theory: due to the material's viscoelasticity, the vertical dynamic stiffness rises as the excitation frequency rises, and the vertical dynamic stiffness decreases with the increase of excitation amplitude due to the damping of the material. An air spring finite element analysis (FEA) and experiment were conducted. The results show that the vertical dynamic stiffness obtained through simulation and experiment is consistent with the theoretical prediction, when various factors such as material nonlinearity, element coupling, and stiffness value sensitivity were considered. This proves that the predicted vertical dynamic stiffness variation law is reliable. The vertical dynamic stiffness obtained from both simulation and experiment showed a strong correlation in numerical values, which verified the accuracy of the FEA model of air spring established in this paper. [ABSTRACT FROM AUTHOR]

Background: Mechanical characterization of materials that solely relies on global responses may overlook important local behavior that significantly affects the characterization of material properties. Field displacements such as from digital image correlation (DIC) can provide high-fidelity experimental data, which combined with finite element method (FEM) can form DIC-FEM inverse method that can better account for complex mechanical properties of materials. Despite its capability, the DIC-FEM inverse method has been mainly applied to an elastic-dominant regime even though inelastic deformation is important in many engineering materials. Specifically, the DIC-FEM inverse method has not been fully extended to viscoelastic materials due to the complex representation of the time-dependent modulus. Objective: This study aimed at establishing a DIC-FEM inverse framework to identify constitutive properties of homogeneous elastic and viscoelastic materials. Methods: Two example materials (i.e., polyetheretherketone (PEEK) and a viscoelastic fine aggregate matrix (FAM) with a bituminous binder) were selected for the elastic and viscoelastic investigation, respectively. Both were experimentally tested using three-point bending incorporated with DIC. FEM simulated the experiment and the Nelder-Mead nonlinear optimization algorithm was implemented to solve the inverse problem. Results: The DIC-FEM inverse method successfully identified Young's modulus of an example linear elastic PEEK and the linear viscoelastic relaxation modulus of FAM. Conclusions: The resulting DIC-FEM inverse method is applicable to various materials with inelastic deformation and can be extended to localized behavior induced by microstructure heterogeneity and fracture. [ABSTRACT FROM AUTHOR]

The components of the stress-strain state of rubber shock absorbers under viscoelastic deformation are investigated. The contraction of rubber shock absorber under the action of a vertical force and a combination of vertical and shear forces is calculated. The dependence of the contraction of the structure on time was obtained. The specific mechanical properties inherent in rubber, such as the weak compressibility of the material and deformation viscoelasticity deformation, the mathematical modeling of which involves significant mathematical difficulties, were taken into account. In the numerical calculation, the weak compressibility of rubber was modeled using a finite element moment scheme for weakly compressible materials, the essence of which is the triple approximation of displacement fields, strain components and volume change function. For the mathematical modeling of the viscoelastic nature of strains, the hereditary Boltzmann–Volterra theory with exponential relaxation kernel is used. On the basis of the Lagrange variational principle, a system of resolving integral equations of viscoelasticity is obtained taking into account the weak compressibility of the material, and an iterative procedure for its solution is proposed. The modified Newton–Kantorovich method is used to solve a nonlinear boundary value problem. The numerical solution is obtained by the finite element method in the case of viscoelastic deformation of rubber material. The calculation is performed for the case when the rubber layer is vulcanized to metal plates. The influence of the viscoelastic properties of the rubber on the value of rubber shock absorber contraction for two cases of mechanical loading is investigated. Calculations were carried out for two rubber grades: 2959 and 1562. [ABSTRACT FROM AUTHOR]

Understanding tissue rheology is critical to accurately model the human heart. While the elastic properties of cardiac tissue have been extensively studied, its viscous properties remain an issue of ongoing debate. Here we adopt a viscoelastic version of the classical Holzapfel Ogden model to study the viscous timescales of human cardiac tissue. We perform a series of simulations and explore stress–relaxation curves, pressure–volume loops, strain profiles, and ventricular wall strains for varying viscosity parameters. We show that the time window for model calibration strongly influences the parameter identification. Using a four-chamber human heart model, we observe that, during the physiologically relevant time scales of the cardiac cycle, viscous relaxation has a negligible effect on the overall behavior of the heart. While viscosity could have important consequences in pathological conditions with compromised contraction or relaxation properties, we conclude that, for simulations within the physiological range of a human heart beat, we can reasonably approximate the human heart as hyperelastic. [ABSTRACT FROM AUTHOR]

Background: The viscoelastic properties of aortic tissue dictate vessel behavior in certain disease states, injury modalities, and during some endovascular procedures. Objective: We characterized the viscoelastic response of porcine abdominal aortic tissue via test and simulation to demonstrate the utility of a viscoelastic anisotropic (VA) constitutive model. Methods: In this study, the measured stress relaxation response for five samples and uniaxial tensile testing for one sample measured with the digital image correlation (DIC) technique were used to identify material parameters for the VA model using an inverse method through finite element analysis (FEA). Results: Based on the stress relaxation test, the values of the stress-like parameter μ , relative stiffness of the fibers k 1 , dimensionless parameter k 2 , angle of fibers γ , dispersion parameter κ , relaxation times for the ground matrix T g 1 and collagen fibers T f 1 and the dimensionless parameters for the ground matrix β g 1 and collagen fibers β f 1 for 0 degree specimen orientation were 12.1 ± 8.96 kPa, 77.3 ± 46.4 kPa, 0.032 ± 0.043, 30.25 ± 6.81°, 0.19 ± 0.06, 0.028 ± 0.016 s, 92.76 ± 26.51 s, 3.46 ± 3.78, 0.24 ± 0.08 and for 90 degree specimen orientation were 13.7 ± 7.7 kPa, 72.6 ± 35.4 kPa, 2.18 ± 4.12, 55.35 ± 7.12°, 0.22 ± 0.06, 23.51 ± 38.90 s, 81.52 ± 29.16 s, 5.14 ± 8.72, 0.21 ± 0.05, respectively. The validation revealed an overall good agreement from cycles 2 and 3 based on uniaxial tensile tests and surface strains data from DIC measurements with the material parameters from inverse analysis using FEA for the response in cycle 1. Conclusions: The identified material model and numerical simulations provide a comprehensive description of the viscoelastic behavior of the aortic wall tissue and a quantitative understanding of the spatial and directional variability underlying aortic tissue mechanical behavior. [ABSTRACT FROM AUTHOR]

In this work, we analyze, from the numerical point of view, a problem including a mixture made of a MGT viscoelastic solid and an elastic solid. The corresponding variational problem is a linear system composed of two coupled hyperbolic equations written in terms of the acceleration of the first constituent and the velocity of the second one. Then, fully discrete approximations are introduced by using the finite element method and the implicit Euler scheme. A discrete stability property and a priori error estimates are proved. Finally, some one-dimensional numerical simulations are shown to demonstrate the accuracy of the proposed approximations and the behaviour of the solution. [ABSTRACT FROM AUTHOR]

We propose new methods for the determination of the thermal stressed state of viscoelastic bodies made of functionally graded materials subjected to annealing. We develop a numerical algorithm for the solution of the corresponding problem and realize it for the problems of heat conduction and thermoviscoelasticity. The thermal stressed state of a hollow cylinder is determined according to the given conditions of annealing. The variations of its temperature and stressed state are illustrated. [ABSTRACT FROM AUTHOR]

Constitutive models exhibiting viscoelastic and micro-inertia with vortex viscosity effects are used for modeling of transport of heat energy, (angular and linear) with conservation laws for dust phase flow. The governing models are solved via the finite element method. The convergence of numerical solutions is guaranteed and mesh-free results are computed in view of a variation of physical parameters. Micro-rotations have shown a remarkable impact on shear stress and wall heat flux. The momentum relaxation (memory effects) time has shown a remarkable decrease in velocity associated with macro-flow. An increase in vortex viscosity increases angular motion. The Deborah number has shown a decreasing trend on flow. This causes a significant decrease in convective transport of heat energy. The temperature of dust particles increases when the ratio of specific heat and fluid particle interaction parameter for temperature is increased. However, the opposite behavior is noted for the case of increasing the relaxation time of the particle phase. The hybrid nanofluid transports much momentum than the momentum transported by mono-nanofluid. [ABSTRACT FROM AUTHOR]

Recurrent neural network (RNN)-based accelerated prediction was achieved for the long-term time-dependent behavior of viscoelastic composite laminated Mindlin plates subjected to arbitrary mechanical and hygrothermal loading. Time-integrated constitutive stress-strain relation was simplified via Laplace transform to a linear system to reduce the computational storage. A fast converging smooth finite element method named cell-based smoothed discrete shear gap was employed to enhance the data generation procedure for straining RNNs with a sparse mesh. This technique is applicable under varying hygrothermal conditions for real engineering structure problems with fluctuating temperature and moisture. Hence, accurate RNN-based long-term deformation prediction for laminated structures was realized using the history of environmental temperature and moisture condition. [ABSTRACT FROM AUTHOR]

This contribution aims at developing a formulation for the large viscoelastic deformation of hyperelastic beams and frames under various loading and boundary conditions. To do so, the kinematics of deformation in two-dimensional space is formulated and basic kinematics and kinetic quantities are introduced. The quasi-linear viscoelasticity theory is employed to capture the time-dependent behavior of the underlying material. The corresponding time integration scheme and the consistent tangent moduli are then presented. Because of the highly nonlinear nature of governing equations at the large regime of deformations including time dependency, a nonlinear finite element formulation in the total Lagrangian framework is developed. Several numerical examples are provided to investigate the applicability of derived formulations. It is observed that the formulation can successfully capture the relaxation and creep phenomena in visco-hyperelastic beams and frames. [ABSTRACT FROM AUTHOR]