• Advances in nano research
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• v.14 no.1
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• pp.45-65
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• 2023

This paper aimed to investigate the nonclassical size dependent free vibration behavior of regularly squared cutout viscoelastic nanobeams. The nonlocal strain gradient elasticity theory is modified and adopted to incorporate the viscoelasticity effect. The Kelvin Voigt viscoelastic model is adopted to model the linear viscoelastic constitutive response. To explore the influence of shear deformation effect due to cutout, both Euler Bernoulli and Timoshenko beams theories are considered. The Hamilton principle is utilized to derive the dynamic equations of motion incorporating viscoelasticity and size dependent effects. Closed form solutions for the resonant frequencies for both perforated Euler Bernoulli nanobeams (PEBNB) and perforated Timoshenko nanobeams (PTNB) are derived considering different boundary conditions. The developed procedure is verified by comparing the obtained results with the available results in the literature. Parametric studies are conducted to show the influence of the material damping, the perforation, the material and the geometrical parameters as well as the boundary and loading conditions on the dynamic behavior of viscoelastic perforated nanobeams. The proposed procedure and the obtained results are supportive in the analysis and design of perforated viscoelastic NEMS structures.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.9
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• pp.3835-3840
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• 2012

Nanoimprint lithography (NIL) is an emerging technology enabling cost-effective and high-throughput nanofabrication. Recently a lot of research for the nanoimprint have been carried out, but almost are about merely experimental result relating to the material operation and the imprint fabrication, and numerical analysis relating to the understanding of the imprint process with R&D level. In this paper, the viscoelasticity analysis model is developed using the finite element method. With this model, the filling process and residual layer formation in nanoimprint are analyzed, which is evaluated by a nanoimprint experiment.

• Land and Housing Review
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• v.11 no.2
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• pp.95-104
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• 2020

This study aims to explore a purely mechanistic pavement analysis approach where viscoelasticity and fracture of asphalt mixtures are considered to accurately predict deformation and damage behavior of flexible pavements. To do so, the viscoelastic and fracture properties of designated pavement materials are obtained through experiments and a fully mechanistic damage analysis is carried out using a finite element method (FEM). While modeling crack development can be done in various ways, this study uses the cohesive zone approach, which is a well-known fracture mechanics approach to efficiently model crack initiation and propagation. Different pavement configurations and traffic loads are considered based on three main functional classes of roads suggested by FHWA i.e., arterial, collector and local. For each road type, three different material combinations for asphalt concrete (AC) and base layers are considered to study damage behavior of pavement. A concept of the approach is presented and a case study where three different material combinations for AC and base layers are considered is exemplified to investigate progressive damage behavior of pavements when mixture properties and layer configurations were altered. Overall, it can be concluded that mechanistic pavement modeling attempted in this study could differentiate the performance of pavement sections due to varying design inputs. The promising results, although limited yet to be considered a fully practical method, infer that a few mixture tests can be integrated with the finite element modeling of the mixture tests and subsequent structural modeling of pavements to better design mixtures and pavements in a purely mechanistic manner.

• Journal of Chest Surgery
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• v.49 no.3
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• pp.145-150
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• 2016

Background: Extracorporeal circulation (ECC) can induce alterations in blood viscoelasticity and cause red blood cell (RBC) aggregation. In this study, the authors evaluated the effects of pump flow pulsatility on blood viscoelasticity and RBC aggregation. Methods: Mongrel dogs were randomly assigned to two groups: a nonpulsatile pump group (n=6) or a pulsatile pump group (n=6). After ECC was started at a pump flow rate of 80 mL/kg/min, cardiac fibrillation was induced. Blood sampling was performed before and at 1, 2, and 3 hours after ECC commencement. To eliminate bias induced by hematocrit and plasma, all blood samples were adjusted to a hematocrit of 45% using baseline plasma. Blood viscoelasticity, plasma viscosity, hematocrit, arterial blood gas analysis, central venous $O_2$ saturation, and lactate were measured. Results: The blood viscosity and aggregation index decreased abruptly 1 hour after ECC and then remained low during ECC in both groups, but blood elasticity did not change during ECC. Blood viscosity, blood elasticity, plasma viscosity, and the aggregation index were not significantly different in the groups at any time. Hematocrit decreased abruptly 1 hour after ECC in both groups due to dilution by the priming solution used. Conclusion: After ECC, blood viscoelasticity and RBC aggregation were not different in the pulsatile and nonpulsatile groups in the adult dog model. Furthermore, pulsatile flow did not have a more harmful effect on blood viscoelasticity or RBC aggregation than nonpulsatile flow.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3435-3441
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• 2014

A dynamic modeling and prediction of polyurethane foam material, which is used as the seat in vehicles is very important for improving the ride quality of vehicle occupants. In this study, parameters to define the nonlinear stiffness and time-variant characteristics of the viscoelasticity of polyurethane foam were obtained using a static compression test. Polynomial functions and convolution integral were used to model the nonlinear and viscoelastic characteristics of polyurethane foam mathematically. The dynamic behaviors excited by the seat floor displacement were analyzed using a numerical integration method for the nonlinear vibration model. As a result, the viscoelastic characteristics of polyurethane foam was found to be an important parameter for improving the ride quality.

• Tribology and Lubricants
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• v.30 no.6
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• pp.378-383
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• 2014

This study predicts the of the hysteretic friction of a rubber block sliding on an SMA asphalt road. The friction of filled rubber on a rough surface is primarily determined by two elements:the viscoelasticity of the rubber and the multi-scale perspective asperities of the road. The surface asperities of the substrate exert osillating forces on the rubber surface leading to energy dissipation via the internal friction of the rubber when rubber slides on a hard and rough substrate. This study defines the power spectra at different length scales by using a high-resolution surface profilometer, and uses rubber and road surface samples to conduct friction tests. I consider in detail the case when the substrate surface has a self affine fractal structure. The theory developed by Persson is applied to describe these tests through comparison with the hysteretic friction coefficient relevant to the energy dissipation of the viscoelastic rubber attributable to cyclic deformation. The results showed differences in the absolute values of predicted and measured friction, but with high correlation between these values. Hence, the friction prediction model is an appropriate tool for separating the effects of each factor. Therefore, this model will contribute to clearer understanding of the fundamental principles of rubber friction.

• Tribology and Lubricants
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• v.34 no.1
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• pp.1-8
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• 2018

This paper presents the analysis of friction master curves for a sliding elastomer on rough granite. The hysteresis friction is calculated using an analytical model that considers the energy spent during the local deformation of the rubber due to surface asperities. The adhesion friction is also considered for dry friction prediction. The viscoelastic modulus of the rubber compound and the large-strain effective modulus are obtained from dynamic mechanical analysis (DMA). We accurately demonstrate the large strain of rubber that contacts with road substrate using the GW theory. We found that the rubber block deforms approximately to 40% strain. In addition, the viscoelastic master curve considering nonlinearity (at 40% strain) is derived based on the above finding. As viscoelasticity strongly depends on temperature, it can be assumed that the influence of velocity on friction is connected to the viscoelastic shift factors gained from DMA using the time-temperature superposition. In this study, we apply these shift factors to measure friction on dry granite over a velocity range for various temperatures. The measurements are compared to simulated hysteresis and adhesion friction using the Kluppel friction theory. Although friction results in the low-speed band match well with the simulation results, there are differences in the predicted and experimental results as the velocity increases. Thus, additional research is required for a more precise explanation of the viscoelastic material properties for better prediction of rubber friction characteristics.

• Structural Engineering and Mechanics
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• v.40 no.6
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• pp.783-800
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• 2011

This paper addresses the finite strip formulations for the stability analysis of viscoelastic composite plates with variable thickness in the transverse direction, which are subjected to in-plane forces. While the finite strip method is fairly well-known in the buckling analysis, hitherto its direct application to the buckling of viscoelastic composite plates with variable thickness has not been investigated. The equations governing the stiffness and the geometry matrices of the composite plate are solved in the time domain using both the higher-order shear deformation theory and the method of effective moduli. These matrices are then assembled so that the global stiffness and geometry matrices of a moderately thick rectangular plate are formed which lead to an eigenvalue problem that is solved to determine the magnitude of critical buckling load for the viscoelastic plate. The accuracy of the proposed model is verified against the results which have been reported elsewhere whilst a comprehensive parametric study is presented to show the effects of viscoelasticity parameters, boundary conditions as well as combined bending and compression loads on the critical buckling load of thin and moderately thick viscoelastic composite plates.

• International Journal of Highway Engineering
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• v.14 no.5
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• pp.1-9
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• 2012

PURPOSES: A viscoelastic axisymmetric finite element analysis code has been developed for stress analysis of asphalt pavement structures. METHODS: Generalized Maxwell Model (GMM) and 4-node isoparametric element were employed for finite element formulation. The code was developed using $C^{+}^{+}$ computer program language and named as KICTPAVE. For the verification of the developed code, a structural model of a pavement system was constructed. The structural model was composed of three layers: asphalt layer, crushed stone layer, and soil subgrade. Two types of analysis were considered for the verification: (1)elastic static analysis, (2)viscoelastic time-dependent analysis. For the elastic static analysis, linear elastic material model was assigned to all the layers, and a static load was applied to the structural model. For the viscoelastic time-dependent analysis, GMM and linear elastic material model were assigned to the asphalt layer and all the other layers respectively, and a cyclic loading condition was applied to the structural model. RESULTS: The stresses and deformations from KICTPAVE were compared with those from ABAQUS. The analysis results obtained from the two codes showed good agreement in time-dependent response of the element under the loading area as well as the surface deformation of asphalt layer, and horizontal and vertical stresses along the axisymmetric axis. CONCLUSIONS: The validity of KICTPAVE was confirmed by showing the agreement of the analysis results from the two codes.

• Korea-Australia Rheology Journal
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• v.20 no.4
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• pp.197-211
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• 2008

The purpose of this study is mainly directed towards present of viewpoints on critical and commentary analysis on blood rheology, blood viscosity models, and physiological flow conditions. Understanding these basics is fundamental to meet the need for a sufficient and reliable CFD model of blood. Most of the used viscosity models on this manner have determined from parameter fitting on experimental viscosity data. Availability of experimental data from literature to define viscosity models of CFD analysis should be accurately chosen and treated in order to avoid any errors. Several basic gaps that limit the CFD model results are identified and given opportunities for future research.