Modeling the Finite Deformation Anisotropic Viscoelastic Behavior of the Cornea

2008 ◽  
Author(s):  
Thao D. Nguyen ◽  
Reese E. Jones ◽  
Brad L. Boyce
Keyword(s):  
Stress Response ◽  
Finite Deformation ◽  
Viscoelastic Properties ◽  
Viscoelastic Behavior ◽  
Element Model ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Model Parameters ◽  
Human Cornea ◽  
Viscoelastic Parameters

This paper presents the development of a finite element model for the cornea as a first step towards a physiologically based model to study the role of cornea and sclera biomechanics in glaucoma. We developed a finite-deformation anisotropic constitutive model of the cornea that considers the effects of the fibrilar microstructure on the viscoelastic stress response. The model was base on the hypothesis that the dominant mechanism for the tensile viscoelastic behavior of the cornea is the viscoelastic stretching of the collagen lamellae. This approach yielded two main results. First, the viscoelastic properties of the cornea are derivable directly from the viscoelastic properties of the collagen fibrils and proteoglycan matrix. Second, the anisotropy in the stress response and creep response are determined solely by the arrangement collagen lamellae, which depends on orientation and material position. This allows the model parameters that determines anisotropy to be obtained from microstructural characterizations, such as the X-ray diffraction experiments of Meek and coworkers [1], while the model parameters that determines viscoelasticity to be determined from mechanical experiments. For this initial work, the viscoelastic parameters were fitted to the uniaxial tensile strip tests [2] and inflation tests with digital image correlation (DIC) [3] of bovine cornea performed by our group. Since microstructural characterizations are not available for bovine cornea, we used the data of Aghamohammadzadeh et. al. [1] for the human cornea.

Finite deformation and fractional order viscoelasticity of an auxetic foam

2022 ◽  
pp. 1045389X2110643
Author(s):  
Eugenia Stanisauskis ◽  
Paul Miles ◽  
William Oates
Keyword(s):  
Fractional Order ◽  
Finite Deformation ◽  
Viscoelastic Behavior ◽  
Integer Order ◽  
Relaxation Effects ◽  
Viscoelastic Parameters ◽  
Rate Dependent ◽  
Improve Model ◽  
Model Predictions ◽  
And Performance

Auxetic foams exhibit novel mechanical properties due to their unique microstructure for improved energy-absorption and cavity expansion applications that have fascinated the scientific community since their inception. Given the advancements in material processing and performance of polymer open cell auxetic foams, there is a strong desire to fully understand the nonlinear rate-dependent deformation of these materials. The influence of nonlinear compressibility is introduced here along with relaxation effects to improve model predictions for different stretch rates and finite deformation regimes. The viscoelastic behavior of the material is analyzed by comparing fractional order and integer order calculus models. All results are statistically validated using maximum entropy methods to obtain Bayesian posterior densities for the hyperelastic, auxetic, and viscoelastic parameters. It is shown that fractional order viscoelasticity provides [Formula: see text]–[Formula: see text] improvement in prediction over integer order viscoelastic models when the model is calibrated at higher stretch rates where viscoelasticity is more significant.

scholarly journals Viscoelastic behavior of yellow pitahaya treated with 1-MCP

DYNA ◽  
2016 ◽  
Vol 83 (196) ◽  
pp. 119-123 ◽  
Author(s):  
Laura Sofia Torres Valenzuela ◽  
Alfredo Adolfo Ayala-Aponte ◽  
Liliana Serna
Keyword(s):  
Quality Control ◽  
Viscoelastic Properties ◽  
Viscoelastic Behavior ◽  
Elastic Behavior ◽  
Stress Relaxation Test ◽  
Minimally Processed ◽  
Rheological Models ◽  
Viscoelastic Parameters ◽  
Food Stability ◽  
Refrigeration Storage

<p>Foods may have both solid and liquid properties, and are described as viscoelastic products. Knowledge on such viscoelastic features is very useful for quality control and/or food stability. The purpose of this work was to evaluate the effect of the application of 1-MCP on the viscoelastic properties of minimally processed yellow pitahaya during refrigeration storage, by using a stress relaxation test. Viscoelastic parameters were determined through Generalized Maxwell and Peleg’s rheologic models. Both rheological models proved suitable to predict viscoelastic behavior; however, Peleg’s model better described this behavior. Samples of treated and non-treated pitahaya with 1- MCP decreased their elastic behavior (firmness decrease) during storage. Fruit treated with 1-MCP showed a greater elastic component than non-treated samples during storage. These two rheological models were suitable for predicting the viscoelastic behavior, however.</p>

On the Extraction of Elastic–Plastic Constitutive Properties From Three-Dimensional Deformation Measurements

2015 ◽  
Vol 82 (7) ◽  
Author(s):  
A. J. Gross ◽  
K. Ravi-Chandar
Keyword(s):  
Constitutive Model ◽  
Tensile Test ◽  
Three Dimensional ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Model Parameters ◽  
Material Models ◽  
Elastic Plastic ◽  
Constitutive Properties ◽  
Deformation Measurements

In this article, a coupled experimental and numerical method is utilized for characterizing the elastic–plastic constitutive properties of ductile materials. Three-dimensional digital image correlation (DIC) is used to measure the full field deformation on two mutually orthogonal surfaces of a uniaxial tensile test specimen. The material’s constitutive model, whose parameters are unknown a priori, is determined through an optimization process that compares these experimental measurements with finite element simulations in which the constitutive model is implemented. The optimization procedure utilizes the robust dataset of locally observed deformation measurements from DIC in addition to the standard measurements of boundary load and displacement data. When the difference between the experiment and simulations is reduced sufficiently, a set of parameters is found for the material model that is suitable to large strain levels. This method of material characterization is applied to a tensile specimen fabricated from a sheet of 15-5 PH stainless steel. This method proves to be a powerful tool for calibration of material models. The final parameters produce a simulation that tracks the local experimental displacement field to within a couple percent of error. Simultaneously, the percent error in the simulation for the load carried by the specimen throughout the test is less than 1%. Additionally, half of the parameters for Hill’s yield criterion, describing anisotropy of the normal stresses, are found from a single tensile test. This method will find even greater utility in calibrating more complex material models by greatly reducing the experimental effort required to identify the appropriate model parameters.

Viscoelastic Properties of Aircraft Tire Materials

1990 ◽  
Vol 18 (4) ◽  
pp. 262-281 ◽  
Author(s):  
J. T. Tielking ◽  
R. R. Hanson ◽  
A. J. Giacomin
Keyword(s):  
Spectral Analysis ◽  
Stress Response ◽  
Viscoelastic Properties ◽  
Viscoelastic Behavior ◽  
Cyclic Strain ◽  
Strain Level ◽  
Test Results ◽  
Specimen Length ◽  
Effects Of Temperature

Abstract Specimens cut from a 40 × 14 nylon cord aircraft tire were subjected to cyclic strain tests to measure the viscoelastic behavior. Spectral analysis was used to quantify nonlinearity in the stress response. Preliminary studies were made to ascertain the effects of specimen length and width on the test results. A bolted end constraint was developed to uniformly distribute the imposed strain through the thickness of the multiply carcass specimens. Test results show the effects of temperature, frequency, and strain level on the viscoelastic properties. Results are generally in agreement with earlier findings made using tubular test specimens.

scholarly journals Thermal–Mechanical Coupling Behavior of Directional Polymethylmethacrylate under Tension and Compression

Polymers ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1279
Author(s):  
Hui Guo ◽  
Chunjiang Lu ◽  
Yu Chen ◽  
Junlin Tao ◽  
Longyang Chen
Keyword(s):  
Strain Rate ◽  
Mechanical Behavior ◽  
Finite Deformation ◽  
Testing Machine ◽  
Polymer Materials ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Correlation Technique ◽  
Material Research ◽  
Strengthening Effect

In this work, the quasi-static and dynamic mechanical behavior of directional polymethylmethacrylate is investigated under conditions of uniaxial compression and tension. The main purpose of this investigation is to discuss the effect of strain rate and temperature on the deformation characteristics and failure of such material. Research was carried out with the use of an electric universal testing machine and split Hopkinson bars, which were equipped with high- and low-temperature control systems. The experimental methods for studying the tensile and compressive response of polymer materials under different testing conditions were validated by one-dimensional stress wave theory and digital-image correlation technique. The finite deformation stress–strain behaviors of the samples under different loading condition were obtained with a constant temperature ranging from 218 to 373 K. The experimental results showed that the uniaxial tensile and compressive behaviors of directional polymethylmethacrylate under finite deformation are strongly dependent on temperature, decreased tensile and compressive stress of the material under different strain levels, and increased temperature. Meanwhile, the dynamic tensile and compressive stresses of the material are much higher than the quasi-static stresses, showing the strain-rate strengthening effect. Moreover, the tensile and compressive mechanical behavior of directional polymethylmethacrylate has significant asymmetry. Finally, a visco-hyperelastic model is established to predict the rate-dependence mechanical behavior of directional polymethylmethacrylate at different temperatures.

scholarly journals Effect of PWHT on the Microstructure and Mechanical Properties of Friction Stir Welded DP780 Steel

Metals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1097
Author(s):  
Umer Masood Chaudry ◽  
Seung-Chang Han ◽  
Fathia Alkelae ◽  
Tea-Sung Jun
Keyword(s):  
Mechanical Properties ◽  
Annealing Temperature ◽  
Tensile Elongation ◽  
Image Correlation ◽  
Frictional Heat ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Friction Stir ◽  
Microstructure And Mechanical Properties ◽  
Dp780 Steel

In the present study, the effect of post-weld heat treatment (PWHT) on the microstructure and mechanical properties of friction stir welded (FSW) DP780 steel sheets was investigated. FSW was carried out at a constant tool rotation speed of 400 rpm and different welding speeds (200 mm/min and 400 min/min). A defect free weld was witnessed for both of the welding conditions. The mutual effect of severe plastic deformation and frictional heat generation by pin rotation during the FSW process resulted in grain refinement due to dynamic recrystallization in the stir zone (SZ) and thermo-mechanically affected zone (TMAZ). Lower tensile elongation and higher yield and ultimate tensile strengths were recorded for welded-samples as compared to the base material (BM) DP780 steel. The joints were subsequently annealed at various temperatures at 450–650 °C for 1 h. At higher annealing temperature, the work hardening rate of joints gradually decreased and subsequently failed in the softened heat-affected zone (HAZ) during the uniaxial tensile test. Reduction in yield strength and tensile strength was found in all PWHT conditions, though improvement in elongation was achieved by annealing at 550 °C. The digital image correlation analysis showed that an inhomogeneous strain distribution occurred in the FSWed samples, and the strain was particularly highly localized in the advancing side of interface zone. The nanoindentation measurements covering the FSWed joint were consistent with an increase of the annealing temperature. The various grains size in the BM, TMAZ, and SZ is the main factor monitoring the hardness distribution in these zones and the observed discrepancies in mechanical properties.

scholarly journals 3D Plotting of Silica/Collagen Xerogel Granules in an Alginate Matrix for Tissue-Engineered Bone Implants

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 830
Author(s):  
Sina Rößler ◽  
Andreas Brückner ◽  
Iris Kruppke ◽  
Hans-Peter Wiesmann ◽  
Thomas Hanke ◽  
...  
Keyword(s):  
Additive Manufacturing ◽  
Bone Regeneration ◽  
Material Properties ◽  
Viscoelastic Properties ◽  
Viscoelastic Behavior ◽  
Matrix Phase ◽  
Patient Specific ◽  
Active Player ◽  
Alginate Concentration ◽  
Alginate Matrix

Today, materials designed for bone regeneration are requested to be degradable and resorbable, bioactive, porous, and osteoconductive, as well as to be an active player in the bone-remodeling process. Multiphasic silica/collagen Xerogels were shown, earlier, to meet these requirements. The aim of the present study was to use these excellent material properties of silica/collagen Xerogels and to process them by additive manufacturing, in this case 3D plotting, to generate implants matching patient specific shapes of fractures or lesions. The concept is to have Xerogel granules as active major components embedded, to a large proportion, in a matrix that binds the granules in the scaffold. By using viscoelastic alginate as matrix, pastes of Xerogel granules were processed via 3D plotting. Moreover, alginate concentration was shown to be the key to a high content of irregularly shaped Xerogel granules embedded in a minimum of matrix phase. Both the alginate matrix and Xerogel granules were also shown to influence viscoelastic behavior of the paste, as well as the dimensionally stability of the scaffolds. In conclusion, 3D plotting of Xerogel granules was successfully established by using viscoelastic properties of alginate as matrix phase.

scholarly journals Coupled Thermomechanical Response Measurement of Deformation of Nickel-Based Superalloys Using Full-Field Digital Image Correlation and Infrared Thermography

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2163
Author(s):  
Krzysztof Żaba ◽  
Tomasz Trzepieciński ◽  
Sandra Puchlerska ◽  
Piotr Noga ◽  
Maciej Balcerzak
Keyword(s):  
Surface Temperature ◽  
Strain Rate ◽  
Rolling Direction ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Response Measurement ◽  
Sheet Rolling ◽  
Inconel Alloys ◽  
The Relationship

The paper is devoted to highlighting the potential application of the quantitative imaging technique through results associated with work hardening, strain rate and heat generated during elastic and plastic deformation. The aim of the research presented in this article is to determine the relationship between deformation in the uniaxial tensile test of samples made of 1-mm-thick nickel-based superalloys and their change in temperature during deformation. The relationship between yield stress and the Taylor–Quinney coefficient and their change with the strain rate were determined. The research material was 1-mm-thick sheets of three grades of Inconel alloys: 625 HX and 718. The Aramis (GOM GmbH, a company of the ZEISS Group) measurement system and high-sensitivity infrared thermal imaging camera were used for the tests. The uniaxial tensile tests were carried out at three different strain rates. A clear tendency to increase the sample temperature with an increase in the strain rate was observed. This conclusion applies to all materials and directions of sample cutting investigated with respect to the sheet-rolling direction. An almost linear correlation was found between the percent strain and the value of the maximum surface temperature of the specimens. The method used is helpful in assessing the extent of homogeneity of the strain and the material effort during its deformation based on the measurement of the surface temperature.

Identification of Nonlinear Viscoelastic Models of Flexible Polyurethane Foam From Uniaxial Compression Data

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Yousof Azizi ◽  
Patricia Davies ◽  
Anil K. Bajaj
Keyword(s):  
Uniaxial Compression ◽  
Viscoelastic Model ◽  
Viscoelastic Behavior ◽  
Model Parameters ◽  
Viscoelastic Models ◽  
Nonlinear Viscoelastic ◽  
Compression Data ◽  
Computationally Intensive ◽  
Nonlinear Viscoelastic Model ◽  
Flexible Polyurethane

Flexible polyethylene foam is used in many engineering applications. It exhibits nonlinear and viscoelastic behavior which makes it difficult to model. To date, several models have been developed to characterize the complex behavior of foams. These attempts include the computationally intensive microstructural models to continuum models that capture the macroscale behavior of the foam materials. In this research, a nonlinear viscoelastic model, which is an extension to previously developed models, is proposed and its ability to capture foam response in uniaxial compression is investigated. It is hypothesized that total stress can be decomposed into the sum of a nonlinear elastic component, modeled by a higher-order polynomial, and a nonlinear hereditary type viscoelastic component. System identification procedures were developed to estimate the model parameters using uniaxial cyclic compression data from experiments conducted at six different rates. The estimated model parameters for individual tests were used to develop a model with parameters that are a function of strain rates. The parameter estimation technique was modified to also develop a comprehensive model which captures the uniaxial behavior of all six tests. The performance of this model was compared to that of other nonlinear viscoelastic models.

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