Measurement and Parameter Identification of Time Dependent Poisson's Ratio for Underfill Materials

When a poroelastic gel is released from a patterned mold, surface stress drives deformation and solvent migration in the gel and flattens its surface profile in a time-dependent manner. Specifically,...

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On relevance of time-dependent Poisson’s ratio for determination of relaxation function parameters

Journal of the Brazilian Society of Mechanical Sciences and Engineering ◽

10.1007/s40430-019-2001-7 ◽

2019 ◽

Vol 41 (11) ◽

Author(s):

Cyprian Suchocki ◽

Rafał Molak

Keyword(s):

Poisson’S Ratio ◽

Relaxation Function ◽

Memory Function ◽

Viscoelastic Model ◽

Three Dimensional ◽

Acrylonitrile Butadiene Styrene ◽

Time Dependent ◽

Poisson's Ratio ◽

Viscoelastic Constants

Abstract The current study concerns the determination of material constants of a three-dimensional linear viscoelastic model. It is assumed that the constitutive equation utilizes a Prony series as a memory function. A method for the evaluation of relaxation function parameters is presented which can be used for arbitrary loading histories. The proposed methodology is applied to the identification of the viscoelastic constants of acrylonitrile butadiene styrene (ABS). For that purpose, a number of rheological tests in tension have been performed on ABS standard dogbone specimens. The significance of the time-dependent Poisson’s ratio for the determination of material parameters is investigated. It is found that taking into account the measurements of specimen’s lateral contraction over time has a particularly strong influence on the identified values of parameters responsible for the bulk behavior. Several boundary value problems have been analyzed in order to assess the influence of the material parameter values on the obtained solutions. It is demonstrated that some oversimplifications assumed during the determination of viscoelastic constants can lead to a loss of precision or even wrong results.

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Biphasic parameter identification of equine articular cartilage from creep indentation data using an optimized 3D FE-based method

Current Directions in Biomedical Engineering ◽

10.1515/cdbme-2018-0115 ◽

2018 ◽

Vol 4 (1) ◽

pp. 481-484

Author(s):

Thomas Reuter ◽

Christof Hurschler

Keyword(s):

Articular Cartilage ◽

Parameter Identification ◽

Young’S Modulus ◽

Poisson’S Ratio ◽

Soft Tissues ◽

Young's Modulus ◽

Poisson's Ratio ◽

Sensitivity Analyses ◽

Fe Model ◽

Marquardt Algorithm

AbstractMechanical parameters of hard and soft tissues are explicit markers for quantitative tissue characterization. In this study, we present a biphasic 3D-FE-based method to determine the biomechanical properties of equine articular cartilage from creep indentation tests (F = 0.1 N, t = 1000 s). The FE-model computation was optimized by exploiting the axial symmetry and mesh resolution. Parameter identification was executed with the Levenberg-Marquardt-algorithm. Additionally, sensitivity analyses of the calculated biomechanical parameters were performed. Results show that the Young’s modulus has the largest influence and the Poisson’s ratio of ν ≤ 0.1 is rather insensitive. The R² of the fit results varies between 0.882 and 0.974. The determined values for the Young’s modulus were 0.806 ± 0.093 MPa, the Poisson’s ratio 0.03 ± 0.06 and the permeability 0.012 ± 0.002 mm4/Ns. Future work will deal with mathematical extensions of the biphasic 3D-FE-model.

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