Characterization of Thermoplastic Elastomers for Design Efforts

2014 ◽  
Vol 905 ◽  
pp. 161-166
Author(s):  
Zoltan Major ◽  
Matei C. Miron ◽  
Umut D. Cakmak
Keyword(s):  
Experimental Data ◽  
Thermoplastic Elastomer ◽  
Material Model ◽  
Thermoplastic Elastomers ◽  
Failure Behavior ◽  
Model Parameters ◽  
Material Models ◽  
Fitting Procedures ◽  
Relevant Material

Different grades of several thermoplastic elastomer types were selected and are investigated over a wide frequency/time, temperature and loading range in a research project of the authors. Relevant material models are selected for different loading situations and based on these experimental data the material model parameters were determined either directly or by applying fitting procedures. These models along with the proper data were used for modeling the deformation and the failure behavior of typical engineering thermoplastic elastomer components. Furthermore, based on the modeling of various elastomers under different service relevant loading situation several design proposals were formulated.

scholarly journals Variation of Passive Biomechanical Properties of the Small Intestine along Its Length: Microstructure-Based Characterization

2021 ◽  
Vol 8 (3) ◽  
pp. 32
Author(s):  
Dimitrios P. Sokolis
Keyword(s):  
Small Intestine ◽  
Orientation Angle ◽  
Axial Direction ◽  
Material Model ◽  
Biomechanical Properties ◽  
Intestinal Wall ◽  
Model Parameters ◽  
Material Models ◽  
Hyper Elastic ◽  
Rat Tissue

Multiaxial testing of the small intestinal wall is critical for understanding its biomechanical properties and defining material models, but limited data and material models are available. The aim of the present study was to develop a microstructure-based material model for the small intestine and test whether there was a significant variation in the passive biomechanical properties along the length of the organ. Rat tissue was cut into eight segments that underwent inflation/extension testing, and their nonlinearly hyper-elastic and anisotropic response was characterized by a fiber-reinforced model. Extensive parametric analysis showed a non-significant contribution to the model of the isotropic matrix and circumferential-fiber family, leading also to severe over-parameterization. Such issues were not apparent with the reduced neo-Hookean and (axial and diagonal)-fiber family model, that provided equally accurate fitting results. Absence from the model of either the axial or diagonal-fiber families led to ill representations of the force- and pressure-diameter data, respectively. The primary direction of anisotropy, designated by the estimated orientation angle of diagonal-fiber families, was about 35° to the axial direction, corroborating prior microscopic observations of submucosal collagen-fiber orientation. The estimated model parameters varied across and within the duodenum, jejunum, and ileum, corroborating histologically assessed segmental differences in layer thicknesses.

scholarly journals Role of smooth muscle activation in the static and dynamic mechanical characterization of human aortas

2022 ◽  
Vol 119 (3) ◽  
pp. e2117232119
Author(s):  
Giulio Franchini ◽  
Ivan D. Breslavsky ◽  
Francesco Giovanniello ◽  
Ali Kassab ◽  
Gerhard A. Holzapfel ◽  
...  
Keyword(s):  
Experimental Data ◽  
Smooth Muscle ◽  
Muscle Activation ◽  
Mechanical Response ◽  
Mechanical Characterization ◽  
Viscoelastic Behavior ◽  
Material Model ◽  
Suitable Material ◽  
Dynamic Mechanical

Experimental data and a suitable material model for human aortas with smooth muscle activation are not available in the literature despite the need for developing advanced grafts; the present study closes this gap. Mechanical characterization of human descending thoracic aortas was performed with and without vascular smooth muscle (VSM) activation. Specimens were taken from 13 heart-beating donors. The aortic segments were cooled in Belzer UW solution during transport and tested within a few hours after explantation. VSM activation was achieved through the use of potassium depolarization and noradrenaline as vasoactive agents. In addition to isometric activation experiments, the quasistatic passive and active stress–strain curves were obtained for circumferential and longitudinal strips of the aortic material. This characterization made it possible to create an original mechanical model of the active aortic material that accurately fits the experimental data. The dynamic mechanical characterization was executed using cyclic strain at different frequencies of physiological interest. An initial prestretch, which corresponded to the physiological conditions, was applied before cyclic loading. Dynamic tests made it possible to identify the differences in the viscoelastic behavior of the passive and active tissue. This work illustrates the importance of VSM activation for the static and dynamic mechanical response of human aortas. Most importantly, this study provides material data and a material model for the development of a future generation of active aortic grafts that mimic natural behavior and help regulate blood pressure.

Microvascular exchange and interstitial volume regulation in the rat: model validation

1988 ◽  
Vol 254 (2) ◽  
pp. H384-H399 ◽  
Author(s):  
J. L. Bert ◽  
B. D. Bowen ◽  
R. K. Reed
Keyword(s):  
Experimental Data ◽  
Osmotic Pressure ◽  
Plasma Proteins ◽  
Venous Pressure ◽  
Colloid Osmotic Pressure ◽  
Model Parameters ◽  
Transport Parameters ◽  
Interstitial Fluid Volume ◽  
Protein Tracers ◽  
Fitting Procedures

A dynamic mathematical model is formulated and used to describe the distribution and transport of fluid and plasma proteins between the circulation, interstitial space of skin and muscle, and the lymphatics in the rat. Two descriptions of transcapillary exchange are investigated: a homoporous "Starling model" and a heteroporous "plasma leak model." Parameters used in the two hypothetical transport mechanisms are determined based on statistical fitting procedures between simulation predictions and selected experimental data. These data consist of interstitial fluid volume and colloid osmotic pressure measurements as a function of venous pressure for muscle and interstitial colloid osmotic pressure vs. venous pressure for skin. The values determined for the transport parameters compare well with data in the literature. The fully determined model is used to simulate steady-state conditions of hypoproteinemia, overhydration, and dehydration, as well as the dynamic response to changes in venous pressure and intravascularly administered protein tracers. Comparisons between the simulation predictions and experimental data for these various perturbations are made. The plasma leak model appears to provide a better description of microvascular exchange.

scholarly journals A hierarchical Bayesian approach for calibration of stochastic material models

2021 ◽  
Vol 2 ◽  
Author(s):  
Nikolaos Papadimas ◽  
Timothy Dodwell
Keyword(s):  
Synthetic Data ◽  
Material Model ◽  
Model Parameters ◽  
Hierarchical Bayesian ◽  
Experiment Data ◽  
Single Experiment ◽  
Inference Problem ◽  
Material Models ◽  
3D Printed ◽  
Approximate Likelihood

Abstract This article recasts the traditional challenge of calibrating a material constitutive model into a hierarchical probabilistic framework. We consider a Bayesian framework where material parameters are assigned distributions, which are then updated given experimental data. Importantly, in true engineering setting, we are not interested in inferring the parameters for a single experiment, but rather inferring the model parameters over the population of possible experimental samples. In doing so, we seek to also capture the inherent variability of the material from coupon-to-coupon, as well as uncertainties around the repeatability of the test. In this article, we address this problem using a hierarchical Bayesian model. However, a vanilla computational approach is prohibitively expensive. Our strategy marginalizes over each individual experiment, decreasing the dimension of our inference problem to only the hyperparameter—those parameter describing the population statistics of the material model only. Importantly, this marginalization step, requires us to derive an approximate likelihood, for which, we exploit an emulator (built offline prior to sampling) and Bayesian quadrature, allowing us to capture the uncertainty in this numerical approximation. Importantly, our approach renders hierarchical Bayesian calibration of material models computational feasible. The approach is tested in two different examples. The first is a compression test of simple spring model using synthetic data; the second, a more complex example using real experiment data to fit a stochastic elastoplastic model for 3D-printed steel.

STRAIN-CONTROLLED BIAXIAL TENSION OF NATURAL RUBBER: NEW EXPERIMENTAL DATA

2014 ◽  
Vol 87 (1) ◽  
pp. 120-138 ◽  
Author(s):  
Francesco Q. Pancheri ◽  
Luis Dorfmann
Keyword(s):  
Experimental Data ◽  
Natural Rubber ◽  
Excellent Agreement ◽  
Biaxial Tension ◽  
Pure Shear ◽  
Material Model ◽  
Loading Path ◽  
Model Parameters ◽  
Biaxial Strain ◽  
Strain Control

ABSTRACT We present a new experimental method and provide data showing the response of 40A natural rubber in uniaxial, pure shear, and biaxial tension. Real-time biaxial strain control allows for independent and automatic variation of the velocity of extension and retraction of each actuator to maintain the preselected deformation rate within the gage area of the specimen. We also focus on the Valanis–Landel hypothesis that is used to verify and validate the consistency of the data. We use a three-term Ogden model to derive stress–stretch relations to validate the experimental data. The material model parameters are determined using the primary loading path in uniaxial and equibiaxial tension. Excellent agreement is found when the model is used to predict the response in biaxial tension for different maximum in-plane stretches. The application of the Valanis–Landel hypothesis also results in excellent agreement with the theoretical prediction.

Uncertainty of the Diffusion Measurements on Scaffolds for Cell Growth

2011 ◽  
Vol 312-315 ◽  
pp. 770-775 ◽  
Author(s):  
Guido Sassi ◽  
Marco Bernocco ◽  
Mariapaola Sassi
Keyword(s):  
Dynamic Properties ◽  
Fluid Dynamic ◽  
Solid Particles ◽  
Liquid Volume ◽  
Model Parameters ◽  
Diffusivity Measurement ◽  
Fitting Procedures ◽  
Definition Of

The regenerative medicine uses gel and porous solid matrices as scaffolds for the growth of the stem cells in 3D structures. The structural and fluid dynamic properties of the matrices have been recognized to highly affect the behaviour and functions of the cells. The procedures of production and the clinical use of the matrices need a reliable and reproducible characterization of their properties, this means that the concepts of metrology must be applied to the measurement and definition of all the relevant properties. This paper deals with the calculation of uncertainty for diffusivity measurement in solids and the role of uncertainty in designing the measurement. Diffusion of a solute in spherical solid particles dispersed in a limited liquid volume where considered as measurement method for a Ca-alginate polymer. The model sensitivity to the concentration measurements, the model parameters and the fitting procedures have been discussed.

scholarly journals BAYESIAN INFERENCE OF HETEROGENEOUS VISCOPLASTIC MATERIAL PARAMETERS

2018 ◽  
Vol 15 ◽  
pp. 41-45
Author(s):  
Eliška Janouchová ◽  
Anna Kučerová
Keyword(s):  
Experimental Data ◽  
Bayesian Inference ◽  
Material Model ◽  
Isotropic Hardening ◽  
Model Parameters ◽  
Viscoplastic Material ◽  
Loading Test ◽  
Model Response ◽  
Probabilistic Description ◽  
Probabilistic Setting

<p>Modelling of heterogeneous materials based on randomness of model input parameters involves parameter identification which is focused on solving a stochastic inversion problem. It can be formulated as a search for probabilistic description of model parameters providing the distribution of the model response corresponding to the distribution of the observed data</p><p>In this contribution, a numerical model of kinematic and isotropic hardening for viscoplastic material is calibrated on a basis of experimental data from a cyclic loading test at a high temperature. Five material model parameters are identified in probabilistic setting. The core of the identification method is the Bayesian inference of uncertain statistical moments of a prescribed joint lognormal distribution of the parameters. At first, synthetic experimental data are used to verify the identification procedure, then the real experimental data are processed to calibrate the material model of copper alloy.</p>

Finite Element Modeling of Aortic Tissue Using High Speed Experimental Data

2005 ◽  
Author(s):  
Muralikrishna Maddali ◽  
Chirag S. Shah ◽  
King H. Yang
Keyword(s):  
Experimental Data ◽  
Finite Element ◽  
High Speed ◽  
Material Model ◽  
Traumatic Rupture ◽  
Aortic Tissue ◽  
Model Parameters ◽  
Fe Model ◽  
Rubber Material ◽  
Material Constants

Traumatic rupture of the aorta (TRA) is responsible for 10% to 20% of motor vehicle fatalities [1]. Both finite element (FE) modeling and experimental investigations have enhanced our understanding of the injury mechanisms associated with TRA. Because accurate material properties are essential for the development of correct and authoritative FE model predictions, the objective of the current study was to identify a suitable material model and model parameters for aorta tissue that can be incorporated into FE aorta models for studying TRA. An Ogden rubber material (Type 77B in LS-DYNA 970) was used to simulate a series of high speed uniaxial experiments reported by Mohan [2] using a dumbbell shaped FE model representing human aortic tissue. Material constants were obtained by fitting model simulation results against experimentally obtained corridors. The sensitivity of the Ogden rubber material model was examined by altering constants G and alpha (α) and monitoring model behavior. One single set of material constants (α = 25.3, G = 0.02 GPa, and μ = 0.6000E-06 GPa) was found to fit uniaxial data at strain rates of approximately 100 s−1 for both younger and older aortic tissue specimens. Until a better material model is derived and other experimental data are obtained, it is recommended that the Ogden material model and associated constants derived from the current study be used to represent aorta tissue properties when using FE methods to investigate mechanisms of TRA.

scholarly journals An inverse problem for the characterization of dynamic material model parameters from a single SHPB test

2011 ◽  
Vol 10 ◽  
pp. 1603-1608 ◽  
Author(s):  
C. Hernandez ◽  
A. Maranon ◽  
I.A. Ashcroft ◽  
J.P. Casas-Rodriguez
Keyword(s):  
Inverse Problem ◽  
Material Model ◽  
Model Parameters ◽  
Dynamic Material Model ◽  
Shpb Test

Material Characterization of Rubberized Aramid for Shock Mitigation

2012 ◽  
Author(s):  
Jagadeep Thota ◽  
Mohammed Saadeh ◽  
Mohamed B. Trabia ◽  
Brendan O’Toole ◽  
Chang-Hyun Lee ◽  
...  
Keyword(s):  
Material Model ◽  
Tensile Tests ◽  
Mechanical Analysis ◽  
Sensitive Material ◽  
Material Models ◽  
Military Vehicles ◽  
Composite Armor ◽  
Critical Components ◽  
Proper Material

Modern military vehicles can reduce transmitted shocks to critical components within it through the use of composite armor and rubberized material at the space frame joints. Therefore, proper material models of these shock absorbing materials are imperative to accurately understand shock transmission. While quasi-static mechanical characteristics of candidate materials may be well understood, their behavior under dynamic conditions has not been studied as much. This research presents the mechanical characterization of rubberized aramid, which is used as a part of a composite armor. Since the rubberized aramid material may be subjected to large deformations due to the high impact loading, a strain-sensitive material model is proposed to describe this material computationally. Tensile tests on rubberized aramid are conducted under various strain rates. Additionally, dynamic mechanical analysis (DMA) vibration tests are conducted to determine the damping property of the rubberized aramid material. These measured characteristics can be incorporated in the material models that will be used in the computational analysis of the armored vehicle under shock loading.

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