Characterization of Viscoelastic Behavior of Stereoregular Poly(Isoprenes) by Relaxation Experiments

1974 ◽  
Vol 47 (1) ◽  
pp. 1-18
Author(s):  
L. Szilagyi ◽  
T. Riccò ◽  
F. Danusso
Keyword(s):  
Viscoelastic Behavior ◽  
Supermolecular Structure ◽  
Relaxation Modulus ◽  
Mechanical Relaxation ◽  
Recent Theory ◽  
Mean Values ◽  
Linear Viscoelastic ◽  
Viscoelastic Theory ◽  
Linear Viscoelastic Theory ◽  
Relationship Of

Abstract The mechanical relaxation of twelve samples of unvulcanized cis poly-(isoprene)s, including both natural and synthetic polymers, was studied over a range of temperatures. Master curves of relaxation modulus obtained from these data were used to derive relaxation spectra according to linear viscoelastic theory. A recent theory was used to calculate mean values of quantities related to the supermolecular structure which occurs spontaneously in these materials and is responsible for their viscoelastic properties. This structure is schematized in a model consisting of a system of macromolecules which interact with each other by elastic forces and frictions corresponding to points of entanglement between chains. The analysis leads to the determination, for each sample, of the number of entanglements per molecule, the physical network density, the value of relaxation parameters, and the relationship of each of these quantities to molecular weight.

Quasi-Linear Viscoelastic Properties of Normal Articular Cartilage

1980 ◽  
Vol 102 (2) ◽  
pp. 85-90 ◽  
Author(s):  
S. L.-Y. Woo ◽  
B. R. Simon ◽  
S. C. Kuei ◽  
W. H. Akeson
Keyword(s):  
Articular Cartilage ◽  
Viscoelastic Properties ◽  
Elastic Stress ◽  
Cyclic Tests ◽  
Nonlinear Viscoelastic ◽  
Linear Viscoelastic ◽  
Strain Relationship ◽  
Viscoelastic Theory ◽  
Linear Viscoelastic Theory ◽  
Relationship Of

A combined experimental and analytical approach was used to determine the history-dependent viscoelastic properties of normal articular cartilage in tension. Specimens along the surface split line direction, taken from the middle zone of articular cartilage were subjected to relaxation and cyclic tests. A quasi-linear viscoelastic theory proposed by Fung [31] was used in combination with the experimental results to determine the nonlinear viscoelastic properties and the elastic stress-strain relationship of normal articular cartilage.

scholarly journals THE EFFECT OF PREGNANCY AND POSTPARTUM RECOVERY ON THE VISCOELASTIC BEHAVIOR OF THE RAT CERVIX

2012 ◽  
Vol 12 (01) ◽  
pp. 1250009 ◽  
Author(s):  
WILLIAM R. BARONE ◽  
ANDREW J. FEOLA ◽  
PAMELA A. MOALLI ◽  
STEVEN D. ABRAMOWITCH
Keyword(s):  
Viscoelastic Behavior ◽  
Collagen Content ◽  
Elastic Response ◽  
Pregnancy And Postpartum ◽  
Normal Functional ◽  
Linear Viscoelastic ◽  
Viscoelastic Theory ◽  
Matrix Organization ◽  
Linear Viscoelastic Theory ◽  
Postpartum Recovery

The objective of this study was to elucidate the normal functional adaptations of the cervix in pregnancy. Utilizing a Long-Evans rodent model, the cervix was divided into distal and proximal portions for virgin, mid-pregnant, and four weeks postpartum animals. The quasi-linear viscoelastic theory describes the elastic and viscous behavior of the cervix. A hydroxyproline assay was used to measure collagen content. The nonlinearity of the elastic response significantly increased throughout the entire cervix during pregnancy when compared to virgin samples (p < 0.05) and was similar to virgin samples postpartum. All viscous behavior, except for the short-term relaxation of the proximal cervix, significantly differed for pregnant specimens (p < 0.05) and remained similar to pregnant samples postpartum. Collagen content was found to increase by mid-pregnancy only in the proximal cervix when compared to virgin. Distal and proximal portions, however, were found to differ in collagen content at all time points (p < 0.05). This study finds that the cervix becomes elastically stiffer with increasing strain and exhibits increased viscous behavior during pregnancy, with incomplete recovery postpartum. These alterations allow for quick dissipation of loads, and are likely related to altered matrix organization and porosity reported by others.

Dynamic, Regional Mechanical Properties of the Porcine Brain: Indentation in the Coronal Plane

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
Benjamin S. Elkin ◽  
Ashok Ilankova ◽  
Barclay Morrison
Keyword(s):  
Large Strain ◽  
Series Representation ◽  
Relaxation Modulus ◽  
Short Time Scale ◽  
Prony Series ◽  
Porcine Brain ◽  
Linear Viscoelastic ◽  
Viscoelastic Theory ◽  
Linear Viscoelastic Theory ◽  
Anatomic Region

Stress relaxation tests using a custom designed microindentation device were performed on ten anatomic regions of fresh porcine brain (postmortem time <3 h). Using linear viscoelastic theory, a Prony series representation was used to describe the shear relaxation modulus for each anatomic region tested. Prony series parameters fit to load data from indentations performed to ∼10% strain differed significantly by anatomic region. The gray and white matter of the cerebellum along with corpus callosum and brainstem were the softest regions measured. The cortex and hippocampal CA1/CA3 were found to be the stiffest. To examine the large strain behavior of the tissue, multistep indentations were performed in the corona radiata to strains of 10%, 20%, and 30%. Reduced relaxation functions were not significantly different for each step, suggesting that quasi-linear viscoelastic theory may be appropriate for representing the nonlinear behavior of this anatomic region of porcine brain tissue. These data, for the first time, describe the dynamic and short time scale behavior of multiple anatomic regions of the porcine brain which will be useful for understanding porcine brain injury biomechanics at a finer spatial resolution than previously possible.

scholarly journals Viscoelastic Characterization of Peripapillary Sclera: Material Properties by Quadrant in Rabbit and Monkey Eyes

2003 ◽  
Vol 125 (1) ◽  
pp. 124-131 ◽  
Author(s):  
J. Crawford Downs ◽  
J-K. Francis Suh ◽  
Kevin A. Thomas ◽  
Anthony J. Bellezza ◽  
Claude F. Burgoyne ◽  
...  
Keyword(s):  
Optic Nerve ◽  
Viscoelastic Material ◽  
Optic Nerve Head ◽  
Material Properties ◽  
Uniaxial Stress ◽  
Species Group ◽  
Linear Viscoelastic ◽  
Viscoelastic Theory ◽  
Linear Viscoelastic Theory

In this report we characterize the viscoelastic material properties of peripapillary sclera from the four quadrants surrounding the optic nerve head in both rabbit and monkey eyes. Scleral tensile specimens harvested from each quadrant were subjected to uniaxial stress relaxation and tensile ramp to failure tests. Linear viscoelastic theory, coupled with a spectral reduced relaxation function, was employed to characterize the viscoelastic properties of the tissues. We detected no differences in the stress-strain curves of specimens from the four quadrants surrounding the optic nerve head (ONH) below a strain of 4 percent in either the rabbit or monkey. While the peripapillary sclera from monkey eyes is significantly stiffer (both instantaneously and in equilibrium) and relaxes more slowly than that from rabbits, we detected no differences in the viscoelastic material properties (tested at strains of 0–1 percent) of sclera from the four quadrants surrounding the ONH within either species group.

Evaluation of the Viscoelastic Properties of the Intact Medial Collateral Ligament in a Goat Model

1999 ◽  
Author(s):  
Theodore D. Clineff ◽  
Richard E. Debski ◽  
Sven U. Scheffler ◽  
John D. Withrow ◽  
Savio L.-Y. Woo
Keyword(s):  
Medial Collateral Ligament ◽  
Viscoelastic Properties ◽  
Analytical Approach ◽  
Cruciate Ligament ◽  
Collateral Ligament ◽  
Future Studies ◽  
Linear Viscoelastic ◽  
Viscoelastic Theory ◽  
Anterior Cruciate ◽  
Linear Viscoelastic Theory

Abstract The time and history dependent viscoelastic properties have been determined for the normal medial collateral ligament (MCL) of canine (Woo, 1981), porcine anterior cruciate ligament (Kwan, 1993), and human patellar tendon in a cadaver model (Johnson, 1994). The objective of this study was to use a combined experimental and analytical approach to quantify the viscoelastic properties of the intact MCL in a goat model. A thorough understanding of the viscoelastic properties at low strain levels is necessary to future studies of the healing MCL. The quasi-linear viscoelastic theory (QLV) (Fung, 1972) was used to characterize the properties of the MCL during stress relaxation.

The Time and History-Dependent Viscoelastic Properties of the Canine Medial Collateral Ligament

1981 ◽  
Vol 103 (4) ◽  
pp. 293-298 ◽  
Author(s):  
S. L.-Y. Woo ◽  
M. A. Gomez ◽  
W. H. Akeson
Keyword(s):  
Medial Collateral Ligament ◽  
Viscoelastic Properties ◽  
Cyclic Stress ◽  
Elastic Response ◽  
Collateral Ligament ◽  
Stress Strain ◽  
Linear Viscoelastic ◽  
Viscoelastic Theory ◽  
Linear Viscoelastic Theory

The viscoelastic properties of the canine medial collateral ligament (MCL) were investigated. Stress-strain relationships at different strain rates, long-term stress relaxation and cyclic stress-strain curves of the MCL were obtained experimentally using a bone-MCL-bone preparation. The experimental data were used in conjunction with the quasi-linear viscoelastic theory as proposed by Fung [15] to characterize the reduced relaxation function, G(t) and elastic response σe (ε) of this tissue. It was found that the quasi-linear viscoelastic theory can adequately describe the time and history-dependent rheological properties of the canine medial collateral ligament.

An Improved Method to Analyze the Stress Relaxation of Ligaments Following a Finite Ramp Time Based on the Quasi-Linear Viscoelastic Theory

2004 ◽  
Vol 126 (1) ◽  
pp. 92-97 ◽  
Author(s):  
Steven D. Abramowitch ◽  
Savio L.-Y. Woo
Keyword(s):  
Stress Relaxation ◽  
Soft Tissues ◽  
Viscoelastic Behavior ◽  
Cyclic Stress ◽  
Elastic Response ◽  
Curve Fit ◽  
Order Of Magnitude ◽  
Linear Viscoelastic ◽  
Linear Viscoelastic Theory ◽  
Experimental Values

The quasi-linear viscoelastic (QLV) theory proposed by Fung (1972) has been frequently used to model the nonlinear time- and history-dependent viscoelastic behavior of many soft tissues. It is common to use five constants to describe the instantaneous elastic response (constants A and B) and reduced relaxation function (constants C, τ1, and τ2) on experiments with finite ramp times followed by stress relaxation to equilibrium. However, a limitation is that the theory is based on a step change in strain which is not possible to perform experimentally. Accounting for this limitation may result in regression algorithms that converge poorly and yield nonunique solutions with highly variable constants, especially for long ramp times (Kwan et al. 1993). The goal of the present study was to introduce an improved approach to obtain the constants for QLV theory that converges to a unique solution with minimal variability. Six goat femur-medial collateral ligament-tibia complexes were subjected to a uniaxial tension test (ramp time of 18.4 s) followed by one hour of stress relaxation. The convoluted QLV constitutive equation was simultaneously curve-fit to the ramping and relaxation portions of the data r2>0.99. Confidence intervals of the constants were generated from a bootstrapping analysis and revealed that constants were distributed within 1% of their median values. For validation, the determined constants were used to predict peak stresses from a separate cyclic stress relaxation test with averaged errors across all specimens measuring less than 6.3±6.0% of the experimental values. For comparison, an analysis that assumed an instantaneous ramp time was also performed and the constants obtained for the two approaches were compared. Significant differences were observed for constants B, C, τ1, and τ2, with τ1 differing by an order of magnitude. By taking into account the ramping phase of the experiment, the approach allows for viscoelastic properties to be determined independent of the strain rate applied. Thus, the results obtained from different laboratories and from different tissues may be compared.

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