Viscoelastic Properties of the Aortic Valve Interstitial Cell

There has been growing interest in the mechanobiological function of the aortic valve interstitial cell (AVIC) due to its role in valve tissue homeostasis and remodeling. In a recent study we determined the relation between diastolic loading of the aortic valve (AV) leaflet and the resulting AVIC deformation, which was found to be substantial. However, due to the rapid loading time of the AV leaflets during closure (∼0.05 s), time-dependent effects may play a role in AVIC deformation during physiological function. In the present study, we explored AVIC viscoelastic behavior using the micropipette aspiration technique. We then modeled the resulting time-length data over the 100 s test period using a standard linear solid model, which included Boltzmann superposition. To quantify the degree of creep and stress relaxation during physiological time scales, simulations of micropipette aspiration were preformed with a valve loading time of 0.05 s and a full valve closure time of 0.3 s. The 0.05 s loading simulations suggest that, during valve closure, AVICs act elastically. During diastole, simulations revealed creep (4.65%) and stress relaxation (4.39%) over the 0.3 s physiological time scale. Simulations also indicated that if Boltzmann superposition was not used in parameter estimation, as in much of the micropipette literature, creep and stress relaxation predicted values were nearly doubled (7.92% and 7.35%, respectively). We conclude that while AVIC viscoelastic effects are negligible during valve closure, they likely contribute to the deformation time-history of AVIC deformation during diastole.

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Viscoelasticity Analysis and Experimental Validation of Anisotropic Composite Overwrap Cylinders

Volume 8: Mechanics of Solids, Structures and Fluids ◽

10.1115/imece2012-87818 ◽

2012 ◽

Cited By ~ 1

Author(s):

Jerome T. Tzeng ◽

Ryan P. Emerson ◽

Daniel J. O’Brien

Keyword(s):

Stress Relaxation ◽

Experimental Validation ◽

Elevated Temperatures ◽

Model Simulation ◽

Viscoelastic Behavior ◽

Pressure Vessels ◽

Steel Cylinder ◽

Viscoelastic Effects ◽

Creep And Stress Relaxation ◽

Composite Cylinders

Stress relaxation and creep of composite cylinders are investigated based on anisotropic viscoelasticity. The analysis accounts for ply-by-ply variation of material properties, ply orientations, and temperature gradients through the thickness of cylinders subjected to mechanical and thermal loads. Experimental validation of the model is conducted using a high-tensioned composite overwrapped on a steel cylinder. The creep and stress relaxation response of composite is accelerated at elevated temperatures, then characterized and compared to the model simulation. Fiber reinforced composite materials generally illustrate extreme anisotropy in viscoelastic behavior. Viscoelastic effects of the composite can result in a drastic change of stress and strain profiles in the cylinders over a period of time, which is critical for structural durability of composite cylinders. The developed analysis can be applied to composite pressure vessels, gun barrels, and flywheels design of life prediction.

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Correlation of Cooperatively Localized Rearrangement on the “Fluidized Domain" of Polymers to Their Nonexponentially Viscoelastic Behavior and Lifetime at Double Aging Processes II: Estimation of Long-term Mechanical Behavior and Lifetime of Polymeric Materials from Short-time Creep and Stress Relaxation Tests

Chinese Journal of Chemical Physics ◽

10.1088/1674-0068/23/02/185-194 ◽

2010 ◽

Vol 23 (2) ◽

pp. 185-194 ◽

Cited By ~ 3

Author(s):

Yan Jin ◽

Ming-shi Song ◽

Gui-xian Hu ◽

Da-ming Wu

Keyword(s):

Stress Relaxation ◽

Mechanical Behavior ◽

Viscoelastic Behavior ◽

Polymeric Materials ◽

Double Aging ◽

Creep And Stress Relaxation ◽

Short Time

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Viscoelastic Effects on Fatigue Behavior of Braided Composites

Materials, Nondestructive Evaluation, and Pressure Vessels and Piping ◽

10.1115/imece2006-14091 ◽

2006 ◽

Author(s):

Jitendra S. Tate ◽

Ajit D. Kelkar ◽

Gary Beall

Keyword(s):

Stress Relaxation ◽

Fatigue Behavior ◽

Resin Transfer Molding ◽

Viscoelastic Behavior ◽

Textile Composites ◽

Braided Composites ◽

Transfer Molding ◽

Out Of Plane ◽

Viscoelastic Effects ◽

Vartm Process

Textile composites include woven, braided, and knitted fabrics. Textile composites are considered when out-of-plane properties are also important. Textile composites generally have better dimensional stability, out-of-plane properties, and impact and delamination resistance. The natural conformability of biaxial braids makes them more cost competitive than woven fabric. These material systems are gaining popularity, in particular for the small business jets, where FAA requires take off weights of 5670 kgf or less. The vacuum assisted resin transfer molding (VARTM) process has proven to be low in cost compared to resin transfer molding (RTM). Thus, the combination of biaxial braids and the VARTM process is likely to considerably reduce overall costs. Before the braids can be confidently used in the primary structures, it is necessary to understand the performance of biaxial braided composites under various loading conditions and especially under fatigue. This will reduce uncertainty and hence reduce the factor of safety in the design This research addresses viscoelastic effects on fatigue behavior of carbon/epoxy braided composites. It is observed that braided composites exhibit creep and stress relaxation. Further it is observed that frequency in axial fatigue loading plays dominant role in fatigue life, but very little role in fatigue failure mechanisms. Rate of stiffness degradation is greatly affected by frequency. These entire phenomena such as creep, stress relaxation, frequency effect, and dependency of stiffness on rate of loading indicate the viscoelastic behavior of braided composites. In this research different tests were performed to confirm viscoelastic behavior of braided composites. Axial tension-tension fatigue tests were conducted at different frequencies and stiffness degradation was studied.

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Creep and Stress Relaxation of Natural Rubber Vulcanizates. Part I. Effect of Crosslink Density on the Rate of Creep in Different Vulcanizing Systems

Rubber Chemistry and Technology ◽

10.5254/1.3544787 ◽

1971 ◽

Vol 44 (3) ◽

pp. 707-720

Author(s):

E. D. Fairlie

Keyword(s):

Creep Rate ◽

Stress Relaxation ◽

Natural Rubber ◽

Chemical Treatment ◽

Crosslink Density ◽

Strong Dependence ◽

Viscoelastic Behavior ◽

Creep And Stress Relaxation ◽

Natural Rubber Vulcanizates ◽

Determining Factor

Abstract The physical creep of unfilled natural rubber vulcanizates, prepared with different vulcanizing systems, has been studied. For each of the three vulcanizing systems chosen there is a strong dependence of creep rate on crosslink density, but the rates for accelerated sulfur vulcanizates are two or three times higher than those of peroxide vulcanizates of similar crosslink density. Supplementary experiments, in which the crosslink structure of sulfur vulcanizates is modified either by chemical treatment or by variations in the vulcanizing conditions, show that the nature of the crosslink itself is not a determining factor in the type of vulcanizate. Other features, such as the type and quantity of extranetwork material arising from the vulcanizing process, contribute significantly to the viscoelastic behavior of accelerated sulfur vulcanizates.

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