Viscoelastic Properties of Semi-Crystalline Thermoplastic Polymers: Dynamic Analysis and Creep

2012 ◽  
Vol 188 ◽  
pp. 211-218 ◽  
Author(s):  
Dan Andrei Serban ◽  
Henry Hanson ◽  
Liviu Marşavina ◽  
Vadim V. Silberschmidt
Keyword(s):  
Viscoelastic Properties ◽  
Polymeric Materials ◽  
Mechanical Analysis ◽  
External Loading ◽  
Thermoplastic Polymer ◽  
Elastic Solids ◽  
Short Term ◽  
Creep Tests ◽  
And Storage

When subjected to external loading, polymeric materials behave in a manner intermediate between elastic solids and viscous fluids. Their mechanical properties depend on a material’s viscous flow, which, in turn, is influenced by (i) temperature, with its different magnitudes determining a ductile or brittle behaviour and (ii) time, through the effect of a deformation rate and long-term relaxation. Short-term viscoelastic properties (loss and storage moduli) of a studied semi-crystalline thermoplastic polymer were obtained using Dynamic Mechanical Analysis, while its long-term viscoelastic properties (compliances) were determined using creep tests.

scholarly journals From hierarchies to markets and partially back again in electricity: responding to decarbonization and security of supply goals

2021 ◽  
pp. 1-17
Author(s):  
Paul L. Joskow
Keyword(s):  
Market Integration ◽  
Investment Incentives ◽  
Wholesale Market ◽  
Security Of Supply ◽  
Short Term ◽  
Institutional Adaptation ◽  
The World ◽  
New Challenges ◽  
And Storage

Abstract Electric power sectors around the world have changed dramatically in the last 25 years as a result of sector liberalization policies. Many electricity sectors are now pursuing deep decarbonization goals which will entail replacing dispatchable fossil generation primarily with intermittent renewable generation (wind and solar) over the next 20–30 years. This transition creates new challenges for both short-term wholesale market design and investment incentives consistent with achieving both decarbonization commitments and security of supply criteria. Thinking broadly about the options for institutional change from a Williamsonian perspective – thinking like Williamson – provides a useful framework for examining institutional adaptation. Hybrid markets that combine ‘competition for the market’ that relies on competitive procurement for long-term purchased power agreements with wind, solar, and storage developers, ideally in a technology neutral fashion, and ‘competition in the market’ that relies on short-term markets designed to produce efficient and reliable operations of intermittent generation and storage, is identified as a promising direction for institutional adaptation. Many auction, contract, and market integration issues remain to be resolved.

Long Term Creep Life Prediction of New and Service Exposed P91 Steel

2018 ◽  
Author(s):  
Muneeb Ejaz ◽  
Norhaida Ab Razak ◽  
Andrew Morris ◽  
Scott Lockyer ◽  
Catrin M. Davies
Keyword(s):  
Tensile Strength ◽  
Creep Behaviour ◽  
Equivalent Stress ◽  
Practical Reasons ◽  
Creep Data ◽  
Short Term ◽  
Creep Tests ◽  
High Temperature Components ◽  
Term Creep

P91 steels are widely used in high temperature components for power generation. Creep data is often generated through accelerated short term creep tests, for practical reasons, via increasing stress or temperature though this may alter the creep behaviour. Through normalising the creep test stress by tensile strength the Wilshire models reduce the batch to batch scatter in the creep data and enable the prediction of long term creep data from relatively short term test results. In this work it is shown that the Wilshire models fitted to uniaxial creep rupture data can be used to predict failure in both as cast and service exposed multiaxial tests. This is provided that the equivalent stress is the rupture controlling stress, as is the case for the P91 tests examined, and the tensile strength is measured as part of the test programme.

Lifetime prediction of high-modulus polyethylene yarns subjected to creep using the Larson–Miller methodology

2019 ◽  
Vol 27 (7) ◽  
pp. 400-406
Author(s):  
Jefferson Morais Gautério ◽  
Leonardo Cofferri ◽  
Antonio Henrique Monteiro da Fonsec da Silva ◽  
Felipe Tempel Stumpf
Keyword(s):  
High Temperature ◽  
Mechanical Behavior ◽  
Polymeric Materials ◽  
Constant Load ◽  
Lifetime Prediction ◽  
High Modulus ◽  
Accelerated Tests ◽  
Creep Tests ◽  
Modulus Polyethylene

The aim of the present work is to apply the Larson–Miller technique for the study of the mechanical behavior under creep of high-modulus polyethylene (HMPE) fibers focused on use as in offshore mooring ropes. Creep is known to be a long-term phenomenon, so in most cases, reproducing such experiments in real time is not feasible, and as the life span of anchoring systems must be in the order of decades, accelerated tests are required to verify the long-term mechanical behavior of the material. The methodology using the Larson–Miller parameter is a well-documented and powerful technique for materials’ lifetime prediction, although seldom applied to polymeric materials. It involves in performing accelerated (high temperature and/or loads) creep tests to determine the parameters that are later used to estimate the rupture time of the material under constant load. It is concluded that the Larson–Miller technique is efficient for calculating the lifetime of HMPE subjected to creep.

The Effect of Ageing on the Micro-Creep Properties of Radiation Cross-Linked Materials

2016 ◽  
Vol 368 ◽  
pp. 134-137
Author(s):  
Martin Řezníček ◽  
Martin Ovsík ◽  
Adam Škrobák ◽  
David Manas
Keyword(s):  
Mechanical Properties ◽  
Polymeric Materials ◽  
Term Effect ◽  
Short Term ◽  
Creep Properties ◽  
Long Term Effect ◽  
Radiation Crosslinking ◽  
Positive Effect

Radiation crosslinking of polymeric materials have placed and nowadays in the field of long-term use of loaded products. This article aims to identify the long-term effect of radiation crosslinking on micro-creep properties. The article compares the micro-creep properties of HDPE measured two years ago with the results of tests conducted under the same conditions and on the same samples now. The effect of time on the mechanical properties of the radiation crosslinked materials was demonstrated in short-term tests. These findings demonstrate the positive effect of time on the evaluated parameters.

Modeling of a Long-Term Creep Curve of Alloy 617 for a High Temperature Gas-Cooled Reactor

2008 ◽  
Vol 385-387 ◽  
pp. 693-696 ◽  
Author(s):  
Woo Gon Kim ◽  
Song Nan Yin ◽  
Ik Hee Jung ◽  
Yong Wan Kim
Keyword(s):  
Least Square ◽  
Short Term ◽  
Creep Tests ◽  
Least Square Fitting ◽  
Creep Curves ◽  
Term Creep ◽  
Good Agreement ◽  
Short Term Creep ◽  
Stress Dependency

This study aimed to model the long-term creep curves above 105 hours by implementing a nonlinear least square fitting (NLSF) of the Kachanov-Rabotnov (K-R) model. For this purpose, the short-term creep curves obtained from a series of creep tests at 950oC were used. In the NLSF of their full creep curves, the K-R model represented a poor match to the experimental curves, but the modified K-R one revealed a good agreement to them. The Monkman-Grant (M-G) strain represented the behavior of a stress dependency, but the 􀁏 parameter was constant with a stress independency. The 􀁏 value in the modified K-R model was 2.78. Long-term creep curves above 105 hours from short-term creep data were modeled by the modified K-R model.

Cellular Iron Metabolism Studies Demonstate Safety of Magnetic Tracking of Mesenchymal Stem Cells.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 4320-4320
Author(s):  
Edyta Pawelczyk ◽  
Ali S. Arbab ◽  
Sunil Pundit ◽  
Joseph A. Frank
Keyword(s):  
Stem Cells ◽  
Mesenchymal Stem Cells ◽  
Light Microscopy ◽  
Iron Metabolism ◽  
Short Term ◽  
Protein Levels ◽  
Cellular Iron ◽  
Magnetic Labeling ◽  
And Storage

Abstract Background: Ferumoxides-protamine sulfate (Fe-Pro) complexes are used for intracellular magnetic labeling of mesenchymal stem cells (MSCs) to non invasively monitor cell trafficking and tissue distribution by in vivo magnetic resonance imaging (MRI). It has been previously shown that there was no short or long- term toxic effects on cell’s viability, proliferation, reactive oxygen species and biological functions including differentiation capacity of MSCs, however the effects of dextran coated superparamagnetic iron oxide (SPIO) nanoparticles labeling on cellular iron metabolism and storage is unknown. Objective: Evaluate the effect of using Fe-Pro complexes for magnetic cell labeling in MSCs on the expression of transferrin receptor (TfR-1) and ferritin, proteins involved in intracellular iron metabolism and storage. Methods: Confluent MSCs were labeled with Fe-Pro complexes at the ratio of 100 ug/mL to 6 ug/mL. After labeling, cells were washed and cultured for 2 months. TfR-1 and ferritin expression were evaluated at the gene and protein levels in total cell lysates, on day 1, 3, 7, 14, 28 and 35 days post-labeling, by real-time polymerase chain reaction (RT-PCR) and Western blotting. MSCs were evaluated for the presence of iron by Prussian blue stain and light microscopy. In addition, TfR-1 and ferritin levels were determined for Fe-Pro labeled and unlabeled MSCs, allowed to slowly multiply, as a result of dividing the cells in half when they reached confluence. Results: All cells were Prussian blue positive on light microscopy following labeling with Fe-Pro. Labeling of MSCs grown to confluence resulted in short-term increase of TfR-1 mRNA (day 1 and day 3, p= 0.0056) without changes in TfR-1 protein levels. Fe- Pro labeled MSC demonstrated an increase in ferritin gene expression on day 7 and 14 (p=0.0003) compared to unlabeled cells, while protein levels were higher compared to unlabeled MSC at each time point (p=0.005). However, ferritin protein levels from Fe-Pro labeled MSCs were not significantly increased after 7 passages. Conclusions: Magnetic labeling of cells with FDA approved ferumoxides complexed to protamine sulfate elicited short-term changes in cellular iron metabolism and storage that was dependent on ability to divide. Fe-Pro labeling did not have any long-term implications validating the safety of Fe-Pro labeling technique for MSCs trafficking studies by MRI.

scholarly journals Simulation mathematical model of expert system for working processes management

2009 ◽  
Vol 55 (No. 1) ◽  
pp. 1-9 ◽  
Author(s):  
O. Syrový ◽  
V. Podpěra
Keyword(s):  
Expert System ◽  
Crop Production ◽  
Material Handling ◽  
Simulation Models ◽  
Short Term ◽  
The Individual ◽  
The Given ◽  
And Storage ◽  
Working Processes

The elementary simulation mathematical models presented in this article are related with the sub-system Crop production of the expert system for the decision support in technological and working processes management and their optimisation. Along with this sub-system, the expert system also involves the sub-systems Livestock production and Material handling which is further divided into the parts Transport and Storage. The boundary between the individual parts of the expert system is usually a short-term or long-term material storage. The relative individual sub-systems are mutually connected through the information flow. For each of the sub-systems, specific simulation models are created. The simulation models in the expert system investigated replace the complex of general standards and norms used in other expert systems. The simulation models allow to take into consideration the concrete natural and production conditions (area, plots shape and inclination, soil type, transport routes length and surface, fertilisers doses, crops yields etc.) and also the technological systems utilised during the realisation of operations in working processes (technical, exploitation, energy, economical or energy means, attached vehicles, machines and equipment and method of their work) and the calculation of the parameters utilised. The simulation models also allow the creation of suitable working, and transport sets to choose their optimal variants for the given conditions. In comparison with the utilised standards and norms, the parameters computed through the simulation models significantly improve the data which represent the output from the expert system.

scholarly journals Increasing Muscle Extensibility: A Matter of Increasing Length or Modifying Sensation?

2010 ◽  
Vol 90 (3) ◽  
pp. 438-449 ◽  
Author(s):  
Cynthia Holzman Weppler ◽  
S. Peter Magnusson
Keyword(s):  
Clinical Practice ◽  
Viscoelastic Properties ◽  
Muscle Length ◽  
Short Term ◽  
Length Increase ◽  
Biomechanical Effect

Various theories have been proposed to explain increases in muscle extensibility observed after intermittent stretching. Most of these theories advocate a mechanical increase in length of the stretched muscle. More recently, a sensory theory has been proposed suggesting instead that increases in muscle extensibility are due to a modification of sensation only. Studies that evaluated the biomechanical effect of stretching showed that muscle length does increase during stretch application due to the viscoelastic properties of muscle. However, this length increase is transient, its magnitude and duration being dependent upon the duration and type of stretching applied. Most of these studies suggest that increases in muscle extensibility observed after a single stretching session and after short-term (3- to 8-week) stretching programs are due to modified sensation. The biomechanical effects of long-term (>8 weeks) and chronic stretching programs have not yet been evaluated. The purposes of this article are to review each of these proposed theories and to discuss the implications for research and clinical practice.

Creep Behavior of Building Silicone Sealant under Long-Term External Loading and its Time-Stress Equivalence

2014 ◽  
Vol 633 ◽  
pp. 451-454
Author(s):  
Xiao Gen Liu ◽  
Yi Wang Bao ◽  
Xiu Fang Wang
Keyword(s):  
Creep Curve ◽  
Creep Behavior ◽  
External Loading ◽  
Nonlinear Creep ◽  
Creep Tests ◽  
Time Stress ◽  
Silicone Sealant ◽  
Term Creep ◽  
Term Performance

The main mechanics behavior character of building silicone sealant is its time dependence£¬which lies in the existence of the interior timepiece or the characteristic time. The creep behaviors were fundamental to evaluating the long-term performance of the building silicone sealant under long-term external loading. A series of creep tests of building silicone sealant were conducted in the laboratory under different combinations of external loads, the characteristics of the creep curve were obtained. In this work, the creep behaviors of building silicone sealant were also investigated under various temperatures at invariable stress. The test measurements show that the creep behavior of building silicone sealant are nonlinear, Nonlinear creep behavior is analyzed by means of the equivalence principle of time-stress, the main creep curve under reference stress was obtained by fitting with the viscoelastic rheological model. So the long-term creep behavior of the building silicone sealant under lower stress can be predicted by short-term creep behavior under higher stress.

scholarly journals Measurable Cytokine Concentrations in Pig Seminal Plasma Are Modified by Semen Handling and Storage

Biology ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 276
Author(s):  
Lorena Padilla ◽  
Isabel Barranco ◽  
Inmaculada Parrilla ◽  
Xiomara Lucas ◽  
Heriberto Rodriguez-Martinez ◽  
...  
Keyword(s):  
Seminal Plasma ◽  
Biological Fluids ◽  
Storage Conditions ◽  
Reliable Measurement ◽  
Short Term ◽  
Gm Csf ◽  
Long Term Storage ◽  
And Storage ◽  
Term Storage

Sample handling and storing are critical steps for the reliable measurement of circulating biomolecules in biological fluids. This study evaluates how cytokine measurements in pig seminal plasma (SP) vary depending on semen handling and SP storage. Thirteen cytokines (GM-CSF, IFNγ, IL-1α, IL-1β, IL-1ra, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-18 and TNFα) were measured using Luminex xMAP® technology in individual seminal plasma (SP) samples (n = 62) from healthy breeding boars. Three separate experiments explored the delay (2 h and 24 h) in SP collection after ejaculation (Experiment 1) and SP storage, either short-term (5 °C, −20 °C and −80 °C for 72 h, Experiment 2) or long-term (at −20 °C and −80 °C for two months, Experiment 3), before analysis. Levels in fresh SP-samples were used as baseline control values. Delays in SP harvesting of up to 24 h did not substantially impact SP cytokine measurements. Some cytokines showed instability in stored SP samples, mainly in long-term storage. Ideally, cytokines in pig SP should be measured in fresh samples harvested within 24 h after ejaculation. If storage of SP is imperative, storage conditions should be adjusted for each cytokine.

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