Incorporating Density and Temperature in the Stretched Exponential Model for Predicting Stress Relaxation Behavior of Polymer Foams

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Bipul Barua ◽  
Mrinal C. Saha
Keyword(s):  
Experimental Data ◽  
Stress Relaxation ◽  
Exponential Model ◽  
Polyurethane Foams ◽  
Relaxation Behavior ◽  
Model Parameters ◽  
Polymer Foams ◽  
Stress Relaxation Behavior ◽  
Stretched Exponential ◽  
Closed Cell

This paper discusses an approach to incorporate density and temperature terms in the well-known stretched exponential (SE) model for predicting the stress relaxation behavior of polymer foams. We have developed this approach for closed-cell polyurethane foams (PUFs) and verified using experimental data for accuracy. The SE model was first examined using short-term experimental data to predict long-term stress relaxation behavior of PU solid (PUS). The corresponding model parameters were then extracted for PUS and two PUFs with different densities (PU404 and PU415) at three different test temperatures. Finally, an expression was developed in conjunction with the modified Gibson–Ashby relationship and the Arrhenius equation and validated for other foam density (PU420) and test temperatures. The predictions were found to be reasonably good with more than 90% accuracy.

Tensile Stress Relaxation Behavior of Thermosetting Polyurethane Solid and Foams: Experiment and Model Prediction

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Bipul Barua ◽  
Mrinal C. Saha
Keyword(s):  
Stress Relaxation ◽  
Rectangular Cross Section ◽  
Tensile Force ◽  
Relaxation Modulus ◽  
Exponential Model ◽  
Relaxation Behavior ◽  
Foam Formation ◽  
Stress Relaxation Behavior ◽  
Stretched Exponential ◽  
Stretched Exponential Model

Stress relaxation behavior of thermosetting polyurethane (PU) solid and foams were investigated in tensile mode using a dynamic mechanical analyzer (DMA). PU solid samples were manufactured in a closed mold to avoid any foam formation, whilst PU foam samples were manufactured inside a woven using a silicone mold. Samples with rectangular cross-section were subjected to a predetermined amount of tensile strain and the tensile force was recorded as a function of time. Relaxation modulus was determined for different temperatures up to near the glass transition temperature. It was found that the viscous part becomes more dominant with increasing test temperature. Although the stress relaxation behavior of PU solid and foam were found similar at lower temperature, the relaxation behavior of the foam was influenced by the cellular structure especially at higher temperature due to the combination of gas expansion and cell wall softening. Different stress relaxation models such as Maxwell model, Burgers model, Generalized Maxwell (GM) model, and Stretched exponential model were employed to predict the relaxation behavior of PU solid and foams. It was found that the GM model (with three or more elements) and the Stretched exponential model were in good agreement with the experimental data in predicting the stress relaxation behavior of both solid and foams. The predicted relaxation time and equilibrium modulus were found to decrease with increase in temperature.

A Unified Continuum Damage Mechanics Model for Predicting the Stress Relaxation Behavior of High-Temperature Bolting

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
J. Q. Guo ◽  
X. T. Zheng ◽  
Y. Zhang ◽  
H. C. Shi ◽  
W. Z. Meng
Keyword(s):  
Experimental Data ◽  
High Temperature ◽  
Stress Relaxation ◽  
Constitutive Equations ◽  
Damage Mechanics ◽  
Continuum Damage Mechanics ◽  
Relaxation Behavior ◽  
Continuum Damage ◽  
Creep Equation ◽  
Stress Relaxation Behavior

Two stress relaxation constitutive models have been developed to predict the stress relaxation behavior for high-temperature bolting according to continuum damage mechanics, Kachanov–Robatnov (K–R), and Othman–Hayhurst (O–H) creep constitutive equations as well as stress relaxation strain equations. To validate the effectiveness of constitutive equations, the predicted results were compared with the experimental data of uniaxial isothermal stress relaxation tests using 1Cr10NiMoW2VNbN steel. The results show that the results obtained by the stress relaxation constitutive model based on the K–R creep equation overestimates the stress relaxation behavior, while the model deduced by the O–H creep equation is more in agreement with the experimental data. Moreover, the stress relaxation damage predicted increases with the increment of initial stress significantly. These indicate that the new models can predict the stress relaxation behavior of high-temperature bolting well.

Effects of accelerator type on stress relaxation behavior and network structure of aged natural rubber/chloroprene rubber vulcanizates

2016 ◽  
Vol 49 (5) ◽  
pp. 381-396 ◽  
Author(s):  
Farzad A Nobari Azar ◽  
Murat Şen
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Network Structure ◽  
Structural Changes ◽  
Relaxation Behavior ◽  
Stress Relaxation Behavior ◽  
Rubber Blends ◽  
Chloroprene Rubber ◽  
Weather Changes ◽  
Behavior Network

Natural rubber/chloroprene rubber (NR/CR) blends are among the commonly used rubber blends in industry and continuously are exposed to severe weather changes. To investigate the effects of accelerator type on the network structure and stress relaxation of unaged and aged NR/CE vulcanizates, tetramethyl thiuram disulfide, 2-mercaptobenzothiazole, and diphenyl guanidine accelerators have been chosen to represent fast, moderate, and slow accelerator groups, respectively. Three batches have been prepared with exactly the same components and mixing conditions differing only in accelerator type. Temperatures scanning stress relaxation and pulse nuclear magnetic resonance techniques have been used to reveal the structural changes of differently accelerated rubber blends before and after weathering. Nonoxidative thermal decomposition analyses have been carried out using a thermogravimetric analyzer. Results indicate that there is a strong interdependence between accelerator type and stress relaxation behavior, network structure, cross-linking density, and aging behavior of the blends. Accelerator type also affects decomposition energy of the blends.

scholarly journals Stress-relaxation behavior in gels with ionic and covalent crosslinks

2010 ◽  
Vol 107 (6) ◽  
pp. 063509 ◽  
Author(s):  
Xuanhe Zhao ◽  
Nathaniel Huebsch ◽  
David J. Mooney ◽  
Zhigang Suo
Keyword(s):  
Stress Relaxation ◽  
Relaxation Behavior ◽  
Stress Relaxation Behavior ◽  
Covalent Crosslinks

Reloading Stress Relaxation Behavior Analysis Based on a Creep Model for High Temperature Bolting Steel

2013 ◽  
Vol 328 ◽  
pp. 950-954
Author(s):  
Wei Wei Zhang ◽  
Hong Xu ◽  
Hong Yuan Li
Keyword(s):  
High Temperature ◽  
Stress Relaxation ◽  
Steady State Creep ◽  
Relaxation Behavior ◽  
Creep Model ◽  
National Research Institute ◽  
Time Intervals ◽  
Stress Relaxation Behavior ◽  
Proposed Model ◽  
Good Agreement

An analytical method based on a creep model is being developed to investigate the effect of retightening on stress relaxation behavior for high-temperature turbine and valve studs/bolts. In order to validate the approach, the calculated results are compared to the results of uniaxial reloading stress relaxation testing, which were performed by the National Research Institute for Metals of Japan (NRIM) for 12Cr-1Mo-1W-1/4V stainless steel bolting material at 550°C. It was shown that the proposed model based on Altenbach-Gorash-Naumenko creep model for the primary and steady state creep could be applied for the present data. The calculated residual stresses versus time curves were in good agreement with the measured for initial stress level of 273.6MPa at 550°C and for specific reloading time intervals of 24, 72, 240, and 720 hours.

Long-term stress relaxation behavior of Polyaniline-EPDM blends using the time-temperature-strain superposition method

2018 ◽  
Vol 6 (2) ◽  
pp. 025318 ◽  
Author(s):  
Muhammad Shafiq Irfan ◽  
Yasir Qayyum Gill ◽  
Motahira Hashmi ◽  
Sana Ullah ◽  
Farhan Saeed ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Relaxation Behavior ◽  
Superposition Method ◽  
Stress Relaxation Behavior ◽  
Temperature Strain
Sign in / Sign up

Export Citation Format

Share Document