scholarly journals Erroneous or Arrhenius: A Degradation Rate-Based Model for EPDM during Homogeneous Ageing

Polymers ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2152
Author(s):  
Maha Zaghdoudi ◽  
Anja Kömmling ◽  
Matthias Jaunich ◽  
Dietmar Wolff
Keyword(s):  
Activation Energy ◽  
Stress Relaxation ◽  
Degradation Rate ◽  
Irreversible Processes ◽  
Total System ◽  
Chemical Relaxation ◽  
Additive Contribution ◽  
Superposition Technique ◽  
Physical And Chemical

To improve the predictive capability of long-term stress relaxation of elastomers during thermo-oxidative ageing, a method to separate reversible and irreversible processes was adopted. The separation is performed through the analysis of compression set after tempering. On the basis of this separation, a numerical model for long-term stress relaxation during homogeneous ageing is proposed. The model consists of an additive contribution of physical and chemical relaxation. Computer simulations of compression stress relaxation were performed for long ageing times and the results were validated with the Arrhenius treatment, the kinetic study and the time-temperature superposition technique based on experimental data. For chemical relaxation, two decay functions are introduced each with an activation energy and a degradative process. The first process with the lower activation energy dominates at lower ageing times, while the second one with the higher activation energy at longer ageing times. A degradation-rate based model for the evolution of each process and its contribution to the total system during homogeneous ageing is proposed. The main advantage of the model is the possibility to quickly validate the interpolation at lower temperatures within the range of slower chemical processes without forcing a straight-line extrapolation.

Stress Relaxation Mechanisms in Rubbers Reinforced with Carbon Blacks

1972 ◽  
Vol 45 (1) ◽  
pp. 82-93 ◽  
Author(s):  
G. M. Bartenev ◽  
N. M. Lyalina
Keyword(s):  
Activation Energy ◽  
Stress Relaxation ◽  
Relaxation Process ◽  
Activation Energies ◽  
Relaxation Processes ◽  
Carbon Blacks ◽  
Multi Stage ◽  
Chemical Relaxation ◽  
Filled Rubbers ◽  
Weight Structures

Abstract 1. In vulcanized rubbers containing blacks a multi-stage mechanism for stress relaxation was observed. It was discovered that the stress relaxation process consists of five fundamental processes: the first three relaxation processes, related to the slow stages of physical relaxation within the bulk of the rubber, have no connection with the fillers (“soft” domains); the fourth process has to do with the relaxation in the black-rubber domain; the fifth process involves the chemical relaxation of vulcanizates. 2. The fundamental mechanisms of the first 3 relaxation processes in the soft domains have the same activation energy values and the same segmental mechanism as the rearranged domains found in supermolecular weight structures, which are also present in unfilled vulcanizates. 3. In the investigated stress range of up to 200% elongation, the activation energy for the first 3 relaxation processes in the soft domains of filled vulcanizates is not a function of the deformation strain, whereas the activation energy of the fourth relaxation process in the black-rubber domains of filled rubbers is a function of the deformation and of the filler content. For these reasons, rubber loaded with carbon blacks, in contrast to unfilled rubbers, possess the typical nonlinearity of viscoelastic materials. 4. The activation energies of the relaxation processes in the black-rubber domains decrease in a linear fashion with the value for the initial tensile stress in filled vulcanizates, and decrease in like manner for vulcanizates containing different proportions of fillers. The kinetic units, determined from the activation energies of these processes, appeared to be segments of chains with activation energies of up to 40% more than the activation energies of the physical relaxation processes in the soft domains. The other kinetic units of the processes proved to be black particles, the dimensions of which were calculated from the values for the coefficients in the formula for relaxation time.

scholarly journals Treated wastewater irrigation effects on soil hydraulic conductivity and aggregate stability of loamy soils in Israel

2015 ◽  
Vol 63 (1) ◽  
pp. 47-54 ◽  
Author(s):  
Karsten Schacht ◽  
Bernd Marschner
Keyword(s):  
Hydraulic Conductivity ◽  
Chemical Properties ◽  
Aggregate Stability ◽  
Treated Wastewater ◽  
Soil Aggregate Stability ◽  
Irrigation Effects ◽  
Physical And Chemical ◽  
The Impact

Abstract The use of treated wastewater (TWW) for agricultural irrigation becomes increasingly important in water stressed regions like the Middle East for substituting fresh water (FW) resources. Due to elevated salt concentrations and organic compounds in TWW this practice has potential adverse effects on soil quality, such as the reduction of hydraulic conductivity (HC) and soil aggregate stability (SAS). To assess the impact of TWW irrigation in comparison to FW irrigation on HC, in-situ infiltration measurements using mini disk infiltrometer were deployed in four different long-term experimental orchard test sites in Israel. Topsoil samples (0-10 cm) were collected for analyzing SAS and determination of selected soil chemical and physical characteristics. The mean HC values decreased at all TWW sites by 42.9% up to 50.8% compared to FW sites. The SAS was 11.3% to 32.4% lower at all TWW sites. Soil electrical conductivity (EC) and exchangeable sodium percentage (ESP) were generally higher at TWW sites. These results indicate the use of TWW for irrigation is a viable, but potentially deleterious option, as it influences soil physical and chemical properties.

Chemical Stress Relaxation of NR Networks Prepared in the Swollen State

1986 ◽  
Vol 59 (4) ◽  
pp. 541-550 ◽  
Author(s):  
Kyung-Do Suh ◽  
Hidetoshi Oikawa ◽  
Kenkichi Murakami
Keyword(s):  
Stress Relaxation ◽  
Network Structure ◽  
Three Dimensional ◽  
Polymer Chains ◽  
Chemical Stress ◽  
Network Chain ◽  
Crosslinking Process ◽  
Dimensional Network ◽  
Chemical Relaxation ◽  
The Difference

Abstract From the experimental results of the present investigation, it is apparent that two kinds of networks which have a different three-dimensional network structure give quite different behavior of chemical stress relaxation, even if both networks have the same network chain density. The difference in three-dimensional network structure for the two kinds of rubber arises from the degree of entanglement, which changes with the concentration of the polymer chains prior to the crosslinking process. The direct cause of chemical relaxation is due to the scission of network chains by degradation, whereas the total relaxation is caused by the change of geometrical conformation of network chains. This then casts doubt on the basic concept of chemorheology which is represented by Equation 2.

Prediction of Stress Relaxation in Power Plant Components Based on a Constitutive Model

2017 ◽  
Author(s):  
Y. Kostenko ◽  
K. Naumenko
Keyword(s):  
Power Plant ◽  
Stress Relaxation ◽  
Constitutive Model ◽  
Evolution Equations ◽  
Material Behavior ◽  
Assessment Procedure ◽  
Reliable Prediction ◽  
Inelastic Material ◽  
Plant Components

Many power plant components and joint connections are subjected to complex thermo-mechanical loading paths under severe temperature environments over a long period. An important part in the lifetime assessment is the reliable prediction of stress relaxation using improved creep modeling to avoid possible integrity or functionality issues and malfunction in such components. The aim of this work is to analyze the proposed constitutive model for advanced high chromium steels with the goal of predicting stress relaxation over the long term. The evolution equations of the constitutive model for inelastic material behavior are introduced to account for hardening and softening phenomena. The material properties were identified for 9–12%CrMoV steels in the creep range. The model is applied to the stress relaxation analysis of power plant components. The results for long-term assessment, which are encouragingly close to reality, will be presented and discussed. An outlook on further developments of the model and assessment procedure is also provided.

Description of long-term stress relaxation in stretching oriented polymers

1990 ◽  
Vol 32 (7) ◽  
pp. 1427-1431
Author(s):  
S.V. Bronnikov ◽  
V.I. Vettergren ◽  
N.S. Kalbina ◽  
L.N. Korzhavin ◽  
S.Ya. Frenkel
Keyword(s):  
Stress Relaxation ◽  
Oriented Polymers

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

Analysis on the Creep Mechanism of 12Cr-Mo-W-0.25V Steel Based on Long-Term Stress Relaxation Test Data

2016 ◽  
Vol 853 ◽  
pp. 158-162
Author(s):  
Jie Zhao ◽  
Tie Shan Cao ◽  
Cong Qian Cheng ◽  
Hui Fang Li
Keyword(s):  
Stress Relaxation ◽  
Test Data ◽  
Activation Volume ◽  
High Stress ◽  
Relaxation Curve ◽  
Relaxation Test ◽  
Dislocation Slip ◽  
Stress Relaxation Test ◽  
Steel Base

The current paper investigates on the creep behavior of 12Cr-Mo-W-0.25V heat resistant steel base on the long-term stress relaxation test data. It is shows that the stress relaxation curve can be divided into 2 stages: the high stress stage has higher apparent activation volume of 79~350 b3 and the low stress stage is 35~78 b3. Besides, the Helmholtz free energy at the high stress stage is 827~1034 kJ/mol which is higher than 210~252 kJ/mol of the low stress stage. Taking both apparent activation volume and activation energy into account, it is assumed that the high stress stage is mainly controlled by dislocation slip and the low stress stage is more related to diffusion.

scholarly journals Dry functional blend with fruit-berry powders for yeast dough

2019 ◽  
Vol 81 (2) ◽  
pp. 177-183
Author(s):  
A. V. Moshkin ◽  
A. T. Vasyukova ◽  
A. E. Alexeyev
Keyword(s):  
Raw Materials ◽  
Long Term Storage ◽  
Chemical Indicators ◽  
Toxicological Studies ◽  
The Russian Federation ◽  
Milk Mixture ◽  
Physical And Chemical ◽  
Term Storage ◽  
High Calorie

The basic information about functional mixtures is outlined, options for compositions and recommendations for use in baking in mass production are proposed. The characteristic of microbiological, physical and chemical indicators is given, and the results of toxicological studies of dry functional mixtures with fruit and berry powders are given. High-calorie, medium-calorie, and low-calorie composite mixtures have been developed for the centralized production of yeast dough. Dry functional mixtures can be produced according to regulatory documents: TU 9161-004-51926638-11 and TI to TU 9161-004-51926638-11. A patent of the Russian Federation No. 2602629 was obtained for dry functional mixtures with fruit and berry powders. The technological scheme for obtaining a dry functional mixture consists of the following operations: sifting, dosing of prescription components in predetermined proportions: dry egg-milk mixture in the amount of 56.2-61.6% sugar – 20.0-24.3% and salt – 14.1-17.2%. Xanthan (1.06-2.43%) or guar (4.25-5.30%) and fruit and berry powders (1.0-1.5%) are introduced as additional raw materials. Then mixing is carried out, preparation for implementation. The resulting mixture is portioned and packaged in paper bags. Fruit and berry powders were prepared from rose hips, aronia, nettle, bananas, apples and carrots. According to microbiological studies, the degree of contamination during storage during the year corresponds to SanPiN 2.3.2.1078-01, which makes it possible to produce dry functional mixtures with fruit and berry powders for long-term storage. They can be stored in a dry, well-ventilated room in compliance with sanitary rules, with a relative humidity of 65-70% and a temperature of 18-20 °C from 0 to 12 months. It was found that during storage for 12 months. in hermetically sealed paper bags, no powder quality changes were observed. Bakery products made using these mixtures can be recommended for medical, preventive and gerontological nutrition.

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