The Stress-Relaxation Behavior of Rice as a Function of Time, Moisture and Temperature

2017 ◽  
Vol 13 (2) ◽  
Author(s):  
Pan Wang ◽  
Li-jun Wang ◽  
Dong Li ◽  
Zhi-gang Huang ◽  
Benu Adhikari ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Moisture Content ◽  
Master Curve ◽  
Superposition Principle ◽  
Relaxation Modulus ◽  
Maxwell Model ◽  
Relaxation Behavior ◽  
Stress Relaxation Behavior ◽  
Linear Viscoelastic ◽  
Single Rice

Abstract: Stress-relaxation behavior of single rice kernel was studied using a dynamic mechanical analyzer (DMA) in compression mode. The relaxation modulus was measured in a moisture content range of 12–30 % on dry basis (d.b.) and a temperature range of 25–80°C. A constant stain value of 1 % (within the linear viscoelastic range) was selected during the stress-relaxation tests. The relaxation modulus was found to decrease as the temperature and moisture increased. A master curve of relaxation modulus as a function of temperature and moisture content was generated using the time–moisture–temperature superposition principle. Results showed that the generalized Maxwell model satisfactorily fitted the experimental data of the stress-relaxation behavior and the master curve of relaxation modulus (R2> 0.997). By shifting the temperature curves horizontally, the activation energy of the stress relaxation was obtained which significantly decreased with increase in the moisture content.

On the Relation between Stress Relaxation and Constant Strain Rate Tensile Behavior for Linear Viscoelastic Materials; An Engineering Approach

2012 ◽  
Vol 729 ◽  
pp. 314-319 ◽  
Author(s):  
Gábor Bódai ◽  
Tibor Goda
Keyword(s):  
Stress Relaxation ◽  
Master Curve ◽  
Superposition Principle ◽  
Constant Strain Rate ◽  
Relaxation Modulus ◽  
Tensile Tests ◽  
Time Frequency ◽  
Construction Methods ◽  
Linear Viscoelastic ◽  
Time Temperature Superposition Principle

The present paper, as a first step summarizes briefly the master curve construction methods applying the stress relaxation and DMTA based approach. Then, authors make recommendation to increase the covered time (frequency) domain of relaxation modulus master curve coming from standard tensile tests-performed at wide temperature range-by utilizing the time-temperature superposition principle. The proposed approach is used for natural rubber, whose tensile tests, for the sake of simplicity, are replaced by calculated engineering stress-strain curves. All in all, the proposed method gives fast and reliable way for engineers to identify the parameters of spring-dashpot models.

Stress Relaxation Measurement of Agar Using a Polymer-Based Microfluidic Device

2013 ◽  
Author(s):  
Jiayue Shen ◽  
Peng Cheng ◽  
Wenting Gu ◽  
Michael Stacey ◽  
Zhili Hao
Keyword(s):  
Stress Relaxation ◽  
Microfluidic Device ◽  
Series Representation ◽  
Relaxation Modulus ◽  
Soft Materials ◽  
Maxwell Model ◽  
Relaxation Behavior ◽  
Relaxation Measurement ◽  
Stress Relaxation Behavior ◽  
Prony Series Representation

In light of the significance of the viscoelastic property of agar to cell-based tissue engineering, this paper presents the stress relaxation measurement of agar using a polymer-based microfluidic device. Comprised of a single polymer rectangular microstructure and a set of electrolyte-enabled distributed transducers, this device is capable of detecting continuous distributed static and dynamic loads. In the measurement, an agar specimen is placed on the device and a rigid probe is utilized to press the specimen against the device with a step displacement input. Consequently, the stress relaxation behavior of the specimen translates to time-dependent continuous distributed loads acting on the device and is further registered as discrete resistance changes by the device. Two agar specimens of 1% and 3% in concentration, respectively, are measured using this device; and the data analysis is conducted on the measured results to extract Young’s relaxation modulus, which is further expressed by a Prony-series representation of the Maxwell model with two exponential terms. The results demonstrate the feasibility of using this device to measure the stress relaxation behavior of soft materials.

The Bending and Recovery of Fabrics under Conditions of Changing Temperature and Relative Humidity

1976 ◽  
Vol 46 (2) ◽  
pp. 113-122 ◽  
Author(s):  
B. M. Chapman
Keyword(s):  
Stress Relaxation ◽  
Relative Humidity ◽  
Relaxation Behavior ◽  
Bending Stress ◽  
Relaxation Data ◽  
Viscoelastic Parameter ◽  
Stress Relaxation Behavior ◽  
Recovery Behavior ◽  
Linear Viscoelastic ◽  
Viscoelastic Element

The bending stress relaxation and recovery behavior of fabrics under conditions of changing temperature and humidity has been investigated. The fabric recovery is successfully predicted, from its stress relaxation behavior and a frictional parameter, using a previously presented model consisting of a generalized linear viscoelastic element in parallel with a frictional element. Furthermore, a viscoelastic parameter, simply obtainable from the relaxation data, together with the frictional parameter, have been shown to correlate well with observed recovery and may be useful as convenient indicators of fabric wrinkle performance.

Tensile Stress Relaxation of Thermosetting Polyurethane Solid and Foam

2010 ◽  
Author(s):  
Bipul Barua ◽  
Mrinal C. Saha
Keyword(s):  
Stress Relaxation ◽  
Rectangular Cross Section ◽  
Tensile Force ◽  
Relaxation Modulus ◽  
Relaxation Behavior ◽  
Characteristic Relaxation Time ◽  
Foam Formation ◽  
Stress Relaxation Behavior ◽  
Different Temperatures ◽  
Cure Temperature

Stress relaxation behavior of thermosetting polyurethane (PU) solid and foam were investigated in tensile mode using a dynamic mechanical analyzer (DMA). PU solid samples were manufactured in a closed mold under compression to avoid any foam formation, whilst the foam samples were manufactured inside a woven using a silicone mold. Effects of cure and the post-cure temperature were also investigated on the stress relaxation behavior. Samples in the form of rectangular cross-section were subjected to a predetermined amount 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 dominant with increasing test temperature. The experimental data was precisely modeled using a generalized Maxwell’s model and the characteristic relaxation time was identified with the corresponding relaxation process. Although the stress relaxation behavior of PU solid and PU foams were found similar at room temperature, the relaxation behavior of the foam was found to be influenced by the cell morphology at higher temperature.

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.

Strain and Age Effects on Behavior of a Concrete Pavement Joint Sealant Material

1996 ◽  
Vol 1529 (1) ◽  
pp. 95-100
Author(s):  
Ashok Gurjar ◽  
Dan G. Zollinger ◽  
Tianxi Tang
Keyword(s):  
Master Curve ◽  
Superposition Principle ◽  
Relaxation Modulus ◽  
Maxwell Model ◽  
Material Model ◽  
Concrete Pavement ◽  
Age Effects ◽  
Joint Analysis ◽  
Generalized Maxwell Model ◽  
Sealant Material

A one-part self-leveling silicone joint sealant material was experimentally investigated in the laboratory. It was found that strain and age had apparent effects on the relaxation modulus of the material. Relaxation tests were conducted under different strain levels. The test samples were exposed to ultraviolet radiation and moisture for artificial aging before testing. For this largely deformable material, finite strain formulas were used in analysis of experimental data. Strain and age effects were successfully normalized in the relaxation master curve by using the superposition principle. On the basis of the master curve, a material model of the generalized Maxwell model in parallel type was constructed. The real time was scaled to the reduced time by time-strain shift and time-age shift factors so as to characterize the strain and age effects. This model is mathematically simple and can be easily applied in finite element programs for concrete pavement joint analysis.

Synchronized Heterogeneous Indentation and Stress Relaxation Behavior of Articular Cartilage Upon Macroscopic Compression: A Preliminary Study

2014 ◽  
Author(s):  
Jiayue Shen ◽  
Wenting Gu ◽  
Xavier-lewis Palmer ◽  
Siqi Guo ◽  
Zhili Hao
Keyword(s):  
Articular Cartilage ◽  
Stress Relaxation ◽  
Viscoelastic Behavior ◽  
Relaxation Modulus ◽  
Relaxation Behavior ◽  
Indentation Modulus ◽  
Cartilage Sample ◽  
Stress Relaxation Behavior ◽  
Bovine Articular Cartilage ◽  
Preliminary Study

By using a newly-developed experimental technique that is enabled by a polymer-based microfluidic device for detecting distributed normal loads, a preliminary study is presented on the synchronized heterogeneous indentation and stress relaxation behavior of articular cartilage upon macroscopic compression. In a measurement, a rigid cylinder probe is employed to exert macroscopic indentation or step input to a cartilage sample on the device. Consequently, the synchronized heterogeneous viscoelastic behavior of the sample translates to distributed normal loads acting on the device and is captured by the device. While the macroscopic load acting on a sample is recorded by a load cell, the deflections of a sample along its length are captured by the device. Thus, the measured results essentially are the load-deflection relations of a sample along its length. Full-thickness lapine and bovine articular cartilage samples are prepared and measured. A thorough data analysis is implemented on the recorded data for extracting their instant and relaxed indentation modulus, as well as Young’s relaxation modulus.

Stress Relaxation of a Twaron®/Natural Rubber Composite

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
N. V. David ◽  
X.-L. Gao ◽  
J. Q. Zheng
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Rheological Model ◽  
Maxwell Model ◽  
Relaxation Behavior ◽  
Stress Relaxation Behavior ◽  
Generalized Maxwell Model ◽  
Rubber Composite ◽  
Long Time ◽  
Different Levels

The stress relaxation behavior of a Twaron CT709® fabric/natural rubber composite under a uniaxial constant strain is studied using three viscoelasticity models with different levels of complexity and a newly developed para-rheological model. The three viscoelasticity models employed are a one-term generalized Maxwell model (comprising one Maxwell element and an additional spring in parallel), a two-term generalized Maxwell model (including two Maxwell elements and an additional spring in parallel), and a four-parameter Burgers model. The values of the parameters involved in each model are extracted from the experimental data obtained in this study. The stress relaxation tests reveal that the stress starts to decay exponentially for a short duration and then continues to decrease linearly with time. It is found that the initial relaxation response of the composite is predicted fairly well by all of the four models, while the long-time stress relaxation behavior is more accurately predicted by the para-rheological model. The accuracy of each model in describing the stress relaxation behavior of the composite is quantitatively compared.

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