scholarly journals Model for a linear viscoelastic medium that has consistent creep and stress‐relaxation properties

1986 ◽  
Vol 79 (S1) ◽  
pp. S62-S62
Author(s):  
Anthony J. Rudgers
Keyword(s):  
Stress Relaxation ◽  
Viscoelastic Medium ◽  
Relaxation Properties ◽  
Linear Viscoelastic ◽  
Creep And Stress Relaxation

scholarly journals PROPERTIES OF COMPOSITIONAL MATERIALS BASED ON THE MIXTURES OF EPOXY POLYMERS AND OLIGOSULPHONES. PART 2. STATIC AND DYNAMIC RELAXATION PROPERTIES

2019 ◽  
Vol 4 (5) ◽  
pp. 140-146 ◽  
Author(s):  
Ю. Кочергин ◽  
Yuriy Kochergin ◽  
Т. Григоренко ◽  
Tatyana Grigorenko ◽  
В. Золотарева ◽  
...  
Keyword(s):  
Molecular Weight ◽  
High Temperature ◽  
Stress Relaxation ◽  
Dynamic Shear Modulus ◽  
Dynamic Shear ◽  
Dynamic Relaxation ◽  
Relaxation Properties ◽  
Epoxy Polymers ◽  
Creep And Stress Relaxation ◽  
Epoxy Systems

The effect of low-molecular polysulfones (oligosulfones) on the static and dynamic relaxation properties of epoxy polymers based on industrial resin ED-20 is studied. It is established that the modification of oligosulfones with terminal carboxyl, phenolic groups and a molecular weight from 1200 to 44500 leads to the formation of epoxy systems with higher performance in terms of development of static processes of creep and stress relaxation. It is demonstrated that the dynamic shear modulus increases with the introduction of the modifier. The magnitude of this effect is proportional to the molecular weight of oligosulfones. The intensities of the high-temperature α-transition at 390 K and the low-temperature β-transition at 208 K decrease with the introduction of the modifier. The improvement of the relaxation properties is associated with an increase in the density of the chemical grid of the epoxy matrix with the introduction of modifiers, its saturation with more rigid and heat-resistant component and the formation of additional intermolecular bonds between the components of the system

Indentation Creep and Relaxation Measurements of Polymers

2004 ◽  
Vol 841 ◽  
Author(s):  
Mark R. VanLandingham ◽  
Peter L. Drzal ◽  
Christopher C. White
Keyword(s):  
Stress Relaxation ◽  
Mechanical Response ◽  
Creep Compliance ◽  
Relaxation Modulus ◽  
Polymeric Materials ◽  
Indentation Creep ◽  
Dimethyl Siloxane ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
Creep And Stress Relaxation

ABSTRACTInstrumented indentation was used to characterize the mechanical response of polymeric materials. A model based on contact between a rigid probe and a linear viscoelastic material was used to calculate values for creep compliance and stress relaxation modulus for epoxy, poly(methyl methacrylate) (PMMA), and two poly(dimethyl siloxane) (PDMS) elastomers. Results from bulk rheometry studies were used for comparison to the indentation creep and stress relaxation results. For the two glassy polymers, the use of sharp pyramidal tips produced responses that were considerably more compliant (less stiff) than rheometry values. Additional study of the deformation remaining in epoxy after creep testing revealed that a large portion of the creep displacement measured was due to post-yield flow. Indentation creep measurements of the epoxy using a rounded conical tip also produced nonlinear responses, but the creep compliance values appeared to approach linear viscoelastic values with decreasing creep force. Responses measured for the PDMS were mainly linear elastic, but the filled PDMS exhibited some time-dependence and nonlinearity in both rheometry and indentation measurements.

The Mechanical Properties of the Pittsburgh Coal at Elevated Temperatures

1977 ◽  
Vol 99 (1) ◽  
pp. 192-198 ◽  
Author(s):  
H. D. Shoemaker ◽  
L. Z. Shuck ◽  
R. R. Haynes ◽  
S. H. Advani
Keyword(s):  
Mechanical Properties ◽  
Stress Relaxation ◽  
Ultimate Strength ◽  
Coal Gasification ◽  
Elevated Temperatures ◽  
Superposition Principle ◽  
Shift Function ◽  
Relaxation Properties ◽  
The Face ◽  
Creep And Stress Relaxation

Mechanical properties of coal have been determined in an effort to advance in situ coal gasification technology. Tests and apparatus were developed to evaluate the directional compressive and shear properties of coal at elevated temperatures. Both creep and stress-relaxation experiments were conducted to evaluate the creep compliance and stress-relaxation properties in compression and shear, at temperatures between 75° and 650°F (24° and 343°C), for the face cleat, butt cleat and normal to coalbed orientation, and four different specimen sizes. Stress-strain relations and ultimate strengths were also determined at three different loading rates for these directions and temperatures. A shift function was used to represent the creep and stress relaxation properties as functions of time and temperature. Four- and six-parameter viscoelastic fluid models were used to represent the data over the time-temperature ranges. Shallow and deep mine coal from the Pittsburgh coalbed was tested. The coal was found to have the greatest ultimate strength and elastic moduli at 200°F (93°C) in all directions in both compression and shear, and to be specimen size dependent. The ultimate strength in the normal to coalbed direction was approximately twice that in the face and butt cleat directions at all temperatures. At 575° to 650°F (302° – 343°C), the coal becomes fluidic and is well represented by a four-parameter fluid model. It also obeys the time-temperature superposition principle.

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