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.

Viscoelasticity Analysis and Experimental Validation of Anisotropic Composite Overwrap Cylinders

2012 ◽  
Author(s):  
Jerome T. Tzeng ◽  
Ryan P. Emerson ◽  
Daniel J. O’Brien
Keyword(s):  
Stress Relaxation ◽  
Experimental Validation ◽  
Elevated Temperatures ◽  
Model Simulation ◽  
Viscoelastic Behavior ◽  
Pressure Vessels ◽  
Steel Cylinder ◽  
Viscoelastic Effects ◽  
Creep And Stress Relaxation ◽  
Composite Cylinders

Stress relaxation and creep of composite cylinders are investigated based on anisotropic viscoelasticity. The analysis accounts for ply-by-ply variation of material properties, ply orientations, and temperature gradients through the thickness of cylinders subjected to mechanical and thermal loads. Experimental validation of the model is conducted using a high-tensioned composite overwrapped on a steel cylinder. The creep and stress relaxation response of composite is accelerated at elevated temperatures, then characterized and compared to the model simulation. Fiber reinforced composite materials generally illustrate extreme anisotropy in viscoelastic behavior. Viscoelastic effects of the composite can result in a drastic change of stress and strain profiles in the cylinders over a period of time, which is critical for structural durability of composite cylinders. The developed analysis can be applied to composite pressure vessels, gun barrels, and flywheels design of life prediction.

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

The Relation Between Collagen Fibril Kinematics and Mechanical Properties in the Mitral Valve Anterior Leaflet

2006 ◽  
Vol 129 (1) ◽  
pp. 78-87 ◽  
Author(s):  
Jun Liao ◽  
Lin Yang ◽  
Jonathan Grashow ◽  
Michael S. Sacks
Keyword(s):  
Mechanical Properties ◽  
Angular Distribution ◽  
Mitral Valve ◽  
Stress Relaxation ◽  
Collagen Fibril ◽  
Biaxial Loading ◽  
Tissue Level ◽  
Collagen Fibrils ◽  
Anterior Leaflet ◽  
Creep And Stress Relaxation

We have recently demonstrated that the mitral valve anterior leaflet (MVAL) exhibited minimal hysteresis, no strain rate sensitivity, stress relaxation but not creep (Grashow et al., 2006, Ann Biomed Eng., 34(2), pp. 315–325;Grashow et al., 2006, Ann Biomed. Eng., 34(10), pp. 1509–1518). However, the underlying structural basis for this unique quasi-elastic mechanical behavior is presently unknown. As collagen is the major structural component of the MVAL, we investigated the relation between collagen fibril kinematics (rotation and stretch) and tissue-level mechanical properties in the MVAL under biaxial loading using small angle X-ray scattering. A novel device was developed and utilized to perform simultaneous measurements of tissue level forces and strain under a planar biaxial loading state. Collagen fibril D-period strain (εD) and the fibrillar angular distribution were measured under equibiaxial tension, creep, and stress relaxation to a peak tension of 90N∕m. Results indicated that, under equibiaxial tension, collagen fibril straining did not initiate until the end of the nonlinear region of the tissue-level stress-strain curve. At higher tissue tension levels, εD increased linearly with increasing tension. Changes in the angular distribution of the collagen fibrils mainly occurred in the tissue toe region. Using εD, the tangent modulus of collagen fibrils was estimated to be 95.5±25.5MPa, which was ∼27 times higher than the tissue tensile tangent modulus of 3.58±1.83MPa. In creep tests performed at 90N∕m equibiaxial tension for 60min, both tissue strain and εD remained constant with no observable changes over the test length. In contrast, in stress relaxation tests performed for 90minεD was found to rapidly decrease in the first 10min followed by a slower decay rate for the remainder of the test. Using a single exponential model, the time constant for the reduction in collagen fibril strain was 8.3min, which was smaller than the tissue-level stress relaxation time constants of 22.0 and 16.9min in the circumferential and radial directions, respectively. Moreover, there was no change in the fibril angular distribution under both creep and stress relaxation over the test period. Our results suggest that (1) the MVAL collagen fibrils do not exhibit intrinsic viscoelastic behavior, (2) tissue relaxation results from the removal of stress from the fibrils, possibly by a slipping mechanism modulated by noncollagenous components (e.g. proteoglycans), and (3) the lack of creep but the occurrence of stress relaxation suggests a “load-locking” behavior under maintained loading conditions. These unique mechanical characteristics are likely necessary for normal valvular function.

scholarly journals Factors influencing mechanical properties of polyurethane foams used in compressible flexographic sleeves

2020 ◽  
Author(s):  
Saša Petrović ◽  
◽  
Nemanja Kašiković ◽  
Željko Zeljković ◽  
Rastko Milošević ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Stress Relaxation ◽  
Polyurethane Foams ◽  
Compression Testing ◽  
Foam Layer ◽  
Cyclic Compression ◽  
Factors Influencing ◽  
Pu Foam ◽  
Flexographic Printing ◽  
Creep And Stress Relaxation

Polyurethanes are a group of polymers which are in many ways different from other types of plastic. They are used in many different areas due to the fact that many different chemicals can be used during their synthesis, resulting in a variety of structures. Sleeves are comprised of hard base often covered with compressible polyurethane (PU) foam layer. PU foam layer can have different composition and level of porosity which are the main factors influencing compressibility of the sleeve and therefore its area of use. Sleeves are also one of the least researched components in the flexographic printing process. However, mechanical properties of the polyurethane, its fatigue, lifespan and parameters influencing all of them have been extensively investigated in different areas and for different types and formulations of polyurethane. The aim of this paper is to investigate factors influencing mechanical properties of polyurethane foams used in compressible flexographic sleeves. Investigated parameters are foam density, level of strain and strain rate, influence of microstructure under different conditions and parameters influencing creep and stress relaxation. The review of the existing literature regarding mechanical properties of the PU foams makes it possible to select the parameters with the greatest possible influence on the flexographic printing process, as well as to find the most suitable methods to investigate the effect of exploitation on sleeve properties. As a large number of parameters influencing PU foam mechanical properties are fixed during printing, it can be concluded, through the review of the existing literature, that the main parameters to be investigated are the resilience of the sleeve compressible layer during cyclic compression testing (residual strain), maximum stress, Young’s modulus, hysteresis loss, and creep and stress relaxation during cyclic compression testing with strain retention.

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