Stresses Stretching

Spaonung, /. tension (gaseous) pressure Mech.) stress stretching, etc. (see spannen) ( 2ec.) potential, voltage tenseness, strain width. 

In semi-cristalline polymers, rate-enhancement under stress has been frequently observed, e.g. in UV-photooxidation of Kapron, natural silk [80], polycaprolactam and polyethylene terephthalate [81]. Quantitative interpretation is, however, difficult in these systems although the overall rate is determined by the level of applied stress, other stress-dependent factors like the rate of oxygen diffusion or change in polymer morphology could occur concurrently and supersede the elementary molecular steps [82, 83], Similar experiments in the fluid state showed unequivocally that flow-induced stresses can accelerate several types of reactions, the best studied being the hydrolysis of DNA [84] and of polyacrylamide [85]. In these examples, hydrolysis involves breaking of the ester O —PO and the amide N —CO bonds. The tensile stress stretches the chain, and therefore, facilitates the... 

This can cause surface cracks perpendicular to the direction of stress stretched elastomers are more susceptible to this cracking. 

Ozone. Although ozone concentration in the atmosphere is only a few pphm, it reacts with mbber double bonds rapidly and causes cracking of mbber products, especially under stress (stretching and bending). For every mbber compound, there is a critical elongation below which cracks do not form. Usually, this is in the range of 5—10% elongation. 

The ozone concentration in the atmosphere is only a few pphm. In certain chemical plants as in electrolytic mercury cell houses in the chloralkali industry, the ozone concentration is higher. Although the atmospheric ozone level is low, it reacts with rubber double bonds rapidly and causes cracking of rubber products. Especially when rubber is under stress (stretching and bending as in the case of flexible cell covers), the crack development is faster. Neoprene products resist thousands of parts per hundred million of ozone for hours without surface cracking. This nature of neoprene is quite suitable for cell house application in chlor-alkali industries. Natural rubber will crack within minutes when subjected to ozone concentration of only 50 pphm. 

Figure 13. Experimental stress-stretch curves for solithane under uniaxial straining at several ambient pressures. A positive pressure corresponds to a negative mean stress. Data are re-plotted from Quested et al. Ref [16].

D. Bradley, P.H. Gaskell and X.J. Gu, Application of a Reynolds Stress, Stretched Flamelet, Mathematical Model to Computations of Turbulent Burning Velocities and Comparison with Experiments, Comb, and Flame 96 (1994) 221. 

To obtain a static stress (stretched membrane), the face area of the glass cups was made lOX larger than the face area of the rubber cups. 

Although small (10%) static stresses (stretching) have no effect on the permeability of Neoprene, ultrasonic agitation increases salt water permeation rates severalfold due to heating by ensonlflcatlon. 

Selectivity coefficient Semicondiictor industry Semi-crystalline Separation - factor - gaseous mixtures - liquid mixtures 9 302.481 38.193,259 9 39,308,472,493 332 Stress Stretched membranes Sublayer Sucrose Surface analysis -energy tension 44 73.289.353 13319J33 221 201 367 368... 

Fig. 28. Stress-stretch response for a Neo-Hookean rubber compared with that of a...

Assuming the membrane material to be isotropic and homogeneous, the stress-stretch (o-A) relations are expressed in the form... 

Figure 10 shows the undeformed shape of the free wall of a normal rat LV and the network superimposed on the wall geometry illustrates the finite element substructure in the model. Uniaxial passive stress-stretch data for fibrous and fibrous muscular aneurysms, obtained from the studies of Parmley et al. (1973), are displayed in Figure 11. For comparison purposes, normal human data are also shown. These data were used to determine the elastic constants.

Figure 11. Uniaxial stress-stretch (o-X) data for fibrous and fibrous muscular aneurysms taken from the studies of Parmley et al (1973). (Reproduced from Janz and Waldron Predicted effect of chronic apical aneurysms on the passive stiffness of the human left ventricle, Circ Res 42 255, 1978 with permission of the American Heart Association.)...

Any material, when stressed, stretches or is otherwise deformed. If the resin and the fiber in reinforced plastics are firmly bonded together, the deformation will be the same in both. For efficient structural behavior high-strength fibers are employed, but these must be more unyielding than the resin. Therefore for a given deformation or strain a higher... 

FIGURE 33.4 Model of initiation of signal transdudion in cells in response to shear stress, stretch, and pressure. Forces may directly activate individual mechanosensors or may be transmitted by the cytoskeleton to intracellular locations where signaling can occur. In either case, cascades of intracellular signaling events are initiated, leading to altered gene expression and cell behavior. (Adapted from Davies, P.F., Physiol. Rev., 75, 519, 1995. With permission.) See text for details. 

Qi HJ, Boyce MC (2004) Constitutive model for stretch-induced softening of the stress-stretch behavior of elastomeric materials. J Mech Phys Solids 52 2187-2205... 

Bertoldi K, Gei M (2011) Instabilities in multilayered soft dielectrics. J Mech Phys Solids 59 18-42 Carpi F, Gei M (2013) Predictive stress-stretch models of elastomers up to the characteristic flex. Smart Mater Struct 22(10) 104011... 

The tensile strength is a measure of the ability of a material to withstand pulling stresses. It is defined as the stress (stretching force per unit area) required to break a specimen. Polymers are approximately 20 % stronger in compression than in tension. 

Qi J H and Boyce M C (2004) Constitutive model for stretch-induced softening of the stress-stretch behavior of elastomeric materials, J Mech Phys Solids 52 2187-2205. Drozdov A A and Dorfmann A (2003) A micro-mechanical model for the response of filled elastomers at finite strains, Int J Plasticity 19 1037-1067. 

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