Compressive stress degradation

The existence of kinks was recently explicitly taken into account by Larson (Fig. 14) as a possible model for chain unravelling in the flow [69]. At the same time, Kausch developed a similar model to explain degradation results measured in transient elongational flow (Fig. 15) [70]. With this difference from the Larson model, kinks in the latter model can support compressive stress chain elastic modulii range from 16 to 110 GPa, depending on the number of defects within the kinked region. 

Gillen, K.T., M. Celina, and R. Bernstein, Validation of improved methods for predicting long-term elastomeric seal lifetimes from compression stress-relaxation and oxygen consumption techniques. Polymer Degradation and Stability, 82(1), 25-35, 2003. 

The concurrently recorded hardness readings (Table I) were employed In Figure 6. Since the retention of hardness appeared to be much less sensitive to the hydrolytic degradation than the compressive stress-strain properties, only the effect on the latter was employed in estimating the useful life of the material. 

The progress of the degradation was observed by monitoring the decay of compressive strength (Figures 3-5) and hardness (Figure 6). Particular attention was given to the compressive stresses over the early and middle portion of the stress-strain plateau. At deflections appreciably lower than 0.2 In. and above... 

The change in property measured up to, and past, equilibrium absorption is likely to show a marked change in the shape of the degradation curve. This is very noticeable in compression stress relaxation results on some rubbers in water at ambient temperature when a rise in modulus can be seen due to swelling at times greater than one year. Serebryakov ct al. [15] demonstrate a similar type of effect for the strength of polystyrene. 

These differences between specimens presumably arise from varying amounts of compressive prestress, which the bronze matrix exerts on the NbaSn reaction layer (because of thermal contraction after the fabrication heat treatment). The compressive strain degrades the initial /c, so that when tension is applied to the composite, the first effect is to relieve the compressive strain on the NbsSn and increase Ic- Eventually, when enough tensile stress is applied to the composite, the... 

To summarize, there is no well-defined total strain at which multifilamentary NbaSn wire electrically degrades—it varies from specimen to specimen, depending on the amount of prestress present in each. The wire can be fabricated and heat treated to optimize /c, as in curves 1, 2, 3, and 4 in Fig. 8, or to optimize strain tolerance, as in curve 7. The difference is that in the first case the compressive stress on the NbaSn was minimized, while in the second case it was maximized. These results indicate, however, that there is a well-defined intrinsic strain at which the NbsSn itself degrades. Critical current degradation becomes significant (exceeds 5 % ) at about 0.2% intrinsic strain. For the remainder of this paper, only the intrinsic strain experienced by the NbsSn reaction layer will be considered. 

As mentioned in the introduction to this paper, scientific study has concentrated on the tensile mode. Except for two forms of break in cotton, all the tensile failures discussed in this paper consist of breaks that run transversely aeross the fibre. However, the fibres arc fairly highly oriented, so that the bonding across the fibre is much weaker than along the fibre. Transversely, there are weak intermolecular bonds plus a small component of the covalent bonding. In use, failure is rarely due to a direct tensile overload, unless this is on fibres weakened by chemical degradation. The common forms of wear in use are due to weakness in the transverse direction, related either to shear stresses or to axial compression. There is no detailed structural prediction of the response to shear stresses or axial compression at a molecular or fine-structure level. All that one can say is that at a certain level of shear stress cracks will form and that at a certain level of axial compressive stress the structure will buckle internally. What can be described is how these stresses occur. 

As regards to FRP reinforced masonry structures undergoing cyclical tensile and compression stress, such as those caused by seismic events and thermal variations, the masonry-FRP adhesion can extensively degrade over the life of the structure. In this regard, it may be necessary to insert the reinforcement into notches, aiming at preventing local instability that applies to mechanical connection devices. 

Pipe applications provide typical examples for the action of chemicals under mechanical load. Here, there is competition between chemical degradation and degradation caused by mechanical phenomena such as stretching and crack formation. The latter is caused by mechanical loads, the former by thermal oxidation. The service life-compressive stress curve is divided into three stages. Figure 5.254 ... 

Recent studies have shown that tensile and shear stresses accelerate the rate of the photochemical degradation of polymers. In contrast, compressive stress generally retards the rate of photochemical degradation (3,4). In addition to stress, other factors may affect the rates of polymer photodegradation. These factors include the ... 

Schneider, in 1986, explored the effect of high temperatures in elements of concrete and examined its influence on the behavior of the set of the concrete. He confirmed that compression stress. Youngs modulus, thermal deformation, and shrinkage that were suffering the materials were depending on the type of aggregate and produced curves to show the degradation suffered by the properties of the material with respect to temperature and load. 

Since the fiber reinforcement grants composites increased strength, it also make them sensitive to temperature and moisture stress, presence of chemical pollutants, etc. During their service time, addition of tensile stress potentiate the negative effect of the weathering, but compressive stress may reduce the propagation of some degradative processes [101]. 

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