Stress weather damage

Resistance to soil stress. The coatings are often subject to very high stresses, due, for instance, to the contraction of clay soil in dry weather, and they must be able to resist such stresses without damage. 

Prolonged exposure to acid rain causes forest soils to lose valuable nutrients. It also increases the concentration of aluminum in the soil, which interferes with the uptake of nutrients by the trees. Lack of nutrients causes trees to grow more slowly or to stop growing altogether. More visible damage, such as defoliation, may show up later. Trees exposed to acid rain may also have more difficulty withstanding other stresses, such as drought, disease, insect pests and cold weather. 

Seen in the light of infections, though, the behaviour of NFkB is consistency itself. Activation of NFkB in Alzheimer s disease, as in an infection, has two complementary effects it fans the fires of inflammation, and at the same time shields our healthy cells from the same flames. In infections, the rationale is obvious the immune system attacks the invader with free radicals that might just as easily harm our own cells. To prevent damage to our own cells, their genetic resistance to oxidative stress is tuned up. A shock that might normally kill our body s cells, or make them commit suicide (apoptosis) is now weathered out until the storm is over. Some cells are stimulated to divide, to repopulate tissues that were less prepared for the storm, and which suffered accordingly. 

Certainly the environmental history of use and method of fabrication of an object will influence its environmental interaction. Weathered surfaces, the orientation of the tissue on the exposed surfaces, mechanical damage from pounding or stress, and changes caused by heating will influence the degradation patterns. 

Comparisons of the results of laboratory corrosion tests with damage sustained in use have revealed differences in corrosion and corrosion products. For example, the constant salt spray fog test leads to a different type of rust formation than that produced by natural weathering, with its alternating damp and dry periods. Test cycles have therefore been developed in which the individual stresses are applied in sequence. A good correlation with natural corrosion in automobiles was demonstrated in the VDA alternating test. The sample is subjected to salt spray fog for 24 h, followed by four 24-h cycles each consisting of 8 h at 40°C and 100% relative... 

Typical mechanical processes include development of internal stress due to local variation in swelling processes or abrasive damage to plastic surfaces exposed to aqueous solutions at high impact rates (e.g., in natural weather exposure). 

These linings are limited by their inability to resist oil or flames and the fact that they are subject to damage by cold weather, sudden extreme temperature changes, or mechanical stresses. In addition, they are not abrasion resistant. 

Subject to damage by cold weather, exposure, sudden extreme temperature changes or mechanical stresses. 

Frost Damage. One of the more destructive agents of weathering is frost. Water expands 9 percent as it freezes. Under certain conditions, such expansion may produce stresses that disrupt the bricks and cause spalling. 

The major weathering stresses that cause degradation of organic coatings are the first four in the list above UV radiation, moisture, heat, and chemical damage. And,... 

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