Protective layer limiting strain

This strain can therefore be used as a criterion for the design of protective layers protective layers must be designed in such a way that the local strains resulting from indentations by objects with edges and points do not exceed the limiting strain. 

The limiting value of 0.25 % for the arch elongation has developed from the consideration that a visual inspection finds only minor indentations, but this criterion has to be able to be quantified by a simple measurement. With 16/32 mm gravel this criterion fits coincidentally with the requirement of plastic technology that even local elongations may not exceed the critical limiting strain. Since it is simple to test and already established, it was maintained as a design criterion within the BAM certification for protective layers. However, 0.25 % still remains a mystery, even for some experts. 

The cracks in reinforced and non-prestressed concrete elements subjected to tension are unavoidable due to differences in Young s moduli and in values of ultimate strain in concrete and steel. It is the task of the designer to select appropriate remedies for the serviceability and safety reasons by adequate reinforcement or prestressing. If perfect impermeability is required, then the cracks are inadmissible or their width is strongly limited. In that case, also, the pore system in concrete should be completely blocked by special admixtures. Another method is to provide protective coatings or tight layers of other materials. 

Resistance of microbial cells.The individual sensitivity and resistance of microbes to microbicides, which depend on the composition and structure of the outer eell layers, are termed intrinsie resistance in contradistinction to acquired resistance, which is a consequence of the seleetion pressure exerted on a microbe population in the presenee of mierobicides. The appearanee of resistant strains within a microbe population that was initially sensitive to an applied microbicide is a eonsequence of mutations and selection of the resistant mutants. Acquired resistanee is important in chemotherapy with antibioties, where it causes serious difficulties. In plant protection with systemic active substances diffieulties are also eaused by acquired resistanee through the appearance and seleetion of strains resistant to the applied microbieide concentrations whieh are limited by the plant s system. In ehemotherapy with antibiotics it is the system of humans or animals whieh limits the concentrations of active ingredients. As eorresponding limitations of microbieide concentrations in material and process protection are not generally neeessary, aequired resistance has minor importance here. Quite opposite is true of intrinsic resistance this must be taken into account whenever mierobicides are used for material protection. 

Die passivation layers were first introduced to protect the metallisation of integrated circuits from mechanical damage during assembly. However, it soon became apparent that the passivation layer was a crucial factor in determining the failure rate in moist ambients. Originally, pure chemical vapour deposition (CVD) silicon dioxide was used, but later phosphorus was added to relieve strain in the layer and thus prevent cracking and loss of adhesion. There is also interest in, and limited use of, other forms of passivation such as silicon nitride, oxynitride and polyimide. 

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