by Acad. Alexander BERLIN Director of the RAS Institute of Chemical Physics named after N. N. Semyonov Materials used by man in his activities have always been playing an important and even decisive role in the development of the civilization. It is not accidental that they gave names to the whole historical epochs: Stone, Bronze, Iron Age... Modern epoch can be called the Polymer Age. While creating material world, people have always turned to the history of nature. To come closer to its best specimens is very exciting but still a challenging task. FROM METALS TO POLYMERS The key function of materials called constructional is to bear mechanical load. That is why strength is a principal requirement. The product shall not be destroyed at high static load, shall not be brittle, i.e. crumble at blow, in other words, formation of cracks in them must be blocked. The first property is quantitatively characterized by static strength (hereinafter-strength), the second property-crack resistance. Conventionally, there are four principal types of constructional materials created by nature and man: inorganic (minerals, ceramics, glass, etc.), metals, organic polymers and composites. From the point of view of their use, all these materials have their own advantages and disadvantages. Thus, metals combine strength and crack resistance, i.e. endure high load and are not brittle (though the higher their strength, the lower is plasticity). But products made of such materials are heavy, as their specific weight is very high (for steel - about 7.8 g/cm3 ). Production and processing require considerable power consumption and labor costs, in particular, in case of high-tensile alloys. Ceramics, inorganic glass and glass ceramic materials are characterized by high strength and stiffness, i.e. deformation resistance (modulus of elasticity) and heat-resistance, possibility to operate at high temperatures, and comparatively small specific weight (2 - 4 g/cm3 ). But such materials are ... Read more

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Точикистон Онлайн · 2025 days ago 0 3164
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Точикистон Онлайн
Душанбе, Tajikistan
27.09.2018 (2025 days ago)
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