Материаловедение: свойства металлов. Матросова Т.А - 5 стр.

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УлГТУ | Ульяновск

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Topic 1. General Overview of Materials and their Structure
The properties of materials are sometimes referred to as structure-sensitive, as
compared to structure-insensitive properties. In this case structure-insensitive
properties include the traditional physical properties: electrical and thermal
conductivity, specific heat, density, and magnetic and optical properties. The
structure-sensitive properties include the tensile and yield strength, hardness, and
impact, creep, and fatigue resistance. It is recognized that some sources maintain
that hardness is not a true mechanical property, because it varies somewhat with the
characteristics of the indentor and therefore is a technological test. It is well known
that other mechanical properties vary significantly with rate of loading, temperature,
geometry of notch in impact testing, and the size and geometry of the test specimen.
In that sense all mechanical tests of material properties are technological tests.
Furthermore, since reported test values of materials properties are statistical
averages, a commercial material frequently has a tolerance band of ±5 percent or
more deviation from a given published value.
In the solid state, materials can be classified as metals, polymers, ceramics, and
composites. Any particular material can be described by its behavior when subjected
to external conditions. Thus, when it is loaded under known conditions of direction,
magnitude, rate, and environment, the resulting responses are called mechanical
properties. There are many possible complex interrelationships among the internal
structure of a material and its service performance. Mechanical properties such as
yield strength, impact strength, hardness, creep, and fatigue resistance are strongly
structure-sensitive, i.e., they depend upon the arrangement of the atoms in the
crystal lattice and on any imperfections in that arrangement, whereas the physical
properties are less strucure-sensitive. These include electrical, thermal, magnetic, and
optical properties and do depend in part upon structure; for example, the resistivity
of a metal increases with the amount of cold work. Physical properties depend
primarily upon the relative excess or deficiency of the electrons that establish
structural bonds and upon their availability and mobility. Between the conductors
with high electron mobility and the insulators with no free electrons, precise control
of the atomic architecture has created semiconductors that can have a planned
modification of their electron mobility. Similarly, advances in solid-state optics have
led to the development of the stimulated emission of electromagnetic energy in the
microwave spectrum (masers) and in the visible spectrum (lasers).

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